• 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.

Calling all Carb Gurus!

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

Guest
I have a 1980 GS750L that I picked up five years ago and am finally trying to get it to run. I have cleaned the carbs accorfing to the "Carb Clean-up Series" and have set the floats to the specs from my Chilton manual. The mmixture screws are set at 1 1/2 turns out. I am getting good spark after replacing the ignitor. The bike will fire if I hold my hand and arm over the intake sides of the carbs and choke the air down. The rpms rise as I choke of the air intake. The carbs have stock jets from a K&L rebuild kit. I am not sure how to adjust the carbs to make it idle right. The choke works, because when I pull it out the RPMS increase, but the bike still dies after a few seconds. Any help would be appreciated.

Brian Morel
 
It sounds like you have the air box off, if so, put it back on, everything is dependant on it.
 
Without an airbox you are way too lean. Once the box is back on adjust each screw for the highest, smoothest idle.
 
Sorry I forgot to include it, but I don't have an airbox for this bike, I have a set of Emgo pods, but have them off. I figured that I am going to need to rejet and everything, but I thought I should be able to get it to idle, before I start that.

Brian Morel
 
put the pods on.
these CV carbs are finnicky as it is, they just don't work right without some sort of air cleaner on them.
 
Yeah, if you're putting pods on that bike you're gonna need to rejet a little if you keep the stock exhaust on there.

And if you change the exhaust into a 4-into-1 you're gonna need to rejet A LOT!

Be prepared for some serious quality time working on your bike if you decide to go the pods & exhaust route. It makes a great difference but it's a "loooooong time coming" (Soundgarden) to get to good.
 
Since you will be rejetting here's a good starting point.


Jetting Recommendations
by Denny Zander

Here is a simple set of jetting guidelines that have worked for me. For those considering jet changes, this might help select a starting point.

1 jet size for custom 4 into 2 exhaust

2 jet sizes for 4 into 1 exhaust

1 jet size for K&N filter (single inside airbox)

1 jet size for drilling out the bottom of the airbox

2 jet sizes for both single K&N and drilled airbox

2 jet sizes for individual filters

2 jet sizes for no muffler (open header)

1 pilot jet size for every 3 main jet size increase

Add up all the jet size increases and subtract one. (Remember they go in steps of 2.5 for each jet size)

Under a mismatch condition, like individual filters and stock exhaust or 4 into 1 header with stock filter and air box, subtract an additional 1 jet size.

Check plug color often, sync carbs after each jet change, make sure the floats are set correctly, and seriously consider purchasing a Color Tune. (See "Color tuning Carburetors" in the Maintenance Section).

Make sure your carbs are in perfect working order before making jet changes


courtesy: http://www.motorcyclecarbs.com/jetting/default.htm
 
Just to keep everyone updated, I have the pods on and it will fire for a few seconds and then die. The RPMS jump and drop in the few seconds that it runs, I pulled the plugs and they are really black. I think I flooded it trying to use the choke to keep it running, when I hit the choke it dies. I have the mixture screws set at 1 1/4 turns out, I am going to clean the plugs and try again tonight and see what I get.
 
Yah, if the plugs are really black then it's too rich. Try finding out what size jets you have in your carbs and report back to us.
We don't have enough info on your particular carb setup to recommend anything surefire.

:)
 
Ok, the main jets are 112 and the pilot jet has no markings, and the air screw says 170. None of the other pieces have any markings. I thought the pilot jet is supposed to be screwed all the way in, and that is what I have. I think I fouled the plugs by using the choke to much. Any advice would be appreciated, I want to get out for a ride.

Brian
 
I was just out working on it, and it still wasn't firing up. I took the carbs off and double checked that the pilot jets, the mixture needles and all the passages in the pilot circuit are clean. I pulled and cleaned the plugs and re-tried, still didn't start. I don't think I'm running to rich, the plugs are wet, but not black. I have the set of pods on whenever I try and start it, except the last time, I got it to fire a little bit by covering the carbs with my arm and hand. I guess I'm just way to lean. How far can I turn the mixture screw out, or should I just order some new pilot jets.

