Jets for carburetor - Proper Size (1 Viewer)

[dv_fj40]

Ok - first, I know absolutely nothing about carburetors and or how they work. But I am learning.

With that being said – I sent a carburetor out for rebuilt. With that – the mechanic was asking me several questions about my driving habits and where I off-road.

I basically told him in the heartland of Death Valley and its surrounding mountains (Panamints, Argus, Funeral, etc.). He laughed and then he understood I was serious.

I asked him why? He indicated it had to do with installing the proper “jets.” He basically told me you need larger jets for higher elevations and so on.

My question to you: I have a stock FJ40 with a 2F engine and late F series carburetor, lifted 3” with 33” tires. I usually cruise about 65/70 mph and my off-roading is moderate. That is too say - nothing serious – most of the time. The highest elevations I reach with my cruiser is about 6,500’. Average driving elevation is about 2,500’.

With all that being said – what jet size should I be using?

Thanks in advance,
Joel Briggs
www.desertdrifter.com

 

[72cruiser]

i have no idea, but there is nice write-up on the earlier aisin carbs (like the one you have) in the tech section

malphrus

 

[72cruiser]

http://www.ih8mud.com/tech/carbinfo.php

 

[IDave]

The cutoff for when you use the High Altitude jets is somewhere above 3500-4000 feet, in my experience. If you average 2500, I would definitely go with the regular jets, because you will probably run too lean and tend to burn things up with the smaller jets at that elevation. I live at 5150 feet and do run the HA jets, and sometimes I think that it is a little lean under some circumstances, but on the whole it is the best compromise.

Depending on your year, you should also have some high altitude compensation built into that spaghetti network of tubes that I don't have. Which means you have less need to reJet.

 

[dv_fj40]

WHOA!!! IDave you lost me. I don't have any smog c-r-a-p on my cruiser. Tubes?!?!? The only tubes I have running are from the (nearest to the engine block) carburetor to the non-usa distrubutor and the a small tube running from the base of the carburetor to the vacuum thingie - U shape formation.

With that, what size are the regular jets?

Thanks,
Joel Briggs

 

[IDave]

Joel, with your late 2F I figured you had all that crap, still. Obviously you've fixed it.

For my carb (and IIRC, they're the same for others) the primary main jet is 1.12 mm and the primary main jet spare is 1.08 mm (smaller). The power jet is .9 mm, and the spare (high altitude) is .8 mm. Size should be stamped on the jet.

Your mechanic was wrong (or you misunderstood him). HA jets are smaller diameter.

 

[Romer]

You have to pull the carb off the engine to swap the jets, right Dave?

 

[Degnol]

No you don't have to pull the carb. On the bowl, the part facing the radiator, there are two nuts at the base. When you remove them, the gas in the bowl drains, but then you have direct access to the installed jets AND a spare jey on the back of the nut. You only change the primary jet, not the secondary. To do this you need a splitblade screwdriver, they used to be plentiful, but with all the FI motors, they're harder to find. I ordered mine from the SnapOn driver. The blade grips the jet and holds it until you start the threads. The jets are brass so magnet no workey. Takes all of 5 minutes.
GL
Ed

 

[folsom50]

That old carb of dv-fj40 probably has the HA jets inside of the plugs on the carb. The heart-land of death valley is like minus sea level elevation, isn't it?

 

[dv_fj40]

IDave - I did in fact misunderstandd what my mechanic was telling me. You cleared it up "crystal clear" and I thank you for that. Got caburetor overload with the amount of information here - which is great. Again, thank you.

Death Valley is a long valley. I usually cruise the local mountains and the northern parts of Death Valley. I try to stay away from the Badlands and the Devils Golf Course - sea level elevation. Lot's to see and cruise out there. Each canyon in the surround mountains all have interesting findings. Been exploring the DV area for almost 20 years and still fine new places to explore and see.

One last question - SOR offers a rebuild kit for the cruiser. Does that come with the jet sizes you mention in your post? For the record - I am not rebuilding my own carburetor - but once upon a time I had a problem with my carburetor out in the heartland of DV. Somehow the float came loose - not sure how this happen - but we had to tear apart my carb out in the middle of nowhere to fix it.

Again, thanks for all the GREAT information.

Joel Briggs
www.desertdrifter.com

 

[Romer]

No you don't have to pull the carb. On the bowl, the part facing the radiator, there are two nuts at the base. When you remove them, the gas in the bowl drains, but then you have direct access to the installed jets AND a spare jey on the back of the nut. You only change the primary jet, not the secondary. To do this you need a splitblade screwdriver, they used to be plentiful, but with all the FI motors, they're harder to find. I ordered mine from the SnapOn driver. The blade grips the jet and holds it until you start the threads. The jets are brass so magnet no workey. Takes all of 5 minutes.
GL
Ed

If I go to ACE hardware or NAPA, are there any specific size "splitblade screwdriver" I should be looking for? never heard of that.

Thanks

 

[IDave]

Just to clear things up a little more. OR, maybe cloud them up a bit. Dunno.

While I hate to disagree with Ed, because he is such an agreeable guy, you do, indeed, have to take apart the carb, and really, take it off, to swap to HA jets and back. This is because that rather than 2, there are 3 jets in the FJ Carb: Primary, Secondary, and Power, which is buried inside (these are 36, 39 and 46, respectively, in the figure). The secondary jet stays the same. You change out the primary and power jets for altitude. There isn't any easy way to get at the power jet without taking things apart: as you can tell from the picture.

IIRC, the SOR kit has all the jets you need, but I could be wrong. Best to call their tech folks and ask. You may end up just buying the appropriate jets from CDan/Toyota.

I think I just used a regular screwdriver once I got things on the bench.

 

[IDave]

Oh, yeah. The spares are in the plugs, as Ed said. At least, they are in most versions of the Aisen carb. But not all. AND note that the power jet "spare" is in the secondary passage plug. That's to confuse you and make you think that the secondary jet is the power jet.

 

[folsom50]

Oh, yeah. The spares are in the plugs, as Ed said. At least, they are in most versions of the Aisen carb. But not all. AND note that the power jet "spare" is in the secondary passage plug. That's to confuse you and make you think that the secondary jet is the power jet.

From what I've seen, the alt. jets are only in the 75 and older carbs. I didn't know there was three jets, learn sumpthin new everyday. I'm still not going to try to rebuild mine.

 

[IDave]

I think I've heard the thing about the spare jets being only 75 and earlier, too.