Rich on needle clip position or worn needle jet? Might explain lumpy running when warmed up. Probably wouldn't explain eye-blurring shakes.

What rpm is the bad vibration at?

 

I just moved the needle clip from Position 2 to Position 1 (weakest mixture) today and before the engine got really hot, the bike was running better than ever. The last time that I took it out, the clip was on the central notch and I still got a lot of vibration once the engine was warmed up, but it didn't seem to pull as well when cold.

I get the heavy vibration at various revs - 3,000-4,000rpm especially. It's also very vibey on the overrun with the throttle closed.

It's not running 'lumpily, in that the cylinders seem to be firing in sync and the tickover is pretty smooth - it's just that the whole bike shakes (as if the big end bearings were worn :|), but only when it has been running for 30 minutes or so. The oil level is normal and I know that if I went out and started the bike now, it would probably run smoothly again ... until it got hot.

Weird!

 

If you have good oil pressure when hot, the big ends will be ok.

 

Hi Andy,

I have a working oil pressure light and that stays off after start up.

Not the same thing at all.

If you look in the workshop manual, right at the beginning of the "General Data" section, it shows the "Oil Pressure Switch" "Operating pressure" as 3/5 psi, "Oil Pressure" "Idling" as 20/25 psi and "Normal running" (afaik, above about 3,500 rpm) as 65/80 psi.

So an o.p. lamp that simply "stays off after start up" is not any sort of indication of "good oil pressure", hot or cold; only a gauge can verify that.

In reality, the o.p. warning lamp is nothing of the sort - if you see it on any time the engine's running, it's an "engine fcuked" lamp; the only "warning" it gives is of the impending GBH to your bank balance.

Hth.

Regards,

 

Yes, I have a working oil pressure light and that stays off after start up.

I must admit, I have noticed that the needle on the left hand carb is always difficult to locate when I try to reassemble the carb, whilst the right hand one just slides straight down into the needle jet with no resistance or fettling. It might be that the copper needle clips, which look a little bent and buckled to me, are forcing the needle off to one side and making it rub on the edge of the needle jet!? For what it costs, I think I will start by replacing both needles and clips (the left needle did look a fraction bent and scuffed to me, come to think of it).

When the engine starts to run 'roughly' and vibrate heavily, it is very similar to the feeling you get when the two throttle slides are not opening in sync and you get an imbalance in the carbs. I know that my cables are pulling together, as I check this every time that I have the air filters off. Still, it does add weight to the theory that it may be carb related :wink2: .

Thanks for the input, TT :wink2:.

Any other opinions out there?

 

The needles should dangle loosely, centrally, from the slides.

You'll be able to see if one is forced off to the side.

A bent, scuffed needle can't be good.

 

Yeah, they both do, but it's odd that the right hand one slots straight down into the needle jet when the throttle slide is replaced, whereas the one on in the left hand carb always seems to dangle back towards the engine and I have to use a little hook to pull it forward and locate it in the needle jet.

 

If the needles show wear I'd replace the emulsion tubes at the same time. Wear is harder to see in them but since they work together, change both.

 

I think Amal calls them needle jets.

 

Yeah, they both do, but it's odd that the right hand one slots straight down into the needle jet when the throttle slide is replaced, whereas the one on in the left hand carb always seems to dangle back towards the engine and I have to use a little hook to pull it forward and locate it in the needle jet.

For several reasons none of which directly effect tuning. It is more common that you have to align the needles into the needle jets when offering the slides to the body than not.

Needles typically show very little wear over time, especially where it would effect tuning. While needle jets routinely wear enough to change the fuel mixture delivered, often in fairly low mileage. Any shop worth its salt will have plug gauges to measure needle jets. Failing the ability to measure the needle jet, it is usually the last thing people think about replacing, but it should be their first!!!!!!!!

 

Yes, that makes sense I suppose. The carbs are tilted back at angle, after all.

As for the needle jets, I forgot to mention that I have several different sizes of these (genuine Amal brand), bagged and unopened, so I can replace those at the same time. The carbs currently have .106 size fitted and they may also be new ones, but I need to check. If not, I only have .105 or .107, so I was thinking of trying one of those sizes before splashing out for more .106s.

So, are we all pretty much saying that the needles/jets are the most likely candidates here for this rough running when hot - I haven't read any other theories :| !?

