Topic: 750F one cylinder woes

[Helo229]

Hi all, so here's the latest in my restoration woes with my 750F. I realized that my rear wheel wasn't true, so I set the bike up on the centerstand and decided it would stay there until I got new spokes, wheels trued, and good rubber on it. While at the auto store to pick up some stuff for my volvo, I decided that I was going to try out some carb cleaner fuel additive on my bike (since they seemed to be working and I didn't want to tear them apart).

So, I got some STP/Gumout (not sure which), pour about 1/4 of the bottle into the tank, and the plan was to run the bike 15 minutes a day until the tank was dry. Day one went great. Day two, the bike wouldn't start, so I left it sit until the weekend.

Come the weekend, I pull each plug, check it for wear, hold it to the engine and crank the start to check for spark. I put it all back together, and try again, turning up the idle screw. Eventually, I get the engine to sputter, but it will die immediately unless I give it just the right ammount of throttle (about 1/4 of turn). I check the pipes, and I find that it's only running on one cylinder.

With this newfound discovery, I assume that it's not a timing issue, so I broke down and removed the carbs. Each bowl had fluid in it, so it's not the petcock. Taking the bowls off, I removed the jets from each, and each was clean as a whistle. I know from other posts that's no garuntee all is well, but I couldn't find a speck of dirt anywhere in them. The entire carb assembly was shiney, everywhere the was supposed to be a hole there was a clean hole.

I haven't reassembled everything yet, figured I'd post and make sure there wasn't anything I was missing before I struggle with the airbox again. Anyone else have this sort of thing happen? The spark from the plugs wasn't super-bright, infact it sort of looked like the spark you get when you drag your feet across the carpet in the dark and shock yourself on a light switch. Could it be the coils?

Also, I had the hose which runs from the valve cover vent to the airbox removed when I was testing everything, and I got a good bit of vapor coming out of it. Being as I had one cylinder running, in retrospect would this mean fuel mix was getting to the other cylinders and just not igniting?

Any thoughts would be most appreciated, we've only got a couple weeks of riding left in PA, and I'd like to enjoy at least one last trip. Many thanks in advance!

[Steve F]

I'm thinking you should start by removing the tank and totally flush it out to remove any remaining carb cleaner and start with a fresh tank of gas.  Some carb cleaners, if in too rich of a concentration will actually stall a running engine.

[Fuzzyone]

Depending on the brand some carb cleaners are conncentrated to  to 1 bottle will treat 20-30 gallons

[TwoTired]

Have your spark plugs fouled?

[Helo229]

The plugs were a little oily, but nothing far beyond ordinary. I only used about 1/3 of a bottle of carb cleaner, it said it was rated for 20 gallons, and I maybe had 1-2 gallons in the tank. I know that's still a bit on the heavyside, but since my plan was to run the tank dry while it sat, I figured it would be alright, since it would be at idle the whole time.

I based my theory off some other thread I found on here regarding Sea Foam cleaner, and how the guy was able to run the bike at idle just off a bottle of it with no gas. Anyways, based from what you've all said on here, I'm guessing that I should just go ahead and reassemble it, put in fresh gas, say a little prayer and watch it fire right up?

[TwoTired]

Well, the reason I ask, is that it only takes a thin film to cover the center electrode insulator and shunt the spark energy to ground instead of jumping the electrodes.

Carbs without accelerator pumps run very rich at idle (is your F a 76?).  And, chamber temps don't get very high to completely burn off combustion deposits.  Plus, you overdosed your engine with chemicals that likely have a low combustible value.

Gasoline is a solvent and will clean things as it flows through fuel system.  Miracle fluids can get an undeserved reputational boost when simply running the engine with or without the fluid would have shown smoothness improvement.  The home use testimonials are very much uncontrolled as to cause and effect and border on superstition.  Basically, if you don't know why something worked under a test case of one, you haven't proved anything, except, perhaps blind faith.

The posts on this forum are mostly well meaning, but not all are correct.  Sometimes free advice has a value based on the exchange rate.

Anyway, if you are confident your plugs are fine, then look elsewhere.  But, I think I would see how it runs with uncontaminated fuel, and spend a few minutes with different spark plugs.  These actions won't hurt and just maybe...

One theory, is that seafoam may be such a good cleaner that it dislodged chamber carbon deposits and redistributed some of it on the spark plugs.  Cause and effect?  You decide...

Isn't it fun doing home experimentation?

I proclaim this post as well meaning. 
Cheers,