I have a Holley 650 DP carb, brand new, I have checked the powervalve, switched squriters, and jets. I just can seem to get the flat spot out. This is what it is doing, when you just punch the throttle it trys to died and then it takes off, but if you just lay in to the throttle it does fine. Any suggestions???

 

it sounds like you have either too much or too little pump shot. you may need to play with your squirter sizes some more.

 

I have already went from 28 through 40 to high flow screws to regular screws that is not working.

 

are you running the 30cc pump diaphrams or the 50cc? the larger ones tend to really help smooth things out...

 

Don't forget pump cams. They can effect the amount of volume, and rate. Most stock Holley's have crappy pink cams. A blue cam on hole #2 usually works well. Just something else to try.

 

I thank everyone for the suggestions but im not really a carb guy what is a red cam and blue cam again i thank everyone

 

If you look at the arms that have the bolt that you adjust for the accelerator pump, the other end of it rides on a piece of plastic (bad description, but hey, it's late). You have a DP so there will be two. If you look at parts places they'll sell a cam assortment that has like 5 different colored cams in it (friggin Holley charges a bunch for a few pieces of plastic...). Since your DP uses two cams, you'll have to get two assortments if you want to run both with the same color. I don't know if a blue cam will be best with a DP, but on VS they usually work well. The colors identify the different ones. Each has a different profile that results in varying discharge rates, and volume. In addition, the cams usually have two different holes where you can screw them in. Screwing a blue cam in hole #1 will make it behave differently than if it was screwed into hole #2. Dave Emanuel's book Super Tuning and Modifying Holley Carburetors has a nice chart showing these differences in the cams. It is a good Holley book all around as well.

HTH

 

Thank you so much for your help I will try the cams and the larger acclerator pumps I really do thank you so much if you need any help with anything on a 3rd Gen give me a call

 

You might chec this.

https://www.thirdgen.org/techbb2/sho...hreadid=251326

 

Thanks alot man i will try this soon and tell you how it turns out

 

let us know how the blue pump cam works out. I am thinging of changing mine also.

 

no problem will do

 

ummm.....I priced the pump cams through my local hot rod shop and you have to buy them in a kit for $20 a piece and I need two off them. Any suggestions on how to get them indiviullay?

 

www.summitracing.com

Type hly-20-12 in the search field. $20 (plus ~$9 S&H "order fee") for an assortment.

I've been watching this thread without comment up to this point. It seems to me that you're chasing a problem that has absolutely nothing to do with the accelerator pump circuits. There's no way a 650 on a mildly-built engine should need 40 squirters or 50cc pumps.

I haven't seen any mention of fuel bowl level or ignition timing. Those things have to be right before you start jetting or fooling around with pump cams or squirter changes.

 

He is right you know. Accelerator pump tuning is usually the LAST thing you do. You need to have the basics first (fuel level, etc.) then tune your jets and power valve. Then once all that is nailed down THEN you can start worrying about the accelerator pump circuit. If your jets are too lean for instance, you might over do the accelerator pump inorder to cover up a lean spot (or a late opening power valve for that matter). If I were you I would baseline the carb to how it came out of the box, check the fuel level, and go from there. Again, wait on the accel pump until you've got the rest tuned. Remember when carb tuning, you have to excercise PATIENCE. One change at a time and observe the effect. I know it is tempting to change that power valve while you are in there changing jets, but it'll save you time in the long run.

Just my $0.02.

 

This is a last resort. The fuel bowls are perfect, the timing is 32 degrees total and has already been turned up and down. The squirters in it now are 35s, the jets is a 68 and 73. Here is what is done to the motor. Trick Flow Kenny Dutiwieler out of box heads, comp XE268 cam, MSD HEI pro billet distributor, Team G intake, steel crank inside of a 355 canidian 4 bolt main blot, eagle rods, and KB pistons with 10:1 compression and a 150 shot of NOS. What is your suggestions?

