GT750-B crankshaft

[Cliff]

What do you mean "the engine got hot and started to diesel"? Did it run with the ignition off and rev up? Mine did that ONCE! Thought the thing was possessed!! I had to pull out the plugs, with the engine running at about 12,000rpm, to kill it!
After that the bike wouldn't pull itself up the driveway. Pulled down the engine and found the bearing had failed between left and center and taken out the seal!
Does engine temp make a difference in performance? If you start it up and hit the road cold, does it run good, lots of power etc., until it get up to operating temp or does it run like when crap cold as well? If engine temp makes a difference, could be the thermostat, or worse, head gasket. Compression leaking into the cooling system will make it run terrible when it warms up. Remove the rad cap, run the engine to operating temp and check for bubbles in the coolant!
Gradual loss of power and fuel milage over a five year period seems to point to something wearing out over time. I'd start with looking at the plugs. Are they wet, dry, black or tanned or white? Are they all the same? Wet or black is over fueling, poor combustion. Dry and tanned is good! White is lean. That's not good!
What do your plugs look like?

[pezcat19]

Hi All,

Thanks for the comments and ideas...

@jabcb - I am thinking an electronic ignition is a great idea. I am not sure this is my problem (see below) however it should make a huge improvement to the bikes performance overall.

@uzidzit - my bikes temp is very stable so this doesn't appear to be my problem (thermo is rather new too).

@GreenMachine - You might be onto something here!!! I have not actually proved it yet, but I did a full re-go-over-everything check again the other day and found everything to check out OK, but I still had the problem. I then filled it up with petrol and bingo - bike was running awesome again! I decided to pull the fuel cock out, test, and check the filters/clean the tank. All checked out OK. The bike has been running great for about 150KM until the problem re-appeared, with around 1/4 of a tank of fuel remaining.... I breifly removed the cap (which is a tight fit), and rode around 6KM home with no more issues...

So I wonder if you are onto something here? (This could still be a fluke though...) Is a combination of "lowish" fuel and some tank vacuum possibly causing this problem? Is this a common issue with the GT750's???

@tz375 - Fuel is new. I have not done the 6 for 6 test, however I hope all is well there as the engine had a full rebuild a few years back and has done very little work since. I am close-ish to Geelong (in relative terms) - I live in Forest Hill (Easter Suburbs of Melbourne).

@Cliff - the "diesel" problem was jonathanblair's, not mine (it doesn't sound like fun!)...

Thanks all for your help so far!

Pez

[tz375]

Pez, At least I guessed the right State.

GreenM/c is on a trail there. Sounds a lot like a blocked filler cap breather hole.

[cac646]

Did anyone come up with a solution to this problem? My bike is doing the exact same thing. Bike was running fine but started to leak fuel out of the center carb overflow. Pulled the carbs thinking they were dirty and found 2 of the three floats fuel logged. I've replaced and set the floats, cleaned the carbs and buttoned everything back up. Bike now will run ok as long as I take it fairly easy. As soon as I run it a little harder or under laod (up a hill) the bike will lose power/stall. Sometimes if the clutch is pulled in it will stay running, sometimes it will stall. Always will fire right back up if I pull off to the side of the road. Bike pulls hard otherwise. Since I just had the carbs off it seems like I may have done something worng but the way it shuts off seems electrical. Also just repalced the rectifier (it smoked) about a week before th efuel issue. Could the rectifier have damaged the coils when it shorted? Thoughts??