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Old 04-05-2013, 07:06 PM
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Dieseling issue

Recently had my engine rebuilt (longblock) and still in the break-in period. I still have a lot to learn about engines, especially one as aggressive as mine is now.

I seem to be having a dieseling problem. Not sure what the issue is. I tried setting the idle down but it doesn't seem to like much below 800rpm in gear. The severity of the run-on is consistent with the heat of the motor.

Plus the lope isn't consistent, when I put a light on it I see the timing occasionally jump (and you can hear it).

Whatever advice you can give would be greatly appreciated!

Specs on the motor:

'72 Ford 400, bored .040 over
270 duration cam with .519 lift, 110 lobe seperation; I was told it was a custom Bullet Racing grind with similar specs to a Comp Magnum 270H.
1:73 Scorpion roller rockers.
Edelbrock performer intake with a 600cfm 1405 carb.
Hooker headers.
MSD-6AL box, Blaster 2 coil, Duraspark II dizzy (24 max advance), 8.8mm wires, stock Motorcraft plugs set to a .050 gap.
180 Thermostat.
Stock fuel pump.

10 initial timing.

Getting 13" of manifold vacuum at idle.

C6 transmission with stock torque converter.

Pic:

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Old 04-05-2013, 07:52 PM
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Put more timing in it. Bump it up to 20*.
Then turn your idle down. You might need to take some timing out of the distributor though. Aim for 12-14 in the dizzy.
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Old 04-05-2013, 07:52 PM
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shut it off in gear,then select park
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Old 04-05-2013, 08:23 PM
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Agree wtih RWENUTS. You need more intial timing. The carb will respond better too. Edelbrocks like as much initial timing as the motor will allow. Which means, you will need to limit your total advance to 12-14 additional (it may like more). Could also try hooking vacuum to the intake. Not sure on Fords, but if it is like a GM HEI, you can limit the mechanical advance in the dizzy and just eliminate the vacuum.
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Old 04-05-2013, 08:31 PM
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Quote:
Originally Posted by RWENUTS View Post
Put more timing in it. Bump it up to 20*.
Then turn your idle down. You might need to take some timing out of the distributor though. Aim for 12-14 in the dizzy.
Yeah I didn't know about how the dizzy needed to be recurved in a performance engine until I read this link literally 10 minutes ago:

Where should I set the timing on my performance engine?

So now I just have to pull apart my dizzy and figure out the best way to set the limiter. I might have to bust out the welder or just use the rubber hose trick.

Thanks!

Quote:
Originally Posted by vinniekq2 View Post
shut it off in gear,then select park
Good info; I'll have to try that.
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Old 04-05-2013, 08:34 PM
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Quote:
Originally Posted by 33Willys77 View Post
Agree wtih RWENUTS. You need more intial timing. The carb will respond better too. Edelbrocks like as much initial timing as the motor will allow. Which means, you will need to limit your total advance to 12-14 additional (it may like more). Could also try hooking vacuum to the intake. Not sure on Fords, but if it is like a GM HEI, you can limit the mechanical advance in the dizzy and just eliminate the vacuum.
Yeah I can plug the advance port but I will have to modify the limiter.

Guide on how to do it on a Ford Duraspark:
Duraspark_distributor_recurve_instructions_index

Last edited by SoCalExile; 04-05-2013 at 09:04 PM.
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Old 04-06-2013, 05:45 PM
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belvedere

Enrich the idle circuit. (Back the idle mixture screws out)
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Old 04-06-2013, 09:25 PM
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Make sure your throttle plates aren't open too far at idle, and you're not compensating for that with the idle mixture. Flip the carb over and check the transfer slot, you might be pulling fuel from the primary circuit.
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Old 04-07-2013, 12:01 AM
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Just throwing out some thoughts on a variety of reasons for the symptom of running on. An item that I'll bet gets overlooked sometimes is the fuel blend used as its said a winter blend fuel that is more volatile and used when the weather is warmer can be an issue in an engine that is prone to doing this. Also too low a grade fuel or fuel that is getting too warm in the carb because its not insulated well enough from the intake and if there is no return back to the fuel tank which helps keep the fuel temps down. It can percolate in the carb and the fuel vapors keep feeding the hot engine.

