I bought a 1990 flhtc. Hadn't been ridden in 4 years. Changed the fuel, cleaned the tank with air and clean gas. also cleaned the gas tank petcock really well. was varnished pretty good. rebuilt carb with stage 1 kit. Adjusted the carb slightly rich. Runs like a champ till fully warm than starts missing and hangs at 3000 rpm's no matter which gear i'm in. Could it be the coil or a cracked plug wire? no clue on my part. is there a sensor in the primary that may be bad? no gas leaks, the breather is working in the screamin eagle air filter setup.idles strong at 750 rpm's can idle smoothly at 500 when it's cooler. I live out in the country and don't own a trailer to get it to the shop, would prefer to do the work myself. Any Ideas out there? Thanks guys and gals. Sunka

 

hello sunka,
from the info you have given, starts good? idles good ?runs good ?
just gets flat and levels off at 3 g? no missing? no backfires? no jerky hesitant feel?
my first gut instinct would be too rich carb jetting for the cam/exhaust flow.
I would say warm it up good and ride it as normal as you can for about 20- 30 minutes.
shut her down and read the plugs. whitish too lean greyish ok dark brown/black too rich.
plugs should be dry and not wet at all any color.

any more info you have may be very important, let us know what you try and or get?

John

 

Not sure which carb and intake a '90 has,the '89 Ultra I had did something like that when the rubber compliance fittings on the intake got old and started cracking and leaking,
It had the old 38 Kehin butterfly carb,a solid intake replacing the rubber fittings was the cure.
I did the same on my '84 FXR but upgraded to a CV carb at the same time,should have done that on the Ultra but I traded it in on a new bike instead.

 

Thanks 85fxsb yes it does miss like crazy and backfires some not lots but consistently when i try to increase the throttle, it also jerks off and on. it has a 40mm kehin cv carb which has a vacuum to a switch below the choke pull. I will set it at 1 1/4 turns out rather than 1 3/4 turns, where it is now and see if that helps. thanks for the advice. i'll let ya know what happens. I live 50 miles in the country so i don't want to get stranded, with a bike i can't leave.

 

Hi,

I would check you don't have any leaks on the inlet past the carb, failing this check the timing.

Hope this helps

 

sunka,

did it run before you did anything ?

when you say, rebuilt the carb, did you replace the rubber slidediaphram in the top of the carb? my 90 did similar as yours at 3000 rpm it would flatten out . it would not get any faster than 65-70 mph. ran excellent until that point. there was a small tear in the slide diaphram in the top of the carb.

there is no sensor in the primary, in my experience, a bad plug wire would leave u on one cyliinder and a coil would skip or not work at all.

just a thought......
later...............................

 

Sounds like a fuel problem. Check for air leaks at the manifold. Make sure you git the diaphragm in correctly at the top of the carb when you put it together also the needle jet (the little silver thing that is above the jet tube, that the needle goes in) could be in upside down, that will do what you are talking about. If you look at it you will see that oneend has square sides and the other end is rounded/tapered on the inside. The rounded/tapered end goes up and the needle goes into it. If you put it in upside down the motor will do as you described. I've had a number of customers come in after "working" on their carbs with that same problem. Check that out first if it is ok then check out your fuel supply, float level, vents, fuel line, etc. Put a piece of fuel line on your petcock and open it up and let the fuel run into a container, you should has a good stream for al least a gallon.
Hope this helps, let me know how you make out.

 

It turned out to be the float was way off. The only part I had a mechanic adjust. Just had it out and 4800 rpm's without skippin a beat. I'm no the road again. Thanks for the advice. I was worried it was electrical rather than plumbing. LOl

 

1990 was a great year! Glad you're sorted.