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Discussion Starter #1
Gentlemen,

I am having a hell of a time with my 72 TR6C Trophy.

I left old gas in it over winter, and probably had a clogged pilot jet in the carb. Based on the great advice in this forum, I took the carb apart and cleaned everything up. However, like most of my projects, this cascaded into a number of other areas, and I am now left with a bike that thunderously backfires with each kick trying to start it. Neighbors are not amused. Here is what happened:

Took the carb apart, focused on the pilot jet. As pointed out by an astute reader of this forum, I had a 260 jet when the specs called for a 230. Ordered and replaced the main jet. put the carb back on. Also gave the contact points a light sanding, reset the gap on the contact points to 0.015. Took it for a short ride. Because I had the throttle stop set incorrectly, engine was idling at a tremendous RPM. Engine reved super high for 10 seconds while I held the clutch in and panicked, then got it together and turned the key off. The exhaust pipe on the left hand side got so hot it fell off the exhaust shoulder. Pushed it home.

I replaced the threaded exhaust shoulders with new ones that were a bit thicker, tightened back on exhaust pipe collars. Went ahead and replaced the spark plugs just because. Checked the contact points again. Had to replace the fuel lines because they were old and kind of leaky. Put in new in-line fuel filters.

Went to test everything out and BOOM, giant backfire when I try to kick start it. Scares the hell out of me. I can't exactly tell where it is coming from. Happens on every kick, and I cant get it started. Try to bump start it down a steep hill. BOOM BOOM no start. I think perhaps it is an air leak where the carb attaches to the manifold. Take off the carb, fit the bigger Triumph o-ring, with some blue hylomar gasket jointing compound to make sure it is air tight, tighten down the bolts to compress the o-ring but not over tighten. Still the same backfire on kick. I then think perhaps it is an exhaust leak, take off and retighten exhaust, no difference. Make sure spark plugs are tightened down, then put back the old plugs, no difference. Try to adjust out the air screw on the carb to lean the mix. No change.

So there you go. I have messed with the carb, plugs, exhaust, and contact points - too many variables for me to know which one caused it. I have tried to set everything back to how it was before but I just cant get it to stop backfiring on kickstart. It also seems like I hear a flute-like sound when I slowly push the kick start.

Any ideas gentlemen?

Regards, A
 

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You have not altered the timing ? I think maybe you have made an error when cleaning,altering the points and one of the contact sets is way out.
 

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Discussion Starter #4
Rambo, Wol, thanks for the replies. I went out and re-re-checked the points. Here is what I am doing:

advance the kickstart slowly until I see the scribe mark on the camshaft almost on the nylon heel of one of the points. Measure the gap with a feeler gauge to 0.015". Make sure I cant quite get a 0.016" feeler gauge in there. Then advance it around and do the other one, by loosening the contact locking screw a bit and tweaking the contact eccentric screw, then tightening the contact locking screw and rechecking the gap. I then hooked up a multimeter, neg to ground, pos to the contact breaker wire. I see 12.7V when the breaker is closed, then a tiny spark and null when the contact breaker is opened. Measured both, kept advancing and re-checking the gap, it seems to be in spec.

I will say that I think I accidentally twisted on the eccentric screw for one of the secondary backplates on a previous check of the points. I thought i returned it to the original position though. I don't know much about contact breakers beyond checking the point gap. In looking at the shop manual it mentions "run-out" in this IMPORTANT NOTE:

"Run out" on the contact breaker cam or misalignment of the secondary backplate centre hole can result in contact between the cam and backplate. This can result in the auto advance remaining retarded or the spark retarding. To check for "run out" check the point gap with the contact nylon heel aligned with the cam scribe mark for each set of points. Should there be a discrepancy greater than 0.003 in. tap the outer edge of the cam with a brass drift with the cam securing bolt tight In cases of misalignment of the secondary backplate hole, check the cam clearance in different positions and elongate the hole only where the backplate rubs the cam.

