First post. Hello everyone! Got a problem maybe someone out there can help.
I bought a 98 FXSTC about a month ago from Indiana. I live in New Mexico. The scooter ran great when I test drove it (in Indiana) and she ran good for about a week when I got her back home, well she's not running so great any more. Now she's coughing, back firing (out the exaust), turning the plugs black with soot. Ive pulled and cleaned the breather, adjusted the idle mixture, checked the jets, it had a 35 slow jet and I put a 48 just to see what it did and it ran way worse. So I put the 35 back in it. She has a 165 main jet, I didnt change the main. Changed the plugs. Gapped the plugs to .30 (when I got them they were gapped at .40) It made it a little better but still backfiring and coughing. When I pull the float cover on the carb it has a very small amount of rusty colored stuff in the bottom of it. Ive tried just about everything except for replace the carb. It is a CV stock carb. Tomorrow im gonna try one more thing that I think could be the problem. Im gonna put a 30 slow jet, but as far as the main jet i dont know what to go to. Up or down. By the way, the alltitude where I live is around 5000 and the alltitude in Indiana is about 800. Any one have any sugestions?
Thanks

 

Plug gap should be .038 - .043.

Stock jets were 165 and 42, I think. They might've been a little leaner on the '98 - my book only goes to '90.

Try leaning the main jet a size or two. Backfiring out the exhaust is usually a sign of being too rich.

 

lv2ridesoft*tails,

I would'nt think that elevation difference would make the bike run that bad, you said it ran good for a week. Did you by chance change the engine oil?

John TN

 

You say it was running good when you got it back home for a week, then you say you found some rust in the bowl, Parts are the same as when you brought it home, I would suspect something lodged in one of the circuits in the carb. Disassemble it and flush/blow out all the circuits and try again along with the same for the tank with some fresh gas too.
Also check your specs on plug gap, sounds a bit low.>> ( Gapped the plugs to .30 (when I got them they were gapped at .40) )
Was it running good before you regapped them?

Back track what you did and recheck it again, usually something a person did in this case that caused the problem.

 

Firing, firing, firing, check your firing. I have a carb bike and live at 3000 elev, but have been as high as 12000 elev, with no problems. You are describing a rich running condition, so the question is there too much fuel (float level too high, carb vent line blocked, too much jet, slide needle too high, etc) or is the bikes firing breaking down and not burning the fuel? Use a timing light and go from there, good luck.

 

*John- I changed everything over to HD synthetic but that was after it started to run not so great. Havent changeg anything else.

*TCSTD- I started changing the plugs and gap and messing with the carb after it started acting up. Ill also check everything again.

*pococj- Thats what my book on dyna's says. I just changed it to see if it would clear it up or make it worse. The original plugs it had in it were splitfire gapped at .35. I replaced them with platinum. Gapped at .40 and then after it ran like shi* I changed the gap to .30, it still ran like shi* so I gapped them back to .40. Maybe ill get some splitfire and see if it changes anything.

*Sincecrazy- Ill tear apart the carb today and recheck the jets, vent line, float level, and slide needle. Ill also mod the carb if it has not allready been moded. as per http://www.nightrider.com/biketech/hd_cv_mods.htm

Thanks for the replies.

 

I don't think your problem is altitude. I live where you do, and have never had one act like that unless something was wrong. I have gone from Farmington to Silverton and back a lot, and bikes will not run quite as good at those 10,000 ft. elevations, but they still run a lot better than what you are describing.

Your bike should have came with a 42 slow jet, and a 45 usually works well here if you have pipes and a free flowing aircleaner. If you are running a 48, you are probably too rich. Also sounds like you are not firing good enough, or the float is sticking and giving you too much fuel.

Let us know how it works out.

Regards,

Bill

 

I thought about this today and came to the conclusion, that the bike is homesick, take it back to Hosier country and it will run fine.

This is a strange case, in that the bike ran good for a week, I almost think you fouled a plug or something along those lines to start with or got trash/water in the fuel tank/carb. What fuel are you running and did you notice the difference after a fill up? Sounds like you have worked on a few motors along the way. You don't want to change or try a lot of things at once, this might make the trouble shooting more difficult.

Do a compression check, put the same spark plug type/heat range that was in it to start with, make sure there is no trash, water,etc in the fuel or carb, drain a little out of the tank in a clear container and look in the bottom. Put the jets back like they were. Talk to the original owner and see if he had ever had any trouble like this before. If the bike stills runs bad, you will have to start checking each system of the bike one at a time.

Good luck keep us posted.

John TN

 

You mention that after a plug change "it made it a little better"

How's your plug wires????

 

Im begining to think it is home sick also.
Yesterday I tinkered some more. I checked for a intake leak (no leaks). Pulled the breather and it blew fire in my face when I torqued it a little. The vacum is working properly. I checked the jets one more time and they are both clean and seem to be working fine. I replaced the plugs and wires. Checked the enricher to see if it was sticking (it didnt seem to be). Drained a little gas into a clean cup and it didnt look to bad. Added some octane booster. Took it down to a harley mechanic localy and talked with him for a little bit (took the scooter with me) and by the time I got there the plugs were already on their way to black, not real bad but alot worse than they should have been. The guy I talked to was showing me a cv carb he had worked on and when I told him that my carb dosent have the accelerator pump, like his, he started to think I was outta my head. He went and checked it out for himself and seen that I wasnt all that crazy. He also said that he has been working on harleys for ever and had never seen a cv carb without the accelerator pump. A little strange. Anyway, on my way down to the mechanic it seemed to run fine, quick accel, no backfire or coughing. After I left the shop I decided to go for a spin to see how long the running good would last. It seemed to do allright until I got on it for a good stretch a couple times, then after that it started to act up again. Doing the same as before. I brought her home, let her cool off and pulled a plug. It was real black and sooty now. So after all this, im still lost being that if it starts to foul the plugs at high speed it has to be the main jet, but then again why were the plugs allready a little black when I just cruzed to the mechanic, and never got into the main jet?

In other words im lost! Next thing is im gonna try a 145 main jet and a compression check, if that dont do anything then i guess im gonna pull the carb, go through it, replace lots of parts, drain the gas tank completely and thoroughly flush it, put it all back and see what happens.

Thanks for all the replies. Any other sugestions are appreciated.