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1976 GT550 hard to start

  • Thread starter Thread starter hoppy1
  • Start date Start date
H

hoppy1

Guest
I've got a friend who has a 76 GT550 in good shape, but is really hard to start. We have rebuilt EVERTHING on it. New Suzuki pistons & rings, rebuilt crank, carbs, starter. New points and condensers. Timing set, carbs synced. Compression is 120. Sometimes it will start, but won't idle below 1500rpm. Any ideas?? Thanks Mark
 
Welcome. Right off the bat there is a problem with your carbs, obviously, if it won't idle. You say you rebuilt them. Did you clean them in carb dip and instal new o-rings?
If you didn't, you need to start there. There is a carb cleaning tutorial on our main page and here: http://www.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf If you don't do it this thoroughly, they will never run right.

In addition, you mention rebuilding everything. When you assembled the engine did you adjust the valves. Tight valves will make for hard starting.

It also could be that you're not getting good spark. Did you test the spark? It is fairly common with older bikes that the coils don't get full voltage due to corrosion and dirt at connectors. You may have 12.5+ volts at the battery and only 11.5 or less at the coils. 1 volt difference can be 10,000+ or so from the coil. You need to ensure all connections are clean and tight.

In addition, if the battery is not strong and runs down quickly, there may be enough voltage to turn the bike over but not enough to also fire the plugs. When battery voltage drops to 12 or into the 11s that is often the case.

In my experience, hard starting is a combination of these things but most likely lack of strong spark and incorrectly functioning carbs.

Let us know more of what have actually done and what you now find.

good luck,
spyug
 
Last edited:
WHAT VALVES HAHAHA. uum they don't have valves.. it is a smoker
Did you happen to REPLACE the crankshaft seals??

If they suck air, it will be hard to start, have a high idle, and burn pistons and blow up too..
 
Don't all "real" bikes have valves :). My bad I just saw 550 not the GT in front of it.

Spyug
 
spyug said:
Welcome. Right off the bat there is a problem with your carbs, obviously, if it won't idle. You say you rebuilt them. Did you clean them in carb dip and instal new o-rings?
Click to expand...

Make sure the o-rings are present on the idle mix screws.
 
The first thing I would check is the voltage to the coils. It is common for old bikes to suffer wiring degradation and consequently you end up with only ten or eleven volts going to the ignition system/coils.
 
and, when you say the timing is set, did you do that with a dial indicator?
 
earlfor said:
The first thing I would check is the voltage to the coils. It is common for old bikes to suffer wiring degradation and consequently you end up with only ten or eleven volts going to the ignition system/coils.
Click to expand...

Actually, it was 9.39 volts going to the coils, so we done the coil mod like for the GS bikes. Spark is WAY better.
 
Big T said:
and, when you say the timing is set, did you do that with a dial indicator?
Click to expand...
I think you may have something here. I set the timing by the marks, but the crank has been disassembled to be rebuilt, so the crankpins may not be in the same position. I'll check that out, Thanks.
 
barnbiketom said:
WHAT VALVES HAHAHA. uum they don't have valves.. it is a smoker
Did you happen to REPLACE the crankshaft seals??

If they suck air, it will be hard to start, have a high idle, and burn pistons and blow up too..
Click to expand...
Yes, we had the crank rebuilt, all new seals,big end bearings and crankpins. The rods were ok.
 
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