I have re-read this section a few times and am not sure what it means. What is the cam securing bolt, and what is the secondary backplate hole? Tapping the actual camshaft with a brass drift seems rather extreme way of adjusting this....

Any further reading on these beyond the Workshop Manual and Parts Replacement Catalogue would be appreciated as I clearly don't understand this mechanism properly.

Thanks, really appreciate the help here. Regards, A
 

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Hi arrosi, Good you are looking at shop manual. Sounds like your points gap is correct. I think the timing is off. How are you checking your timing? At this point I would recommend a static check to get engine running good. If you have a timing light, you can then use timing light to verify the timing is good. I find static timing tends to be within .5 deg if set carefully. I've done it both ways many times.

While point gap should be set to .015" it is not very fussy. If you are off a few thousands either way it will still run fine, you'd not know or feel it in performance.

Remember the timing is set when points opening, not closing.

First you should verify points are closing properly.

Turn engine until points are closed. Take a small screw driver & pry points open slightly & let go quickly. The points should snap shut smartly with no sign of binding. Sometimes the points tend to bind & can cause poor running & hard starting. If binding they will close slowly, not snap smartly closed.

Back to the manual, to set timing statically which actually works well, you need to lock the points cam at full advance. Not hard to do, but you need to understand the procedure.

Don't worry about the points cam running out of true. If bike was running good last year it's good. I've never had to tap a points cam into true. I've had many off & on. If a person installs advance unit gently the taper makes it true automatically in my experience.

Back to locking at full advance. Take points cam bolt out. Technically the bolt holds the advance unit on. Don't worry nothing will fall off. Don't knock around on points cam with a hammer or screw driver handle though or you could possibly dislodge the cam.

Now turn the points cam with your fingers & notice how the cam rotates on the center part. The idea is you get a flat washer that will clear the center part & only nip up on the movable cam itself. A regular washer often won't do. What tends to work good is something like a copper or aluminum seal ring such as used on an automotive drain plug for the engine oil. A steel washer of suitable size is fine as well if you find one.

So take this washer & place it over the end of points cam. Then I install a 1/4" fender washer (from Ace Hardware) which is a larger diameter washer, then the bolt. Hold the drain plug seal centered on the end of points cam & temporally snug up the bolt. This will pinch the movable points cam & keep if from rotating on its shaft.

I don't have the finger strength to turn the points cam fully advanced & I don't like grabing it with needle nose pliers. Here's what I do.

Now take a small screw driver (I actually flattened a piece of metal coat hanger to use for a tool). Notice the larger notch on end of points cam. Stick the screw driver or tool in this notch. With tool in the notch, slightly back off the points bolt & rotate & gently rotate points cam clockwise until you feel it stop. Now snug up bolt. Make sure points cam is indeed pinched by the washers & bolt. Do this a few times until you get the feel of it. Understand how the washers can pinch the points cam. Once you are sure cam is locked at full advance (clockwise) you are ready to check timing.

I don't like to use volt meter to set timing as it can make the coils very hot if not done quickly. Set meter to ohms. Leave key off, remove spark plugs. Remove round cover on primary cover You could also use the timing plug & tool behind cylinders if you have one, but I find it easier to just look at the pointer in primary case).

Meter hook up will probably be same as how you did it. I do it like this. Using alligator clips hook ohm meter, one lead to the black/white wire on a coil (or blk/wht on condenser if easier). Make sure clip is on just the metal of connector of coil or condenser not accidently touching anything else. The other lead to a cly head fin. Now with bike on center stand put in 4th gear & rotate rear wheel. Observe ohm meter. Watch how it changes when points are open or closed. Memorize which is which. Again we set when points just open.