Hi Andy,



Not the same thing at all.

If you look in the workshop manual, right at the beginning of the "General Data" section, it shows the "Oil Pressure Switch" "Operating pressure" as 3/5 psi, "Oil Pressure" "Idling" as 20/25 psi and "Normal running" (afaik, above about 3,500 rpm) as 65/80 psi.

So an o.p. lamp that simply "stays off after start up" is not any sort of indication of "good oil pressure", hot or cold; only a gauge can verify that.

In reality, the o.p. warning lamp is nothing of the sort - if you see it on any time the engine's running, it's an "engine fcuked" lamp; the only "warning" it gives is of the impending GBH to your bank balance.

Hth.

Regards,

:grin2: Noted!

 

I'm not convinced worn carb parts are the issue, but sometimes when nothing obvious jumps out I fix whatever I find wrong to eliminate it from the equation. If the parts I removed turn out to be ok they become spares. This is why my workshop is so full, spares.

 

:laugh2: Well, that's something I'm trying to avoid - once I've sold this bike, I doubt that I'll ever buy another old British bike (waaaayyyy too temperamental for me). Good point though.

No, not really. But that is the direction the discussion has taken since you mentioned the needle and lowering it making the bike run better. A fair observation, but like duc I don't think it is related to the vibration.

With engine vibrations the possibilities are nearly endless. It could be anything from a cracked frame, frame hardware just touching the crankcase to some internal problem. This one of the rare times I would pull the crankcase drain plug looking for bits of metal in the oil. But my search wouldn't stop there...

It's always hard to describe these kind of 'faults' in words :|, but the established pattern is that the engine power drops in line with the increase in vibrations and that happens after many miles. Each time I start it up and ride it from cold, it's all good for the first 30 mins or so.

Anyway, I'm going to try just dropping the new needles into two brand new .107 Amal needle jets and see what happens. It might run a tad rich, but if I get a noticeable drop in the 'bad symptoms' then at least I will know that I am on the right track and could then just buy a pair of the correct (.106) jets.

Will report back next week :wink2: .

Thanks again to everyone who has contributed so far :smile2: .

Andy

 

So, are we all pretty much saying that the needles/jets are the most likely candidates here for this rough running when hot - I haven't read any other theories !?

No, not really. But that is the direction the discussion has taken since you mentioned the needle and lowering it making the bike run better. A fair observation, but like duc I don't think it is related to the vibration.

With engine vibrations the possibilities are nearly endless. It could be anything from a cracked frame, frame hardware just touching the crankcase to some internal problem. This one of the rare times I would pull the crankcase drain plug looking for bits of metal in the oil. But my search wouldn't stop there...

 

One thought I had , since it happens when warm, was maybe a bad coil ? If you have a firing indicator check both sides when you're getting the symptoms for a strong consistent spark.

 

It's a worthy suggestion, but I can rule that one out quite quickly. The bike no longer has its two ignition coils, as I replaced the whole electrical system a month or so ago. It now has a Wassell electronic ignition kit, a 12v dual (solid state) coil etc. Also, I have tried pulling one plug lead off each side and it runs about the same on each cylinder with no real hint of misfires.

 

Errrm ... ... clearly you don't realize it isn't supposed to do that ...

Neither should you lift a coil wire in the first place without providing a path to ground to cause it to do that!

Well, you should NEVER do that!!! Voltage energy is in a constant state of wanting to finding a path to ground. If there is no easy path it will take any path it can find. This means when you lift a plug wire, and deny its rightful path, it will find another and that's by burning a path though the coils insulation. This is not going to make a happy coil...

Wth is a "(solid state) coil"?

Probably a phrase cooked up by the marketing department like Lucas and the "welded" rotor.

 

Hi Andy,

Neither should you lift a coil wire in the first place without providing a path to ground to cause it to do that!

Well, you should NEVER do that!!!

+1. Albeit, had you "provid[ed] a path to ground", you wouldn't have found that the engine carries on running when the HT circuit is supposed to be cut ...

Regards,

 

It can be quite invigorating to pull a plug wire while the engine is running. That was one electrical test I never did twice.

