GS750 -77 dies after a while on full throttle

[Warlock]

Hi. My GS750 -77 dies after 2 min of full throttle run and on full throttle it will not go higher than 5000rpm on 4:th gear.
I know that my fuel level high in carbs is wrong. I will correct this when my new pilot jets will arrive later this week
If I measure the float level high it is now 18mm... it should be 26 but if I'm not stupied right now it means that I have too much fuel in the carbs... right? (18mm with the carbs up side down)
this means that It cannot be problem that it gets too little fuel?

I have pods and have rejetting the main jet to 118... now I waiting for my 22,5 pilot jets .
And a couple of weeks ago I replaced all the sparkplug caps.
That do you think... fuel or ignition problem? will a coal problem show this problem?

[tkent02]

This cutting out at wide open is a very common problem. Most likely the petcock isn't letting enough fuel through into the carbs, under wide open the fuel level in the float bowls slowly goes lower and lower, when it gets too low the engine cuts out. Check the flow rate of the fuel going into a bucket or gas can. Could be the screen in the petcock, the fuel hose (kinked) and vacuum hose (cracked), it could be the vacuum valve in the petcock itself. It could also be a clogged fuel tank vent, or a clogged inline fuel filter if you have one, or just the wrong type inline filter.

The part about not going over 5,000 RPM is something else. Could be the fuel level or jetting, maybe not.

118 is not a Mikuni jet size, some aftermarket jets? Also the stock 15 pilot jet usually works well on a two valve 750 with pods.
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[Warlock]

Thanks for the fast answer. Yes 118 is not a Mikuni jet size. It's hard to find the right stuff at my local store... they don't know anything about old bikes ... I tried some jets and this ones fits.
The old jet was 103 and that's not a mikuni size either

I got my pilot jets today in the mail... z1enterprises do really have fast shipping to Sweden... only four days ... and god prices too.

I guess its a petcock problem... the former owner plugged the vaccum hose and put a on/off thing after the petcock.... maybe this will cuase the problem... maybe I have to always run on Prime.... right now I only use ON on the petcock. Or maybe I should put a new vaccum hose to the carb and check?

[headsbikesmopars]

My sons GS750E 16 valve did the same thing. The pet cock 'O' ring on the diaphram shaft (valve) was old and stuck in the hole when diaphram was retracted it didn't and was only allowing a trickle amount of fuel to flow even on prime ..the same. Arround town it was ok but on the road it would lean out and die with a full tank of fuel, he was out of gas! save those old petcocks they are great for parts.

Terry

[Warlock]

Thanks for your response.... Last night I solved the problem. It were two things that were wrong.

First the easy thing with the fuel. I have no problem with the fuel now... Went for a highspeed round yesterday with the petcock set on "Pri".. no problem... I switch it to "ON" and it dies after a while. As I have a on/off after the petcock I can always use Pri... so that problem is solved

The problem with RPM.... this sounds strange but it as I put the new pilot jets on and make changes on the airscrew I noticed that nothing happened when I screwed on the third carb (from kick side). That cylinder didn't have a spark... the strange thing is that I didn't notice that. When I had problem with the first cylinder a couple of weeks ago I noticed that right away... strange

Now new plugs, new jets and a happy owner....
Now I'm waiting for my new seat and new heavy duty clutch springs

[kpotter16]

ive been having a similar problem with my bike as well. it will ride but to only about 5000 rpm then starts to cut out. idleing as well it will everyonce in a while rev up but usually only till 5 or 6000

[tom203]

ive been having a similar problem with my bike as well. it will ride but to only about 5000 rpm then starts to cut out. idleing as well it will everyonce in a while rev up but usually only till 5 or 6000

Put your bike in your signature (82 750 ? ). Looking at earlier postings,you have had this problem for 6 months? Follow warlocks lead and check out similar simple stuff, like petcock flow.