Bonneville America Forums Forums Technical Forums General Tech ....banging on one cylinder

So I noticed that my bike is only running on one cylinder. I get some occasional back firing when I rev the throttle a bit. Plenty of spark at the end of the wire to the frame. Tried swapping coils, the primary wiring and the secondary wiring to see if the problem would follow a specific coil. It did not. I removed the carbs, poked around with them a bit, the float bowls are getting gas, the slides appear to be operational. Everything looks clean, no gunk, no goo. Sprayed some starter fluid into the back of the carb in question and I got some idle raise. Im at a loss as to what to check next. Do I just do a complete tear down of the carbs? It would appear that I have 2 parts of the air/fuel/spark combination thats required for combustion..... Any tips? Pointers? Something really simple that I'm missing?

I am sure you are going to get more informed help than this, but you might want to check out this site if you decide to tear down your carbs. http://www.dinqua.com/Triumph/carbs0.html

If it wasn't for Dinqua, my bike would still be in parts.

I expect you already tried to adjust the idle screw, just in case a gremlin twisted it on you whilst you weren't looking.

Ted

I haven't checked the idle adjustment screw yet. The carbs are just seated on the back of the heads at the moment so that'll be 1st thing I check tomorrow.

had that intermittently. was a coil. other thing to check is the pickup wire on stator.

Faulty CDI?

Sorry Keith, I'm not sure what the CDI is. If it's part of the ignition system I'm pretty sure that's all intact. The left cylinder is the one that's running. If I pull the spark plug wire on the left head while the bike is running it stalls. I rolled all the wiring from the top of the coils down to the plugs. I was hoping to see the right cylinder fire, pull the right spark plug wire, and see the bike stall. That would point me in the direction of a bad coil, or plug wire...... Im thinking I've got some kind of vacuum problem, or a glogged carb or something. I've got a nice big blue spark on both sides. I think I'm not getting fuel.......Meh.

First I would check that the right carb has free fuel flow by opening the float bowl screw and watching the fuel run out of the bowl with the petcock open. You'll want a clear container to catch the gas so you can look for dirt and water. Then I'd check both squirrel condoms for dry rot and insure the manifold rubber is intact and is in fact right side up and oriented correctly front to back. Have you had the top off the carb? Because the diaphragm can be hard to re-seat sometimes and that's another source of frustration. What else have you tried?

I haven't had the top off the carb. The squirrel condoms look good, I won't say with 100% certainty that the rubbers are on correctly but I am pretty meticulous. They were only off once before to rejet. Aside from what I stated above, I haven't tried anything else..... I am at work right now trying to come up with a list of things to check so that I have some kind of game plan at 3:30 when I get out. I though about trying that smoke test to see if the right side is pulling vacuum, and I had a friend mention a compression test.

For a quickie compression test you can just put your thumb over the spark plug hole and spin the starter; it should have enough pressure to push your thumb off the hole pretty stoutly. You can also replace the condoms with a section of fuel line tying both nipples on the same cylinder together as another test. All of this is predicated on the fact that you do have spark to the right side and the igniter isn't at fault.

It could also be the pickup coil gap under the right side engine cover. The book says a gap of 1.0~1.2 mm but that's been updated by a service bulletin and that gap now is 0.8mm and it does make a difference as that one thing has been a common source of misfiring bikes.. You can check that gap without losing more than a tablespoon of oil when the bike is on the side-stand but you'll almost certainly need a new gasket...mine shredded when I removed the side cover.

I have been looking around and I have seen the pickup gap issue mentioned in quite a few places. I'd like to be pretty positive about it though before I ruin a gasket.

Is it possible to have a faulty ignitor and still have spark at the end of the plug wire?

I've been reading and correct me if I'm wrong, the ICU,CDI,ignitor are all the same thing? It fires off a voltage to the ignition coils right?

The Haynes manual describes the test of the ignition system and basically sums up with "If the test results are good the entire ignition system can be considered good" So according to their logic, if you have "a fat, blue spark" everything is a-ok.

Okay.... update.

