79 Yamaha xs1100 Special suddenly won't start

[Nynatv]

I ran my xs1100 for 120 miles yesterday. It ran sharp and excellent all day then all of the sudden, it started to pop, skip, lose power.. Sounded like it was only running on 3 cylinders for about 3 miles then died completely.
Turns over but will not fire. Has fuel.
Any thoughts?

[jetmechmarty]

What is the condition of the battery? Quitting on you the way it did makes me think your battery gave up the ghost.

[Nynatv]

Good battery voltage. It turns over when I try to start it but will not fire

[GLoweVA]

Okay, it turns over. Next step, Do you have spark? Pull the plugs and ground them to the head and then crank. Spark on all 4?
Also check to see if the plugs are wet/dry/sooty, etc.

No spark, check the pick up coil wires. (left side cover)

[jetmechmarty]

What is the condition of your fuse box? Is the IGN fuse in tight? Did you test the battery, or assume it's OK because it cranks the starter?

It wasn't raining while you were riding, was it?

[fredintoon]

I ran my xs1100 for 120 miles yesterday. It ran sharp and excellent all day then all of the sudden, it started to pop, skip, lose power.. Sounded like it was only running on 3 cylinders for about 3 miles then died completely.
Turns over but will not fire. Has fuel.
Any thoughts?

Hi Darrin,
did you get it home before it quit or is it still parked someplace?
Easiest thing to do first is pull the plugs and check for sparks.
If you see all 4 with nice fat blue sparks as you crank, it's fuel.
If you don't it ain't.
Has fuel, you say, but where? Unless it's actually being sucked into the engine the fuel does no good.
Check the octo, switch to "prime" and check fuel into carbs, then the big one,
pull the carbs and clean them.

[GLoweVA]

For the 79 Special: the main fuse (30 ) is on the left side of the fuse panel and continuing from left to right are the headlight fuse (10 ), turn signal fuse (20 ), and ignition fuse (10 ).
Looking at the wiring diagram, it looks like the ignition fuse feeds the starter solenoid thru the right handlebar 'kill' switch, so If it's cranking, then that fuse should be good.

[jwhughes3]

pickup wires

Sounds suspiciously like broken pickup coil wires.

Intermittent as random connections are made until it goes out completely.

Under left timing cover, check each wire by gently tugging on insulation - every 1/2 inch or so - should be firm - if you find a spot that pulls apart easily then its broken inside there.

When mine went out it would run (badly) at about 45mph on the 2 cylinders I could get power to until I fixed it.

John

[skids]

On 2 of my standards, at about 60 mph or so, I get a fuel delivery problem that is instantly rectified by switching my left petcock to PRIME. I suspect that there is an issue with vacuum pressure to operate the petcocks to where two of the cylinders start dropping out. I really should couple the output fuel lines together and then branch them out to the carb T's. Long story short, try switching over to prime if it happens again (both sides) just to see what happens.

[xs11lover]

Did the vacume line pop off the carbs?

[mjpxs11sh]

+

your description sounds exactly like when u run out of gas and have to flip the petcocks to reserve. not getting fuel into the combustion chamber? fuel, air, spark, and compression is simply what it needs. easy to check them all to see whats missing. good luck.

[DiverRay]

If you try to run a special on a low tank, it will do what you describe. Check to make sure the petcocks were on the RUN position, and NOT PRIME. 120 miles you should be on reserve if you are getting good mileage!