Hello & New Carb For FZJ73 (1 Viewer)

[thebill]

Hello HDC!
I am in Santa Fe and am working through this 94 FZJ73. I ordered a new OEM carb, which came today, as the original one to this truck was beyond repair for me and I was having trouble finding what I needed to get it going.

My question going into a new carb is jetting for 7000’. It came with the stock 150/220 main jets as expected. Should I put the carb on there as-is and see how it does or should start with smaller mains? I am pretty sure I have a functioning HAC and that the vacuum lines are plumbed correctly.

Do the slow jets get sized-down along with the mains or is there another way of determining proper size of those? If it is the former, is there a ratio to stepping them down in relation to the mains?
I have a set of Mikuni main jets on the way and hope to get this sorted this weekend.
I look forward to coming to a meet up when I am up and running!
Thanks!

 

[pappy]

I would recommend you post this question up in the 70-series forum: 70-Series Tech - https://forum.ih8mud.com/forums/70-series-tech.86/

Then specifically tag @65swb45 and @FJ40Jim since they are the carburetor gurus here at MUD, and see if they have any suggestions.

 

[pappy]

Also, if this is an FZJ73 why does it have a carb and not fuel injected.

 

[thebill]

Also, if this is an FZJ73 why does it have a carb and not fuel injected.

It’s a South American truck with the carbureted 1FZ-F. The 1FZ-FE didn’t arrive down there until later.

 

[thebill]

I would recommend you post this question up in the 70-series forum: 70-Series Tech - https://forum.ih8mud.com/forums/70-series-tech.86/

Then specifically tag @65swb45 and @FJ40Jim since they are the carburetor gurus here at MUD, and see if they have any suggestions.

Thanks. I’ve posted there a couple of times about this with not much response. Onur suggested I post here for a more local take.

I’ve also emailed Jim directly with no response. My understanding is he has quite a busy schedule and it’s a matter of persistence.

 

[FJ40Jim]

Install proper carb, connect validated HAC valve.
Adjust idle mix & speed per the FSM. Advance timing 6° from sea level setting.

Drive truck, then change jetting as indicated by AFR gage.

 

[thebill]

Thank you,

Install proper carb, connect validated HAC valve.
Adjust idle mix & speed per the FSM. Advance timing 6° from sea level setting.

Drive truck, then change jetting as indicated by AFR gage.

Thank you, Jim.

 

[thebill]

New carb is in. It’s a stark contrast with the one I was hoping to bring back to life.
In going through the vacuum diagram, I learned that both of the bi-metal vacuum switches in the circuit were broken so while I wait for those to arrive, I am wondering if brand new OEM carbs come fully set up per pages 333-340 of the FSM. If not, I’ll have to figure out how to fashion the SST that measures the various angles of the valves (there’s one on eBay right now for $500) and how to apply vacuum to check the rest of it.
I know it’s prudent to always check someone else’s work, but do these leave the factory ready to drop in?
Thanks!

 

[FJ40Jim]

Yes, a new OEM carb is set up using the factory angle gauges. The only things that might need adjusting are the normal tune-up settings that are done on your engine: idle speed, idle mix, choke speed.

 

[thebill]

Yes, a new OEM carb is set up suing the factory angle gauges. The only things that might need adjusting are the normal tune-up settings that are done on your engine: idle speed, idle mix, choke speed.

Thanks, Jim.

 

[Dizzy]

I just installed a new factory 2F OEM carb 21100-61012. I have a 2F from '75. The new carb had a 138 main installed, and, I believe a 134 in the spare cap (primary). I left it that way. I assume that the smaller ones are high altitude jets, but, richer jets seem like a better pairing if the throttle plate is at a steeper angle for the same mass of air?

I was running the original carb for about a year - 1.44 main, 2.30 secondary. It wasn't nearly as efficient as the new carb, I picked up about 3 mpg (up to15-mpg, now), and some fuel range for a tiny tank. The 2F is set at about 7 degrees static BTDC, and there is a new non-USA F vac advance distributor with igniter/points 1mm spark gap. I tried 15 degrees BTDC, and it made a noticeably more difficult warm start.

