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Discussion Starter #1
My confidence is building the more I tinker, but as they say - a little knowledge can be a dangerous thing.

1969 TR6R. Won't idle. Starts ok (now I'm getting better at kick starts). Runs ok with throttle open. When I close the throttle the revs drop but it doesn't idle - just dies.

That's not directly what my question is about. As a result of the above I went hunting through the workshop manual for a potential solution. Came across the Throttle Stop and Air Screw on the carb. I began with the Throttle Stop - turned it about an 8th of a turn one way. No change in the idle. 8th of a turn the other way. no change. Then did the same with the Air Screw. No change there either. I put them both back where I found them.

Then I did a bit more research and I read about how I can blow the engine up if it's running too lean and the spark plugs get too hot. My question therefore is how sensitive is the air screw thingy? I reckon I've put it back to the position it was before, but how far out would it need to be to make a difference?

Russ
 

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Russ,

It would be good if you provided a history of your bike. It makes a difference to the experts who have the knowledge to advise you.

The baseline for the air screw is 1-1/2 turns out. I can tell you that, behind the air screw is a tiny jet that measures .016". It must be clear for the bike to start and idle properly. A #78 drill bit is just the thing to clear that jet. Some recommend an old guitar string or a bread tie but the drill bit is better. You can order them online for cheap.

There are also two tiny holes at the bottom of the throat of the carb on either side of where the slide contacts the bottom and toward the intake side. These must also be clear.

Go to this link to learn all about your carb.

http://www.jba.bc.ca/Bushmans Carb Tuning.html

You could have other issues as well such as a warped float bowl and others but my money is on a clogged pilot jet.

Henry
 

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Henry is right,and the pilot jet is likey to ble blocked up.
When it's cleared out,you'll be able to push a small wire (or 78 drill) at least 1-1/2" into the carb body.

You won't cause any engine damage with the wrong idle mixture.The amount of fuel being burned at idle is not enough to overheat anything.
You'll just be happier when the mixture is right and it idles smoothly.
 

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The part about not idling... You need to screw that idle screw in 1/2 turn at a time until the bike will idle, cleaning that jet is going to help alot but it also could be you just don't have the slide raised enough. Once you get it to idle, adjust the slack out of your cable. Readjust the mixture screw and the idle speed once it's well warmed up. If your choke isn't working right, it won't want to idle when cold , anyway. I have no chokes, I just have to keep it running til it warms up.
 

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Discussion Starter #5
I am extremely grateful for all the help. It's great to find people so passionate about these bikes.

Before I get into the details - is there somewhere I should be posting the history of my bike, or do you mean it's useful to repeat it when I start a new thread like this?

Russ
 

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Bushmans site is a great read and tuning to his method does gain positive results. I would add that it is a good idea to know what jets and needles are in your bike and provide that info for the "real" experts on this site. An example would be the 70 Bonnie I recently picked up. I ran great and was tuned for riding in the SF Bay area. Unfortunately I happen to live a 5000 ASL. Needless to say the bike was a little too rich. It hat 210 Mains. Picked up sets of 180 thru 200 inclusively and will start tuning it this week. Always remember it is better to be a little rich than to be a little lean.
 

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Go to your local music shop and buy a .016" guitar string.
Straighten it for about 3 inches and file the end so that there are no burrs.
Remove the horizontal mixture screw.
Check the round rubber seal.

I use a LED penlight so that the jet can be seen.
Insert the wire into the jet hole as far as it will go (about 1.5" as Pete says).
Turn it and push it in and out a couple of times.
Spray some carb cleaner into the jet, the spray can be seen exiting the small holes in the carb body (ventura).

Now you know the jet is clear, screw the adjuster-screw fully in and unscrew 1 1/2 turns.

Turn the throttle-stop screw in until the slider begins to rise.

Start the motor and adjust the throttle-stop screw for a fast tickover (1000+ish rpm).
Now turn the air/mixture screw IN (slowly) until the engine begins to stutter, then unscrew for nice, even tickover.
You might like to mark it with a felt-tip.
Repeat the above by unscrewing it OUT and screw it back in.
The `sweet` point is half-way between the stutter points.

