Labor Day Putting down your wrenches or time for
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| | | | Joined: Jan 2011 Posts: 237 'Bolter | | 'Bolter Joined: Jan 2011 Posts: 237 | good morning to all,
we have been working on my sons 1953 chevrolet canopy it has a 250 motor in it. the gas tank has been cleaned out, new gas lines, new fuel pump, two gas filters added, rebuilt carb, new pipes, new spark plugs with points and condenser replaced. when i drive the truck, runs fine now but when i get home and turn it off, the motor "diesels" in other words it still wants to run
any ideas? thanks in advance | | | | | Joined: Apr 2005 Posts: 7,440 Bolter | | Bolter Joined: Apr 2005 Posts: 7,440 | Timing and/or you have the idle set too high.ðŸ›
Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne (Emily)
‘39 Dodge Business Coupe (Clarence)
“I fought the law and the law won" now I are a retired one!
Support those brave men/women who stand the "Thin Blue Line"! Hug a cop!
USAF 1965-1969 Weather Observation Tech (I got paid to look at the clouds)
| | | | | Joined: Feb 2004 Posts: 29,742 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,742 | Check for vacuum leaks, and slow the idle speed down. 500-600 RPM is a good target to shoot for.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Nov 2005 Posts: 6,100 'Bolter | | 'Bolter Joined: Nov 2005 Posts: 6,100 | Hy oldmemoriescc, what r.p.m. is the engine idling at? The throttle may be open too far at idle allowing the engine to get air after you turn the ignition off, the engine may have carbon deposits in the combustion chamber that remain hot enough to ignite fuel if there is air (oxygen) present. Hope that helps. | | | | | Joined: Mar 2014 Posts: 4,475 Moderator, Electrical Bay | | Moderator, Electrical Bay Joined: Mar 2014 Posts: 4,475 | When ignition switches fail, occasionally they won't immediately break the circuit which keeps the coil energized when you turn the key off. This will cause a condition which almost exactly mimics dieseling because usually the engine will run for another 5 to 10 seconds before the ignition switch contacts can "let go."
The 250 sixes had HEI ignition...or at least I know for a fact some of them did. If a relay wasn't added between the heavy gauge wire needed to supply the coil then that could definitely cause the ignition switch to fail. And I am a shining example of this oversight. I recently added HEI to my 235 and forgot all about the high amp demands of the HEI coil.
So now I have to wire at least a 20 amp relay (preferably 30) connecting the 10 gauge coil wire straight to the battery (the ignition switch will then be operating that relay in the same manner it operates the starter solenoid). Otherwise my engine will continue to run every time I turn it off until the ignition switch finally burns out.
As I recall the original switch was designed to handle a maximum of 15 amps and with the HEI coil that isn't enough. And yes, I am irritated that I made such a boneheaded error, but I did and now I know. Good luck on your search of the problem. One way to check for this is to (a) find the coil (some were mounted on the engine) and (b) have somebody turn the engine off at the same time you disconnect the plug from the coil. If it stops without continuing to run, you've found the culprit.
~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
| | | | | Joined: May 2005 Posts: 8,983 Sir Searchalot | | Sir Searchalot Joined: May 2005 Posts: 8,983 | Agree with others. Idle too high.
To test the switch, just pull the hot wire off the switch to stop motor.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
| | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | Engines will also backfire when going downhill(throttle off) if there is an ex. Manifold leak.
Ec
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
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