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Old 02-23-2011, 03:42 PM
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Holley Hesitation

I put a Holley 570 cfm Street Avenger on the 350 in my pickup today and everything seems to work fine except I get a slight hesitation or bog if i'm driving around town and touch the throttle to speed up in normal driving. I took off a 1850 Holley 600 cfm and it didn't bog or hesitate like the Street Avenger does. My old truck is a driver and dose'nt see any WOT , i'm just concerned with drive ability. Is this an accelerator pump problem maybe ????

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Old 02-23-2011, 09:33 PM
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Quote:
Originally Posted by 57halfton
I put a Holley 570 cfm Street Avenger on the 350 in my pickup today and everything seems to work fine except I get a slight hesitation or bog if i'm driving around town and touch the throttle to speed up in normal driving. I took off a 1850 Holley 600 cfm and it didn't bog or hesitate like the Street Avenger does. My old truck is a driver and dose'nt see any WOT , i'm just concerned with drive ability. Is this an accelerator pump problem maybe ????

Make sure there is no slack in the pump arm.
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Old 02-24-2011, 07:52 AM
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I've tried both a little play and no play in the pump arm. Im thinking of looking at the squirters and pump cams to see if theres any difference between the 1850 600 cfm and the 570 street avenger.
Gene
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Old 02-24-2011, 02:16 PM
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I changed the squirters , they were both the same #31's. I also swapped the pump cams there was a slight difference and the cam was mounted in a different hole on the 570 cfm (upper hole) than the 600 cfm (lower hole) so I tried the 600 cam in the lower hole and it seems to have helped a lot but there is still a little bog. It still looks like the 600 has a better pump shot than the 570 does. I'll look at accelerator pumps, float bowls and gaskets next.
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Old 02-24-2011, 07:32 PM
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Im running a 670 avenger on a 388 stroker and having the same problem. A "fall on your face" bog when under light driving condition and just touch the throttle to speed up.

I've pulled plugs and it's showing a lean condition-very lean. Have you checked plugs?

I changed squirters which did help a little with the bog. Im going to look at the power valve next as stock is a 6.5 and I believe Im going to try a 9.5 (waiting for weather to clear up a little so I can drive around with a vacuum gauge before changing)

Also going to up the jets a little in hopes of curing this lean condition....
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Old 02-25-2011, 11:31 AM
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No , have'nt looked at the plugs yet but I will. I will look at the jets also along with the power valve and compare them with what the 600 cfm carb has in it. I bought this 570 Street Avenger for my 66 Corvette with a 300 hp 327 and had the same problem but instead of dealing with it I put the old 600 double pumper back on it and it runs fine. This Street Avenger is new right out of the box and has only been driven less than 50 miles.
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Old 02-25-2011, 12:01 PM
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The reason is 600 cfm is a non-emission carb and the street avenger is a emission carb. Changing the jets or power valve or accel pump cam will not cure the problem. It's the low idle circuit so leaned out that need to be addressed. The jets and power valve only come into play at around 1500 rpm. Changing the pump cam may help but it is only a bandaid.
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Old 02-25-2011, 12:10 PM
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Quote:
Originally Posted by lg1969
The reason is 600 cfm is a non-emission carb and the street avenger is a emission carb. Changing the jets or power valve or accel pump cam will not cure the problem. It's the low idle circuit so leaned out that need to be addressed. The jets and power valve only come into play at around 1500 rpm. Changing the pump cam may help but it is only a bandaid.
Agree^^^. You need to enlarge the idle fuel feed restriction to get a richer fuel emulsion to the idle circuit and the transition slot.

Just turning the idle mixture screws out richer won't really help, as the idle mixture needles feed a pre-mixed air/fuel emulsion to the idle hole and transition slot, turning the mixture screws richer just feeds more of this preset mixture to the engine(not richer, just more of it). What it really needs is a richer mixture delivered to the idle mixture screw, which means you need to increase the size of the idle feed restriction in the metering block.

I have no idea if this restriction is easily accessable in the Avenger metering block like it is in the older Holleys. Size is changed by drilling them bigger with a pin vise and small number drills size 61-80. Get them at a Hobby store or Industrial Supply.
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Old 02-25-2011, 03:10 PM
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If this street avenger carb is a emissions carb all i'm doing is banging my head against the wall trying to get this slight bog out of it. The rest of it seems to work great. IDEA !!!!! how about using the primary metering block from the 1850 600 cfm carb on the street avenger carb. Or should I just put the 600 back on my pickup ?
Gene
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Old 02-25-2011, 03:27 PM
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I have not thought about that. If the fuel passage line up then try it.
I think it could work. good luck
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Old 02-25-2011, 03:29 PM
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Quote:
Originally Posted by 57halfton
If this street avenger carb is a emissions carb all i'm doing is banging my head against the wall trying to get this slight bog out of it. The rest of it seems to work great. IDEA !!!!! how about using the primary metering block from the 1850 600 cfm carb on the street avenger carb. Or should I just put the 600 back on my pickup ?
Gene
Should work, but you will want to check to see if the idle air bleed (in the choke tower, the outer bleeds) is the same as is on the Avenger. Idle fuel feed restriction and idle air bleed influence each other.
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Old 02-25-2011, 04:23 PM
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I'll check them out next time I get a chance in a day or so, its going to rain again soon. Gene
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Old 02-25-2011, 04:29 PM
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I do not know if this will help, but it might. A lot of times If you are not careful, by the time you get the idle speed set, the throttle plate is starting to uncover the transition ports in the throttle body.

I had a annoying off idle bog, with a Holley two barrel "Bugspray" carburetor on a VW powered sand rail. The problem was cured by actually setting the idle speed slower, and it improved the off idle response.
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Old 02-25-2011, 04:45 PM
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It dose'nt seem to be an off idle bog like when you take off from a stop , its more of a bog when im already rolling and want to speed up a little more.
Thanks , Gene
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Old 02-25-2011, 05:30 PM
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OK, new idea. Have you checked the float level, or fuel level in the bowls?
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