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Discussion Starter #1
just put a new (old) 74 motor into my 69 cruiser. <IMG SRC="smilies/smile.gif" border="0"> 60,000 original miles
When I shut ift off it diesels and wont turn off. It only does it when the truck is warmed up.
Shuts of fine when its cold.
Anyone tell me what they think the problem could be?
Thanks
Brian
 

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Damn - I thought people wanted diesels <IMG SRC="smilies/biggrin.gif" border="0">

Your ignition timing is probably the culprit, or a lean mixture, or running too hot (bad radiator/cooling system) - BTW, timing and lean mixture cause motors to run hot. Good luck.
 

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One of the major causes of dieseling in petrol (gas) engines is carbon deposits somewhere inside the cylinder ie on the piston crown or the valves etc. The carbon stays very hot after the combustion stroke, sometimes long enough to cause ignition on the next compression stroke, even without a spark. This is similar to the effect of a glow plug in a model aircraft engine which runs without an ignition system.

I suggest (with all the usual disclaimers) that you should go for a long hard highway drive. This will allow the pistons and valve to reach their maximum operating temperature and, hopefully, burn off the carbon. Get it out on the open road and sit at the highest speed you feel comfy with. Try to keep the throttle setting as constant as possible.

Hope this helps
 

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Discussion Starter #5
Originally posted by morgan:
<STRONG>Is the fuel shut-off solenoid on your carb working? Should have switched 12V, and click when the body of the solenoid is grounded.

morgan</STRONG>
HOw do I test the selonoid?
The truck is not running hot but may have carbon deposits . Ill try the highwy drive test . <IMG SRC="smilies/smile.gif" border="0"> Thanks for the info
 

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Originally posted by flexlarson:
<STRONG>HOw do I test the selonoid? </STRONG>
Take the solenoid out of the carb, switch the key on but don't start the motor, ground the body of the solenoid against the engine block. It should click.

Since the problem is only evident when it's hot, then the problem might not show up in this test, if the problem is the solenoid.

morgan
 

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Originally posted by flexlarson:
<STRONG>If the timing was off wouldnt it diesel all the time?</STRONG>
if the ignition is too far advanced it might cause "pinging" under load (pre-detonation), which is similar to dieseling. Are you having pre-detonation problems?? Have you checked the timing?
 

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Dieseling, if we are talking about the same thing, is when your engine continues to run when you try to shut it off. When you shut of the engine it turns off the ignition system, so I don't think that it has anyting to do with timing or other ignition system faults. I also doubt that it has anything to do with fuel shut off. Shutting the fuel off will not stop the engine right away. At minimum there is still some air/fuel mix in the inlet manifold that the engine can run on.

Just take it out on the highway and sit on the speed limit for a few hours. Let me know how you go.
 

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my guess was also carbon deposits in the combustion chamber . i have seen this as a problem before and was cured by pouring water down the carb while it's running . dont laugh it works ..
take a cup of water and slowly pour it into the carb a quarter of a cup at a time at the same time the engine will want to stall keep it running by giving it throttle . i learned this in an advanced autoshop class in college
the water helps clean out carbon deposits .
carbon is chrystaline and it's the very sharp edges of the carbon build up that retain heat after the enginge is shut down , when an engine diesels it still draws fuel because it is creating vacum when more fuel is drawn into the engine it will keep dieseling until the deposits cool enough to allow it to stop .. hope this makes some sense ...

[ 08-25-2001: Message edited by: fj junkie ]
 

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What grade gas are you using? My Cruiser will diesel on lower octane gas, but not on higher grade stuff. The low octane gas burns awfully quickly and can cause this sometimes.
 

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Discussion Starter #12
I have not had a chance to take it out on the road yet to try to burn the carbon out.
I might try it today if I have time.
How long do you thik I should drive. You mentioned one hour or two.

Im a bit leary about pouring water into my carb .

The truck only does the dieseling (continues to run after I shut it off. Or at least tries to run, Sputtering and stuff. ) when I shut it down when Its hot not when Its cold.

Thanks guys Ill keep you posted
<IMG SRC="smilies/smile.gif" border="0">
Brian
 

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LOL my pickup diesels all the time. <IMG SRC="smilies/biggrin.gif" border="0"> I just let the clutch out as I shut it off, it's funner than fixing it. A stock 22r and a huge suped up carb don't really go together!
 

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shut it of fin gear , or run 92 octain gas and try the timeing and your good to go! jiMMy
 

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Discussion Starter #15
Tried to take it out today but it kept popping through the carb.

What do you guys think?
Gonna put a lite on it in the morning and see whats up.

Any more thoughts?
Thanks.
It doesnt diesel when I first start it up only after iot warms .
 

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Popping through the carb, eh...

Let's go back to basics:

1. Did you check the fuel cutoff valve? To check the valve (it's on the back side of the carb and has a single wire) turn vehicle of and touch the wire to +12V. it should click. If so, the valve is good. re-connect and switch the vehicle to run (not start) it should click again.

2. Look at the sight glass in the front of the carb while the engine is running. The fuel should be at the 1/2 way point. If not, its time to adjust (at least) the float in the carb. Good time to rebuild it, if that's the case.

3. Timing?

4. Could be the power valve in the carb is sticking, or as was the case with mine, missing the jet. This is pretty remote though.

Definately sounds like gas is dumping into the beast. How's your milage? What's your exhaust smell/look like?

More clues will get you closer to the truth....
 

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oh man what ever you do don't our water in your carb while it running. This will cause broken pistons and probably some fractured valves. The trick that whomever refers is to put DROPLETS of water in your mixture. I've done this, it works, however i would not recommend this unless you know what your doing. When i say a drop i mean a drop, one at a time, very slowly. This cold water will jar the carbon loose, hopefully, and fix the problem. Without being there to see whats going on, i'd say that you have this problem, its common with motors that don't get driven much. highway miles are important, heating the motor all the way to operating temp and running it is important. Driving 5 blocks to work and back daily will cause huge amounts of carbon deposits. Another easy fix is to pull the head and physically clean all the chambers, i would suggest this if you don't feel comfortable with the water trick. good luck.
 

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Originally posted by noonan:
<STRONG>oh man what ever you do don't our water in your carb while it running. This will cause broken pistons and probably some fractured valves. The trick that whomever refers is to put DROPLETS of water in your mixture. I've done this, it works, however i would not recommend this unless you know what your doing. When i say a drop i mean a drop, one at a time, very slowly. This cold water will jar the carbon loose, hopefully, and fix the problem. Without being there to see whats going on, i'd say that you have this problem, its common with motors that don't get driven much. highway miles are important, heating the motor all the way to operating temp and running it is important. Driving 5 blocks to work and back daily will cause huge amounts of carbon deposits. Another easy fix is to pull the head and physically clean all the chambers, i would suggest this if you don't feel comfortable with the water trick. good luck.</STRONG>
sorry noonan you are not going to hydrolock an engine with a 1/4 cup og water slowly poured into a running carb and it works great for getting rid of carbon deposits
 

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i didn't say anything about hydrolock did i? When you introduce drastically different temperatures to valves and pistons during combustion it makes them crack. After rebuilding many many engines, i've kinda seen it before. I think most will agree, pouring water into your intake is pretty much insane. Ask any one at your local track.
 
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