D
dezert
Guest
Hello,
After spending about two weeks just reading through the posts and testing different things I decided to start posting my findings and perhaps get some advice, as there is not much more that I can think off that could be worth chcecking.
So my bike is 1978 GS 500 E (it's a sleeved down version of 550 for Swedish market) four cylinders, VM22ss mechanical carbs, points, cast wheels with double rotors.
My problem is the power. The bike starts right away, idles without problem, and accelerates rather OK up to about 4k rpm, then it flattens out, it's smooth and revs to redline on 2nd but develops no more power. In any gear its maximum speed is 120 kph (ca. 75 mph).
These are the checks/maintenance/parts I did
1. All valve clearances within 0,05-0,01mm
2. Carbs stripped and cleaned 3 times, I followed VM carb rebuild. Boiled in acid solution, and also in ultrasonic cleaner, they are clean. New orings.
3. Manifold rubbers replaced with new ones incl. orings.
4. Stock airbox and very lightly oiled new foam filter. I do not have the lid, but made one out of cardboard to about right opening size.
5. The exhaust is 4into1 Marving. Tried running without it with no noticeable difference (so it's not clogged)
6. The points were cleaned with 500 grit sand paper and gaped at 0,3mm.
7. The condensers were checked by disconnecting them briefly - the bike run bad with either one disconnected.
8. Coils checked for resistance, primary ca 4ohm, secondary ca 35kohm, tried running with gsxr 1100 '89 coils/caps - no difference.
9. Caps and plugs are new, also cut off some 10mm HT cables where caps attach.
10. Tried running with a wire between a main braker to white/orange double connector for the coils - no difference
11. I had some problem with valve timing adjustment as I couldn't get the #1 mark to point at the gasket face (either above or below). In either case the engine is running the same (which is really confusing). Now I have the #1 mark slightly below gasket face.
12. The petcock is giving a lot of fuel, tried draining tank to a bucket, so no problem there, checked for "On" position.
13. I had the fuel filter for a while, but recently got rid of it just to eliminate a possible fault, no change after that.
14. Carbs are synced with manometers at idle speed.
15. Needles at middle position with thick nylon washer below the shim
16. Pilot jet #15 as per spec, main jet #102,5. Tried running with #92,5 jet, and it made the bike worse I think. tried also #134 and that properly bogged the motor.
17. Choke is as it should be, meaning when cold - it make rpm higher, when warm it bogs the motor.
18. There is no difference when I pull the choke while at max speed (75mph) no matter what gear/rpm I'm in.
19. Timing and advancer working fine (checked with strobe light). Although the strobe is not flashing above ca 4k rpm. But I blame it on weak strobe pickup, besides the bike run much higher rpm, and the headers all have same temperature.
20. The compression is low at 90psi (warm, WOT) on all cylinders. (they have been lightly honed as I had suspected glazing, did ca 30 miles after that). The rings are not stuck, I had the cylinder off, and rings are free, and gap within spec.
21. While I had the head apart, I checked valve spring free length (it was well within spec), and did a leakage test with ethanol on both in and ex side (no leaks).
22. The internals looked normal, no signs of burning, or excessive carbon deposits, or friction etc.
23. The float bowl levels were adjusted on the bench to ca 3 to 4mm below the carb body split line. No fuel leakage from the carbs.
24. The electrical system is OK. The stator was re-winded (did it myself) and is charging OK. Went through stator papers. Also cleaned all connections with spray cleaner.
25. There is no drag/binding in the drive chain or wheels (brakes).
What else could/should I check? I don't really want to do the piston/rings/bore before I am absolutely sure all other things are working as they should be. I suppose a low compression problem is more pronounced in the low rpm region so then it would not apply to my case.
I could make a run with a camera, to illustrate the problem perhaps.
Regards,
Dezert.
After spending about two weeks just reading through the posts and testing different things I decided to start posting my findings and perhaps get some advice, as there is not much more that I can think off that could be worth chcecking.
So my bike is 1978 GS 500 E (it's a sleeved down version of 550 for Swedish market) four cylinders, VM22ss mechanical carbs, points, cast wheels with double rotors.
My problem is the power. The bike starts right away, idles without problem, and accelerates rather OK up to about 4k rpm, then it flattens out, it's smooth and revs to redline on 2nd but develops no more power. In any gear its maximum speed is 120 kph (ca. 75 mph).
These are the checks/maintenance/parts I did
1. All valve clearances within 0,05-0,01mm
2. Carbs stripped and cleaned 3 times, I followed VM carb rebuild. Boiled in acid solution, and also in ultrasonic cleaner, they are clean. New orings.
3. Manifold rubbers replaced with new ones incl. orings.
4. Stock airbox and very lightly oiled new foam filter. I do not have the lid, but made one out of cardboard to about right opening size.
5. The exhaust is 4into1 Marving. Tried running without it with no noticeable difference (so it's not clogged)
6. The points were cleaned with 500 grit sand paper and gaped at 0,3mm.
7. The condensers were checked by disconnecting them briefly - the bike run bad with either one disconnected.
8. Coils checked for resistance, primary ca 4ohm, secondary ca 35kohm, tried running with gsxr 1100 '89 coils/caps - no difference.
9. Caps and plugs are new, also cut off some 10mm HT cables where caps attach.
10. Tried running with a wire between a main braker to white/orange double connector for the coils - no difference
11. I had some problem with valve timing adjustment as I couldn't get the #1 mark to point at the gasket face (either above or below). In either case the engine is running the same (which is really confusing). Now I have the #1 mark slightly below gasket face.
12. The petcock is giving a lot of fuel, tried draining tank to a bucket, so no problem there, checked for "On" position.
13. I had the fuel filter for a while, but recently got rid of it just to eliminate a possible fault, no change after that.
14. Carbs are synced with manometers at idle speed.
15. Needles at middle position with thick nylon washer below the shim
16. Pilot jet #15 as per spec, main jet #102,5. Tried running with #92,5 jet, and it made the bike worse I think. tried also #134 and that properly bogged the motor.
17. Choke is as it should be, meaning when cold - it make rpm higher, when warm it bogs the motor.
18. There is no difference when I pull the choke while at max speed (75mph) no matter what gear/rpm I'm in.
19. Timing and advancer working fine (checked with strobe light). Although the strobe is not flashing above ca 4k rpm. But I blame it on weak strobe pickup, besides the bike run much higher rpm, and the headers all have same temperature.
20. The compression is low at 90psi (warm, WOT) on all cylinders. (they have been lightly honed as I had suspected glazing, did ca 30 miles after that). The rings are not stuck, I had the cylinder off, and rings are free, and gap within spec.
21. While I had the head apart, I checked valve spring free length (it was well within spec), and did a leakage test with ethanol on both in and ex side (no leaks).
22. The internals looked normal, no signs of burning, or excessive carbon deposits, or friction etc.
23. The float bowl levels were adjusted on the bench to ca 3 to 4mm below the carb body split line. No fuel leakage from the carbs.
24. The electrical system is OK. The stator was re-winded (did it myself) and is charging OK. Went through stator papers. Also cleaned all connections with spray cleaner.
25. There is no drag/binding in the drive chain or wheels (brakes).
What else could/should I check? I don't really want to do the piston/rings/bore before I am absolutely sure all other things are working as they should be. I suppose a low compression problem is more pronounced in the low rpm region so then it would not apply to my case.
I could make a run with a camera, to illustrate the problem perhaps.
Regards,
Dezert.
