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Old yosh pipe. Jetting.

  • Thread starter Thread starter Billyboy
  • Start date Start date
B

Billyboy

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I have an old yosh pipe and maybe the right jets. Not sure.

The main jets in the donor bike are all marked with an "R" then a small square in a larger square, 117.5.

The pilot jets are marked with the same double square thing and 15. They are the same across the rack.

Is this different than stock on a 78 GS1000? If so, then I think I've got a matched set for pods and this pipe.[-o<

What are the stock jets?
 
Stock jetting for a '78 1000 is #95 mains, jet needle e-clip in the 3rd position and #15 pilot jet.
A 117.5 main jet wouldn't be nearly large enough for a quality pipe and pod filters.
You would need something around 130 to 132.5 Mikuni mains. This suggestion based on a quality pipe, which the Yosh should be and K&N pods. Drop about 2.5 to 5 off for cheaper pods.
If running stock jet needles, you'll probably need 17.5 pilot jets. If you go with a DJ stage 3 kit, then you should be able to use the factory 15 pilot jets. The more tapered DJ needle effects the pilot circuit that much.
As for the jet needles, the factory ones just don't work in many cases. I always suggest DJ jet needles. If you do try to make the factory needles work, only chance they have is with the e-clip in the bottom position.
Also, remove the 2 float bowl vent lines when running any pods.
 
Thanks for the detailed response, Keith. Looks like there's a lot more to know about jetting.

Do you think I might get by with the 117.5's and still use the airbox? Just asking.
 
Billyboy said:
Thanks for the detailed response, Keith. Looks like there's a lot more to know about jetting.

Do you think I might get by with the 117.5's and still use the airbox? Just asking.
Click to expand...
The 117.5 are an increase of 22.5 over the stock mains. That MAY work if you run the stock air box with the TOP LID REMOVED and of course a decent filter. 117.5 are way too rich for the stock box with the lid on.
You would have to test and get plug reads to see if the 117.5 work well with the lid removal. They certainly seem "ballpark" to me but they could still be rich or lean. Just off the top of my head I'd guess 120 would be correct for your set up but try the 117.5
If using the stock jet needles, you'll need to go AT LEAST 1 position richer for the box with no lid. I don't have as much experience with the box mod as I do with pods, but I'm positive you'll need to raise the needles at least 1 position from the factory 3rd position. Test at 1/3 throttle. If lean, then it depends on plug color. If obviously lean, go to the bottom position. If just a little lean, placing the e-clip in the bottom position but with a .022" jetting spacer directly on top the e-clip will give you position "4 1/2". I'm thinking either position 4 or 4 1/2 will work but I can't guess as to which one really.
If using the stock needles, you can try using the stock 15 pilot jets with richer pilot fuel screw adjustments. If minimal throttle position (pilot circuit) plug reads aren't acceptable by the time the pilot fuel screws (underneath) are out 3 turns, then you need to go with 17.5 pilot jets and return the pilot fuel screws to something close to factory, say 1 turn out from LIGHTLY seated.
Any time you disturb or change the jet needle positions on VM carbs, you MUST bench synch the slides and the bench synch needs to be followed by a vacuum tool synch to get accurate performance/plug reads.
Before the vacuum synch, check ignition timing and valve clearances, and then the side air screws must be adjusted using the highest rpm method, THEN you can accurately vacuum synch and check your re-jet.
 
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Keith, I hope you see this:

I've got yosh pipe on and it sounds great, after a little welding on a rusted part.

I just put on emgo filters and removed the vent lines like you said. It's running really lean, (like you said it would). There is no power at all above 5000 and the plugs are white. I have to feather it at 1/3 throttle to get highway speed.

You say 130 - 132.5 mains. I believe it. (so I guess 125-127.5 with the emgo's). Where do I get them? I'd like to get the DJ 3 but funds are low, as always.

When you say needle clips in the bottom, does that mean to put the clip in the slot closest to the tip, or to the top of the carb?

What is the model of these carbs. I see things like vm11/22, vm28. I thought these where 26mm??

Your help and expertise is very appreciated!!:-D
 
Just saw this as I'm out the door. I should be able to reply tonight.
You think you may have 28mm VM's?? Can you show a close up pic? Do you see an accelerator pump underneath?
 
take a caliper and measure the motor side ID of the opening of the carb, that will tell you how big they are. I know funds are low but do your self a favor and put the air box and filter back on till you can get the DJ kit and quality filters. Other wise you are just going to have a head ache fighting things.
 