Opened the float bowl drains and have a steady flow of clear, clean 93 coming out.

Compression check was fine.

I don't have a carb balancer atm, but I hooked up a vacuum gauge and I'm pulling 20hg at all 4 vacuum points.

Took apart the right side carb, everything is spotless. Took out all the jets. They're clear. Floats look fine, not full of gas or anything.

Hidden fuel filter is clean as a whistle.

With the bike running,I stuck a scope in the airbox side of the carb, started the bike and physically watched the slide actuate as I worked the throttle.

I Basically paralleled the spark plug circuit with a separate spark plug, thinking maybe the spark is breaking down under load. Not the case......

I'm really baffled here.

Help, please, anyone......

If you swapped the inputs as well as the outputs of the coils and both coils came up good then I'd say you're down to the pick up coil gap or the igniter. Buy the $5 gasket and pull the right side cover and insure that gap is 0.8mm; you really want to eliminate all other items before you go for a replacement igniter. Right now is when you want a friend with a spare or an identical bike you can borrow an igniter from.

If the gap was incorrect wouldn't the pick up coil just not send the signal to the igniter telling it to fire off to the right side?

On a side note, the crimp for the ignition coil end of the spark plug wire just stuck to the end of the nub on the ignition coil..... So it's either find a way to crimp a new one on or order a new set of wires. ::::Sigh:::::

That gasket is a dealership item? Mail order?

.....Pulled the right side cover. Shreaded the gasket but who cares, I only have one spark plug wire right now anyway so I doubt I'm going to get anything running tonight.

The pick up coils clearance was .635 Set it to .8 Now I have to get a gasket and some wires.....

Longshot......

If you are getting spark on both cylinders and you have fuel, the only thing I can figure, other than a mechanical issue like a burnt valve which would show up on the compression test, is timing. Pull both plugs ground them and spin the engine over. Try to see if the spark alternates from side to side. I don't know if it is possible but given the fact that you have spark and fuel, then it must be firing at the wrong time?

I'm assuming you have switched your spark plug (hasn't been mentioned in the thread).

You can make a gasket with some gasket paper obtained from an auto parts store. Just get a small ball peen hammer and lay the gasket material against the edge to be sealed on the cover and tap. I've done this many times in the past on engines when gaskets weren't available. Once the outline if made, you can cut with scissors if needed.

You can also repair the plug wire by cutting a half inch off the damaged end and crimp another male end in place. It should contact the core of the plug wire.

Greggor, I tried switching plugs. No avail, that was actually the first thing checked.

I buttoned it all back up, and still the same story morning glory. Same gasket, jumpered the end of the wire to the coil just to test it out.

It runs on the left cylinder only. The spark is there, defintly, with out a doubt. I don't think im getting fuel up to the right side.....I just can't figure out a way to prove or disprove this theory. I think I have air and spark.

I will see if I can ground both plugs..... that spark jumps quick though, not sure if I'll be able to tell if its alternating with the naked eye.

If you discount the electronics then you're left with either an obstruction in the right manifold or an intake valve that's not opening. Both of those choices seem so unlikely that I think, unfortunately, that you need a replacement igniter.

Ryan,

You have to confirm that you are getting spark on both cylinders when it is running on only one.

You didn't switch out the CDI unit for one out of a Bonneville or Thruxton by chance. They are set up for 360 degree firing, not 270. Someone pulling a fast one on you???

Can you clarify when the engine runs on one cylinder? All the time, at idle, mid range or full throttle. Trying to see if the engine runs on two cylinders some of the time? Have you adjusted your idle mixture screws yet previously requested?

Roadie, If the igniter was bad would I still get spark at the plug of the cylinder that is not working?

Gregger, it runs on one cylinder all the time. It won't start off the right cylinder and if you pull the plug off the left cylinder while the bike is running it just dies. There is spark at the right cylinder when the bike is running off the left. No one has changed any parts on this bike besides myself. I turned in and turned out the idle mixture screws just for good measure, no effect. I can get some back firing out of the right side when I manipulate the throttle a bit.

