C2 Replacement Holley-wont clear to idle

[John P.]

I have seen threads on this issue in the archives. i replaced service carb some time back with new Holley 4150-60 series. Never wants to consistently idle at 750 unless I try to "clear it" with heavy pedal push.

Im just wondering if all agree the throttle return spring is at fault and where to obtain the best replacement. Thanks all

[Stephen L.]

Re: C2 Replacement Holley-wont clear to idle

John, You could install a temporary new spring bought at the hardware store. Cheap and it'll show if that is possibly the cause.....
Have you tried to adjust the float levels. They may be slightly high allowing slight amounts of fuel into the engine......

[Duke W.]

Re: C2 Replacement Holley-wont clear to idle

Does the VAC pass the Two-Inch Rule for the engine configuration? If not, idle issues are absolutely, positively guaranteed unless the VAC is connected to ported, not full time manifold vacuum.

Duke

[David H.]

Re: C2 Replacement Holley-wont clear to idle

John

Vacuum secondaries? If yes, by any chance are you running a high lift cam?

Dave

[John P.]

Re: C2 Replacement Holley-wont clear to idle

Mechanical secondaries I believe. Not sure but no reason to think cam changed vac is the one duke recommended to me some time ago, and I think it complies with the rule .to the best I could tell at the time. It is a 65 L-79

Seems like I was under the impression that full manifold vacuum is recommended . Not so?

[David H.]

Re: C2 Replacement Holley-wont clear to idle

Mechanical secondaries I believe. Not sure but no reason to think cam changed vac is the one duke recommended to me some time ago, and I think it complies with the rule .to the best I could tell at the time. It is a 65 L-79

Seems like I was under the impression that full manifold vacuum is recommended . Not so?

John

My original comment was NOT related to your vacuum advance can.

Vacuum secondary Holley carburetors coupled with "high lift" camshaft sometimes have idle issues (cannot adjust idle speed with idle adjustment screw). Issue generated with off idle circuits supplying fuel.

Google search will show common fix of drilling holes in secondary plates.

As your carburetor has mechanical secondaries, my comment does not apply.

Dave

[Owen L.]

Re: C2 Replacement Holley-wont clear to idle

Never wants to consistently idle at 750 unless I try to "clear it" with heavy pedal push.

I'm unclear on the issue; is it that it won't return to idle from higher rpm and blipping the throttle seems to fix it?

I discovered that my Holley 3811 throttle plates were dragging on the bore and not closing easily to allow the carb to return to the idle setting. If I blipped the throttle, I suppose the rapid release had enough force to overcome the dragging. Fixing it required removing the carb and separating the base plate from the body, slightly loosening the staked screws holding the plates to the shaft, allowing them to seek center upon closing, and then snugging down the staked screws again.

[Tom E.]

Re: C2 Replacement Holley-wont clear to idle

I had the same exact problem on a new replacement Holley 3810 I bought for my 67 327/350. A much heavier spring would make the carb return to idle so I knew something was binding somewhere. I spent hours fiddling with it to no avail. I finally contacted Holley and they asked me to send it in to them. The repair ticket did not state what they did but it has worked perfectly since then. On mine the throttle plates would not completely close requiring a slight bit of force to close them the last little bit. This slight open condition was causing the high idle.

[Mark E.]

Re: C2 Replacement Holley-wont clear to idle

I had the same exact problem on a new replacement Holley 3810 I bought for my 67 327/350. A much heavier spring would make the carb return to idle so I knew something was binding somewhere. I spent hours fiddling with it to no avail. I finally contacted Holley and they asked me to send it in to them. The repair ticket did not state what they did but it has worked perfectly since then. On mine the throttle plates would not completely close requiring a slight bit of force to close them the last little bit. This slight open condition was causing the high idle.

They may have repositioned the butterfly valves to better align in their bores.

[James W.]

Re: C2 Replacement Holley-wont clear to idle

John,

I had this same problem for years with my '65 L-79 and kept chasing what I though were carb issues. I took Duke's and others advices and changed my B1 distributor vacuum advance cam to a correct B28 vacuum cannister and it solved my idle problem and made the car run so much better.

James

[John P.]

[Bill B.]

Re: C2 Replacement Holley-wont clear to idle

John,

If it is not carburetor related, it could possibly be your centrifugal weights in the distributor intermittently hanging up, giving you more advance, thus a higher idle speed. Happened to me a few years ago and I couldn't figure out the root cause for months!

My symptom was replicated by bringing the engine speed up to approx. 2500 rpm, then slowly releasing the accelerator back to idle. Would always have a higher idle for that. When I released the throttle quickly from the 2500 rpm, it would almost always idle at the expected rpm.

When I removed the distributor cap and rotor, I manually rotated the mechanical advance to replicate the slow vs rapid delecerations, I saw the hangup of the weights during the gradual release.

A little TLC on the weight bearing area, and the buttons the weights rested on (plus polishing the weights where they rest on the buttons) completely resolved my issue.

[David H.]

Re: C2 Replacement Holley-wont clear to idle

Won’t easily clear to idle or stay at 750
Even when hot will bump up to 1100 at a stop

I cannot tell how to loosen and reposition the primary or secondary flappers Holley support offered nothing Makes sense to me that mechanism is not quite functioning properly but cannot tell I was told not to lube anything

I do have the recommended vacuum can on it via Dukes suggestion

John

Is your issue inconsistent idle or a HIGH rpm idle that won't adjust down?

Dave

[Duke W.]

Re: C2 Replacement Holley-wont clear to idle

Seems like I was under the impression that full manifold vacuum is recommended . Not so?

Yes, but all you said is C2 and replacement Holley, so I attempted to cover all the possibilities . Ported vacuum advance was used on most exhaust emission controlled engines going back to K-19 on '66 models sold in CA.

BTW the B28 VAC has the same specs as the 8" 236 16 used on 30-30 cam engines and L-79, but since L-79 typical idle behavior with an OE or OE equivalent cam is 14" @ 750 the B28 is more aggressive than necessary and the 12" B26 is a better choice. Always use the least aggressive VAC that passes The Rule.

At the same time the L-79 has a very lazy OE centrifugal curve, 30 at 5100, so lighter springs to bring it all in by about 3000 with provide a noticeable SOTP improvement in the low to mid range performance.

More info is in a thread titled L-79 distributor blueprint/overhaul from circa 2012 if you can find it.

Duke

[Mark F.]

Re: C2 Replacement Holley-wont clear to idle

...More info is in a thread titled L-79 distributor blueprint/overhaul from circa 2012 if you can find it...Duke

this looks like the thread: https://www.forums.ncrs.org/showthre...int%2Foverhaul