Gt750J revving out

[graciesdadpaul]

Hello everybody,

I was riding along happily on my GT750J when i started to slow for an upcoming motorway roundabout only to find that the engine rev'd uncontrollably when the clutch was pulled in. Very scary indeed but I managed to stop safely whilst fearing for my life from the 3 lanes of oncoming vehicles coming at me, I survived so first problem solved. I checked the obvious like a stuck open throttle and all three carbs are opening and closing ok and whilst there I checked the choke cables and plungers and all seem fine. No issues with carb boots or airbox either that I can see. I've obviously got a major air leak somewhere and I suspect one or more of the crank seals has failed even though it's only done 1500mls since a full rebuild.

I will carry out a leak down test before I start stripping her down but I'd also appreciate any advise on where else to look for the leak. bare in mind that I cant run the engine as it will go straight to full throttle.

thanks in advance.

[barney01]

Hi. This happened to me on my 550j. It turned out to be the throttle valve pin which keeps it facing the correct way had dropped out and the valve had spun around causing the same symptoms.
Good luck

[badgereng]

Good spot!

[graciesdadpaul]

Thanks for the response. I don't know what you mean by throttle valve, I have Mikuni VM32s with throttle slides on mine as its a J, not CV carbs. I have looked to see if one of the needles has come loose and they haven't.

[mick 63]

Hi Barney is calling the slide a throttle valve , in the carb body there is a brass pin /peg that keeps the slide in its correct position , these have been known to fall out allowing the slide to turn in the body , cheers.

[barney01]

The pin is in the carb body and fits into the groove on the throttle valve to keep it facing the right way.

[graciesdadpaul]

Ah I understand, I will have look and see if that's what's happened. Fingers crossed its that simple.

[Alan H]

If it isn't that simple, it'll be something else.
Hope this helps......

[graciesdadpaul]

i looked at the carbs last night, and found that the pin on the middle carb had indeed worked its way out. Easy to punch back in and seems solid for now. Fairly sure that was the problem so that's a massive relief. I haven't run it yet to be certain as im waiting for some petrol hose to be delivered. Thanks to Barney01 I owe you a beer mate.

[barney01]

Great news! I put a dab of thread lock on the pin to prevent it coming out again.