 

As a naive teenager, I'd taken the magneto off my Matchless G9 twin. I'd taken the HT brush holders off and thought that the slip ring looked dirty so I moistened a piece of cloth, pushed it down the hole with my finger and slowly turned the armature. I only ever did that once and learned a valuable lesson.... A good magneto will deliver a spark at very low revs!!!

 

I taught myself this valuable lesson once. I had my finger over the spark plug hole on my magneto once, spun the shaft...........as the cob webs cleared from my brain as I picked myself up from the floor on the other side of the room, I learned that all it takes is to break the connection on the points in that mag to generate voltage, not even one full revolution. It's a lesson that seldom needs to be retaught.:frown2:

 

Glad i am not the only idiot -- many years ago had a 1973 Honda 250 ( sorry) -- would not start on a rainy day ( a rare occasion in the UK ?) so with wet gloves took a spark plug out and held it on the engine - hit the start button -- my hand gripped the bars tightly holding my finger on the start button - after my brain realised what was happening i had to make the effort to tell my hand to slide my finger off the button because that was the cause of the pain -- seemed an eternity - lesson learnt !! (including dont buy hondas)

here is another painfully situation -- working under a car lying down on your back with minimum space - bang your head on the underside of the car - automatic reaction is to move your head away - your head moves away and hits the ground - automatic reaction - head hits car -- repeat ! --- i think it was 3 or 4 impacts before i forced myself to stop - painful but so stupid it made me laugh out loud

 

Hi,

Glad i am not the only idiot

Mmmm ... last one I remember was several years ago, I was doing some sort of cutting job in somewhere without good lighting, I pressed my thumb on the Stanley knife (US = boxcutter) blade to push off the cover ... only I'd already taken the cover off ...

1973 Honda 250
would not start on a rainy day

My learner too.

I can tell you why it wouldn't start in the wet, though. :thumb For reasons best-known only to themselves, they fitted (and, well over fifty years since they first flogged bikes in GB, they still do arn) a length of close-fitting rubber hose over each HT lead. The caps at either end don't seal on it so the tube and HT lead are a perfect path for any water that lands at either end to work its way to the other end by capillary action. :Not again Then, with a nice low-resistance path past the plug, why would the HT go to the trouble of jumping a high-resistance gap in one?

The valve clearance tends to get greater with hot engine.

:surprise: Perhaps you might want to re-read that and clarify?

replaced the stock late type 1973 mufflers with the later Emgo repro mufflers. The Emgo are about 1.5-2# lighter & built very different internally. Also they are quieter.
it vibrates way less on freeway. I cannot explain that.

Any object vibrates. What you perceive as "vibration" is a combination of all the components' vibration frequencies and amplitudes. In a recent BritBike thread, John Healy recalled that a particular bike felt to vibrate less when a crashbar was bolted to the frame's front downtubes; as he posted there, bolting on the crashbar simply changed how the frame vibrated, so how it contributed to the total vibration of the bike experienced by the rider.

If, as you say, the new mufflers are lighter and built differently, they will vibrate differently and contribute differently to the overall 'vibration'.

Hth.

Regards,

 

Hi Snapper, Interesting. On my bike ,73 Tiger 750, I had carb way lean & so rich it 8 stroked. Didn't seem to effect vibration to a great degree.

I ride often & far. I can say for sure how the motor changes as it heat soaks. We were discussing this very thing last Saturday on a 200mi. ride. Me & Robert swapped bikes for some miles. In town & on freeway. Robert has '68 Bonnie well maintained & a good runner.

Interesting how even transmission sounds & feels different when hot.

Sounds like to know & can tell the difference between "vibration" & misfire.

The valve clearance tends to get greater with hot engine. So if you have any clearance at all cold, that is not a factor. A really loose valve will tick loudly, you don't complain of that.

One thing that changes pretty much on a hot motor is primary chain tension. I've checked the primary chain cold & hot several times. Hot meaning after 30+ miles of riding. Check it cold, then after riding 15 miles at least, check it again right after shut off. You want to feel some play hot. I use a stiff bent wire & a small stick of wood. I hook wire under chain & put wood on top. Trap the chain & move up/down. You can mark wood with pencil. Practice cold until you get the feel of it.

A too tight chain puts great pressure on the crank & transmission bearings as well as the tensioner. Will do great damage.

