• 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.

'79 850 vm main jet question

  • Thread starter Thread starter raistian77
  • Start date Start date
R

raistian77

Guest
doing a second strip and dip (found some trash in the lines)

Noticed that the main jet is set to the 2nd slot down, is this normal? When I did the original strip and dip the PO had jacked all the mix screw positions up trying to fight a lean condition caused by bad boot o'rings. Did he move this also?
 
:confused: You mean needle jet position, the main jet just screws into the breather pipe which screws in the carb body
 
Last edited:
srsupertrap said:
:confused: You mean needle jet position, the main jet just screws into the breather pipe which screws in the carb body
Click to expand...

yes, needle position seems like there are 5 positions avalible all 4 are set to the 2nd down.
 
raistian77 said:
doing a second strip and dip (found some trash in the lines)

Noticed that the main jet is set to the 2nd slot down, is this normal? When I did the original strip and dip the PO had jacked all the mix screw positions up trying to fight a lean condition caused by bad boot o'rings. Did he move this also?
Click to expand...

Yes, he moved the needle setting and in the WRONG direction

Having the clip lower on the needle richens the mixture
 
Big T said:
Yes, he moved the needle setting and in the WRONG direction

Having the clip lower on the needle richens the mixture
Click to expand...

Not so. The '79 GS850 VM carbs had 5DL36 -2 needles. The -2 means that they were positioned 2 slots from the end of the needle. This is slightly leaner than in the middle position as the needle is sitting lower into the main jet at idle.

You should find they are fine in that position once the pilot circuit passages have been cleared of gunk and you have no air leaks anywhere in the intake system.;)
 
Last edited:
49er said:
Not so. The '79 GS850 VM carbs had 5DL36 -2 needles. The -2 neans that they were positioned 2 slots from the end of the needle. This is slightly leaner than in the middle position as the needle is sitting lower into the main jet at idle.

You should find they are fine in that position once the pilot circuit passages have been cleared of gunk and you have no air leaks anywhere in the intake system.;)
Click to expand...

Thanks, Thats a relief. On the first strip and dip the pilot screws were 4 turns out and the pilot air screws were all bottomed.

Bike has been running great, easy start and such. But I have a vibration that comes in at about 3,500 rpm. Thinking its an imbalance somewhere in the carbs.
 
I have noticed that on other forums the main complaint about the GS VM carbs is they are so lean. Is this accurate?
 
raistian77 said:
I have noticed that on other forums the main complaint about the GS VM carbs is they are so lean. Is this accurate?
Click to expand...

Yes, the '79 VM's were deliberately set lean from the factory to meet more demanding global emission laws. These laws became so strict in some countries, that plugs were fitted to the CV carbs covering the fuel adjustment screws of the idle circuit. Service manuals had sentences such as "under no circumstances must these screws be altered", touting suggestions that the factory had a magician finely tuning each primary circuit. This occurred on the CV carbs from '80 onwards.

When you richen the stock VM needles by moving the clip to the 3 rd position, you will loose some crispness in the mid range. You can shim an intermediate position ( I used a .016" washer) to gain the desired Air Fuel Ratio for your midrange performance. You need to do the appropriate plug chops, or use a dyno to confirm this.
 
49er said:
Yes, the '79 VM's were deliberately set lean from the factory to meet more demanding global emission laws. These laws became so strict in some countries, that plugs were fitted to the CV carbs covering the fuel adjustment screws of the idle circuit. Service manuals had sentences such as "under no circumstances must these screws be altered", touting suggestions that the factory had a magician finely tuning each primary circuit. This occurred on the CV carbs from '80 onwards.

When you richen the stock VM needles by moving the clip to the 3 rd position, you will loose some crispness in the mid range. You can shim an intermediate position ( I used a .016" washer) to gain the desired Air Fuel Ratio for your midrange performance. You need to do the appropriate plug chops, or use a dyno to confirm this.
Click to expand...

good deal, I'll run by radioshack tommorow and get the washer assortment to shim the needle a hair richer.
 
raistian77 said:
Thanks, Thats a relief. On the first strip and dip the pilot screws were 4 turns out and the pilot air screws were all bottomed.
Click to expand...
Where do you have them set now? :-k

In stock trim (airbox and exhaust), the fuel screws (the ones on the bottom) should be about 3/4 turn out and the air screws (the ones on the side) should be about double that, or 1 1/2 turns. When the bike is warmed up, tweak the air screws for highest idle speed.

.
 
Steve said:
Where do you have them set now? :-k

In stock trim (airbox and exhaust), the fuel screws (the ones on the bottom) should be about 3/4 turn out and the air screws (the ones on the side) should be about double that, or 1 1/2 turns. When the bike is warmed up, tweak the air screws for highest idle speed.

.
Click to expand...

When I got the bike, my local dealer mechanic gave me the service manual for the bike. it states the pilot is 5/8 out and the pilot air is 1 1/4 out
 
raistian77 said:
When I got the bike, my local dealer mechanic gave me the service manual for the bike. it states the pilot is 5/8 out and the pilot air is 1 1/4 out
Click to expand...
And those settings were to satisfy the EPA, and the bike ran like crap.

It works much better if you go to 3/4 and 1 1/2.

.
 
Adjust the air screws for highest idle. Then do a carb sync. It will amaze you
how much smother the bike runs.
Those washers Radio Shack pn 64-3022
 
SqDancerLynn1 said:
Adjust the air screws for highest idle. Then do a carb sync. It will amaze you
how much smother the bike runs.
Those washers Radio Shack pn 64-3022
Click to expand...

thanks, gonna grab some this afternoon

Ok Steve I'll try the 3/4 and 1 1/2 instead
 
ok, back together and running. Used 4 washers which raised the needle .5 mm. Now, just have to hunt down a manometer and adaptors so I can sync it.
 
tas850g said:
where do you live? I don't think you have told us. Maybe someone lives near you with one.
Click to expand...

Clarksville TN, next to the military base. The loacl bike guy can do it, but he charges a TON on old bikes
 
If you don't have this resolved in the next week and half, let me know.

I can change my route home and stop by for a little "hands-on" if you are interested. :eek:

.
 
Steve said:
If you don't have this resolved in the next week and half, let me know.

I can change my route home and stop by for a little "hands-on" if you are interested. :eek:

.
Click to expand...

lol

Appreciate it, if money were not so damn tight I would order the color tune and a carbtune and be done with it.:)
 
You must log in or register to reply here.
Back
Top