I took the truck for a longer drive and when I turned off the ignition it gave a couple of shakes and bangs. I don't know the technical term. Self-detonation, spontaneous combustion maybe?

The previous owner added a electric fuel pump. He reconnected the airpump/smog stuff and it everything seems to be working fine.

The engine runs great. It does not hesitate and pick up nicely. It didn't happen yesterday, but today the weather is a lot warmer.

I figured that carbon deposits might cause self detonation.
Where should I look first?

Should I change the spark plugs? If so, which ones would you suggest. I have a N20 engine. I don't know what spark plugs I have now.

Should I try higher octane fuel? (I use regular)
The gastank was on 1/4 when it happened. I just filled it up again with regular and noticed it had created some vacuum in the tank. Not sure if that is important to mention.

Could it be that the carb is too rich causing carbin deposit?

Should I take a look at the valve clearance?

Could it be the timing?

 

Some people call that dieseling. A frequent cause is the fuel in the carb having the float set too high. When you shut it off, it sort of boils over and keeps running for a few seconds. With automatics, we often shut them off in gear (lower idle and more resistance to stop it). You should check your float level, set the timing, and look for vacuum leaks. NGK V-power spark plugs work great in toyotas, and they are less than $2 each. This is probably a temp related issue, colder days or short drives don't make it happen, correct?

 

Dieseling make sense.
I didn't happen before, but I just bought the truck. It didn't do it yesterday during a 20 mile drive in the rain. But today it did it twice (when my gas tank was on 1/4). It is definitely warmer then yesterday. I filled her up with fresh fuel on the way home. And it didn't happen after that.

I am still trying to baseline it and iron out the quirks.

 

Several things can cause that one mentioned carbs and high idle wrong heat range plugs and over advanced ignition timing ..so give it a look over see how it's doing

 

You will get it sorted out. If you are still using a stock carb, swap to a weber. Should help simplify and iron out some more problems. Btw where are you from? Sweet looking little hilux

 

Oh, I'm sure I will. Thanks, it is a nice little truck. I am very happy with it.
I just picked it up yesterday. Here is my introduction thread.

I'm from Ontario Canada BTW

 

You said everything I was thinking

 

You might try slowing down the idle. I know with my last truck it dieseled until I made it idle lower

 

That's exactly why we shut autos off in gear. Holds the idle down a few hundred rpm.

 

Add one more sometimes on carbed vehicles with high mileage carbs the throttle plate / butterfly's bushings Get old and oval out letting to much air or throttle not closing well do to to much play rare for Asian carbs . But seen it a few times on rodchester quadra jets and ramjet carbs all crappy ... But check your throttle linkage for correct operation and lube cable and linkage if necessary

 

Great tip! ^^ Also make sure its not all gunky and the return spring is snug but not too tight. That will lead to the shaft being pulled too hard and ovaling out like he was saying.

 

I tried fixing the dieseling and I thought for a moment that I had found it. I used a timing light and noticed that the timing was off (I think retarded). I adjusted the timing so that the marking on the engine aligned with the BTDC marking on the pulley. As stated in workshop manual I disconnected the vacuum line to the distributor.
I took it for a drive but when I parked it and turned off the ignition, it started stumbling again. Close but no cigar..
I also adjusted the idling speed, but that didn't do the trick either.

 

Have you checked your valve adjustments closer to spec or on spec . ..and does your carb still have or have the fuel cut solenoid .. ? Your float level maybe just set to high. Also check those plugs for carbon build up or a higher than normal heat range .. Another thing while your all in there get you a big can of carb cleaner ... Wedge that carb open and spray alot really hose her down .. Let it sit for a bit before you crank it cause it won't wanna start .. For a bit This is just to remove built up gunk on top of the valves and or general top end of the motor

 

Could it be related to the fact that the PO reconnected the smog pump?

 

I have to correct myself. I stated that the timing was retarded but I was wrong The timing was way too advanced. I put it back to factory spec and for a while it seemed to do the trick. Even today I had a good run and it didn't diesel. But when I got home it was back. So I retarded it some more, just a couple of degrees. Let's see if that helps. I will also fill up wit premium next time. Fuel isn't what it used to be. Playing with the timing makes a difference so I am concentrating on that for now.
I haven't checked the valves yet. I think it has a solenoid. There is a wire running to the carb.
I took the spark plugs out and they looked good light brownish tint. They are NGK BPR5EY, V Powers. They looked pretty new and had no carbon build up.

 

Well retarding it more didn't change it. So I put it back to stock specs.
I found a bottle of octane booster and put it in the tank.
I also connected the electric fuel pump to the 'on' key position. It was on 'acc'. I thought that it might have an effect because when I turn off the ignition, the pump will still run with the motor off. Only turning the key all the way back will stop the pump. Now it will stop pumping the moment the engine stops which makes more sense.
I also checked the solenoid and it seems to work. When I disconnect the plug, the engine dies immediately.

I took it for another drive this morning (about 50 miles) and the stumbling is definitely less. I only had one little hick-up. But the weather is somewhat colder so that could be a factor too.

It was half full so I topped it off with premium and drove home again. So far so good, no stumbling. But I am not fully convinced yet that I have solved the problem.

 

Little update:
I used the truck today for some home renovation work. I had to drive to the building centre a couple of times and NOT ONCE did it run on. Every time I turn off the iginition I still pray a little. It will take a while to get that out of my system. Fingers crossed.

 

$%^& ! After a longer drive today, it had the shakes again. Just once but still.

I decided to seafoam it today I hope it gets rid of any carbon buildup. Man, did it smoke !!
I also lowered the idle some more.
Let's hope this finally fixes the dieseling.

 

Well, I took it for a longer drive. And it didn't diesel. My guess is that lowering the idle in combination with sea foaming might have done the trick. The engine definitely feels different.

I am sure there is carbon build up. I found a sticker under the hood. The previous owner replaced some belts and the diff oil at 17.226 miles. That was in december 2007.
I bought it with 20.500 on the odo. So that amounts to about 600 miles a year.
I try and drive it as much a possible and that seem to help.

 

Yes drive it as much as you can motors especially carbed motors don't like to sit around and dry out