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Old 11-25-2013, 08:50 AM   #1
Hivolt5.0
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Default Dieseling

I have a problem with my Y dieseling when I turn it off. The distributor is less than a year old points type. The carb is a 600 Holley. I double checked the timing this weekend; I was running 8 degrees advance and pulled it back to 6. I checked the air/fuel ratio with a vaccum gauge and am running a little more that 15 in, if i remember correctly. I know the timing chain has some slack in it. Tuning these engines is not my forte but I'm trying to learn as much as I can.

The engine runs great and has excellent response but just wants to diesel when turning it off.

thanks in advance for the help!
David
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Old 11-25-2013, 09:27 AM   #2
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Default Re: Dieseling

Try timing with a vacuum gauge. The light method uses the marks which have been known to move after all these years. If you really like the performance when its timed where it is, try switching to one grade better fuel.
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Old 11-25-2013, 09:30 AM   #3
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Default Re: Dieseling

Timing with a vacuum gauge...I have not heard of that before. How do you do that?

as for gas, I'm currently running ethanal free 87 octane.
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Old 11-25-2013, 11:01 AM   #4
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Default Re: Dieseling

Try a slower idle
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Old 11-25-2013, 12:30 PM   #5
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Default Re: Dieseling

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Try a slower idle

Billwill is the man. Dieseling is generally caused by idle speeds that are too high. This was resolved later on by using an electrical solenoid for the throttle to stop and ide on. When the key is turned off, the solenoid releases and the carb goes to lower setting (too low to idle).

You can also shut the engine off (if an automatic trans) in gear to eliminate the dieseling if you can't resolve it by slowing the idle speed down.
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Old 11-25-2013, 12:58 PM   #6
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Default Re: Dieseling

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I had actually bumped the idle speed up just a touch because it was wanting to die when I'd clutch in to slow down and stop. Guess I'll try to adjust somewhere in the middle to see if that will help. However, even before I adjusted the idle up it would want to diesel periodically.
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Old 11-25-2013, 02:21 PM   #7
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Default Re: Dieseling

The objective is to get the engine to idle with the least throttle opening. Do it by carb idle air adjustment and timing. 15 sounds a little low for that engine. Be sure the carb is adjusted as it can cause the the engine to die when you clutch.

The timing by vacuum is done by adjusting the timing to the highest engine vacuum, then lower the timing one degree. You already know the current setting, so if it doesn't work for you it can be returned to the present setting.

You can experiment with connecting your vacuum can to manifold vacuum. This should increase your idle speed, enabling you to decrease the carb throttle opening farther. This won't have any negative effect on performance since ported vacuum can only deliver what is in the manifold.

Best of all, it can all be reversed if you find no improvement.
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Old 11-25-2013, 02:30 PM   #8
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Default Re: Dieseling

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The objective is to get the engine to idle with the least throttle opening. Do it by carb idle air adjustment and timing. 15 sounds a little low for that engine. Be sure the carb is adjusted as it can cause the the engine to die when you clutch.

The timing by vacuum is done by adjusting the timing to the highest engine vacuum, then lower the timing one degree. You already know the current setting, so if it doesn't work for you it can be returned to the present setting.

You can experiment with connecting your vacuum can to manifold vacuum. This should increase your idle speed, enabling you to decrease the carb throttle opening farther. This won't have any negative effect on performance since ported vacuum can only deliver what is in the manifold.

Best of all, it can all be reversed if you find no improvement.

Ok, I'll give it a shot! thanks
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Old 11-25-2013, 07:25 PM   #9
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Default Re: Dieseling

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I had actually bumped the idle speed up just a touch because it was wanting to die when I'd clutch in to slow down and stop. Guess I'll try to adjust somewhere in the middle to see if that will help. However, even before I adjusted the idle up it would want to diesel periodically.

