no fire in cylinder #3

I had both coil resistances out of spec so I replaced the coils with new original units. I replaced the plug caps too. I fired the bike up and the #3 cylinder exhaust pipe is cold. I checked for spark in that cylinder and it was present. What do I start checking next? Do a cylinder pressure? Any suggestions would be appreciated.

 

Obviously, compression check would show if #3 is up to snuff and equal with the others. It will also give you a snapshot of your valves at a glance, especially if you do a leakdown check as well as a cranking compression check (do the cranking test with WOT)...this will tell you if your valves are sealing reasonably well.
Many times I will find on a cold cylinder, the culprit is actually no, or not enough, fuel getting to the cylinder and many times it's solved by a thorough cleaning (or RE-cleaning) of the carbs, esp. the pilot jet and idle mixture circuit, or setting the float height properly.

 

Well I performed the compression test and these are the results.

DRY
#1 - 151
#2 - 150
#3 - 151
#4 - 149

WET
#1 - 180
#2 - 185
#3 - 195
#4 - 240

So what is the wet test showing us? The dry test looked good. Each cylinder maintained pressure. I found another test in a search. I put things back together and started the engine. I applied a little choke and the #3 exhaust pipe started to heat up. Telling me not enough fuel is getting to the cylinder. I did a carb cleaner test for vacuum leak but found nothing. The idle is creaping up as the bike warms up. The idle is not smooth. It looks like the carbs come back off. Go through them again. Look at the float settings. When I get them back on I think I will do a propane test. I have not done this before so I think outside would be a good place to perform this test. All I have is a propane bottle and torch I use for soldering copper pipes. is that ok or are you folks using these little butane units?

 

Start the bike up, get it warmed up, and off of the enrichment circuit.. Now, open the propane torch but don't light it, hold it near and around the carb boots at each carb, and both sides of the carbs. If you get a surge in RPM, you just found your leak.

It COULD be simply that your sync is way off. But, have you ever cleaned the carbs? Or synced, or color-tuned them? Considering the compression, I doubt it's anything to do with the shims, BUT.....have you checked clearances?

Last, where in NY are you? I"m south of Utica, and there's a bunch of us around the state now........some of us are from the REAL upstate NY-----

Dave F

 

Compressions are about as close as you could get them on a real, live engine. Your problem is fuel-related

 

Real Upstate?

Utica is Mid-Central NY

Upstate is the Adirondack Region.
I'm an Upstate guy.
Saratoga Springs!

 

hogfiddles I am just north of Schenectady. I will try the propane test before I pull the carbs. Maybe I do have a leak at the inlet boots or shaft seals. Did not break the rack but did a Carb clean last winter. Checked diaphragms for holes. Put new o-rings on fuel adjustment screws. Had to change out two jets. Idle circuit jets cleared. I was able to synch the carbs and used a color tune plug to adjust each fuel adjustment screw. Bike sounded great. Took it out for a ride ran well but idle climbed when it got hot. Came home and noticed exhaust pipes 1-3 were bluing. Pulled plugs and #1 was a light brown, #2 and #3 were white, and #4 was black. Went back in and color tuned again. Increased richness on 1-3, leaned out #4. Resyched again. Ran the bike again but could smell unburnt fuel. That's when I did an ohm measurements on the coils and found them out of spec. Replaced both of them. Spark looked good in all plugs. Same thing happened. Also wondered if float levels were off. Valves were checked about a year ago. Had to replace some shims to get in spec. Try to get back to it 4th of July weekend. Thanks for your help.