NOT AGAIN. Stock jets with non-stock airbox and pipe

[RipRoaringFun]

So I pull the carb bank from my '81 gs1100Ex and find stock jets (107.5 mains and so on).

Yet the exhaust is a Supertrapp 4-into-1, medium-loud. And the box that normally surrounds the stock air filter was also removed (see the photos below of current conditions).

So I need some advice from you folks -- what main jet should I bump up to, and what pilot jet, and which needle setting? I'm at sea level where I live.

I'm thinking to go up 2 main jet sizes from 107.5 to 112.5 and 2 steps on the pilot, and drop the needle clip one notch (thus raising the needle upward).

Does that sound about right?

Plus I found some cracks on the insides of my intake manifolds (see pics). The general condition of my 4 rubber intake manifold boots is "Poor due to age", lots of little cracks, but I can't find any cracks going *all the way through* but it would not surprise me if there were some/many small ones.
I am ordering all 4 new intake boots today.

BIKE IS RUNNING WAY LEAN.
Spark plugs are white.

What's a good main jet/pilot jet/needle clip combo for this situation?










All four rubber intake boots look pretty good on the outside........




Most look gnarly on the inside, though........

[Steve]

I don't know how the UNI flows compared to stock, but I would think that only two sizes for the 'Trapp is not quite enough.

Probably no need to increase the pilots. If you do, only one size, not two.

You sure you have adjustable needles? Most '81s don't, unless they already have a DynoJet kit in there.
If you don't have adjustable needles, you can still raise them by removing the thick nylon spacer above the clip and installing a couple of thinner washers that total about half the thickness of the nylon spacer.

.

[Big T]

You have adjustable needles?

How many notches?

I agree with Steve, 2 sizes will probably not be enough

It will be a good start tho, once you get new boots on it

I'd also add more back pressure to the SuperTrapp for now (make it quieter)

You can order up some new jets here www.jetsrus.com

Get a couple sets of different sizes and save on shipping

So, new intakes, bigger mains, somewhat bigger pilots and see what you got from there

Is that Uni oiled?

[mlinder]

My guess is you'll end up at 115 or 117.5 mains. Probably only need next size up on pilots.

[headsbikesmopars]

On my 1981 GS1100EX, std. bore with a massaged head (mild) 95 cfm , 10.20 C.R. and a set of 1983 GS1100 cams, stock air box, no airbox lid, K&N filter, With factory stock exhaust and has 125 mains and runs excellent with them. Very crisp throttle response. Runs strong on the mains up top.
just FWIW.
Terry

[TheCafeKid]

Ditch the crap wannabe filter, get a set of KN pods and a DJ kit... Or find the rest of the box, and get a stage one DJ kit. Either way, dont bother with the stock needles. That pipe is rough to dial in for. I NEVER EVER EVER got mine to quit back popping. Stg 3 kit, bigger pilots, moving the needle, etc etc etc.. Just wasnt working. I ditched the pipe in favor of a Yosh and the bike was dialed in to the letter after that. BTW, any less than 5-7 discs in that pipe is more restrictive than stock..

[RipRoaringFun]

My guess is you'll end up at 115 or 117.5 mains. Probably only need next size up on pilots.

I buy my jets from a local shop that sells them cheap ($3.99 each) and they have bike mechanics too, that's part of their service business. Big T, thanks for that JetsRus URL, I have bookmarked them. Nice to have a lower-cost provider, I though my local favorite shop was the cheapest.

So the employee busts out a huge box of labeled pockets with all different Mikuni round jet sizes. "What main jet size do you need?" he asked. One of the mechanics was at the counter, taking a breather, asks "What's going on with the bike, why are you going with bigger mains?" he asks.

I reply "It's a '81 gs1100Ex, with a Supertrapp, medium loud, the stock air filter enclosure box is removed, and it is running very lean, and it still has the stock 107.5 mains in it now (I show him one of the 107.5's I took out today)."

The mechanic: "You should go up to 115's with that setup."

