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GS550 1977 accelleration problems at high throttle when under load

  • Thread starter Thread starter xxmagnus
  • Start date Start date
I would check to see if the engine is set up for the stock VM carbs. If it is, it will have intake ports that are 22mm in diameter. The CV-type carbs are 32mm, the difference in diameter would create a bit of turbulence at the step.

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Okay guys, im back with some new information and questions.
I have now completely picked apart my carbs except the butterflyvalves and the rod they sit on.
The jets have these following numbers stamped on the side:Needle jet 925, main jet 40, air jet 120.
Im having trouble finding what to use for dip, as this is a small country with limited shops and wares, can i use weak vinegar or some other weak acid for carb dip?
Also, what is important to replace when i`ve cleaned them?
Planning to change all o-rings, one of the pilot screws that had a almost stripped head and one of the float seats that didnt look too healty.
When it comes to adjusting valves, can i get a machineshop to make shims of the thickness i need, or do i have get "real ones" for them to function properly?
The reason i ask is that there is a local ship builder, and i was hoping i could get them to make me some.

Edit: added info
 
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The valve shims need to be precision ground/lapped after being hardened- this is tough for most machine shops to do. Typically, you can move the shims around and maybe only need to acquire a few new ones. You can have a shop make you a thinner unhardened shim to use as a measuring device to determine what new thickness you need- this would just be used for measurement purposes, not for running.

but do what Steve said here

"....I would check to see if the engine is set up for the stock VM carbs. If it is, it will have intake ports that are 22mm in diameter. The CV-type carbs are 32mm, the difference in diameter would create a bit of turbulence at the step."

Since it ran ok up to 4000 rpm, I guessing the carbs are pretty clean since this is the range where gunked up carbs give problems.your jet numbers make no sense to me, but someone else will know.
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Just measured the intake, was around 26-27mm inside diameter on the engine. needle jet is probably 92,5 (didnt see a comma, but im pretty sure it has to be 92,5)
 
Wait, we might be having terminology problems. What you are calling the "needle jet" ,we call the "main jet" - the thing that the needle goes up and down in. A 92.5 main jet would be probably be the stock main jet size on 1980 gs550 with CV carbs and stock airbox and stock exhaust . Your 4 into 1 exhaust will change things a bit, but any "step" in intake manifold would be more problematic to airflow as Steve said.
 
Aha, yes english is not my first language so when things get technical, i dont always get the parts names right. When it comes to the exchaust i really dont know, i tried to change needle height(by moving the clip) first for richer mix (testdrive) then leaner(testdrive again), did not notice much difference. Here is the place i measured the engine intake, its larger diameter than the vm specs you mentioned, so i hope that means it has cylinders with cv intakeDSC_0478.jpg

Edit: I will try to supplement my posts with pictures of the part/parts we discuss so i make less confusion with my scandinavian/english mixed terminology:)
 
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If I had a cylinder head off a 1980+ gs550 lying around , I'd measure the intake hole for comparison to your 26 to 27mm reading.i'd think it would be a lot closer to 32mm of the CV carb. Someone will chime in!
 
Actually got a cylinder head with the bike, will measure it. Btw thank you very much for your time and help so far:)
 
Unfortunately i was in a spot with too heavy clouds to see all of it, got a glimpse in the end though.But was special when everything went dark and quiet, even the birds were silent
 
Update: Bought a 78mod bike locally with engine,vm carbs,original intake and airbox boots, airbox, what looks like original exchaust and seller assured me that the gear was ok on this one.
Planning to make the engine ready to start in the bike its in now, and if it seems to run okay, im going to do a transplant.
This way i have original setup(engine,carb,exchaust,airbox all from the same bike) and i have a better chance of getting stuff right.
 
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