Flat spot on rebuilt carb (72 fj40)

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Aug 8, 2007
Murrieta, Ca.
Well I just got my rig back; 5/1972 fj40 out of the shop; had a vacuum advance distributor and rebuilt SOR vacuum advance carb installed; runs fine through the whole range except when I first take off there is a 'flat spot' upon acceleration. Has to be just a minor adjustment, I hope. I want to fix it myself so if anyone has any wisdom, it would be appreciated. P.S. I had the original carb rebuilt, so it is for sale.
i see that no one has ...

bothered to reply to your question. the only experience that i have is with newer toyota factory carburetors. i experienced the same issue on my 2wd truck carb. the solution was a combination of the float valve and the lower throttle valve. i do not know if your carb is the same or even close. but that's something to look at. my symptoms were when pressing accelator for powering up to speed, it just stopped delivery of the fuel, based on the engine stopping if i held the peddle steady. then, hit the peddle a bit more and wham, power back on. as i know it now, there was that missing cordination of the two, fuel delivery and the throttle opening for additonal air to fuel mixture.

i am not any kind of an expert, but that is the explaination the toyota tech gave me when he finshed my carburetor rebuild/install.

he suggested that the linkage may have also caused some of the issue, and he reset-up the whole thing for me.

best to you in figuring out this issue. i'd be tempeted to call a toyota tech somewhere that still has carburetion engines. they may have an answer right off for your carb and year.

i know that there are several guys here that are good with carbs on the mud. so, my responce will "pop" ... "bump" your question back to the top.

May i suggest that you post up a picture of your carb to help the guys "see" your set up, esp the linkage side of the carb.
Well, I adjusted the idle mixture screw out 3 turns (it was about 5.5 previously) and lowered the idle a little ( I always thought it was running too high an idle) and the 'flat spot' disappeared! So I don't know what that did, but it worked. I read a post saying flat spots are sometimes caused by too much fuel coming in and not too less. I guess one just has to tinker and fine adjust new carbs. :eek:

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