Hey guys, been lurking for years but finally decided to make myself known. Just picked up another yota. Its an 84 and of course it has carb issues. Basically it runs perfect when cold, starts right up, choke is in adjustment, high idle perfect and all that.... but as soon as it gets warm and kicks off the last step of high idle it starts runnin like crap... missing and sputtering... engine shakin around as it misses... and to top it off once its warm it dies everytime i stop hard. its not the booster, and it doesn't stall when i stop hard in reverse, just forward....Its all stock underhood, 212k miles on stock motor i believe. Just threw in new plugs, wires, cap, rotor, fluids and filters and rebuilt the carb (cheap autozone kit, basically just replaced all the diaphrams, gaskets and blew out all the ports with carb cleaner and compressed air) but... its still runnin like crap. It gets better if i open the throttle more or if i close the choke by hand just a little... but still not perfect.
Thanks in advance.

 

Aisin, not Asian.

:wabbit2:

 

What is this "booster"?

Neither Aisan or Toyota uses this word to described any part of the carburetor. Except for the brake booster. Please give clarification on what you mean.


1) Check that the fuel level in the sight glass is in the middle.

2) Check to make sure the vacuum advance of the distributor is working correctly. If you don't have the factory service manual (a.k.a. FSM), there is a electronic PDF version on this forum somewhere. You'll have to search, though.

3) Since the vehicle is new-to-you, check the timing. With your symptoms, I don't think that is an issure here, but check to make sure.

4) Check for general vacuum leaks, e.g. the rubber vacuum hoses, intake leaks, carburetor leaks, etc.

5) is the metal cap for the Idle Mixture Screw still in place? That idle screw may have been mis-adjusted which can cause a faulty idle.

 

Sorry for the confusion, i meant i ruled out the brake booster as being a source of vacuum leak causing it to stall when brakes are applied.

Fuel is right in the middle of the window when engine is running. (not sure if it matters if its running or not)

The vacuum advance seems to be working, the hose closest to the front of the truck has strong vacuum when engine is running and warm but i don't feel anything in the other one....

I drilled the cap off the mixture screw, i'm running like 6 turns out right now. it gets better the further out (richer) i go on the screw but its not nearly enough.

Is it possible fuel pressure could be a problem? i kind of ruled it out because the window level looks good.

also i've spayed brake cleaner in all the obvious spots under the hood looking for vacuum leaks and can't seem to find any. are there any hot spots i might be missing? Ive also changed most of the small vac hoses.

I'm kind of leaning toward vacuum leak now because if i cover the top of the carb with my hand when running the idle goes up which i figure means its suckin air from somewhere else and thus getting leaner so idle goes up.

 

Having the fuel in the middle is important. So now, starvation can be ruled out for now.

It's not so much the vacuum source, as what that vacuum is doing to the vacuum advance on the distributor. What you'll need to do is rent/buy/borrow a hand-operated vacuum pump with a vacuum dial gauge and connect it to the vacuum advance. From there you apply vacuum and watch the gauge to see if the internal diaphragms will hold the vacuum. Then remove the distributor cap and reapply vacuum to see if the arm inside moves when vacuum is applied.


That's normal.


Well, now I would say check your timing for sure.



The stock carburetors run at a fairly low psi, somewhere around 4-5 psi. I don't have my book in front of me so I can't give the specs. Since the fuel level is in the middle of the sight glass you should be OK.

Fuel pressure is not as critical with a carb as the EFI system is. The carburetor is more concerned with volume, how much fuel is in the bowl.

 

update.... set the timing at 8 degrees btdc. tried 5 and slowly went up further and it got a little better at 8 but still far from perfect... vacuum advance is definitely working i would say because when i unplug and kink the line the idle drops and it misses a whole lot more...
I realized there is no vac applied to the advance when the choke/high idle is on... which is when it runs smooth. then as soon as the choke turns off and the vac is applied to the dist it starts missing horribly. so........ i'm thinkin a leak in one of the thermo vac valves or in the steel hoses thereafter but definitely can't find or hear it..... haven't had a chance to get a manual vac pump yet. possible the dist. isn't advancing enough?

 

Typically that is what is done to smooth out the idle by advancing the distributor. That's why I had mentioned to check it as the carburetor idle mixture screw has been turn so far out.

You did set the timing with the vacuum hoses off the vacuum advace on the distributor, yes? The hoses need to be off and then plugged to set timing.



The vacuum source for the distributor idle vacuum advance is not routed through any Vacuum Switch Valves (VSV). It comes directly from a port on the carburetor. A rubber vacuum hose connects the carburetor port to the metal rail, then the vacuum rail ends at the front of the valve cover where then a rubber vacuum hose connects the rail to the port on the distributor.



That is possible. Once the timming is set to 0 degrees with the hoses off & plugged, then attaching the hoses, the timming should advace anywhere from 8-12 degrees.

 

You need to go back and source a vacuum leak. Runs fine when airflow is reduced throught the carb either by choke or obstruction. Runs like crap when the choke is off. Even with the vacuum advance disconnected completely you should have a decent idle.