As you rotate wheel in forwards direction the ohm meter should change at the instant timing pointer lines up with line on rotor. Don't worry about which line. Back up wheel & come forwards again. Go easy & you'll see how it works. With meter on floor you can see it change as the points open. Now slacken off the secondary backing plate screws & move this plate to set timing. Verify point gap hasn't changed as you set timing. Gap can change as timing plate is moved. You may have to reset gap, then recheck timing. If points are anywhere from .014-.016 you are fine. Adjust until the ohm meter changes (points open) as the pointer & line just line up.

Now move to the other points which have a black/yellow wire to coil & it's condenser. Set timing on these as above. Doesn't matter what side you do first.

Some times you'll find the secondary backing plate for setting timing doesn't have enough range to set timing. Could be the front or rear set of points. In this case you need to loosen the 2 pillar nuts & rotate the main backing plate on it's slots. This will move both points assemblies to a more desirable position.

This process seems long & complicated. Until you memorize the procedure expect to spend a few hours or more. However once you understand how it all works together it is quite simple & easy. With practice you can set static timing in well under 1/2 hr.

On a side note, well maintained points work quite good & are very reliable. As a side bonus bike can be started with a dead battery. Also since you have in essence a left & right ignition system, failure on one side will still leave bike running on one cly. which can often get you to a safe place.

Regarding your main jet, that cannot cause your problem. If bike was running good prior I'd put the larger jet back in. Generally speaking I've been finding with our USA fuel you often will need to go 5-10% richer on most jets. Running lean you can hole a piston. Also don't let bike ping at all. Down shift & spin motor higher if you hear ping at all.

Also double check your valve adjustment just to be sure all is ok there.

Try this & let us know what happens.
Don
 

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Discussion Starter #6
Don, thank you so much for taking the time to write this up. I will give this a try on the next rainy day and report back.

One thing you mentioned is to check if the point smartly clicks back. I do notice that one of them audibly clicks and one does not. How can the binding be corrected? Take it off and give it a bit of a bend?

I knew that some day I would need to learn how to do timing. Wish I had a center stand....

Thanks again!
 

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backfire

If I remember correctly, Most symptoms for backfire is usually,..... Too low a fuel bowl level which causes a lean condition, Timing incorrect or valves not not seating. Most of everything I've read so far only talks about timing? Maybe there's some other culprit other than timing. Before it sat up for the Winter, Was the carb running normal?
 

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Discussion Starter #8
Hi Lespaul59 - Yes, for the past few years it has run like a top. Carb is about two years old. I have taken it apart three times and went through it, I think the carb is not the issue.

Valves not seating - I have not checked this. Will use my little scope camera....

Thanks!
 

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rpms

Did you have a nice thick o-ring for the carb gasket where it meets the intake manifold? I rebuilt my Amal carb a few years ago and that gasket in the kit was the right diameter but the thickness of it was about 50 percent less. I reused the original thick one. Any vacuum leak like that would cause a very high idle like you spoke of. MIGHT WANNA CHECK THE VALVE Gaps to see if it's good along with actually seeing if they're moving. Just a heads up. By the way, When you did start it up with that high idle, Did it backfire then????? Remember that if the pipes get too hot where they turn blue half the length of the total exhaust then it's most likely a lean condition like my other Triumph was.
 

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Discussion Starter #13
Yep, I am using the thicker triumph o-ring rather than the one that came with the amal carb.

When it ran with high idle, it was not backfiring. The problem is after this happened, I "messed" with the points again, checking the gap. I have been in there a few times, and I am worried that I accidentally twisted the eccentric screw for the secondary backplate on the left side when I meant to adjust the eccentric screw for the contact point. Is it possible that this messed things up enough to cause this horrendous backfire?

There is one other thing that I did that is probably not correct. In checking the point gaps, I was turning the exhaust cam directly with a wrench, rather than advancing the kickstart. Can this mess things up? In subsequent attempts on checking the points, I have used the kickstart as the shop manual advises.
 

