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77 GS750 tuning w/ VM26's, stock air box, and Vance & Hines exhaust

  • Thread starter Thread starter SocialAnomaly99
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SocialAnomaly99

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Just got my Vance & Hines exhaust for the 77 GS750. The V&H jetting recommendations seem a little hamfisted to me.
They are as follows.
"GS750 2V -> Increase the main jet to a 115. Pilot Jet should be increased to a 17.5. The needlemay need to be raised one notch (lower clip)."

They say nothing about the air box & filter(s), and doesnt 17.5 Pilot seem a little large to anyone else? They also don't mention which carbs these settings go with (VM26 or BS32). I'm running the VM26's with the stock airbox and just want to see what you gents have to say about these tuning recommendations before I go changing things.
Thanks
 
Agemax said:
the 77 750 only came with VM26's. the BS carbs didn't get fitted to a few years later
Click to expand...

Well dang. That clears THAT part of my query. How bout the Pilot jets, Main jets, and airbox parts?
 
i would run it with standard jets and see what the plugs look like. i ran a GS1000 with 26's on standard airbox and jets with a Harris race pipe and the jetting was perfect. ( i just raised the needle one notch, like they suggest)
 
Agemax said:
i would run it with standard jets and see what the plugs look like. i ran a GS1000 with 26's on standard airbox and jets with a Harris race pipe and the jetting was perfect. ( i just raised the needle one notch, like they suggest)
Click to expand...

+1, don't touch a thing and see how it runs. Do you know what pilot and main you've got in there now?
 
I haven't had the carbs on this bike apart yet. The PO had a 4 into 1 pipe on there and could only tell me that "it has been jetted for the pipe". It ran ok, but I feel like it could run a lot better. I'll have a peek into those carbs after work today and see what we got. Thanks for the input!
 
So I got the carbs all cleaned up. Took them to my buddies shop, removed all jets, needles, etc, and cleaned them in the ultrasonic cleaner. They look great aside from a little permanent discoloration on the outside. The current main jets are 120s and the Pilot jets are 15s. The clips on the needles were on the 3rd notch down from the top(not the pointy tip) of the needle, but I raised the clips one notch(lowered the needle) as I feared the previous setting would be too rich with these 120 main jets.
Like I said before, the bike ran fine with the 120s and the MAC pipe that was on there. But I don't really have anything to compare its performance to. Im thinking I might just have to take it to the strip one of these days and do some jet swapping and needle adjustments.
If I do buy new jets, I think I'll go with the V&H recommended 115 mains and 17.5 pilots.
 
SocialAnomaly99 said:
So I got the carbs all cleaned up. Took them to my buddies shop, removed all jets, needles, etc, and cleaned them in the ultrasonic cleaner. They look great aside from a little permanent discoloration on the outside. The current main jets are 120s and the Pilot jets are 15s. The clips on the needles were on the 3rd notch down from the top(not the pointy tip) of the needle, but I raised the clips one notch(lowered the needle) as I feared the previous setting would be too rich with these 120 main jets.
Like I said before, the bike ran fine with the 120s and the MAC pipe that was on there. But I don't really have anything to compare its performance to. Im thinking I might just have to take it to the strip one of these days and do some jet swapping and needle adjustments.
If I do buy new jets, I think I'll go with the V&H recommended 115 mains and 17.5 pilots.
Click to expand...

Those V&H instructions are probably aimed at people running pods and 4-1 pipe combo. With the airbox fitted, you'll be way rich at 115 mains.

I run 105's in my VM26's on my 850, with a 4-1 exhaust.

With your more aggressive cams in the 750, I'd start at 107.5 and do some plug chops.
 
Something to consider: The V&H instructions were written by guys in California; real close to sea level.

If it ran well as currently jetted with the MAC pipe, I'd start there. I used to run a 77 GS750 with a R.C. Engineering pipe (very similar to the V&H). I ran 120 main jets and stock pilots. It ran great. I'd much rather be too rich than too lean. Running too lean makes it run hot and you run the risk of burning valves. Stock jetting was 100 and I ran 107.5 to start and it was too lean.
 
Yeah, you need to fart around to find the right main jet - could be anything between 105 - 115. Also leave the 15 pilot in, 17.5 is too much even running pods.
 
So I got the carbs and exhaust back on the bike and it runs. I havnt had the chance to synch the carbs or take it for a test drive yet, but things are sounding good. Its been pretty cold here in MI the last couple days(50degrees or so when I started the engine). So getting it to start wasnt the easiest task. Took a little while of cranking on full choke to get it to fire. I will let you guys know how it runs when i can get it on the road and crank on it.
 
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