no ldle!?

[harshman]

I’m stumped.
I changed my cam (twice – flattened two lobes), springs, timing chain and switched to an HEI and now i can’t get the flippin’ thing to idle below 1,000 rpms. The HEI has 12+ volts going to it. The cam is set dead on; it seems that the only thing left would be the carb. Holly 750 – 4150 1 year off a rebuild, jets are 69 prim and 79 second with power valve block off on second - I have set the idle screws from ½ turn to 1 ¾ turs at ¼ increments and still no luck. It sounds like it wants to idle but after 3 seconds or so it sounds like its loading up and then dies. Test driving above idle it screams. I haven’t checked fuel pressure yet. My friend in Phoenix said that possibly there isn’t enough vacuum pulling fuel through the idle circuits and they might have to be drilled. Any ideas?

More specs

396 bbc w/ comp magnum cam 213-3 - 244/244/.550”

[dhardison]

Maybe you have dirt/sand/trash stuck in one of the carb needle/seats which is causing the loading up of the carb? Above idle the engine could handle the extra fuel, but at idle it can't. It can't hurt to pull the carb bowls and take a look.

HTH,
Dan

[harshman]

The floats are perfect. I have already pulled them and inspected them.

[harshman]

Called Comp Cams and the tech guy said that the cam should idle at 1k rpms. I ran a narrow band air/fuel sens. and with both fans running the best I can squeeze is 975. It still seems odd. You engine guys... does this sound right?

[chicane67]

..............never mind, I have your phone number................

and you have mail

[justanova]

any luck? I am curios to the answer myself.

[ProdigyCustoms]

Try unhooking the vacum advance to be sure it is not sticking and holding the timing up, sometimes they can stick when you rev the motor, hold the idle up for a few minutes, you turn your back and it relaxes and drops 400RPM. Also, make sure the air bleeds in the carb are clear.

[Little Bob]

Check to see if you have a intake leak. Sometimes gaskets don't seat all the way. Could be a carb gasket leak also.

[chicane67]

It requires emulsion jet tuning.........and thats in work.

[MrQuick]

did you guys get it? Are you getting air past the secondaries? Try to stick a rag in the 2 secondary venturies. Unless you running 4 corner idle circuit you should get no idle response from the rears. I've had weak advance springs f with me too...

[harshman]

I sent the carb to B and R Automotive (old friends that know their …..) in Phoenix for the metering block to be drilled and the air horn to be milled (removing the choke tower and what not). I did a thorough inspection of all parts and interviewed many builders and experienced friends and came to this conclusion. Basically the cam is allowing the motor to idle at 1k rpm and the burn is perfect. It is flowing “too good” and the only way to get the idle lower is one of two things. Install something that will restrict the exhaust (cat converters etc.) or enlarge the idle circuits to allow more fuel at idle. I chose the latter in hopes it will give it some good street manners. Hey Tom – got the email and I will be getting the bible but time is short and so I had to send it out. When it is all said and done, I will figure this carb thing out and know how to tune these damn things. That is something I have never been able to do before. Thanks for all the help.

[chicane67]

Let me know when it comes back around. Maybe I'll be in town for more than mere seconds and can stop by for the retune.

[harshman]

yup, i will! BTW, i'm on page 22 of the carb bible - great read.