Aisin secondary tuning ideas (1 Viewer)

[CruiserTrash]

I changed too many other variables so the stock spring is still in there for now.

I did test the springs on a scale though. I compressed each one about 90% and wrote down that number. Then I figured out the resting height of the spring when it’s inside of the vac pot - about 26mm. It has a little preload on it in other words. I compressed each one to ~26mm and measured the force. I wrote that in parentheses after the main number. All measurements in grams. The AED aftermarket ones go from claimed weakest (at the top) to claimed strongest at the bottom (black). For the most part they are accurate in the instructions.

All of the springs are stiffer than the Toyota spring except for the white one.

 

[CruiserTrash]

30 minute highway run, including some long 20-30 second WOT burns on uphills. Still no action from the diaphragm. Scratching my head now…

Is it simply an altitude thing? Is the vacuum created by the Venturi effect just less at 5000’, and that’s not enough?

 

[Spike Strip]

What Jets are you running. Primary and secondary? Still the stock 1.47 and 2.00?

Do you have an in-cab vacuum gage (FSM spelling )?

 

[CruiserTrash]

What Jets are you running. Primary and secondary? Still the stock 1.47 and 2.00?

Do you have an in-cab vacuum gage (FSM spelling )?

Didn’t realize the FSM uses “gage” haha. Yes, I have manifold vacuum, water temp, and air/fuel “gages” in the cab with me.

Should be on stock jets. I rebuilt this carb over a year ago and I forget - but I didn’t replace or change them, and I don’t recall seeing anything aftermarket or out of the ordinary.

 

[CruiserTrash]

Chatted with @RDub this morning trying to make sure Venturi vacuum is being generated and finding it’s way to the secondary vac pot. The secondary butterfly is open enough. The vac passage goes along the phenolic spacer and I’ve tried the spacer with it’s baked-on gasket and extra fiber gaskets. I’ve tried the paper o-ring between the carb body and the vac pot dry and soaked in oil. I manually tested the vac pot off the carb and it holds suction.

What else? I’m going to swap the paper gasket between the vac pot and carb body to a rubber o-ring. The paper gasket sits in a recess and it doesn’t appear to get much squish. I’m also going to run the vac pot with NO spring as a sort of dummy check. The butterfly shaft has a coil spring to keep it closed, removing the vac pot spring will just give the diaphragm the easiest possible movement. That test will only be to verify that vac signal is getting there at all - I won’t run it like that permanently.

Last resort - and I loathe this thought - a small amount of sealer where the vac passage runs up against the phenolic spacer? I would use the extra fiber gasket so no goop got on the phenolic’s bonded gasket material. Removing goop would damage that. Removing from the metal carb body would be easy enough. Not enough to squish out and plug an holes inadvertently, just enough to make it air tight.

 

[CruiserTrash]

@LazarusTaxa I forgot that we discussed the secondary diaphragm at altitude in this thread.

Anything to report back on that? Ever get it working?

 

[LazarusTaxa]

@LazarusTaxa I forgot that we discussed the secondary diaphragm at altitude in this thread.

Anything to report back on that? Ever get it working?

Nope.. Never figured it out or got it to work. I still assume it has something to do with operating at altitude.

I also have a no-start issue where it seems like if I let the 60 sit for more than 24 hours all the fuel drains back to the tank (my guess) as it takes forever to crank/start... After that, it will start fine until I let it sit for another 24 hr+ period.

I have plans to put a sniper in it, hopefully this winter, which will fix both items and have therefore quit wasting time on them.

 

[CruiserTrash]

Nope.. Never figured it out or got it to work. I still assume it has something to do with operating at altitude.

I also have a no-start issue where it seems like if I let the 60 sit for more than 24 hours all the fuel drains back to the tank (my guess) as it takes forever to crank/start... After that, it will start fine until I let it sit for another 24 hr+ period.

I have plans to put a sniper in it, hopefully this winter, which will fix both items and have therefore quit wasting time on them.

I've had two carbs where the float bowl drains within 10 minutes of shutting it off. It ends up in the intake, likely coming through the vent at the top of the bowl - although why the entire bowl empties, I don't know. Nobody has cracked the code on that as far as I can tell. When I cold start it takes about 8-10 cranks to get a little fuel in the bowl, the two stomps on the gas pedal to prime, then start and she goes. I've learned to live with that.

@RDub and I were talking today and got back into Bournouli's equation. The pressure drop through a venturi is definitely less when the air density is lower. My only unknown right now is whether or not the gasket is tight where the carb body and base meet (the vac passage for the secondary runs along the gasket. I'm going to try the thinnest smear of sealant there tonight then test again. If the secondary still isn't opening, I've 100% narrowed it down to altitude. The pressure delta across the diaphragm just doesn't meet the threshold to defeat the spring pressure. Pressure delta being atmosphere on one side, and the low pressure through the venturi on the other side, which would make the diaphragm move.

