running rough when warm

[jeffe]

I bought a 1978XS11 this summer. It had been parked for about 5 years. I had to reline the tank and get the carbs rebuilt. It ran fine for about a 1000 miles but started to get a miss or stumble as you would advance the throttle. Also it would have problem idling.This would occur only after the bike was ridden for 5 to 10 miles. I did find one of the pick up coils wires bad and fixed it. I got that one fixed but I think I caused a cascade effect and the others went bad to. I decided to get new pick up coils and have installed them. The problem is still the same. The main coils check OK with an ohm meter. Any ideas? Could it be the ballast resistor for the ignition system. It's mounted right above the engine and could be effected by heat. Hope someone can help. Before this started the old girl ran great. Plenty of power and about 40MPG on the road.

[steelcat]

It could be the ballast resistor, the ingnition module, or possibly the main coils breaking down w/ heat. It could also be the carb boots alowing a vacuum leak after getting hot. Also check your vacuum adance for leaks. I'd check the carb boots and vacuum lines first, then start trying to trouble shoot the electrical system. Use a hair dryer to induce the failure, or after you get the bike warmed up & the problem occuring use a can of air (the type for cleaning keyboard etc) turned upside down to freeze the suspected part. You kmay also want to check the connections on the back of the fuse box.

[jeffe]

The bike had new carb boots installed with the carb rebuild. The old ones fell apart when the guy removed the carbs. That was $160 I wasn't planning on. What exactly does that ballast resistor do? As an owner of old Chysler products I know they can go bad. I always carriied a spare in the glove box. Thanks, Jeff

[jeffe]

I've also replaced the fuse box with inline GM style fuses.

[John]

Jeff, You sound like a good old Mopar owner. Back in 77, I had a 72 Charger and the thing died on me...in the middle of a four way intersection. Luckily, I was right by a Dodge sealer, so once I got the car out of the way, I went to the service manager there, and he called up one of the mechanics. I told him what the symptoms were and he went back to his tool box and grabbed a test light and a spare resistor. One quick probe of the test light revealed the problem. He plugged in the new resistor, and it busted right off, I then drove him back to the dealership, bought two new ones, and gave one back to him, and put the other in my glovebox. Never needed it, but was good to know it was there . Cheap insurance, ya know.
Anyway the resistor reduces the voltage to the coils to about 9 volts when the engine is running. A full 12v or 14v actually will overheart the coils and they will fail. The resistor is bypassed when the bike is cranking, to allow the most voltage to the coils to provide a hotter spark and to compensate for the voltage drop caused by the starter.

[xExcessive 1120]

Jeffe's Miss

Jeffe, your introduction to your '78E spoke of having to line the tank and rebuild the carburetors. Are you running inline fuel filters? A common problem with lined tanks is areas inside to which the liner does not properly adhere. Sometimes fairly large pieces of the liner will delaminate and float around, block the petcock filters causing intermittent fuel starvation because when you stop, the fuel flow no longer holds the flap of rubbery liner against the petcock filter and at start up she runs great until it happens all over. Also, if problem is not intermittent, the area of tank metal exposed by the delamination provides rust particles which will get back to the carbs or plug the filters and...back to fuel starvation again. Just a thought, Christopher. "The Gimp"

[John]

Kreem Fuel Tank Liner

It's funny you should mention this. SWMBO's current FJ11 had exactly the same problem. It was the day she bought it and was riding it home. She had just filled the tank 20 miles prior, and then it 'ran out of fuel' a few miles from home. Subsequent inspection of the gas tank showed that the Kreem lining had become detached from the top of the tank and had floated down over the petcock. The petcock also had no tower screen, and was plugged very easily. I removed the Kreem with acetone, and reapplied the Kreem liner, and it has not failed in 10 years.

[jeffe]

The bike still has the tower filter in place. And it is has twin petcocks.