I'm still curious about the slow jets, the power valve, and the accelerator pump jet, particularly when using medium throttle on a cold motor, it stumbles a bit lean. The absence of a choke breaker/throttle-positioner-diaphragm on the new one isn't fun with the new carb, but the old ones had minor vacuum leaks, so I won't mess with factory peened screws to swap in that part from the old carb. I installed a hand-throttle, so I can have a fast-idle without using much choke because that is when I get a lean symptom. I have a non-heated O2 sensor installed behind headers, and a readout gauge in the cab, the results appear to be inconsistent enough to alone warrant changes in carb tuning.

Someone in the 40/55 section mentioned that Mikuni jets were a bit different thread pitch?

6,800' in my backyard; 10,300' to the top of the hill. The new carb performance is, so far, acceptable. I'd rather be a bit rich. Understand that my 2F might have some vacuum or compression shortcomings due to wear and neglect.

 

[thebill]

I just installed a new factory 2F OEM carb 21100-61012. I have a 2F from '75. The new carb had a 138 main installed, and, I believe a 134 in the spare cap (primary). I left it that way. I assume that the smaller ones are high altitude jets, but, richer jets seem like a better pairing if the throttle plate is at a steeper angle for the same mass of air?

I was running the original carb for about a year - 1.44 main, 2.30 secondary. It wasn't nearly as efficient as the new carb, I picked up about 3 mpg (up to15-mpg, now), and some fuel range for a tiny tank. The 2F is set at about 7 degrees static BTDC, and there is a new non-USA F vac advance distributor with igniter/points 1mm spark gap. I tried 15 degrees BTDC, and it made a noticeably more difficult warm start.

I'm still curious about the slow jets, the power valve, and the accelerator pump jet, particularly when using medium throttle on a cold motor, it stumbles a bit lean. The absence of a choke breaker/throttle-positioner-diaphragm on the new one isn't fun with the new carb, but the old ones had minor vacuum leaks, so I won't mess with factory peened screws to swap in that part from the old carb. I installed a hand-throttle, so I can have a fast-idle without using much choke because that is when I get a lean symptom. I have a non-heated O2 sensor installed behind headers, and a readout gauge in the cab, the results appear to be inconsistent enough to alone warrant changes in carb tuning.

Someone in the 40/55 section mentioned that Mikuni jets were a bit different thread pitch?

6,800' in my backyard; 10,300' to the top of the hill. The new carb performance is, so far, acceptable. I'd rather be a bit rich. Understand that my 2F might have some vacuum or compression shortcomings due to wear and neglect.

I’ve also read that the mikuni jets are slightly different (M4/.8 vs M4/.7) but couldn’t find the thread where I saw that so wasn’t sure if it applies to the 1FZ carb or not. I meshed the threads of one of the Mikunis against one of the OEM and they seemed to line up but it’s probably a different story when trying to thread them into something. I will be picking this project up this coming weekend and will test one out very carefully to see.

For now, I’m planning to follow JimC’s advice and install it as-is and see how it does, then move from there.

 

[Dizzy]

Have you done a vacuum or compression test?

 

[thebill]

Have you done a vacuum or compression test?

I haven’t yet. I want to get it running normally first.

 

[alia176]

14 messages and not a single pic of this cool ride?

 

[thebill]

14 messages and not a single pic of this cool ride?

Alright, alright. Thanks for the prod, @alia176
My kids have been thoroughly enjoying having a cool place to read and hang out while I wait for parts & try to find time to work it.
I'm determined to have it on the road by June!

 

[evanz80]

That's a nice looking truck!

You mentioned that it's "South American" - any idea what the country of origin was? Just curious.

 

[thebill]

That's a nice looking truck!

You mentioned that it's "South American" - any idea what the country of origin was? Just curious.

Originally from Colombia.

 

[thebill]

Someone in the 40/55 section mentioned that Mikuni jets were a bit different thread pitch?

I pulled the old carb today and checked one of the Mikuni jets in it and it went in and tightened down without any issues. Threads felt the same as the jet that was originally in there.

 

[alia176]

Alright, alright. Thanks for the prod, @alia176
My kids have been thoroughly enjoying having a cool place to read and hang out while I wait for parts & try to find time to work it.
I'm determined to have it on the road by June!

View attachment 2674517

that gives a whole new meaning to "yard art" . Good looking rig. Sorry if mentioned already but how did you acquire it and for how long?

Surely, one can move from a carb to a modern injection of some sort, no? I suppose just swap in a 1FZ-FE is one option but I'd rather have a 1HD-T in it, if I had a large wallet.