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Timing and Dieseling Issue

Collin

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Having some issues with the 383. We have 383 stock heads, stock intake, Carter AVS and running a comp cam xtreme energy hydraulic roller (230-236 at 50). Running stock ignition. The motor diesels when we shut it off.

We are not sure if the dieseling is a problem based on the timing or based on the fuel. We suspect there may be a hairline crack in the base of the carter AVS. Initial timing is about 15 and total of 34.

We also noticed that when the car idles warming up on choke the RPM seems to climb steadily until we manually kick the throttle down off the fast idle cam.
 

69hemibeep

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How many degrees of advance are ground into the cam? Might try backing the timing off a bit.
 

Ranger

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Sounds just like mine (used to) and I'll bet your problem is carbon. I solved it by plugging a length of vacuum hose into whatever vacuum port you are not using on the carb (there should be 2 at the base). Run the engine up to about 2000 RPM and stick the hose in a glass of water. It'll suck it down pretty quickly, but it will clean the carbon from the combustion chamber and your problem will be solved. It's an old trick from way, way, way back and it works every time. Now I shut down without loading the engine in 1st gear. Just turn the key and she shuts down like a good girl.
 

69hemibeep

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My old shop teacher said you should use distilled water when you do that but I doubt tap water will hurt. Make sure the engine is hot or the water will beat the crap out of the pistons it will act like a solid
 

IQ52

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Well it didn't come from the factory with the XR280HR-10 camshaft. What else have you done to the engine? The idle increase while warming up is perfectly natural and as it should be. I wouldn't start sucking water, orange juice or milk through the engine just yet.
 
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Ranger

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My old shop teacher said you should use distilled water when you do that but I doubt tap water will hurt. Make sure the engine is hot or the water will beat the crap out of the pistons it will act like a solid

Good point and I should have mentioned that.
 

ACME A12

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Collin's engine, like his entire car, is a brand new build. Carbon is not the issue.

Collin - you've had issues with both this carb and with a vacuum leak before. I'd concentrate my search here, although like Bob suggested, I'd back the timing off a few degrees and see if it has any impact.

If you think that carb has a cracked base, then you may have already identified your issue.
 

bigmanjbmopar

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I had this issue when I switched from a 850 dbl to a 780 vac sec. It was a combination of timing and idle. If you are using the vac on your distributor make sure it is adjust properly as well. all these things along with today's gas and heat make for a bad dieseling effect but can be solved with the correct adjustments.

Check out this article, it has helped me get to at least a decent baseline tune. http://www.mopar1.us/engine2.html

a lot of factors in all of your equipment. Let IQ52 walk you through it.
 

IQ52

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15 degrees initial distributor timing is the very least I would run with that camshaft so if it must be retarded then something else is wrong and we are missing some very important information. A hairline crack in the carburetor base may contribute to the problem. Do you have vacuum advance hooked up? If so, did you time the engine with the vacuum advance disconnected and them hook it back up? What is the static compression ratio? Piston design and deck height? Head gasket? Head casting number and cc's? Where is the cam timed, i.e. what is the ICL degree? What spark plug part numbers are being used? Thermostat degree? Fuel octane?
 

ACME A12

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What is the static compression ratio? Piston design and deck height? Head gasket? Head casting number and cc's? Where is the cam timed, i.e. what is the ICL degree?

He bought the engine already assembled by an engine builder local to him - so he may not be able to provide you with this degree of detail...

It sure would be nice to know how they set that cam up...
 

69hemibeep

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He bought the engine already assembled by an engine builder local to him - so he may not be able to provide you with this degree of detail...

It sure would be nice to know how they set that cam up...

Did you remember that or go back and look :nachos:
 

Collin

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No I had the engine built with my specs:

10.1 to 1 compression ratio. Flat top diamond racing pistons at zero deck .020 steel head gasket. Timed with vacuum advance disconnected. 906 mopar cylinder heads. 93 octane.

180 thermostat. Champion spark plugs RL12Y.
 

ACME A12

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I had found a post where you said you traded in your worn out engine for this one...so I mistakenly assumed that they already had it together. So how did they set up the cam?
 

IQ52

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Have the heads been milled extensively? I have that design right at 9:1 compression. If it truly is 10.1:1, there is your problem as your dynamic compression will be too much for pump gas with that open chamber head design and that small of a camshaft. Have you run a cranking compression test? Is the vacuum advance connected?
 
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