Ok everyone heres the situation I have a 1990 fltcu bone stock when I ride down the road and hit 65 to 67 mph the bike begins to act like it is running out of gas. I cleaned out the fuel tank, put in a new petcock and screen, put on a larger diameter fuel line and put a inline filter in and the problem persists. When I let off the throttle the problem doesnt immediately go away. When I let off the throttle the engine goes completely quiet like it died then kicks back on at about 45 mph(lots of fun on the slab) then I can slowly accelerate back to about 65 again. I can run at 65 all day long but as soon as I pass it the problem starts again. And as the gas tank gets emptier the problem starts sooner. Once the needle gets into the red I cant even do 55mph. I have never even got down to the reserve it starts becoming unrideable long before that. I have run with the gas cap off so its not a vacuum lock. Im thinking the float is set to low but could it possibly be a electrical problem of some kind? Anyone have this happen to them? I was thinking of replacing the voes but if that was it the problem should go away the second airflow dropped below the switches level.

 

Main jet clogged?

 

Is your gas tank vent clogged? I have a 1991 FLT and cannot remeber if gas cap or tank is vented. If cap is vented, loosen cap and ride it to see if problem is still there with loose gas cap.

 

Crud in the tank clogging up the screen? Look down the hole with a flashlight and shake the bike. See if anything is floating around in there.

 

You stated you don't belive it's vacuum lock because you take the cap off and there is no air exchange, so we will delve into this a little deeper. You need to remove the carb and look into the bowl for debris,etc. If you find some you will need to examine the tank as well. The screws are soft so use a good #2 phillips or break them loose first with a pair of needle nose vice grips. If there is crud in there you will need to take some carb cleaner and some lacquer thinner and a one gallon empty paint can (you can get this at Lowe's, etc. wash ou the carb with carb cleaner, then put it in the gallon can and pour in enough lacquer thinner to cover the carb then leave it there for at least an hour or two. While it's cleaning examine the diaphragm for holes and tears.
When this is done take the carb out and blow out all the passages. Re-assemble the carb, set the idle mixture screw at two turns out to start. When it's warmed up set it where it idles best. Make sure the slide goes up and down without sticking and check for vacuum leaks after you re-install it. Also make sure the enrichner cable is fully seated.
You should have a 45 slow jet and a 185 main jet, they are fine for a "stock engine". You can use the 1988 Sporty needle, it may cost you 2-5 miles per gallone depending on how you ride, but it will help the mid range. Do not drill the slide or cut/change the spring on a stock engine as any gains are more than offset by the decrease in rideability for the average rider. Hope this helps.

 

I'm guessing that there's a fuel flow restriction. The symptoms you describe don't sound like a jetting issue to me.

Maybe a partially clogged float needle seat or something preventing the needle from opening fully. Check your carb float for binding or for something else that's preventing its free movement.

Also, possibly something partially clogging the carb fuel inlet, the tank petcock outlet, or the fuel line itself.

 

Thanks everyone for the advice. I know fuel is getting to the carb. The tank has been emptied and cleaned. New screen and petcock put in and new inline filter and all new fuel lines. And I have run it without the cap on so its got to be in the carb. I am fairly mechanical but something about taking the carb apart freaks me out but I will give it a try if I get in over my head I can always just take it to a shop and have it rebuilt. Thanks MiaCycles for the detailed advice I will follow it to the letter tomorrow morning.

 

Just take that CV carb apart and clean everything, take pictures as you disassemble so you'll know what goes where, follow the manual, take notes if necessary, you'll figure it out, good luck. If that's the original CV carb and it hasn't been apart there is probably your problemo.

 

Had the same problem with mine, got bike used, didnt know if it had a cam change or not but at 70mph experenced the same as you. Changed the needles to 45/185 and it was like I had a new scoot.

 

This may be wild! Did you @ 65 mph shut off the petcock, starve it for fuel, pull choke, open up throttle, suck all the carp thru?

Cleaned up my carb when it acted-up... But I have a butterfly carb. Tho it works on my honda ATV. Needle type carb like the CV.