one cylinder flooding after short sit

[dainsmoland]

Hi. Newbie here. Did lots of searching/browsing, still could use some advice that I feel like you kind folks will have.

I have a '78 GS400. These have the Mikuni BS 34 carbs. It was running great until I left it sitting for about a month on the side kickstand, now the right cylinder (the one elavated during the sit) is continually flooding I'm guessing--the plug is wet before and after running, the right exhaust smokes bad and it smells of gas. much trouble starting it, and wouldn't idle at all at first (it seemed like the right cylinder was only igniting once out of every 2 or 3 revolutions), but after replacing just that plug, it starts, idles, and drives fine, but still smells of gas and the right exhaust still smokes a lot (compared to no smoke on the left).

some kind of carb problem, I guess--does the fact that the right cylinder is the one causing problems suggest a certain problem? did something dry out that wasn't supposed to? anyway out of doing a carb teardown/cleaning?

Thanks very much,
Dain

[earlfor]

do you have your petock turned to the run position? The fuel flow is off with the petcock in the run position when the bike is not running. Run is a vacuum operated position. If you have the petcock set to the prime postion, prime is gravity feed and fuel flows regardless of whether the engine is running or not.
It should always be set to the run position.

If the petcock is set to the run position and it still leaks fuel from the 2 carb overflow, then the fuel inlet valve/needle seat is probably leaking or corroded to the point of the needle not being able to close off the fuel flow. It can also flood if the float bowl tang is set for too high a fuel level in the bow, but if you have not adjusted that, it is probably no the float height setting causing the problem. It is likely debris in the bowl.

The bowl can be removed and cleaned and the fuel inlet valve cleaned out without removing the carbs, but it is not easy. I prefer to remove the carbs.
However, on my 450, to remove the carbs, the airbox must be removed and to remove the airbox, the battery and battery tray must be removed. My airbox slides through the right side after removing the right side cover. Yours may be different

Earl

Hi. Newbie here. Did lots of searching/browsing, still could use some advice that I feel like you kind folks will have.

I have a '78 GS400. These have the Mikuni BS 34 carbs. It was running great until I left it sitting for about a month on the side kickstand, now the right cylinder (the one elavated during the sit) is continually flooding I'm guessing--the plug is wet before and after running, the right exhaust smokes bad and it smells of gas. much trouble starting it, and wouldn't idle at all at first (it seemed like the right cylinder was only igniting once out of every 2 or 3 revolutions), but after replacing just that plug, it starts, idles, and drives fine, but still smells of gas and the right exhaust still smokes a lot (compared to no smoke on the left).

some kind of carb problem, I guess--does the fact that the right cylinder is the one causing problems suggest a certain problem? did something dry out that wasn't supposed to? anyway out of doing a carb teardown/cleaning?

Thanks very much,
Dain

[ccratin]

Actually, check the petcock vent line. If it's wet inside or smells really strong of fuel, it's likely that the petcock is the culprit. It's certainly possible you have both a float needle problem and a petcock problem, but I can tell you from experience that if the diaphragm in the vacuum petcock is bad, it will flood the right cylinder very quickly. That vacuum line should be bone dry.

[earlfor]

That is confusing to me. ????? The petcock vacuum line attaches to the vacuum fitting on the top,front of the #1 carb (left). The two vent lines on the carbs are located on the inside face of both carb bodies and are left open to atomsphere. I never even put a hose on those fitting, just leave them as is.
The bike sitting on the sidestand would have the #1 carb low. If one bowl was going to be more prone to flooding, it would be the #1 carb.

If there is a leaking petcock problem, there will be in an increasing oil level in the crankcase and crankcase oil will smell like gas.

Earl

Actually, check the petcock vent line. If it's wet inside or smells really strong of fuel, it's likely that the petcock is the culprit. It's certainly possible you have both a float needle problem and a petcock problem, but I can tell you from experience that if the diaphragm in the vacuum petcock is bad, it will flood the right cylinder very quickly. That vacuum line should be bone dry.

[dainsmoland]

so, the petcock vacuum line seems dry and only a very slight smell of gas down there, at least after sitting overnight--is this something I should check right after running?

also, I've noticed that the petcock itself is leaking a very slight amount around the lever (not dripping or anything, just enough to attract some dust and make the thing dirty). does that point to a bad diaphram on the petcock?

Also, checked the crankcase oil, and there is a noticable gas smell--though the oil level doesn't seem abnormally high.

thanks for your quick replies already...

[ccratin]

On my 450 the vent line was connected to the #2 right cylinder, not the left. It had this exact problem. The 400 may be different, I'd have to check my manual. Dain, you'll want to confirm.

Yes, check the vacuum line right after running to see if it's wet. If it's been sitting it certainly could flash off. It really shouldn't flood after sitting for a while either. Earl's suggestion to check whether or not it's on prime is definitely recommended. If the oil smells like gas, change it. Don't risk it. The fact that it does smell like gas still doesn't point only to the float needles. If they are leaking badly, the oil level will definitely rise. However, it's possible to get gas in the oil from a cylinder not firing and washing down the cylinder. There would be much less quantity, but still the smell.

You'll have to put a fresh plug in more than likely to get it to run right. To test the petcock, you can try sucking on the vacuum line if you don't mind gas in your mouth! Or you can use a vacuum tester with clear line. That will show you if you've got gas coming through it.

The petcock leaking where the lever is doesn't necessarily indicate a bad diaphragm. There's an oring that seals that shaft and it is probably bad.

Just for clarification, which 400 do you have?

[dainsmoland]

OK. checked the petcock vacuum line after taking it out for a little spin, and there did seem to be some gas on the carb end of the line and a little bit of moisture inside. But my vacuum line goes into the left carb--which is not the side showing problems.

Also, this new spark plug on the right is not coming up wet anymore after running (and does not seem to be misfiring), but is showing lots of black soot for a brand new plug and also that right exhaust is still smoking grey and smelling gasy...

I'm pretty sure this model is the regular 400--I don't think it's the "X."

[earlfor]

It appears Suzuki did make some changes on the carbs on the 450's. My 81 450L has the petcock vacuum fitting on the left side of the #1 carb. Now I understand why you said the #2 carb would the the one likely to overflow. :-)

Earl

[QUOTE=ccratin]
On my 450 the vent line was connected to the #2 right cylinder, not the left. It had this exact problem. The 400 may be different, I'd have to check my manual. Dain, you'll want to confirm.