Adjust the throttle-stop screw for the desired tick-over. (about 1000-ish or less rpm)
 

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I don't want to hijack this thread too much but if I could for a moment ask a jetting question to Caulky and others. My bike is a '70 T100C. I just put a brand new Amal Premium carb on (best thing I've done for the old girl yet by far). It is all setup with the stock slide, main, pilot and needle. Starts and idles lovely, but seems a tiny bit lean at about 1/4+/- throttle. Needle is already in the highest position available.

I say a "tiny" bit lean, as once it is good and hot, it runs sweet, but for the 1st 5-10 mins of running it needs the choke to be closed, if temps are 70F or lower, to take any substantial throttle without banging and popping. Choke on and it goes away, which to be confirmed a lean condition rather than rich. Float height is right on spec.

Since needle is already all the way up, the only way I can think to add more fuel would be a larger main, or raise float height...aside from a richer needle which I'm not sure is even available? Suggestions?
 

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Discussion Starter #9
I'm understanding about 75% of what's being said. Some things are still a bit of a mystery. I read the Bushmans article which sounds very good but whether I've got the skills to take the carb off and strip it down I'm not sure.

Caulky's email suggests I can have a go at cleaning the pilot jet with the carb and everything still attached to the engine - just by removing the air screw to gain access to the pilot jet.

My workshop manual says the approximate position required for the air screw is 2 1/2 turns out, not 1 1/2. Any reason why this is different?

My interpretation of your instructions is that the throttle-stop screw physically raises or lowers the slider - is this correct?

Russ
 

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My workshop manual says the approximate position required for the air screw is 2 1/2 turns out, not 1 1/2. Any reason why this is different?
Because 1-1/2 turns always worked,but 2-1/2 turns didn't.

Don't take the carbs off;just pull out the mixture screw and clean the jet.Most other adjustment can be done without removing the carb.

Adjust the idle stop until it just touches the slide,then tighten it another 3/4 turn.That should be a good starting point.
 

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Discussion Starter #11
OK, I've pretty much formed a plan of action, involving checking the sparks, making sure the battery is properly charged and cleaning the pilot jet as Caulky described. Just got a few last questions before I set to work...

I can't find anything in the workshop manual about the torque settings for putting spark plugs back in. Any suggestions?

Battery is showing 12.17 volts. Too low?

I have some guitar string arriving tomorrow - do I definitely need the carb cleaner too or is it worth my while poking the jet anyway?

Doesn't clearing the jet with it in situ just push gunk back into the fuel passageway where it will block up the jet again? Sorry, bit confused on this point.

Regards,
Russ
 

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You need the spray carb cleaner to flush all the crap you just reamed out. Put a rag over it when you spray in the screw hole to prevent getting it on you, and give 3 or so shots, then run the string into it about 1 1/2 " or so, then spray again. 12.17 at the battery posts sounds a bit low. Did you give it a good charge ? I don't know the torque on a plug, google it. I pull the wrench til they're gutundtite. Aluminum threads, remember.
 

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I can't find anything in the workshop manual about the torque settings for putting spark plugs back in. Any suggestions?

Doesn't clearing the jet with it in situ just push gunk back into the fuel passageway where it will block up the jet again? Sorry, bit confused on this point.
Plug torque:2 fingers at about 6" radius should be enough.If it doesn't unscrew itself,it's OK (they never do).Use anti-sieze on the plug threads.

Push the crud back past the jet.Remove the float bowl drain plug.Blow WD-40 or carb cleaner through the jet,and all the crud will drain out at the float bowl.

Zero volts could be enough if you have points.You sort of need 12V for electronic ignition.The volts will be more with the engine running.
 

