Not firing on #4 cylinder

[Anonymous]

Hi
I've had my '83 gs650l down for a while. During that time I installed a new MAC exhaust system (4 into 2). Cleaned the carbs and installed brand new float valve assemblies. Then I couldn't get it to start. So I bought Accel super coils and brand new NGK spark plugs. Now it runs, but I noticed that it was shooting gas out of the right side exhaust. So I checked and the fourth cylinder is not firing. So I did a compression test and I have 170 on all four. Any Ideas? I would apreciate any help.

Josh

[earlfor]

Re: Not firing on #4 cylinder

Do you have spark on the #4 plug?

Did you set the float heights? (new assemblies do not come set for height)

Earl

Hi
I've had my '83 gs650l down for a while. During that time I installed a new MAC exhaust system (4 into 2). Cleaned the carbs and installed brand new float valve assemblies. Then I couldn't get it to start. So I bought Accel super coils and brand new NGK spark plugs. Now it runs, but I noticed that it was shooting gas out of the right side exhaust. So I checked and the fourth cylinder is not firing. So I did a compression test and I have 170 on all four. Any Ideas? I would apreciate any help.

Josh

[Anonymous]

Yep, I have a nice fat blue spark, and I the float height is set correctly.

[earlfor]

Does #4 not fire at idle only and fires OK at higher rpm, or does it not fire at any rpm?

Have you vacuum synched the carbs? Are you sure #4 is drawing the same vacuum as the other three cylinders?

Have you removed the float bowl drain plug on the #4 bowl, and drained the bowl into a cup to be certain there actually is fuel in that bowl and in the correct amount?

Earl

Yep, I have a nice fat blue spark, and I the float height is set correctly.

[earlfor]

Having raw fuel coming from the right side exhaust does not guarantee it is coming from the #4 cylinder.

Is the spark plug wet on the #4 cylinder?

Earl

[Anonymous]

I did a bench synch before I put them back on the bike. It isn't firing at all on any RPM that is why all the fuel is coming out of the exhaust.

[earlfor]

Sounds like the slide in the #4 carb is stuck and unable to raise.

Earl

I did a bench synch before I put them back on the bike. It isn't firing at all on any RPM that is why all the fuel is coming out of the exhaust.

[Anonymous]

Well I guess that is possible, but when we were trouble shooting, we swaped the #1 and #4 slide, along with the float assembly and all jets. The #1 continued to run correctly.

[earlfor]

Well, you have a blue spark on #4 plug and #1 runs normally, so it is not an ignition timing problem. Youre blowing fuel out the exhaust, so not a fuel availability problem. Fuel is passing from the carb, through the cylinder and out the exhaust, so not a clogged jets problem. It appears to be a mixture problem. In this instance, all fuel and no air. That would likely be a synch problem with the #4 carb. Swapping slides and jets with the #1 carb would have no effect on that condition. Try raising the slide height setting for the throttle off position. Also, I would change the spark plug as the #4 plug is probably fouled out now.

Either the #4 slide setting is way off, or the #4 slide is not raising. I dont see any other possibility

Earl

Well I guess that is possible, but when we were trouble shooting, we swaped the #1 and #4 slide, along with the float assembly and all jets. The #1 continued to run correctly.

[Anonymous]

I'll check that next, thanks. I will keep you posted.

[earlfor]

You DO have the vacuum tube connected on the #4 carb?

Earl

[Anonymous]

what vacum tube?

[Anonymous]

#4

So the pipe on #4 is cold after start up and you have the spark plug wires in the right order, and not crossed

[earlfor]

Between the 1 and 2 carb there is a vacuum balance Tee, and between the 3 and 4 carb, there is another vacuum balance Tee. The 1,2 Tee should be connected to the 3,4 Tee. If you run a vacuum operated petcock, there needs to be a middle Tee between those two to provide a "draw off" to operate the petcock.

Also as Gee-s-is says, you do have the left coil spark plug leads going to the 1,4 cylinders and the right coil powering the 2,3 cylinders?

Earl

what vacum tube?

[Anonymous]

Are you talking about the vent tubes? These are not cailifornia style, the only vacum connection is on top of the #2 which runs to the petcock. Yes, the coils are running to the correct cylinder. This is what is really getting me, all three of the other cylinders are running fine. In fact if it were'nt for the gas coming out of the exhaust I wouldn't have even known it wasn't firing. It idles fine and the throttle is crisp like it should be.