Am I "lean surging" ?

[Mac]

The patient in question is my almost daily driver `63 C-10. 283 stock except for HEI dizzy, dual 2" exhaust and an Eddy Perf. dual plane manifold. The truck came with a Holley 750 dp which I swapped for an Eddy 600 mech. seconday I had laying around. That carb proved to have some "issues" so I made a homemade 3/4" thick phenolic adapter plate and bolted on a 350cfm Holley 2300 2 bbl I also had around. The adapter is made with separate holes for each bore to feed the dual plane mani..
Now, it idles nice and even, accelerates strong and cruises nice but conditions of light accel. or pulling a grade it will chug or lightly buck. Plugs are pretty nice and tan color.
Does it sound like a need for upping the main jet size or is maybe fuel the wrong tree to bark up?

[wayne petty]

before you go any farther.... can you do a cranking fuel flow test... open line into a plastic bottle...

should flow almost a quart in just a few seconds or cranking... (this is better done on a cool or cold motor) to avoid the chance of a flashover...

i had a car two weeks ago that the driver was complaining about the stalls under load or going up a hill... i was thinking vapor lock.. when i finally got to diagnose it... with an open line cranking test... it got 2 big squirts then nothing but a dribble...

i changed teh fuel filter in teh suction line.. and used my brass hand held vacuum pump from the hf brake bleeder kit to prime the line from the tank... funny thing is... it pulled like 24 inches of vacuum...
and had a really hard time getting any gas at all....

not a good thing...  i did not have any compressed air source... so i tightened the spray nozzle into the end of the hose from the tank.. and used the pressure and solvent  to back flush the line...

it opened it up enough to drive it a few days..


on another mopar motorhome with a 440-4 bbl... it would overheat only going up long grades...  after a few t stat changes.. a pressure gauge was installed to watch the fuel pressure during the hill climb... it dropped... only at 3/4 or more throttle.... seems the rv store employee had used a multi barb plastic tee fitting in the line... and had not cut it open above the tiny size...and there is even a big warning on it to not use on fuel lines...

[Mac]

Well, I ruled out any kind of fuel delivery starvation because it runs fine during extended "romp on it" sessions.
Also, I've set the float meticulously; even bought a Holley clear viewing sight plug that replaces the regular plug. And I adjusted the idle mixture by the book procedure. The mix. screws did not end up way out from bottomed like you would expect from underjetting either.

[tomslik]

sounds like more of a power valve issue to me or possibly a step or two lean on the jet size...

[Leon]

Vac. leak?

[chimp koose]

I'm with tomslik, sounds like its going lean with light acceleration.I would try a power valve that will open at 2" less vacuum than you have at idle. Often in the winter my manual choke truck will buck like you mention at part throttle ,when I choke it more for extra fuel the bucking stops.Another option might be to check the position of the accelerator pump cam. The holley will allow the cam to be put in 2 positions,the second position gives pump shot farther into the throttle opening . If your cam is on position 2 move it back to position 1 this will give pump shot as soon as you dip into the throttle.You could also increase pump shooter size but i doubt that is the problem.

[Mikej]

You probably need to change the springs or metering rods. Go to the edelbrock site.

[enjenjo]

On the Edelbrock web site they have instructions on tuning that should point you in the right direction.

[DrJ]

About 40 years ago, I described those symptoms to my Dad, the best * mechanic ever, and he said "Change the plug wires."

I'm trying to think of a time his diagnosis was ever wrong...

(He's been gone 25 years, but he still sometimes "tells" me how to fix stuff.)

[bucketmouth]

Good to see that you fixed the problem. I was wondering how you measured the vac at idle.
The way I do it is to put the car in drive with your foot on the brake and what ever the reading go down two sizes. This has worked for me over the years.
Holley say to go 1/2 of the vac reading is something I didn't know. I thought I had been doing alright :?