gt750 starting problems

two-stroke-brit · Post by **two-stroke-brit** » Fri Sep 25, 2009 12:52 pm

i purchased said gt750 that has been standing for some time defenitly months or more. and when i got it home ,charged the battery added some fresh gas and after 10 minutes of crankin and kickstartin it came to life ,allbeit slugish and the revs kept wantin to climb on there own.
so i checked the points and the gaps were small i decided to fit a newtronic ignition and this would help the starting and running.

now i cannot get it to start prob seems to be it is not getting gas to the plugs.

new plugs also.
have installed newtronic now and have compression (about 110 in each cylinder) ,i have stripped and cleaned carbs.
it as sparkin in the correct order and at correct plug and the timming is checked with an indicator. etc.so i dont think it is the ignition. i am hopping it wasnt a death rattle from the crank seals.would this cause the not suckin the gas tro to the pots.
i am stumped.
any help will be greatly appreciated.
cheers mark.

water cooled · Post by **water cooled** » Fri Sep 25, 2009 2:07 pm

well...there's a number of things that can contribute to the engine not wanting to start, but it sounds like you have compressionand that you have spark in the correct order. Recheck the battery voltage. How old was the gas that was in there...sounded like you added new gas and maybe there was some old stuff in the tank or bowls.

The run-away revs almost certainly has to do with your carbs. Check the rubber boots to make sure they are tight and no air is getting in or that cracks exist.

What year is the bike...i.e early models '72-73 used VM carburetors and 74 on used CV.

Are you kicking it over or using your electric start?

two-stroke-brit · Post by **two-stroke-brit** » Fri Sep 25, 2009 2:16 pm

the carbs were not fully into the air box side boots so i think thats where the air was getting in and it is the vm32sc carbs on a 73 model. but i have cleaned and refitted the carbs back properly. i have put the battery back on charge and i tryed the electic start and kick start alternativly until to knackered to kick any more.

tz375 · Post by **tz375** » Fri Sep 25, 2009 2:36 pm

Seals may be shot, but let's start with the cheap stuff.

Assuming that there was NO old gas, proceed to clean the carbs. If there was stale gas in teh tank or crabs and you added fresh gas on top, darin it all into your car or truck and start with only fresh gas.

Pull the carbs and strip them. Old gas blocks small passageways and covers everything in varnish. Blow through every passageway with carb cleaner and then do the same on the other two carbs to compare "flow". When all three are spotless, reassemble and synch the carbs so they all open together. Set all 3 air screws to 1.5 turns out and try starting it.

Check for leaks around the intake rubbers

Use fresh plugs B8ES seem to be OK but I prefer thinner tips like Iridium or Platinum.

Pop the baffles out and repack them.

jkevinlilly · Post by **jkevinlilly** » Fri Sep 25, 2009 3:00 pm

Another thought. If the battery does not have enough power to run the electric start, even after charging, may be time for a new one. And a low battery can effect the starting, especially since you have switched to the electronic ignition. Easy way to check it is jump start it using cables, then the bike is using the other vehicles electric, not just what is in the bike battery. It may be a combination of factors, but this will eliminate the battery as the cause. Plus it will give your leg a break while you work on the other suggestions.

Kevin

water cooled · Post by **water cooled** » Fri Sep 25, 2009 3:14 pm

Once you are sure you have voltage and a fully charged battery, you might want to try push starting the bike. Sometime you might get excess raw gas settling in the bottom of the crank area and it can make it hard to kick start.

If you have room, you might want to get a mate or two to help you. Hold the clutch in and put the bike in 2nd gear. Have them push you and drop the clutch once you get up a little momentum. With the throttle wide open, air will get into there to help clear out the excess fuel. If you have to push for more than 100 ft, and it still doesnt start, we need to look elsewhere.

Just make sure you have a good spark by laying the plug on the cylinder head to ground it and kick the engine over, checking each plug for a strong spark. Double check the firing order by placing a drinking straw in the spark plug hole and you should see the spark when its respective piston is very near TDC. (Use a long straw)

Post by **Suzsmokeyallan** » Fri Sep 25, 2009 3:21 pm

You should look at removing the fuel tank and petcock for cleaning, then make sure fuel is in fact flowing to the carbs. It would be best to rebuild the petcock and check the vacuum diaphram in it as well.

Buffalo-guy · Post by **Buffalo-guy** » Fri Sep 25, 2009 5:24 pm

I hate to state the obvious, but are your choke slides working properly, and are you leaving the throttle closed as you use the choke? Thats the only way they work. Did you use the prime setting on the petcock to fill the float bowls before trying to start the bike? Like Allan suggested, make sure that fuel is actually getting to your carbs, or a strong ignition won't do you much good. Sometimes,as most of us has experienced, its the simple solution that sometimes eludes us. I hope you found the solution as I was posting this reply. Cheers.
Fred

Coyote · Post by **Coyote** » Sat Sep 26, 2009 6:44 am

Remove the plugs and put a few drops of gas in each hole. Put the plugs back in and hit the starter. It should fire instantly. If it fires and then dies, it's not getting fuel. Make sure the vacuum hose thet hooks the the petcock is not split or cracked or set the petcock to prime.
If it doesn't fire after adding fuel in the spark plugs holes, the problem is elsewhere.