• 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.

open air filters, jet size?

  • Thread starter Thread starter horror1972
  • Start date Start date
H

horror1972

Guest
Hi,

i'm sure some of you do drive wih open air filters.
I own a '78 gs750.
Stock main jet is 100, I'm planning to drill the exhaust for more noise and remove the standard airbox.(Pods are those cheap ones, no k&n.)

who know's the size off the mainjets? (assuming it needs a bigger one since the airflow is more)

I was told the jet needs + 3 sizes for open pods, and 2 for open exhaust, gets me to a 125 main jet, but not sure...
 
You should check the dynojet website, they list all the parts in their kits. Buy the jets they recomend, and you should be set. That's what i did when I switched to pods. However, it's a real pain, why don't you just get a k&n filter for your airbox?
 
80gs1100 said:
You should check the dynojet website, they list all the parts in their kits. Buy the jets they recomend, and you should be set. That's what i did when I switched to pods. However, it's a real pain, why don't you just get a k&n filter for your airbox?
Click to expand...

Do you remember what size you went on your jets when you went to
pods? Was it worth it, does it run better? I would love to be able to
get to my battery without messing with an airbox but I know it
would be hard to get the carbs right. Do you have a 4 into one
and stock engine?
 
Last edited:
open air filters, jet size?

80gs1100 said:
You should check the dynojet website, they list all the parts in their kits. Buy the jets they recomend, and you should be set. That's what i did when I switched to pods. However, it's a real pain, why don't you just get a k&n filter for your airbox?
Click to expand...


I'm rebuilding the frame to a lowered kind a chopper, so battery and air box must go.......
 
80gs1100 said:
You should check the dynojet website, they list all the parts in their kits. Buy the jets they recomend, and you should be set. That's what i did when I switched to pods. However, it's a real pain, why don't you just get a k&n filter for your airbox?
Click to expand...

Dynojet doesn't sell a kit for the two valve 750s, you are on your own. Search the archives, it has been discussed at times.
 
i have the V&H 4-1 and pod filters...if i remember correctly im at something like a 128.5 mainjet...but then again i cant really remember because i had the carbs off 45 times trying to get it right..On the pilots i think i drilled them out 2 sizes, but once again cant really remember.


I never rode my bike stock so i cant really compare...but i know my gas mileage is crap, but the bike is running rich..im just too lazy to take the carbs back off before the season is over...lol
 
Last edited:
I originally took the carbs off to clean them, and after I put them back on I discovered that I had air leaks from the boots that hold the carbs to the airbox. So, I put in 140 size dynojet mains and pod filters. This setup makes good top end but the rest kind of lacks. It ran better overall with the stock airbox with the cover off, and got better gas mileage. My bike started to smoke really badly after I switched to pods, so I tore it down and found that the cylinder head had two cracks at the inner cylinders spark holes. It probably wasn't the switch to pods that caused this as the bike had 80,000 miles on it.
 
open air filters, jet size?

slow_heavy_750 said:
i have the V&H 4-1 and pod filters...if i remember correctly im at something like a 128.5 mainjet...but then again i cant really remember because i had the carbs off 45 times trying to get it right..On the pilots i think i drilled them out 2 sizes, but once again cant really remember.
Click to expand...


well, the dynojet site says use a 124 or 130 main jet (stock or open exhaust), so the 128,5 can be right...
the pilots drilled out 2 sizes; dynojet says the use a 5/32 drill..is it somewhere near you 2 sizes (as far as you can remember :-D )
all this is for a '80 gs750, so slighty different, but worth a try..


All I need is a basic tune up, own a "colortune" , so mustn't be hard to get it good enough....


thx all
 
you might need to experiment a bit because 126 might work if you are in lower altitudes and the air is cold and dense, but if you have warmer thinner air and higher altitude 116 might be ideal.

the rule of thumb I use is 10% maximum change at a time on main jet sizes.
--first change--
100~110 main jet change first then do needle clip changes for mid range rideability check the plugs for rich or lean

if it is still too lean
110~121 or closest number you can get into the range that your engine requires.

get some new spark plugs and do plug chop tests stage 3 jetting takes time and patience.
 
Mods to a stock exhaust is always difficult to guess right the first time. Not a good flow match for the pods.
Giving the modded pipe the benefit of the doubt, I'd probably try a 122.5 Mikuni main, which is approx' the same as a 130 DJ main.
You WILL have to raise the stock jet needles at least 1 position. Your stock e-clip position is position 3 (middle). It may require you to place the e-clip in the bottom position (5th/richest) but place a .022" jetting spacer directly on top the e-clip. That will result in "1 1/2" positions richer. I really doubt that 2 full positions would work...probably too rich. Just 1 position (position 4) would likely be still too lean. So I'd probably try the 1 1/2 positions first. Be sure you re-install the two factory plastic jet needle spacers in correct order...thicker on top the e-clip and any jetting spacer, and thinner spacer under the e-clip.
I'd probably try a 17.5 pilot jet. But you can try to make the stock 15 work by richening the pilot fuel screws (underneath) up to approx' 3 turns out. If no joy by that time, go with the 17.5 and return the pilot fuel screws to something close to stock...about 1 turn out from LIGHTLY seated.
REMOVE the 2 floatbowl vent lines to avoid fuel starvation when running pods.
The carbs must be vacuum synched to get accurate performance/plug reads. Whenever the jet needles are disturbed, you must re-synch the VM carbs.
Before the final vacuum synch you should bench synch, and set the side air screws to approx' 1 3/4 turns out. After start up and warming up fully in prep for the vacuum synch, adjust the side air screws using the highest rpm method.
Also, the valve clearances and ignition timing must be correct before doing the vacuum synch. Everything depends on another thing when re-jetting. Everything must be tuned or the re-jet will probably get frustrating.
Test the main at full throttle, the jet needle at 1/3 throttle, and the pilot circuit at minimal throttle (steady cruise, uphill or level at 35/40 in 4th gear is good).
 
open air filters, jet size?

thx keith , this was the info I was looking for. :-D

Thanks all for the quick replies....
 
Here is my setup with 130 mains 170 air jets and plus two sizes on the low speed jets, adjustable needles set in the third hole from the top, If my terminology is wrong please correct me [-o<

Here is a video of it idling:
http://www.youtube.com/watch?v=OTuCkJolDFE

It runs great on the street also, on a hard shift into second it will hold a burnout:shock: let me know if you guys have seen similar performance from your bikes

Thanks willy
 
Willy, thanks for the info but the bike we're jetting in this thread has completely different carbs than your '81 so there's no comparing them.
 
Oops my bad still new to the GS world but I am learning quickly:oops:
 
You must log in or register to reply here.
Back
Top