Loss of power at high speeds

[ntrthamatrix]

Today, I was heading to lunch and going 75-80 on the interstate. After a few minutes of going those speeds it started slowing down and I really couldnt keep it above 70. It would surge in speed for half a second and kept doing that...I made it to lunch. On the way back pretty much the same thing happened. It accelerates nicely and if I sustain lower speeds it seems fine. I do have a hard time getting it started after it has sat for a few days. I have to use starting fluid but after the initial start it works great for the rest of the day.

Also when I got the bike in 2010 the carbs needed to be cleaned. I did as much as I could but I probably need to do an acid bath or something. It would probably fix the issue..I assume its the carb. Anyway Im just trying to give you as much as info as possible. Thanks for the help and if I think of anything else I will add it...

I have a 1980 XS11 Special

[TopCatGr58]

Oh Goodie,

I get to answer first! Okay, you have a Special, do you still have the OCTYPUS vac. controlled valve...that funny thing with all of the fuel hoses coming out of it sitting on the top of the #2 carb body? If so...then the control valve/vac valve/diaphragm may be damaged or stuck so it's not allowing the proper fuel flow....and at higher sustained speeds the carbs are running LOW. OR...it could be just the vac. hose from it to the intake boot that has gotten cracked or such so that you're not getting enough vac. to keep the valve open enough? Or...your gas cap vent may be partly clogged so that it creates a vac. lock and prevents the fuel from flowing.

SO...first diagnostic is to turn the petcocks to PRIME and ride it at speed and see if the problem persists. IF not, then you've narrowed it down to the OCTY. IF problem still happening, then pop open the gas cap and test again, if problem solved, then gas cap suspect...take apart and clean.

It sounds like lack of fuel flow problem....you're hitting a wall at 70 mph, it's not like it's actually loosing power which would point you towards the pick up coil wires.

Depending on how well you cleaned the carbs, and IF you have an inline fuel filter could determine how dirty they may have gotten in 2 years, also whether it sat for time during winter getting gummed up? Not starting easily after parked for days....again lack of fuel....turning petcocks to PRIME will fill the float bowls without the engine running. Also, there's a small jet/port in the float bowl that gets easily clogged and it feeds the choke/enrichener circuit, and that could also be a problem area for poor difficult starting.

T.C.

[BA80]

All what TC said plus........check the gascap vent. If it is starting to clog that's pretty much the symptom you'll experience as the fuel tank drains and the air is having a difficult time getting in to replace the volume it will create a vacuum and slow or stop fuel flow.

[Yard Dogg]

If the octy is frozen then it may be letting fuel dump into your carbs while sitting making it flood. Pull your fuel lines off the carb and suck on the vacuum tube to see if the fuel flow starts and stops as it should. But the gas cap test is easier to do first.

[BA80]

I agree with the Dog on the octy. If the diaphragm is going bad it will do that too. Ive experienced fuel starvation because of a bad octy diaphragm.

Easy check is to put the petcocks on prime, that bypasses the octy. I had to do a whole 1700 mile round trip like that once.