Yet another rejetting thread

[Deros514]

Hello everyone, new member from San Jose, CA. I picked up a 92 GS a few days ago and have been doing some maintenance stuff. I've poured over the wiki and searched the forum on recommended jet sizes and have a few questions. I've ordered a 40 pilot jet as that seems to be the general consensus. Now for the main jet it seems that with the K&N lunchbox and a Jardine exhaust I'd need a much larger main jet. I picked up a 147.5 as this seems to be the middle ground on what people recommend. So far so good? Next question is when people talk about turns and washers, I assume that means the jet is fully tightened and then backed out the number of turns? The washers go on the needles of the main jet? What size washers are being used? I've read #3 #4 etc

So far what I'm understading:
40 pilot all the way tight no washers on needle
main jet around ~150 but with washers under the needles and the jet backed out a few turns
more turns out = richer mixture
more washers = richer mixture

The page that seems to be linked a lot around here "the poor mans rejetting" also says something about removing a plug to access a screw that is also adjusted during tuning. The wiki isn't clear on that. Also where can I get a carb rebuild kit as I'm pretty sure I'm going to need some o-rings and gaskets when I tear it apart. I'm coming from EFI tuning so carbs are a little new to me. Although for what its worth I did race nitro r/c so maybe a tad of carb tuning =). Also I don't know about bikes but when I tuned naturally aspirated cars I got best results by leaning out the original map to 12.5-13 AFR with more timing and at the cost of having to run premium fuel. Anyone tune with a wideband sensor hooked up?

[jeremy_nash]

no, you tighten the jet all the way down, and you set the mixture screws at X turns out from tight

I have a k&n lunchbox with v&h pipe  and run a 40 pilot, 142.5 main and around 3 turns on mix screw

we dont tune with wideband, we tune for smooth power with good throttle response

[Paulcet]

Another place to look for other setups.  'Course that may just confuse the matter.

http://beergarage.com/GSMatrix.aspx

[black and silver twin]

I tuned mine with a wide band, I have v&H and lunch box. But I have newer three circuit carbs so my jet sizes would be all wrong probably. the one jet that may be similar is the main jet, I originally went with a 147.5 and ran a 15:1 afr (yikes!) I eventually ended up with a 152.5 main and a 12.8:1afr.

And you need to tighten the jets all the way otherwise they could fall out. the turns out your referring to is on the mix screws, they are in front of the float bowls under a brass cap. the cap needs to be drilled out then you can turn the screws out a few turns. this only effects idle and very low throttle.

[The Buddha]

92 is 150 for K&N and pipe.
3 turns out is on mix screw.
1-2 washers under the needle.
Its large round mikuni mains, while you're in there replace the float bowl screws with allen head stainless bolts.
Set floats to top of the bowl, and make sure its all clean and its fine.
Cool.
Buddha.

[utgunslinger13]

Listen to the Buddha! He knows his Shiz!

[The Buddha]

I tuned mine with a wide band, I have v&H and lunch box. But I have newer three circuit carbs so my jet sizes would be all wrong probably. the one jet that may be similar is the main jet, I originally went with a 147.5 and ran a 15:1 afr (yikes!) I eventually ended up with a 152.5 main and a 12.8:1afr.

And you need to tighten the jets all the way otherwise they could fall out. the turns out your referring to is on the mix screws, they are in front of the float bowls under a brass cap. the cap needs to be drilled out then you can turn the screws out a few turns. this only effects idle and very low throttle.

13-14:1 is good and 12.8 is a bit rich, however you run fine in summer and winter, that's what counts. Just check on hot days and make sure its not stumbling.
Colder needs richer, humid needs richer, and a place with dry winters and humid summers will work great on the same jetting, no need to touch anything for weather.
Cool.
Buddha.

[black and silver twin]

I tuned mine with a wide band, I have v&H and lunch box. But I have newer three circuit carbs so my jet sizes would be all wrong probably. the one jet that may be similar is the main jet, I originally went with a 147.5 and ran a 15:1 afr (yikes!) I eventually ended up with a 152.5 main and a 12.8:1afr.

