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Jetting: '78 GS1000 w/ Kerker 4-1 and stock airbox, currently stock at 95

  • Thread starter Thread starter lemonshindig
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lemonshindig

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From what I gather, my jetting (Main 95) is stock, even though I have a Kerker 4-1 and a stock airbox. I say stock airbox, but the PO cut two 1" holes in the box and replaced the filter with an oiled filter.

It seems to run fine after a good cleaning, sync, and colortune adjustment. But I haven't done plug chops yet.

So I'll do some full throttle plug chops just to be sure, but I am expecting it to be lean.

What's your guess for correct... 100? 105? I'll order a few different sizes soon.

Thanks
-Matt
 
102.5 or 105's should be real close if your muffler still has some packing in it.
 
On my 78' 1000 I had it all stock with the exception of a 4-1 Marving exhaust. I tried increasing to 102.5 mains but after a bunch of mucking around the bike ran best with the stock 95's. Not sure if the Kerker flows more than the Marving though and the fact that you have an aftermarket K&N air filter is going to make a difference. I can't imagine you're going to need a larger pilot but if you did it would be a 17.5. The Mikuni main jets come in 2.5 increments, you could order 97.5, 102.5 and 105 if you really wanted to but do your plug chops first.
 
Up 2.5 - 5 on the main & raise the needle a notch (because of the air filter).
 
I just overhauled the stock carbs on my 1000EN I picked up a few weeks ago.

The PO was running stock jetting with a 4-into-1. It was getting the characteristic lean pop when I cut the throttle and during engine braking. When I reassembled my carbs I bumped the pilots from 15 to 17.5 (1 step) and bumped the mains to 100 (2 steps). Left the needles alone. My stock air box has a K&N SU1250 replacement filter in it. I will be anxious to see how it runs. Back in the day we used to set up our GSs likewise and we had pretty good results. If anything the mains may still be 1 step lean.

Kerkers flow pretty well; I have no experience with Marving systems. They look nice, it would be a shame if they didn't flow as well as they look and for as much as they cost.


lemonshindig said:
From what I gather, my jetting (Main 95) is stock, even though I have a Kerker 4-1 and a stock airbox. I say stock airbox, but the PO cut two 1" holes in the box and replaced the filter with an oiled filter.

It seems to run fine after a good cleaning, sync, and colortune adjustment. But I haven't done plug chops yet.

So I'll do some full throttle plug chops just to be sure, but I am expecting it to be lean.

What's your guess for correct... 100? 105? I'll order a few different sizes soon.

Thanks
-Matt
Click to expand...
 
azr said:
On my 78' 1000 I had it all stock with the exception of a 4-1 Marving exhaust. I tried increasing to 102.5 mains but after a bunch of mucking around the bike ran best with the stock 95's. Not sure if the Kerker flows more than the Marving though and the fact that you have an aftermarket K&N air filter is going to make a difference. I can't imagine you're going to need a larger pilot but if you did it would be a 17.5. The Mikuni main jets come in 2.5 increments, you could order 97.5, 102.5 and 105 if you really wanted to but do your plug chops first.
Click to expand...

Is that with VM26s? Mine with VM28s (standard on a UK S) and a Marving (every thing else stock) runs best on 102.5s
 
I ran a Yoshimura Race bend system on my 1000ST. It, of course had BS34SS (CV) carbs stock. The stock jetting was 107.5 (I think). I shimmed the needles, bumped the pilots 1 step to 42.5, and bumped the mains to 120. I also enlarged the intake opening on the airbox; basically made it one large oval instead of two small round holes. Also opened up the pipe by drilling six 3/8 inch holes in the end plate and 4 in the front plate. The bike ran flawlessly and sounded great. Better driveability on the low end. smooth midrange and she was killer on top. Started easily with out choking it unless it was a little chilly or it sat for a couple of days.
 
Last edited:
Well, I ordered 100s, 102.5s, and 105s from Z1 today. We'll see...
 
At 72' elevation, the OP can't get much closer to Sea level for riding conditions.
I stand with 102.5 or 105 main jets and leave the needles in the stock location. (center) :-$
 
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