Jet sizes on a GS750EN with pods

[PoPr]

Anyone here who has some info on what size jets you use on a GS750(EN) with Mikuni VM26SS carbs and conical air pods?
Besides the pods, exhaust etc are all original.

The only thing I know at this point is that I have Main Jet 125. I'm opening up the carbs again this week, and I'll have a look at what the other jet-sizes are.

Just want to know if I'm in the right ballpark, when before I order new jets...

 

[KEITH KRAUSE]

I don't recommend running those cheaper pods (or K&N's) with a stock exhaust. Kind of defeats the purpose. Not a good match. I'd stock air box it.
But if you still want to, I'll give it a guess. Just guessing though.
I believe your stock mains were 102.5, so I'd try 115 or 117.5
Raise the jet needle at least one position. Factory I believe has the jet needle e-clip in the 3rd position. Try the 4th position from the top.
Keep the stock 15 pilot jets and try about 1 1/2 turns out on the pilot fuel screws (underneath) for starters. If no joy by the time they're 2 1/4 turns out, go to a 17.5 pilot jet and set the screws back to something closer to factory...say 1 turn out.
Set the side air screws by using the "highest rpm method" with 1000 rpm's as a base.
REMOVE the two floatbowl vent lines and leave the ports open. Fuel starvation will result with them on while running pods.
Bench synch the carbs carefully at the very least. This should be followed by a vacuum tool synch. If you disturb/change the jet needles in the future, you MUST re-synch the VM carbs.
You should be sure the bike is in decent tune and take it for a plug chop test first at full, 1/3 and minimal throttle positions to see if the main, jet needle or pilot circuits need adjustment. Do what the plugs/performance say.

 

[PoPr]

I've got 125 mains jets and these pods (ignore the red-painted ring), dont know what brand they are? Does the main jet size seem right for these pods?
What vacum-tool should I buy to synch the carbs with?

 

[KEITH KRAUSE]

I've got 125 mains jets and these pods (ignore the red-painted ring), dont know what brand they are? Does the main jet size seem right for these pods?
What vacum-tool should I buy to synch the carbs with?

I can't tell what brand they are.
I still suggest the jetting from my first post. It may be right, it may be wrong, but if it was my bike, that's where I'd start.
I use a Motion Pro vacuum tool, about $40. Morgan carbtune is an easier to use tool because it doesn't use mercury. Morgan is about $100+. Both work as well as the operator.

 

[PoPr]

Im building my own sync-tool, this one for about 3 bucks.

"REMOVE the two floatbowl vent lines and leave the ports open." What do you mean? Should I remove the rubber hoses, and leave the ventports open with no hose? Why?

 

[PoPr]

I tried adjusting the air screws using the "highest rpm method" - BUT I only got the engine to rev up with carb #2?? The other carbs did not respond AT ALL to the airscrews... Why is this?

 

[KEITH KRAUSE]

"REMOVE the two floatbowl vent lines and leave the ports open." What do you mean? Should I remove the rubber hoses, and leave the ventports open with no hose? Why?

You've got two floatbowl vent lines. One vents carbs 1/2, the other vents carbs 3/4. Look at the brass nipples that look just like the vacuum nipple at carb #3. Remove the hoses when running pods. Leave the nipples/ports open. They'll be fine. Just be careful if you use a hose on the bike.

 

[KEITH KRAUSE]

I tried adjusting the air screws using the "highest rpm method" - BUT I only got the engine to rev up with carb #2?? The other carbs did not respond AT ALL to the airscrews... Why is this?

Could be several things. Obviously they're not effecting air flow to increase/decrease with your adjustment, though one is working. If the screws look all the same, then you've got some dirty/blocked passages or air jet in the carb throat, filter side. You could also have intake leaks that will not allow the adjustments to work. Check the screws for being the same as the screw in carb #2, they should be identical and probably will be but I'm just mentioning the possibility. They should be removed for best cleaning of the passages anyway. A more likely cause...try cleaning/compressed air in the air jets and all passages. If OK, check for intake leaks.

 

[odl777]

were are you from, I ran stock needles and jets with my for into 2 exaust and it ran great not lean either. I now have a 4-1 and i put my needle on lowest position with some 120 mains didnt mess with pilot because i got those cheapeer pods also. I live in new mexico mile high area so it may be a lil different for you. Also my mixture screws are about 1 and a half turns out. Good luck

 

[KEITH KRAUSE]

were are you from, I ran stock needles and jets with my for into 2 exaust and it ran great not lean either. I now have a 4-1 and i put my needle on lowest position with some 120 mains didnt mess with pilot because i got those cheapeer pods also. I live in new mexico mile high area so it may be a lil different for you. Also my mixture screws are about 1 and a half turns out. Good luck

Didn't I help you a while back too? Glad to hear the bike is running good.

