[EvilPuppet]

hi all,
Here is my question...
i have 66 mustang with 289, mild racing cam and holley 4160.
It runs and drives fine however after 15-20 minutes drive the engine will run at 1100 RPM instead of usual 900 RPM at idle.

i can back off the idle screw and it will not make any difference. The car will stay at 1100.

When the engine is cold it starts fine and runs at 900 RPM idle.


Could this be an issue with vacuum secondaries staying open after driving the car?

Let me know what you think

Alex

 

[mhuggler]

I've heard that feeding them tobacco gets rid of worms real well. > Seriously though, you're obviously pulling air from somewhere or your carb. butterflys aren't closing completely just like you thought. What intake are you running? Any spacer plates or adapters under the carb?

 

[EvilPuppet]

ha ha ha :grin: .... I was typing on my cell. I hate spell check. "WARM" is what the author wanted to say

There is a ticker gasket under the carb. I will tighten the bolts it and see if that does it.
any way of testing if vacuum secondaries are staying open without taking the carb off after the drive?
Thanks
Alex

 

[Tony 64]

Even 900 is high RPM at idle, should be sitting at around 700 -750RPM.

 

[EvilPuppet]

hi
no way, I got the mild racing cam... the engine is not stock. if it was idling at 700 it would die at 550 in gear.

it just seems happy at 900
vacuum at idle is about 22 hg
here is the car running
https://www.youtube.com/watch?v=DiEz1afn_M4
Alex

 

[kenash]

hi
no way, I got the mild racing cam... the engine is not stock. if it was idling at 700 it would die at 550 in gear.

it just seems happy at 900
vacuum at idle is about 22 hg
here is the car running
https://www.youtube.com/watch?v=DiEz1afn_M4
Alex

Yeah, leave it at 900. If it's happy there, you'll know it. I run an aggressive cam making 17"hg. It's happiest at 900-1000.
Does your carb have manual or vac secondaries? I had a similar problem running a Holly XE and had to "back-off" the secondaries a tad.

 

[64Thunderbolt]

First of all, which 4160 carb is it? We can't really troubleshoot it without knowing which version it is (single feed, dual feed, mechanical or vacuum secondary, etc.)? What jets are in the front and back? What power valve is in it (assuming that it has a power valve)?

What intake are you running? Are you sure that the carb to intake gasket doesn't leak between them? We had a HUGE idle problem due to the carb to intake gasket not sealing properly. Had to buy a goof plate gasket set from Summit which fixed that problem.

What exactly are the cam specs: lift, duration at .050", hydraulic or mechanical lifters, etc. IMHO, 22" of vacuum at idle is a lot of vacuum! A "nasty" cam will kill vacuum at idle = carb won't operate properly at idle because it depends on vacuum/air flow.

Have you checked the fuel air ratio? Read the plugs?

 

[Lime1GT]

Does this carb use an electric, manual or no choke setup? Are the choke setup adjustments set correctly per version of choke system? Were all vacuum lines and linkages to intake/exhaust manifolds, if required, installed that will affect choke operation? I'm getting a sense from watching the video, the choke comes back On slightly after you kicked the throttle.

 

[woodz428]

When I have a vacuum leak that is hard to pinpoint, I use a can of flammable contact cleaner and spray possible areas and it gets me to the source in a very short time.

 

[Tony 64]

hi
no way, I got the mild racing cam... the engine is not stock. if it was idling at 700 it would die at 550 in gear.

it just seems happy at 900
vacuum at idle is about 22 hg
here is the car running
https://www.youtube.com/watch?v=DiEz1afn_M4
Alex

I have an XR GT (Aussie muscle car) spec cam in mine too with a 600 Holley, mine has a lumpier sound to yours and is very happy at 730 rpm.
It sounds like, as suggested above, that your choke might not be fully disengaging. That's probably why it is happier at 900 rpm.

 

[64Thunderbolt]

I listened to your video and that is NOT a nasty cam. It is a mild cam as it sits there and idles like a charm.

What are you basing your idle RPMs off of? I hope it's not that small tach in the console as that is NOT going to be accurate at all. You need to have an accurate tuneup machine or a real tach (such as an Autometer) to gauge the RPMs.

 

[64Thunderbolt]

When I have a vacuum leak that is hard to pinpoint, I use a can of flammable contact cleaner and spray possible areas and it gets me to the source in a very short time.

Use any spray flamable liquid (such as starting fluid) SPARINGLY as too much of it can give you false results.

Just spray a VERY little in one spot and wait to see IF the engine's RPMs pick up. If they do, they you have a possible vacuum leak somewhere near that spot you sprayed.

 

[64Thunderbolt]

Has anyone heard back from him as to what we all asked?

OBTW, it says "Rookie" under my userid which is FAR from the truth. I've been working on vehicles (cars, big trucks, and military jet aircraft in the Navy) for almost 60 years (started when I was 9) so it's not my first trip to town!

 

[ralc]

Disconnect the vacuum line to the distributor. It should be connected to the port midway up the jet plate near ihe idle mixture screw

 

[kenash]

BTW, I'm guessing y'all know the term "Rookie" has to do with the number of posts and not your experiences?