Summit Carb is Calling
Moderator
Joined: Dec 2007
Posts: 7,987
Likes: 104
From: Boise, Idaho
That would be my guess. That sounds like a recipe for all manner of carb to intake flow working how it shouldn't.
Postmaster
Joined: Dec 2006
Posts: 3,603
Likes: 10
From: Spokane, WA
That theory also works when using a carb on a C manifold without a spacer. Some have found a 4 hole spacer on the open plenum of a C helps with lower engine speed performances. The spacer provides for a more columnar flow through the carb and gets the carb base away from the turbulence of that big opening of the C manifold. No such situation with a DP. The bores in the DP are more than deep/long enough that a spacer does nothing but take up space and lighten the wallet.
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Lead Driver
Joined: Mar 2008
Posts: 7,184
Likes: 382
From: Near Los Angeles
I'm not quite sure how to proceed with an issue. I've never experienced a carb that after warm up and I clear the fast idle, then drive and it comes back up in rpm. Sometimes just driving down the road I'll let off the gas and I'm idling at 1k rpm. Other times it runs on. If I jab the throttle after shifing to park and before turning the key off, the idle drops and it shuts down fine. And that is when it is hot, after driving for some time.
I've tried about all I know, float level, ck for v.leaks, throttle cable, idle screw, afr, timing, and then the phantom returns. Now I'm just standing back, so to speak, and scratching my head.
Aside: I wonder is Summit is having financial issues with this carb, or their carb line in general. With all products purchased from them their return policy is beyond fair. However, with the Summit Carb it is no go. You'll get some guy who doesn't know a thing about this carb and has to read in a book what it says about the carb, and they give you the company line: No return.
I've tried about all I know, float level, ck for v.leaks, throttle cable, idle screw, afr, timing, and then the phantom returns. Now I'm just standing back, so to speak, and scratching my head.
Aside: I wonder is Summit is having financial issues with this carb, or their carb line in general. With all products purchased from them their return policy is beyond fair. However, with the Summit Carb it is no go. You'll get some guy who doesn't know a thing about this carb and has to read in a book what it says about the carb, and they give you the company line: No return.
Postmaster
Joined: Dec 2006
Posts: 3,603
Likes: 10
From: Spokane, WA
Maybe what you are experiencing with that carb is part of why Holley discontinued it after a not very long run. It didn't catch-on very well.
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Moderator
Joined: Dec 2007
Posts: 7,987
Likes: 104
From: Boise, Idaho
I dealt with this problem on one of mine for quite a while. It finally turned out that the weight on the end of the kickdown arm had snapped off.
The weight was what really brings it back down to idle.
Not saying yours is snapped off, but what about just trying to make it heavier?
When mine didn't have it, sometimes it'd idle at 700, sometimes at 1200, sometimes at 1500, etc. Hitting the gas with my foot would sometimes bring it back down to idle, sometimes not. Very frustrating until I figured it out.
The weight was what really brings it back down to idle.
Not saying yours is snapped off, but what about just trying to make it heavier?
When mine didn't have it, sometimes it'd idle at 700, sometimes at 1200, sometimes at 1500, etc. Hitting the gas with my foot would sometimes bring it back down to idle, sometimes not. Very frustrating until I figured it out.
Lead Driver
Joined: Jul 2009
Posts: 6,477
Likes: 19
From: Sheffield, AL
Once, I had a similar situation and determined the throttle return spring I was using did not provide enough tension. Once replaced with a slightly heavier one, the problem disappeared never to return.
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Lead Driver
Joined: Mar 2008
Posts: 7,184
Likes: 382
From: Near Los Angeles
Since I am getting such terrible mpg, I was considering trying something: Using the venturi drop in tubes that I tried with another carb, and dropping to .046 jets in the primaries, where the 1.08 4100, a 480 cfm carb, usually runs. Something like this below:
Holley also does this and makes the reducer sleeve for some models:
If it runs well then I've created a spread bore, hopefully more responsive, and the supreme benefit would be better mpg produced by higher velocity mix flow? 'You just can't leave well enough alone.'
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Lead Driver
Joined: Mar 2008
Posts: 7,184
Likes: 382
From: Near Los Angeles
I was modifying my throttle bracket when I noticed fuel dripping out from around the throttle shaft. I called Summit and they are sending a new carb. They now openly say it is Holley who makes them! There has been a few problems with the shaft seal being pressed all the way in. I tried to convince them to refund the cost or to apply it to a Holley 1848, but that had the chance of an ice cube in hell.
I believe I will sleeve the venturi and drop the jet size.
I believe I will sleeve the venturi and drop the jet size.
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Lead Driver
Joined: Mar 2008
Posts: 7,184
Likes: 382
From: Near Los Angeles
Wow, it looks like I have the option to a refund. I just don't know if I will have confidence in a new carb. I'm considering going over to the dark side...to a Holley 1848.