Hi there, I'm new here and need some help with my recently acquired 87 pickup. Here's the facts:

Condition:
22r, manual (w55 according to the vin plate) nearly 100% stock, seems to have seen little more than preventative maintenance in the 180k miles before I got it. Only real change is a aftermarket muffler (probably one of those cheaper-end flowmasters) bolted up after the Cat, without a tailpipe at the other end. Looks like the old one probably just fell off. Dunno if it matters but thought I would include it.

Work So Far:
I've replaced the timing chain (first valve check showed me the infamous double gouges of chain/cover "interface"), changed all fluids, done valve timing, new dist. cap/rotor, new plugs, replaced leaking clutch master cylinder with a late model unit, new air and fuel filters, and new battery. everything else is probably as it was when it left Japan. plug wires look OK so far.

THE PROBLEM:
Sometimes, when getting up on the freeway, a few minutes after getting up to speed (sometimes sooner) I will get a very severe "Chugging" i.e. drop in power, engine stumbling. It can be so severe and violent that I will push the clutch to coast it / return the engine to Idle, and sometimes at that point it will just wind down to a stall. The weird thing is that I can start it up again almost immediately after this. I've had to do it on the road before, while still moving.(I DON'T RECOMMEND IT) The stumble severity increases with throttle position; feathering the throttle, going really easy on the gas seems to reduce it. It won't go away if the engine is under load/ in gear, but if the engine returns to idle (say, in neutral) for long enough, it seems to fix itself. The stumble is a very steady "chug chug chug chug" like its missing half it's cylinders or lugging REALLY badly. What's even weirder is that whenever this doesn't happen, the little truck runs like a champ, EVEN at highway speed (70+). It accelerates aggressively and willingly at lower speed starts; the problem never really manifests till about 4th gear under moderate to hard acceleration, such as accelerating up onramps that require aggressive throttling to merge with traffic. (making this problem SO much more fun, ha!)

Thanks so much in advance for any tips you can offer.

 

carb'd right? (you said 22r)
have you checked your plugs?
are all you spark-plug wires are in good condition (no cracks) and well seated and not grounding out anywhere?
have you checked the coil?
have you checked the float chamber fuel level (sight window on the side of the carb) and the fuel level is half-way up the glass?

 

Yeah it's carbed with the stock aisin unit. Plugs are brand new, wires show no obvious wear and are seated correctly. They will probably be the next step, though, since they are cheap and easy.

I've checked the float level but I'm not sure I'm doing it right. I thought it should be showing fuel even when the engine is off, but I've seen it without anything showing in the sight glass... not sure if it was overfull or underfull. FSM said to check when it's running though, which I admit I haven't done. I wouldn't think it would matter, right?

I didn't have starting problems after seeing nothing in the glass, but float-bowl level issues were suspected, since to me the problem "feels" like fuel starvation. Fuel pump maybe? I plan on pulling the air-horn while leaving the rest on the truck, just to check the state of the floats, though fiddling with carbs has never been a favorite of mine. Will any parts fall through if I pull it off?

The coil will probably be a last resort... a replacement coil is pricey, and junker yota's are scarce around here.

What about timing? I thought I was timing it correctly, but I've read some conflicting opinions as to whether the two vacuum advance lines should be disconnected or not. Should they be left on, or taken off and plugged? I plugged them.

Thanks for the quick reply.

 

You need to do it running so you can verify fuel pump and float are maintaining the fuel level in the chamber. While it's running you can also twist the throttle quickly wide-open (maybe have someone inside stomp the pedal down and hold it at 3/4 for a few seconds) and verify that the float level drops some then comes right back up to the middle within a couple seconds at most. If it doesn't recover, the fuel pump may be going out. If it over-fills, the float may be sticking low and not shutting the needle valve/cutting off the fuel.

As for the timing, if you're using a light, you need to pull and plug the hoses from the distributor. If you want to do it by ear, you can leave them on then go driving and advance it in little steps until you hear either detonation under light acceleration in 4th gear or under full throttle in any gear, then retard the timing til it just goes away.