I looked for gas with the scope.... I didn't see anything obvious. I also checked the side that runs. It looked exactly the same. I am not sure how fine atomized fuel is... regardless, I couldn't see any form of fuel on either side.

I'm frazzled man....... Really just feel defeated.

Don't feel too bad; my bike decided to run on one cylinder right after I replaced the rear tire...no warning before hand. I parked it and took off the rear wheel and when I got the new tire on it would only run on the left cylinder. I spent a week trying everything I could think of. Turned out to be the igniter but without a known good one to use as a test I just bit the bullet and bought a used unit from Pinwall Cycles eBay site at less than half of the dealer cost. Good folks at Pinwall and the igniter is still working.

Well I woke up at 1 AM and had a brain fart. If I offset the carburetor and hook up the right carb to the left cylinder and the bike runs I can eliminate the fuel/no fuel debate.

I don't know if you can actually do this, and I don't know if I will have the time to test it out today. If it works I'll be ordering a new igniter.

Anyone have a quick link to somewhere I can pick up a right side engine cover gasket?

Sounds like more work (for dubious results) than dismantling and checking/cleaning the carbs.

....The carbs have already been dismantled and cleaned and checked. Offsetting the carbs would be a last ditch effort to get the bike to run off the right carb. If I know the carbs are good then I'll feel a little more comfortable laying out the cash for the new igniter.

If the igniter is bad, why would I still be getting spark on the right side of the bike? I'm confused by this. And I cant seem to find an answer.

Maybe fire up the bike, letting it run on one cylinder. Shut it off then pull the plug on the dead cylinder. If it is wet, it's getting fuel.

I just went through this entire thread, and maybe i missed it, but have you tried a new spark plug on the right side? I didn't see any mention of you actually pulling the spark plug out. Did i overlook it?

Okay. We have some progress to report. I took the carbs off, and seated the right carb on the left head and left the left carb floating so to speak.....the bike ran like garbage. As soon as i touch the throttle it stalls. Almost like it's running just on the pilot.

I took the carbs off again, lifted them over the frame and seated the left carb on the right side head, and floated right side carb. The bike ran on the right side cylinder alone, exactly the same way it runs when the left side cylinder is working properly. Rock the throttle and she roars.

So, I think I can say with some certainty that the ignition system is without a doubt, operational and intact. The right side carb is going to be the culprit here. There has to be some kind of blockage that I can't find or see or a mechanical issue that I'm missing.

I've sprayed every port,jet and orifice on the carb with carb cleaner. I spray in one hole, watch it come out another hole. Looked threw the jets. Pulled the needle, diaphragm, and slide everything looks like it's in working order. I didn't remove the float, just because that little spring that holds it on looks like a mofo to put back on.

The new gasket for the right side engine cover won't ship for about 10 days, so I have some time to figure out what to do next.

Well I have to say that was an ingenious way to test the carbs for fuel. Glad you have isolated the issue.

Have you pulled your idle mixture screw on the bad carb out? I don't think you stated that it was ever adjusted or the circuit cleaned.

Also, Ed asked if fuel flowed freely from the bowl drains. I'm concerned about the needle valve that is attached to the float. If it is stuck closed, no fuel will flow. You did state that there was fuel in the bowls but just making sure.

If only to rule it out, you should check the float and float needle. Measure the float height too. The Haynes manual has pretty good instructions and pictures. I would also blow compressed air through every orifice you can.

Ted

I have not pulled the idle mixture screw out. I turned it all the way in and backed it out 2 3/4 turns. I'll yank it out and look around. I'll definitely check the float needle and height and adjust if necessary.

There is fuel in the bowls and it flows free if I open the drain. I'm just going to have to take the plunge and take the whole assembly apart.

And it for no other reason than comic relief... maybe think about changing your signature. You could be jinxing yourself!

Sounds an awful lot like the needle valve to me. I had the same problem on an old Honda that would only run on one cylinder with dual carbs. Take the bowl off and wiggle the float, make sure you see the valve pin moving and not getting stuck up inside it.