I pick a 115 out of the huge jets container and compare the holes. The 115 center hole should be bigger a bit than my stock 107.5 main jet, right? I mean I should be able to do a side-by-side comparison visual and see that the 107.5 hole is a bit smaller than the 115 hole.

NOPE. My 107.5 hole was TWICE as big as the new 115 main jet. The po must have drilled the stock jets. My 107.5 stock mains have been seriously opened up.

I started pulling jets out of that Mikuni jets box.
- 122.5: still had a smaller diameter hole than my "107.5" jet.
- 147.5: still had a smaller diameter hole than my "107.5" jet.
- 157.5: this was slightly larger-diameter hole than my "107.5" jet.

So the po *really* went to town on the stock 107.5's didn't he.

AND THE BIKE STILL RUNS LEAN ?!

So here's my running theory:
- the po mis-diagnosed the lean running condition that the bike has
- he thought "I'll go bigger on the mains, I'll drill 'em out to save some $$"

But going with a hugely bigger main jet (from the looks of it, he drilled out the stock 107.5 main jets to about 150 or so) -- the bike is still super lean.

Why? Because the intake rubber manifold boots were leaking. That's my theory so far. I ordered the 4 new manifolds (total of $60, not bad) from the Suzuki dealer.

I went ahead and bought the 115 main jets too. Once the new leak-free intake manifolds are on, the mains I have now (the drilled-to-150 mains) -- those will be WAY rich. And buying stock 107.5 jets wouldn't be correct, it will be too lean.

Also, since I'm used to re-jetting VM carbs, this was the first time in my life that I opened up CV carbs -- surprise surprise, no designed-in way to adjust the needles. So I'm going to skip that for now and try the 1/2 height washer approach later if I need to tackle it (thanks for that tip Steve!).

So basically the intake manifold boots were leaking *really* *really* bad -- the bike is running with 150 mains and is burning the plugs white. I think the PO might have mis-diagnosed this because on the outside, the intake boots look pretty darn good -- but if you pull them off the head and inspect them, there are age cracks on all of them, some go 1/2 way around the circumference right near and under the clamps.

I'm going to do an inspection of the carbs to see if everything's where it should be (no missing block-offs or etc.) to make sure there are no other possible air leaks.

By the way -- the carb interiors are very very clean. Almost zero sediment in the bowls.

[Steve]

BTW, any less than 5-7 discs in that pipe is more restrictive than stock..

And is sounds funny, too.

Even though it was louder, it sounded much better with more disks. What was it Josh, 10, 12?

ISo basically the intake manifold boots were leaking *really* *really* bad -- the bike is running with 150 mains and is burning the plugs white.

How often did you get it past half-throttle?

If you never got that far into the throttle, you were only running on the pilot and needle,
so the extra-large mains wouldn't really matter too much.

.

[RipRoaringFun]

And is sounds funny, too.

Even though it was louder, it sounded much better with more disks. What was it Josh, 10, 12?




How often did you get it past half-throttle?

If you never got that far into the throttle, you were only running on the pilot and needle,
so the extra-large mains wouldn't really matter too much.

.

I had it cranked. I put in new plugs and really opened her up then checked them. White.
I also noted that, while the bike is powerful, my gut told me it was missing power on the top and all over the RPM band. An 1100 should really really pull my arms straight and leave my stomach 1/2 way down the block behind me when I get on it like that. This 1100 would not do that. It was a seat-of-the-pants sort of intuition but at 51 after riding since I was 16, bikes of all sizes, I felt disappointed at the power even though it was noteworthy. Something told me I shouldn't feel disappointed on an 1100.

[mlinder]

You can buy shims for needle position. We use em.

[TheCafeKid]

Don't.

Stop.

You're wasting your time. Period. Stop listening to those idiots at the parts counter, or the mech who probably hasn't touched one of these bikes in 10 years or more if at all. There are tens if not hundreds of people on this board who have done, do, and will continue to do these very things. Now, you cab fiddle fart around and play with different mains or pilots or futilely attempt to shim the stock mikuni needles in an attempt to get it to run right. And, after days, or weeks, or maybe a season, you might actually get it close. You might also end up bald and in the nutter house from trying too.

