acceleration q/problem

[75_chevy]

so here's the thing I have a 1975 stepside swb c10 with a nothing-special 350 crate 350trans, brand new edelbrock 1406 (600cfm) carb. truck runs way better with the new carb, originally had the holley 90670-1 (piece of garbage.) here's the deal, she runs great for the most part but here's my question, when I floor it from a complete stop it runs all the way up to about 4k and without me lifting my foot up it drops down to like 1 or 2k for a sec then fires up pretty high again. I'm assuming the float bowls weren't filling up fast enough but I'm not sure. also thought it could be a vacuum leak but I ethered the intake while it was running and no rev up. I have a vacuum gauge coming in the mail but until then do you guys have any suggestions what it could be? thanks
Steven




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[75_chevy]

not sure if this should have been posted under "engine" but I figured it was a performance issue


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[rich weyand]

What's hooked to the "ported vacuum" line on the carb?  (Passenger side vacuum tap)  Distributor should be hooked to the "manifold vacuum" tap on the driver side.  That will affect off-idle performance and is not the issue you describe, but you should change it.
http://www.corvetteactioncenter.com/forums/c3-technical-performance/60830-ported-vs-manifold-source-vacuum-advance.html

What metering needles and jets are you running in the carb?  What pop-up springs are you running in the carb?  Which 350 crate is it?  (GM part number from the invoice is best, rather than a description.)

Is the performance you are talking about temperature (outside temperature) dependent, or does it happen when it is cold out and when it is hot out?

[75_chevy]

I watched some troubleshooting videos straight from edelbrock and if I'm not mistaken he said the distributor vacuum should be connected to the ported (passenger side) line. so I have it connected to that side. the motor is p/n 10067353. I don't put the pedal to the floor when the motor is cold if that's what you mean, but weather wise it does it cold or warm. as for metering rods and jets I'm not sure. whatever came from edelbrock in the 1406 carb. I'll look into that and see if they should be changed. same for pop up springs not sure what those even are. thanks for your help. while were talking about it I may add that the motor has some slight surge or hiccup at idle, more noticeable at low idle like 600rpm.


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[75_chevy]

actually if you open the picture you can see where the vacuum advance line is currently hooked up


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[75_chevy]

also I should add that it does fine accelerating on to the freeway, and if I floor it on the free way it just accelerates normal and hauls ass, it's just when I floor it from a slow speed and those tires spin it revs up then drops back down


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[rich weyand]

Read the article I attached above.  The ported vacuum connection for the distributor is emission stuff, and Edelbrock's installation instructions says so in the chart on page 3.  Without all the emissions garp, hook the disti to the driver's side port.
http://www.edelbrock.com/automotive_new/misc/tech_center/install/1000/Performer_Thunder_Carburetors_130815.pdf

With the distributor on ported vacuum, you need to run the timing at like 4* - 6* BTDC.  Put the distributor on manifold vacuum and set the idle timing (with the vacuum disconnected) to 16* BTDC and your engine will be much happier at idle, and coming off idle, you won't have an off-idle sag until the distributor catches up.  Trust me on this: the 1406 on a 350 is something I have done a lot of experimentation and research on.

You should read this to understand your carb better:
http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf

You probably want to put in the 8# step-up springs, and lean that carb out a little.  An air/fuel ratio meter like the NGK helps a lot.
http://www.amazon.com/NGK-Powerdex-Air-Fuel-Ratio-Monitor/dp/B0018MUNTM/ref=sr_1_1?ie=UTF8&qid=1389768656&sr=8-1&keywords=ngk+meter

Alternatively, you can copy my tune for that engine and carb setup, which is here.  Should be very close for you, since you have headers and all, basically same setup as me.  This tune was determined with an air/fuel ratio meter monitoring the exhaust for correct mixture.  You don't need a new accelerator pump, but the rest of this post applies to you.  Make sure you adjust the float levels on the Edelbrock; new from the factory they are seldom set right, and that can screw up a lot, including giving you the problem you are seeing if they are set too low.
Reply #12 in: http://forum.73-87chevytrucks.com/smforum/index.php?topic=26985.msg225757;topicseen#msg225757

[rich weyand]

actually if you open the picture you can see where the vacuum advance line is currently hooked up

The two vacuum lines disappear behind the valve cover, so I wasn't sure where they went, but it looked like it was probably wrong.

[rich weyand]

also I should add that it does fine accelerating on to the freeway, and if I floor it on the free way it just accelerates normal and hauls , it's just when I floor it from a slow speed and those tires spin it revs up then drops back down

In that case, it could just be that distributor vacuum connection.

[75_chevy]

well rich thank you for all your help I'll let you know how it goes!!


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[Boone83K10]

so here's the thing I have a 1975 stepside swb c10 with a nothing-special 350 crate 350trans, brand new edelbrock 1406 (600cfm) carb. truck runs way better with the new carb, originally had the holley 90670-1 (piece of garbage.) here's the deal, she runs great for the most part but here's my question, when I floor it from a complete stop it runs all the way up to about 4k and without me lifting my foot up it drops down to like 1 or 2k for a sec then fires up pretty high again. I'm assuming the float bowls weren't filling up fast enough but I'm not sure. also thought it could be a vacuum leak but I ethered the intake while it was running and no rev up. I have a vacuum gauge coming in the mail but until then do you guys have any suggestions what it could be? thanks
Steven

are we all going to just ignore that he has 3 blue plug wires. Where is the #6 plug wire? Why do you have the #2 wire going to the #4 plug. The #3 wire going to #2 plug. You have no vacuum line to the PCV valve either?

You said from a dead stand still it runs up to 4K then drops to 1-2K. Is that when it shifts to 2nd gear? or is it staying in 1st?

[75_chevy]

I have all my plug wires, I pulled all of them off to put the headers on and just numbered them 1-2-3-4, also I found out one of the boots was ripped so I just put a red wire in its place.


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[75_chevy]

drops back down to 1-2 in first then revs back up and shifts normally


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[75_chevy]

no vacuum on PVC I was just using it as a breather cap pretty much


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[dvdswan]

I know I'm being picky but you should always number your plug wires correctly 1,3,5,7 dr. side and 2,4,6,8 pass side from front to back respectively.  as far as your issue I was think you distributor as well but the mechanical advance weights.