has compression, has spark, not running one cylind

got my bike up and running today! but.... the #4 cylinder is not running. the exhaust is cold. i took out the spark plug and laid it on the engine and i have spark. did a compression test and it was over 100. i cleaned the carbs before starting it up. does anyone know whats going on? what i should look for?

I had the exact same problem: spark but a cold pipe. Redoing the spark plug wire connections solved the problem.

joshjones84 wrote: got my bike up and running today! but.... the #4 cylinder is not running. the exhaust is cold. i took out the spark plug and laid it on the engine and i have spark. did a compression test and it was over 100. i cleaned the carbs before starting it up. does anyone know whats going on? what i should look for?

Does the spark plug tip appear damp with a gasoline odor? Perhaps dripping wet with gasoline? Or dry?

Could spray starting fluid into #4 air intake to see whether #4 begins combusting, which would indicate fuel starvation (for whatever reason) in #4 cylinder.

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The only way to tell if you have a spark under compression is to hook up a strobe light when it's running. If the lamp doesn't flicker, you do not have a spark. If it shows a reliable spark, this particular cylinder doesn't get a mixtur that will burn.

Vacuum cap on carb holder/boot missing? I'm not sure if your bike has vacuum ports in the holders but if it does and the cap is missing it can cause it to not fire at idle.

UPDATE! i switched the spark plug wires off from the running cylinder to #4 and..... no luck. i unscrewed the drain on the float bowl and.... im getting fuel into the float bowl. i took out my spartk plug and.... i dont smell any gas. what the sh_t. what should i look for next?could something be sticking in the float bowl? i have a new valve in there. does the float need adjusted or is it a bigger problem? im running out of time for this summer! i want to ride it at least once!

If you haven't tried it, try swapping spark plugs as well - even brand new ones can be bad.

That said, a strobe light will immediately tell you if it's sparking inside or not.

If you have a reliable spark and you have compression, only fuel is left. Try starter fluid and see of it fires.

I would say if theres not any gas on the plug, and its completely dry, Id start with the carbs.

Blocked carb pilot circuit could be why fuel mixture isn't entering the combustion chamber.

Here's one way to clean the pilot circuit.



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UP DATE!!!! i took off the float bowl, took out the jets, cleaned everything, put it back together and...... NOTHING!!!!!! so i left the bike running and decided to pack it up. went down to pick up my tools and i heard a faint pff pff pff pff pff pff pff... i reached around the carb area and i found an air leak. i put my finger over it and it started to idle real smooth! i left my finger on for a few and reached around to the #4 exhaust and....ITS HOT!!!!!! no i just need to find a plug for it and i should be set.

Hey Josh,

I have literally the exact same problem as you. Where was the leak that you plugged with your finger?

V/R

Kev

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