GT 750 irratic running over 3000 revs

[VintageKiwi]

Hi Everyone.
My 76 GT750 has started to play up.
It starts well and runs well up to about 3000 revs then the fun starts , it then feels like there is a rag in the airbox, it is sluggish and feel like it is running on 2 cylinders and has a mild miss fire. feels like the RH cylinder
I have done the following
Cleaned the carbs , with carb cleaner and syncd them.

checked the timing with a strobe, all good.
Fitted new battery.
checked the coils with a multimeter primary and secondary.
new plugs and leads, caps.

next i am going to check the battery charging, thinking about the condensors as well

Any Ideas of the fault are much appreciated.

Jim

[Alan H]

It starts well and runs well up to about 3000 revs then the fun starts , it then feels like there is a rag in the airbox,

You sure there isn't a rag in the airbox?

(coughs, then runs and hides!!!)

I'm afraid the favourite is the carbs. Use an ultrasonic cleaner and blow all the jets and hols through with carb cleaner or similar.
Then battery and possibly either a loose/poor electrical connection between battery and points or even a component in the ignition circuit on its way out. Check loose HT leads and plugs as well. This is the main cause of heartache on old bikes.

[jabcb]

Does the problem depend on throttle position & load? (accelerating vs. just putting along)

Could be coils or condensers.
They can test ok at the low voltage used by a multimeter but then have problems at high voltages.

Check voltage drops.
As Alan indicated, could be a wiring problem.

[T350guy]

Check to make sure all your slides are moving up when the throttle is opened.
A pinched diaphragm can cause a leak or even a small tear.
This will not allow the slide to move up creating a rag in the box feel.
My old 83 BMW did this years ago and my 77 GT 750 last year (diaphragm not seat correctly)

Ian

[VintageKiwi]

After replacing the coils , it still ran crazy.
So replaced the points and condensors with a Accent electronic ignition, easy to install, fired up first time and now runs really good, so must have been crook points or condensors.
Thanks everyone for your ideas.

Jim

[GT750Battleship]

hi,thanks for the "heads up" on the Accent System,must fit one to my 76 A model,been thinking about doing this for years
Cheers,
Roger.

[T350guy]

I have one fitted to my 74 GT 750 and just installed another Accent Iggy on my 77 GT 750..Love these..just plug & Play.