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Hi Arrosi, I find when the points bind & don't snap shut the curved point spring is not aligned properly in relation to the points. It can rotate slightly were it is riveted to the points. This pulls points crooked causing the bind.

The cure is taking points off & slightly rotating spring on rivet. Go easy. Trial fit points & spring so spring sets on it's stud such that it doesn't pull crooked. Trial & error is needed here.

Just backing off nut for points wire may make points move freely. Look close & see how tightening nut moves spring & that will give a clue on which way to swivel spring.

There are insulated washers & bushings for the points spring stud. Most important they are installed correctly & the wire to coils is properly placed on the studs. If point spring or wire are "grounded" to the stud it will not spark. Since you were getting spark replicate how they were placed.

Turning motor by the advance unit bolt on cam is very bad. Hard to say if you caused damage or not. If it damaged the advance unit or slipped on the taper you'll not be able to set timing. If you can't set timing you'll have to dig into that. I'd expect no damage though. Luckily you didn't break bolt head off.

Since you can't turn rear wheel you'll have to use kick starter as best you can. I've had to do that on some bikes & the motor friction makes in difficult to go slowly & smoothly. You can turn crank with alternator nut but be mindful it can want to unscrew nut & leave rotor loose. Be mindful of that. In every case remove spark plugs.

A bore scope is not a good tool to see bent valve unless it's bent bad. Just do a compression test. Cold motor will show low. Put oil on piston & it will read higher. Normal for a 9.1 compression motor is about 180# warm. If valves are bent oil on piston will not help. Compression will be very low like 50# or lower. Slightly bend valve bike will start & run compression may be only slightly low.

I've seen many bent valves. In almost all cases the valve adjustment on that valve is decidedly looser than others. Often .020 or more.

You've got a lot going on at the same time. Carb is the last step.

Start with valve adjustment. Then points & timing. Then carb.
Don
 

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Discussion Starter #15
Turning motor by the advance unit bolt on cam is very bad. Hard to say if you caused damage or not. If it damaged the advance unit or slipped on the taper you'll not be able to set timing. If you can't set timing you'll have to dig into that. I'd expect no damage though. Luckily you didn't break bolt head off.
Don, thanks for the info. I am worried this is what caused my trouble. Is there any way to check if the cam is slipped on the taper? Can it be removed and re-installed? How does that bolt come off?

Regards, A
 

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Discussion Starter #16
To further expand on this, it seems that when I advance the engine with the kickstart now, one of the contact points opens where I expect it to (right as the scribe line is touching the nylon heel of the point) but the other one seems to reach its most open point a little before the scribe line gets to the heel of the point. It seems to me though that this problem is more likely caused by the secondary backplate being a little shifted, rather than the cam itself being moved off its taper, as it would seem that both contact points would be off on the scribe line.

Argh, always causing problems for myself. I will add this to the "Don't do this anymore you idiot" list that I keep for my bike.
 

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The points advancer cannot slip on the taper if the cam still has the alignment nib in it; however, DO NOT try to turn your engine over by turning that bolt!

Sounds like you've monkey too much with the points and you've goofed the timing on one or both sets of points. While turning the backing plate advances and retards the points pairs together, opening and closing the gap ALSO technically advances and retards the ignition.

You've got the book, and the long explanation that should serve to set it right. Both points should exhibit as near to identical behavior relative to the timing scribe marks on the points cam as possible; and both should be with correct gap set.

If you have points that either have significantly different wear on the contacts or plastic cam feet, you'll never get them to behave the same relative to each other. You might need to get two new sets of points and start over.
 

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Now is a good time to consider electronic ignition but thats another learning curve.
 

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Now is a good time to consider electronic ignition but thats another learning curve.
Or a good time to learn how to troubleshoot ignition problems...:grin2: Has anyone mentioned the condensers??? I had one fail on a car that caused loud backfires...
My experience on the timing being way off was a whole lot of nothing or kick starter kick back....
 
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