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History.
The bike has been through a number of PO and a “rebuild” at a price. However we basically have a 1978 GS1000 with VM carbs.
So we have a 4into1 exhaust which should be equivalent to original in terms of back pressure. The original air box has been removed with foam filters in their place. The carbs were stripped and examined, two of the carbs had over tightened pilot fuel screws (the one underneath) with snapped tips. Two new bodies obtained and all 4 ultra sonically cleaned and new O rings fitted. The original main jet was way over the top, 10 steps up, so played with the jet size following advice on this forum, settled on 102.5 main jets. So started getting some miles under the belt and chasing various problems using the Factory Pro article as a guide. However had bigger issues to resolve before coming back to the carb. So finally got around to the oil consumption issue which required a top end overhaul due to glazed bores. Task completed and new air filters added as the foam ones were starting to crumble.
So current fit.
105 mains (New pods have less resistance)
#15 slow jets
All O rings have been replaced.
Carb rubbers are sound and air tight.
Valve clearances are good and well within limits.
So after a 15 mile shake down ride, carbs synced and timing checked and adjusted. Slow running was 2,500RPM, made a bit of town driving interesting!
Out for a good 50 mile test and see how she’s going. Good bit, pulls really well with 3/4+ throttle, big grins under the helmet, so I think I have the right main jet. However, there is always a however, under mid throttle cruise conditions you can hear and feel a hunting/note change from the carbs/engine which goes if you add a bit more throttle. The really big issue is when you pull up to a junction and the engine quits if you don’t blip the throttle and even then I can end up with a dead engine.
So today carbs out and a few checks.
Float height checked,24mm.
Pilot screw removed, carb cleaner squirted and reset to 7/8 turn out.
Air screws removed, carb cleaner squirted and set to an initial 3 turns out.
All reassembled and carb balancer fitted and the bike fired up and warmed up.
Timing checked and minor adjustment, carb balance.
So here come the non normal symptoms.
As the engine gets hot, when the throttle is blipped the revs hang at 3,000RPM or more before setting to about 1,500 or less. Quite often the engine would just die before I could blip the throttle or adjust the throttle adjuster. I have tried to adjust the air mixture screws however as I can not get a consistent slow idle I felt I was wasting my time. So my best guess is I have a lean issue here, if so how to progress. Do I adjust the fuel level, change the needle height or do I need to go for bigger slow running jets.
Advice and suggestions please. As always thanks in advance for your advice.
Greg
The bike has been through a number of PO and a “rebuild” at a price. However we basically have a 1978 GS1000 with VM carbs.
So we have a 4into1 exhaust which should be equivalent to original in terms of back pressure. The original air box has been removed with foam filters in their place. The carbs were stripped and examined, two of the carbs had over tightened pilot fuel screws (the one underneath) with snapped tips. Two new bodies obtained and all 4 ultra sonically cleaned and new O rings fitted. The original main jet was way over the top, 10 steps up, so played with the jet size following advice on this forum, settled on 102.5 main jets. So started getting some miles under the belt and chasing various problems using the Factory Pro article as a guide. However had bigger issues to resolve before coming back to the carb. So finally got around to the oil consumption issue which required a top end overhaul due to glazed bores. Task completed and new air filters added as the foam ones were starting to crumble.
So current fit.
105 mains (New pods have less resistance)
#15 slow jets
All O rings have been replaced.
Carb rubbers are sound and air tight.
Valve clearances are good and well within limits.
So after a 15 mile shake down ride, carbs synced and timing checked and adjusted. Slow running was 2,500RPM, made a bit of town driving interesting!
Out for a good 50 mile test and see how she’s going. Good bit, pulls really well with 3/4+ throttle, big grins under the helmet, so I think I have the right main jet. However, there is always a however, under mid throttle cruise conditions you can hear and feel a hunting/note change from the carbs/engine which goes if you add a bit more throttle. The really big issue is when you pull up to a junction and the engine quits if you don’t blip the throttle and even then I can end up with a dead engine.
So today carbs out and a few checks.
Float height checked,24mm.
Pilot screw removed, carb cleaner squirted and reset to 7/8 turn out.
Air screws removed, carb cleaner squirted and set to an initial 3 turns out.
All reassembled and carb balancer fitted and the bike fired up and warmed up.
Timing checked and minor adjustment, carb balance.
So here come the non normal symptoms.
As the engine gets hot, when the throttle is blipped the revs hang at 3,000RPM or more before setting to about 1,500 or less. Quite often the engine would just die before I could blip the throttle or adjust the throttle adjuster. I have tried to adjust the air mixture screws however as I can not get a consistent slow idle I felt I was wasting my time. So my best guess is I have a lean issue here, if so how to progress. Do I adjust the fuel level, change the needle height or do I need to go for bigger slow running jets.
Advice and suggestions please. As always thanks in advance for your advice.
Greg
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