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4 to 1, Pods, Re-Jetting ISSUES!

  • Thread starter Thread starter Scudder
  • Start date Start date
S

Scudder

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I know that this topic has been frequently talked about, and I've done some research with the search function on this site. I've worked on Honda CB's before and basically followed the procedure outlined below, and things have been fine. But... With the GS, I'm a bit confused. I would appreciate any suggestions for solving the problem that I have. So far this is what I've done to my 1978 GS750

1. Acquired it with a 4 to 1 exhaust. Didn't sound too good, or go over 55 mph when I got it.
2. Installed air pod filters.
3. Rejetted to 127.5.
4. Air screw is totally closed
5. Fuel screw is 1 1/2 turns

It tends to die when I take it off choke. Sometimes it will idle for a while, but when I twist the throttle, it sounds like it's sucking air and not getting enough fuel, to sound, or run the way I'd like it to. Seems to me that using a larger jet 130 or 135 would help balance out the fuel and air flow. But I'd like some advice before I dive in.

Any suggestions is appreciated.

Scudder
 
prolly getting to much air through the pods, did the pods get filter oil??
bigger main/pilot will even out a lil, , check the pilot jets see if there clogged up
air screws must be opened, it will not run right, 2 open from closed is max i believe
check the compression see if all cyls are close to each in psi, jetting isnt going to fix a wore out motor
dont mess with float level keep it factory,, make sure the floats are shutting off the fuel, in each carb.or it will flood and blubber and drive you crazy
new needles and seats might be needed
make sure air vent tubes are clear
jet needles in the 2nd position is a good start
make sure the tank and petcock are clean,and fuel line flow well
start with these things :)
 
Rebuild the carbs. Clean em, clean clean clean.
Did I mention clean?

Then at least you'll have a starting point.

Check Dennis Kirk for recomended stage three jet kit for your model.
 
Scudder,

You have to go back to the basics. You bought an old bike that doesn't run well. So,

1. Adjust valves
2. Clean carbs with new O rings
3. Sync carbs
4. New carb boots?

There's all the info you need to do this on the site.

Your bike should run rich on 127.5s. Having the air screw closed isn't helping anything either

Your problems are not based on the jet size. The PO has the bike all screwed up, so get your motor ready and work from there.
 
I do believe the VM carbs have an adjustable needle. Raise it two notches (two notches down on the needle).
 
You are fast Bill! I was going to suggest you would be along soon ;)
 
Yah, turn the pilot screw on the bottom out about 1 turn clean the carbs and move the needle up by moving the clip down a notch and 125 main jets work well enough for me. Also having the floats adjusted properly makes a world of difference. Make sure you adjust them with the float gasket out of the carb to about an inch. I did a custom exhast pack job with header wrap on the ends of the baffles and a little steel wool in the center makes it sound great.
 
127.5's could be in the ball park, but more likely 125's will be needed.
I believe 130's are way to big.

1) adjust valves
2) replace intake o-rings
3) check and adjust point gaps
4) static time the 1-4 point set, then the 2-3 point set
5) check the resistance from plug cap to plug cap on the 1-4 and 2-3 coils; should be around 22k (22,000 ohms)
6) place the clips on the needles at the 4th notch down from the top
7) bench sync the carbs
8) externally check the fuel levels and adjust to factory spec's
9) set pilot air screws to 1-1/2 turns from lightly seated
10) set pilot fuel screws 1-1/2 turns from lightly seated
11) vacuum sync the carbs
12) final pilot screw(s) adjustment(s) as needed

when finished, plug chops will tell you what jetting changes, if any, you will need to make.


http://www.thegsresources.com/_forum/showpost.php?p=324909&postcount=43
http://www.thegsresources.com/_forum/showthread.php?p=994610#post994610
http://www.mtsac.edu/~cliff/storage/gs/GS750_Service_Manual_early8valve.pdf
 
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Needles

Needles

I move the clip on the needle down to the 4th position, and made some of the sugggested adjustments. Runs a little better and I seem to be making some progress. However... I notice the needles are basically dull. They don't come to a point. With the CBs I've worked on, the needles are pretty sharp and too a point. Is a rounded needle appropriate for a GS, or do I need to replace them? Would you recommend I get rebuilding kits for all 4 carbs? I've already cleaned the carbs and they really were in good shape considering other bikes that I've worked on.

Scudder
 
The adjustment screws for the air side (on the side) of the pilot circuit have a kind of blunt/rounded tip. the fuel screws (bottom of carb) are pointed, not needle sharp, but definitely pointed.

think of it this way, instead of having a fixed orfice air jet, the VM's have a adjustable orifice (air screws). then you supply the correct metered amount of fuel with the fuel screws.

if in doubt, post pictures of them.

unless something is worn or broken in the carbs, all that will be needed are new orings and possibly new bowl gaskets.

Scudder said:
and made some of the sugggested adjustments. Runs a little better and I seem to be making some progress.
Click to expand...
There are no short cuts...
 
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