Also what about the clutch cush hub rubbers? When hot they can become very mushy & allow the spider to oscillate. I found mine did that. Finally a loud clack that would startle you came on. I was surprised at what a difference new rubbers made. The old ones will fill the space, but they don't have the capacity to hold the spider properly.

Moving to the chassis. Does the vibration happen similar at a stand still? Wheel balance can make bike feel very rough at 50 mph+. If rear wheel is pretty far out of balance it can vibrate bike too. I like to static balance both to perfect as I can. Usually balance problems will show up cold too though.

Also look into mufflers for any loose baffles or loose parts. Are your push in pipes loose in head? I found my left pipe would get quite loose with hot head. With all the other vibration I don't know if it make a difference though.

My Tiger after out of 34 years storage vibrated horribly. The rear shock rubber bushings allowed shocks to move over & rub the tabs that are on frame & swing arm. Were wearing the tabs. I made some Delrin spacer washers. Made a decided improvement. Then I lowered compression, again an improvement.

This is weird.... A few weeks ago I replaced the stock late type 1973 mufflers with the later Emgo repro mufflers. The Emgo are about 1.5-2# lighter & built very different internally. Also they are quieter.

Here's the weird part. Bike runs much better at speed & idles better, but... it vibrates way less on freeway. I cannot explain that. I had old mufflers off various times. Was always most careful the have them aligned perfectly & mounted tension free. I even used spacer washers under mounts as needed to get tension free. I did the same with Emgo. For some reason they just make bike vibrate less. My hunch, & only a hunch is the less weight.

I've put about 350 miles on the mufflers now in all riding conditions. I very much tried to have an open mind on the sound, feel. I did back to back road test on same route before & after new mufflers. I'd expected them to give less power, not the case. Reduced vibration was pleasant surprise. I cut old muffler open expecting to see rusted baffles or clogging. No, they looked good. Just shell rusted out at rear end area.
Don

 

Surely valve clearances reduce as the engine gets hotter. That's the point in having a clearance at all isn't it? In a perfect world where all metals expanded at the same rate it wouldn't be necessary to have valve clearances. The idea of setting the clearances cold is that when the engine becomes hot the clearances are reduced and the valve timing optimised.

 

Surely valve clearances reduce as the engine gets hotter. That's the point in having a clearance at all isn't it? In a perfect world where all metals expanded at the same rate it wouldn't be necessary to have valve clearances. The idea of setting the clearances cold is that when the engine becomes hot the clearances are reduced and the valve timing optsimised.

Heat an engine up and check. It's not the sort of thing that can be settled by debate.

The pushrods are aluminium, which expands more with heat than does cast iron. The pushrods don't get as hot as the aluminium cylinder head or the cast iron cylinder.

If you can work out changing clearance from that, in your own head, you're pretty good.

 

More questions than answers.

 

Hi Hinklyhowler, I know what you are thinking, but that is not correct.

For instance on the Mercedes cars I work on a OM617 turbo diesel valve adj. cold is I .004", E .014", while hot is .006 & .016.
A gas M110 cold .004 & .010, hot .006 & .012. These are overhead cam motors.

I've found push rod motors tend to get even looser when hot. Often about .003-.004" looser.

I worked at Harley Davidson 1969-1970. Old Sportsters don't use feeler gauges to adjust valves. You adjust tappet screw until push rod is just free to rotate, then back off adjuster a whisker until push rod has just a slight wiggle in the cup. That gives about .001-.002".

Occasionally we'd get a bike in that was hard to start & ran poor cold, but ok hot. If the bike was already hot, we'd pop the push rod tube open & see if the push rod was free to turn & how much wiggle. A hot motor would have lots of wiggle if it was ok. Often they would be just free hot though. When cold would hold valve open slightly.

Cold set or hot set is always a point of debate. Some say hot is where the engine runs so it's best to set hot. Many air cooled motors are only set cold. I don't think it makes any difference. After doing both cold & hot set as a mechanic I just follow specs. Cold is normally 68f. Hot is normal operating temp whatever that may be. Here in summer cold set would be closer to 80f. Close enough.

I worked at Porsche-Audi after my Harley days. Was there 12 years. We pushed in the air cooled every morning to do the valves. Thank God the lot was level.
Don

 

Hi Stuart, Yes, the vibration puzzle is interesting. One would think a 180d crank would be better, but it's not. Seems the 170d is better as some current production Triumphs use that with out balance shafts. v-90d like Ducati better?? I've not ridden one. To me old Sporsters are about like our old bikes. Of course balance shafts really work good. Even old BMW twins have a shake to the motor. However those never seem to wear you down.

