Possibly not firing on one cylinder

Thanks

Thanks for the reassurance.
I’ve jut found another thread here of a guy who had a similar problem and found he’d accidentally mixed up pilot/main fuel jets and the cylinder was flooding. Worth looking at...
I’ve ordered a compression tester, colourtune plug and carb balancer.
I’ll update when I’ve done some more testing

 

Could a torn slide diaphram cause a cylinder not to fire?

 

Would it be possible for a torn slide diaphram to cause a cylinder not to get fuel?

 

I would not help that is for sure. I would guess someone else will chime in here and get more technical. You will have to seal the torn diaphragm before that carb will work correctly. If the slide inside the carb will not move up, the pin that goes down into the main will not move. As you roll on the throttle the pin will not move up so the fuel mixture will not increase. There are some good links here that show you how to check (hold them up to light and look for holes, tears) and seal them with form a gasket or other RTV type sealer. Not the best but it will work to get you on the road.

 

That would definitely be unhelpful but I already replaced all four slide diaphragms with new ones when I rebuilt the carbs.
I’ll pull the carbs again and quadruple check them

 

I don't know if you can just pull the rear carb boots off when you start it and see if all the slides are working when you roll the throttle? That would be better then taking them off again and having a look. As long as they all function the same way when you roll on the throttle that would tell you the diaphragms are just fine.

Using your hand on the back of the carb/cylinder that you think is not firing will also force gas up from the bowl and then into the cylinder (and on your hand) to see if that is in case the issue. I don't want you to pull the carbs off unless you think you have jet issues and have to replace them.

 

If the carb and cylinder do fire with a hand blocking the intake what does that tell you?

 

Thanks for the tip timbox,
With pods off I can see that the slides are working fine and when I cover the rear of the carb it does indeed have vacuum and gas comes out onto my hand.
Exhaust on second cylinder still not as hot as other 3 which sizzle when touched with wet hand.
Spark plug wet with fuel when pulled (from cutoff at high revs)

 

Have another thought swap the plug caps from a hot cylinder to the cylinder that is cold see if the cold cylinder heats up ...could be a bad plug cap .

 

Thanks jet, I already swapped the spark plug leads 2&3 without success

 

No. The main jets don't come into play at idle.

 

you could just have a bad plug

 

The plug has been changed twice and checked on a different cylinder

 

Well f*** me sideways with a chainsaw!
In frustration I thought I’d better take one last look at the carbs.
Pulled them last night and somehow (I’m guessing I just didn’t tighten it properly) the pilot jet was sloshing around by itself in the fuel bowl
Just took her for a run. Still not quite 100% there but at least no backfiring blue flames.
Colourtune plugs and compression tester in the mail, hopefully I can get her running properly before too long.
Thanks to everyone that posted

 

Way to stick with it and get results! Glad she is running again and at least putting a smile back on your face.