Dead Cylinder

Agent · Mar 27, 2014

The right cylinder on my 1979 Yamaha XS650F has gone dead. I just cleaned the carbs and when I put them back on, the right cylinder wouldn't fire. With the bike running, I pulled the spark plug boot off and nothing different happened. I stuck a screwdriver into the boot and held it up to the plug. The spark jumped about 3/8 inch and the cylinder fired up and ran like nothing was wrong. Moved the screwdriver closer to the plug and the cylinder died. Put it back on the plug and nothing happened.

I changed the boot on the plug wire and got the same result.

I checked the gap on the plug and it is fine.

Left exhaust pipe smells like exhaust. Right pipe smells like straight gas.

I need some help. Can anybody help me figure this out? Has anyone experienced something similar?

Thanks,
Andy

L.B.S. · Mar 27, 2014

What did the plug look like despite the gap being ok? Wet and black? Sounds like it's being flooded. Check the float level?

Try tapping the side of the (bad) carb with a screwdriver handle or small plastic hammer. Sometimes the slides can get hung up, or the floats can stick.

Agent · Mar 27, 2014

The plug was black. I don't remember if it was wet or dry. I'll check that and the float level tonight.

Thanks.

silverhound · Mar 27, 2014

I would pull the plug wire and check for continuity. Perhaps sticking the screwdriver into the boot made contact where the plug wire by itself does not when attached to the plug. You could have pulled something loose. Swap/switch both plug wires and see if the other cylinder fires.

L.B.S. · Mar 27, 2014

Agent said:
The plug was black. I don't remember if it was wet or dry. I'll check that and the float level tonight.

Thanks.

Good hunting! Carbs can suck (lol pun intended) sometimes, for sure.

Agent · Mar 27, 2014

Thanks, Silverhound. I'll give it a try tonight.

LBS, truer words may have never been spoken.

Agent · Mar 28, 2014

Changed the spark plugs last night and sure enough, the right cylinder bathed the plug with oil in the 3-4 minutes I had it running. Looks like I'll have to pull the engine apart to check for valve guide seals and/or rings.

Brillot2000 · Mar 28, 2014

Agent said:
Changed the spark plugs last night and sure enough, the right cylinder bathed the plug with oil in the 3-4 minutes I had it running. Looks like I'll have to pull the engine apart to check for valve guide seals and/or rings.

This sound a lot like what someone did to my CB360 when I got it. I had to teardown engine and remove the cylinders. I found out that some "Genius" lined up all the grooves on all the rings. This will allow oil to slip right into the combustion chamber and wet the plug and through oil on the exhaust pipe too. I’m not saying that's the case, but sure sounds a lot like it.

FYI... The rings on the piston are supposed to be offset by about 120° from each other, in the case of 3 rings. I am not implying that you did, but it's a possibility that needs to be explored. There's also the possibility of a "Broken" ring or rings on that piston too...

Agent · Apr 23, 2014

Thanks, brillot. I'll get into it sometime this summer. I've got too many irons in the fire right now. Parts aren't terribly expensive for the xs650, but things got busy fast.

Sent from my SCH-I535 using Tapatalk

HONDABIKEPRO · Apr 23, 2014

Agent said:
Thanks, brillot. I'll get into it sometime this summer. I've got too many irons in the fire right now. Parts aren't terribly expensive for the xs650, but things got busy fast.

Sent from my SCH-I535 using Tapatalk

Why don't you do a leak down, or compression check first?? Dale

Chris · Apr 23, 2014

Agent said:
I just cleaned the carbs and when I put them back on, the right cylinder wouldn't fire.

This might be the problem itself, you don't mention any other changes. If the bike worked ok before the carb clean maybe something went wrong whilst cleaning the carbs - plenty of problems can happen leading to flooding the cylinder due to a wrong re-assembly of one of the carbs.

This is where I'd start if the problem really did occur just after you cleaned the carbs - if I'm reading more into your description than happened then that's also allowed - half the time when we explain what happened we get the explanation more or less right, the other half we don't.

Old Can Ride · Apr 23, 2014

HONDABIKEPRO said:
Why don't you do a leak down, or compression check first?? Dale

Great idea!

Cyclerosis · Apr 23, 2014

Agent said:
The right cylinder on my 1979 Yamaha XS650F has gone dead. I just cleaned the carbs and when I put them back on, the right cylinder wouldn't fire. With the bike running, I pulled the spark plug boot off and nothing different happened. I stuck a screwdriver into the boot and held it up to the plug. The spark jumped about 3/8 inch and the cylinder fired up and ran like nothing was wrong. Moved the screwdriver closer to the plug and the cylinder died. Put it back on the plug and nothing happened.

I changed the boot on the plug wire and got the same result.

I checked the gap on the plug and it is fine.

Left exhaust pipe smells like exhaust. Right pipe smells like straight gas.

I need some help. Can anybody help me figure this out? Has anyone experienced something similar?

Thanks,
Andy

Does that bike have coils? A bad coil would cause the symptom you describe.

kjang · Apr 24, 2014

HONDABIKEPRO said:
Why don't you do a leak down, or compression check first?? Dale

Dale has a good point. Perform a compression check and leak down. This will tell you which way to go.

Ken

Dead Cylinder

Agent

L.B.S.

Fixed Idea

Agent

silverhound

New Member

L.B.S.

Fixed Idea

Agent

Agent

Brillot2000

Active Member

Agent

HONDABIKEPRO

Supporting Vendor

Chris

Old Can Ride

Active Member

Cyclerosis

kjang

Member

Similar threads

Forum statistics

Online statistics

Newest members