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Russ, 12.1V is no good at all for E.I.
Recheck the ignition timing, most important!
When I begin to try to start the engine after a overhaul or major service, I charge the battery (maintenance charger for a day or so).
The voltage is over 13V...this is just the surface charge which drops to 12.6V [fully charged] after a kick-over or two.
[6 cells at 2.1V each]

The more it is kicked, the more the voltage will drop, if it doesn`t fire up.
Get a couple of new Champion N3? plugs.
Charge the battery and with the plugs out, tape both to somewhere bare metal (frame/earth) next to each other. (not near the plug holes and fuel OFF)
Voltmeter across the battery.
Ignition on, kick-over.
Both plugs should have nice blue sparks, at the same time.
Yellow or intermittant sparks are no good and the plugs will soot-up quickly, causing further misfiring or a stall.
Watch the battery voltage...less than about 12.4V needs a re-charge.
I put the charger on (fuse out) between adjustments/fiddling, until the led goes off.

I use a ring spanner 11/16? until the plugs bite, then a quick/light tighten to crush the washer.
Plugs do not need to be very tight.
Electrics now sorted.

Now fuel delivery.
2 1/2 turns out makes the mixture very weak...too much air.
Do a fuel flow check by unscrewing the carb drain plug. (fuel tap off)
Use a clean container to catch the fuel, throw it away.
Turn the fuel tap/s on.
You should get 300ml or more per minute.
Check for air leaks around the carb joints.
Check the tappet gaps.
How old is the fuel?
If its more than a few months old, drain the tank and use new stuff.
The ethanol attracts water which is denser than the fuel.
Check the tappet gaps.
Clean the air filter.
I dont have chokes on my bonnie, just the ticklers.
Have you got an aluminium float needle?
 

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Discussion Starter #15
Update and conclusions based on all the info supplied so far:

I have points not electronic ignition. So battery voltage probably not a factor here.

Cleaned the pilot jet with guitar wire as instructed - drained the float bowl, bits of crud came out. Fired it back up, idling much better but still a little erratic.

The air screw was originally about 1/2 a turn out or maybe less. Must have been a very rich mix. Any special reason why this would be? It was tuned by an experienced shop so no reason why it would have been done badly. Anyway, after I cleaned it all out I set it to 1-1/2 turns out and then adjusted the throttle stop to get the idling speed right. The idling revs dip and rise across a 500 rev range so I had to set the throttle stop such that it was wavering between 1000 and 1500 revs otherwise it dipped too low at times and would stall.

Obviously I still have more to do. You've all mentioned other checks I can do which I will do to pre-empt any further problems: sparks, points, carb gaskets etc. There is crud visible in the bottom of the reserve fuel pipe and in the bottom of the fuel tank. Looks like metal filings! My thought is that this is not an immediate problem unless I run out of fuel and have to switch to the reserve line but I probably ought to get this cleared fairly soon. My bet (as was your consensus) is that my immediate idling problem was due to clogged pilot jet. Other little symptoms make me think the carb needs reconditioning, and now I understand a lot more about it, I could do with taking it back to the local guy and have him show me a bit more about tuning in practice. But it's running!

Thanks for all your help. This may seem like basic stuff to you guys, but I am working up to a 6 month road trip next year and my hope is that I will be confident enough with basic maintenance to take this bike. Your help has got me off to a great start.

Follow-up question: am I right that beyond about 1/4 throttle, the fuel/air is drawn in by a different route, not via the pilot jet?

Russ
 

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Russ,

I would get that tank cleaned out. I would also squirt some carb cleaner in the air screw hole and make sure it comes out both holes on either side of where the slide bottoms in the throat.

If your slide is badly worn, it may be difficult to get the bike to idle evenly.

On the Bushman's carb tuning secrets there is a chart that shows the various features of the carb that come into play as the throttle goes from closed to wide open.

Henry
 

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Update and conclusions based on all the info supplied so far:

The air screw was originally about 1/2 a turn out or maybe less. Must have been a very rich mix. Any special reason why this would be? It was tuned by an experienced shop so no reason why it would have been done badly. Anyway, after I cleaned it all out I set it to 1-1/2 turns out and then adjusted the throttle stop to get the idling speed right. The idling revs dip and rise across a 500 rev range so I had to set the throttle stop such that it was wavering between 1000 and 1500 revs otherwise it dipped too low at times and would stall.

