Running on 2cyl

[jamiem753]

Hi guys im new to the forum i have a 1978 xs1100E. It only runs on cylinders 1 and 2. I checked for spark on three and four and got spark but they refuse to run. i pulled the plug on cylinder 4 and it was wet with gas but it dosent run. Any ideas what could be causeing this?

Thanks

[rpgoerlich]

One coil is for 1 & 4 the other for 2 & 3. Carbs 1&2 get fuel from the left petcock, 3&4 from the right.

So you either have a problem with the plugs/coil wires/plug caps (on 3&4), or carbs.

[b.walker5]

Try swapping the plugs from the known working cylinders to 3 and 4, and see if your problem swaps sides. If it does, replace the plugs, if it doesnt, do a compression test.

[prometheus578]

Alright, could be several things.
Now, you mention that the plugs for 3+4 are wet with fuel.
What do the plugs look like otherwise? It they don't look white/light tan, replace them. Carbon fouled plugs, especially when wet won't fire.
Now, I know you already said that you have spark there...
Odd as it may seem... when checking for spark by laying the plugs against the head and cranking.... a badly fouled plug may show spark, but once back inside the different environment of the cylinder the damned thing won't fire.
So, if the plugs are badly fouled, replace them.

Ok, you say you have spark, next would be a fuel problem. In this case, too much fuel... making it a carb issue. Floats may be set way too high... float needle may not be seating and sealing, flooding the carbs and then the cylinders, etc. Quick test would be to set the petcocks on prime and wait and watch to see if flooding fuel comes dripping out of the air box.

[jamiem753]

Thanks guys there is gas coming out of the airbox when on primary on carb 3 also the plugs were a little foulded but I cleaned them up good before i put them back in. I guess ill pull the carbs clean them up and check the float levels. i have a sync tool coming so ill sync them when i put them back on.

[TopCatGr58]

Hey Jamien,

If your carbs are leaking into the airbox, then you need to fix the leak first! The floats can get small pinholes in them and then sink causing flooding, so you'll want to check them for that by putting them in near boiling water, use something to push it down under the water, look for bubbles=leak=bad! Some have successfully repaired with small bits of solder...YMMV!

Also, you can clean the metal contact areas of the float seat and the float needle using chrome or other polish on Q-tip.....! Can't remember the exact procedure details...Prom posted it some time back, a search should find it.

Also, check your OIL, it's easy for the fuel to go forward into the intake, into an open cylinder, and down past the rings. Gas contaminated fuel can be a quick way to bearing damage and engine death!

T.C.

[79XS11F]

Don't over look the carb bowl vents including the metal tubes inside the air box. If the vent for 3 and 4 is plugged they will flood into the air box.
Rob

[jamiem753]

Thanks for all the help guys

[jamiem753]

Can anyone explain why when i take off the gas tank and run the bike it runs on all four but when the gas tank is on it only runs on 2 cyl.

[DGXSER]

Provided you are not using an alternate fuel source, then by running the engine with no fuel to make up, the bowls that were over full are emptying and your getting a good fuel mix instead of flooding out.

Add any type of fuel supply to the carbs and they will most likely go back to flooding out and not fire.

[Rasputin]

Can anyone explain why when i take off the gas tank and run the bike it runs on all four but when the gas tank is on it only runs on 2 cyl.

Depending on what you are using for a fuel source when the tank is off...

1-The fuel lines may be getting kinked when you install the tank.
2-The vacuum to the petcocks or octy may not be hooked up properly.
3-You may have the fuel line routing mixed up

I am not sure I recall which bike you are working on and your profile does not say. Would be helpful for us to assist you if it were in your signature.