Still adjusting jets - Now with charts and stuff!!

[Soloratov]

Ok, so I still have an annoying dead spot...but after some testing I decided to not only mark the throttle, but make a pretty chart too!
I also adjusted the valves ever so slightly since the intakes were a bit tight. Anyway. The test setup:

1990 - 17K miles
40/150, 1 washer, 3 turns
K&N Lunchbox
883 Sportster Exhaust slip-on

What I notice is between 1/4-1/2 throttle, the bike just bogs down hard. It hesitates and surges a little until I get past that 1/2 way mark. Then it's off like a rocket.

[BockinBboy]

Can't believe no one has commented on this yet... but then again... there is 'jetting' in the title! 

Props on the chart - Diggin' it!

That sounds like a transition issue between the jets.  Another washer might help.

Have you done a plug chop at that spot and WOT?

When my carbs in my three jet '04 were stock, I had a surge between 6-8k at half throttle - it pulled harder there than any other spot - so much, it kinda' set me back in the seat (yes, I'm talking about a GS! lol) That surge seemed a little exaggerated on the seat because just before it pulled, it seemed to hesitate for a second. I did a plug chop there and found my plugs were white.  But brown at idle and WOT.  I added a washer, and then it pulled smooth all the way up - plugs looked pretty darn consistent after that too...

It just sounds very similar, but more prominent in your case - possibly more prominent due to two jets vs three 



- Bboy

[bombsquad83]

The first thing before doing any jetting changes is to make sure the float height is spot on and stable.  The clear tube test I'm sure you've heard us mention before.

Your jetting seems reasonable for your set up.  Have you replaced your old diaphragms?  Old diaphragms can be stiff and cause problems on transition.  My bike performed much smoother once I replaced the diaphragms. There may be something you can do to condition the old rubber, but new diaphragms are relatively inexpensive.

[Soloratov]

I will start with, thanks for the replies....

First, Bombsquad:

I did a float check as one of my first tests and everything is spot on. I also checked the sync and both carbs are nice and in line. The diaphragms were removed when adjusting the current setup, and they are nice and soft. No dry areas or splits.

Bockin:

I figure it has to be either tail end of the pilot jet, or the washer-main jet transition. So I planned on either going up one pilot jet, or adding another washer. I'm guessing as you mentioned it's probably very pronounced due to only 2 jets. I did a plug chop, a good one, and to be honest I wasn't really sure what to think. I have iridium plugs, and the insulator was nice and brown, and the strap was maybe a bit lighter than I would like so I will try a washer and see what happens. I can't imagine an 883 muffler is all that different than say...straight pipes that use the standard 40/150/1 washer setup....I guess I could pick up some 42.5 pilots just to try but that's really just a pain.

[The Buddha]

Your symptoms get better when you open the throttle slowly ... sorta open only a little and as the motor starts to catch up open more and so on ?
If it does that, then your slides are rising too fast. You may need to close 1 hole in the slide.
Does the bike run fine when you are holding steady throttle @ just under 1/2 lets say ? Then, your problem is definitely the slide rising too fast.
If it acts pops and misfires or surges and what not at steady throttle, then its lean and your float may be low.

Remember problems when opening throttle are rich.
Steady throttle problems are lean. And you can be either, and still have slide rising issues, or be spot on and have slide rising issues.

Cool.
Buddha.

[The Buddha]

42.5 pilots will give you really really crappy take off, unless you rev it to 3500 everytime at take off, or the motor has had flow work done on the head.
I've read your post again, your jetting is fine. Brown is fine, anywhere brown is OK, the parts that will get the color is where it will get color ...

Cool.
Buddha.

[bombsquad83]

Buddha makes a really good point with carb tuning that makes sense to me in his second paragraph.

Remember problems when opening throttle are rich.
Steady throttle problems are lean. And you can be either, and still have slide rising issues, or be spot on and have slide rising issues.

However, in his first paragraph I don't agree with plugging a hold in the slide becuase it's rising too fast.  I think that plugging a hold would actually make it rise faster because there would be more vacuum exerted on the top of the diaphragm. 

It makes more sense to me that your diaphragms are stiff or leaking (possibly not sealing around the edge due to age?) and not rising when they should.  I would think in this case you would see the behavior you are describing, which is basically like taking away the 1/4 to 1/2 throttle.

[Soloratov]

I completely disassembled the carbs (just in case I missed some cleaning), and did some checking. Everything looks great. Decently clean, nothing weird.

I double checked the diaphragms and they really are very nice. Soft and rubbery, fit nicely and seal well. I'm going to have to go with The Buddha here, only because what he describes is spot on. No matter how fast or slowly I accelerate between 1/4-1/2 she just gives up. I could roll on as slow as grandma and I hit the mark, she's down for the count. I hold steady, and it's like I'm forcing it to run against it's will, but get it past 1/2, and away we go.

I'll stick with the current jet setup, but double check the floats, spray around for some air leaks, and then add a washer at a time to the needle and see if I can get it richer. Testing shall resume tomorrow.

