Carb Rejet Question(s)

[ccs]

Hello everyone;

Well... I got my MAC 4-1 header on my 82' GS850G and like the way it sounds WITHOUT the baffle. (Some of you may recall, from another post, that I received a used MAC, but CRC2ONLINE took very good care of the problem -- I recommend them -- their customer service is TOP-NOTCH.)

Anyway, I need to rejet the carbs as it does not have the "get-up-and-go" it had with the stock exhaust and has some backfiring when decellerating. If I accelerate slowly, the bike runs pretty OK and I can hit 80-85 MPH -- but you can hear that it's not running it's best. When I accelerate quickly it runs pretty crappy, bogs down, etc.


I found the following specs (for my carbs) here on the forum:

1982 GS850GZ Carb. Specs.

Idle rpm/min 1050 +- 100 rpm
Carb. type: Mikuni BS32SS
I.D. no. 45160*
Bore size: 32 (1.26)
Float height 22.4 +- 1.0 (0.88 +- 0.04)
Fuel Level 5.0 +- 0.5 (0.2 +- 0.02)
Valve seat 2.0
Starter jet 32.5
Pilot screw pre-set (well.....maybe)
Pilot air jet #180*
Pilot jet #40
Jet needle 5D50
Needle jet X-5
Pilot outlet 0.7
By pass 1.0, 0.8, 0.8
Main air jet 1.7
Main Jet #115

Before I remove the carbs to rejet, I'd like to get an idea of which jets need to be replaced and with what size (that way I can purchase them in advance).

I've been looking at: http://www.pro-flo.com/proflo_carb_p...#Jet%20Needles for jets, but have not idea of which ones I need.

Can anyone provide some input/advice on what to get and whether the jets at PRO-FLO are good?

TIA.

Charles...

[chef1366]

I would start with a 125 main jet and raise the needle two notches. If your jet needle is not adjustable raise it with 4 washers (shims) from Radio shack. One washer = 1/2 notch. This is only a base start and you will have to do plug chops to determine if you need a smaller/larger main jet or lower/raise the jet needle.
If you don't know what a plug chop is do a search. I myself have discussed it many times along with many others.

http://www.denniskirk.com/jsp/produc...Id=41306&mmyId=

[ccs]

I would start with a 125 main jet

OK.

and raise the needle two notches. If your jet needle is not adjustable raise it with 4 washers (shims) from Radio shack. One washer = 1/2 notch.

OK -- but what size washers from RS? Can you give me a thickness so I can get them anywhere? Also, I think I read somewhere that the notches on the jet needles were removed after 81', and I've got an 82'. Guess I'll have to open the carbs to see.

This is only a base start and you will have to do plug chops to determine if you need a smaller/larger main jet or lower/raise the jet needle.
If you don't know what a plug chop is do a search.

I know what one is, but am wondering if I need to do it or would using a colortune tell me?

http://www.denniskirk.com/jsp/produc...1306&mmyId=ote

and... thanks for the link. Are Kirk's jets better than PRO-FLO

[chef1366]

Dennis Kirk has Mikuni jets which are the same.
I bought a bag of assorted small washers and there were some that were the same size as the one on the needle.

[ccs]

Well... I called DennisKirk.com and spoke with a guy there about re-jetting my bike. He said I need to buy the DynaJet Stage 3 kit for $120 (http://www.denniskirk.com/jsp/produc...ductId=p171808).

Is this really true? (I think they just want to sell me $120 worth of parts instead of $15).

Also... do I need to replace other jets such as the 1) Starter jet, 2) Pilot air jet, 3) Pilot jet?

Could sure use some additional advice.

TIA.

Charles...

[Mark whiz]

The jet kit will "fix" several issues with the stock carbs, like factory-induced leanness to meet emission standards as well as address richening things up for the headers. The kit also has adjustable needles so you can fine tune your setup a tad easier.

All that said, all you really NEED to do is go with a bigger main jet and raise that needle a bit (or find a different needle that will allow a slightly richer mixture throughout it's travel. Don't bother with the pilot and starter jets, they aren't going to help the problems you originally spoke of.

[chef1366]

Ditto Mark
With the 4-1 pipe all you really need is a bigger main jet and raise the needle.

[KEITH KRAUSE]

For just a pipe and totally stock intake, I'd try 7.5 to 10 larger on the mains. That's one and a half to two sizes up.
For the jet needles, I'd probably try a 1/2 position richer. A typical jetting spacer used for 1/2 position changes, is approx' .022" thick. If you want to try a full position, double that. Solid 1/3 throttle chop tests will tell.
As for the pilot circuit, maybe a small richer adjustment on the mixture screws will be needed. About 1/2 turn additional?
You may have to get larger air jets too but try the stock ones and test.
Don't bother with a stage 3 kit, that's only for pod filters.