1980 LF not revving

Spitfire79 · Post by **Spitfire79** » Sat Dec 31, 2005 3:07 pm

I just picked up a 1980 Liquifire. It has not run this year although the engine was fogged when put away last year. I put clean fuel, plugs, etc and after a few pulls it fired. Took a couple tries but it ran . Here's the problem, it starts and idles fine and runs up to 7500 rpm when cold. As soon as it warms up it won't rev up and won't idle. With the throttle wide open, it runs up to 4000 rpm but not beyond. Lots of spark, fresh fuel. Any ideas?
Thanks Jeff

Spitfire79 · Post by **Spitfire79** » Sat Dec 31, 2005 4:11 pm

I went and played with it more. If I let it cool for 5 minutes or so, it will start and idle at 2000 revs. When I try to run it up it sits at 4000 and no more. It almosdt seems to run on one cylinder but I checked and both have spark. Runs great after its cooled.

sportnut · Post by **sportnut** » Sat Dec 31, 2005 4:52 pm

Sounds like a stuck choke. Have you checked it ?

Spitfire79 · Post by **Spitfire79** » Sun Jan 01, 2006 3:50 pm

No I didn't. I tried to get the air box off but it seems like the carbs need to come off with it. Tight fit. Any certain way to check the choke?

Spitfire79 · Post by **Spitfire79** » Sun Jan 01, 2006 5:03 pm

Well it's not a stuck choke. Checked both and all is good. It's warm here and the engine runs great for the first 5 min or so then it loses power / won't rev. I changed external coils and it does the same. Next is the cdi. Any ideas where to get one or how to test it? What about the internal coil?

MuskyBear · Post by **MuskyBear** » Sun Jan 01, 2006 10:48 pm

Dennis Kirk has them or Image Enterprises in Eagle River, Wi. has rebuilt CDI boxes.

JDXspec · Post by **JDXspec** » Sun Jan 01, 2006 10:57 pm

You could try unplugging the rev limiter box down on the right side near the jackshaft on the mainframe. (little black box with a 5 spade connector) I have heard this before and its easy to try and doesn't cost anything.

bob15 · Post by **bob15** » Mon Jan 02, 2006 11:08 am

I have had both rev limiters and CDI boxes both go. When both rev limiters went, both sleds wouldn't run to 7500 when cold or hot. They wouldn't rev at all. Had a CDI go on a LF last year and it would begin to foul plugs after about 8-10 miles. The sled would idle, but couldn't rev after idling. Change plugs, start and leave and it would run. However, the sled would run worse as time went on and at the end would idle, but wouldn't rev at all. But, you would have spark all the time.

The thing with spark and spark plugs, is that it might show spark, but if you put it under compression (when in the engine), the ignition system can be weak enough that it will not spark or be a very very weak spark.

bob

sledchad · Post by **sledchad** » Mon Jan 02, 2006 9:04 pm

how warm is it when you are running the sled? These LF"s do not run well at all with temps above 35 degs. The power jet carbs are very finiky carb system. Try unplugging the rev limiter if that isnt the culprit then i would lean towards the cdi box.

Spitfire79 · Post by **Spitfire79** » Thu Jan 05, 2006 8:16 pm

I unplugged the rev limiter with no change. The chokes seem fine ( not sticking) Could there be a fuel problem or would it be electrical. It seems to be electrical but I'm stumped. I'll pull it apart this weekend and see. I'm wondering if it's starving for fuel. Perhaps a line collapsing or a weak fuel pump. Temp is around 28 deg. Any isea where to get a manual for this?