FYI I put the white aftermarket spring in this morning - it provides less force than the stock spring. Zero change on the paperclip. You can see the different spring forces at the top of this page.

 

[CruiserTrash]

Back in the game

Took the carb apart again. Last week I installed the paper gaskets that come with the rebuild kits - just on a whim. That was a mistake - it creates a vacuum leak in the half-moon shaped vac passage. Do not use this type of gasket, just use the phenolic spacer.

While I had it apart I took a better look at the vacuum passage where it runs through the body of the carb and then next to the phenolic spacer.

First of all the ports in the venturis have orifices in them to delay the diaphragm opening.

I used compressed air in a can (so I could fit the straw into the passages, and flexible little welding tip cleaners to make sure the orifices weren’t plugged up.

Then I looked at the routing of the passages. As other threads mention, the vac diaphragm gets vacuum from both venturis and needs a total vacuum of some certain level to open. Vacuum from one venturi isn’t enough.

I started thinking about those aluminum plugs. The casting was open so Toyota could install the orifices, then they plugged the holes. I got a wild hair and thought maybe those weren’t air tight. I painted some gasket shellac on them, making sure it got all around the base of the plugs where it contacted the carb casting.

After that I took it for a test drive and the Paperclip showed full opening of the diaphragm! Success.

One of you in this thread is Ryan from Instagram - not sure which Mud handle is yours. Anyway, Ryan was suggesting that because there’s play in the three bolts holding the carb together, it’s possible that a slight shift when reassembling is the ticket to sealing up the vacuum passage for the secondary. Whether it was that or the gasket shellac on the plugs, we’ll never know.

 

[CruiserTrash]

Back to the original intent of this thread: tuning.

I only had about 20 minutes of driving last night after I got things back together so I really can’t comment on how the secondary action is playing out.

Changes I’ve made:
-“first touch” is probably 20 (typo) 10 degrees sooner on the primary
-“kick up” angle is opening the secondary about 4mm instead of the 25 degrees in the FSM (good for about 1-1.5mm opening)
-white aftermarket spring installed

Last night I didn’t feel the secondary “kicking in” abruptly. The truck felt like it had a little more guts though, emphasis on little. I’m wondering if my first touch and kick up settings, or the white spring, are bringing the secondary to full opening too soon. Or maybe the way I have things set provides a smoother transition. I need more seat time.

First half of the trip I was putting the hammer down a lot, several WOT burns up some hills, merging onto the highway, etc. Halfway through the test drive I reset the paperclip and tried to drive a little more relaxed, keeping to regular roads. The goal was to either stay under the diaphragm opening threshold or just barely get it started opening. That was successful.

I guess the way I have the secondary tuned now must be intuitive if I was able to do that. More to come today and this weekend as I drive it.

 

[ryyount]

Back in the game
View attachment 3871445

Took the carb apart again. Last week I installed the paper gaskets that come with the rebuild kits - just on a whim. That was a mistake - it creates a vacuum leak in the half-moon shaped vac passage. Do not use this type of gasket, just use the phenolic spacer.
View attachment 3871448

While I had it apart I took a better look at the vacuum passage where it runs through the body of the carb and then next to the phenolic spacer.

First of all the ports in the venturis have orifices in them to delay the diaphragm opening.
View attachment 3871455
View attachment 3871456
I used compressed air in a can (so I could fit the straw into the passages, and flexible little welding tip cleaners to make sure the orifices weren’t plugged up.

Then I looked at the routing of the passages. As other threads mention, the vac diaphragm gets vacuum from both venturis and needs a total vacuum of some certain level to open. Vacuum from one venturi isn’t enough.
View attachment 3871452
View attachment 3871454

I started thinking about those aluminum plugs. The casting was open so Toyota could install the orifices, then they plugged the holes. I got a wild hair and thought maybe those weren’t air tight. I painted some gasket shellac on them, making sure it got all around the base of the plugs where it contacted the carb casting.
View attachment 3871457
View attachment 3871458

After that I took it for a test drive and the Paperclip showed full opening of the diaphragm! Success.

One of you in this thread is Ryan from Instagram - not sure which Mud handle is yours. Anyway, Ryan was suggesting that because there’s play in the three bolts holding the carb together, it’s possible that a slight shift when reassembling is the ticket to sealing up the vacuum passage for the secondary. Whether it was that or the gasket shellac on the plugs, we’ll never know.

That’s me! Glad you got it going man. I need to actually measure my paperclip movement - I’ve had a larger clip on in the past and it always ends up sideways from hitting nearby things on its way back down.

