GT 750 loss of power

[matthewjw]

I have a 1984 GT 750 which is running like a pig - previously had strong output.
It has not been sitting around - it just started to run rough. Low power - horrible sound - doesn't rev past 4/5000

I replaced the air filter and oil, then pulled the plugs - it looks like its running rich. With the new plugs, it was back to its strong self - for about two minutes - then runs awful again. So the plugs are foulling. I have thought there may be a problem with the choke - it doesn't seem to make any difference to the engine weather its in or out - possibly its struck and too much fuel is getting through to the spark?

Does anyone know how to fix - can I shoot some carb cleaner at the choke? How do I get access to the butterfly valve?
Could it be something else - I haven't touched the air / fuel screw.

Any comments / ideas appreciated.

[oldman]

If the choke makes no difference in or out that is probably the problem. The choke on a carby model is just a butterfly valve, usually right at the intake of the carbys. When activated it closes off the air intake creating a vacuum in the carbys while the motor is running or you are trying to start it sucking more fuel through the carbs. By taking the air cleaner off you should be able to see these butterflys at the carb opening. The throttle has butterflys or a slider, (I'm not familiar with your year or model) but they will be way further in the carb inlet. If the choke butterfly is closed there is your problem. I cannot see it being flooding carbs, (such as a stuck float or leaky needle and seat) as it is unlikely that all the carbs would start flooding at the same time. Good luck and any trouble shooting is accomplished more efficiently when the mechanic has had a few Jim Beams and beer, (not tooooo many). Cheers! let us know what you find.

[mike-s]

Just a note, not all bikes use "chokes" often "enricheners" are used which when pulled out proportionally open another galley for extra fuel to flow through (behind the butterfly & slider if relevant) into the engine. Same principle though, just adding fuel instead of subtracting air & forcing the engine to compensate with more fuel draw.

[devo]

Just a thought but maybe this is not carb related , I think these Gt's have an advance - retard mechanism , try that it may be stuck and not throwing out when you rev out the bike .

[jefflthomas]

Just a thought but maybe this is not carb related , I think these Gt's have an advance - retard mechanism , try that it may be stuck and not throwing out when you rev out the bike .

it's a possibility

but i'd add whatever you guys use for carb gum and varnish remover to the gas.. run it then let it sit for a few days

you might get lucky

[matthewjw]

Accessed the choke and jammed some carby cleaner through them - looks to have fixed it. Thanks guys.

MJW