Jets for Aisin 60205 9/74 carb

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So my first post/question is on High Altitude jetting.
I am restoring my 9/74 FJ40 that I bought after graduation from CU Boulder and went into the Navy. I had done a refresh in 1986 but was recked in 1991, but I kept it and have been restoring it after 15+ years of sitting idle. I live in Glenneagle, Co at 7000 ft

I have been researching threads and found one attributed to FJ40 Jim where jet line up as follows for 8000 ft:
114 primary
120 secondary
50&50 or 60 slow
60 power

My questions are:
1. Can I use two 55’s for slow jets? Installed were 55 and 80 and have only those in kits over the years. The 80’s are longer, does that make a difference, if I put a 55 in the secondary slow hole?
2. My factory manual says to use an 80 in the power valve. Has MUD experience shown the 60 in the power valve a better choice? Hence FJ40Jim’s recommendation?
 

65swb45

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1. Chances are that the longer slo jet will not fit in the primary hole , so the point is academic.

2. 1.20 is too small for the secondary.

3. Since the’window’ between the power valve opening and the secondary opening is usually very brief, you will probably find the relief you are looking for in a larger secondary main jet.

4. I always recommend making changes incrementally, that is, one at a time. Start with the secondary. 1.80 is a good place to start with an F1.5
 

Dizzy

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I'm all about fuel economy. Well, that and fuel range. I'm at 6,800' and I regularly go to 10,300.' I say go as rich as it was stock, to start. If you are getting 10-13mpg, then fine. If your manifold vacuum is high, like 16" or more, then further tuning might be rewarded. My vacuum is low, and, it seems to create a kinda lean symptom on the throttle, so I'm running the (original) richer jets on a 'non-USA,' OEM carb, it is fine as long as the motor is warmed up, I'm getting 11 to 13 mpg.

Your '74 has a wing nut on the air cleaner for hot air intake, right? Winter is my biggest lean symptom hurdle, as the exhaust manifold has been replaced with headers, and I bet that my alone in the cold intake manifold isn't having the best of conditions to perform in.
 
Joined
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colorado springs
I'm all about fuel economy. Well, that and fuel range. I'm at 6,800' and I regularly go to 10,300.' I say go as rich as it was stock, to start. If you are getting 10-13mpg, then fine. If your manifold vacuum is high, like 16" or more, then further tuning might be rewarded. My vacuum is low, and, it seems to create a kinda lean symptom on the throttle, so I'm running the (original) richer jets on a 'non-USA,' OEM carb, it is fine as long as the motor is warmed up, I'm getting 11 to 13 mpg.

Your '74 has a wing nut on the air cleaner for hot air intake, right? Winter is my biggest lean symptom hurdle, as the exhaust manifold has been replaced with headers, and I bet that my alone in the cold intake manifold isn't having the best of conditions to perform in.
I misquoted the secondary in original post. It should have been 1.80 not 1.20, 😬

As far as slow jets holes, the primary and secondary are the same depth so a 55 or longer 80 will fit. On disassembly there was 55/80 slowjet arrangement.

Anymore thought on best power valve with this arrangement?

OBTW thu I purchased the FJ in CO, I did a refresh in ‘87 while in MI so I believe I jetted it for low altitude. Thu I can’t recall what was in the per-rebuild it explains why I have such an array of jets.
 

Dizzy

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Part of what tuning should address is an overall balance of the carb functions. When you go up in altitude, air density changes, significant changes would be noticed in engine vacuum, all other variables remaining constant. Okay, so, common sense is that you need to get more air volume in the engine, just to compensate for its lack of mass in that given volume. So, you bump up the angle of the throttle plate for idle, but what in effect you do is modify the way that fuel mix makes its way thru the various passages / circuits. Ultimately, it is the speed of air moving across these openings that causes a pressure drop, and fuel mixed with air make its way thru the bowl into the carb throats. When the vacuum gets really low, your idle setting is a very open primary throttle plate, and it doesn't make a difference if you change the idle mix screw, because you are idling on progression circuits to a greater extent than when the throttle plate is set for idle at sea level.

On the carb for my Nissan pickup, the technique was actually to drill a 1mm hole in the primary throttle plate, opposite the progression holes. This allows me to keep the throttle plate consistent with the architecture of the overall carb. Changing jet sizes, although it can be helpful, wasn't necessary, just getting more air thru. Without that hole, no amount of tinkering would get me from idle to throttle, without a lean 'hickup' symptom. I do realize that common sense tells folks that carbs run rich at high altitude, but, that isn't really my observation, on a couple of engines.

Yes, the Aisan factory made a high altitude carb, but, maybe only Jim or Mark actually know the rest of the specs of the carb. I wouldn't be inclined to match numbers with a different build, just keeping things how they were from the factory, as the throttle plates and Venturi's changed across carbs as well. I realize that we aren't sure what those figures are for jets, etc. I feel that a rich condition is where you want your margins, as lean tends to create thermal wear on engines, and, it really eats performance at the gas pump and on the road, not good for straightening out shade-tree mechanic uncertainty. Plus, most people use vacuum advance, which allows more time, than a stock factory USA F.5 '74, for the engine to make use of what oxygen is in the fuel charge.

