Aisan Carburetor Rebuild

[RicardoJM]

Which rebuild kit did you use? I posted somewhere else that I was surprised at the variability in the parts list included in the different kits. Even the Keyster kits vary quite a bit.

I used a Keyster kit. Yeah, I can understand a "minor rebuild" kit would be just gaskets, but do not understand why there is such variability in the "major rebuild" kits. I was particularly confused at why there was one idle/slow jet in the carb kit and not two.

 

[AxleIke]

GREAT write up Ricardo!

 

[subzali]

Ricardo,

Have you been tracking your gas mileage since you did the rebuild?

Also, I've been reading that there is a 38/38 and a 38/40. Is the 38/38 the 2 barrel carb for F engines while the 38/40 is the 2 barrel carb for 2F engines? Do you happen to know the venturi size difference between the two? I think on a 38/40 the venturis are 31/35. And from Ed Cook's writeup I think the 38/38 has 28/31 venturis. Do those numbers flange up? I think I'm going to tackle my carb at some point and figure out what I have. I know it's a '78 Federal spec, just don't know how it's jetted and if everything is working properly. How is your secondary actuated? Is it linkage actuated?

Sources:
http://forum.ih8mud.com/60-series-w...gs-can-you-change-them-out-2.html#post3043800

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

EDIT: Started a thread about my carb here:
http://risingsun4x4club.org/forum2/showthread.php?t=15074

 

[Jacket]

On the mileage question, I've tracked mine since did the my rebuild in 2009 - no measurable improvement over what it was like before. Many performance improvements, but none in the way of mpg's.

 

[RicardoJM]

Have you been tracking your gas mileage since you did the rebuild?

Yes, I keep a log book and calculate mileage with each fill up. After the rebuild, I average 12-14 mpg. Up until recently, I was not running vacuum advance. As soon as I started running vacuum advance, I had to deal with the cracked block and just after getting the rebuilt engine in my odometer stopped working. I got it fixed this past weekend.

I'm looking forward to seeing what my mileage is now. Then, I am going to increase my jet size.

Also, I've been reading that there is a 38/38 and a 38/40. Is the 38/38 the 2 barrel carb for F engines while the 38/40 is the 2 barrel carb for 2F engines? Do you happen to know the venturi size difference between the two? I think on a 38/40 the venturis are 31/35. And from Ed Cook's writeup I think the 38/38 has 28/31 venturis. Do those numbers flange up? I think I'm going to tackle my carb at some point and figure out what I have. I know it's a '78 Federal spec, just don't know how it's jetted and if everything is working properly. How is your secondary actuated? Is it linkage actuated?

Sources:
http://forum.ih8mud.com/60-series-w...gs-can-you-change-them-out-2.html#post3043800

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

My research indicates the DD38 was used from 69 through 74. After that, I have not really paid much attention - but it would make sense that the carb specifications (jets, venturi size) would have changed with the "more powerful" 2F.

I'm not sure I understand your question about the "numbers flange up".

My secondary is mechanically actuated. I can tweak the linkage arm to get it to start opening earlier or later. I have not really worked with it to see how adjusting it would affect performance.

I am not a carb guru/expert but have come to understand through experience that the optimum setup (tuned for power or tuned for mileage) is something that will vary for each truck.

 

[subzali]

Cool. Thanks for the info. I'm wondering if anybody has an F engine carb, if they could look to see if there are numbers stamped on the venturis, as shown in this thread:
http://forum.ih8mud.com/60-series-wagons/205289-carb-rings-can-you-change-them-out.html

I am expecting to see 28 primary, 31 secondary. If that's true, then those numbers would "flange up" to the research/reading I've done.

EDIT: Matt, what kind of MPG are you getting? What performance improvements did you see?

Ricardo, are you still jetted to these settings? IIRC, you went from a F block to the F1.5 block when you did the latest rebuild right? And you say the F1.5 uses the same 2bbl carb the F block does?
http://risingsun4x4club.org/forum2/showpost.php?p=128635&postcount=8

EDIT AGAIN: I think I found my answer about 38/38 being on F engines:
http://forum.ih8mud.com/fj25-owners...rrel-big-window-f-carburetor.html#post6235972

 

[Jacket]

10-12 mpg for me, but I have heavy steel wheels and 33" MT's (as compared to Ricardo).

