Weber 32/36 Backfire (1 Viewer)

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Joined
Nov 28, 2008
Threads
103
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867
Location
Sparks, NV
Just installed a New Weber 32/36 onto the F145, idles better then ever...but...when I step on the gas the engine boggs down and the carb backfires. :confused:
 
Mine does that til it warms up. Since I have a header and not the stock manifold it takes about 5 miles on a cold day to warm the big turd of a motor.(and the carb)
 
I am sure you have done this but you need to check your vacumn line from the distributor to the carb and make sure in is vacumning:D:D.
 
Lack of timing (aka vacuum advance not working or incorrectly hooked up) too lean (aka vacuum leak, or accel pump needs more fuel dumped when opening throttle or idle/transition jetting too lean).

Does this happen once it's warmed up? IF it's only when cold, then it's too lean. If it happens after the engine is warm, then it's 50/50 lack of timing or too lean.

Does it happen if you snap the throttle or slowly accelerate, or both?

If it happens when you snap the throttle, check for vacuum leaks, then adjust the accel pump to give more fuel. If it happens even if you slowly accelerate, then suspect a lack of timing. You should be on ported vacuum on the carb for vacuum to the dist. That's the one that only has vacuum after the throttle plates are opened.
 
Just installed a New Weber 32/36 onto the F145, idles better then ever...but...when I step on the gas the engine boggs down and the carb backfires. :confused:

you still have to tune it,and possably have the distributor recurved, it should have come with tuning and jetting directions, webers are in world of there own. but it will work great when it is done right ,, dr smash is great with weber carbs and reasonable
 
Sent the carb back to EMPI, and they "Said" they could find nothing wrong with it and ran it on there test engine. Got the carb back today and installed with no changes. When the secondary opens the thing falls on its face. My vacuum is a little low, but the Toyota carb performs O.K...well doesn't fall on its face anyway.
 
You need a Weber tuning book and a little time.

Falling on it's face when the secondaries opens is a sign of improper tune somewhere. You need someone to follow you and watch the tailpipe. If you get a big cloud of black smoke when they open, and it keeps pouring black smoke as it stumbles it's too rich and falling on it's face. If you get a black puff then the engine falls on it's face, it's too much carb opening, too soon and loss of venturi vacuum, leading to the stumble.

Normally, if you have mechanical secondaries and you are stumbling when you open the secondaries, it's a sign of too low rpm for the added airflow from the carb. It will dump a bunch of fuel for just and instant, then the vacuum will drop due to the carb adding more air than the engine can use, the velocity of the air past the booster falls and the fuel quits flowing into the engine, causing a lean out and it falls on it's face.

I'm just going to throw out some guesses here, so I might be completely off.

The factory F motor probably won't use more than the primary side of that carb until after 3K rpm. If you dump open the secondary side, under 3K rpm, it's likely to fall on it's face if you open them too fast. If you lean into them as the tach climbs past 3500, and be wide open at about 3800-4000 rpm, I bet the stumble goes away.

You have several things working against you here.

1. Low compression.
2. High altitude.
3. Stock camshaft.
4. Poor head port flow.
5. Stock exhaust.
6. Heavy rotating assembly, made more for low rpm grunt than high rpm running.
7. Too tall gearing.
8. Heavy vehicle.
9. Heavy tires/wheels.

The quickest way to cure your issue is to not jump into the secondaries too soon, jet it for the altitude, and clean up the exhaust and intake flow so that motor can use that big carb.

It's far, far easier to make power and mileage with a carb that is too small and an engine that is very efficient, than it is to put a good carb on an engine that just can't handle it.
 
The factory F motor probably won't use more than the primary side of that carb until after 3K rpm. If you dump open the secondary side, under 3K rpm, it's likely to fall on it's face if you open them too fast. If you lean into them as the tach climbs past 3500, and be wide open at about 3800-4000 rpm, I bet the stumble goes away.

You a funny guy, an F motor spinning past 3500 rpm :lol::lol:

I agree, it sounds like too much too soon.

Gotta remember you are dealing with a 40's technology motor (GM design) that was kept alive for a reallllly long time. Putting a "big" carb on a slow turning torque motor that originally ran a small single barrel is going to be a little bit of a challenge to "tune" correctly. As others have said, get the info and start addressing it methodically and you will be happy. I don't think you will happy with it any other way.

Jack
 
I really should find out which Weber I have on my FJ40, it out performs the stock Asin carb by a long shot. Foreign Automotive did the swap, they used to be over on Gentry but have been gone for years.
 
Gave up on the Weber, complete disappointment, could not even get close to getting it to function. Will probably sell it on EBay. What a waste.
 
Before you do that, have you gotten someone else to help you that has tuned one before?

Don't give up, it's always right before you torch the rig that you figure out something stupid was holding you up.
 
Gave up on the Weber, complete disappointment, could not even get close to getting it to function. Will probably sell it on EBay. What a waste.

a weber kit is a direct bolt on but needs to be fine tuned to work right
 

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