Codeman has a 1977 T140 motor in a 1970 T120 frame. Converted trans to right foot shift. I had for a long time felt the 650 was smoother than the 750 twin. I figured this was due to the short 750 rods. I also wondered if the OIF transmitted more vibration to the rider.

Codeman & I swapped bikes. They felt the same to me. Maybe mine was a little smoother.

John has '69 T120 all stock. To me his bike used to be a little smoother, but his handle bars vibrate worse. I think mine is smoother now.

Then Robert's 68 T120, all stock. Mine seems a little smoother.

I just feel like I got lucky. For sure no science went into this.

If I was a rich man I'd pull my motor apart & check the actual balance factor both static & dynamic, then dynamic balance it to 85%. But that will wait until it needs a complete tear down.

That would be most interesting.... See what is was & how it changes with as good as balance as could be done.

Don

 

Hi Don,

One would think a 180d crank would be better,

Nope, if you read more widely (there is much written on BritBike), the least vibration from a parallel twin engine is when one piston is moving at its fastest when the other is at TDC or BDC; otoh, a 180-degree twin is only cancelling out the vertical component of engine vibration.

Seems the 170d is better as some current production Triumphs use

Specifically on Triumph 650 and 750 twins, 76 degrees between cylinders is when one piston is moving at its fastest when the other is at TDC or BDC; this has been known for so long that certainly Nourish in GB has made 76-degree cranks for Triumph twins commercially for years.

I don't know if "170d" is a mistype; if it isn't, I've never heard of this and, if "current production Triumphs use that with out balance shafts", something else is going on to reduce overall vibration.

Otoh, if you mean 270 degrees, that's aka 90 degrees, which is close enough to 76 degrees as not to matter in production engine vibration terms; Nourish have also produced 90-degree cranks for our old heaps for many years.

Also, certainly Yamaha used the configuration in the 1990's TRX when they attempted to adapt the TDM twin engine to produce a Ducati/Moto Guzzi V-twin-sounding sports bike without actually producing another V-twin engine.

John has '69 T120 all stock.
his handle bars vibrate worse.

Solid- or rubber-mount top yoke? If rubber-mount, are all the components (especially the hemi washers) assembled correctly?

Robert's 68 T120
Mine seems a little smoother.

As with John's.

Also, how well are the carbs. balanced and the timing done? Both twin carb. bikes, yours is a single

check the actual balance factor both static & dynamic, then dynamic balance it to 85%.

Just as a matter of possible interest, in a recent BritBike post, John Healy cast doubt on that figure, and the often-quoted 74%, when described checking actual balances; it came out more like 68%.

Hth.

Regards,

 

This debate has become so big and wide that I can't really respond to every point that has been made, other than to say a big THANK YOU to everyone who has contributed :smile2: .

I can report that I have replaced the throttle needles, clips and needle jets and tested the bike out again. One of the (.106) needle jets that I took out did appear to have a slight blockage. Having moved up to a brand new .107 needle jet (because that was the only size I had available in my box of spares), the mixture was a little too rich and the exhausts were puffing out white, petrol-smelling smoke in the cold, damp English air. I compensated for that, to some degree, by weakening the idle mixture screws and that stopped it from smoking. However, the important thing to say is that, although the bike seemed to be a little more 'vibey' from cold than I remember it being before, it didn't worsen as I rode on as much as it had before and the power did not drop at all.

My conclusion is that the carb settings were to blame for the loss of pulling power on the previous test run, as it looks as though one of them may have become contaminated. I now need to either clean or replace the .106 needle jets, as that's what the bike is supposed to have and then do my best to set up the carbs for optimum performance. If I can't do that myself, I will have to take it to a garage and get an expert to do it.