I had major issues with climbing at elevation: backfiring, sputtering, and nearly a complete loss of power (there's a thread here somewhere about it) at times. Sometimes I'd be crawling up Eisenhower at 20mph in second gear having to feather the throttle to keep my speed. It would also lose power at high speeds > 45 mph around town; just randomly cut out. And cold idle and cold driving were iffy at best.

Those issues have all disappeared since the rebuild. It still runs rough in the winter if I don't give it a few minutes to warm up, but I think that's "normal." All the hesitation stuff is completely gone.

 

[RicardoJM]

Cool. Thanks for the info. I'm wondering if anybody has an F engine carb, if they could look to see if there are numbers stamped on the venturis, as shown in this thread:
http://forum.ih8mud.com/60-series-wagons/205289-carb-rings-can-you-change-them-out.html

I am expecting to see 28 primary, 31 secondary. If that's true, then those numbers would "flange up" to the research/reading I've done.

Ricardo, are you still jetted to these settings? IIRC, you went from a F block to the F1.5 block when you did the latest rebuild right? And you say the F1.5 uses the same 2bbl carb the F block does?
http://risingsun4x4club.org/forum2/showpost.php?p=128635&postcount=8

EDIT AGAIN: I think I found my answer about 38/38 being on F engines:
http://forum.ih8mud.com/fj25-owners...rrel-big-window-f-carburetor.html#post6235972

I'll have to check on the stamping. It may take a few days as I spending my evening giving Sascha a hand with his rig. I do recall seeing numbers stamped into the barrels and they were the same so on that recollection - they don't "flange up".

Yes, I am still running the jet sizes in that post. I did try smaller jets (matching what was in the FSM for altitude) and found that I had a stumble coming of the idle circuit to the primary circuit. Very significant and not good with jet size 112, almost bearable at jet size 114 and gone at 116.

I've actually had 3 engines and 2 rebuilt carbs in my truck over the past year. You need a scorecard to keep track.

My understanding and experience is that the F.5 engine came with the DD38 carb that was also used on the late F engine. Albeit, in 1974 the throttle mechanism was linkage and not cable.

The Blue Mule is running a DD38 on a 2F and many others have success running the combination - I think that Martin has this set up in his rig. Regarding jetting, we put in a slightly larger jet (118 IIRC) in the Blue Mule and noticed a performance improvement. I don't think that Randy tracks MPG so we don't know what the economy impact is. That said, I don't think the Mule will be going back to the smaller jet size.

 

[subzali]

Cool, great info Ricardo!

Well I would imagine that someone would have a 38/38 sitting on a bench somewhere and could check it (I think the stamps are visible with the air horn on), but while you're working on Sascha's rig it would be neat if you could take a quick look at his DD38/40 (I'm assuming that's what he has) and see what his venturis are stamped. I'm guessing 31 primary and 35 secondary If we can't get the whole flange to line up then maybe we can at least get a couple bolts started

 

[Air Randy]

The Blue Mule is running a DD38 on a 2F and many others have success running the combination - I think that Martin has this set up in his rig. Regarding jetting, we put in a slightly larger jet (118 IIRC) in the Blue Mule and noticed a performance improvement. I don't think that Randy tracks MPG so we don't know what the economy impact is. That said, I don't think the Mule will be going back to the smaller jet size.

I dont track mpg closely, but when I have done it it worked out to 10-11 mpg. I think the Mule is really heavy with all of the tube work and the 37" tires with steel beadlocks probably add a lot of weight too. And, I know my speedometer is 5 mph slower than actual vehicle speed so that probably factors in.

I had a significant increase in power when I went from the stock jet sizes to the larger ones. It still runs smooth, no black smoke, no plug fouling and the power is much better. It ran good on the snow run too so getting a little higher up didn't seem to make it too rich either.

