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Starting/Idleing Problems 78 GS400

  • Thread starter Thread starter khardrunner14
  • Start date Start date
K

khardrunner14

Guest
Problem: The bike is very hard to start and does not run well. It won't hold idle, and has no power.

- The left cylinder (looking from the riding position) is running lean as evidenced by a plug chop.
- The right is so rich that the plug is wet and smoke/gas fumes poured out of the plug hole when I did the plug chop. The plug is very dark.
- Gas drips from the overflow line in right cylinder, but not the left.

What I've done:
- stripped, cleaned and rebuilt carbs with new o-rings (used the same needles and jets)
- 2 new air screws/o-rings at 1.5 turns out
- new intake 0-rings
- checked spark plug gap
- checked point gap
- 2 different, charged batteries

The bike ran great for over a year. 1-2 kicks to start it. Then, I began to have problems getting it started, and after a while it was a real bear to start (if I could get it to). So I did the above, and it has not been right yet. I can get it to start if I blow in the two top hoses, but even then it is tough.

Help me get the bike back on the road! Thanks!
 
The lean cylinder sounds like it is still a carb issue:
1) Check the float level settings again.
2) Sounds as if the choke circuit is still plugged, did you soak those babies and run a small wire through all the passages?

The rich cylinder sounds like adjustments to that carb still need to be made:
1) Float settings.
2) idle adjustment screw?

Did you sync the carbs yet? A bench sync will get you close enough to cure any problems with out of sync carbs.

Compression #'s would be good to know.
 
I bench synced the carbs after the rebuild. I stripped and dipped them, then checked passages. I also sprayed carb cleaner through each passage to be sure they weren't blocked. I didn't do anything with float levels or the clip settings since they worked well at one point.
 
Check your compression numbers. Something is "fishy" here. Orings on the intakes? If everything was set the same between both carbs, there has to be another issue causing your problems.
 
I replaced the O-rings on the carb boots going to the motor (aka intake boots in my little brain).

I'll try to get compression #'s tomorrow. Let's pray that isn't the issue, I don't have the $$ to rebuild the entire motor.
 
bump...any other ideas? I should have compression #'s later today or tomorrow.
 
I checked the compression by kicking the motor over until I reached max compression. The numbers I got are 142 in the left and 146 in the right. This shouldn't be a problem.

The right cylinder is not firing at all, which explains a lot. I am 90% sure the coil is bad.
- I have spark at the points
- I have juice in the wires prior to the coil
- I have juice at the condenser
- plug does NOT spark (tested several different plugs)
- checked plug gaps and point gaps

Any good ways to test the coil without the special tool in the manual? Also, will the Dyna coils from Z1enterprises swap right in (are they a direct swap)?
 
Also, check the spark plug cap (they unscrew from the wire). Switch right to left before swaping coils like tkent recommended.
 
Flooding right Cylinder

Flooding right Cylinder

Check your Fuel petcock. I had all of the same symptoms on my 80 Gs400. You probably have Vacuum carbs and the vacuum line going into your petcock is sucking in fuel. Next time you start up your bike pour fuel directly into the fuel line and plug the vacuum line with your thumb. (The vacuum line is the one coming out of your right carb.) If it starts running well, you know that the issue is your fuel petcock. it probably needs a rebuild. There is probably a hole in the diaphragm and the vacume line is sucking raw fuel into the cylinder and flooding out.

I hope you follow me and good luck. It took me 3 carb rebuilds and 2 months to figure this out so I hope that it didn't take you as long.

Darnell

64 Honda ct90
84 Honda CM250
80 Suzuki Gs 400
93 Honda VFR 750
 
I don't have the bike hooked up to the fuel tannk. I rigged a tank to direct feed into the carb, so the vaccuum lines are not hooked up. I don't think I have a vaccuum petcock anyway, but thanks for the advice!
 
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