 

[CruiserTrash]

That’s me! Glad you got it going man. I need to actually measure my paperclip movement - I’ve had a larger clip on in the past and it always ends up sideways from hitting nearby things on its way back down.

Your name seems obvious now haha! I honestly didn't go back through to check. Thanks for the moral support behind the scenes on this!

And yes, try the smaller sized paperclip and look for 11-12mm of movement.

 

[greenEFSI]

@ryyount In your post Jorge @RodrigzCrzr posted a link to this thread:

Builds - 78 Mustard Yellow FJ40 #Tiger40 - https://forum.ih8mud.com/threads/78-mustard-yellow-fj40-tiger40.1301194/page-30#post-15690161

There's some good stuff in there about being VERY careful that the holes in the gaskets line up with the vac passages where the carb sections meet. I wonder if I was careful, but not careful enough.

That was my thread I too had a heck of time getting my secondary to work. The egr spacer gaskets that come in the kit caused the same vacuum leak issue so I took them out. The secondary would not properly work until I bent the tang to touch the lever with no gap. That way when I gave it full throttle the Venturi vacuum is strong enough to open.

Another thing to consider is the power valve operation. I had to sand mine with 2000 grit because it was getting stuck. Lastly, I went through all the gaskets and opened up any thing that was partially blocking holes. The base gaskets also had generic matching holes that I had to open up to the correct size.

 

[CruiserTrash]

That was my thread I too had a heck of time getting my secondary to work. The egr spacer gaskets that come in the kit caused the same vacuum leak issue so I took them out. The secondary would not properly work until I bent the tang to touch the lever with no gap. That way when I gave it full throttle the Venturi vacuum is strong enough to open.

Another thing to consider is the power valve operation. I had to sand mine with 2000 grit because it was getting stuck. Lastly, I went through all the gaskets and opened up any thing that was partially blocking holes. The base gaskets also had generic matching holes that I had to open up to the correct size.

View attachment 3872736

View attachment 3872740

View attachment 3872737

Good stuff and thanks for your work. As I often say: I stand on the shoulders of others around here.

At this point I’m really thinking there’s a high likelihood that these carbs leak at the vac passage plugs. And it might not just be the secondary circuit - maybe all the plugs are suspect. Time, heat, vibration … sealing air tight is hard.

 

[CruiserTrash]

got some highway miles in yesterday. My daughter had a lacrosse game in Fort Collins, about 75 minutes away. The highway doesn’t go into the mountains but has a few slight uphill grades 1-2 miles long.

This is where the secondary really makes the difference. Before I would have fallen off whatever speed I was trying to hold, but now I can accelerate up these long gentle grades. It’s a 2F, so we’re not talking Ferrari-level acceleration here. Maybe 1mph every 2 seconds. But that’s better than losing 10-15mph going up hills like that. Huge difference, and it makes the truck way more drivable.

Regarding how I have the carb tuned:
-first touch as soon as the linkage will allow
-kick up on the secondary is about 5mm open (FSM is about 1-1.5; 5mm is about as much as you can make it
-white diaphragm spring
-> these three are the absolute “max” you can tune this carb to. They’re the most aggressive settings. I do think elevation makes a difference so these might have even more of an effect at sea level.

Here’s how that played out:
-the secondary will open with about 75% throttle or more
-Takes about 3 seconds of being above that threshold for the secondary diaphragm to start working
-Takes about another 3 seconds for the diaphragm to fully open the butterfly

What’s next:
-I’m going to monitor fuel economy - I know the 2F isn’t a Prius but I also don’t want to be needlessly dumping gas as I commute around town.
-The first touch and kick up cracking open the secondary sooner and further than the FSM gives a little more juice in the mid range (1800-2500rpm?). I’d like to keep that as it’s great for starting to get on a highway, or being able to pass somebody on a city street, or get out of harms way. Not a ton of power, but just enough to feel good.
-The diaphragm has a propensity to open when driving down city streets. I’m going to back off the spring back to stock and try that. Maybe I’ll go one stiffer. With the secondary being cracked earlier and more (helpful for a little mid range power), it’s building more vacuum on the diaphragm faster. I just need to counteract that vacuum with the right spring.

So far no bogs, stumbles or other issues. I’ll report back with air:fuel gauge info after I’ve had time to monitor that more. We had a weather front move through yesterday and the change in temperature and pressure through all my gauges off.

 

[RevISK]

Standing on shoulders you may be but this is some amazing work here Jim... I smell FAQ status soon.

