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Old 03-07-2012, 05:44 PM
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Cold Bog...tuning mystery...

Hi all

I've got a tune up issue that has me stumped. Chevy 350. When I get on the throttle from a stop, the car hesitates or bogs momentarily and then regains power. No backfire through carb that I've heard. It only does this under 2000 rpm.

It doesn't do it at all once the engine is warm. It's also tough to get started when it's cold.

It has a very recently rebuilt edelbrock 1405, (new everything including floats, rods/jets, accelerator pump, springs) running 8% lean on the primaries and secondaries. (I'm at 5300 above sea level). Edelbrock mechanical fuel pump at 6psi.

HEI ignition @14 degrees inital advance and 34 degrees total all in at 2500 rpm. Spark plug gap at .45.

Vacuum guage holds steady at 17 lbs., drops to 2-3lbs. and rises back to 17 with a quick snap of the throttle, goes up to 23 lbs. then settles back to 17 when throttle is closed.

I've got everything set the way I think it should be...any guesses as to why the engine is doing this?

Thanks,

Mike

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Old 03-08-2012, 07:18 AM
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Do you have a working choke?
Sounds like no heat to the intake when it's cold. Fuel is puddling in the intake. You're getting a lean bog.
Do you have the exhaust cross over under the intake open?
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Old 03-08-2012, 07:37 AM
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bog'n carb

IMHO... i'd be buy'n a edlebrock tune up kit.. got springs and other stuff to fine tune it... also reset ur xcellorator pump lever.
ur pushing the limit on the pressure too...
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Old 03-08-2012, 08:25 AM
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Quote:
Originally Posted by delawarebill
IMHO... i'd be buy'n a edlebrock tune up kit.. got springs and other stuff to fine tune it... also reset ur xcellorator pump lever.
ur pushing the limit on the pressure too...
That occured to me last night after I posted this. I have the spring assortment and tonight I'm going to try the pink 7" springs instead of the orange 5" springs I re-installed when I rebuilt it. Going to advance my timing to 16 degrees inital also and see if that helps.

The accellerator lever is set to Edelbrock's recommendations, what do you recommend I change it to?

By pressure are you referring to my vacuum level? I think it's on the low side of acceptable due to the camshaft. I'm not sure what the specs are, but it definately has a mild street cam in it.


Quote:
Originally Posted by RWENUTS
Do you have a working choke?
Sounds like no heat to the intake when it's cold. Fuel is puddling in the intake. You're getting a lean bog.
Do you have the exhaust cross over under the intake open?
It's a 1405 so it has a manual choke, which is hooked up and working. It doesn't seem to make much difference on startup however. As for the manifold, it has a weiand dual plane, not sure if the exhaust crossover is open or not....

Thanks

Mike
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Old 03-08-2012, 04:24 PM
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vacumn

no i was taking about fuel pressure of 6# be'n at the high edge. i like to be under 5#.. for the acc pump.. without going out and looking.. just connect the arm so the pump get the largest stroke for the shortest throttle movement..
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Old 03-08-2012, 08:00 PM
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Quote:
Originally Posted by delawarebill
no i was taking about fuel pressure of 6# be'n at the high edge. i like to be under 5#.. for the acc pump.. without going out and looking.. just connect the arm so the pump get the largest stroke for the shortest throttle movement..
Ok I'll give that a shot...thanks...
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