3F Carburetor Info/Rebuild (1 Viewer)

[Honger]

If I'm lucky this thread will be helpful to at least one person. I'm rebuilding my 3F carburetor and MUD has been a big help in doing that. I figured I'd chronicle a bit of info about this carb and the rebuild process. I'll probably sprinkle a few questions for the experts in here as well.

First, do yourself a favor and watch the @Pin_Head video's on Aisan Carburetor rebuilding. Links are as follows:
Part 1, Part 2, Part 3, Part 4, Part 5, Part 6

Next, do a search for all carburetor-related posts by @FJ40Jim (click here) and @65swb45 (click here). These gents are wizards of carbs and are best suited to actually do your rebuild. I'm a glutton for punishment and I have time on my side, so I opted to rebuild mine on my own.

The 3F carburetor I have is a GCC, or general market, carb. It is VERY similar to the general market 2F carburetor on my FJ40. I've de-smogged my 3F set up which makes the throttle position sensor and the AC idle-up largely redundant at this point. They are there, but they don't do much. My carb generally ran well enough and it fired right up every time (except when parked for awhile while hot and the fuel would boil off, which necessitated a bit of pumping). When choked the acceleration had issues. It was obviously well used and it had been awhile. I had a Chinese carb laying around that had been barely used on another guy's 3F Troopy, so I figured I'd swap them and dive in on the Aisan rebuild. The Chinese carb does NOT run nearly as well as my un-rebuilt Aisan did. I'm anxious to swap this one back in.

Some pre-rebuild photos.

Part number 21100-61300.

Side views...

The fesh-fesh was strong on the backside of my unit.

Here's the AC idle-up components.

Datecode on my respective unit denoting a June 21, 1991 build date (or 2001 I suppose). Given my truck is a June of 1991 truck by VIN, it seems likely I have the original carb on my truck.

Some other markings on my carb air horn. I have no idea what they denote.

 

[65swb45]

You should retain the AC idle up and put a toggle switch in the cab to operate the solenoid for it.

Handy for bumping the idle up for hill climbs.

 

[Honger]

I started with this Keyster kit. The gent who's 3F had gone south and gave me the Chicom carb also gave me this kit. He said that @cruiseroutfit had supplied it, so that's your best place to find it I'm sure.

I snagged the Hygrade 791B kit as well for the better air horn gasket as well as the secondary diaphragm. This came from Rockauto.

I also snagged a Hygrade float so I could replace that. It turned out to be an Aisan unit which was nice. Also from Rockauto.

 

[Honger]

You should retain the AC idle up and put a toggle switch in the cab to operate the solenoid for it.

Handy for bumping the idle up for hill climbs.

Man... I freakin' love this idea.

I've actually been considering rigging this one back up to the vacuum switch anyway. I'm using the original AC controller, so it should still work. The diaphragm still holds vacuum, I checked it out during this rebuild.

 

[Honger]

So I dove in. I'd snagged the OEM carb tool kit while overseas and it was handy for this job.

As you can see, my fesh-fesh was extensive.

Even the float bowl had a nice layer of accumulated fesh-fesh from over the years. Pretty crazy. This had to take a long time I'd imagine... perhaps indicating its never been rebuilt.

The needle valve was really stuck good. The OEM bit couldn't budge it and I ended up buggering it up a good bit. So I finally just used vice grips to break it free. This makes me think it's likely never been replaced.

Venturis were well soiled.

My workspace.

A pre-dip shot of the air horn.

The dip I went with. I only did 4 hours per part... didn't need to do overnight.

It blew my mind how clean things came out of the dip (I pre scrubbed off the really badly-caked stuff).

So purty...

And doing the linkage bit by bit...

This scoring seemed odd to me. Perhaps this has been removed and rebuild at some point.

 

[Honger]

The main jets in the unit.

The power valve jet.

And the slow jets.

I'm curious if anyone else has opened up their 3F carb and seen what their jets are? I'm assuming this is a basic set designed to run well in various conditions. My carb doesn't have a High Altitude Compensator.

 

[RHINO]

wish i recorded my jet sizes when i rebuilt my Omani spec rig

if you dont have the butterfly measring SST, theres a handy metric allen wrench chart somewhere,, i'll look for it.

