throttle hesitation and mild power

[buffblazer]

well i got my new 350 in my 86 k5 and i have adjusted my rockers and played with my timing and i still have a hesitation when i hit the gas

its a 350 .040, flat top pistons, comp cams 4x4 camshaft, hydro lifters, stock heads, edlebrock performer intake, edlebrock 600cfm carb and stock HEI.

for my timing im at about 8 degrees BTDC and i have adjusted my carb to the best of my ablitys

for denver colorado is 8 degrees about right for timing?

it hesitates a little when you stomp on it and doesnt seem to have all the power it should have for being what it is

what else do i need to adjust or re adjust or look into?

 

[1979jimmy350]

can you adjust your accelerator pump to give you more of a hole shot and richen up your mixture?

 

[buffblazer]

can you adjust your accelerator pump to give you more of a hole shot and richen up your mixture?

im not a big guru on carbs but correct me if im wrong but i didnt belive edlebrock had accelerator pumps?

unless the two big screws that adjust your mixure also controls it?

 

[1979jimmy350]

they should, if you look at your carb you will see a lever that pushes on a plunger i think there is a way to make the link longer and shorter for more or less fuel.

 

[buffblazer]

they should, if you look at your carb you will see a lever that pushes on a plunger i think there is a way to make the link longer and shorter for more or less fuel.

oh ok i know what your talking about now, well which way would i go to richen it up? push it down more or back it up some?

 

[1979jimmy350]

you want it to push down sooner to get more gas into the engine quicker in acceleration

 

[Kenny78]

Short answer is switch to a Qjet. I calibrated my edelbrock and lessened the impact. I am not an expert by any means, but I did a lot of fiddlin. The acc. linkage on the webers have two holes, so its one or the other. Try the other one and see. I put STRONGER step up springs? to push the needles up faster. Still felt like it would run out of gas if it wasnt warmed up. Parts stores can get you a calibration kit and my local library had a book about webers.
Best of luck

 

[454k30]

I've tinkered with the exact same carb you have for about 10 years now and I have found that that hesitation you are talking about is best solved by putting a stiffer spring under your mixture rods.

If you still have the book that came with the carb it will talk about these springs. What these springs do is control the cruise/power modes of the carb. With my carb what would happen is that the vacuum of the engine would pull the rods down to easily and cause the cruise mode to lean the mixture to much and hence the hesitation.

Changing out the springs can be done in about 5 minutes, costs about 10 bucks, and can give you immediate results.

Your timing sounds about right. Try adjusting the lever on the accelerator pump first to the hole closest to the carb and if that doesnt solve it then get the springs. The springs come as a set with different vacuum values and are color coded for ease of identification. Put in the stiffest ones first and if that helps. Then put the next lighter set in and try driving it again. Repeat this until you find the lightest spring that that does away with the hesitation.

Also you might want to consider going 1 stage richer on your rods as well.

A combination of these two changes solved all of my problems.

 

[Kenny78]

Edited my post when i reread. I was thinking the springs were the other way

 

[GNERGY]

Is your vacumn advance working. I had a problem where the weights were hitting inside the rotor and not letting them open up. You could always go with heavier weights and lighter springs to get it to advance quicker.
Tarey

 

[Kenny78]

Is your vacumn advance working. I had a problem where the weights were hitting inside the rotor and not letting them open up. You could always go with heavier weights and lighter springs to get it to advance quicker.
Tarey

That would be mechanical advance right? Also, check your vac. advance by disconnecting and sucking on hose.

 

[buffblazer]

I've tinkered with the exact same carb you have for about 10 years now and I have found that that hesitation you are talking about is best solved by putting a stiffer spring under your mixture rods.

If you still have the book that came with the carb it will talk about these springs. What these springs do is control the cruise/power modes of the carb. With my carb what would happen is that the vacuum of the engine would pull the rods down to easily and cause the cruise mode to lean the mixture to much and hence the hesitation.

Changing out the springs can be done in about 5 minutes, costs about 10 bucks, and can give you immediate results.

Your timing sounds about right. Try adjusting the lever on the accelerator pump first to the hole closest to the carb and if that doesnt solve it then get the springs. The springs come as a set with different vacuum values and are color coded for ease of identification. Put in the stiffest ones first and if that helps. Then put the next lighter set in and try driving it again. Repeat this until you find the lightest spring that that does away with the hesitation.

Also you might want to consider going 1 stage richer on your rods as well.

A combination of these two changes solved all of my problems.

well awhile back i called edlebrock and talked to their techs and told them what carb i had, what motor, my altitude and that i wanted the most power i could get.

the recommended certain rods, springs and jets and i cant remember the rod or jet number but i do remember he said stock springs so that maybe my problem.

my vaccum advance is working i tested it and i do have a new dizzy, cap and rotor also

 

[Hogback Fabrication]

I've only messed with a couple Edelbrock carbs, so I can't give you specific advice on adjustments.

Edelbrock simply can't tell you the correct rod/jet/accelerator pump to run. Their techs might get you in the ballpark but its up to you to determine the fine adjustments.


Bogging under initial acceleration is either too much or too little fuel, changing the accelerator pump settings will change that.

Any of the part throttle stuff is based on rods and jets. Adjustment depends on what isn't acting right: low power or bogging at part throttle requires a different change than bogging or low power at WOT.

As for tuning, you have a few options:

1: Tune via the color of the plugs. Drive the truck for a bit at cruise then park it and pull a plug or two. White means too lean, brown/black means too rich, light tan is perfect. This really only works for adjusting cruise mixture and only if the choke is off and you shut the truck off quickly after cruising.

2: Install an O2 sensor in the exhaust and read the voltage from it, they vary from .000V to 1.000V. Graphs of the ideal mixture are easy to find online, seems like ~700 mV is ideal (a bit more at WOT)..

3: Dyno time, the best option but the most expensive. Wide band O2 sensors and the experience of someone who does this for a living is tought to match but it will probably run a couple hundred bucks.

 

[GNERGY]

I put the 780 edelbrock carb on my 383 stroker and bought the other rods and springs for it. We put it on a dyno at dynojet in eastlake and it was jetted just right from the factory. If you know what jets and springs you might need let me know, or I'll see what I have and sell it to you cheap. They are still brand new in the factory blister packs.
Usually chassis dyno's go for about 75 bucks an hour, thats all it took for mine.
Tarey

 

[79rustyk10]

Hve you tryed an adjustable vacuum advance? I had to use one when I had my old Nova, always had a stumbe at 1600 rpm or so when driving nice, WFO it ran like a scalded dog.
It had a tired 350 with TBI heads, edelbrock RPM intake, and .420 I .442 E lift and 204/214 deg. duration camshaft, with the 600 cfm manual choke edelbrock carb. I put the heavier step up springs in the carb, as mentioned which helped, but after I did the Mr Gasket advance curve (weights and springs) and the adjustble vacuum andvance, Once it was warmed up you could hardly tell the difference between the tired carbed engine and a TBI chevy. Remember this was a car on the road though, not a truck climing over boulders.