Weber jetting...again...yes I know. Specific questions.

[HRH]

I realize there are a bunch of threads on this topic, but I cruised all of them and didn't find any consensus.

 

I built a 521 for a customer. New L20B .020" over, .030" off the U67 head, and a Weber 32/36. The weber in question is an original Made in Italy Weber which was from Pull and Save courtesy of Len, not sure how long ago or the condition of the car or even what it came off of.

 

Anyway, had massive air leak issues with the manifold. Ended up planing the shit out of it, making an adapter plate, and got the air leaks fixed. Also took the carb and dunked it in Pine Sol for a couple hours, which works wonders by the way. Manifold is the same size as the intake ports, not port matched exactly, but close enough. Cam is stock.

 

The motor runs sweet. Carb, not so much. I started with it at baseline settings.

 

Idles: 50/60

Pump jet:50

Air correctors: 170/160

Mains: 140

 

It would fall on it's face in transition. Ran it by Joe, Joe seemed to think it needed more fuel on the primary side, which I agreed. We drilled out a 150 jet for about 160, made a huge improvement. Ended up going with a 150 main in the secondary side. She's almost perfect, but still has a slight hiccup in the transition. It's odd, because for basically stock besides a little higher compression, I've never had to jet a Weber so big to make it run well.

 

I'm tempted to blame the carb, but I doubt that's the case. I cleaned it, blew it out with air, throttle shafts seem good. Venturi oval holes are in the correct position. Etc. etc.

 

Has anyone else run into issues like this on a fairly stock L20b? I'm going to try one more size up on the primary side tomorrow morning and see if that cures the last of the issue.

 

Oh, and also, unlike previous Webers, I have to unscrew the idle mixture screw much farther out to make it run right. But needed more than a 50 or 60 idle jet it certainly excessive. I almost pondered if somehow the idle mixture hole had gotten enlarged or something. Yet I can turn it in and shut off the carb, and pull it out, gets richer, just like it should.

 

If anyone has any brilliant nuggets besides buy a new one (I already told that guy I'm building this for that may be the option should it not be able to get perfect) I'd love to hear them.

[mklotz70]

If I lived up there, I'd be asking Creepy!! :)

 

Any chance it's the vac advance not coming on quick enough?

[EricJB]

I've ran into a few setups ( L16 with a huge exhaust comes to mind ) where the primary idle was too small. If you give it real light throttle in 1st gear does it rev up to a point and then stutter? I have had to go as big as a .70 idle to get rid of transition stumble. Good luck.

[HRH]

Both good suggestions, thanks. Think I'll try disconnecting the vacuum advance first and seeing what changes.

[Stupid_fast]

Does it cut out and then accelerate(lean stumble), or sputter accelerate slowly then pick up(rich stumble)?

 

Idle is too lean, a 60 main/ 55 secondary should be sufficient for a stock L20b.

 

A 160/150 (primary/secondary) seems too rich for a stock motor, is yours cammed? should be more like 145/150. Maybe 150/155.

 

I've been working this out of my car, but with a heavily cammed (.490 lift) L20b.

[D52E]

couple things to check:

Throttle shaft for vacum leak - aftermarket sealed bearings available (I think 8mm ID and 12mm OD)

Also brass tube inside the secondary venturi that supplies fuel - tube loosens and rotate so the slot faces up not down

 

 

http://www.bmw2002fa...ighlight,weber/

[EricJB]

Does it cut out and then accelerate(lean stumble), or sputter accelerate slowly then pick up(rich stumble)?

 

Yes, it is important to distinguish between the two, or you can go the wrong direction. This is why I always go 1 jet size at a time so I dont go from one side to the other. Rich will be more of a chug ( rut rut rut rut) but it wont nose over and spit. Lean will sputter, spit and nose over. Based on the #'s I would agree that the primary idle is lean.

[HRH]

D52E, yep, checked that.

Stupidfast, yep, seems to rich for a stock L20b in my opinion too.