 

[Skreddy]

@CruiserTrash I’ve been following along waiting until I could try this out.
Today before my drive to work, I put on the paper clip (I’d done this previously and knew I was getting some travel but not as much as if I moved the linkages by hand). I also bent the tang to get first touch much earlier; it’s around 1/2 throttle now. To get any sooner, I’d need to pull carb or linkages and didn’t have time. I didn’t adjust anything else as I wanted to see if this by itself made a noticeable difference.
Sure did! First thing I noticed was my slight bog on acceleration when cold is pretty much gone. I left with engine colder than normal just to test this. My first 2 miles to work is a slight uphill, winding road. I normally am a little too high of rpm’s for 3rd, but too low and boggy for 4th. I was able to use 4th with no downshifting without the bog and easily accelerate. More of the same the rest of the way to work. 8 miles on a hilly freeway and the bigger hills I still drop rpm’s in 5th, but not as bad. Can easily gain speed and rpm’s in 4th where before, it was a very slow gain.
Going to drive it a couple more days, then go on to the next change. I’m running an Amazon Aisin knockoff that I went through when I first got it.

Thanks again for this thread!

 

[CruiserTrash]

@CruiserTrash I’ve been following along waiting until I could try this out.
Today before my drive to work, I put on the paper clip (I’d done this previously and knew I was getting some travel but not as much as if I moved the linkages by hand). I also bent the tang to get first touch much earlier; it’s around 1/2 throttle now. To get any sooner, I’d need to pull carb or linkages and didn’t have time. I didn’t adjust anything else as I wanted to see if this by itself made a noticeable difference.
Sure did! First thing I noticed was my slight bog on acceleration when cold is pretty much gone. I left with engine colder than normal just to test this. My first 2 miles to work is a slight uphill, winding road. I normally am a little too high of rpm’s for 3rd, but too low and boggy for 4th. I was able to use 4th with no downshifting without the bog and easily accelerate. More of the same the rest of the way to work. 8 miles on a hilly freeway and the bigger hills I still drop rpm’s in 5th, but not as bad. Can easily gain speed and rpm’s in 4th where before, it was a very slow gain.
Going to drive it a couple more days, then go on to the next change. I’m running an Amazon Aisin knockoff that I went through when I first got it.

Thanks again for this thread!

View attachment 3873641View attachment 3873642View attachment 3873643

Looks like you’re fully opening there. Awesome!

The “bog” when cold is probably due to decreased airflow from the choke being engaged. It would also restrict airflow through the venturi, meaning less vacuum pull on the diaphragm - the secondary doesn’t open up in other words. I think there’s a linkage that slightly opens the choke when the secondary is engaged but I haven’t dug into that yet, so I might be wrong.

That first touch looks really aggressive, but the geometry of the aftermarket carb linkages might be slightly different. I might pull my carb in the coming weeks and measure the first touch and kick up angles just for documentation purposes. But if you like the way it drives like that, that’s fair.

One thing that bugs me is the mechanical nature of the kick up, or initial cracking open of the secondary or whatever you want to call it, is that when you push the throttle all the way to the floor the secondary actually comes closed about 25%. So best power is at like 95% of the pedal travel. This is because two of the linkages kind of bypass each other a little at the end of their throw. Maybe the pedal stop bolt needs adjusted to limit travel, but I don’t want to keep the primary from opening to a full 90 degrees. I’ll have to dive into all that later.

 

[Skreddy]

I noticed the secondary closing with mine when fully open as well, haven’t looked close enough yet but my guess is that vacuum holds the blade at or near vertical.

As for my bog, I didn’t have the choke on when I drove off. I think the kick open for the secondary coming open sooner just helps with a little more airflow to distribute the fuel in the intake runners, but I could be wrong in that. Haven’t done enough to see if it’s a lean bog or rich bog. Could’ve just been coincidence as well. Will see when I leave work this morning.

 

[CruiserTrash]

I noticed the secondary closing with mine when fully open as well, haven’t looked close enough yet but my guess is that vacuum holds the blade at or near vertical.

As for my bog, I didn’t have the choke on when I drove off. I think the kick open for the secondary coming open sooner just helps with a little more airflow to distribute the fuel in the intake runners, but I could be wrong in that. Haven’t done enough to see if it’s a lean bog or rich bog. Could’ve just been coincidence as well. Will see when I leave work this morning.

Another possibility:

If the choke is not engaged, then you’re getting a ton of air flow from a cold carb into a cold intake and the fuel isn’t atomizing very well. Lots of air, and lots of big, liquid fuel droplets. That might lead to a crappy burn in the cylinder. Just a guess, as what happens inside the cylinders is still black magic to me - ignition, flame fronts, squish, etc., are all pretty technical and mysterious subjects to me.

And yes, perhaps the vacuum is enough to hold the secondary blade open even if the mechanical opening retracts a bit. Good call.