Weber carb upgrade took the "lope" out of my cam? -
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Unread 02-11-2013, 09:37 AM   #1
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Join Date: Apr 2009
Location: Covington, LA
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Weber carb upgrade took the "lope" out of my cam?

Ok, somebody school me on this please. I have the 258 with a mild cam in it and had been running an MC2100 carb. It ran great and one of the things I like about the setup was it really loped at idle. It sounded like an old school V8 at about 600 RPM. I had a Weber 38 in the garage and finally got around to buying the adapter plates for it and installed it this weekend. It runs great, has amazing throttle response and returns to idle very smoothly. The odd thing is it now idles much smoother and does not lope. The difference is noticeable. I always attributed lope to having a good cam. Can some explain why changing the carb would affect the lope or the sound of the motor at idle?

1981 Jeep CJ7
258,T-5, D300, NT AMC-20 & Dana 30 (4.10)
Locked front and rear
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Unread 02-11-2013, 10:30 AM   #2
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1981 CJ7 
Join Date: May 2011
Location: Elbert, CO
Posts: 15,654
As I understand it, the "lope" is caused by valve overlap, which is not necessarily a good thing.

I think people equate the "lope" with race car engines, so they think that's how the idle is suppose to sound. In reality, those engines are designed to run at extremely high RPMs, and their long duration cams causes rough, inconsistent, and inefficient idle quality.

It sounds like your 38 is tuned better for your engine than the 2100 was. I love the Weber 38 for a 258.

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