Russ
Hi Russ,
The air screw adjustment should be in the range of 1-1/2 to 2-1/2 turns and 1/2 a turn will be fuel rich.

Try this method:

Turn the throttle stop screw in so that the idle rpm is 20% higher than normal and adjust the air screw slowly left or right until the highest rpm is obtained.

Then bring the idle back down and do the same adjustment for highest rpm and back off just slightly on the lean side.

If your carbs don't respond you may need to try again with the filters off and see if there's a difference.

Lightly turn in the air screw until it bottoms out and then back off to 1.5 turns as a starting point.

After 3 turns and no change the spring will lose the ability to control the adjustability of the screw.

Hope this makes sense. . .
Naturally the bike needs to be warmed up and a new set of plugs will help to see what's going on.
My own bike likes to idle at 1000 rpm so I set it at about 1200 to do the initial adjustment.
Having two carbs makes it a bit difficult to judge the exact 'sweet-point', but some tuners like to err on the side of rich vs. lean.
 

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Discussion Starter #19
Yes, both the air screw and the throttle stop change the idle rev. I left the motor running for about 5 or 6 minutes and the revs did not settle down during that time. It's as if every few seconds it surges up by 500 revs and then falls back down again.

I just did it roughly and it's my first time. I think it would be wise for me to go through the tuning exercise again and see if maybe it's just that I haven't got the mix right.

A couple of people in the thread have described a tuning process that involves repeated adjustments and I don't quite get what they mean. I'll go through the instructions again and see if I can get it to sink in.

Russ
 

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The air screw was originally about 1/2 a turn out or maybe less. Must have been a very rich mix. Any special reason why this would be? It was tuned by an experienced shop so no reason why it would have been done badly.
No,it was probably lean because the blocked jet wasn't allowing enough idle fuel.They've closed the air screw to compensate.
The air screw is like a hole in the side of a drinking straw,but it's adjustable.

One of the fixed holes near the front of the slide does a similar thing when the throttle is closed.As you open the throttle more,it gets enough vacuum to become a discharge hole and allow more fuel.All these holes and the pilot jet orifice need to be in correct proportions to work properly.

The idle circuit doesn't have much effect above 1/8 throttle,but even at full throttle about 1% of the fuel is supplied thriugh the idle jet.

Above idle,fuel starts coming out of the needle jet.Needle jet size is critical from idle to about 3/8 throttle.Needle jets do wear,and are worn out at about 10,000 miles.0.0005" wear will cause richness.

The throttle cutaway has an effect on the amount of suction on the needle jet.Cutaway is most effective at just under 1/4 throttle.

Above 1/3 throttle,the tapered part of the needle comes out of the needle jet to allow more fuel.Needle clip position will have a big effect from 1/3 throttle to 3/4 throttle.

Above 3/4 throttle,the main jet stops too much fuel coming through the needle jet.Main jet size doesn't have much effect below 3/4 throttle.Below 1/2 throttle,you don't even need a main jet.

It sounds like your idle variation is an advance curve problem.The ignition timing is probably not staying retarded at idle,because of weak springs on the AAU.If you're getting full advance at less than 2000 rpm,that's probably the case.You could also test this by locking the AAU in the retarded position;pull the centrebolt and put a 7/16" washer against the AAU cam,then tighten the original washer and bolt against it.

You can't ride the bike with the timing locked retarded,but you could test the idle.

I would replace one spring on the AAU,if you can get Lucas part number 54417992.This is supposedly the only spring that is supplied thesedays,and it's heavier than the original spring.Sometimes called "HD" spring (heavy duty spring).You can just tighten the original remaining spring (about 0.015").

That should give you an advance curve that starts advancing at about 1200 rpm-1400 rpm,and reaches full advance at about 3500 rpm.

If you've still got original Lucas points,just clean them.Don't change them for low-quality modern replacements.
 
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