#4 carb acting the fool

[patrickhimself]

I had done that before, but I gave it a second go.

Results: at 3k rpm I can get it all right across the board, sits about 1800. When I drop it down to 1100 carbs #1-3 all sit even, except #4, which sits at about 1/2 their level. I'm using a Morgan Carb Tune. Still no changing when I adjust the pilots screws.

I'm not special enough to have found some fancy new problem no one has ever heard of, so I must be doing something wrong, I just don't know where to look next... I can literally just grab the #4 header and hold on all day...nothing is coming out of there...

 

[Guest]

You should be adjusting you throttle slides when you are syncing the carbs not the pilot screws. You need the bench sync the slides first then set up you gauges, and do a final sync of the slides. if you pick up the #4 slide just a touch I bet the cyl. starts firing at the idle stage. Did you read the tutorial on Basscliffs site on how to set up the carbs? Pilot screws are for highest idle after a proper sync

 

[patrickhimself]

Yeah, I've read that. Went back over it and realized I'd done a couple things slightly wrong (it's been a while).

Additionally, took a look in the airbox and noticed that the filter wasn't seated properly, so I reset that and cleaned up some of the sealing bits.

Anyway, it got too late to keep working, so I went and had a few beers instead. I'll try again tomorrow.

 

[patrickhimself]

Bench synced and vacuum synced and I've still got a cold pipe. I even added more weather stripping to the air box. Everything I'm doing is making the other three carbs run better, but I'm not getting anything going on #4.

The boots all seem good (pliable, no cracks) but I'm beginning to think I ought to just buy a new set to make sure that's not the problem. The intake orings were replaced about 6 months ago...

 

[Guest]

Screw off the spark plug cap, trim it and rethread it.

 

[patrickhimself]

Screw off the spark plug cap, trim it and rethread it.

Done. Still cold. Still, if I rev above 4k I get a plume of black smoke.

This is super frustrating. Bike starts like a treat, even with just the three cylinders...I'm about ready to check if a bird made a nest in the header over the winter...I just want to ride!

 

[patrickhimself]

Well, it's back in the soup for the #4 carb. Gonna try to clean it again and see if I missed something. I also bought new boots for the air-box (the horns in the box were a bit brittle) and new spark plug caps (PO fit one NGK cap and left the rest stock).

My thoughts: when I sync the carbs at 2k and drop it back down to idle, #4 vacuum drops significantly lower than the other 3 carbs. This is consistent with the compression being equal across the board at WOT, but being 20psi lower on #4 (as compared to the other carbs), with the throttle closed.

Soooo...to my not so experienced brain, this is indicating that there is not enough air getting into the pistons when the carb slides are closed. Does this seem accurate?

 

[gustovh]

Verify spark in the #4, run the bike at idle and shut it off and check #4 plug for signs of fuel. If it is wet, or smells of gas, it is not a carburation problem.

You broke a ring and replaced it, which one was it, did you hone the cylinder? Your low compression in #4 is yelling at you, find out why.

jmo
V

 

[patrickhimself]

I haven't gotten into the pistons as of yet. The plug does get wet, and the spark is definitely there.