 

I'm going to swap out the distributor just to eliminate one more variable. I did find one issue. The 50 and 60 idle jets were reversed. They had 50 on the primary side. I now have a 65 on the primary side and a 60 on the secondary side. Turned up the timing to 17 and "almost" got rid of the issue completely. It's too much advance for it though. Consequently, I'm trying the distributor just to see if something is wrong with the matchbox or internals. If it doesn't change, I'm headed over to Joes to use his gas analyzer. I was going to do that yesterday but I got it so close I figured I was going to get it.

 

This truck is kicking my ass left and right. Sigh.

[Stupid_fast]

Its carb, a stock motor that is easy to tune out by feel.

 

Swap the idle jets, 60 primary/ 50 secondary, make sure it feels good 1500-2500rpm, then start messing with the primary jets.

[I'm BLUE]

Go to where that diagnostic's machine is and dial the sucker in

 

Sounds like you're having non-carb issues that you're trying to compensate with richening the carb ? ( as you said you've NEVER had to run one so rich on a stocker L20b )

Vacuum leak ?

Slipped or sloppy timing chain ? ( stick your timing light and check to see if it bounces around = if it does it's stretched or loose ( credit---: MicroMachinery ) )

 

*Distributor not pulling around is going to cause headache's ... it has and did to me on my L24 ( which by now a good portion of these distributor's are dis-integrated inside lolz )

*Old School = stick a vacuum gauge on the engine and record condition's/issue's. ( tell a lot from a vacuum gauge as you know )

*Power Valve = check/tested/replace ?

*Float = was it changed out ? Not cracked or per-forated by now ? ( They crack/or fill up with gas as well )

*Pump Jet = I've had to go "up" on a few of my Holley and Weber 32/36's ,,, along with cam profiles on the Holley ... Big difference and least intrusive/more-sanity than swapping 1,000,000 jet combination's lol.

*Make damn sure the muffler isn't clogged ... even partially.

*I always tune my Holley's by Holley Spec's = 2 jet size's up or down whichever way ... then fine tune once in ball-park ... I imagine 1 jet size at a time is best approach. Holley state's more than 2-jet size's in either direction ... then you probably need a different carb lol (luckily not me)

*Throttle shaft's/bushing's (even on webber's) get worn as you well know , and sometime's harder to catch !

 

I've never jetted or owned an L20b.( or a 4-cylinder datsun for that matter )

I personally wouldn't worry about the idle's as much as the rest.= idle is idle lol.

 

Usually when people think they are fighting carb's (myself as well) they are fighting other issues not-calculated or found in the picture imho.

 

Overly rich condition = is compensated for broken/lack of dizzy advancement or vacuum leaks that I've experienced. Whether that be over-torqueing the carb fastener's or even a pcv valve not hooked up correctly lol.

 

Pine-Sol ? stuff can't possible be as good as Carb Dip anything/any-brand can it ? ( I like berryman's fine )

 

I'd make a check-list and tripple check everything

 

Best Luck :)

[HRH]

Thanks for all the help guys. I figured out a big problem I should have looked at in the first place. Had the butterfly open too far, it was going past the air bleeds, causing vacuum. Dialed that in, re-timed. Repositioned the cam for #2 hole. Set on #3, forgot this wasn't a lumpy cam. Anyway, she's running now on stock jetting, there is still a slight hesitation but it's almost not noticeable. It does smell too rich on idle. I think a .55 jet would be better than the .60 in there now, but I don't have a .55 and .50 is too lean. So that's the way it's going down the road. I told him he can take it to get it dyno-tuned with a wideband if he so desires.

 

I'm still annoyed at my inability to tune this thing. Wish I would have made him buy a new carb, that way at least that variable is out. Whatever, tomorrow morning it should be gone and then I will have much less stress again. And maybe I'll even get to enjoy my vacation! :D

 

It also reminded me of just how much I love my hardbody! Especially the drum brakes on the 521. Definitely needs a disc upgrade. Scary stopping.

[I'm BLUE]

:thumbup:

 

(that's how he really feels folks)

 

enjoy your vacation.

[mklotz70]

Just as an added note of info for future readers of the thread..... The matchbox dizzy really prefers a dedicated ground to it's body. I've seen several running issues fixed with a simple wire on multiple vehicles. with the matchbox. It uses a lot more current than the point dizzy and the old, oily bolts just don't provide enough contact through the engine.

