Tuneing Guru's

[Craig]

I have a 83 GS1100. It was over bored to a 1168 and has APE cams, slotted cam sprockets set at 8 intake and 9 exhaust (to the best of my recolection). I have 36mm Mikuni flat slide smooth bore carbs. I was running MAC 4-2 pipes and had it running not too bad. It only showed around 99 HP on dyno. I figured that the exhaust was the limiting factor. I got a V&H 4-1 and we cannot get things running well. On dyno, it has a very big flat spot in mid range and it never gets going much past that. The peak HP is less that on the MAC. We were wondering if i am having any "pulse" problems with the layout of the collector? We thought about cutting the collector in half just downstream of where the 4 pipes become one, and welding in a "splitter" that would seperate out 1-2 and 3-4 so that they collect together and then the "two" would then become one. Is anyone running this same kind of set up? I need help

Kind regards...Craig

[80GS1000]

No guru here but here's a stab taken at the issue-

Did you rejet your carbs for the pipe? Are you running the stock airbox or pods? I would suspect your flat spot is from the V&H pipe leaning out your mixture since it flows better than that other pipe.

If you're running the stock airbox, a Dynojet stage 1 kit would sort you out nicely. Nice thing about that kit is it comes with stage 3 jets as well in case you ever decide to lose your stock airbox and go with K&N pod air filters.

I'm running a V&H 4 into 1 with K&N pods and a Dynojet stage 3 jet kit and it runs like a fat kid to a Twinkie. \\/

[Craig]

Sorry...I should have said that I was running with pods. We have tried a few different main sizes, with no luck. Running all other carb parts as stock for Mikuni.

Craig

[Steve]

With pods and a V&H pipe, your main jets should be about 20 numbers higher than stock. Looking at the carb sticky at the beginning of this forum, in post #21, it says that stock jets were 112.5, so you will want to start with 132.5 and see how it runs.

If you are going to do any chopping in the collector, you will want to pair 1&4 and 2&3 as they are opposite each other in the firing order. Personally, I would hold off on cutting the pipe and concentrate on jetting first.


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[Craig]

The 112.5 main size is for the stock carbs...I am running flat slides...does that make a difference?? Still go to the 20+ larger??

Craig

[Steve]

OK you caught me on that one.

I also just re-read your original post and noticed the big-bore kit. :shock:

I am going to have to defer to what Keith Krause might suggest. If he does not see this post in a day or two,
you might want to drop him a PM to see what he says.


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[KEITH KRAUSE]

No experience with chopping up pipes. None with those carbs either.
I can't just throw out some jet numbers when the carbs are so different.
Sometimes the mods are just a poor match and you have nothing but problems.
Wish I could even offer some ballpark numbers.
With the limited info provided, I'd run the bike as is on the 3 basic jetting circuits and see what the plugs look like at those 3 throttle positions. After a full throttle run (main), 1/3 throttle run (jet needle) and then a minimal throttle run (pilot circuit), I'd see what the plugs look like after each run and go from there. Based on the current settings, we should be able to make sense of it. There could be necessary changes needed though, beyond the typical main/jet needle/pilot jet changes. Your needle jets, air jets, etc, may all need changing.
Right now, I don't see any info to suggest it's lean or rich, etc.
The bike must be ready to re-jet though. All basic tuning/maintanance must be done first. The carbs must be otherwise set up and ready too. Fuel level, synched, mixture screws set correctly for highest rpm, etc.

[chef1366]

I would post this in the performance mod section. 98 HP is under stock numbers. With that 1166 kit, I would assume .340 to .348 lift cams and your other mods you should be closer to 125-130 HP.

I hope your cam sprockets haven't slipped out of timing. Did you use loctite on the bolts?

You have my dream setup with those 36mm flatsides. My bike runs like a raped ape and so should yours.

I would follow Keiths advice and do plug chops (do search) and jet it in seperate circuits.

What are you're compression numbers like?