Just rejetted, new problems

[BlkMage]

After hearing how bad it was to be running so lean from the guys at the Tahoe rally, I decided to follow the tech tip on here about rejetting. Because I have aftermarket 4-2 pipes and the pod air filters, I took the mains from 110 to 117.5 and 120 to 127.5, also taking the pilots from 42.5 to 45. However, now it doesn't sound like it's running right and I can't get much power out of it. All 4 cylinders are firing (spray water test) and I didn't change anything else. I really hope you guys can help me again, Street Vibrations is coming up soon...

[John]

It sounds like you are too rich. I would try 115's and 117.5 to start. I am running 140's or one size up on the 78 carbs I have in my bike, and I have a 1179 big bore, aftermarket filter, and aftermarket 4-2 pipes. That's all the increase I needed.

[BlkMage]

Well, for me 1 size would be 112.5 and 122.5 mains, but should I leave the pilots up or go back to stock?

I really don't want to have to buy multiple sets of jets here. And the opinion of someone from the ralley that heard it run would be nice.

[79XS11F]

The pilot jets affect all others because they supply fuel through all setting. Given your set I would leave the pilots and go down on the mains.
Rob

[John]

Duhh. I should have read the post more thoroughly. What I meant to say was start by going up just two sizes on the mains, and possibly just keep the stock pilot jets, and turn the pilot screw out about one extra turn. I stated my jet sizes just to show you how little I needed to up size when I did all my mods.
If you have an independent bike shop nearby, they may be willing to trade jets with you.

[TopCatGr58]

Hey Mage,

Was it your dad that maybe read the specs in the manuals about the staggered jetting, and set it up that way??

Many folks have reported that in the later year models, that their machines came stock with straight 110 jets across all four carbs, I know mine did, and I have the 81 Special.

So...when I did my rebuild big bore, and have 4-1 pipes, Indy filters, I have gone up to 117.5's from 110's on all four, and it runs great and has good plug color on all 4!

So...you might want to just replace the 2 with 127.5 with 117.5's and you'll probably be good. You may need to tweak the pilot jet screws, as well as your float heights, all interact with each other!
T.C.

[BlkMage]

Actually TC, I'm the one that found the different jets for 1,4 and 2,3. I'll see on Tuesday if I can get a pair of 117.5s and try it out.

[scott0757]

My 1980 SG had 110 mains in all 4 carbs. When I replaced the rusted out OEM pipes with a MAC 4 to 2 system, I left the pilot jets alone, but bumped the mains to 115 on 1 & 4 and 120 on 2 & 3. Seems to run well for me and plug color looks good.

I do notice a slight flat in performance when transitioning from pilot to main circuits, but it quickly passes. Maybe the 120's are too much and I should look into the 117.5's...

Even so, my pipes still blued on me...Kind of disappointing...

[BlkMage]

Still here...

Ok, been trying stuff for the past couple of days, got it down to 115 mains on all 4 and the 45 pilots. Just cleaned the plugs before today's test ride (had been fouled from the bigger jets) and it's still not quite right. However, it seems like the problems are at the low-end. As soon as I give it a good twist, it lights right up! Does this make any sense?

Oh, and scott 0757, I also have pod air filters.

[John]

Go back to 42.5 pilots, and make sure the three small orifices in the top of the throttle body are clear. They also supply fuel during low rpm operation. The throttle plates cover these orifices at idle, and some guys aren't aware of their purpose.

[trbig]

It's been said that you don't have to change the pilots until you go up 3 sizes on mains... So I agree. Go back to the originals.

To test the mains, stick a spark plug wrench in your pocket and maybe even a rag or oven mit to keep from getting burnt... go out and run the bike for several miles... keeping the rpm over 4,000 to make sure you're just using the main jets. Then when you get somewhere safe, immediately pull in the clutch and kill it... coasting to a stop. This will make sure you don't use the pilot jets. Pull over and pull your plugs and look at the color. That will tell you if the mains are ok... or if you need to go up or down any more.


Tod

[Hired_Goon]

Originally posted by trbig
It's been said that you don't have to change the pilots until you go up 3 sizes on mains... So I agree. Go back to the originals.

Tod

But with individual pods, he should be up 3 sizes anyway.

My 78 is running pods and four into one. My jetting is 145 from 137.5 and up one pilot size. Runs sweet.

Change in pilot size means you need to use less adjustment on the mixture screws. Do you use a colourtune to set the mixture?

My screws are less than 1 and 1/4 turns out to get perfect coulour at idle.

For your configuration 117.5's should be right and up one size pilot. Should be just fine tuning from there.

And I think same jetting across all four is much easier to dial in.

[BlkMage]

Originally posted by Hired_Goon


But with individual pods, he should be up 3 sizes anyway.

My 78 is running pods and four into one. My jetting is 145 from 137.5 and up one pilot size. Runs sweet.

Change in pilot size means you need to use less adjustment on the mixture screws. Do you use a colourtune to set the mixture?

My screws are less than 1 and 1/4 turns out to get perfect coulour at idle.

For your configuration 117.5's should be right and up one size pilot. Should be just fine tuning from there.

And I think same jetting across all four is much easier to dial in.

...I don't even know how to set the mixture, I thought the book (Clymer) said that they don't need to be adjusted.

I'm so freaking new at this...

[TopCatGr58]

Hey Mage,

The book talks about the brass caps that were installed at the factory that seal the preset idle mixture/pilot screws! But once you start making mods, you need to remove them so you can tweak them according to your and your bike's needs!

Check out this fine tech tip by Ken Talbot for tuning your pilot circuit by ear if you don't have a colortune!

Hang in there, you'll get it eventually!
T.C.

[BlkMage]

Originally posted by TopCatGr58
Hey Mage,

The book talks about the brass caps that were installed at the factory that seal the preset idle mixture/pilot screws! But once you start making mods, you need to remove them so you can tweak them according to your and your bike's needs!

Check out this fine tech tip by Ken Talbot for tuning your pilot circuit by ear if you don't have a colortune!

Hang in there, you'll get it eventually!
T.C.

Thanks for the tip, but that might be a while off (still gotta rewire to get my tach back in Neutral). Would this be ABSOLUTELY required to change jet sizes? If so, I can drop it back to stock and just run a little lean till winter.