And you need to tighten the jets all the way otherwise they could fall out. the turns out your referring to is on the mix screws, they are in front of the float bowls under a brass cap. the cap needs to be drilled out then you can turn the screws out a few turns. this only effects idle and very low throttle.

13-14:1 is good and 12.8 is a bit rich, however you run fine in summer and winter, that's what counts. Just check on hot days and make sure its not stumbling.
Colder needs richer, humid needs richer, and a place with dry winters and humid summers will work great on the same jetting, no need to touch anything for weather.
Cool.
Buddha.

Its been like this for two years with no stumbling ever. When I had the 147.5 main it was surging at any speed and throttle above 50mph. when the bike was bone stock the AFR was 13:1 rock solid, smoothest fuel curve ive ever seen on a stock anything. I work at INTENSE Racing, modifying and  dyno tuning cars every day, we always try to get a 12.8:1 on N/A vehicles and 11.8:1 on  boosted ones, so thats what I went with on my bike. It definitely made more power with a 12-13:1 afr (152.5jet) than it did when at 15:1 with the 147.5 jet. the 150 jet gave it about 14:1ish afr, that was much better (more power and no surging) than the 147.5, but the 152.5 gave much more power above 9000rpm than the 150.

the stock power peak was at 9200rpm and fell of sharply after 9700. with the 147.5 jet it was almost the same curve.
with 152.5 jets the power peak is 10000rpm and stays virtually flat to 10800.

[Deros514]

Yeah that's what I thought the AFR should be around at. 13-14:1 sounds lean especially for an air-cooled engine. So it looks like I should get some bigger main jets because it looks like the 147.5 will be a bit small. Are you running any washers with the 152.5 Twin? I'm wondering if the same size would work on the older 2 jet carbs. What effect does going the next jet size up have compared to adding washers?

I've search online to find the o-rings and gaskets but only come up with ebay listings. Anyone have a good source or could I just find similar sized o-rings at a hardware store? In regards to tuning and elevation change. I'm in a valley at almost sea level(~15-50') the hills around here are around 2600' at their peaks. How much does altitude affect tuning?

[black and silver twin]

I have 1 washer, but my carbs have a mid jet so you probably need two. ask the buddha on that.

That big of an altitude change will greatly affect the tune.

[The Buddha]

Wow you did 152.5 on an 01+ bike.
See I never ran a 01+ bike ... I started making packs for 01 based on piper5177 and a few others requests, and following that feedback.
150 is in a 89-00 and I always got over .5 v on my O2 sensor in that. That is .5 @13.5 or so isn't it. Dont recall, but it usually read over .6.
I can switch to 152.5 ... you're giving me good data.
Cool.
Buddha.

[black and silver twin]

With my current jets, 20-62.5-152.5 +1 washer and 3.75 turns out, the afr is 13ish from 2500 to 8000rpm. it then starts to richen up gradually until 11000rpm, eventually ending up at 12.5 ish. so my avarage is around 12.8:1. But as I am trying to describe, the afr curve is far from flat, it looks like a stock car afr curve (lean at low rpm gradually richening up as rpms increase) with many bumps of a few tenths in both directions in-between. I think another washer or a 65 mid would smooth it out; although a 65 might be too much and push it into the low-12/high-11-afr in the mid 3000-8000rpm range. I dont think I would try to fit another washer in there though, it was a PITA to put the little cap back on with just one.

I think the 20 primary jet is perfect though because at idle/just-off-idle the afr was good at 12:1

For reference the stock afr curve was dead flat at 13:1 from 2500 (start of dyno) to 11000, my bike came stock with 17.5-60-130 jets and had .5-1 turn out on the mix screws, they really tune the gs500f well from the factory!

[The Buddha]

Your bike was set to .5-1 turn out form the factory ? They're supposed to be 2.5 I thought, though 01+ no idea.
Now here is the thing, I may just copy your jetting and start switching out the 147.5's for the 152.5's. However I got a couple Questions.
What did you do to the float level.
Then where did you find 62.5's. Heck you could do 65 and lose that 1 washer entirely, saves you a lot of headache, that top O rings and spring and all if it crammed into a tiny freaking hole is just a huge PITA. Yea top it off wiht parts made of plastic stuffed into parts made of eggshells and all of em being un obtanium or costs 30-40 bucks ... nightmare.
Anyway gimme some feedback, and we'll make a new jetting formula. I have never owned a 04+ I went with what was people's impressions from riding with those jets. Then people just asked me so many times I decided to go with the crowd.
Cool.
Buddha.

