Quick jetting question

[retrex]

I have been itching to put a V&H header that I have on my bike for some fall foliage riding, real soon, and I only have 115 main jets to pop in my carbs. I don't think I have time to investigate and order the correct sizes and fool with the needles and springs. So what am I facing if I do this? Can I still have reliable performance with just changing the mains to 115 or should I go with the stock pipes and work it out over the winter. Oh yeah, I am running a stock air filter and airbox. Quicker replies would be better since I am taking the mains out of my other bike, too long a story to go into, and unless it will give me acceptable performance I don't want start something that doesn't get me to where I want to go. Thanks.

[the_journeyman]

You'll run a little lean. My GS1150 hadn't been jetted for the pods OR the 4-1 exhaust that's on it. It runs ok but not great. I don't think you'll hurt anything ~

JM

[Steve]

The question is...do you have the stock 107.5 jets in there now?

In '81, stock jets were 107.5. In '82 they were bumped to 110, in '83 they were bumped again to 112.5.
If you have the stock jets and go to 115s, you will be going up 1 1/2 sizes.
That will get you close, but only reading the plugs will tell you the full story.
With the stock airbox, you might actually end up with 117.5 or 120, but the 115s will definitely be better than stock.


.

[retrex]

The question is...do you have the stock 107.5 jets in there now?

Hi Steve, Yes I am running the stock 107.5s and as the_journey man rightly points out I guess my main concern is the valves. I know that I won't get optimum performance, but I wanted to give the headers a try, just to see if there would be any noticable performance gains. And oh yeah, to get to hear the cool sound of the big girl with a 4 into 1 on her. I haven't run a header since my 78 GS750. I have got the carbs off on my other GS11 and unless someone thinks I'm going to cause some damage I'm going to put the 115s on the to be "header bike". I got time this afternoon, it's raining, so I'll start the task and keep checking in for further replies and or comments. Thanks for your responses guys.

[Nessism]

I don't think you will hurt anything by running the 115 mains with a stock airbox, assuming you are going to do general purpose riding and not a lot of full throttle blasts. Not sure how the low end will respond, you may have a flat spot. It wouldn't hurt to try raising the needles a smig since it effects quite a range of different circuits.

[retrex]

Another find and another question

I don't think you will hurt anything by running the 115 mains with a stock airbox, assuming you are going to do general purpose riding and not a lot of full throttle blasts. Not sure how the low end will respond, you may have a flat spot. It wouldn't hurt to try raising the needles a smig since it effects quite a range of different circuits.

Thanks Nessism I appreciate the input.

I just noticed that the 115 carbs have also got 170 slow air jets vs the 160s on the 107.5s, would moving these over be of any benefit.

I got both sets of carbs on the bench and I am going to start to switch the mains. I'll check in after I get them swapped before I do, if it's of any value, the slow air jets

[monte]

jetting

been down that road (jetting) 750's and 1100's .use a k & N replacement filter in your stock airbox for a little better breathing and also go higher on the idle jets otherwise you will get a creaping rev problem.

[03svrider]

what about the same question for an 81 gs450 with a 2 into one exhaust?
sorry to threadjack.

[retrex]

Idle question

been down that road (jetting) 750's and 1100's .use a k & N replacement filter in your stock airbox for a little better breathing and also go higher on the idle jets otherwise you will get a creaping rev problem.

Ok monte, this is definately getting into the winter project thing that I was trying to avoid, but it's started now so let's finish it. I am a little confused at to what you mean by idle jets, do you mean pilot jets? If so what combination of main jet/air jet/pilot jet would be good if I did go to the K&N filter later on? If you mean the idle mix screws, mine are still under the protective metal plug. I have never had the urge to fiddle with them since my bike has always been stock, 26 years, and it has always run relatively well(knocking on wood). I have experimented with removing the plug and trying to adjust the idle screw on a set of parts carbs without much luck. I got the plug out easy enough but the idle screw was jammed in there pretty good. I ended up stripping the head of the screw. I don't think I want to try this at this time. Also I recently saw a comercial for filters that look like K&Ns but don't need to be oiled. I think they are made of some type of polymer material. You just blast them inside out with air or water to clean them and they last forever. Any experiences with these?

[salty_monk]

He means the pilot jets. With the stock airbox I reckon you may be lucky & be able to get it rich enough on the mixture screws without going up jet sizes.

If yours are all still plugged you'll be running around 1.5 turns out.... plenty of turns left!!

You'll want to tweek them using the "max rev" theory. Tweek one till you get max revs then tweak just a smidge more. Reset idle stop. Attack carb 2... etc etc.

Make sure engine is warm before you fiddle but don't let it overheat!

Kent has an 1,100GL 8 Valve with in box K&N & Vance & Hines. He runs 120 Main jets (he's also run the 115's but says the 120's are better), larger pilots (I think) & The needle moved up a notch or so using a dynajet kit.

Dan

[BentRod]

a note on the heat
While I am all for the proper tuning of your crabs, it sounds as if your time is pressed thin. If you find you are running ok, but you are running hotter than you like, you can switch to a spark plug with a higher heat rating. I believe this will help keep your engine cooler, and run smoother.

[Thomas Kenny]

I am running half the CC's you are on my GS550ES. I just installed a period Vance and Hines 4 into 1 header and cannister. My stock jetting was 95's in 1 and 4 and 102.5's in 2 and 3. I jetted up to 105's and installed 40 mm emulsion type pilots. The bike was way too rich with the 40mm and nearly strangled on fuel at idle. I reinstalled stock 37.5mm pilots. The 105's ran good to about 7500 rpm and the motor just nosed over. Up to 107.5's and it is spot on. I can certainly tell a definate improvement in performance and the sound is just awesome :-) I guess if I were you I would hold off going any bigger on the pilots until you run your new pipe and see how it idles. K&N is a cheap improvement in stock airbox that will gain you CFM. Good luck :-)

[chef1366]

Lose the airbox lid. Put in 47.5 pilot jets and 117.5 mains. It will run like a champ.

[retrex]

With the best intentions we do fail.

First I would like to thank all you guys for responding so quickly, but I don't think it is going to work out. After reinstalling the carbs and running the bike for a few minutes it was very evident that the setup I have available to me at this time is not going to work. There is a good deal of popping even when I close down the throttle from a modest rpm of 3k. I was able to tame it a bit by putting the air cover lid back on, but not enough to eliminate it even at that low range. Forget about the upper ranges, it sounds like a gunshots, pop, pop, pop, pop when I roll back the throttle. I guess I'll just have to use my old factory exhaust. One last question and I'll let this dream die for now, to be resurected of course over the winter. I assume that I should have no problems with running the 115 mains and 170 air jets with stock exhausts. I can take the lid off the airbox and run it that way right? Again thanks for the help.