• Required reading for all forum users!!!

    Welcome!
    Register to access the full functionality of the GSResources forum. Until you register and activate your account you will not have full forum access, nor will you be able to post or reply to messages.

    A note to new registrants...
    All new forum registrations must be activated via email before you have full access to the forum.

    A Special Note about Email accounts!
    DO NOT SIGN UP USING hotmail, outlook, gmx, sbcglobal, att, bellsouth or email.com. They delete our forum signup emails.

    A note to old forum members...
    I receive numerous requests from people who can no longer log in because their accounts were deleted. As mentioned in the forum FAQ, user accounts are deleted if you haven't logged in for the past 6 months. If you can't log in, then create a new forum account. If you don't get an error message, then check your email account for an activation message. If you get a message stating that the email address is already in use, then your account still exists so follow the instructions in the forum FAQ for resetting your password.

    Have you forgotten your password or have a new email address? Then read the forum FAQ for details on how to reset it.

    Any email requests for "can't log in anymore" problems or "lost my password" problems will be deleted. Read the forum FAQ and follow the instructions there - that's what we have one for...

  • Returning Visitors

    If you are a returning visitor who never received your confirmation email, then odds are your email provider is blockinig emails from our server. The only thing that can be done to get around this is you will have to try creating another forum account using an email address from another domain.

    If you are a returning visitor to the forum and can't log in using your old forum name and password but used to be able to then chances are your account is deleted. Purges of the databases are done regularly. You will have to create a new forum account and you should be all set.

problem with carbs and diaphrams

  • Thread starter Thread starter madmaze
  • Start date Start date
M

madmaze

Guest
Hello everyone,
ive been messing around with my carbs on my 83 gs450 this weekend since my bike doesnt run.
Ive narrowed it down to the diaphrams not moving up enough to let the fuel by the needle, ive cleaned everything i can think of and i just cannot get it to run..

Now if I take a screwdriver and jack up the diaphram a little it will come on but die as soon as the screw driver fall out from the vibrations.. lol

anyone have a clue what i could try/do/clean to fix this?
Ive spent way too much time on this and ive come up with nothing..

thanks

03052009030.jpg

*btw yes that air jet is clean.. atleast on the inside.
 
Please tell me you tried running it with the air filter and air box installed.
 
yes I did, but im using k&n filters. Does that make alot of a difference?
 
YES! The bike will have to be completely rejetted for Pod KN filters. They let WAY more air in, and as such the bike will be insanely lean without a rejet. Also, your slides LIFT by vaccum. They are not mechanical. So they're not going to lift untill you have the bike moving to the point the engine causes enough vaccum to lift them..
 
Hmm so that means I need larger main jets? or also air jets?
Is there anyway to calculate/guesstamate the new jet size?
 
The most important part of a jet kit is the needles. You can go up on the mains, raise the needles, and adjust the pilot screws but there is nothing you can do about the taper of the needles.
 
so I have 120 main jets in there right now.. what would make sense as a reasonable next higher step?
Can i just up the main jet size and not do the needles or is it recommended to do both?
also you mentioned "jet kits"? where can i find decent ones of those?

Thanks for the info
 
You have 120s in there now? What is stock? :-k

Not sure about the two-cylinder bikes, but for the fours, you might bump the mains about two or three sizes for a pipe and three to five sizes for pods. If doing both, figure on about seven or eight sizes up.

Somebody more familiar with the twins can give better suggestions, I'm sure.

.
 
stock is 115..
two or three sizes for a pipe
Click to expand...
hmm what do you mean with pipe?
I currently have 1 "pod" per carb with a 3" pipe extension to make it fit past some frame pieces.
so maybe I should go up to 185 or 195's then..
 
By "pipe" I mean a custom exhaust pipe, usually called a "header".

Most of them are freer-flowing than stock, requiring larger jets in the carburetors.

With your 120s, you are already two sizes larger than stock.

Where did you come up with that "185 or 195"? :confused:
Stock is 115? two to three sizes for a pipe or three to five sizes for pods would mean 135, at most, that's eight sizes larger.

.
 
Last edited:
not sure what you ment with sizes LOL
I just figured 10 is an even number:D

so since, for now, i have stock pipes i might want to go up to a 125 or 127.5?
 
madmaze,

Your initial description started out sounding like you had a problem getting the "little engine that could" to IDLE correctly.

Somehow through this message traffic it morphed into a high speed, on the freeway, not running right on the top end throttle response, main jet issue.

You may want to put into words at what throttle position or operating condition the engine seems like it "runs out of gas" (most common) or sputters / backfires (less common).

Houdini (back again)
 
Well actually it doesnt run at all at this moment.
I think it is because it doesnt get enough fuel.
which makes sense since i just got rid of my air box and replaced it with pod filters.

So im hopeing that bigger main jets will solve the problem.
any other suggestions?
 
Look at Figure 7 of this link: http://www.iwt.com.au/mikunicarb.htm

You said it ran (probably like it was about to run out of gas) when a screw driver was in the slide taking it to something like 1/4 throttle...

From the figure you by-passed the idle circuit and started on the needle jet circuit... probably means you need to richen up the idle circuit several larger sizes of the idle jet and most likely raise the slide needle either 2 notches, to start, or add a couple .023 washers under the needle clip if no adjustment possible.

Sudco sells individual parts pilot jets, washers, etc.

What a lot of folks have suggested, because the 450 is sensitive to inlet side changes, is to return to the stock airbox to avoid having to fuss with rejetting the carbs (KISS)...not sure if you indicated what your compelling reason was for pods.

Last year some fine folks here helped me get my bike tuned nearly perfectly (using stock airbox / cleaner) here was my results:
http://www.thegsresources.com/_forum/showthread.php?t=126350&page=2

Do a search on Mikuni carb tuning guide...and take your time figuring out the conditions / symptoms 1 at a time...and keep the GS group informed.
 
Thank you for all that information.
My reason for switching to pods was that my airbox had mice it in and a crack.
So instead of getting another one i just put pods on.

My pilot jets are plugged since that is how they were when i got them.
I will try to mess with the needle and i have bigger main jets coming in the mail.

I dont have time until this weekend to work on it, so then ill report back if and how it runs.
 
You must log in or register to reply here.
Back
Top