Author Topic: fine tuning for altitude/jetting question (Read 3943 times)

andrewsw · « **on:** September 02, 2006, 10:33:59 PM »

yes, I know, another jetting thread

I've got a '93 B4 with Yosh 4-2-1 and K&N filter. Its got a Factory Pro stage 1 jet kit with 100 mains installed. These carbs came from Krautwagen who lives at 800 feet. I live at 2000 feet, so its reasonable to assume that it'll be a little rich...

Symptoms:

slight idle lean surge/hang
slight stumble at 5.5k-6.5k when cruising steady and you roll on a little bit more throttle (maybe another 1/8 or so). Clears up if you give it more throttle.
otherwise pulls really well and is a monster above 8k (hits the rev limiter quicker than snot).

WHat I did:

1. richen the pilot air screws by 1/8th turn so they're now at 2 3/4 turns. this almost completely cleared the idle problem, but not quite. Revs clean and hangs for a couple seconds at about 1750 rpms before settling back down to idle.

2. lower the needles another notch (were at 2, now at 1). so this cleaned up the stumble problem and it pulls clean from anywhere in the rev band at any throttle.

The problem/question: it seems a little weak in the mid-range. is very loud out the pipe, but doesn't necessarily pull as much as I think it should when you whack it from 4-6k or so. I'm wondering, since I've got the needle all the way down, should I maybe move to a smaller jet? maybe that would allow me to raise the needle a click or two and get some more mid? I suppose probably not as it mixture is good at all levels based on engine response to various throttle actions at various speeds. but maybe?

insight appreciated.

thanks

PitterB4 · « **Reply #1 on:** September 02, 2006, 11:07:41 PM »

A smaller main might work. One step down, 97.5, was part of the FP stage one kit. With a full 4-1 system and the filter, it seems to me you're gonna strangle it up top. With a full system and a K&N, I had 110 mains and ~1 inch holes in the airbox on either side of the stock hole. It wasn't perfect. I had a little bit of a roll-on to WOT stuble at 7k or so (like powering on hard out of a sharp turn). My point is that maybe getting it more air is the answer. I'd see if KW or one of the other guys parting out a bike has an airbox you can screw around with. Actually, Ianyeager is parting out his bike and he's got my old airbox. Just a thought.

andrewsw · « **Reply #2 on:** September 03, 2006, 12:00:51 AM »

Quote

A smaller main might work. One step down, 97.5, was part of the FP stage one kit. With a full 4-1 system and the filter, it seems to me you're gonna strangle it up top.

yeah I was kinda thinking that too. and yes, KW included all the extra parts so I've got 95, 97.5 and I think 102.5 mains.

Quote

With a full system and a K&N, I had 110 mains and ~1 inch holes in the airbox on either side of the stock hole. It wasn't perfect. I had a little bit of a roll-on to WOT stuble at 7k or so (like powering on hard out of a sharp turn). My point is that maybe getting it more air is the answer.

you know I honestly hadn't thought of that. I was so focused on the fact that I had LESS air and trying to get the fuel down to that level that I didn't even think of giving it MORE air. I'm not afraid of duct tape on the air box if it doesn't work out

. This raises another question: I've got no snorkel on the airbox intake. I know that makes the hole bigger, but I figure the extra induced turbulence around the opening probably decreases flow rather than increases it. Thoughts?

Thief400 · « **Reply #3 on:** September 03, 2006, 12:35:41 AM »

I haven't had much riding time this year, the new job is killing my fun time. I finally got the jetting sorted of perfectly. Here's what i ended up with but you must remember I use only mikuni jets and stock needles. Canadian bikes have adjustable needles hehe. If some of you don't already know mine is a 91 bandit with a Yosh 4,2,1 zyclone pipe, a K&N filter and 2 extra holes in the air box. My altitude is 660 feet. Main jet is a 125, air screws at 2 turns the needles in the middle groove. I had them in the 4th groove and had what seemed to be a rich spot right at 6000 rpm so I call Marc Salvisberg @ Factorypro and talked to him for over an hour.
Seems we have a lot in common but that's another story. His thoughts on my rich spot were that a carb can't be rich in a very narrow 200 rpm band. He suggested that i drop the needle and retest. Well the man was right. The bike runs great. Any one who is serious about making more power has to get a pipe, slipons make more noise, A well designed pipe make way more power. So keep hunting on ebay

PitterB4 · « **Reply #4 on:** September 03, 2006, 09:53:12 AM »

For any of the newbies reading this... there's significant difference between Andrew's carbs and Chris'. First - Chris' Canadian bike has 33mm carbs rather than the 32s the US got. Second (and probably more importantly) the Factory Pro needles are a skinnier taper than the OEMs. That's why Chris can use that firehose 125 main that would probably drown Andrew's bike.

Chris - you're running the OEM air filter, right?

