Calling all Carb Gurus!

[Anonymous]

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

[lhanscom]

It sounds like you have the air box off, if so, put it back on, everything is dependant on it.

[Billy Ricks]

Without an airbox you are way too lean. Once the box is back on adjust each screw for the highest, smoothest idle.

[Anonymous]

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

[focus frenzy]

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.

[Detman101]

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.

[Anonymous]

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

[Anonymous]

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.

[Detman101]

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.

[Anonymous]

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

[Anonymous]

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

[flyingace]

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.

[Anonymous]

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

[Anonymous]

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

[KEITH KRAUSE]

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.