 

Oh yeah and to vacuum at idle on the baseplate is 11psi so it has a 5.5 powervalve in it

 

Sorry one more thing the carb was brand new when i purchased it and out of the box it barely ran. I have got it to the point it is now with patience so I know patience this is just my last resort

 

Well I don't have any experience with DPs but your jets and PV seem reasonable to me. I'm running a 35 squirter in my 750 VS on my 383. Don't know how that translates to DPs, but again that sounds like it should be in the ballpark. If I were in your situation, I might look into an air/fuel gauge. The narrow band O2s aren't the greatest, but they could help you know if your accelerator pump problem is from being too lean or too rich. It is easy to mix the two up without something like a 02 sensor to help you. Something else is that sometimes people confuse the procedure for setting the pump arm. Some people give it the .015" clearence at idle. Doing that will give you a nice bog off idle. Make sure that spec is set holding the throttle wide open (engine off of course) and push the pump lever down while holding the throttle. A quick test I do is with the engine off and fuel in the bowls, I like to give the throttle just a small turn. A few degrees. Even with small movements, you should see a good shot out of the squirter. If not there is some slack in the linkage.

Also if you do look into getting a cam assortment, I think that a green cam on the #1 hole is similar to the blue cam on the #2 hole. So you might be able to get away with just one assortment. Again, I am not familiar with DPs so hopefully someone more knowledgeable will chime in.

And for some in depth Holley tuning discussion search on this board for the user name Chickenman35. The guy knows his stuff and you will learn ALOT by reading his posts.

Good luck

 

Thanks for your help i will try your suggestions, but i do have a A/F ratio gauge and it says it is pretty perfect. but thanks for your help

 

well theres your problem...driving a DP carb is different then a VS carb...think about it this way...your at idle and your fully opening the pri and sec butterflies all at once...dumping all the fuel down there before your motor has begun to suck any air...
you said it yourself. if you lay into its fine...well open up the primaries for a second or 2 then put the wood to the floor

my combo is a little hotter then yours and i had the same problem when trying to launch...although i have a 5 speed, a WOT launch anywere under 2 grand it wasnt happy..you adjust your driving style and all will be good..

 

A 650 DP properly tuned is okay going WOT on a 355 from about 1200 RPMs and higher. That means it won't "bog" on that kind of a setup.

However...

The cam is a different story. Comp says the XE268 is the largest cam you can use with a stock converter, with a powerband of 1600-5800 RPMs. That doesn't mean a stock converter is going to work well in "the package". 2500-3000 stall would be much more like it.

A non-bogging engine will climb slowly in RPMs when the stall is lower than the "real" powerband, then pick up suddenly as "the package" starts working well together. Your description of "it trys to died", however, sounds like a bog. Is it really sputtering out, or do the RPMs just climb very slowly?

When I was running a q-jet and Holley VS with 2200 stall and a cam with 1500-5800 RPM powerband (270 adv duration), it would come off the line lazily until RPMs hit 3000 - then it would feel like the secondaries finally opened up. However, when the DP went on with everything else the same, it acted exactly the same way - but, of course, the secondaries were completely open immediately, not suddenly opening at 3000 RPMs. Going to a 2800-3200 advertised stall converter (it actually stalls slightly higher) was "eye opening". Through all this, though, the engine wasn't "bogging", it just wasn't getting up into the "reality" powerband until 3000 RPMs. Sure felt like a dog until it did, though.

 

The car when you take off (hard hit to the gas petal) the rpms drop to about 500 then hold on in about 1/2 a second to 1/3 of a second. The car is really strong all the way to 6k or more. but i have trouble trying to run it at the drag strip it is not the street i am concerned with. the car runs in from 12.50s to 12.20s on motor but i think i can get 11s on motor if the carb didnt die out on take off.

 

Here is my car by the way I JUST GOT IT PAINTED!!!

 

What's your timing set at? Perhaps if you advance the timing a little you will lose the bog. It worked for me.

 

thanks i will try to set the timing a little bit higher

 

Would you be able to post some pics of the carb as installed?

 

Yea sure but it may be this evening or tonight before i can.