Aisin carb questions (1 Viewer)

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Hey Guys,

I have a '76 FJ40 with the stock carb, plugged off AI and EGR, condenser in place of igniter, otherwise stock. I rebuilt the carb with Jim Chenoweth's kit (included new float and new secondary diaphragm) about 3 years ago and it has worked great until Thanksgiving weekend at Land-Between-the-Lakes when I noticed it began to miss big time intermittently at anything between idle and full bore pedal to the metal. That is it idled nice and smoothly but at anything off idle it missed unless I really tromped the pedal when I could feel a surge from the accelerator pump jet of fuel and I could feel the second throttle open in 3rd and 4th gears. Being a few hundred miles from home and not looking forward to removing the carb and rebuilding it with 6" of snow in my driveway and temperatures below 20F, I have been adding a bottle of fuel cleaner to each tank of gas and I'm on my 3rd or 4th tank now. The problem of the miss has greatly dimished in the past few days and seems to sort of come and go but I'm not ready to say that it is completely gone. By the way, I could smooth it out when it was missing badly by choking it a little, even with the engine warm. I also tried some carb cleaner spray through the holes in the bowl to try to hit the jets and also inside th throats but I don't think I got it where it needed to go.

My diagnoses is she was/is not getting enough fuel at anything but idle or unless gettting juice from the acclerator pump jet or the secondary jet. I've been hoping the problem was some dirt or varnish build-up in the primary or main jet/circuit which the fuel system cleaner in each tank of gas might clean up and this seems to be working slowly. Could it be something like the power valve or other internal mechanisms I don't really understand malfunctioning? Doesn't it seem a little soon, 3 years or so, to have to rebuild the carb? By the way, the fuel level in the site glass is right where it should be, even when she was missing badly, and I did a full tuneup last summer (valve adjustment, new cap-rotor-points-condenser-plugs-plugwires, set dwell and timing, new pcv, air and fuel filters). It's been getting me back and forth to work OK and whatever the problem was may have been cured by now but interested in your thoughts. I'd really like to avoid having to remove th ecarb and properly rebuilding it until spring/summer.

Thanks,
Pete
 

65swb45

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Pete said:
Hey Guys,



My diagnoses is she was/is not getting enough fuel at anything but idle or unless gettting juice from the acclerator pump jet or the secondary jet.

Doesn't it seem a little soon, 3 years or so, to have to rebuild the carb?

Thanks,
Pete
A carb can go bad in 5 minutes if it gets dirt in it! I once had a customer who didn't make it 5 miles from my shop back home because he was too impatient to let me install a new fuel filter before he left. When I opened the air horn in front of him and showed him all the sheit in the fuel bowl, he was way embarassed.

I think your diagnosis is good enough to say that you have some blockage in the primary. Good idle and good heavy throttle response, when the power valve kicks in to suppliment [also bypass] the primary jet, and then the secondaries. Mark Whatley [tech writer for Toyota Trails] had a GREAT photo of a piece of a weed stuck in a primary jet to illustrate just this situation .

If you have the skill to rebuild the carb, and it sounds like you do, it shouldn't take more than 10 minutes for you to clean this out.

Get to it.
 
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Thanks! Do you think the blockage is at the primary jet or downstream from there? I could live with removing the air horn to clean out the bowl/jet...I'd like to avoid pulling the whole carb until spring if I can.

I saw Mark's pic in Toyota Trials I think.

Thanks again,
Pete
 

65swb45

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If the primary emulsifier has a good spray pattern once the power valve opens, then the trouble is confined to the primary jet.
 
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The fact that it is intermittent suggests that it is dirt in the bowl plugging the primary jet as Mark suggested. If not, the off idle of transition slot above the throttle plate might be plugged. If so, you might get lucky and blow it out with compressed air through the idle screw hole or the primary "slow jet" hole (after removing the screw or jet). This even might blow out a plugged primary jet if you can't get it through the bowl. You can remove the primaries w/o removing the carb.
 
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PH and Mark,

Thanks for the comments guys. I think I'll first remove the jet bolts (? drain plugs?) in the bottom of the float chamber and try to get some carb cleaner into the primary jet from the outside. I'll also try some compressed air or carb cleaner through the idle mixture screw. PinHead I'm not sure what you mean by the transition slot above the throttle plate. I know I can clean things out much better if I remove the air horn and I have a gasket on the way to replace it but it's cold and snowy here and I don't have a heated garage so I want to avoid doing that if possible. Several years ago I learned what blockage of the main jet can do....I had removed the air horn on another rig to reset a float level that was too high and not having a gasket to use when I put the air horn back on, I used a little silicone on the torn gasket I had. A month or so later the Crusier would run for a few seconds and die. Pulled the carb for rebuild and found a tiny flake of silicone almost completely covering the primary jet. Nothing so stupid this time but I agree that something may be partly blocking that jet.

Thanks again guys,
Pete
 
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My carb hasn't acted right since I replaced the fuel filter. Just dies once it is warmed up. Sounds like I may be dealing with the same thing.
 
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I've had similar problems a few years ago on my 80-FJ40. Turned out that bad gas had crudded up the carb and filters. Don't buy Bradley gas.

...
 

65swb45

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dfmorse said:
I've had similar problems a few years ago on my 80-FJ40. Turned out that bad gas had crudded up the carb and filters. Don't buy Bradley gas.

...
Or really good gas with those special 'additives' in it that finally broke the shellac loose from inside the factory metal lines. :eek:
 
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Pete said:
PH and Mark,

PinHead I'm not sure what you mean by the transition slot above the throttle plate.

Pete
Check the primary first as it seems more likely. The transition or off idle fuel circuit is shown in the FSM. It provides fuel when the throttle is initially opened from 500 RPM to about 1200 RPM, before there is enough vacuum in the bore to pull fuel out f the main nozzle.
 

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