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Message started by eanon on 03/29/08 at 09:49:36

Title: Carb Jetting Question
Post by eanon on 03/29/08 at 09:49:36

Ok, so I finally got a chance to play with the carb a little. The closest mc shop actually had some main jets, so I picked up a 150 and a 152.5. I was running a 145. They didn't have any pilot jets though, so I've still got a 45 in there. She is desnorkeled, and I have a screaming eagle. Over the weekend, I dropped in the 152.5, and shaved half of the white spacer. Now, when I roll off throttle, or especially just let it slap closed, I loose power, my rpm's drop, and if I don't give it a little gas, the engine dies. :( I am going to try putting a washer under the spacer to "fatten" it back up a little, 'cause as I understand it, the main jet only affects 3/4 to wot. Right? I tried to tune the carb with the mixture and idle screws, got her sounding good, but still dies. I have to push the idle to almost 1800 rpms before she won't "bottom out" and die. Any suggestions?

Title: Re: Carb Jetting Question
Post by KwakNut on 03/29/08 at 11:18:34

At what sort of revs/power are you rolling off the throttle? Roll-off is a useful test for main jet at ¾-full throttle with a few revs dialled in.
When you roll off (from smooth full throttle acceleration to, say, 7/8 throttle), the tendency is for the mixture to richen a little, so if she actually ‘gains’ when you roll off that means you were too lean and can go up a jet. If the motor is unhappy at roll-off (as your seems to be), you were probably too rich anyway and should drop in the smaller jet.

3 jets is a big jump for a muffler and de-snorkel – I suspect you’ll have a happier bike with the 150.

Half a spacer shouldn’t be far off. As for the idle, have you uncovered the mixture screw and adjusted it? Raising your needle shouldn’t affect idle speed too much, but it can affect idle stability on roll-off.

To set idle mixture, best to have the bike ticking over slightly high (just turn the idle screw to give the motor a couple of hundred revs more than normal idle).
With the idle speed set a little high, turn the mixture screw by ¼ turn at a time until you get the highest variation engine speed (maybe just a perceptible change in tone for 20rpm or so) – turn left until it starts to drop and note where it is, turn right until it starts to drop and note that also, then set the screw midway between. When you’ve done that, set your idle speedback to where you want it.

With that set right, she shouldn’t stall.

Title: Re: Carb Jetting Question
Post by eanon on 03/29/08 at 12:31:47

Haven't had a chance to ride her yet, so rpms around 3k, in neutral in my carport. I just switched the main out for the 150, and now she floods at idle. Yeah, I've uncovered the mixture screw. I had it dialed in for the 145, did a quick dial for the 152.5, and now that the 150 is in there, I will give her a little bit, then try and turn her over again. (she's flooded right now!) If I can get her idling nicely, then I will do a quick mixture adj. I installed a tack, so setting the mix screw is relatively straight forward. I'm starting to think the spacer might be to blame. I read somewhere on here of similar problems when messing with that little thing.

Title: Re: Carb Jetting Question
Post by Reelthing on 03/29/08 at 13:08:00

you doing the normal things 1/2 the spacer is general good - maybe a little less, 3 jets is a big jump if you weren't lean to start with from the factory - the 150/152.5 is a very good place to start - soft seat the mixture screw and come out 1 3/4 turns should have you in the ball park - small adjustments from there - if you a flooding out bad it's something else -

you did have washer under the main jet didn't you? - pretty easy to drop the thing - then it's flood city for sure

the slide was as clean as clean right - no oil no nothing?

Title: Re: Carb Jetting Question
Post by eanon on 03/29/08 at 13:15:06

yeah, I got the washer under the main jet. Dropped it once though! Man, that sucked disappears quick... Spark plug is black and sooty. Inside of the carb was immaculate. Gave it a quick once over with carb cleaner anyway. Sounds like it running rich, flooding, black plug. I will try the 1 3/4 on the mixture, (once she starts again!) and dial in from there.

Oh yeah, don't think it's that big of a deal, but I shaved off a little less than half of the spacer. More than a third, less than half.

Title: Re: Carb Jetting Question
Post by Reelthing on 03/29/08 at 13:21:41

5F5B5455543A0 wrote:

ok place to start on the spacer - dang if we only had multiple groved needle stinkin EPA!

anyway .... you should be close - that slide can get real nasty if dirty or it was oiled, or the big spring wasn't straight, or the little tab wasn't in the slot and such

that washer holds the needle jet tube in place with out it the tube will jump up and you end up with an jet about 1/4" wide - not good!

Title: Re: Carb Jetting Question
Post by eanon on 03/29/08 at 13:53:26

yeah, that doesn't sound like it would be! we'll, she's running again, with the 150. Now for a test ride... Hopefully she doesn't stall.

Title: Re: Carb Jetting Question
Post by eanon on 03/29/08 at 14:08:58

Well, she runs like greased owl sh!t now. The rpms still dropped pretty far when pulling the clutch to stop, though I don't know how far because now my tach isn't working! Ah, the joys of the DIY mechanic. Should be a quick fix, atleast. (loose wire) Thanks for the input!

Title: Re: Carb Jetting Question
Post by Reelthing on 03/29/08 at 15:02:40

carry a little screw driver with you for a bit - may need a 1/8-1/16 turn to get to right on - and some fuel, and a long ride through west - hey a run to llano down to enchanted rock should just about break in the new jet!