[The Buddha]

I'm going to have to go with The Buddha here, only because what he describes is spot on. No matter how fast or slowly I accelerate between 1/4-1/2 she just gives up. I could roll on as slow as grandma and I hit the mark, she's down for the count. I hold steady, and it's like I'm forcing it to run against it's will, but get it past 1/2, and away we go.

No its not slide coming up too fast ... if you open it like a grandma - it should accelerate pretty much without any symptoms of the issue. Unless you grandma's name is Danica Patrick ...

I'm Stumped.

Cool.
Buddha.

[The Buddha]

Buddha makes a really good point with carb tuning that makes sense to me in his second paragraph.

Remember problems when opening throttle are rich.
Steady throttle problems are lean. And you can be either, and still have slide rising issues, or be spot on and have slide rising issues.

However, in his first paragraph I don't agree with plugging a hold in the slide becuase it's rising too fast.  I think that plugging a hold would actually make it rise faster because there would be more vacuum exerted on the top of the diaphragm. 

It makes more sense to me that your diaphragms are stiff or leaking (possibly not sealing around the edge due to age?) and not rising when they should.  I would think in this case you would see the behavior you are describing, which is basically like taking away the 1/4 to 1/2 throttle.

We plug a hole. It does slow the slide, the air on top gets out slower and the thing rises slower. Its well known. DJ supplies these plugs and drill and tap ... and I suggest you use a 4-40 tap available @ homedepot and a plastic screw (also HD issue)
A diaphragm with a leak (either @ the edge or the middle) will not come up past a certain point at all. The result will be a bike that refuses to rev past a certain throttle position. Remember - throttle position, not rpm is what carburetion is all about.
Cool.
Buddha.

[The Buddha]

Solaratov - all I can think of is - well your exhaust can.

Its a weird issue I have never before heard of or experienced, and I've done over 50 bikes personally (OK OK before you think I am some sorta super man mech - 18 of them were mine) ... the 150/40 setup on a 89-00 with pipe and K&N is almost a slam dunk. If people got issues its either a second washer or a air screw or float type issue.

So I'm guessing your pipe is the culprit, cos no one I know has run a sportster can. Either remove it and try it or see if you can persuade a local guy to donate a can to fit and try. I would bet it changes ...

Cool.
Buddha.

[Soloratov]

Thanks Buddha. I actually found a few things. I had taken the carbs off to do some checking and cleaning, and I found the floats were off after all. I had the covers off and with the carbs upside down I measured and they were sitting way low...sitting at 11.5-12mm. So, I adjusted to the 14.5 in the book. Also, I reset and made sure both sides were synced, and then reset my mix screws at 3 turns...figure it's easier to count off the bike. So...I will get it all put back on, and test with 1 washer, then 2 if needed. If it improves great...if not...I'll be sad because I really like the low slung exhaust, and it sounds great! All part of the experiment I suppose.

[The Buddha]

He he, OK. Make sure the float level is @ the top of the bowl via U tube method.
Cool.
Buddha.

[The Buddha]

The first thing before doing any jetting changes is to make sure the float height is spot on and stable.  The clear tube test I'm sure you've heard us mention before.

He he, Bullseye - bombsquad ... Now being bombsquad is that success or failure ? Or both.

Cool.
Buddha.

[Soloratov]

In all fairness, I did the tube test...but now that I think back it was during a time of frustration, and I only did it when I went to drain the carbs....on the side stand....

[bombsquad83]

The first thing before doing any jetting changes is to make sure the float height is spot on and stable.  The clear tube test I'm sure you've heard us mention before.

He he, Bullseye - bombsquad ... Now being bombsquad is that success or failure ? Or both.

Cool.
Buddha.

Just hope that I was able to help.  Thanks for the educating on the slides.  That has to be one of the most complicated pieces of tuning CV carbs.

[Soloratov]

Any input is help Bomb. Even if it just got me to double check things...which obviously I needed to do!

[Soloratov]

Well...I think...THINK i have it fixed. The hesitation is now extremely subtle, and only noticable when I settle into a constant speed. Even then it's very slight. But...LOOK AT THIS RIDICULOUS ADJUSTMENT!

3 Turns
40 Pilot
150 Main
5...yeah. 5 WASHERS

Doth me thinkst I need to go up another main size?

[bombsquad83]

I still think your diaphragms are causing this.  This is only a theory, but I think bikes of our vintage (early 90s) that have likely sat without use for a long time suffer from a stiffening of the diaphragms.  They may look soft and not have any pin holes, but it takes more vacuum than it should to get them to lift out of the resting position that they have sat in for so long without use.  I know my bike suffered from this and didn't appear to have anything wrong with the diaphragms. Anyway, it's just a theory.

Other thing is, what is the marking on that needle?  I believe if it's stock it should read "O-3".  Looks a little fatter at the bottom than I remember, but it's probably unlikely it's anything but stock.

EDIT: O-3 is actually the needle jet number for a stock carb.  The jet needle you pictured should have "5DH8" on it if it's stock.

Oh, and it's still very possible you should need 2 to 3 washers even with an otherwise perfect carb set up.

[bombsquad83]

By the way, I hope nobody here mistakes me for any type of expert.  I'm just sharing my thoughts based on my (limited) experience, which I hope will be helpful.