2F Carb Problem Help ? (1 Viewer)

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I got a 1976 FJ40

it starts fine and idles good

but when you get it on the road it hesitates a lot

it runs much better with choke 1/2 way out

it has been smoke tested and has 20" of vacuum at idle, doesnt seem to be an intake manifold leak

ignition / timing / vavle clearence all checked and set to specs

any ideas before i rip the carb out of it, i keep thinking its something simple because it starts/idle's so good

mechanic says its leaned out and the next move is to rebuild the carb

i was going to check the jet size with a split screwdriver and see if i could solve problem with a bigger size, stock should be 1.44 according to sor

thanks
:confused:
 
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What do you mean hesitates a lot on the road?

Hesitation usually happens only under acceleration: You give it gas and it bogs down rather than accelerating. If it is happening at high, steady speed it is usually misfiring. If it bucks and spits back through the carb, it may not be getting enough fuel.

What is a smoke test?
 
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its during acceleraton, doesnt really backfire/buck

mechanic has a snap-on smoke generator that he floods intake with and looks for leaks, there was a real small leak at the heat shield gasket where the intake/exhaust manifolds bolt together but he tighted bolts and it stopped
 

65swb45

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Are all of the emissions components still installed?

If so, have they been tested per FSM to see if they are working?

If not, do you know what provisions were made during the desmog for the carb to work as a 'stand-alone'?

Best

Mark A.
 
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mark

it was totally restored with all oem smog equipment and rebuilt smog pump

got another big clue this am

if the vacuum hose to the power vavle #8 is removed at the air horn and plugged the truck runs perfect. no hesitation during acceleration and it runs worse if you pull the choke out 1/2 way

with the vacuum hose off of the power vavle this allows the vavle to open at less than full throttle and it gets more gas

sure looks like 1st main jet problem ?

dont have time to remove jet and check size today

thanks
 
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Unplugging the power valve line just makes it always open and it will run really rich. Carbs don't typically need to be rejetted unless it went from a high altitude environment to sea level. Rejetting it would probably be a band aid for what ever the real problem is. Is the EGR valve stuck open? The primary main jet on a '76 CA carb is 124 to 134. I have seen both.
 
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checked egr vavle with procedure in toyota emmissions manual it opens/closes just as per manual specs

since opening the power vavle solves problem wouldnt you say its not ignition and has to be in the carb
 
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I wouldn't rule out ignition timing contributing to this just yet, even though enriching the mix cures the hesitation. Make sure that the mechanical advance is working properly. If you live in CA, just putting in a larger main jet may cause it to fail SMOG check because the CO may be too high. Rejetting it would be easy if you have an air fuel ratio meter, but taking it to a smog check station to see if the jet is correct could get expensive.
 
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Hard to say. Do you have to pass smog? If not, just change out the primary jet for the next larger size and see if the problem goes away. You don't need to remove the carb to do this.


If you need to pass smog, then I would do a complete tune up first by the book checking everything first and if this doesn't help, I would remove the carb and rebuild it.
 
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no dont need to pass smog , thats about where im at removing the carb and hope something is stuck in the jet or its the wrong jet

what about this oklahoma fix i read about, can it hurt anything

run it up to 2500 and block off intake and let it die, is that how u do it ?
 

65swb45

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checked
since opening the power vavle solves problem wouldnt you say its not ignition and has to be in the carb

You could just as easily hypothesize that the truck is running lean because of a vacuum leak [albeit a really small one if you are truly pulling 20" of vacuum] and the extra gas from the PV being short circuited is compensating for the otherwise lean mix from the leak.

IOW, I am with Pin_Head that the jets are probably NOT the problem.
 
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update

im 99% sure there are no vacuum leaks

the mechanic ruled this out last week but today i checked manifold/insulator/carb base with a can of carb cleaner, no change in rpm's at all, still pulling 20-22" at idle

can i pull the main jet with a split screwdriver while the carb is still on the truck or do i have to remove carb ?

what size should the main jet be for 6/76 2F non-cal. sor says 1.44 ?

if i need a rebuild where should i send it ?

thanks for the help
 
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problem solved , not carb

looks like i solved problem

its not the carb, i went thru everything one more time before i was going to remove carb today and realized that:

during rebuild they put in a non-usa performance distributor which is vacuum advance type

its connected to the usa setup smog system thru the vsv valve which should be connected to a vacuum retard distributor

removing / plugging the vacuum line at the distributor solved the hesitation problem . when the vsv opened vacuum is about 15" and it advanced distributor way to much and made it hessitate

i purchased this from a guy who spent $85k on a over the top 100% body off restoraton back to oem, its only got 83 miles on it . since its a collector and not a daily driver i will get correct distributor for it. if i was going to drive it i would change carb to non-usa disconnect smog system and use this high performance distributor

ps... yes he lost his a** off when he sold it, but cash is king !


thanks to everyone who posted help, jim c, mike a, if you read this you were highly recommended to rebuild carb if it would have been needed
 
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pic

here's a fast pic
Dsc08206 resized.jpg
 

Trollhole

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looks like i solved problem

its not the carb, i went thru everything one more time before i was going to remove carb today and realized that:

during rebuild they put in a non-usa performance distributor which is vacuum advance type

its connected to the usa setup smog system thru the vsv valve which should be connected to a vacuum retard distributor

removing / plugging the vacuum line at the distributor solved the hesitation problem . when the vsv opened vacuum is about 15" and it advanced distributor way to much and made it hessitate

i purchased this from a guy who spent $85k on a over the top 100% body off restoraton back to oem, its only got 83 miles on it . since its a collector and not a daily driver i will get correct distributor for it. if i was going to drive it i would change carb to non-usa disconnect smog system and use this high performance distributor

ps... yes he lost his a** off when he sold it, but cash is king !


thanks to everyone who posted help, jim c, mike a, if you read this you were highly recommended to rebuild carb if it would have been needed

Yer welcome. How about a pic of the throttle knob installed?
 
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throttle knob pic

man, you proud of that throttle knob restoration you did

it looks brand new like the rest of the truck
Dsc08215 resized.jpg
 
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another question if anyones still reading

for now im just going to run the non-usa dizzy with the vacuum advance disconnected and plugged at the vsv

most of the mid range hesitation is gone but its probably still not running like it should/would with the correct dizzy connected to the vsv

will it hurt anything running like this, its not knocking or anything, i drive i real eazy since the engine is still being broken in and im only putting 50 miles a month on it right now
 

UltraFJ40

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:clap: Good on you for getting it sorted out.

I think I went through something very similar when I swapped dizzies and carbs the first 10 times. Frustrating as all get out.

IIRC, that's the reason I'm running a HEI (Davis Unified) and a Holley.

:hillbilly:
 

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