Title: Re: Carb Jetting Question
Post by eanon on 03/29/08 at 15:02:57

So she stalled a couple of times on the ride. :( When shifting through gears, she runs GREAT!, but when I come to a stop, the rmps drop by at least 500. (had the idle set around 1100, came to a stop, watched my tach drop to roughly 600, then dead) This happened every time I came to a stop. Didn't always die, but came close! If she didn't die, the rpms smoothed back out to 1100. Thoughts?

Title: Re: Carb Jetting Question
Post by Reelthing on 03/29/08 at 15:12:00

likely the mixture is still off a little - idle it up just a bit until you get it right - real small changes from here - like less than 1/8 turns on the screw - any backfires?

Title: Re: Carb Jetting Question
Post by eanon on 03/29/08 at 15:17:58

yeah, a couple times when shifting. (ie - rpms drop for a second) none on shutdown, though I haven't had any on shut down for a while. Will try to tweak the mixture up a little. Thanks, Reel. Best way's to adj. the mixture screw while watching my tach for the highest rpms, then set idle screw accordingly, right? or is it just trial and error? tweak then ride, so to speak.

Title: Re: Carb Jetting Question
Post by gj859 on 03/29/08 at 15:35:19

eanon are you sure you put the tab back in the slot on the diaphragm?

Title: Re: Carb Jetting Question
Post by Reelthing on 03/29/08 at 16:51:34

tach will get you very close - then at least for me it's trail and error - I know I sound like a broken record - little adjustments 1/8 one way or the other and ride a bit - tweek it a bit a more and such - if you have the time, a place to do it, and half dozen on the cheap spark plugs you can do the ole plug chop to find high,mid,low range spot on

Title: Re: Carb Jetting Question
Post by eanon on 03/29/08 at 20:56:13

yeah, I got all the tabs in the correct spot. was real careful about all that. reelthing, you seem to on the money. I dialed out 2-3/8's, and she seems to be running better. Have to go party with the friends now, it is sat night! Will try and do a real fine tune tomorrow and let you know how it goes.

Title: Re: Carb Jetting Question
Post by YonuhAdisi on 03/29/08 at 20:59:10

That is eaxactly what is happening to the FireLizard that I keep posting about, but nothing works. I have tried everything suggested on here.

Title: Re: Carb Jetting Question
Post by Reelthing on 03/30/08 at 07:45:05

696D6263620C0 wrote:

if you @ 2-3/8's your getting out to where a one up on the pilot jet makes sense @ 3 or bit before the mixture screw stops doing much of anything - might consider thinning the spacer a bit more

were you able to lay hands on the stainless hex key bolts for the carb ?

and be sure the clamps on both sides of the carb are tight you need a good seal

Title: Re: Carb Jetting Question
Post by eanon on 03/30/08 at 08:59:26

sorry, I meant 2 to 3 eights past 1 & 3/4, as the initial starting point for tuning. So I guess I was at 2, maybe 2 & 1/8. I went to get some replacement bolts, but freaking Lowe's didn't have any short enough. The had some m8s, but all were too long. Gonna go to home depot today.

Title: Re: Carb Jetting Question
Post by Reelthing on 03/30/08 at 09:07:59

Don't know if you have one around there but the a Sears Hardware/Applnce store here seems to carry a very good supply of stainless metric bolts

Title: Re: Carb Jetting Question
Post by verslagen1 on 03/30/08 at 09:10:40

Long ones can always be made shorter.
And they are not blind holes long ones are ok except for the extra effort. ;D

Title: Re: Carb Jetting Question
Post by eanon on 03/30/08 at 09:12:31

Extra effort? Extra effort? Who do you think I am? Superman? ::) They didn't have any #4 washers either, nor could the girl in the hardware dept. help me at all. Not a big shocker. I just got fed up and left.

Title: Re: Carb Jetting Question
Post by verslagen1 on 03/30/08 at 09:20:38

Was she a distraction or an anoyance? :o

Title: Re: Carb Jetting Question
Post by eanon on 03/30/08 at 16:17:34

not a distraction, unfortunately! :o just annoying....

Title: Re: Carb Jetting Question
Post by eanon on 04/04/08 at 15:07:36

So she's still bottoming out. It's starting to get really annoying, not to mention dangerous. (down shift and hold the clutch in for a turn, and dead bike) Apparently YonuhAdisi is having the same problem. KwakNut and Reelthing both suggested the idle mixture screw (thanks for the input, guys) , which I've been messing with for the last week, and still haven't found the "sweet spot". The only things I changed were the main jet (145-150), and the spacer (took a little more than a third off, just a bit more than half left). She's desnorkeled and has a screaming eagle, if that helps. I'm gonna try putting a washer under the spacer to bring it back up a little. Anybody have any suggestions?

Title: Re: Carb Jetting Question
Post by YonuhAdisi on 04/05/08 at 08:51:42

I know am no longer have that problem (so far anyway).

What I did was take the carb apart again and used some fine emery cloth the sand the slide lengthwise then shot the snot out of it with carb cleaner. I also completely removed the pilot air screw o-ring and all and re-installed it to be sure everything was seating correctly.

I still get a backfire on shut down (sounds like a weak black cat fire cracker going off) but decel doesn't have nary a one. I can now even fire the bike up without even touching the throttle and it idles without holding the throttle open until it warms.