Engine Run On

[Shamu70]

A huge thank you to Lefty71 for pointing out what I needed to do to post.

I’ve got a 493 that runs on when you shut it off after a half hour of cruising.
Temp is about 190 & I’m going to replace the water pump just because.
No info on the cam timing; screws on Edel. 800 are 1& a half turns out.
I’ve been told that maybe the RJ12YC is too hot of a plug & I’m open to trying a colder
one. But is it colder as the numbers go up or down?

 

[Davea Lux]

A huge thank you to Lefty71 for pointing out what I needed to do to post.

I’ve got a 493 that runs on when you shut it off after a half hour of cruising.
Temp is about 190 & I’m going to replace the water pump just because.
No info on the cam timing; screws on Edel. 800 are 1& a half turns out.
I’ve been told that maybe the RJ12YC is too hot of a plug & I’m open to trying a colder
one. But is it colder as the numbers go up or down?

Stock plugs are RJ11Y, in today's terminology that will be RJ11YC, the C is for copper. (Bigger number is hotter) Before springing for plugs, check your idle speed as too high an idle speed will also cause run on. Going to a 180 stat should also help. If you are running too much advance on the timing, that will sometimes heat up the piston tops and cause run on as will having the plugs gaped to narrow. The ethanol blend fuels also can cause problems because the factory carb settings do not always work well because of the different flow patterns of the modern fuels. You should be running a premium grade fuel not a regular grade.

Dave

 

[jct]

MOPAR Big Block hi flow water pump

Robertshaw 370-160 Series hi flow thermostat

 

[live4theking]

This is a phrase I'm not familiar with. What is run on? Is this what others call dieselling?

 

[Davea Lux]

This is a phrase I'm not familiar with. What is run on? Is this what others call dieselling?

Yes

 

[live4theking]

Yes

Thanks

 

[rkrochen]

Stock plugs are RJ11Y, in today's terminology that will be RJ11YC, the C is for copper. (Bigger number is hotter) Before springing for plugs, check your idle speed as too high an idle speed will also cause run on. Going to a 180 stat should also help. If you are running too much advance on the timing, that will sometimes heat up the piston tops and cause run on as will having the plugs gaped to narrow. The ethanol blend fuels also can cause problems because the factory carb settings do not always work well because of the different flow patterns of the modern fuels. You should be running a premium grade fuel not a regular grade.

Dave

Do the easiest thing first slow the idle down a bit. If that doesn’t work then you need to dig deeper.

 

[Shamu70]

So I backed down the timing a little, which really calmed down the demeanor of the engine (can’t say I like it yet) & that cured it. But I was in a hurry & didn’t compensate the idle; but at least now I know.
Think I’ll still go with the RJ11 s though.
Thanks guys! Car is still the street beast!

 

[saforwardlook]

I would think that on a car modified as yours has been, 1 1/2 turns out on the mixture screws would be too lean - I would expect maybe 2 1/2 to maybe even 3 turns would be closer to optimum. If richer, you probably could turn down the idle screw speed setting and that too should stop the run-on - then you can leave the timing where you like it possibly (you should adjust the mixture screws to where you get the maximum idle speed at a given idle speed screw setting. Worth a try.

 

[detmatt]

Your plugs should be fine, you want the hotter plug these days. As long as they’re clean and gapped properly.

 

[Shamu70]

Thank you, I’ll try that as well. Thought I’d had the thing tuned (by ear & feel) by now, but I love tuning and playing.

 

[Shamu70]

I want the RJ12YC that are in there now because of today’s fuels? I always use Shell or BP 93.
And a couple of times a year I add 110 octane race gas from a Citgo.

 

[Shamu70]

So on the Edelbrock 800 the mixture screws are now 2.5 turns out, idle turned down & timing is retarded a little. That's pretty vague info I realize, but while the run on is gone, now it knocks when you step into it.
More fuel mixture & back off timing a little more? Just put half a tank of 93 in too. Octane booster?

 

[stubs300]

Thank you, I’ll try that as well. Thought I’d had the thing tuned (by ear & feel) by now, but I love tuning and playing.

I used to do that until I got a vacuum gauge to go along with my timing light. Hook them both up then set your timing for MAX vacuum, regardless of what your timing is! Then tweak your carb to try and get more vacuum. Then go back and re-tweak your timing for more vacuum, then re-tweak the carb again for MAX vacuum. Set it and forget it! Good Luck

 

[Shamu70]

6/28 morning: turned the distributor back until the vacuum canister hit the tallish RPM intake & set the idle; sweet spot! Locked down and happy. It's already 80 so it ran a little hot, but that's ok.
Thank you everyone for great advice.

 

[Shamu70]