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carb jetting

  • Thread starter Thread starter jonny-rock
  • Start date Start date
J

jonny-rock

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wondering what size jets should i use. I'm putting straight pipes on, headers with pipes on them. anything would help. looking at a dynojet stage 3 kit, would that be a sufficient?
 
jonny-rock said:
wondering what size jets should i use. I'm putting straight pipes on, headers with pipes on them. anything would help. looking at a dynojet stage 3 kit, would that be a sufficient?
Click to expand...

No, it will need fine tuning.
 
What bike? Are you running pods or the stock airbox? Pods with free flowing exhaust is a stage 3. Just the exhaust is a stage 1.
 
Refered to as a 'black art' by some, I really don't think carby work is all that hard. Perhaps I've gotten lucky so far. Anywho, this should give you a nudge in the right direction.

First step is to adjust the mainjets. I'd suggest going up one size to begin with if you're just doing the exhaust. Test the bike once its warmed up, paying attention to its performance in the upper rev range and at full throttle. Go up or down a size as needed until you get the best performance at these higher throttle and rpm settings.

After that, adjust your needle height and test for performance in the mid rpm and throttle regions. You're looking for smoothness and acceptance of throttle without loss of power.

Prior to testing on the road, ensure that your airscrew settings are at least moderately correct. It'll help if you synch the carbies as well. If you're really anal, you can tune various jets (such as the pilots) and even things down to the float height (looking for best acceptance of full throttle at low rpm) - after the mainjet and needle settings are done first, of course!

Cheers - boingk
 
i have an '80 850G. has cv carbs. sicking with the stock air box, with k&n filter.
 
I agree first try playing with needle positioning and if you can't get it correct then get a jet kit.
 

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Stages are arbitrary, but generally stage one is intake or exhaust only. Stage two is both fitted with performance items. Stage three usually incorporates some kind of additional performance upgrade such as an aftermarket camshaft, big bore kit etc.

As before, I really don't like the idea of carburettor 'kits'. The best way IMO is to start with a mainjet upgrade and roadtest, then once the correct mainjets are fitted you can adjust the needle height etc etc.

Cheers - boingk
 
i havent yanked my carbs yet, so i was wondering if anyone knows what the stock jets are? what size is a good starting point. i cant road test yet because it gonna be below zero here for a while. smallest jet i can find is 100.
 
Stage 1 is pipe only, stage 3 is pods. I have never seen a stage 2. Though a stage 3 will have a couple different size mains for pods only or pods with pipe. The advantage of jet kits is they hit it pretty close with a couple of tweaks instead of a long frustrating period of stabs in the dark trying to find the right combination. They also sometimes include a restrictor for the air jet.

Pipe with a K&N in the stock airbox is a stage 1 with maybe the main bumped up 1 more size (the mythical stage 2 perhaps).
 
jonny-rock said:
... i was wondering if anyone knows what the stock jets are? ...
Click to expand...
I find it rather amazing that people don't notice the "stickies" at the very top of this forum. :oops:

The very first thread is a rambling discussion that includes the stock sizes for most of our bikes. It is many, many pages long, so to make things a bit easier, go into the User CP tab at the top of this page, got to Edit Options, then scroll down to near the bottom of the page, set your preferences to display the maximum number of posts per page, which is 40. This will minimize the number of times you have to flip to a new page.

.
 
doctorgonzo said:
Stage 1 is pipe only, stage 3 is pods. I have never seen a stage 2. Though a stage 3 will have a couple different size mains for pods only or pods with pipe. The advantage of jet kits is they hit it pretty close with a couple of tweaks instead of a long frustrating period of stabs in the dark trying to find the right combination. They also sometimes include a restrictor for the air jet.

Pipe with a K&N in the stock airbox is a stage 1 with maybe the main bumped up 1 more size (the mythical stage 2 perhaps).
Click to expand...

I was just asking for the fun of it, lol.

My kit included a little glue in insert for the air jets. Also included was a drill bit (with no size marked, go figure) to drill the air hole in the slides.
The thing is, the cost of jets X's 4 can add up by the time ya get it figured out. 2 or 3 sets of jets and you're already over the cost of the kit.
To me the instructions that come with it are worth their weight in jets, even if I did have to read em a dozon times:oops:

I just with DJ would number their jets like mikuni. But then again that might make it too easy.

Jonnyrock, ask for a jet kit for Christmas before its too late.
 
Steve said:
I find it rather amazing that people don't notice the "stickies" at the very top of this forum. :oops:

The very first thread is a rambling discussion that includes the stock sizes for most of our bikes. It is many, many pages long, so to make things a bit easier, go into the User CP tab at the top of this page, got to Edit Options, then scroll down to near the bottom of the page, set your preferences to display the maximum number of posts per page, which is 40. This will minimize the number of times you have to flip to a new page.

.
Click to expand...

LMAO!!
Corn Flakes contained PeePee.
Grouchy old fart!
 
i have 115 mains in my carb now. would 125 be a good starting point? also how do you adjust the float needle?
 
Octain said:
I was just asking for the fun of it, lol.

My kit included a little glue in insert for the air jets. Also included was a drill bit (with no size marked, go figure) to drill the air hole in the slides.
The thing is, the cost of jets X's 4 can add up by the time ya get it figured out. 2 or 3 sets of jets and you're already over the cost of the kit.
To me the instructions that come with it are worth their weight in jets, even if I did have to read em a dozon times:oops:

I just with DJ would number their jets like mikuni. But then again that might make it too easy.

Jonnyrock, ask for a jet kit for Christmas before its too late.
Click to expand...

Chef may correct me, but I think it's Dynojet X .9375 = Mikuni

I'm running a 170 dynojet, so that's a 159.38 in Mikuni terms.
 
Greetings and Salutations!!

Greetings and Salutations!!

Hi Mr. johnny-rock,

It seems that you've been spending most of your time in the Performance and Appearance sections of the forum. I haven't said a proper "Howdy" yet. Here ya go...

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", the Carb Rebuild Series, and the Stator Papers. Now let me roll out the welcome mat for you...

Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike! :D

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff
 
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