carburator dieseling problem

[levikepsel]

I have an 1986 Toyota pickup i just put a new 22R motor in. I bought a weber 34/34 DGEC carb to put on it and i'm having a hard time getting it to turn off. It consistently diesels(spits and sputters and tries to fire) after I turn the key, sometimes up to 20ish seconds. Here's what I have tried over the last five months: I have eliminated all emissions junk. I have rejetted the carb's idle jet from .25 up to .50 and back down( that's the entire range possible for this carb). I have tried multiple sets of spark plugs to lower internal cylinder temperatures. I am running NGK BP7ES plugs right now, that's 2 temp ranges lower than stock. I have put a holley fuel pressure regulator on it and am running about 2 PSI. weber recommends 1.5 to 3 PSI and I have adjusted to try different PSI levels as well. I have alternately advanced and retarded the timing +/- 15 degrees with and without the vacuum advance hooked up. I have repeatedly checked for vacuum leaks and have found nothing. My engine has amazing vacuum and great compression. I have even sent it back to weber carbs 2 times and they've gone through the whole carb and have found nothing wrong. I'm probably missing something obvious so i'm offering my problem to the y'all. If anyone can offer suggestions i'd be much obliged and if I can't fix than i guess you'll see a toyota engine for sale soon. OH yeah, and my truck runs fantastic aside from turning off. Accelerates smooths, way more power than stock, and great mileage to boot. A real head scratcher. Thanks.

 

[waynehartwig]

Run it in the driveway (with the air filter off and lines plugged) and while you look down the carb, turn it off. See if gas is spilling out of the carb keeping it running.

If so, you can put a spacer between it and the engine to keep the carb cooler and keep the fuel from boiling/expanding in the carb and then seeping out.

Along the same lines, make sure the float level is correct.

 

[kowe69]

Dieseling problems are most often caused by excessive carbon build up in the combustion chamber and on the valves. The carbon creates hot spots inside the engine that act much like glow plugs. When you turn the key off you cut power to the ignition system but the hot carbon can still ignite the fuel that is available from the carb because there is a venturi effect pulling fuel into the engine as the engine spins. Carbon build up is caused by poor fuel quality and low speed/rpm driving. I would buy a good quality fuel system cleaner and start using a fuel with techron. And then rev the piss out of the engine in the freeway. Remember if you want to remove carbon build up, RPMs are your friend! Hope this helps.

Edit: I just noticed you said "new" engine. Is it really new or is it just new to the vehicle (used)?

 

[UNSTUCK]

Use a waterbottle to mist water into the carb while the engine is running. That will help brake up the carbon.

 

[78mitsu]

may also want to check your timing, if you've got too much advance in the base curve, when you shut the motor off, it discharges the coil and fires the cylinder. In an older rig, often the alternator isn't isolated from the ignition light the plug spin the motor alternator give enough current to partially charge the coil and do it all over again. retard the timing enough, and the problem goes away, I'm pretty sure a 22r needs about 35* of total time at this elevation.

 

[levikepsel]

New in this case means spanking new. less than 2000 miles and i've put all of them on it. I'm pretty sure there is no carbon buildup. I've run premium and lucas fuel cleaners multiple times. I've revved this thing up and poured water straight down the carb and nothing black came out the exhuast. I've retarded the timing back to 15 degrees behind zero to lower the cylinder temp and it hasn't seemed to change anything. I'll play with the timing a bit more after work. Thanks for the suggestions. I'll keep working on it.

 

[SLC97SR5]

I'm not familiar with the Weber carb, but the factory Aisin has a Idle Fuel Cut Solenoid that closes upon key off to prevent dieseling.

Does the Weber have a provision for this and is it wired correctly?

 

[levikepsel]

it does not come with a fuel cut off, the guy from weber is checking to see if one is available from europe.

 

[levikepsel]

I am interested in what this means, could you add some punctuation? "In an older rig, often the alternator isn't isolated from the ignition light the plug spin the motor alternator give enough current to partially charge the coil and do it all over again. retard the timing enough, and the problem goes away, I'm pretty sure a 22r needs about 35* of total time at this elevation."

 

[waynehartwig]

I am interested in what this means, could you add some punctuation? "In an older rig, often the alternator isn't isolated from the ignition light the plug spin the motor alternator give enough current to partially charge the coil and do it all over again. retard the timing enough, and the problem goes away, I'm pretty sure a 22r needs about 35* of total time at this elevation."

I think he's trying to tell you that you turn the key off, but the alternator is still keeping the ignition system alive.

 

[bryson]

Is your idle set really high...?

 

[levikepsel]

I just adjusted my fuel pressure down to 1.5 PSI and readjusted my idle and my idle mixture down as low as possible while still running decent. didn't make a difference. I also rejetted the main primary down 1 size to a 20 and the idle jet is at a .40. still diesels. aargh.

 

[Ratm3at]

22r dieseling

I just adjusted my fuel pressure down to 1.5 PSI and readjusted my idle and my idle mixture down as low as possible while still running decent. didn't make a difference. I also rejetted the main primary down 1 size to a 20 and the idle jet is at a .40. still diesels. aargh.

I know it's been years since The last post on this. Did you ever resolve this issue? I recently picked up an 86' 22R. Everything was stock with California emissions stuff on it. It had many vacuum leaks and was running poorly. I decide to remove all the smog equiptment and for now keep the factory carb until I can buy a Webber. I rebuilt the carb, blocked off all the smog ports on the engine. It's running great now but it has started dieseling after the smog removal. I haven't checked the timing yet though. Any suggestions?

 

[BlueWolfFab]

How's your coolant level and coolant temps while the engine is running? If your coolant is low and you're getting air pockets in your head and therefore your head isn't getting the proper cooling it needs, the head will get hot enough to create self combustion of the gasoline without the need of spark.

What's your compression ratio? A high compression ratio could cause it too on a hot engine.

That's how I would know when my old 350 SBC was low on coolant, it would "diesel".

 

[lhracing]

Is your idle set really high...?

Dieseling is almost always caused by the idle set too high and too low of Octane fuel. If you are having problems keeping it running you may need more advance in the timing and/or premium fuel.

 

[RogueJeepr]

I had an aftermarket electric fan keep a car running for 20seconds after key was off.
It was wired to an ignition source so it was always on when key is on then would send power back during shut down.


Dont need big tires to have fun.