Author Topic: How to tune a weber carb? (Read 11209 times)

TRHS1980 · « **on:** Dec 10, 2006, 08:44:56 PM »

I put a weber carb on my fresh hybrid motor a few months back. I know these things can be a little tricky to tune, and since this is my first carb'd vehicle I have a few questions. Truck diesels sometimes, sometimes it doesn't. I'm pretty sure it's because the carb isn't tuned right, but I'm not sure how to make it go away. Aside from the truck dieseling about half the time, it seems to run really good. Starts up nicely, and once it's warm it seems to work really well. I DO notice a little less power than anticipated, and I also think this may be because of the carb. Questions...

- How could I tell what jets would best suite my application?

- How do you go about tuning the carb to get the air/fuel mixture just right?

- Has anyone bought any of the weber manuals and used them with good results?

- And lastly (a bit off subject but...) what timing is everyone running on the hybrid motors? (and how worked your motor is would help too)

I know this is kind of a dumb question, but I'm more than willing to admit it if I can get some help in the long run. Thanks for the help!

Eliot

kneedownnate · « **Reply #1 on:** Dec 10, 2006, 10:00:56 PM »

The truck PROBABLY diesels because it's idling too fast.

Jetting is a pita, as you can probably guess if you checked my recent thread on jetting a weber. How you jet it will definately depend on how your engine is set up and what elevation you're at. I'd try starting with maybe a 145 main and 160ish air, and leave the secondary alone for now.

I think to get the air mix right you let it warm up then slowly turn the screw in till it begins to stumble or sputter, then back it out till it does it again, then go back in one full turn. I'll hafta see if I can dig that weber tuning page up to be sure though.

Never bought a manual, my manual was my brother but he moved.

I run my hybrid at 8 degrees btdc, just like stock, cause ever since they changed cali gas it detonated slightly under loads, etc. I have a stock 81 block, stock 76 celica head and a mikuni cam (unsure of grind)

TRHS1980 · « **Reply #2 on:** Dec 12, 2006, 04:28:02 PM »

Nate, thanks for the reply. Played with the carb some more today and I think I've got it to stop dieseling... but now the exhaust smells pretty bad. I keep bouncing back and forth between truck smelling and truck dieseling... I'm sure if I ef around with it enough I can probably find a happy medium. What speed you got your truck idling at? I know 850 is stock for 20R and that's what I've been pretty much shooting for. 8 degrees is where I've got mine set as well... seems like I could probably raise that though I may have to put 89 octane in it if I did. I'll try the tip you posted for tuning. Seems like you're right about the idle causing the dieseling, but anything else I should check out? Like I've stated previously, motor is fresh... almost everything in the engine bay is new... thanks for the help man!

Eliot

79coyotefrg · « **Reply #3 on:** Dec 12, 2006, 05:59:36 PM »

mine idles at about 1000, a little fast but with my cam thats a smooth idle

TRHS1980 · « **Reply #4 on:** Dec 12, 2006, 06:19:59 PM »

Yeah... I've heard that lumpy cam of yours...

blackdiamond · « **Reply #5 on:** Dec 12, 2006, 06:59:49 PM »

I have a weber on my 22R and it likes nothing but quality brand premium fuel. It runs great on the stuff, but anything less and it gets rough and starts to diesel. I'm not much of a mechanic and it runs fairly well so I have not messed with the carb much and I know the timing isn't perfect but the last time I played with it the truck only ran worse so I wet it where it was and moved on. I'm looking forward to the 89 4Runner and regular fuel.

kneedownnate · « **Reply #6 on:** Dec 12, 2006, 10:42:33 PM »

When you say fresh hybrid, does that mean the top of the pistons and combustion chambers were totally clean? I ask because carbon buildup can cause dieseling too, and a can of sea foam is supposed to get rid of that.

When I put mine back together it was idling about 600-650 and had a lopey idle. I got it up to around 800, maybe a tad higher, and it idles smoother but still has a little lope. Not sure if it's due to my cam or? I may hafta bump it up a little, but it sure beats the 1000-1100 it idled at before I went back through it.

I tried to get everything set back by eyeball when I did the headgasket, and it ended up at 7 degrees so I left it there. I also adjusted the air mix screw just after bumping up the idle, and while it had nothing to do with idle speed or smoothness it did drastically decrease my throttle response and nearly squash my hesitation.

TRHS1980 · « **Reply #7 on:** Dec 13, 2006, 10:43:43 AM »

Fresh hybrid meaning completely rebuilt motor with all new or rebuilt parts... only has like 2000 miles on it. I think maybe this weekend I'll pull the plugs and see what they can tell me. Like I said before, I know the stock idle for 20R is 850, so I would imagine with a mild cam in there it may not idle completely smooth until even higher than that. But with idle set at 850 the truck is dieseling and that confuses me a bit. I found some instructions on tuning the carb that are a little more in depth than anything else I've come across. Hopefully if I follow those the truck will idle nice without smelling up the place or dieseling... If not then

I'll post my results when I find the time to play with it some more.

TRHS1980 · « **Reply #8 on:** Dec 14, 2006, 12:50:40 PM »

Okay, well I just used my lunch break to try and get the carb tuned right again. I followed the instructions found here http://www.redlineweber.com/html/Tec...lean_best_.htm since they were much more in depth than the instructions that came with the carb. Truck seems to be running real nice, idle probably about as smooth as it's going to get, and I'm pretty sure the exhaust won't be suffocating me anymore. Only time will tell if it fixed the dieseling problem, but I think it's probably gone. As I already knew, the truck needs rejetting badly. Haven't gone back and counted how many turns the idle mixture screw is out, but I'm pretty sure it's around 4 or 5 turns meaning bigger jets here I come! Anyway, once I know the dieseling problem is gone, I'll post up exactly how many turns it took and how things are going. Also think I'm going to up the timing to about 10 and see how she likes it.