Have you tried to adjust the two idle mixture screws at all ? Especially if you changed the idle speed. Maybe it dies when you put the clutch in because the idle mixture isn't optimum. Maybe that will help get rid of the dieseling too if the mixture is off.
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Old 11-26-2013, 11:26 AM   #10
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Default Re: Dieseling

Also, check the float level. If its dumping a bit extra when you come to a stop, that could affect idle. Then, check the spark plugs. Check color now, and if the tips look as if they have been hot. With so many computer controlled cars now, its hard to find a wide heat range any more. I like NGK the past few years. They seem to burn anything you throw at them, and they last.
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Old 11-26-2013, 11:32 AM   #11
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Default Re: Dieseling

That engine may need a dash pot
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Old 11-26-2013, 01:20 PM   #12
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Default Re: Dieseling

Scicala - I did check the idle mixture with a vacuum gauge and it was pretty spot on. I tried turning the mixture screws in and out and the vacuum would drop so I ended up back where I started.

Ole Don - I'll check the float level. Sure wish the carb had a site glass.

billwill - I'm not sure what a dash pot is.
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Old 11-26-2013, 08:59 PM   #13
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Default Re: Dieseling

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Scicala - I did check the idle mixture with a vacuum gauge and it was pretty spot on. I tried turning the mixture screws in and out and the vacuum would drop so I ended up back where I started.

Ole Don - I'll check the float level. Sure wish the carb had a site glass.

billwill - I'm not sure what a dash pot is.
A dash pot is something they used to put on carbs for cars with an automatic trans. It's a small round (about 1 1/2" dia ) that looks similar to a choke pull off diaphragm. It's designed to slow the throttle from slamming shut all the way during a hard stop to avoid stalling. It could help you're issue if everything else checks out.
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Old 12-10-2013, 03:08 PM   #14
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Default Re: Dieseling

take the dashpot off and throw it away
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Old 12-10-2013, 04:25 PM   #15
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Default Re: Dieseling

My '57 312/w automatic with a Holley 4 barrel would die every time I took my foot off of the gas. The carb had a too complete of a cut off, enough to kill a fast running engine. It didn't have a dash pot on it when I bought it. So, I had to go and find a dash pot to put on the throttle so that it would have a slower cut off. It works perfect now.
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Old 12-18-2013, 08:05 AM   #16
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Default Re: Dieseling

Ok, I finally had some time to tinker with the Ranchero. I hooked my vacuum gauge, my timing light and my dwell/tach meter. I think the engine feels a bit violated now. haha!

Once the engine warmed up I rechecking the timing with the light and the advance was solid a 6 degrees. The vacuum read 18.5 or so inches of Hg. I tried adjusting the distributor to increase the vacuum and I could increase it but when checking with a timing light it put the advance at 30 degrees! I knew this would be too much so I put it back at 6 degrees with the light. Next I adjusted the idle. Initially my meter read just below 800 rpms so I adjusted it to a 600 rpm idle speed. This brought my vacuum down to 15 inches of Hg. Adjusting my dwell/tach meter to read dwell it looked like it could be a bit high. Honestly I didn't look at it long enough and I should have spent more time on it.

So after adjusting the idle speed down and with the advance set back at 6 degrees I took it for a spin. There is light pinging under hard acceleration but I'm running 87 octane gas. Other than that it ran good. When I got back home and turned it off the engine shut off nicely as it should.

What else should I check or do I leave it alone and put some premium in it?
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Old 12-18-2013, 08:17 AM   #17
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Default Re: Dieseling

When setting the idle mixture, be sure the trans is in neutral and idle the engine down to about 500 RPM. Then after adjusting the mixture, you can idle it back up so that you get the desired RPM in drive. This assures that the idle circuit holes in the carburetor are in full effect. Otherwise, you will not get the correct mixture at idle.
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Old 12-18-2013, 08:22 AM   #18
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Default Re: Dieseling

really. That is very interesting. I'm a novice at carburetors so I do appreciate the advice. I'll tweak the mixture as you've instructed.

thank you!
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Old 12-18-2013, 11:14 AM   #19
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Default Re: Dieseling

For what it is worth, the Motors manual shows 3 degrees BTC for timing and 475 as hot idle speed.
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Old 12-18-2013, 11:29 AM   #20
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Default Re: Dieseling

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When setting the idle mixture, be sure the trans is in neutral and idle the engine down to about 500 RPM. Then after adjusting the mixture, you can idle it back up so that you get the desired RPM in drive. This assures that the idle circuit holes in the carburetor are in full effect. Otherwise, you will not get the correct mixture at idle.

