Larrys'66

So first, some important stats..

The car is running strong but rpms flutter while cruising and the spark plugs are white. I am using a 455 with 750 cfm (1407) carb, torker intake, 350 automatic transmission all in good condition. Vacuum lines are new and tight.

I have the carb calibration kit #1480 and about to move up to the first stage rich jets /rods. I could call Edelbrock but i wanted to ask the forum about their experiences, it's a lot more fun.

My questions:

1) Should I first replace the 5" Hg step up spring with the 7" or 8" to see if lean condition subsides and/ or extend the pump arm linkage to the next hole?

2) If I go right for to the #10, 4% rich jets/rods setup, do I keep the 5" Hg step up springs or choose a richer version? The calibration kit manual did not specify which spring to use to correspond with jet/rod combinations.

3) Something else entirely.

Thanks guys

firefrost gold

I had the opposite problem with my 750 was an a low comp small cam tall geared 326 pontiac . My point is i found that jets needles made more impact on the tune than anything else. Good luck the help line was a good source for me if you need some top carb gaskets let me know I think i have some had to buy i bulk on time.

Larrys'66

Thanks FFG, I'll let you know about the gaskets. Maybe I will call the tech line for some tips.

TripDeuces

The pump are linkage is not going to effect your mixture so leave it alone for now until you get the mixture correct. One step at a time.
It sounds like you are lean so going richer can't hurt. Without some sort of meter to tell you exactly where you are you're playing a guessing game. I would go richer one step and see how it likes it to start. On a Edelbrock carb this is easy so not much to deal with.
The spring I would leave alone also until you know exactly what your cruising vacuum is. You need to hook up a vacuum gauge and drive around normally and find the lowest reading indicated. At that point I would go one or two points below that for the spring.

joe_padavano

As opposed to, oh, reading the tuning guide that came with the carb?

Larrys'66

Actually, I asked the forum because of what the manual said on page 8. I have been reading the manual and researching the Edelbrock you tube videos. I thought the forum might have some experience to share.

The manual does explain to try the spring changes first but does not mention the spring to accompany the jet/meter changes. When I called the tech line he agreed and explained how to use the stock springs for the jet/rod changes and observe running vacuum conditions for further changes. All of which, I found very helpful.

My cruising vacuum is around 8" Hg and varies down to 16"Hg.

Larrys'66

Thanks TripleDeuces. I just did the first step richer jet/rod change-out and left the orange springs in place. Easy peazy...

Time to go for a ride...

jpc647

The springs are dependent on your vacuum at idle. Depending on your vacuum at idle, you divide it by 2 and use the correct spring on the chart.

Larrys'66

The performance is better, the stumbles during low RPM cruising are almost gone. I need to have a look at the plugs and I may need to insulate or relocate the fuel line as it routes above the engine.

grampy

That bucking feeling while in cruiseing steady MPH in high gear is a lean condtion. up the rods first. The stock jetting is usally close.I would play with a higher vacume metering rod spring for best heavy part throttle. Half of idle vacume in gear is too low. try 2 to 4 inches lower then vacume in gear. that carb is ok for small blocks but with big block in a heavy car , the secondaries open too fast and create a lean stumble on tip in when going to full throttle quickly. The only way I found to help this is to add solder to the counter weight. sometime even this wont fix it compleatly.

Larrys'66

Thanks Grampy- Most of the bucky, stumbles during part throttle went away with the #10, 4% rich jets/rods. I am considering the next step richer to see if more of a good thing works.

My vacuum went from 8" to 10" Hg in gear with just the the jet change.

Larry

cutlassefi

Too much timing will make it buck and jerk during cruise as well.

grampy

First how big is the camshaft is in the motor ,10 inches of vacume is not much.you made need to power time it to get more vacume .I time the engine backwards first. I set the total first at 34 to 36 at max advance ( @ 2500 to 3500) ( lighter advance springs in the dizz with a kit ) with the vacume advance hose off.let it come to idle and check the idle advance. Oldsmobiles like 15 to 20 .if it is lower you need to limit the advace slots in the dizz to bring it in this range. bigger cams over 225@ 50 need closer to 20 to help with idle vacume.I would get the timeing right before messing with the carb.

Larrys'66

My timing was left at 8 advanced, any more made the valves float under WOT. I have often seen the recommended 32 to 36 total list on the forum. Unfortunately, the cam is an unknown and I really wish I knew more about the build. It came out of a car that was sitting for a while after it was completely rebuilt and waiting for paint. The cylinder hone marks were still clear when I examined the bottom end. I think the previous owner passed before he could finish the car and he kept the secrets. The engine is strong, I am just working to improve and learn along the way.

My last carb change was moving from the 5" springs to the 7" springs, a recommendation from the Edelbrock tech. This seemed interesting as it was not the typical half of vacuum value in previous recommendations. The throttle seems to react quicker and the stumbles at low throttle cruising remain.