Hilux92 · « **Reply #9 on:** Jan 03, 2007, 09:28:03 PM »

Changed my jetting last night on my 32/36. Primary fuel 140 with 170 air. Secondry 142 with 160 air. Ran well this morning on the way to work untill my acccelerator cable broke

kneedownnate · « **Reply #10 on:** Jan 03, 2007, 10:46:22 PM »

Quote from: Hilux92 on Jan 03, 2007, 09:28:03 PM

Ran well this morning on the way to work untill my acccelerator cable broke

$I\'m Down$ that's a bummer man!

TRHS1980 · « **Reply #11 on:** Jan 03, 2007, 11:32:48 PM »

Sorry to hear that man

But please do keep us up to date on the overall performance, once you get that fixed.

te51levin · « **Reply #12 on:** Jan 03, 2007, 11:53:41 PM »

I just spewed out the method I use in kneedownnate's thread at http://board.marlincrawler.com/index.php?topic=28989.msg317358#msg317358, if you want to take a look there. It's less complicated than it sounds.

79coyotefrg · « **Reply #13 on:** Jan 04, 2007, 06:55:36 PM »

i have been talking to Bud at Redline/weber and he is going to help us ALL

stay tuned

kneedownnate · « **Reply #14 on:** Jan 04, 2007, 07:27:36 PM »

I thought weber was in the middle of a 3 year strike

Or is redline just the western distributor for weber parts?

79coyotefrg · « **Reply #15 on:** Jan 04, 2007, 08:27:44 PM »

mickeyfinn · « **Reply #16 on:** Jan 04, 2007, 08:32:30 PM »

let me know if you need any jets for these carbs. if you get a # i can probably get it

Hilux92 · « **Reply #17 on:** Jan 04, 2007, 09:02:05 PM »

My truck is running so well now withthe current settings I am not touching it. I can travel at say about 120kms hour and still accelerate. I dont need to stand on the gas to get it going. I can cruise on the 1st stage with great economy. Off road this carb does not miss a beat

. Love it.

TRHS1980 · « **Reply #18 on:** Jan 04, 2007, 09:10:25 PM »

Quote from: te51levin on Jan 03, 2007, 11:53:41 PM

I just spewed out the method I use in kneedownnate's thread at http://board.marlincrawler.com/index.php?topic=28989.msg317358#msg317358, if you want to take a look there. It's less complicated than it sounds.

Yeah I've been keeping up with that thread as well. Thanks for all the info!

Quote from: 79coyotefrg on Jan 04, 2007, 06:55:36 PM

i have been talking to Bud at Redline/weber and he is going to help us ALL

stay tuned

That's way cool coyote.

TRHS1980 · « **Reply #19 on:** Jan 04, 2007, 09:15:39 PM »

Quote from: Hilux92 on Jan 04, 2007, 09:02:05 PM

My truck is running so well now withthe current settings I am not touching it. I can travel at say about 120kms hour and still accelerate. I dont need to stand on the gas to get it going. I can cruise on the 1st stage with great economy. Off road this carb does not miss a beat . Love it.

Nice! That's what I want to hear. Can you please provide specs on the engine? Is it stock? Miles? Thanks

Hilux92 · « **Reply #20 on:** Jan 05, 2007, 01:51:03 AM »

I have the 4y, 2.2 litre and have 6000kms on it since I rebuilt it.

yoter4x4 · « **Reply #21 on:** Feb 22, 2010, 05:42:21 PM »

can someone possibly help a brother out here as well? i've got a reman 20r in my truck now, about 2000 miles on it and my weber treats me like total crap..

i don't know what my timing is set at, but truck runs fine on some days and like crap on others, i have tuned the carb a few times and been happy with the results, but it always goes back to kinda sputtering as i drive at a steady speed or hesitating at acceleration from a red light or something. i'm losing my mind having to pull the screwdriver out every day and adjust the srews over and over..

Can someone school me on what screw is what? i have, i'm guessing, a throttle adjustment screw with a spring on the screw which is on the bottom passenger side of the carb, i have a brass/gold colored screw underneath the air filter on the passenger side of the carb, and another brass/gold colored screw on the driver side of the carb right under the air filter. the driver side screw doesn't seem to affect how it runs no matter where its at, the passenger side brass screw brings the idle way down to a sputter every time i back it out.. but my response seems much better when its backed out. and of course my throttle adjustment screw just turns the idle up and down.

i know this same thing has been asked a few times in here, not trying to jack a man's thread... but this damn carb is driving me nuts

thanks guys for any advice to get this thing somewhat on trrack.

79coyotefrg · « **Reply #22 on:** Feb 22, 2010, 06:06:12 PM »

wow way to bring up an ancient thread

you had to have seen the main weber thread since you replied to this one

weber knowledge, read--> http://board.marlincrawler.com/index.php?topic=45126.0

THE ROCK · « **Reply #23 on:** Feb 22, 2010, 07:40:17 PM »

:twocents:Most webers are running way too rich! I purchased a "Haynes" manual from the local parts depot..it was very informative..they are actually easy to overhaul and tune..read the chapter sevral times.. $Beer Chug\'n$ then it all makes sense! I run a the 38DGAS (outlaw) carb on my 22R/ 20R head, cammed, header, the whole 9!

A lot of the problems are associated w/ improper fuel pressure( My stock mech. pump was pushing 5 PSI), float levels, and mis-adjusted linkage..Buy the book!

jcm · « **Reply #24 on:** Feb 22, 2010, 07:54:29 PM »

I also have the Haynes weber carburetor manual #10240 it really helped

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