View Full Version : Carb jets for 5280 feet

11-10-2009, 08:45 AM
I have a 1971 FJ40 with the F135 engine. It runs fine, my son drives it every day (5,000 to 6,500 feet elevation) and it does some light wheeling in the mountains up to 12,000 feet. The ignition system is electronic; distributor from 1978 FJ40 and coil/igniter from 1984 FJ60. The current carb base does not have the ported vacuum, so the dizzy is only using mechanical advance. The VSV has been removed. The carburetor was rebuilt (not by me) about 18 months ago when I could not pass emissions. After the rebuild, a local shop was able to make adjustments to get it to pass emissions - but just barely. The best vacuum I been able get out of the engine is 12. I've looked for vacuum leaks (not found any) and have the valves adjusted to spec. The truck runs rich (you can smell it) and averages 10-11 mpg pretty consistently.

I picked up the FJ40 because I've always wanted to learn more about auto mechanics and over the couple of years I've had my truck I have learned a bunch.

While the truck is running OK, I really want to get experience rebuilding a carb. To that end I picked up a couple of carbs and rebuild kit a while back. They have been sitting around and now I'm ready to take the project on. My starting point is a H2662 model that has 2I4 (built September 4, 1972) stamped on the air horn. The carb base is not drilled for ported vacuum. The rebuild kit is in a old, beat up Keyster box from SOR which has many numbers; SOR 042-03E, Original Kit No. 04211-60142, Carburetor No. 21100-60202. 60203 and on the side the number K11-358A. While the box has seen better days the two packages with parts are still sealed in their plastic wrappers and in very good shape.

I have a few questions regarding the jets to use as I put the carb back together. On the disassembly, I managed to mangle the head on the secondary jet and I did not realize the size of the slow jets was different:o. In short, I have incomplete information on the jets that were in the carb. I do now have some custom modified screw drivers so I'll not be making the trashed carb jet head mistake again:D. Probably not too big a deal because I am more interested in what jets should be in the carb when I put it back together.

The jet sizes that were in the H2662 carb are:
Primary Jet - 118
Spare in Primary plug - 060
Secondary Jet - UNK; trashed the head
Spare in Secondary plug - 141
Power valve jet - 070
Slow Jets - 80 and 50; but I didn't make a note of which was on what side

The Keyster kit has the following new jets:
114 - Primary
180 - Secondary
60 - Power valve
50 - Slow jet, but the kit only has one

From some other carbs, I've also got a few jets of the following type and size;
Primary/Secondary - 180, 159, 114, 103
Power valve - 070, 040 and 060

I understand that many variables come into play when deciding which jets are the best starting points for a particular carb, on a particular engine in a particular geography. As I've researched jet size, I have been able to gather that at altitude a smaller primary and power valve jets together with timing advance are the general direction to follow in optimizing a carb.

Locally, MDH33 has rebuilt a couple of 73-74 carbs using; 112/114 Primary, 180 Secondary and 50/50 for the slow jets with good results. This seems like a reasonable starting point. However, given the subtle changes between 72 and 73-74 I am interested in input from the group as well.

Given my situation, what recommendations would the group have regarding jet sizing as I put the carb back together? Is 103 a too small starting point for the primary jet? Even though I don't have one, should I look for a 112, 110 or 108 jet as the starting point?

11-10-2009, 09:32 AM
This is a great thread and I will be following along closely. Re-jetting will be a winter project as my 40 is running rich as well based on the "smell test".

11-10-2009, 12:45 PM
I went round and round on the rejetting thing while I was rebuilding my carb, and my conclusion was to stick with the original jets. :rolleyes: Like yours, my truck was running well most of the time, with the exception of one known issue (which may not even be related to the carb). I hope that the rebuild address it, and if not I'll continue my troubleshooting. I figure why mess with something that seems Ok, and if necessary tune the carb slightly to get the desired lean/rich result. And if after all that fails and it still runs too rich, then once you've had the carb out a couple times and have rebuilt it, swapping out jets becomes a relatively simple task.

All that said, I'm subscribing to hear others' feedback on the topic.

11-10-2009, 12:53 PM
That 060 you said was in your "spare" primary is your high elevation primary (106). Use that one and the 180 in your secondary. The 60 Power jet should be fine. For the slow jets, go with two 50's, or if you don't have two, then use the 80 in the left hand side when looking at the carb from the front.

11-10-2009, 04:47 PM
I rebuilt a '76 Carb on my FJ55, which was just a hair to rich. After carefully rejetting with different (leaner) fuel and air jets, it ran richer and worse - not what it should have done. I was sufficiently disgusted that I stuck a stock, Federal emission spec carb on it, and it ran great. My '78 FJ40 with a federal spec carb (original jets) runs great until you get very high - 13K feet or more, where it runs rich and belches black smoke on occasion. The idle speed also drops a little bit. Still runs ok, but you can skip using the choke ;-).

I think a stock rebuild and setting the idle per the lean-drop method will result in a decent running truck. I agree that you need vac advance, however. I wish I had been wildly successful in rejetting my carb, but I sure wasn't. I would love to have an engine on a dynamometer and a test stand, and really set out to learn something, but that will likely never happen.


11-11-2009, 10:01 AM
Not sure if you've already bought your rebuild kit, but I found the kits to be widely variable in terms of what they include. I ended up buying 3 different kits in order to get everything I needed

- first Keyster kit I bought did not include any jets
- I tried a second Keyster kit that included all primary and secondary jets, plus a couple of options for rejetting
- both Keyster kits were missing the gaskets that go between the body or flange and insulator section. The Napa kit includes gaskets for these sections. But if you look at the carb diagrams, there isn't a gasket shown here (in all cases), so maybe the factory spec doesn't include gaskets there?

I found the Napa kit to be the most inclusive of parts, and also the most expensive at ~$40. The Keyster kits were $20-25.

11-11-2009, 01:08 PM
The Carquest in Colo Springs had a '78 FK40 carb rebuild kit in stock a few months ago. The counterman was shocked to find it in inventory at the store. The kit includes a secondary diaphram (discontinued by Toyota), but I don't know about jets. Not a Keyster brand, but looked similiar to the NAPA kits. It was significantly cheaper than NAPA, too - $37-ish out the door.

12-07-2009, 07:24 AM
The rebuilt carb has been in service for just over a week. It has been up to 9,500 feet on a snow run (http://www.risingsun4x4club.org/forum2/showthread.php?t=11496). I could not find a size 60 idle/slow jet from Toyota or a local carb shop. I went with the following jet sizes:

114 - Primary
180 - Secondary
60 - Power valve
50 - in both slow jets

There is a very noticeable improvement in the operation of the choke and starting of the engine. The last couple of days the temps have been in the single digits. Above idle the truck runs about the same (maybe a bit stronger) as it did with the older carb.