74 Gt 750 surging

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spark
Cucciolo - the Lil Pup
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74 Gt 750 surging

Post by spark » Sat Sep 22, 2012 11:33 pm

Hi i recently retimed using a globe from coils and a home made timing wheel. The bike is surging a bit now when on constant speed, not bad under power though. Maybe i had better recheck timing. Has road and race coils for the Dyna S ignition on it.

My750GT
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Re: 74 Gt 750 surging

Post by My750GT » Sun Jan 27, 2013 3:32 am

My 72 does the same. I'm thinking it might be fuel related though. But having said that, I've never properly checked the timing after fitting a Dyna S electronic ignition. Just did it be trial and error. Must be close as it rides pretty well.
'72ish 750 GT
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Western Australia

wdietz186
888
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Re: 74 Gt 750 surging

Post by wdietz186 » Tue Jan 29, 2013 3:13 pm

You should probably check your float levels and make sure the carbs are synched before you mess with the timing too much.

dden
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Re: 74 Gt 750 surging

Post by dden » Fri Feb 01, 2013 10:28 am

There seems to be a few people having these same problems lately. I think its gas related. Clean your carbs, check floats as mentioned below. I'm wondering if the gas itself is a problem with ethanol in it these days. Maybe try emptying your tank, go through your carbs, and fill it with some race gas which doesn't have ethanol for the first tank or 2. See if there are any problems, then switch back to pump gas and see if the issue starts to resurface.

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Re: 74 Gt 750 surging

Post by BevHevSteve » Sat Feb 02, 2013 8:36 am

Since you mention ethanol - I suggest you all get in the habit of putting treatment into your gas all the time now - I do, and have been the past year.....
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My750GT
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Re: 74 Gt 750 surging

Post by My750GT » Tue Feb 05, 2013 3:14 pm

I've discovered that my issue may not be fuel starvation. My main problem was the rear cylinder not firing regularly. I took the cap of the dizzy and played around with the Dyna S adjustment with little improvement. I studied it for a while and then noticed that the static pickup for the rear cylinder had slotted screw holes. I loosened them off and moved it back and forth a little, and guess what? The rear cylinder roared to life. So it turned out the the Dyna was not set up properly from factory, or not for my bike anyway. Have not taken the bike for a ride on the open road yet. It will be interesting to see what the performance is like now.
'72ish 750 GT
Functional bitser
Western Australia

thessler3
Mariana
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Re: 74 Gt 750 surging

Post by thessler3 » Sun Aug 04, 2013 4:17 pm

The Dyna installation instructions on Bevel Heaven do say to adjust the rear Dyna pickup to time the rear cylinder. The range of adjustment is quite small. My rear cylinder was about 5 degrees off until I adjusted the rear pickup.

As fas as surging goes - it is probably not ethanol related. I have a fiberglass tank and have avoided gas with ethanol completely. I have been using 100 octane low lead aviation gas that has no ethanol. My bike still surges at low loads but runs great when pushing it harder. I think I need to play with the carb needles to find a sweet spot.

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