Dropping cylinders; probable cause

Hey all, I have a friend of a friend's '81 1100 interstate. He brought it to me for some brake work and a little tune-up but it was only running on 3, hadn't been on the road in a few years, I got all the old gas out, added some SeaFoam, drained the carb on the dead cylinder, ran it a bit, worked on brakes, Now it's running on two. How can I tell if it's carbs or what?

The 2 front run on one coil the 2 rears on the other but don't let it fool you cleaners can pick up/off debris and cause another clog, To determine take the air cleaner off and out and get a syringe or other device small enough to dribble gas in front of the offending cylinder while running if it picks up it then it isn't getting gas.

sounds like a good plan, BTW it's the left two not seeming to fire (no heat on exhaust) so knowing the coils are paired front and rear makes it less likely to be electrical I suppose. I will try this

Left 2 are the last to get fuel it circles around like a horse shoe so not coils it could have picked up garbage and deposited it in the carbs. Under the float seats are tiny screens made of fabric that get old and tear and if so will let small particles in the bowl these should always be checked and replaced if needed just gently take a blunt pointy object an push on the screens and see if the are separated but that is later and if you need to remove them.

But do squirt some fuel into the carbs on the left side see if it picks up.

So I pulled the plugs on the left bank to check for Spark turned it over and vomited gas out of the left rear cylinder so I’m thinking stuck float needle seat dumping gas through the carb into the cylinder so a carb rebuild is in order no?

I would say vomiting gas out of a cylinder is good enough reason to rebuild the carbs! No argument there!

It certainly wouldn't hurt. It's a big job that takes patience and following directions to the letter. The outside of the carb looks pretty varnished and dirty. The insides could be just as bad - let's hope not. I have used a few different kits over the years. I've found that Randakk has the best quality and most complete kits available. I have not bought one since he sold it, so I can't vouch for them now - but they should be a good place to start. You might consider removing the leaking carb, clean it out (thoroughly) and see if that fixes the sticky float needle. A proper rebuild on ALL the carbs, with tuning and proper synchronization will really make your Wing sing like it should! But, WARNING, it's a BIG job to do it right. Best of luck!

When your done fill them on a bench using an elevated fuel source you can even go cheapo with plastic bottle and a hole drilled into the cap to fit a tight fitting fuel line I use cheap plastic clear line from a hardware store raise it up 5 Ft. to simulate the pressure of the pump and look for leaks and while your in there make sure your accelerator pump nozzles are clear just pump the throttle by hand it takes 10-20 pumps to prime the tubes you should get a squirt out of each carb throat.

Okay, good insight. It’s not my bike. It’s a friend of a friend and I don’t want to go that deep. Something I don’t want to do means it would cost the owner far more than the bike is worth. One of my own bike’s need this level of work and I haven’t done it in yet! Honestly what is an 81 interstate worth that needs carb rebuild, brake rebuild, new tires and valve stem seals worth? (Fair chrome, exhaust leaks and mediocre paint) $500? I will probably tell him to come get it or give it to me for the hours I have into it already. It was a “tune up and brake work” when I begrudgingly agreed to look at it. I think we’re a bit beyond that.

It is probably worth more in parts if he doesn't fix it if you can get it to turn over and check compression you could sell the motor for 300 bucks alone without carbs the carbs I seen on ebay bring 100 fairly easy and any add on`s are always snatched up.

He did ride it to my house. 1.5 miles with zero brakes and running on 2 maybe 3 cylinders

Probably 2 they run smooth even with cylinders out they just lack power

Well, it won’t idle. it’ll run ok if you rev, it sounds terrible at idle, lots of knocking which I understand is normal when only a couple cylinders are firing. And it won’t stay idling without throttle input. I think it’s highly unlikely this thing is gonna resurrect itself without a complete carb rebuild in which case I’m out.

All I can add is that I rebuilt 2 sets of 1100 carbs and they were pretty simple to take apart, clean and rebuild. There are great tutorials here on the site that will walk anyone through step by step if they are willing.

If it was my bike would probably be done by now, i’ve done bike carbs a million times but it’s somebody else’s. Even if he was willing to pay me a fair rate to do it I really don’t think I want to. BTW I assume these carbs have an overflow drain because I wonder why gas is in that cylinder. it shouldn’t be able to get in the cylinder right?

I have the plugs out and the airbox open and I was gonna try one last time to get it fire on all four.

Javandyke said:

If it was my bike would probably be done by now, i’ve done bike carbs a million times but it’s somebody else’s. Even if he was willing to pay me a fair rate to do it I really don’t think I want to. BTW I assume these carbs have an overflow drain because I wonder why gas is in that cylinder. it shouldn’t be able to get in the cylinder right?

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They don't have an overflow like the older ones did.

DaveO430 said:

They don't have an overflow like the older ones did.

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So it will dump into the cylinder eventually then yes?

So I left the air filter off and the plugs out and let everything air out for a couple days, petcock off of course. Fired it up, smoke everywhere, ran on two, 10 seconds and shut it down, and there is fuel everywhere on the ground, under left side crank case and left exhaust, fuel dumping through en mass.