Maxim 400 with dead cylinder

Yesterday, I thought I was at the very tail end of restoring a girlfriend's 82 Maxim 400. I was zooming around local streets, and braking hard to break in the new front brake pads, and then I took her for a ride. Halfway through that ride, the bike started to hesitate on acceleration, and once we returned, noticed a little (white?) smoke coming out one of the mufflers. I pulled the plugs and one seemed ashen and the other oily, but I'm not so sure anymore. I started it up a while later, and realized that only one cylinder (the left) was firing. When I pulled out cylinder 1's spark plug and ground it against the cylinder head, it was sparking. So, I'm assuming it's a problem with the fuel flow and thus carb number 1. I had cleaned these out previously. I did a compression test last fall after adjusting the valves and got 130 and 134 I think, which is respectable for a 400.

Anyways, I wanted a little confirmation that pulling the carbs off again and looking inside is the best course of action. Not sure what I should be looking for in there though.... Advice appreciated!

 

I am going through a somewhat similar problem. I have rebuilt my Xj650 and had it running great for about 2 months. Left it outside for a few days in the rain and now cylinder 4 is miss firing. Still fires just squeaks out of the right boot now. My troubleshooting goes as follows and this might help you.

Switched lead to see if it was a coil issue. Nope.
Replaced spark plug. Nope
Re-synced carbs with Manometer. Nope.
Got really irritated. Yes.
Tapped Carburetor with a hammer. Thought it might be stuck as it was leaning on its side for a while

Next in line for me to do.

Check boot for vacuum leak. Spray with quick start and see if engine revs. If it does there is a leak. I am going to use propane, its what I already have.

Check battery for charging issue. Bad battery, weak spark.

Gently play with mixture screw. I don't have a colortune so this is last.

Anywho, this is what I am doing and maybe it will help you. I have already rebuilt the carbs, did Valve adjustment , heck I rebuilt the top end.

If you have any other idea's they are welcome.

Cheers,

Jason

81 Xj650

 

Back to the original problem, on a 400 twin.

I'm confused; you said the left side was firing OK but then all sorts of discussion about issues with the #1 carb. The #1 cylinder IS the left cylinder.

I would suspect if it was running fine and now it suddenly "lost" one pot, that the most likely culprit would be that you've sucked a piece of crud into the carb. Even if it had a MASSIVE vacuum leak on the right, I don't think you rode it far enough to have blown it up.

 

OK, so here's the update. I was barking up the wrong tree, imagining carb problems.

I might be in trouble. Here's the deal: I have oil fowling my right (cylinder 2) spark plug. After 5 minutes running or whatever, it will fowl it to the point where it stops sparking. I'm thus assuming that there are only 2 options: either my piston rings are worn and leaking, or my valve seats are. Correct? Well, maybe a 3rd - a leaking head gasket; it's my understanding that the oil for the cams goes up the right rear head stud.

I'm testing 134 PSI on the right, 130 on the left. These are within spec, but maybe my compression gauge is reading high? After I put the valve clearances (shims) within spec last year, and got those readings, I didn't expect to have engine problems.

So first things first: am I correct that I need a valve or ring job? If so, how do I diagnose which one? Should I do a leakdown test? Maybe I should also remove the carbs and right carb mount and take a look into the intake port and see if there is oil on the right intake valve.