Tuning a 650 Holley DP

[RRSweden]

Hi.
I'm running a 650DP on my 383 and I recently installed an air/fuel-meter.
The enginge has problems when moving from standing still on first gear (manual trans).
The air/fuel meter showed that the mixture gets really poor at that moment so I guess thats the problem. I have to give a lot of gas, otherwise it dies...

So my question is where to start.
New power valve (now I got 6,5)? Im thinking of buying a 8,5 Pv...
Or a 50cc acc-pump? or new acc-pump cam?

 

[Frank Mopar]

A bog? What do you mean poor? Rich or lean?

Engine vacuum dictates what power valve you need. Measure your vacuum and the size is 1/2 of the engine vacuum. PV comes into play under full throttle not off idle.

Holly has great instruction videos on their website and YouTube

 

[hunt2elk]

You don't need a 50cc pump. Start with the idle circuit to get your A/F in range. Unhook the secondaries and concentrate on the primary circuit after the idle is decent.

 

[RRSweden]

Idel is good. A steady 13:1 +\-.

I guess it’s called a bog when I start to roll and it wants to die at clutch release. At that moment the gauge says 16:1 -20:1.

 

[RRSweden]

I’m running 69 primary jets and a 6,5 Pv.
Vacuum is 11 at idle.

The plan is to change pv to a 8,5, and the primary jets to 71.

Spark plugs is now white after a day of normal driving.

 

[hunt2elk]

Like stated above, power valve isn't in the circuit coming off idle gently. Experiment with a different pump cam and squirter on the primary side. Also, first make sure your timing is advanced enough and set correct for your motor.

 

[hunt2elk]

Don't mess with jets or pv yet.

 

[RRSweden]

Ok. What CAM would you recomend?
I have the red one now.

 

[RRSweden]

And what squirter? I have a 28 now.

Engine is a 383 with 915 heads.
Xe268 cam and a 10,5:1 compression ratio.

 

[65-440]

The pink cam will give you the longest duration of squirt, that's what I run in street cars and have had no driveability issues off idle... I think you'll be fine with that squirter #, just make sure the pump is adjusted properly, want it to start shooting fuel as soon as the throttle is touched. between that your idle mixture will help tremendously on off idle performance.

 

[RRSweden]

The pink cam will give you the longest duration of squirt, that's what I run in street cars and have had no driveability issues off idle... I think you'll be fine with that squirter #, just make sure the pump is adjusted properly, want it to start shooting fuel as soon as the throttle is touched. between that your idle mixture will help tremendously on off idle performance.

Thank you. I Will try with the pink cam as a start.
The idle ha been adjusted in a standard manner. Clockwise until lower rpm and then backed 1/2 turn...

 

[66Satellite47]

It seems to need more accelerator pump shot. You'll need to try larger shooter sizes & I'd get the pump cam set, then try different combinations of cam & shooter size.

 

[91r/t]

Yea the 28 is the standard squirter size for the Holley's out of the box. I would definately change the squirter and cams before anything else. Also check your idle mixture and maybe give it a 1/16th turn richer on them all and see if that helps.

 

[hunt2elk]

Every motor is different. I ended up swapping the pink cams on all 3 of my cars for others. Whites and reds worked the best on mine, some in the first hole, and some in the second. There are charts on the web showing how much cc and when it comes in for the various colors. I think brown is the most aggressive followed by the pink. Like I stated previously though, make sure you have all the initial timing your motor will take before messing with the carb. More initial timing has a huge impact on taking off smoothly with a stick car.

 

[coloradodave]

First things first. It is imperative to get the timing set correctly BEFORE messing with the carburetor.
How did you set the initial timing? Can you adjust it to more than 11" or is that the highest?
Are you using a distributor with vacuum advance?
Have you used a timing light to see when the timing starts to advance and what the total advance is?
If the carburetor is a list #4777 (on the front of the airhorn), the stock primary jetting is #71 and the 6.5" power valve would be stock. If the highest idle vacuum is 11", then, as has been said, a #5.5 valve would be advised, although I think the 6.5" should work and wouldn't be responsible for a 'bog' or 'hesitation' off idle.
Answers to the above questions will help get you fixed up...

 

[RRSweden]

The timing is at 18 degrees initial. Total 38 without vac adv.
it seemed to like this setting

 

[coloradodave]

The timing is at 18 degrees initial. Total 38 without vac adv.
it seemed to like this setting

AND, is 11" the highest vacuum that can be attained at idle? When you do hook-up the vacuum advance to full manifold vacuum, how much extra advance do you get?

 

[coloradodave]

Or not. Guess there's no more problem...

 

[Paul_G]

Hmmm...

Timing is first thing to get right. Sounds like he has it close.

Adjust floats is next.

Then adjust fuel mixture to highest vacuum at idle. Some like to turn the screws back in 1/8th turn from this point. Then set idle speed, most mild to moderate street engines like it around 800.

Then adjust accelerator pump linkage, No play at all in the linkage. Should see fuel out the squirter at lightest touch of the throttle. (this may be his problem)

That sets the carb up to a basic tune. Start changing parts from that point.

Or not? (or just buy parts, people at Holley got to eat to)