I can't say that I agree with this. Idle speed and mixture should be adjusted in gear if it's an auto trans. You don't adjust the mixture, then change the idle RPM again without re-adjusting the mixture screws again.

I think you can get a higher vacuum that 15" if you re-adjust the mixture screws after going back down to 600 RPM. It doesn't sound like you re-adjusted the mixture at 600 RPM. It sounds like your car is running better though, so that's good.
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Old 12-18-2013, 11:35 AM   #21
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Default Re: Dieseling

dont trust the timing marks of the crank damper, if im not mistaken they are a two piece damper with a rubber insulator between the two metal pieces, over the yrs the outer part of the damper will creep around the inter piece, the one bolted to the crank because it slips on the rubber insulater, throwing the timing marks off, pingining on hard excelleration usually means timing is to far advanced, back timing off about two degrees, to find top dead center pull # 1 plug, put a wooden dowel in hole and turn engine over by hand till the dowel stops rising, that should be top dead center unless the timing chain is pretty streched, to check play in timing chain, take dist cap off, turn engine over by hand then turn the opposit direction, see how far the crank turns before rotor moves, turn the engine in the direction when running then back it up, that takes the play out of the chain
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Old 12-18-2013, 11:38 AM   #22
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Default Re: Dieseling

Gene, Do you think the Isky cam would affect what idle speed the engine "likes"? I printed off a spec sheet from either John Mummert's web site or the Y blocks forever web site that gave specs on idle speed, timing, dwell, etc and it agrees with what you just mentioned for a stock cam. I know the E-4 cam isn't real "hot" but I wasn't sure if I should treat it like a stock cam or lean some towards a "hot" cam.
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Old 12-18-2013, 11:47 AM   #23
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Default Re: Dieseling

Thanks scicala and ford3. I'll give both of those a try. I know there is some slack in the timing chain. The last time I changed the fuel pump I stuck my finger in the hole in the cover and felt the slack.
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Old 12-18-2013, 11:53 AM   #24
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Default Re: Dieseling

if the timing chain is streched much you will never be able to time the engine right, the rotor should move as soon as you turn engine
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Old 12-18-2013, 08:35 PM   #25
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Default Re: Dieseling

[QUOTE=scicala;786646]I can't say that I agree with this. Idle speed and mixture should be adjusted in gear if it's an auto trans. You don't adjust the mixture, then change the idle RPM again without re-adjusting the mixture screws again.

I respectfully submit that you want to keep the butterflies closed as much as possible to assure that you are not approaching the transition ports which are just above the idle ports. The way you do this is by putting the transmission in neutral and reducing the idle to close the butterflies. Then after you set the idle mixture, opening the butterflies a bit to idle up in gear is the proper way to go. While you may idle up to the point that it is approaching the transition ports, the idle mixture will remain correct.
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Old 12-18-2013, 10:05 PM   #26
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Default Re: Dieseling

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Quote:
Originally Posted by Hivolt5.0 View Post
Gene, Do you think the Isky cam would affect what idle speed the engine "likes"? I printed off a spec sheet from either John Mummert's web site or the Y blocks forever web site that gave specs on idle speed, timing, dwell, etc and it agrees with what you just mentioned for a stock cam. I know the E-4 cam isn't real "hot" but I wasn't sure if I should treat it like a stock cam or lean some towards a "hot" cam.
The only way I would know about the idle speed question is to see how the engine responds to the suggested idle speed. I don't think that cam has enough duration to affect idle speed much. If it continues to die when you cut ignition you are probably OK around 550 or 600 rpm.

The timing chain was new when the engine was built. With no more miles than it has, I doubt it is out of specs. I recently had the timing cover off my 302 at about 85,000 miles. There was a little wiggle in the chain between the gears. I found the way to measure for excessive wear and it was no where close to being too loose. I think some looseness is normal.

You didn't mention if you had the vacuum can disconnected while performing the timing checks, or how the vacuum can is connected to the carb. Using manifold vacuum on the distributor will help get the engine to the high timing you mentioned that it likes. It will also let you close the idle speed screw some more. It will give a crisp throttle response from idle and not give any extra advance at cruising speeds.
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