Edelbrock Performer RPM 1910 idle tuning for more cam.

[avmechanic]

Hello.
I have an Edelbrock Performer RPM 1910 Qjet on my Buick 455. I have had this carb for years and it is an excellent performer. A number of years ago I gave it a rebuild and Cliff built me a kit to help tune it better for my engine. That engine was a basically stock 70' Stage 1 455 with factory Stage 1 cam. It had a particularly rich idle. Cliff sold me some primary metering rods and idle tubes to tune it along with the rest of the rebuild kit. It worked fairly well. Now forward ahead to today and I just dropped in a fresh 455 with some more performance modifications done to it. This engine is also a 70' 455. Heads are ported with Stage 1 valves. I am still using stock pistons but did all I could to get the compression as close as possible to true 10:1. In the end it calculated out to 9.89:1. I am running quite a bit more cam than the factory Stage 1 cam it had before. This is a TA C113. It is 229/243 at .050 on a 113 lobe separation installed 3 degrees advanced. Lift is right at .500" on both intake and exhaust. This cam has 11 degrees of overlap. I am also running a TA SP1 single plane intake now.  I just got the engine in and running before I had to leave for a work shift away. The cam broke in nicely and I managed several trips out driving with it. Performance seems excellent. I have some tuning to do yet though. Particularly idle. I do not have a lot of control of the idle circuit with the screws and can not get it to idle down well with the speed screw. I am pretty sure the butterflies are open a little to get the idle air needed. Unfortunately I ran out of time to deal with it before I had to go away for work. I am trying to come up with a plan to sort it out when I get back. Cliff's book shows .110" idle bypass air on the 1910. I can look to confirm that when I get back home. My thoughts are I need just a hair more bypass air. I do have a air fuel ratio gauge in the car and where I got the idle to work best was showing about 13.5:1 when warm but it is quite lean until the engine is warm. The idle is pretty rough and not always stable RPM wise. The cam is not huge so I should be able to get it to idle a little smoother than it is. I am at about 800 in gear and close to 1000 in park. Do you have any suggestions on what to try? I thought to increase the bypass air to .120" then try to tune. I am also thinking of moving the vacuum advance to manifold rather than ported. Current timing is 15 initial 19 mechanical for 34 total on the MSD distributor. Thanks in advance for any advice.
Greg

[Kenth]

The 1910 has .055" idle bypass air from "factory".
Are, yours modified?

[avmechanic]

I have not modified my carb as far as drilling out any orifices. I was just going by the info in Cliffs book as I am away from home and can not go check my carb right now. Cliffs info lists the Idle Bypass air as .110" but the idle channel restrictions as .055".
Greg

[Kenth]

My NOS 1910 i checked orifices on indeed has .055" idle channels and also .055" idle bypass air. FWIW

[avmechanic]

OK. Well when I get back home next week I will be working on this. I will pop the carb off and see what I have. I want to check to see where my transfer slot is with the butterflies too.
Greg

[avmechanic]

Turns out the bypass air holes were .055" so I opened them up to .110" that helped a bunch I could close up the butterflies a fair bit but they need to go more. I only have 9.5 to 10" of vacuum. My plan is to add some more initial timing and reduce the mechanical some more on my MSD distributor. I have the Black 18 degree bushing in there so I can't reduce it more with what I have. I ordered a kit with a 14 degree and 10 degree bushing so will try one of those and bump the initial up. I did it temporarily and could get it idling nicely with more like 14" of vacuum but would have too much total timing if I left it that way. If I still need more bypass air after adding some timing I will drill the bypass holes out a hair more.

[Kenth]

With 10" of vacuum i would open the idle tubes to at least .040", the downchannels to .062" and idle needle holes to .095"-.099".
If you have vacuum in the ported source for distributor vacuum advance after this mod you may need some added bypass air.

HTH

[Cliff Ruggles]

Not all 1910's have the same idle calibration.

I've observed at least four different calibrations on virgin/unmolested units sent here over the years. 

In any and all cases record all the items related to idle fuel delivery before making any changes.

IFR's, DCR's, upper and lower IAB's, bypass air and the size of the holes under the idle mixture screws.

I've had at least two 1910's in here without any idle bypass air at all, and several with .038" IFR's and others with .040" IFR's, for example. 

Upper and lower IAB's have been consistent and most have had .055 DCR's as Kenth mentioned........