KEITH KRAUSE said:
Just saw this as I'm out the door. I should be able to reply tonight.
You think you may have 28mm VM's?? Can you show a close up pic? Do you see an accelerator pump underneath?
Click to expand...

No, I mean online I see VM28, and vm11/22. There's no pump. I'm asking what model of main jets to buy. I'm positive that they're 26.

I'm thinking it may only be a month or less till I can get the dj, but if I can get it close by buying the right or close mains then I'll do that till winter.
 
And you were going to use a beer can and some clamps? :-D That Yosh pipe and pods are going to add to the total package that you've got going!!! \\:D/ GOOD CALL!
 
Dave8338 said:
And you were going to use a beer can and some clamps? :-D That Yosh pipe and pods are going to add to the total package that you've got going!!! \\:D/ GOOD CALL!
Click to expand...

I actually did! It didn't hold.
Thanks
 
OK, FINE!

I ordered the DJ 3. $151 US to Northern BC from Bikebandit.

Keith or others in the know: Is there anything special reccomended for my setup? I suppose the instructions will tell, but this is new to me.
 
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I would start with the needle one notch richer then reccomended. (One notch lower) They tend to be two notches lean but with those pods who knows. You can also mess around with 1/2 notches with washers. I have my DJ needle on a 1/2 notch.

P.S. Spend another $120 for K&Ns. :shock:
 
OK, Jet needles. is richer raising the needles, by lowering the clip???

K&N's soon. One thing at a time here.
 
OK. I was gonna give you some jetting suggestions using the stock jet needles and separate Mikuni jets but since you've ordered the DJ kit...
My typical sermon first.
Be sure the bike is ready to re-jet. Clean carbs, floats set very close to .94", fresh inner o-rings and manifold o-rings, good condition manifolds, fresh fuel/vacuum lines, good fuel flow, clear venting, valve clearances, good spark/ignition timing, etc.
That kit is designed for use with K&N filters and a quality pipe. Your Yosh pipe should be a good pipe, based on Yoshies I've seen before. I hope it has no leaks though. That also means no leaks at the head due to re-used gaskets. Don't try to over-tighten the bolts if you get leak related decel' pop. About 10 ft/lb is max' for the header bolts or you risk stripping.
Use the DJ 138 mains. Test/plug reads at full throttle.
Place the jet needle e-clip in the 4th position from the top. The lower (down the needle) the e-clip is positioned, the richer the setting. Be sure the two factory plastic spacers are re-installed in factory order...thicker (ring) directly on top the e-clip and thinner spacer directly under the e-clip. Test/plug reads at solid 1/3 throttle.
Keep the stock 15 pilot jets. I'm assuming your pilot fuel screws (underneath) are at factory settings, about 1 turn out from LIGHTLY seated? If so, then turn them an additional 1/2 turn out (CCW) richer. Fine tuning may be necessary later. Test the pilot circuit at steady 35 mph (minimal throttle) in 4th/5th gear.
Initially set the side air screws to 1 3/4 turns out.
Remove the 2 floatbowl vent lines and leave the ports open.
Bench synch the carbs for both fully closed and fully opened positions. I have a detailed easy to do VM carb synch post around here somewhere. A search should find it. If you need it and can't find it, it's part of Hoomgar's thread ("GS1K bad fuel economy/re-jet attn Keith Krause"), or something like that.
After all the above is done, you can start up and adjust the side air screws using the highest rpm method. The bike should be on the centerstand and it must be fully warmed up.
At a base idle of 1,000 to 1,100 rpm's max, start at any carb. Slowly turn a screw in either direction until you hear the rpm's max out. The sweet spot is generally between 1 1/2 and 2 turns out. Once that carb is set, return the idle, if necessary, to the base idle by using the idle adjuster knob. Repeat to the other 3 carbs.
Now you can hook up your vaccum tool to vacuum synch the carbs. This is a mandatory part of jetting in my opinion. You can't really trust the plug reads and gauge any performance issues unless the carbs are synched well. Use two large fans and don't over-heat the motor. If synching is new to you, ask for any tips before synching.
Now you can test at the various throttle positions.
Good luck!:)
 
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