Intake manifold gaskets are sealing properly ? Carb sealing properly to manifold ? I'd run all the mating surfaces with propane or some type of cleaner. How's the throttle shaft bushings on the carb ? These are the areas that visually will look fine yet could be a source of a leak.

 

Yes timing was set with both hoses unplugged from the vac advance and kinked off.
I sprayed brake clean all over the mating surfaces of carb/intake, intake/head and throttle shaft to no avail. Only place i could think of would be bottom of intake/head mating surfaces since i couldn't get down there very well. I will try again with propane and see if there's any difference.
Thanks a ton for all the suggestions and help so far everyone.

 

Sounds like the same issue I'm having with mine except that mine has a backfire in the carb. '84 22r 2wd 4 speed with Aisan carb.

I took a video of what it's doing and posted it on youtube -
http://www.youtube.com/watch?v=lchH-...ature=youtu.be

It starts and runs fine when cold but as it warms up it idles rough and I start getting that backfire in the carb and sometimes it stalls out, as you get into the higher rpm's it will run fine. I haven't tried adjusting anything on it yet, waiting to check timing. However I don't know what would be causing this backfire?? Anyone seen something like this before?

 

I have no experience with something like that. The only thing I can think of is your timing is off. I say that because the only way to get cumbustion in the carburetor is the spark plug would need to fire while the intake valve is still open. Therefore, fuel would ignite backwards into the fuel source, the carb.

All of that is only a guess. So wait till others can chime in to tell me I'm loco, and give you the real reason.

 

Here's a video... Seems to get worse as truck warms up more.... When its first warming up and the choke turns off its not too bad but after i drive it and it gets nice and warm/hot it gets horrible as you can see in the video.... Sprayed a whole bottle of ether and one of brake clean in all the obvious spots (throttle shaft bushings, intake manifold gaskets both at the carb and head, steel vac lines on intake, etc.) and the only change in idle i get is when the vapor cloud sucks down the carb throat.

 

http://www.bluebassdesign.com/boonin/carb_faq/

 

That makes sense to me, I haven't been able to check the timing yet but I did do a compression test and I'm only getting about 100psi in each cylinder. It's never smoked and I hardly ever have to add coolant so I doubt it's a head gasket, it seems to be a timing issue unless one or more of the valves are bad. Hopefully I will get some time to check the timing this weekend.

 

hmmm...the only other thing I can think of, besides what has been already discussed or besides faulty carburetor internals, is the EGR system. Here's a link from another member who had a running issue as well and it turned out to be a faulty EGR system. I can't remeber if it was the modulator or the valve itself but here's the link to do some more reading:

https://www.yotatech.com/forums/f115...-range-234830/


However (here's my mussing), from the video, when putting your hand over the carb throat, the engine runs better. That would mean than you are alterering by restricting the air of the air/fuel mixture by using a physical obstruction, your hand. You are decreasing the air intake to what the carburetor is already metering into the engine. That would mean you have some kind of intake vacuum leak. The engine is sucking in more air than necessary. As you have already checked for vacuum leaks around the carburetor itself, the EGR uses intake vacuum from a Vacuum Switch Valve (VSV) to control the EGR system. Once the VSV reaches a certain temperature it will operate off of the intake vacuum. The EGR does not function on a cold engine as the VSV senses engine coolant.

 

Thanks for the link! You think just unplugging and capping the vac lines going to the egr modulators will change anything? I will try it as soon as i get some time and report back.

Another interesting fact.... I recently read that one of the main drawbacks to a stock carb is they cut out when on steep uphills but will run fine on steep downhills... mine is just the opposite. It dies immediately on almost any downward slope (or when hitting the brakes).... but when i point the nose toward the sky the idle kicks up to about 2500rpm and runs pretty smooth... weird huh?

I'm gettin so tired of this thing i'm about ready to just go with a weber but I need the Cali emission one which is about $400... unless anyone has a used one they want to sell me?? haha

 

I specifically can not say for sure.

In all my 25-years of ownership of my 1987 22R truck I never had an issue with the EGR system, either with the valve or the modulator. After I installed my new engine I did replace the EGR modulator & valve from Autozone. The modulator turned out to be a Toyota part with Toyota written on it for much less money than the Toyota dealer, either online or local.

Yes, very weird.


I would say check that EGR system and if still nothing, rebuild the carburetor. That's only if your mechanically inclined. Rebuilding the internals of the carb is not that difficult, it is all the external linkages and getting them to go back to where they work again.

Rebuilding the carb, if you can do it, will cost the price of the rebuild kit, a gallon of the carburetor chemical dip, and time. Heck, since you made the California comment, if you're near Sacramento, I can give you my carburetor dip.

 

Thanks for the offer... i'm about 2 hours south of sac up in the foothills. I actually already rebuilt the carb about a month ago... thats what i started with. Then proceed to take it apart twice since then and blow out all the ports to make sure nothing lodged its way in there haha. But you're right its pretty simple... especially after doing it 3x.. only thing i could think at this point is maybe something in the body of carb beyond the scope of the rebuild kit is messed up.