So, to answer your question about the best power valve, it is hard to say. Probably, richer, but, I'm really not sure. The power valve is just a crutch at times of low vac, so, it has to do some quick temporary enrichment, then the engine should be back on regular settings.

A few tuning aids, a measure of vacuum at idle, an O2 sensor in the downpipe, or a heated one behind the exhaust collector, and a air/fuel readout gauge. Also, looking at your spark plugs, 'reading' them visually, with good up close photos (please). The O2 readout is a great temporary dash tool, as once you verify performance, put it back on the parts shelf, it is like EFI technology lends a hand to the best of the pre-smog (simpler is just plain better) auto world - yes, I'm calling FI a kind of 'smog equipment.'

Was there any corrosion in the bowl on this carb? I always wonder how minerals, and oxidation affects the flow of fuel thru the various passages on these things, and I don't really know how to deal with it.
 
Joined
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Messages
3
Location
colorado springs
Part of what tuning should address is an overall balance of the carb functions. When you go up in altitude, air density changes, significant changes would be noticed in engine vacuum, all other variables remaining constant. Okay, so, common sense is that you need to get more air volume in the engine, just to compensate for its lack of mass in that given volume. So, you bump up the angle of the throttle plate for idle, but what in effect you do is modify the way that fuel mix makes its way thru the various passages / circuits. Ultimately, it is the speed of air moving across these openings that causes a pressure drop, and fuel mixed with air make its way thru the bowl into the carb throats. When the vacuum gets really low, your idle setting is a very open primary throttle plate, and it doesn't make a difference if you change the idle mix screw, because you are idling on progression circuits to a greater extent than when the throttle plate is set for idle at sea level.

On the carb for my Nissan pickup, the technique was actually to drill a 1mm hole in the primary throttle plate, opposite the progression holes. This allows me to keep the throttle plate consistent with the architecture of the overall carb. Changing jet sizes, although it can be helpful, wasn't necessary, just getting more air thru. Without that hole, no amount of tinkering would get me from idle to throttle, without a lean 'hickup' symptom. I do realize that common sense tells folks that carbs run rich at high altitude, but, that isn't really my observation, on a couple of engines.

Yes, the Aisan factory made a high altitude carb, but, maybe only Jim or Mark actually know the rest of the specs of the carb. I wouldn't be inclined to match numbers with a different build, just keeping things how they were from the factory, as the throttle plates and Venturi's changed across carbs as well. I realize that we aren't sure what those figures are for jets, etc. I feel that a rich condition is where you want your margins, as lean tends to create thermal wear on engines, and, it really eats performance at the gas pump and on the road, not good for straightening out shade-tree mechanic uncertainty. Plus, most people use vacuum advance, which allows more time, than a stock factory USA F.5 '74, for the engine to make use of what oxygen is in the fuel charge.

So, to answer your question about the best power valve, it is hard to say. Probably, richer, but, I'm really not sure. The power valve is just a crutch at times of low vac, so, it has to do some quick temporary enrichment, then the engine should be back on regular settings.

A few tuning aids, a measure of vacuum at idle, an O2 sensor in the downpipe, or a heated one behind the exhaust collector, and a air/fuel readout gauge. Also, looking at your spark plugs, 'reading' them visually, with good up close photos (please). The O2 readout is a great temporary dash tool, as once you verify performance, put it back on the parts shelf, it is like EFI technology lends a hand to the best of the pre-smog (simpler is just plain better) auto world - yes, I'm calling FI a kind of 'smog equipment.'

Was there any corrosion in the bowl on this carb? I always wonder how minerals, and oxidation affects the flow of fuel thru the various passages on these things, and I don't really know how to deal with it.
Dizz,

Thanks for the follow up. Some of my issues with this restoration is that the FJ was disassembled some 25 years ago after a bad wreck on a dark icy road. I initially started a rebuild immediately, and collecting parts and vehicles to complete the overhual.
Unfortunately kids, long cold NY winters, cancer, and college tuitions took time, money and effort away. I also have a ‘63 TR-4 which took my ‘spare time’ to keep in decent shape to take to State Fair snd other shows. My kids earned spending money helping take apart parts vehicles and maintaining the family cars.

Soooo, I can not report plug or fuel bowl condition from a running FJ, which would give me much info on what to adjust. I am not a carb savont so have learned much on the actual working of the carbs from yours and other posts. The carb was untouched for 20 years so yes it was gummed up pretty bad. I soaked the heck out of it, blew all passages and then ran pressurized carb cleaner thru each. Since I am at 7000 now and know I rejetted for low altitude I am looking for the best starting point on this overhaul. I have changed Primary/secondary jets on the truck- not that hard with right screwdrivers but of course power jets and slow jets mean full removal.

Unfortunately Covid labor shortages has crippled my Frame guy which is next step (NY guy did not take out all the twist) then off to have body parts mounted to ensure proper fit. Paint the tub, sand blast and powder coat the frame. Maybe by Christmas have back to start mounting all the ‘goodies’

So engine start isn’t on the schedule until Feb/Mar depending on how cold this winter is!

Thankyou for sharing your knowledge/experience. I think I will go with MDH33’s running lineup at 6800 as a starting place - he said it came from Jim C. Adjust if plugs, vacuum and engine response call for it based on your suggestions.

I’ll try and post my progress thru the winter.
Lou
 

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