 

[PoPr]

Keith,

Actually, I saw during my latest de-assembly that my main jets are 135! Pilot jets are 15. Are these mains just to big? I don't know why the previous owner had them put on.

Any recommendations? I have 115 jets at home, should I put those on instead?
Thanks man, you are a real help.

 

[KEITH KRAUSE]

Keith,

Actually, I saw during my latest de-assembly that my main jets are 135! Pilot jets are 15. Are these mains just to big? I don't know why the previous owner had them put on.

Any recommendations? I have 115 jets at home, should I put those on instead?
Thanks man, you are a real help.

I'd try the 115's. 135 is too big.
Your 135's could be DJ or other brand? If there's a symbol, looking like a box with a smaller box in the corner, then it's a Mikuni jet. A 135 DJ would be about the same as a 125 Mikuni jet...still too large in my opinion though. Try the 115's.
Don't forget to check the reads at 1/3 throttle for the jet needles. Minor pilot fuel screw (underneath) adjustments should help with any pilot circuit issues. Always adjust the air screws for highest idle after adjusting the pilot fuel screws.

 

[PoPr]

Thanks Keith, you're the man.
The 115's are Mikuno original, but the 135's sitting on right now are labled "PACCO"?

 

[KEITH KRAUSE]

Thanks Keith, you're the man.
The 115's are Mikuno original, but the 135's sitting on right now are labled "PACCO"?

Go with the 115's. I wouldn't trust Italian jets.:lol:

 

[PoPr]

Raise the jet needle at least one position. Factory I believe has the jet needle e-clip in the 3rd position. Try the 4th position from the top.

What is considered the "top"? 4th position counting down from A or from B in this image?
They are at position 2 from A as of now...

 

[KEITH KRAUSE]

What is considered the "top"? 4th position counting down from A or from B in this image?
They are at position 2 from A as of now...

When I say "from the top", I mean from the top of the jet needle. A stock jet needle has 5 positions to place the e-clip. As you lower the e-clip, the needle raises, which richens the mixture.
It's generally best to take some plug reads before making adjustments but since you have the carbs apart...
For whatever reason, there seems to be some conflicting info as to what position the factory places the e-clip on your 750. I've seen info saying position 2 AND 3.
In your case and without benefit of plug reads, I'd say your stock position is #2, so you'd want to lower the e-clip to the 3rd, or middle position. One position richer should work. That will hopefully be right for your pods/stock exhaust. Be sure to re-install the thicker and thinner stock plastic spacers in exact factory order.
You MUST do a good bench synch whenever you disturb the jet needles on the VM carbs. The bench synch should be followed by a synch with a vacuum tool. Otherwise, you'll probably get innaccurate/uneven plug reads.

 

[PoPr]

Sorry, have tried the search-thingy, but they're all CV-stuff.
How do I synchronize my VM-carbs? I've heard of small plugs on the inlet-rubbers, but I dont seem to have any???

 

[PoPr]

I did see small hexagon screws on the aluminium after the inlet rubbers (towards engine), are those the ones I should use?

If I'm checking, say, #3 and #1 carb, should I remove the screws on #2 and #4, or leave them be while I', checking #3 and #1?

 

[PoPr]

btw, this is my synch-tool I have made...

 

[KEITH KRAUSE]

I did see small hexagon screws on the aluminium after the inlet rubbers (towards engine), are those the ones I should use?

If I'm checking, say, #3 and #1 carb, should I remove the screws on #2 and #4, or leave them be while I', checking #3 and #1?

Yes, those are the bolts you remove. Then you install the threaded adapter tubes with an o-ring or rubber washer tightened snug with a nut to avoid leaks, then your tubing to the synch tool.
Any cylinder not being synched, must have it's bolt tightened to avoid intake leaks.
I don't like the idea of a tool that only synchs two at a time. When synching the regular way, all four at a time, you can see how even minor adjustments at one cylinder can effect the others at times. You won't see this to the same degree when seeing only two at a time. Also, after final torquing of the throttle shaft holder nut (3.5 ft/lb) it's easy to compromise (lose) your setting. You'll be doing half a job, then the other half. You'll have to try to match each set of reads/levels at separate times. You'll have to rely on memory or marks. If you get any condensation (water-gaps) mixed in your lines, that'll be even worse.
If you did previous vacuum synchs on four cylinder bikes, you'd know what I'm trying to say and how your tool complicates the procedure and getting good results.
A simple, but good tool is made by Motion Pro for about $40. I've used this or similar for 30 years with good results.