Brian
 
You may be a victim of doing two things at once and not knowing which is causing the problem. Was there a time the bike ran after you swapped the ignitor and before you starting playing with the carbs? Just because you get a spark doesn't mean everything is OK with the ignition. It has to be a proper spark at the right time. If your plugs are wet - that's an indicator of no spark or a mistimed spark.
 
I haven't had the bike running at all. I think I am getting plenty of spark at the right time, because it will fire and run for a few seconds if I put my arm over the carbs and partially choke them off.

Brian
 
Time for a good news update. I went out and got some NGK spark plugs to try instead of the crappy champions I had in. I also took off the tank and used a hose and funnell to get gas in the engine, as I thought maybe I was not getting enough fuel to the engine. I used a little bit bigger of a hose and it fired right up and ran till the gas was gone. It was running at 2500 to 3000 RPMs with the idle adjustment all the way backed off. I pulled the carbs back off and realised that I had one of the throttle plates on wrong and it wasn't letting the throttle close all the way. I am in the process of changing oil right know and am about to go pull apart the petcock to check the filter. Hopefully I'll be able to go for a ride soon.

Brian
 
You just mentioned what I was going to say...bench synch the carbs and follow that with a vacuum tool synch.
For the pod filters, you'll have to re-jet all 3 circuits or you'll run very lean.
 
Keith, how exactly do I bench synch the carbs. I found a post of yours about the VM carbs, but is the process the same for the CV carbs?

Brian
 
Get a small drill bit, with the carbs off the bike, set the idle so the drill bit just fits under the butterfly in the carb throat. Then set the other butterflys using the sync adjusters until they're all the right spacing, then readjust your idle to where it was. I've also done it with a bright light, and just comparing the light shining thru the carb bodys, but the first method is probably more accurate. A vac sync should be done as soon as the bike is running, it's the only way to get it right, as having the butterflys the same, may not be what you want exactly, but it will get you close.
 
bjmorel said:
Keith, how exactly do I bench synch the carbs. I found a post of yours about the VM carbs, but is the process the same for the CV carbs?

Brian
Click to expand...
Those Chilton manuals don't even show basic stuff like a carb synch? :?
I think Luke answered you good enough. The idea of the bench synch is to get the carbs close enough to run decent and then the vacuum tool synch must be done. Be sure to put a couple of fans on the motor.
If you still need more detailed synch info, I'm sure someone will help.
 
KEITH KRAUSE said:
For the pod filters, you'll have to re-jet all 3 circuits or you'll run very lean.
Click to expand...

what would you suggest for jets for the pilot circuit? Is it the same rule of thumb as with the main jets? 2 sizes up for 4into1, another 2 sizes for pods?

also what are the the 3 circuits? Idle, Pilot, High Speed?
 
fast_7 said:
KEITH KRAUSE said:
For the pod filters, you'll have to re-jet all 3 circuits or you'll run very lean.
Click to expand...

what would you suggest for jets for the pilot circuit? Is it the same rule of thumb as with the main jets? 2 sizes up for 4into1, another 2 sizes for pods?

also what are the the 3 circuits? Idle, Pilot, High Speed?
Click to expand...
Those "rules of thumb" are intended to get you in the ballpark. It depends on how the filters flow in this case. On Brians bike, for the pilot circuit, I would try mixture screw adjustments first. Nothing to lose. If by 4 turns out you don't get it rich enough, then I'd go up on the pilots a step and return the mixture screws to where they were and test. The air jet may have to be changed too. Do what the performance/plug reads tell you. I just cruise around at mimimal throttle position to get pilot plug reads.
Vacuum synch the carbs before getting plug reads.
The 3 circuits I'm talking about are the pilot, jet needle and main.
 
You must log in or register to reply here.
Back
Top