With my current jets, 20-62.5-152.5 +1 washer and 3.75 turns out, the afr is 13ish from 2500 to 8000rpm. it then starts to richen up gradually until 11000rpm, eventually ending up at 12.5 ish. so my avarage is around 12.8:1. But as I am trying to describe, the afr curve is far from flat, it looks like a stock car afr curve (lean at low rpm gradually richening up as rpms increase) with many bumps of a few tenths in both directions in-between. I think another washer or a 65 mid would smooth it out; although a 65 might be too much and push it into the low-12/high-11-afr in the mid 3000-8000rpm range. I dont think I would try to fit another washer in there though, it was a PITA to put the little cap back on with just one.

I think the 20 primary jet is perfect though because at idle/just-off-idle the afr was good at 12:1

For reference the stock afr curve was dead flat at 13:1 from 2500 (start of dyno) to 11000, my bike came stock with 17.5-60-130 jets and had .5-1 turn out on the mix screws, they really tune the gs500f well from the factory!

[black and silver twin]

Your bike was set to .5-1 turn out form the factory ? They're supposed to be 2.5 I thought, though 01+ no idea.
Now here is the thing, I may just copy your jetting and start switching out the 147.5's for the 152.5's. However I got a couple Questions.
What did you do to the float level.
Then where did you find 62.5's. Heck you could do 65 and lose that 1 washer entirely, saves you a lot of headache, that top O rings and spring and all if it crammed into a tiny freaking hole is just a huge PITA. Yea top it off wiht parts made of plastic stuffed into parts made of eggshells and all of em being un obtanium or costs 30-40 bucks ... nightmare.
Anyway gimme some feedback, and we'll make a new jetting formula. I have never owned a 04+ I went with what was people's impressions from riding with those jets. Then people just asked me so many times I decided to go with the crowd.
Cool.
Buddha.

I got all my jets from carb parts warehouse .com they have all jets from 2.5 to 160 (i think) in increments of 2.5

My float level has never been checked (accurately) or changed. I tried checking it once and it looked like the fuel was 1/4" over the gasket which is impossible because if I leave the bike off and switch the petcock to prime no fuel leaks out. so I figured Im tarded and stopped.

I went with 62.5s and 1 washer because they do adjust a few thing differently. the mid jet just bumps the midrange fueling up by a set amount, while the washers change the shape and acceleration of the fuel curve. basically a larger mid will just richen up 2000-8000 rpm range the same across the band; a washer will richen 2000-4000 a tiny ammount, then 4000-6000 a little more, and 6000-8000 will richen up alot.

just to let you know the difference the jet sizes made, my lunchbox V&H +5* timing combo only made 41whp with the 147.5 jet (stock was 39whp) but with my current setup (152.5 jet) she makes 44whp, a gain of 3whp more for a total of 5 over stock. so basically moving from a 15:1afr with the 147.5 to a 12.8ish:1 with the 152.5 gained 3whp with the same hardware setup. and the washer got rid of my surging at slow cruise.

All my testing was done in two days with a total of 12 (yes 12) dyno runs, both days were approximately 80*f but we were in the shade and there was a large fan blowing on the front of the bike. We are in ohio so the elevation was like 620 feet or so above sea level. also I did the testing with midgrade gas (89 octane [ron+mon]/2), I have since switched to regular gas which probably leaned it out a touch (not enough to matter though) and have no knock even with the added timing.

P.S. sorry about the thread jack Deros514, I just love talking mod.

[utgunslinger13]

Where in Ohio?  I live in Dublin....anywhere near Cbus?

[black and silver twin]

Where in Ohio?  I live in Dublin....anywhere near Cbus?

I live in dublin! near 161 and 33 (riverside drive) intersection

[utgunslinger13]

HA!  I live just south of where Tuttle Crossing and Wilcox meet!  We will have to meet up sometime and ride!