Definitely I have had issues with large truck engines that see a high load right to the point where its stopped moving and then turn the key off with that super heated engine, it sure can run on where as if left idling for a minute the cooling system equalizes the heat and also cools down any hot spots that may be in the combustion chamber. Having the idle speed set too fast really exacerbates the problem in cases like this too.

Hopefully you don't have some issues with sharp edges in the combustion chamber such as a sharp valve edge or even spark plugs that are too hot a heat range.

Does the engine temp gauge seem to compute with the thermostat as a hot running engine sure wouldn't help in a case like this.
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Old 04-07-2013, 07:01 AM
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The throttle plates in the carburetor are not closing completely when you shut off the engine. That will allow the engine to pull air and run-on. It is a common problem with radical camshafts that must idle from 900 - 1200 RPM. This run-on problem is different from dieseling due to preignition when the engine is hot and when using cheap low octane gasoline.

68NovaSS wrote the correct approach to the problem.

It is a problem. For example, the 1969-70 Pontiac Firebirds and GTO with the Ram Air IV engines had a problem with engine run-on due to the long duration camshaft. The Ram Air IV engine idled at 1100 RPM. To solve the problem, GM equipped the Ram Air IV engines with a adjustable solenoid that closed the Q-jet primary throttle plates completely when the solenoid was de-energized and choked off the engine completely when the ignition switch was turned off. You set the idle on the Ram Air IV engines by adjusting the solenoid plunger in or out.

I used that system of a couple of my cars that were equipped with a radical camshaft.
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Old 04-07-2013, 02:33 PM
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Ok, so I busted out the welder and recurved my dizzy to about 12* of max advance, then set it to 20* of initial timing. I tried to set it lower but the engine seemed to want more.

Seems to run better, still diesels a bit in park, but not at all in gear. ETA: It doesn't run-on as much as it just gives out a "gasp" or "sigh" when I shut it off.

Now the only thing that concerns me is an uneven idle. It's not like a regular lope and seems to have no pattern. I do have a bit if an exhaust leak at the collectors, but I. wondering if I also have a vacuum leak in the intake manifold.

The rpms will vary 25-50 or so at a stop. I also have to set the idle in park to around 950-1000rpm, which will translate to about 800-850 in drive; if I set the park idle any less the in-gear idle will drop to 550rpm or less and it'll die.

Last edited by SoCalExile; 04-07-2013 at 02:41 PM.
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Old 04-07-2013, 02:36 PM
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Quote:
Originally Posted by 68NovaSS View Post
Make sure your throttle plates aren't open too far at idle, and you're not compensating for that with the idle mixture. Flip the carb over and check the transfer slot, you might be pulling fuel from the primary circuit.
Thanks.

How do I adjust them?
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Old 04-07-2013, 02:47 PM
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The attached files should give you what you need on the Edelbrocks. 1405/1406 are the same carb, one with a choke.
Attached Files
File Type: pdf 1405_6 carb install.pdf (234.5 KB, 29 views)
File Type: pdf 1405_6 carb owners manual.pdf (422.0 KB, 31 views)
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Old 04-07-2013, 03:45 PM
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Quote:
Originally Posted by 68NovaSS View Post
The attached files should give you what you need on the Edelbrocks. 1405/1406 are the same carb, one with a choke.
I don't think I'm seeing it in those instructions. I mean I see the slots, just not how to close them up.

Pic of the bottom of my carb:

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Old 04-07-2013, 03:58 PM
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I would take a look at and repair your collector leak if I was you because I've been surprised sometimes how a leak on the pipe to flange of a cast manifold of a stock engine can cause it to run somewhat poorly and assume its throwing the scavenging off from one side of the engine to the other. Because you know its leaking, better to repair it now then assume it couldn't have any effect on what your dealing with at the moment.

I assume a carb like this doesn't have the option to put on ether an anti stall dash pot or solenoid to help with that transfer from idle under no load to being loaded in gear. Not to say it may need it once the carb is set properly as per prior comments and as I have no experience with carbs like this so I'll leave that to others for the answers there.
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