xs11 79 special number 2 cyl is cold

[BigalG]

After rebuild last year everything was running tip top, my son brought it back to me said it was limping with reduced power. Found number 2 cylinder is not firing , headder pipe is cold all others are hot. I tested for spark and it is fine, adjusted the idle screw, no change , fuel in the bowl. I pulled the carbs and went tru 2 top to bottom. Checked the others and spot cleaned but everything looks fine. Checked the boots when off and all are fine as were replaced last year. Put it all back together and .... same thing no fire in 2. Any help would be appreciated.

[Bax]

BigalG Hi, Can you do a compression test? Since it's only one cylinder out of four with waste spark coils it's very unlikely there is an ignition issue. You already went through the carb, next thing I would be looking at is the exhaust valve.....

---Bax

[BigalG]

i will get a gage and test the compression and report back

[Socer4m]

after compression check,,,maybe pop out the number 2 sparkplug, rest against engine to see if its sparking on turnover,,,if not also check your pickup wires, do search how to check,,can cause exactly same syptoms,easy fix also,,,, and check plug wire end to see if its fully screwed into spark plug cap,,,also check with another spark plug for giggles....keep us informed.....Mike in Sun Diego

[bikerphil]

If you rev the engine to 3 or 4K does the pipe heat up?

[cajun31]

After rebuild last year everything was running tip top, my son brought it back to me said it was limping with reduced power. Found number 2 cylinder is not firing , headder pipe is cold all others are hot. I tested for spark and it is fine, adjusted the idle screw, no change , fuel in the bowl. I pulled the carbs and went tru 2 top to bottom. Checked the others and spot cleaned but everything looks fine. Checked the boots when off and all are fine as were replaced last year. Put it all back together and .... same thing no fire in 2. Any help would be appreciated.

It sounds to me like you still have a clogged pilot jet on number 2. I fought the same problem with a rebuilt set of carbs and once I replaced the pilot jet with a brand new one all was well. The old jet looked clean but obviously wasn't. Like Phil asked if you rev the engine up to higher rpms to kick in the main carb circuit does the pipe heat up. if not then you need to do a serious clean on that carb. One other thing that could be messing it up are air leaks. The butterfly shaft seals may not be sealing. If never replaced they are suspect.

[bikerphil]

If the pipe is cold only at idle, the sync could be off leaving the #2 throttle plate closed more than the others preventing that cylinder from getting any fuel and firing.

[cajun31]

If the pipe is cold only at idle, the sync could be off leaving the #2 throttle plate closed more than the others preventing that cylinder from getting any fuel and firing.

Not saying that is not possible, however he did state the bike was running tip top after rebuild last year.

[bikerphil]

Not saying that is not possible, however he did state the bike was running tip top after rebuild last year.

Yep, just sayin', if someone mistakenly turned the wrong screw, that would do it.

[HymesX]

The guy who just rebuilt mine had this issue. Took it back apart and there was a piece of something stuck on the exhaust valve seat keeping it from closing all the way.

[shutchis]

The #2 intake manifold has a vacuum line going to the fuel "octopus" system. This vacuum line operates a check valve, which supplies fuel to the petcocks. Just for grins, Remove the vacuum line from the manifold and plug the manifold port. Turn the petcocks to "P" for Primary; this petcock setting bypasses the check valve. Start the engine and search for vacuum leaks. I'll spray starter fluid around the manifold clamps and carb butterfly shafts. WD40 works too and is less volatile. If the engine rpms increase while spraying, you have a vacuum leak. If the #2 cylinder starts firing at idle, you may need to service the octopus system, it's an amazing maze of fuel line hoses. In closing, we have all seen your problem. There are multiple possibilities. As stated by the thread, compression, valves, electrical, and dirty carbs are all a source. God's speed. Good luck. Stay safe.

[BigalG]

Thanks everyone, i realy appreaicate the help found here, great community! Turns out it was a spark plug. even though I did the inital test of pulling the plug on the dead cylinder and grounding it out and running the starter.... it looked to be sparking normally. Well then, when doing the compression test I pulled all 4 plugs, everything was equal across the 4 so i randomly replaced the plugs and fired it back up. Cold number 1!
after realizing the simplistic solve of this i ran in to order some plugs from my local store only to return 15 min later to the garage to find fuel flowing out all over the floor from the air box. Yes I had pulled the octi during the rebuild and have been so careful to shut the fuel off. but during the solution phase and compression testing i turned them on and off several times and ....well....just forgot. After wrestling the air box off , if you have done it several times on the 79 special you know how dredded that task is, i drained the fuel dried out the air filter and had to wait a full day to fire it up with new plugs. Back to sounding like a sewing machine out on the road. ..............................Thanks again.
BigalG

[Radioguylogs]

Congratulations on solving your problem., especially so easily.

Thanks for reporting the conclusion so we all can learn.

[cajun31]

Thanks everyone, i realy appreaicate the help found here, great community! Turns out it was a spark plug. even though I did the inital test of pulling the plug on the dead cylinder and grounding it out and running the starter.... it looked to be sparking normally. Well then, when doing the compression test I pulled all 4 plugs, everything was equal across the 4 so i randomly replaced the plugs and fired it back up. Cold number 1!
after realizing the simplistic solve of this i ran in to order some plugs from my local store only to return 15 min later to the garage to find fuel flowing out all over the floor from the air box. Yes I had pulled the octi during the rebuild and have been so careful to shut the fuel off. but during the solution phase and compression testing i turned them on and off several times and ....well....just forgot. After wrestling the air box off , if you have done it several times on the 79 special you know how dredded that task is, i drained the fuel dried out the air filter and had to wait a full day to fire it up with new plugs. Back to sounding like a sewing machine out on the road. ..............................Thanks again.
BigalG

Sorry to hear that about the gas. The very reason I always tell folks to keep the octi and just put a new diaphragm in it. I know you probably have already but as a word of caution before you ride it too much. Did you take a look at your oil view window on the right side of the bike to see if the level of the oil was still OK. Sometimes flooding carbs can also drain back the other way into the crankcase. Obviously running it that way can cause serious problems.
Congrats on finding the reason tor the cold cylinder.

[Bonz]

Good work! Swapping things around is always a first resort for me to rule out something more extensive such as a mechanical issue in the valve train, etc.