High Idle issue - mild 360

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TheMrAMack

TheMrAMack

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Hi guys, new to the forum! Just posted my welcome post, but I have a technical question I can’t quite figure out.

My 71 Duster currently has a mild 360 in it.

After installing the motor, it will not idle. Have to keep it around 2500 rpm.

Running 31 degrees timing.

750cfm Holley stay carburetor.

The kicker is, when I shut the hood it gets worse… Will jump another 500 rpm or more.

The only thing I can think off is it might have a leak around the carburetor due to a bad gasket. Runs like a champ otherwise, no backfiring or anything.

Thoughts?

Thanks
-Andrew
 
31 degrees initial timing? If so that is a bit high for a mild build. I have a moderate build 360 and my initial timing is about 15 degrees.
Also closing the hood and having your rpm increase is indicative of you running lean since you're restricting the airflow to the carb once you close the hood coupled with high initial timing I'm surprised you're not pinging like mad.
That is if you indeed have 31 degrees initial timing.
 
Last edited:
Cuprum-74 said:
31 degrees initial timing? If so that is a bit high for a mild build. I have a moderate build 360 and my initial timing is about 15 degrees.
Also closing the hood and having your rpm increase is indicative of you running lean since you're restricting the airflow to the carb once you close the hood coupled with high initial timing I'm surprised you're not pinging like mad.
That is if you indeed have 31 degrees initial timing.
Click to expand...
Should’ve clarified. It won’t run at all below 31 degrees. Would that be indicative of it being lean?
 
TheMrAMack said:
Should’ve clarified. It won’t run at all below 31 degrees. Would that be indicative of it being lean?
Click to expand...
Not really, it could be other issues as well.
Ignition issues. Specifically the distributor.
Fuel flow problem.
Carb tune.
Not sure how savvy you are with carbs, especially Holley's, it is also likely that the carb's tune is out of whack.
I'm more familiar with Eldelbrocks and Street Demons.
Another important question is: Did you own this car for awhile or did you just pick it up from somebody?
Was this car sitting in one place for awhile?
Just need some history on the car.
 
Cuprum-74 said:
Not really, it could be other issues as well.
Ignition issues. Specifically the distributor.
Fuel flow problem.
Carb tune.
Not sure how savvy you are with carbs, especially Holley's, it is also likely that the carb's tune is out of whack.
I'm more familiar with Eldelbrocks and Street Demons.
Another important question is: Did you own this car for awhile or did you just pick it up from somebody?
Was this car sitting in one place for awhile?
Just need some history on the car.
Click to expand...
I’m not terribly savvy with carbs. I do understand the basics.

I did just replace the ignition: maybe I need to go through it again.

Yes: I’ve had this car for 14 years, but I got busy during college and grad school and had to store it for about five years.

The 408 stroker I had in it initially kept blowing seals due to a bad build by the engine shop, so I swapped in this 360 and it’s the motor that is having idling issues.
 
The carb could have blocked idle jets, requiring the throttle to be cranked open & run on the main system. I think this is unlikely, but is possible.
Most likely you have a large air leak. I would try another carb if you can.
Even though your ign timing may be incorrect, it is not going to cause such a huge increase in idle speed.
 
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