Author Topic: Quick jetting question (Read 4380 times)

rider123 · « **on:** March 30, 2006, 05:03:51 PM »

I'm having some popping occur on de-acceleration, not alot but it definately means I'm a little lean. However if I turn out the mixture screws to try and cure the popping it eventually runs really rich on the pilots. The popping usually occurs around the 3K - 2500 rpm mark just at the transition from mains to pilots. Also under acceleration it seems a little lean here. IT's almost as if the mains are just slightly lean and my pilots are a little rich. Here are my settings so far:

Snorkle removed
Muzzy Slip on
Stock pilots and mains
1 .5 mm (.020) shim
Mixture screws right now set at best idle which is about 1/4 turn out from stock. Maybe even slightly richer

Would adding another .5 (.020) shim help a bit on the popping so I don't have to turn the mixture screws. For example when I do the "blip" test which is rpm at 1000 and lightly blip the throttle to test pilots it's perfect. However, if I rev it a bit more, to get the mains online it seems a little lean, and I mean a little. My theory is that if I add another shim and adjust the pilots down a bit it may equalize the mixtures out better. What do you guys think? Or is the popping all pilots screws?

I also believe it's slightly lean on the needle hence my question about adding another .5 mm shim. I'm wondering if I can kill two birds with one stone.

Bob Holland · « **Reply #1 on:** March 30, 2006, 05:46:59 PM »

I would really susspect that you need bigger mains. My experiance is that any time you open up the air box or improve the exhaust flow, you need bigger mains.

I would try the shims first.
The way I check my mains, is to run the bike at around 6000 rpms for 1/4 mile or so, pull in the clutch, kill the engine, and coast to my garage, then pull the plugs and look at them. They should be light tan, if they are white, it is to lean. If they are to black, then to rich.

rider123 · « **Reply #2 on:** March 30, 2006, 06:56:20 PM »

Thanks I'll give it a try. It definately runs better now that its warmer and with a little mor humidity. I'll try just one more shim and see what happens. At the rpm level it's getting lean at it is right at the transition period from pilots (up to 2000-2500 rpm or so) and the mains. If I add another shim I probably don't have to compensate as much with the pilots and they can be turned in a bit, which should crispin up the bottom end.

For now I'll pop the snorkle back in which should fix up the mid-range.

DaveG · « **Reply #3 on:** March 31, 2006, 11:06:16 AM »

i will likely install the shims tonight (thanks)
i have the tank off and am ready to go.

Was going to install just 1 shim for now, but maybe i'll start with 2.

even at 4 truns out i got a bit of popping in this colder weather.
during the even warmer weather there was no popping. but like you say it is a bit too rich on idle.

rider123 · « **Reply #4 on:** March 31, 2006, 01:14:51 PM »

Try 2 shims Dave. 1 seems slightly lean. Put your pilots down to near stock (2.5 turns- 3.0) and leave the snorkle in then adjust up. It seems to work better that way and is a little easier to tune.. I'm going to stick another shim in there and leave the snorkle in and see how she runs. She runs pretty good now (wheelies at 3700 rpm) but I think I could use a little more juice on the pilots with only 1 shim. If I de-accelerate I get some popping and if I go from full de-acceleration to on the gas there is a bit of a lean lag. Another benefit of not having tot turn the mixture screws out too much to compensate is the smoother transition between the jets and slightly better gas milage. Ironically I'm also gettting slightly better gas milage with that crap stock pipe off, even with me fooling around with super rich settings for a bit on the same tank of gas. More effecient I guess.

As far as the decision to leave the snorkle in or out. I believe you would need more than 2 shims or larger jets(102.5 or maybe 105's) to get full benefit from the snorkle out. There is a huge difference it mid to top end power though when there is a little more air getting in there. There is a big hit around 5000 rpm and it pulls hard but unfortunatly the stock mains are way undersized to meet EPA to get full benefit. I'm sure if I fooled around enough with shims I could get it running well with snorkle out but this is a temporary measure untill I determine which jet kit I'm going with so I'll stick with probably 2 shims and snorkle in. I may just for fun drill a 3/8th inch hole or two a la Ivans(the kit I'm leaning towards) I can always tape it up if it doesn't work. The extra hole(s) would give it a little breathing room at high rpm and leave the snorkle in there for low rpm.

Ideally if I was working at Suzuki I would have made this bike with 105 mains and used the RF900 can as stock. I'd increase the snorkle size to maybe 1.75 inches instead of 1.5. This would probably have made the bike get around 110-112 HP(Triumph Sprint ST territory) with only maybe 1 or 2 mpg less with much better driveability. If it left the factory like this it would have much better and slightly cheaper by using off the shelf parts (RF900 can). I also believe the RF900 can doesn't sound like a sewing machine either.

DaveG · « **Reply #5 on:** March 31, 2006, 02:36:28 PM »

yep, just changing the can increased my "kilometerage"
i have a few holeshot items and like Dale alot,,,but i too would choose Ivan's kit.

I'm not really unhappy with the current performance. just know that things are running a little lean and fixing it up will get rid of the coldbloodidness at part throttle at least.

DaveG · « **Reply #6 on:** April 03, 2006, 09:38:57 AM »

2 shims runs great

99er · « **Reply #7 on:** April 07, 2006, 06:40:42 AM »

Dude!
You installed a pipe. If you don't have the time to make full throttle runs and check plugs, just go up 2 steps on the mains and then go from there. Shims just affect midrange and 1/4 to mid throttle, depending upon load. Mains affect almost every circuit! Your mileage should have increased as you're now running even leaner than stock. You DO wnat to have more full throttle power, right? Change the mains. It's the best $10 you'll spend.
With a can, you will always risk some popping but the idle screws should have enough range to limit it to a very light pop. As you decel, only the idle circuit is in play. Adjusting the screws should do it for ya' once the mains are correct. I hear that the second gens run better with a richer pilot circuit as well but, mains first.
Go to factorypro.com - product support - CV Carb Tuning - High RPM engines and learn all about it. The mains are the key. Anyway, it's always worked for me and has made carb tuning pretty simple.
Marc/Atlanta
'99 B12
2" mod
K&N
Full Holeshot
135 main/35 pilot/3 turns

rider123 · « **Reply #8 on:** April 07, 2006, 01:39:13 PM »

Thanks for the info. Well I figured out 9/10th of my woes. The damn dealer who did my first service forgot to fully tighten Number 1 cylinder's carb boot! Well I've learned my lesson ALWAYS DOUBLE CHECK THE DEALERS WORK. I should have assmumed that any bike dealer that also sells cars is going to be a little suspect. You'd figure with all their fancy crap they have in the shops(and the amount of money I paid) at the dealer they would have at least been able to find a phillips screwdriver. Anyway bike is much better at 3.25 turns out. Number 3 cylinder is slightly richer on the needle than the other 3, so I'm going to check the shims and make sure they are fully seated against the circlip and measure needle lift again to make sure. Seems a tad rich on the needles with snorkle in at full throttle, so I may pull it out once I get all four plugs with the same colour for fun. It's also still cold here in igloo land so that is going to be a factor. It's still winter driving, for people in Florida it would be like driving in Siberia!!

Thank God I never have to go back to that dealer! First service, thanks for the warranty, Good riddance!