The simple fact of the matter is this: these bikes , and their carbs, were set up on the teetering edge of stupidly lean from the factory. Why? You can thank the EPA or uncle Sam or whomever you want for that, but it's true. These bikes were set up to run well enough with all the restriction and still comply with the EPA regulations. Removing even one component will throw the set up teetering off the edge into a lean mix that's nearly unburnable in at least somewhere in the circuits. The major cause, minus the mains, is the jet needle. It's fat, blunt, has a very slow taper to it. You can try to shim it out, to cause the taper to happen "faster" in the needle jet (which allows more fuel into the mix to compensate for the additional air it's sucking or blowing due to less restriction) and it might work for most of the rev range, but somewhere, that needle will still be too fat to feed the necessary fuel to motor needs to be..less disappointing. Buy a Dynojet kit. The jets are not important, what you need are the needles. They're adjustable, the taper is faster, and even on a stock bike, it's an improvement. You get those puppies tuned right, and even a mostly stock 1100 will have you grinning from ear to ear and rubbing aspircreme on your shoulders and elbows

[RipRoaringFun]

You can buy shims for needle position. We use em.

Thanks -- do you have a source? Someone mentioned getting a K&N stage 'X' kit -- have you used one of those and gotten some flexibility with needle height?

[RipRoaringFun]

Don't.

Stop.

You're wasting your time. Period. Stop listening to those idiots at the parts counter, or the mech who probably hasn't touched one of these bikes in 10 years or more if at all. There are tens if not hundreds of people on this board who have done, do, and will continue to do these very things. Now, you cab fiddle fart around and play with different mains or pilots or futilely attempt to shim the stock mikuni needles in an attempt to get it to run right. And, after days, or weeks, or maybe a season, you might actually get it close. You might also end up bald and in the nutter house from trying too.

The simple fact of the matter is this: these bikes , and their carbs, were set up on the teetering edge of stupidly lean from the factory. Why? You can thank the EPA or uncle Sam or whomever you want for that, but it's true. These bikes were set up to run well enough with all the restriction and still comply with the EPA regulations. Removing even one component will throw the set up teetering off the edge into a lean mix that's nearly unburnable in at least somewhere in the circuits. The major cause, minus the mains, is the jet needle. It's fat, blunt, has a very slow taper to it. You can try to shim it out, to cause the taper to happen "faster" in the needle jet (which allows more fuel into the mix to compensate for the additional air it's sucking or blowing due to less restriction) and it might work for most of the rev range, but somewhere, that needle will still be too fat to feed the necessary fuel to motor needs to be..less disappointing. Buy a Dynojet kit. The jets are not important, what you need are the needles. They're adjustable, the taper is faster, and even on a stock bike, it's an improvement. You get those puppies tuned right, and even a mostly stock 1100 will have you grinning from ear to ear and rubbing aspircreme on your shoulders and elbows

Okay *excellent*, I mis-called them 'K&N stage X' but yep now I remember buying one in 1987 for my '86 gsxr750 I bought new back then. I removed all the epa stuff from the gsxr then bought a Yosh pipe and a jet kit, when you said 'Dynojet' I remembered the name.

Thanks for the tip about the needle. Not surprised to hear about the epa/running lean issue. Its what killed 2 strokes here too (epa).

Next tues/weds. when my new rubber intake manifold boots come in from Suzuki, I'm going to install the 115s and manifolds.

Then post the results and yep, I will most likely end up buying a Dynojet kit -- thanks for the tip.

[mlinder]

I haven't had a lot of trouble on these particular CV's with a bit of de-restriction, proper jetting, and adjustment.

These are quite easy, honestly, unlike a couple of other CV's I've tried.


I don't remember the source, but will find out for you. For the shims, that is.

[RipRoaringFun]

Okay, so here is a photo of plugs from #1 and #2. All four spark plugs look like this.

This despite drilled-out main jets of about 150 (107.5 mains are stock). These plugs were pulled after a 'get on it hard' run that ended as I approached my house. I can't wait for my 4 new intake manifolds to arrive on Wednesday and restore some 'intake sanity' to this bike.