 

OK good, I was using a light so it should be fine.

Thanks! The symptom = diagnosis parts are especially appreciated, the Haynes and FSM I have neglect to include such simple field tests. I'll try it tonight, hopefully that will tell me something more conclusive.

Thanks again!

 

Maybe pull the air horn and spray some good cleaner in there and make sure the float's not sticking and see how it goes first.

 

Any recommendations on good ones? And is it safe to spray it down the carb throat too? I definitely need to use some to free up the fast idle linkage... its a little stubborn, not that its much of an issue here in florida.

 

Sounds to me like you're on the right track by looking at the fuel delivery/float situation. Maybe a rebuild of the carb is in order.

Since you have a low pressure carbureted system, you might also put a bowl type fuel filter in there somewhere so you can see if the fuel is being contaminated. I've seen it happen with older vehicles -- it might be contamination/corrosion in the fuel tank.

Goofy/inconsistent timing can also cause this sort of thing, but with the symptoms you describe, my vote is for fuel system/carburetor.

 

I had the same "symptons" before I replaced my Cylinder head. Not sure if it was just a coincidence or not even now but it would run ok after spraying carb cleaner through it for awhile then start acting up again, but did it all the way up to the head replacement ... which the head had a small crack which was allowing coolant slowly into the first cylinder.

Anyway, I haven't done anything to the carb since, not even sprayed cleaner through it besides when I did the head job obviously. But motor runs great.

I was thinking my symptoms were related to coolant fouling the #1 plug so mis firing essentially... loss of power, chug chug chug etc only on the highway.

Just throwing that out there. =)

 

looks to me like the fuel pump

 

I'm partial to berryman's but just about any carb cleaner is okay, as is throttle body or maf cleaner. You can use any of them to spray down the throat as well, but the intake runners on the 22r tend to stay cleaner than the 22re since the fuel will remove residue.

I feel it's probably the fuel pump but I would try the cheap stuff first- cleaning it up.

 

Good deal... I'm going to check the float level behavior first, maybe tinker with the carb then go from there. I'll keep you posted. You guys have been fantastic with the help!

 

OK, so I cleaned up the carb bowl after pulling the top off and finding a nice thick layer of rust-sludge built up at the bottom. shot everything that looked like a jet or port with carb cleaner, and when I buttoned it all back up and it idled like crap... sputtering and stumbling... cylinder firing sounds very erratic. Going down the list, I moved on to a new fuel pump, got that in and to my (wallet's) dismay, it made no difference. My mechanic's shop monkey of a younger brother suspects the alternator. I'm going to go get it checked tomorrow.

Moving back to the fuel side of things, could someone familiar with the layout of the Aisin carburetor tell me which of the uptakes in the float bowl do what? Is there something I might have missed, other than just doing a carburetor rebuild?

BTW, I still can't get the float bowl to stay full, but from the strong gas smell the engine puts out when it's stumbling, I'd tend to agree with my brother, that what we have now is possibly a charge problem, not a fuel problem.

I'm kinda out of ideas here. Any theories would be great.

 

it will idle like crap if there's carb cleaner left in the float chamber. how long did you let it run?
if a new fuel pump didn't help, I wonder if there's a problem between the fuel tank and the pump?

 

The carb cleaner is a possibility, I will try and run the engine for a bit more to make sure that's not the problem before pulling and checking the alternator. I might have underestimated how long it takes to clear it out of the carb. I'm pretty confident that there aren't any problems in the fuel line from the tank, even the older pump flowed a decent amount when I did the "how much fuel will it pump with ten seconds of cranking" test. Is it possible that my old gasket isn't sealing properly? It looked to be in good condition and suffered no damage when I removed the top. I know it's supposed to be a one-time-use gasket, but I'd heard it could be reinstalled without issue. Is it likely that there is a vacuum leak in the carb causing stumbling?