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  #16 (permalink)  
Old 05-09-2011, 08:49 PM
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You need more base initial timing at idle. 24 to 26deg.

shorten the mechanical advance curve from stock 20-22 to around 10-12ddeg.

limit the advance travel

This will allow 24-26deg at idle without excessive max advance.

This will allow the carb to be closed up some and the combustion chamber to run cooler.

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  #17 (permalink)  
Old 05-09-2011, 09:28 PM
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my experience with { Dieseling} has always been carb related, not that any of these other ideas could be your issuse, If the idle is adjusted to high opening the blades to much or a rich mixture, it will tend to Diesel when you try to turn off engine.. check the primary accelerator pump adjustment as well, maybe adjusted to tight causing raw fuel feed
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Old 05-09-2011, 11:35 PM
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Quote:
Originally Posted by hotrod937
Like I said up top I've got a Probillet mech advance MSD with the 6al and blaster 3.. So I need more initial timing? I was gonna dumb down the timing to fight denotation and bring the combustion temps down.. I think I need to bring the idle screw down and find another way to get my idle up around a grand. I'm under the assumption that I need a bit higher idle due to my solid roller set up for cam oiling. I've not messed with the idle mix on the carb either so that could be another way to get more rev with less blade. I'll mess with it when I get done working and report back.
If you are idling at 1000, that's probably a good part of the problem.
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Old 05-10-2011, 07:23 AM
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A cam that big needs to idle high. 900 to 1100 is a good range.
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Old 05-10-2011, 09:21 AM
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Quote:
Originally Posted by 67-4-fun
my experience with { Dieseling} has always been carb related, not that any of these other ideas could be your issuse, If the idle is adjusted to high opening the blades to much or a rich mixture, it will tend to Diesel when you try to turn off engine.. check the primary accelerator pump adjustment as well, maybe adjusted to tight causing raw fuel feed
What about setting the carb up with an idle let-off? Part of the manual choke linkage works good for that. Set your normal idle at the choke high idle at near full open, then ramps off the last little bit to shut down rpm 500 or so. I take it there probably wont be a choke blade in there anyway?

Thoughts ?
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Old 05-10-2011, 03:46 PM
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Quote:
Originally Posted by 454C10
A cam that big needs to idle high. 900 to 1100 is a good range.
Very true,
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Old 05-10-2011, 04:35 PM
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Okay, here's what I did. First I put 25* timing in at idle with it in drive.
Next I turned down the idle screw to about 900 1000 rpm (in drive)
Then I turned the idle screws on the metering block up while watching the vac gauge. Thus bringing the idle up to like 1300rpm..

I drove it and shut it down several times. NO MORE DIESELING! Now I've got to take some fat out of the primary idle mix screws to bring it down to 1100rpm in drive.. I also need to get some different springs in my MSD mech distributer (brand new) to bring down the all in timing of 43* down to about 38* where it popped 489hp on the dyno.

The car has a lot more throttle responce just by putting in 25* idle timing and seems to be running about 7* cooler water temp (could be cause of a light rain). This thing is getting dialed in. Also I'm not running Speedway 92 anymore. I'm gonna start running Shell 93. I was affraid to beat on it too bad because of the 41-43* timing and detonation issues as I have no idea what "ping" sounds like or if I would even be able to hear it if it was happening. Thanks a ton guys. I'll update you if I get any more run on..
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Old 05-10-2011, 06:45 PM
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Quote:
Originally Posted by mumbles
What about setting the carb up with an idle let-off? Part of the manual choke linkage works good for that. Set your normal idle at the choke high idle at near full open, then ramps off the last little bit to shut down rpm 500 or so. I take it there probably wont be a choke blade in there anyway?

Thoughts ?
Good thinking. Maybe just an electric throttle kicker.
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Old 05-10-2011, 08:00 PM
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No choke blade
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Old 05-11-2011, 05:06 AM
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Quote:
Originally Posted by willowbilly3
Good thinking. Maybe just an electric throttle kicker.
Sounds even better. I have a manual choke on my holley that was doing a little throttle up at the first amount of pull. But electric with a toggle switch would be just as effective. As for detonation detection when you can't hear it.
Is there any ideas for a knock sensor with a warning light??
I like to use a fuel mixture monitor, Edelbrock 6593, (Best 140 bucks you'll spend) combined with a vacuum guage to tell when my power valves, idle mixtures, and main jets are all dialed in. But to run max timing at the same time as fine tuning you carburetor, without detonation, is key.
You can get close, but when you adjust timing, or fuel quality changes, you end up starting over again, because your mixtures get thrown off. So it would be nice to have this info on board all the time. Esp. some way to detect detonation. It's usually the first thing. But if you can't hear it ??
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Old 05-11-2011, 12:38 PM
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I've got a vac gauge I think I'm gonna mount under the hood and am planning on running the AEM wide band O2 gauge.. I need to get the carb dialed in more.
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Old 05-11-2011, 01:48 PM
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don't adjust the mixture screws to get a lower idle speed. Turn down the idle speed screw for that.

Always adjust the idle mixture screws for highest vacuum (highest rpm). That is what the engine wants.
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Old 05-11-2011, 04:43 PM
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The vacuum guage just needs a longer hose to bring it in the cabin. You really need to observe under load conditions. Use a couple tie wraps on the steering column. Lean conditions, and lags in power are sometimes accompanied by detonation and hot cylinder situations. With drops in vacuum. Under steady up hill loads and consistent pedal positions. You feel like you need to give it a little shot to get it going. It's just a bit lean most of the time. Sudden rich conditions show up as black smoke. But who's looking backwards with 489 hp ?? Either way, it's all about how fast your engine recovers it's optimal vacuum while under any given load. This is why short cams with small carbs work good in tow vehicles. Maintain vacuum for adequate fuel atomization within an engines intended operating conditions. This is pretty much the standard for naturally aspirated engines.
( V.E.)
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  #29 (permalink)  
Old 06-04-2012, 12:48 PM
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Alright, A while ago I found that my MSD dist needs to be at around 25* initial and 38* all in. None of the pucks they give will do that. I remember seeing some custom pucks a while ago but now I can't find the site. Anyone know what I'm talking about?
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Old 07-11-2012, 08:21 PM
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It is your metering blocks what happens when you sit up a holley is the left over fuel in the metering blocks turns into a corrosive varnish which in turn pits up the fuel galleries in the block and makes them porus and causes it to leak down into the intake runner there fore causing runon detination and in sever cases top end or hi rpm lean out
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