340 Trailfire runs poorly at low RPM

[Liquifire 4/6]

I just finished doing a whole pile of work on my 1982 Trailfire LX and I fired it up today to find it running very poorly at low speed. Once you get it past 15 mph or so, it does seem to run quite strong. It seems as if it is loading up at low RPMs. But is it fuel or ignition/timing related? I should mention that the engine in my LX is a 340 from a 1979 Trailfire.

I have to have the idle screw turned in all the way until the spring bottoms out in order to get it to idle and even then, it barely keeps running and will die out after a minute or less.

I had the engine completely apart last week and installed all new crank seals, O-rings and all new gaskets. The pistons and rings looked almost brand new and the cylinder walls also were as near perfect as you could get in a used engine. I cleaned the carburetor and tested the inlet needle/seat assembly and it was holding very well so I did not replace it. I didn't bother to write down what jets it had in the carb but they were all nice and clean. The engine is actually from a 1979 Trailfire 340 so the jetting is likely whatever was stock on a 79 Trailfire 340.

Fuel is fresh Premium at 50:1 and the fuel pump appears to be pumping very well. I have cleaned both clutches and inspected both for wear and they both look good. I've also replaced the driveshaft and jackshaft bearings.

Would anybody have a good recommendation on what proper jetting for a 340 Trailfire should be? I do have the proper 340 gearing and clutching components in it.

Also, could ignition timing be a factor here? Could either by improper positioning of the stator in the slotted holes or a whacky CDI be causing my problems? I set the stator in the exact same position as it had been in prior to dismantling the engine but it's anyones guess whether the original setting was correct. I hadn't run the sled in over three years and I can't remember exactly how it ran before but I seem to recall that it idled well and took off ok.

[Matt]

The low-speed coils on the stator could have an issue. You can check them with an ohm meter. Here's a link to the Liquifire's numbers. I don't imagine a Trailfire would be much different, but maybe someone has correct Trailfire numbers: http://www.jdsleds.com/community/viewto ... f=6&t=7303

[Liquifire 4/6]

Thanks, Matt. I think I may have it figured out. I disassembled the carb and checked the jetting and found it was still jetted to stock 79 Trailfire 340 specs. Even worse, the jet needle c-clip was in the fourth slot down from the top adding to the already rich jetting set up. The jets were #35 pilot, 210 main, 6FL14 jet needle, 166 P-0 needle jet, and a 3.0 slide. That is exactly what my 1979 Trailfire parts manual shows as standard jetting.

But afer hours of digging, I finally found my 79-83 Fine Tune manual and for all Trailfire 340 models, it is recommending a #30 pilot, #200 main, 6F27 jet needle with the c-clip in the middle slot, 166 0-6 needle jet, and a 3.0 slide.

So really, the only component that is still the same would be the 3.0 cutaway throttle slide. All other pieces are considerably leaner than with the stock 79 jetting. I never did ride the sled very much previously and the few times I did get to ride it, the weather was bitterly cold which likely allowed it to run reasonably well. Yesterday, the outside temps were hovering right around the melting point so I assume the jetting was just way too fat for the day.

I had all the components on hand aside from the 166 06 needle jet. I ordered one of those this morning and it should be in tomorrow. Ill give it a whirl then andsee how it goes. If there is not a significant improvement, I will definately start checking those stator output specs.

[buckeyetrailfire]

make sure your choke plunger is seated all the way down. I had a similar problem with my sportfire and that is what fixed it .

Mark

[Liquifire 4/6]

I put the revised jetting components in the Trailfire today and the sled runs fantastic. Almost too good I think. I'll need to keep an eye on the plug color.