Spark,Comp,Fuel,Air, no go on cyl. #3?

[robgusto]

My apologies to anyone who has already seen this topic posted in the carb. section but I think my issue may be with the engine itself. I posted a topic called What Next Colortune or carbsync where I tried to figure out what to do next. I encountered a problem with a cold pipe on cylinder #3. I have good compression, the Carbs have all been rebuilt and taken apart several times, there is spark for sure, but the #3 cylinder is not functioning well if at all. All other pipes get very hot at idol where #3 gets warm I assume from radient heat from block. So I have all the elements to make it run but the pipe is still cold? Is there anything in the engine that would make this happen?

[Big T]

Rob

What bike are you talking about?

Why isn't it in your signature yet?

[Rudeman]

You said you cleaned the carbs. How thoroughly did you clean them? The only thing i can think of that woul dbe causing your problem is an extremely rich fuel to air mixture. If you cleaned them w/o disassembly you may have some debris or old fuel deposits remaining. Most knowledgable guys will recommend that you dip them at least overnight. Replace all the rubber parts when you reassemble. Also, did you or the PO replace any jets? Make sure you have the correct jets installed. Inspect them closely because many jets are similar in appearance but are completely different. Just because they fit does not mean they're the right ones. Learned that one the hard way back in 1980. Some idiot parts guy sold me what he said were the correct jets for my 77 GS750B. They fit but the bike ran like S**T. Check your needles and make sure they AT LEAST match and are correctly adjusted. In extreme cases oversized mains can dump fuel into the mix during idle. Especially if the pilots are plugged or restricted.

[mike_of_bbg]

If you didn't sync your carbs yet could it be that #3 is very closed and not letting any air in at idle? Does it heat up some off idle?

[robgusto]

1981 GS 750 pipes 2 into 1 no mufflers or baffles, K@N pods, dyno rejet stage 3. I have talked to dynojet and I belive that I have a close match to equipment. I have done a complete cleaning, and O ring replacement, then took off again to recheck jets on carb #3. I will be synching carbs on Monday and will report back. I will take it for a ride to see if it heats up off idle.