What is the differenece between the tube type squirters on holley carbs and the straight ones?

And just out of curiosity how would you tune your main jets on a holley double pumper carb for the street? I've never used a double pumper and usually tune my primary jets by plug color, then add 8 to the secondaries for the PV difference.

Do double pumpers even have power valves? Do they have 1 for EACH bowl?

Thanks,

I think you're pretty close to having it. I have a 650dp on my 350, and I tune the primary jets the same way, for good street manners and plug life. The stock jets were 67 and 73's, so after I get the primarys right, I start with a 6 spread to the secondaries. I think the best way to tune the secondaries is for max mph at the track. I haven't tried that enough to know if thats best. I've just had buddies follow me to make sure I'm not clouding up the road with severe richness when I stomp it.

Yes, double pumpers can have PV's. Mine came with only the one in the front. I think sometimes they are jetted square and have a PV in the back too. I don't know why, and I haven't tried it.

chris

I was told to use the tube type to 'center the shot over the bore better', and since I was buying new ones, I ordered the tube type.

DPs are the same as vac secondary carbs, other than the mechanical secondary opening and second accel pump. Some have two PVs, some have one.

If I am not mistaken any Holley DP that is 800 cfm or more has 2 power valves. One in the front and one in the back. I know my 850 has them.

Check this chart out, if the carb has a sec PV there will be a number in parens (12) next to the pri PV size... Reference the number at the bottom of the chart to see the sec PV size...

http://www.holley.com/HiOctn/ProdLine/CarbList.pdf

Casey, to tune the primary side on the street is really all done by seat-of-thepants ( my famous AZZDYNO), and reading the plugs. Keep in mind that the carb is an interelated system between idle circuits/main circuits/power enrichment circuit and accelerator pump.

So if you drop or increase jet size, you certainly might have to increase or drop squirter size or adjust the pump cam. Just keep the interelatedness in mind when you start tuning. Be prepared to tweak squirters as you change jets, etc. But I use the plugs as my guide on jetting primaries. Drive it normally and stay out of the secondaries while you are dialing in the correct cruising A'F ratio.

I personally prefer a fat PV and lighter jetting for the primary side for better economy. But it doesnt always work!

I don't mean to sound like an a$$, but I don't have a DP. I was just curious and wanted to know for future reference.

Are the primary and secondary butterflies linked on a 1:1 basis? Or do the secondaries open up after, say, 1/3 throttle or something?

I just wanted to know because I don't see how you would tune your jets, by examining your plugs, if you couldn't keep your secondaries closed for a while.

I understand carbs VERY well (at least holley carbs anyway). I've tuned/rebuilt/fixed quite a few of them. Only thing is that they were all vacuum secondary holleys.

And is there any advantage to using the tube type squirters over the straight one? I've used both, and when it's one of my "better" build ups, I tend to use the tube type. I use the "you get what you pay for" thinking on that... but is it true in this case?

On my 650dp the primarys open first (maybe 1/3 to 1/2 way), and then the secondaries open up. They both become fully open at the same time. That's controlled by a link on the side that connects the primary shaft to the secondary shaft. I beileve that Holley sells a replacement link that allows the secondaries to open at the same time as the primaries.

So to tune the primaries, I just don't give it more than 1/3 or 1/2 throttle. You can feel in the gas pedal when you touch the secondaries. (you can feel extra hp too smile.gif )

chris

OK, the DPs are now clarified. Thank you all.

Now, about the discharge nozzles (squirters). What's the difference between the straight type and the tube type (aside from price)?

Is it to "center the shot" like 427L88 said?

Tube type directs the shot a little better!