2F Aisan Carburetor Jets and Venturi question/help (1 Viewer)

samatulich

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I am currently in the process of rebuilding two 2F Aisan Carburetors. One was stamped 5J27 (1975 October 27) and the other 6B3 (1976 February 3). The one built in October 1975 was the original carb for the 2F in the 1976 FJ40, never been rebuilt. The second one (February 1976) I purchased a few years ago. I was told that it had been rebuilt and desmogged.
Both carburetors were used on my 1976 FJ40. The original one ran until I had it replaced with the 6B3. At that point in time I had a dizzy, coil and ingnitor from a mid '80s 2F installed. The set up worked for a little over a month, then I could not get it to start and run. That was 2 years ago, I decided this past week to remove the carb and rebuild both of them at the same time.
They are both apart, soaking in carb dip or drying out.
Here are the specs from each carb with respect to the jets and Venturi:
Carb 5J27: Primary side: main jet (144); slow jet (65); Venturi (5*). Secondary side: main jet (230); slow jet (90); Venturi (3)
Carb 6B3: Primary side: main jet (103); slow jet (55); Venturi (1). Secondary side: main jet (230); slow jet (70); Venturi (5).
*this Venturi has been damaged due to a backfire, it is missing 1/3 of the ring(s) surrounding it. I would post a pic, but I am having trouble figuring that out right now.

Here are my questions:
1) Are these both considered to be 1976 2F carburetors?
2) Are the jets (main and slow) and venturies interchangeable? I am not sure if I could use the primary Venturi from my February carb with the jets from the October carb.
3) How should I consider rebuilding the carbs? Keep them the way they were, mix and match jets with venturies or purchase new jets (Mikuni) and drill them out to a specific size.

I have been searching the forums and read that for a 1976 Aisan carb a main jet sized 150 is perfect. When I get this '40 back on the road, I would like it to be desmogged and driven from sea level (I live in Olympia WA) up to 8,000' (looking to drive it up in the Sierras around the Sierra Buttes).
I will continue to use the search function and read up on this topic, so far it has been helpful and informative.
Lastly, thanks Pin Head for your videos, very easy to follow and really has helped me understand more about this carbs.

Thanks for your help.
Sam
 

samatulich

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Here is the primary venturi from the 1975 carb. Any idea what the rings are for?

Aisan 2F Primary Venturi.jpg
 
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Those are actually main fuel nozzle assemblies. The ring is known as a booster ring and increases the velocity of the air flow past the nozzle. The bore in the carb body in which the booster ring sits is the venturi. Both carbs would be from '76 model years. I'm surprised that one has a 103 primary main jet. This seems way small.
 

samatulich

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Thanks for the clarification on the main fuel nozzle assembly. Looking then at the venturies for both carbs, they are stamped differently as well. The October 1975 primary is (31) and secondary (35), the February 1976 carb primary is (28) and secondary (31). My guess is that the nozzles are sized for a specific venturi diameter. Probably best to keep them matched and only change the primary and secondary jets, both main and slow. I will double check the 103 primary main jet, perhaps I am miss reading it or it has been drilled out. Like I mentioned before, the carb that the 103 primary jet came from was rebuilt a number of years ago.
 

pjohnson

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I'm rebuilding a 5/76 carb right now and was wondering about the oem jet sizes. Is there any tech article or Web page with this info?

My primary is 120 and secondary is 165.

Also, where can I find the carb videos.
 
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thebigredrocker

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From the research I've done on mud the stampings on the main nozzle doesn't have a rhyme or reason, it's just a casting number. I would guess you could use the 75 primary nozzle in the 76 I have blown air through various single ring nozzles(early 70's) and believe they have different flow rates as based on auditory feedback. I haven't spent time to come up with a scientific testing method for nozzle flow. I'm sure the pro's have a method, which is why they get paid.

If you search stuff posted by FJ40Jim you may run across some mention of jet sizes. I've also found some useful carb info that Stumpalama has posted. I had been looking at buying a selection of Mikuni jets to test, did a mud search and found that Stumpalama beat me to it. He posted they do fit. So if you don't want to hog out jets you could try Mikuni's. I am going to soon test out the Mikuni "hex" jet which is different from what Stumpalama posted about. I like the idea of being able to use a socket to remove and install different sizes without fear of fumbling a slot head jet. It might not work, I'll post up how they fit.
EDIT: MIKUNI hex jets will not fit. They are M5.5 x .90. My Aisan main jets are M5 x .8

And yes Pin_Head has been helpful to many like myself who want to be more self sufficient in the boonies should a carb issue arise. I tip my cap to @Pin_Head an others who share knowlege on this site. I believe that's what woody had in mind. A common place to share ideas and experience.
 
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