Early D-40 Carburetor Question

[rckhound]

Hi All-

I am wrestling with an early 1968 D-40 carburetor and have a question for the early single barrel carb folks out there. The carb I have installed on my 1/69 FJ40 is an early 68' carb that uses the step rod and large diameter main jet. I am having lean issues under load and getting some popping through the carb. I am doing some digging and trying to determine what main jet size should be in the carburetor. Currently it is running at 230 and I have read in another post that possibly a 270 is required. Talking with another mud memeber we determined that an SD-40 runs a 230 main jet but has a different profile to the step rod then my current set up. From some of the early manuals I have I was able to pull up the diagrams but the specifications section does not list the single barrel carb. Can someone with the knowledge confirm which jet size is in their D-40 carb that still includes a step rod similar to the one pictured. I have a late 68' D-40 carb also but it is not in very good shape and that is when the transition was made to remove the step rod and that carb runs a 150 main jet.

 

[rckhound]

Another picture. I have tried adjusting the rod height also with minimal difference.

 

[rckhound]

Another picture. I have tried adjusting the rod height also with minimal difference.

 

[CruiserTrash]

Did you use an adapter to put a two-bolt D-40 onto a four-bolt, dual-barrel carb intake manifold? Early 1969 would have had the earlier manifold with two studs, and by March of that year it went to the large-runner intake with four studs, right? Or is what I'm seeing the January-March/69 stock setup?

 

[rckhound]

That is the factory configuration. Early couple months of 69’ used the single barrel with this intake configuration. Then they went to the short funky 2 barrel and then in the end the went with the taller nor traditional 2 barrel to my understanding. They used three different carburetors in 1 year.

 

[CruiserTrash]

That is the factory configuration. In 1969. They used three different carburetors.

I'm aware of the three carbs - beginning-3/69, 3-9/39, 9-end/69. I was under the impression that two different intake manifolds were used though.

 

[rckhound]

I'm aware of the three carbs - beginning-3/69, 3-9/39, 9-end/69. I was under the impression that two different intake manifolds were used though.

It’s interesting because I have seen this set up before. It appears to be factory and it’s utilizing all factory hardware and the PVC tube and vacuum line tube that comes out of the phenolic spacer is in the same style as Toyota would have designed. It may have just been one of those funky things that they did in transition years. I could most certainly be wrong though.

 

[CruiserTrash]

It’s interesting because I have seen this set up before. It appears to be factory and it’s utilizing all factory hardware and the PVC tube and vacuum line tube that comes out of the phenolic spacer is in the same style as Toyota would have designed. It may have just been one of those funky things that they did in transition years. I could most certainly be wrong though.

Wasn't calling you out Steve! Just trying to learn and dial in the info in my head ... and maybe jump your post up to the top of the list.

Did the earlier intake manifolds only have two studs? Or were they all four studs and used an adapter for the SD-40 & D-40 carbs?

 

[rckhound]

Wasn't calling you out Steve! Just trying to learn and dial in the info in my head ... and maybe jump your post up to the top of the list.

Did the earlier intake manifolds only have two studs? Or were they all four studs and used an adapter for the SD-40 & D-40 carbs?

I didn’t think you were calling me out. I just assumed it was a weird factory thing for split year the way it was. Early trucks I have owned had intakes like this with the SD-40.

 

[Subterranean Nik]

Current elevation you run at? 6500’ or so?

Nik

 

[rckhound]

Current elevation you run at? 6500’ or so?

Nik

Yes

 

[CruiserTrash]

I didn’t think you were calling me out. I just assumed it was a weird factory thing for split year the way it was. Early trucks I have owned had intakes like this with the SD-40.

View attachment 4198469

I realized I had never taken a close look at one so thanks for the photo. It must have been a transitional thing with the introduction of the 2bbl carbs. Seems like Toyota goofed up the rollout on those - the intakes were ready but the carbs were not, so some "patches" were made to cover the gap until both were ready.

 

[rckhound]

Another photo from the service manual. 2 barrel intake with what looks like a single barrel adaptor plate.

 

[CruiserTrash]

Another photo from the service manual. 2 barrel intake with what looks like a single barrel adaptor plate.

View attachment 4200468

Wild. Thanks for the photo. Knowledge gap filled.

I really do think Toyota decided to move to a 2bbl carb and split up the project between the carb engineers and the manifold engineers who goofed it all up. The manifold engineers finished first and the carb engineers were lagging, so Toyota starting using the manifold while throwing stopgap carb stuff at the motor until the first legitimate Land Cruiser specific 2bbl carb was ready in September 1969.

That's my theory anyway.

 

[rckhound]

Wild. Thanks for the photo. Knowledge gap filled.

I really do think Toyota decided to move to a 2bbl carb and split up the project between the carb engineers and the manifold engineers who goofed it all up. The manifold engineers finished first and the carb engineers were lagging, so Toyota starting using the manifold while throwing stopgap carb stuff at the motor until the first legitimate Land Cruiser specific 2bbl carb was ready in September 1969.

That's my theory anyway.

I agree it’s funky. Here are a couple more pictures of the actual plate.

 

[JohnnyC]

you most likely have Taiichi Ohno to blame (the father of the toyotas production system and lean manufacturing... as well as other systems)... he hated waste ... muda... one of the core focuses of toyota production system was eliminating waste.... and overstock is waste... large stock of single carbs when they are going to be soon transitioning to 2bbl carbs most likely came up with the adapter ... this uses stock and keeps the manifold in production for 2bbls for the areas that were requiring it

toyota made a habit of introducing new parts before the need was 100% there.... kinda fazing them in ... and making them available before the need for the larger masses

 

[rckhound]

Bump. Still trying to learn if anyone knows the correct jet sizing.