 

[Honger]

wish i recorded my jet sizes when i rebuilt my Omani spec rig

if you dont have the butterfly measring SST, theres a handy metric allen wrench chart somewhere,, i'll look for it.

Did you put in new jets, or just replace originals?
Did the rebuild net you any improvements?

 

[65swb45]

Man... I freakin' love this idea.

I've actually been considering rigging this one back up to the vacuum switch anyway. I'm using the original AC controller, so it should still work. The diaphragm still holds vacuum, I checked it out during this rebuild.

That’s what the like button is for.

 

[RHINO]

Did you put in new jets, or just replace originals?
Did the rebuild net you any improvements?

no new jets

float level adjusted properly made the biggest improvement because it was off, seemed to smooth out all around after being rebuilt though

 

[Honger]

no new jets

float level adjusted properly made the biggest improvement because it was off, seemed to smooth out all around after being rebuilt though

Any leaking around the throttle linkage rod where it passes through the housing?

 

[RHINO]

not that i can see, i also ran propane around the carb to check for leaks, all seems tight.

 

[Honger]

So the Keyster kit comes with different jets...

Jet	As Installed OEM	Keyster
Primary Main	135	120
Secondary Main	230	180
Power Valve	110	114
Primary Slow	55	55
Secondary Slow	90	80

Based on my understanding of fluid dynamics, I'd think that 31 years and 260,000 kilometers of use would result in some wear in a brass part. That said, is it really enough to matter? @RHINO put his jets back in as is. These jets do have some appearance of having been removed/replaced at some point but generally appear undamaged.

It seems like the smaller orifices in the new jets would result in a leaner fuel mixture. Perhaps too lean for the 3F?

Curious if @65swb45 and @FJ40Jim have any thoughts here... do you always re-jet on a rebuild or only in an as-needed situation?

 

[Honger]

They Keyster jets for reference...

 

[RHINO]

Interesting to me anyway, I would have thought a GCC spec rig from a lower elevation would result in rich running at the 5k plus I live and play, however, on further inspection Oman, in particular the region/town my cruiser was used sits at elevation.

Upon further examination I found my Troopy was originally owned by an oil company and the rigs are low elevation, later it was bought and used for a village school at elevation.

There isn't any spec for jetting that I know of from Toyota, just a selection of jets available, so I have no idea if my jets are factory supplied, or supplied after the fact for the Omani elevation it lived.

When rebuilding my carb, the jets in it were close to what is recommend so I kept them in, the fueling issues I was experiencing were directly related to high fuel level in the bowl, once lowered to correct level the darn thing has been running extremey well.

If you are having fueling issues that aren't apparent on inspection of the carb, I'd say give jetting a shot.

 

[65swb45]

IOW, if it ain’t broke, don’t fix it.

GCC for the F carb primary was 1.20. For the 2F, it was 1.5. Since the 3F is closer to the F in CID, 1.35 doesn’t seem like a bad range.

 

[Honger]

A bit more research:

Jet, 1st Main Part# 90999-41135 (seems to support the 1.35 being stock)
Jet, 2nd Main Part# 90999-42230 (seems to support the 2.30 being stock)
Jet, Power Part# 90999-43110 (seems to support the 1.10 being stock)
Jet, 1st Slow Part# 21024-61060 (not sure this part number correlates to a jet size as directly, can't imagine stock was .60 and larger than the 2nd Slow)
Jet, 2nd Slow Part# 21024-61010 (not sure this part number correlates to a jet size as directly, can't imagine stock was .10)

At this point I'm planning to go with the advice above regarding not fixing something that ain't broke... and reuse the jets that were already in place.

 

[Honger]

After grabbing the Hygrade 791B kit mainly because it came with a new secondary diaphragm, I ran in to a bit of a problem...

My secondary diaphragm is shorter and has a bend at the end of the linkage.

As luck would have it Toyota still sells my secondary and it's available here in the US supply chain.

I'll be snagging another one since it is the same one on my general market carb on the FJ40's 2F.

 

[RHINO]

Hows it goin?

 

[Honger]

Actually finished up... but have just not had the time to get under the hood and re-install it.

I bought some fresh vacuum hose... 90999-92006 (this is a 600mm length of hose that is meant to be cut to length as needed). I think the hoses were original.

Here's some final shots. I'm floored at how well it cleaned up.