I'm stumped. One side won't fire

[Paul57]

I have cleaned and rebuilt the carbs, which have all the original stock jets. And yes, they are very clean! When I fire up the engine, it seems like only the right side is working. If I pull the right plug wire off, the engine dies. Pulling the left wire does nothing.

If I have full enricher, both sides fire and the engine revs up to 5 or 6 k. Once I push it in all the way, (or halfway), it idles down to 1200 or 1500 nicely, but then if I pull the right wire, it dies.

Both mufflers are hot, but the right muffer seems quite a bit hotter, as in some discoloration of the chrome near the engine, which I haven't seen before (I'm the original owner). The left one is still too hot to keep your hand there, but not as hot.

I know I have old plugs and wires that aren't in great shape, but switching plugs and wires from left to right had no effect.

I took the carbs off and opened them up to look for a stray piece of something blocking a jet. Nothing. All clean.

I've checked the valve lash. Twice.

I've pulled both plugs and get a spark. I've also used a spark/light thing and it flashes on both sides, so I think I'm getting a decent spark.

The fuel mix screw is 3 turns, but I've played with it in and out and see no real effect on the left side while the engine is idling.

I attempted to synch the carbs with a manometer yesterday, but to be honest, now I don't know if it was meaningful because maybe the right side wasn't firing. They are bench synched, so they should be close enough to let it run.

I've checked the airboxes for trash etc. They are ready to be replaced, but it's not the issue here.

Compression on both sides seems to be the same.

Frankly, I'm out of ideas! Any suggestions on where to look next? Thanks.

 

[16VGTIDave]

First thing - DON"T pull off a plug wire when the engine is running unless you want to buy ignition coils. Each spark has to go somewhere, and the insulation inside the coil is often the weakest point.

Sounds to me like your left carb needs further cleaning. I'm going to guess that the pilot circuit passages are plugged. Or the pilot screw is broken. There are plenty of topics here about carb cleaning. And you won't be the first to have to clean them 4 or 5 times...

 

[Paul57]

Good point about pulling the spark plugs. I'll be more careful about that.

Well, today I pulled the carbs and boiled the left one in vinegar for a couple hours. Rechecked all the jets, etc. Put it all back together and .... the left will only run with the enricher out to the first stop.

I even switched coils just in case it was a weak spark.

Sigh... I'm running out of ideas fast.

 

[16VGTIDave]

Did you probe all the passages with a fine wire? The corrosion that builds up in the passages is difficult to remove by chemical action alone.

 

[Paul57]

Just to close out this thread, I took the carbs apart again. I traded the jets from one to the other. I don't think that did anything, but it was a diagnostic. At the same time, I replaced the tiny O-ring in the fuel mix screw because the old original one looked somewhat flattened.

Put it all back and YAY, it runs, it runs! Got the carbs synched the last few parts put on. Almost ready to hit the road after a 25 year hiatus!

 

[willem]

congrats

another xs400 saved !