#2 dead cylinder (same old story)

[Anonymous]

Alright guys, I know this topic appears very often and I have been going through the previous post but still not sure.....please indulge me.

1982 GS550L. Stock exhaust, carbs haven't been touched. New coils.

This has been an ongoing problem. #2 cylinder has been finicky over the last couple of months. Would take a while to warm up but would warm up after riding a while. Some days would drop out while riding but would later come back.

But now #2 has become very stubborn. The cylinder not stays dead predominantly the entire time. The plug when pulled is wet. I was able to get #2 to fire for a while this weekend after swapping plugs b/w #1 and #2. But getting on the bike this morning she's dead again.

So, the plug is getting gas and with the new coils spark should be good (but I need to check the spark with the pug out) and still no fire.

One side note...not sure if its my imagination but when riding the bike around 4th/5th gear the bike seemed t surge under acceleration as if the cylinder was kicking back in...but not sure. Also, very isloated occurrence.

Thanks guys.......
curt2005

[daveo]

Have you checked the valves, especially the exhaust, for being too tight?

[AOD]

what happens when you pull the spark plug boot off #2, put in a good spark plug, ground it to the head and crank the engine? does it spark good?

try closing the mixture screw on the #2 carb...and see if leaning it out a little helps it fire...

if this doesn't work, do a compression test.

[argonsagas]

It's not entirely clear if you are running a twin or a 4 cylinder bike.

You said it began firing when you swapped plug wires between # 1 and #2, and at another date the faulty cylinder was running intermittently.

Faulty valves usually are pretty constant: once faulty, they stay that way, so you could have problems there, but intermittent problems suggest you look elsewhere.

You may have a carb problem, although it is seems to be at least temporarily functional.



Problem is you cannot swap wires between cylinders 1 and 2 on a GS -4 and expect it to run well, as the coils are supposed to fire 1-4 and 2-3 , respectively.

If there is any confusion in the present wiring, then you should check all plug connections before going further.

Also, you said the plugs were wet. With what? Oil or gas?



What you describe seems likely to be a bad plug wire.

The solution was already given..pull the plug from the engine, put the wire back on, lay the plug on the engine, turn on the ignition and turn over the engine. The coils are new, so, if you get no spark, or a very weak spark, you just identified the problem....replace the wire and ride!

If the spark is strong, then look at your carbs. (I would also do the compression check at this point...remember to do it with the throttle OPEN)

Note: you MUST clean and dry the suspect plug before doing this check.

[Anonymous]

ok. the coils are replacements but have been on the bike for several months. When I said I swapped plugs, I meant that I took the plug out of 1 and put it in 2 but i didn't switch plug wires. #1 still on #1, etc.

This is a four cylinder engine. The #2 plug is wet with gas when I pulled it. When grounded against the case there is spark.

And yes, it is intermittent. Got on the bike this afternoon and after a few minutes of riding #2 heated up and the bike smoothed out.
So hopefully that rules out a valve/ring problem.

The suggestion to adjust the mixture on #2.....I should try leaning that carb?

Thanks.

[RacingJake]

I still have a GS550 that I rode from LA to Tampa Bay a long time ago when one of the cylinders went dead. The problem was a coggled main jet in one of the fuel bowls.

jake

[argonsagas]

The only reason it can be intermittent, but otherwise run well, is a poor spark. Pull the plug wire off #2 and replace it. If one is gone, others are likely to be in similar condition. Consider replacing all of them.

It is also barely possible that you have an automotibile resistance-type spark plug that has an internal wire for radio noise suppression, instead of the usual bike-type standard plug. If that were so, the plug itself could be faulty, and it could work intermittently.

Plugs are cheap. Be sure to use the right ones.

[gs650gt]

the fuel petcock leaking to #2 intake boot thru the vacuum hose ?

[Anonymous]

Curt,

Ilpo is right on. I had the same problem on my 81 650G.
To check it pull the vacuum hose ... if even a hint of fuel comes through, you'll need to replace the petcock assembly.
Good news, it's easy and cheap.

Kurt Worden

[nert]

Plug the vacuum line. Put the petcock in the "prime" position, and drive around, check the results.

[Anonymous]

nert,

plug the vacuum line, put the petcock on prime and what are the results im looking for?

thanks
curt

[gs650gt]

When You do what Nert suggested, the bike should run normally (if the faulty fuel petcock diaphragm is faulty).

Just remember to switch the prime-position on just for the test run, otherwise You could cause more gas problems...

[nert]

jcurt2005
plugging the vacuum line and running the petcock in prime position, will be an easy way to eliminate the possiblility of the vacuum line sucking fuel from a leaking petcock directly into the engine and fuel fouling the spark plug. The prime position will allow fuel to flow with out a vacuum source to the petcock. Be sure you have it in "prime" otherwise you will run out of gas!. On my gs, "run" position the handle on the valve is vertical. Looking at the valve and rotatong the handle Counter clockwise, so the long part of the handle is pointing to the rear is "prime" position. The long part of the handle rotated clockwise and pointing forward is "reserve".

[gs650gt]

The "prime" position of the fuel petcock allows the gas to flow from tank to carbs all the time.

What I meant with the dangers of the prime position was that if Your needle valves leak, the excess gas can flood... even to the cylinders in the worst case.

So that's why You should switch the fuel petcock back to "on" or "reserve" position after the run.

[gs650gt]

...forgot to say: if the fuel petcock appears to be faulty, buy a repair set (new diaphgram and seals) to fix the problem.

In the long run this "prime" trick with plugging the vacuum hose is not good.