 

[Rzeppa]

I don't see where anyone answered this so I will: The carbs for 2F engines have a vacuum actuated secondary, those (2 bbl) for F engines have the mechanical actuated secondary. You can actually feel the secondary engage through your foot on the carbs for F engines. You can not feel it on the ones for 2Fs.

Jim Chenoweth told me that the 2F carbs do flow more CFMs than the F style carbs, and that the later ones used on late FJ40s and all the FJ60s flow more still. He also said that all of the 2F carbs flow more than either Weber 38/38 or Holly 350s.

 

[subzali]

Thanks Jeff for that description of the actuation of the secondary - my PO has always maintained that they weren't sure that the secondary was kicking in, even when swapping carbs. I found the problem and documented it in this thread:
http://risingsun4x4club.org/forum2/showthread.php?t=16462

I found that my Aisan 38/40 (12/78 build date) has 31/33 venturis. I'm guessing the change to 31/35 venturis came about in '81 or so, with the introduction of the FJ60 model, but would have to check out a few to know for sure.

From my research on MUD, it would seem then that an Aisan 38/38 (F engine) has 28/31 venturis. All very interesting stuff.

I believe a Weber 32/36 is rated for 300 CFM, a Weber 38/38 (with 26/26 venturis) is rated at 375-400 cfm, I *think* the Holley 350 is rated for 350 CFM, and the Aisan 38/40 (for the '75-'76 model year) is rated for 425 CFM:
Jim C. on the subject

By the way, a 2F needs at least 300 CFM when turning 4000 rpm (and probably closer to 373 CFM if you take 0.8 volumetric efficiency). If you have a balanced engine that can make use of more air (ported, cam, etc.) and run higher rpms than 4000 you could calculate what you need, could be as high as 466 CFM at 5000 rpm (depending on your V.E.).
CFM formula based on engine displacement/rpm

I'm not sure about the other Aisan 38/40 carbs (which Jim says are almost as big) or the Aisan 38/38. I've been trying a little bit to calculate it out, but my numbers aren't quite working out yet. I think they're usually rated by bench testing rather than calculation. Not sure why the '75-'76 would have the highest flow, unless I'm wrong with my guesses of venturi size changes over the years, or unless there's some other factor limiting flow...

Clear as mud?

Another post on the subject:
More from Jim C.

 

[subzali]

BTW Ricardo where can I buy forceps to remove the clip under the accelerator pump? Online or local??

 

[RicardoJM]

BTW Ricardo where can I buy forceps to remove the clip under the accelerator pump? Online or local??

The nearest fishing supply business; flyshop, sporting goods store, Walmart will have them.

 

[Jacket]

Or head shop.

 

[ZIronPig]

Reading this post brings back all sorts of memories

 

[PabloCruise]

Ricardo, this thread is bueno!

I can't wait to spend a little more time reading through it a second time...

Thanks

 

[nuclearlemon]

Ricardo, this thread is bueno!

I can't wait to spend a little more time reading through it a second time...

Thanks

gettting ready do this, fj? pighead and i are getting ready to do at least two, maybe his also. he got the build dates and i just have to order the kits now.

many have said the napa kits are more complete than the keyster kits. anyone have an opinion/knowledge on the quality comparison?

 

[RicardoJM]

gettting ready do this, fj? pighead and i are getting ready to do at least two, maybe his also. he got the build dates and i just have to order the kits now.

many have said the napa kits are more complete than the keyster kits. anyone have an opinion/knowledge on the quality comparison?

It really is a mixed bag, even within the Keyster line. I used a parts store kit for a rebuild on a 22R all the rest have been Keyster kits purchased from Kurt at Cruiseroutfitters. If a part is not damaged, I prefer to clean it up and put it back in versus using a new part from the kit. Typically, I end up using the gaskets and rubber housing for the accelerator pump from the kit and ignoring the rest.

I have had isssue with the rubber cup on new accelterator pumps getting destroyed upon installation and really prefer to use (most often reuse) the ones with the leather.

 

[nuclearlemon]

napa carries accel pumps with the leather boots. don't know if that's what comes in the kit or if you have to order them seperately