Andrew - I never messed with the snorkel so I'm not sure whether that's helping or hurting airflow. Like I said before, I'd get a new lid and mess around with it. Swapping airbox lids takes like 10 minutes. At least for me, it was good learning experience on the effects increased airflow.

andrewsw · « **Reply #5 on:** September 03, 2006, 12:18:51 PM »

firehose! lmao

that's a huge main! dude you must get all the girls

I'm definitely going to look into putting some holes in my airbox, though I've not got enough of a selection of mains I think to really use it at this point. But a small change would probably make the most of the main I've got and bring that needle back up a click for some more mids. And like I said. I'm not afraid of duct tape as I've spent my m/c budget for a little while.

Thief400 · « **Reply #6 on:** September 03, 2006, 04:14:34 PM »

Just to show the differance the holes make, while jetting the bike I would tape off one of the holes and see if that made it better or worse, with 1 extra hole and the air horn removed the main jet was 117.5 with 2 extra holes my main is now 125
Rob I'm running a K&N

SRwitt · « **Reply #7 on:** September 03, 2006, 04:59:17 PM »

Kinda off topic but Andrewsw I notice you're in Spokane, I live right across the border in Rathdrum, ID. Have you checked out www.pnwriders.com?

andrewsw · « **Reply #8 on:** September 03, 2006, 11:10:29 PM »

Thief400, wow, those holes make quite a difference. maybe more than I want at this point as I'm not sure how far I really want to go. gotta start saving some pennies...

SRwitt -- yeah, I pm'd you about hooking up since we're so close. I don't really know this area from a motorcycle point-of-view... I know there is a regular monday night ride that start up in hillyard, but haven't been to check it out yet. I'm free midmornings-midafternoons for rides if you're into it. or some weekend days too. ALthough I see from you other recent post that you may not be on the road just yet...

Herr Tod · « **Reply #9 on:** September 04, 2006, 12:59:36 PM »

Quote from: Thief400

Just to show the differance the holes make, while jetting the bike I would tape off one of the holes and see if that made it better or worse, with 1 extra hole and the air horn removed the main jet was 117.5 with 2 extra holes my main is now 125
Rob I'm running a K&N

What did this do to the fuel consumption? When I did this on my 2-stoke bike it went from 1:22 (liter : km's) to 1:17. Felt like it had a little more torque but that was not worth the fuel.

Thief400 · « **Reply #10 on:** September 04, 2006, 01:42:47 PM »

OK going to set the record straight here, YOU CAN'T HAVE OPTIMUM FUEL MILEAGE AND MAX HORSE POWER. IT'S ONE OR THE OTHER. if your riding the bandit for gas mileage your on the wrong bike. It has a higher specific output than most 750 and 1100's
Now as for the jetting changes my milage has stayed about the same. but it's something i NEVER worry about. I just want it to run well and pull hard!!!!!!!

Herr Tod · « **Reply #11 on:** September 04, 2006, 06:59:20 PM »

I know, but there are other means of getting (loads of) extra power and sacrificing the same amount of fuel milage

andrewsw · « **Reply #12 on:** September 05, 2006, 08:20:45 PM »

Update:

so I thought I had the mids dialed in pretty good with the needles at 1, but went for a longer ride today in the heat (94 F or so) and it was definitely acting up between 5.5k and 6.5-7k. Its just a little "soft", stumbly, when just the slightest roll on throttle. probably not even an extra 1/8th throttle. if I go just a little more on the throttle, it clears right up. ITs annoying though as its right where I like to ride and feather the throttle for the medium speed sweepers.

SO I definitely need to either: go with a smaller main or drill the airbox. Any pointers on what amount of drilling starts to make a noticeable difference? I'd rather not go smaller on the main. I mean, would a 1/2" hole actually be enough to show up? or does it take more than that? I'm perfectly happy to start drilling holes, just looking for some guidance on what makes a difference.

oh, and BTW I am running a 195 degree thermostat

thanks

andrewsw · « **Reply #13 on:** September 07, 2006, 02:48:35 AM »

Spoke to FP today and got some good insight. COuple of possibilities.

1. its possible that my main jet is too big, but with the k&n and no snorkel, its probably okay and would be the last thing to check.

2. might be worn emulsion tubes, gotta check that out.

3. could be oversized pilot jet

4. might be float level.

so much to check, but he thought it was most likely worn emulsion tubes as the needle drop didn;t really clear up the problem as much as I thought it had.

Also, for the record, the do not recommend any different jetting for altitude until you get above 4000'...

andrewsw · « **Reply #14 on:** September 08, 2006, 09:25:02 PM »

just to follow-up my results.

turns out the float levels were a little off on two carbs. they were low (rich) by 1 mm... but that wasn't really the problem.

It was the emulsion tubes. definitely worn, as were the slide carriers -- the white/grey plastic inserts that the slide runs up and down in. Luckily, the ones from the old messed up carbs were in good shape