As far as the vibration issue is concerned, I think that Don may be on the right track when he pointed out how the various mechanical parts can be affected by an increase in temperature :| . I'm mostly feeling the vibrations coming through the saddle, more than the bars or pegs and that may have something to do with the way the saddle is mounted. It's a Wassell (aftermarket) job and came with crappy, mild steel mounting brackets, which bend under my weight and make the saddle slide over to one side (making direct contact with the frame in the process). Each time I get off the bike, I have to lift the saddle and bend the brackets back over so that the saddle sits centrally again. Amazingly, I discovered this when I took my hands off the bars (to test the 'tracking' after having the front wheel off) and felt the bike pulling hard to the left. I couldn't find a problem with the wheel alignment, but once I had straightened the saddle up, the bike would go arrow straight when I took my hands off the bars. Subsequently, if I ever want to know if the saddle has gone crooked during a ride, I can test it by just taking my hands off the bars and seeing if I get pulled towards the gutter :grin2: . I've ordered some more rubber stops and some rubber insulation clamps to go around the frame tubes. Hopefully, with these fitted, I can stop the saddle from moving and dampen some of the vibrations in one go :smile2:.

 

Hi Andy,

My conclusion is that the carb settings were to blame for the loss of pulling power

Errrm ... I hate to rain on your parade but, although you might've forgotten, and the bike also had/has carburation problems:-

dual
coil
I have tried pulling one plug lead off each side and it runs about the same on each cylinder with no real hint of misfires.

it isn't supposed to do that ...
if you "pull one plug lead off", you should break the HT circuit and the engine should stop.

... if you haven't fixed this, 'fraid the bike still has a faulty coil.

Hth.

Regards,

 

First reply on thread mentions worn needle jet.

It's the usual reason a mixture gets too rich during use of the bike.

 

78 Tiger.

How old is the seat foam? How heavy are you?

I am 6ft and 15 stone ( 200 pounds ) back in the seventies folk were smaller and lighter!

I had similar vibration issues coming up through the seat that got worse as ride time increased. Putting my hand down onto the engine revealed no extra vibes so I put it down to seat foam compressing. We have overhead gantries in the UK that are used to convey information to road users, I noticed this particular type of vibration caused the words to kind of 'wiggle' around when I looked at them!

Remember the only thing separating you from the vibes from a vertical twin most of which most go up and down is your seat and your gluteus maximus! I stuffed 3 or 4 layers of bubble wrap between the seat cover and foam which made a noticeable difference and I intend to talk to a seat maker to get a good quality seat foam made possibly with a gel pad in.

I did a pretty much 2000 mile trip around northern France this summer, the bike performed fantastically but I did notice vibes creeping in the longer I rode. A 10 minute rest the bike felt smooth again, I put it down to the cumulative nature of being exposed to vibration, your bodies way of telling you to take rest.

 

Wasn't sure if this post was aimed at me or not, but it seems to answer my concern that maybe most of what I am experiencing is down to the vibrations becoming more noticeable (and annoying) rather than them actually increasing their ferocity at source. Anyway, TT, your experience offers me some hope that I may not need to 'fix' the bike; it may be my perception that needs the adjustment :wink2: .

 

Hi Stuart, Yes it was a boo boo I meant 270 crank. What I meant regarding a 180d crank such as my Honda 305 & 350 had, it would seem from the way the pistons move it would be smooth, but in real life it's not.

I suppose Triumph went with the 360d crank so they could use single carb. That is simple & saves costs.

The Harleys use a single carb & in fact the rear cyl. tended to run a fair bit richer. They suggested it helped cooling the rear jug since it didn't get as much air flow. Fuel injection changed all that. Funny the xr750 racer had dual carbs.... Indeed rear cyl cooling could be an issue on those. Mainly got its air from deflecting off rider's legs.
Don

 

Hi Stuart, Regarding balance factors in real life, that is exactly why I would check them before & and after. Maybe that's why some machines just feel smoother?? Is 74 or 85% really best?? I have no idea.

Both my 650&750 manuals state 85% as does the 750 race prep paper Triumph published. Here they give instruction on how weigh the parts & determine the balance weights.

I have heard 74% many times, but have not seen it in a manual. (Not saying it doesn't, but I don't know which one says 74%)

Is there anybody that really knows about the balance & can say what gives the best results for a daily rider bike? Cruising 60-70mph on highway. About 4k rpm.
Don

 

Hi Don,

Is there anybody that really knows about the balance & can say what gives the best results for a daily rider bike? Cruising 60-70mph on highway. About 4k rpm.

Probably John Healy (@johntioc;)?

Regards,