 

Also...glad you figured out the butterfly being open. I was going to mention that, but it sounded like you've dealt with webers before. They're really touchy about how they're adjusted. As you found out, they like to have the butterfly closed as much as it possibly can be......that's the number one goal with the weber DGV. I've also found several webers that had to have the butterfly on the secondary loosened up and re-centered because it was open slightly.....but that cause a high idle typically. Anyway.....glad you got it fixed :)

[fivetenguy]

So much good info here, guys. Thank you all....

[LenRobertson]

Hey Matt - It is a good thing you traded me out of that carb. If I'd kept it, I'd probably just have bolted it on and run it with it running like crap and lived with it! Although I may (or not) have noticed the missing idle screw and replaced it. Now I know a whole lot more about Webers, which is good cause it is hard to tell what may be wrong with the electric choke one I still have. Not that it matters, but I'm wondering if the carb you have came from the same 620 guy in Hillyard I got the other three from. That would explain why I don't remember taking it off at P&S. Anyway, good to know you can get the PU out of your shop. And start on your KA swap, right? Eagerly waiting for your build thread on that one!

 

Len

[HRH]

Truck should be gone around 9:30 this morning. I'm almost too scared to go back it out of the garage. I don't even want to breathe in the wrong direction at it. ;0 I think I'm going to do a few more things before I start on the KA swap. Need to swap all the T12 fixtures in the garage for T8s. Did you know it's cheaper to buy an entire light replacement than it is to buy a ballast? Freakin' silly.

[HRH]

HOLY DOG BALLS! I figured it out. So I went at it again this morning, before my customer came to pick it up. Kept wracking my brain trying to figure what in the carb could be bad still. All of a sudden it occurred to me: What's the one major piece that doesn't come in a Weber rebuild kit?

 

Yep. Power valve. The bottom in the bowl is usually never an issue being just a brass spring needle. However, the top power valve that actuates the bottom has a three hole diaphragm. And I didn't have a spare, so guess what wasn't changed? Luckily, Litehouse in town stocks some Weber parts. After being raped for $32 for a power valve, it runs damn near perfectly. Best $32 bucks I've spent in a long time.

 

So now, I can get rid of the truck without worry. My tuning skills aren't shit. Apparently my Weber revival skills need some work. In retrospect, I should have disassembled the carb entirely, soaked it in pine sol for a day, and ordered a rebuild kit and power valve so I could get it within a week at less cost. One friggin' part I just overlooked. And simple too!

 

Truck is now gone, yay!!!!! ;)

[Farmer Joe]

okay, so what jetting did it end up having?

 

were having the same issue with wides KA with the weber.

 

you can roll into it, but if you punch it into the secondary it falls on its face. it could very well be the same power valve issue...

 

i already enlarged the primary idle jet ever so slightly to get it to idle with the 2400.

 

would i enlarge the secondary idle jet to get the transition smoothed out?

 

im pretty sure it needs main jet adjustments too, but thatll wait.

[HRH]

Jetting ended up being back exactly at Weber original spec. 50 idle primary, 60 idle primary, 140 mains, 170 air primary, 160 air secondary. Odd huh? I'd go for the power valve or float misadjustment.

[HRH]

For the head flow of a KA24, I'd say you're going to need quite a bit more jetting. I'd say at least 1.50 mains, 180/170 air correctors, and probably 60 and 70 idles. The idle mixture screw has a lot to do with the transition. You're going to notice the secondary quite a bit more on a 2400 as it's really too small for that motor. I was going to do a 32/36 KA, but I was going to use dual 32/36s.

 

Either way, the power valve may not be operating. Even too small for the motor, it should transition smoothly, you just won't get any power out of it.

[mklotz70]

I've always heard that the stock weber 32/36 was designed for a 2.5 motor. If so, it should work pretty nicely without mod, but if not, I wonder what size it was actually built for.

[HRH]

More like 2 liters. 2.2 you can still do it, but the 3236 is only about a 200 cfm- 250 cfm carb. More displacement just needs more to run right.