Another Holley Carb jetting question?????

[Greaser]

I have a Holley 850 dp, that I am needing to jet down.
Here is the info on my engine
BBF
bored 60 over, with dish top pistons
hydraulic flat tappet cam, w/ 276/286 duration, .503/.503 lift
stock electronic ignition
stock D0ve heads
Weiand Stealth intake
Bassett OT headers
Holley 850 Double pumper carb
The reason I need to jet it down is, Its kinda haer to start up, like its flooding out, and it acts like its trying to flood at wot, and also it will die when I get back to idle after a hard run.
I talked to my engine builder and he says I need to jet it down. He recomended that I start with 71's in the front and 74's in the back.
My question is, what do you guys think I should start with?

[Moneypitt]

The Holley tuning guide tells us not to change more than 4 jet sizes from original. If you need to change more than that, change the CFM of your carburator of choice. IMO 850 is too big, but that is probably not your starting problem. Even an 850 should start without the WOT if it is not leaking somewhere into the intake. We have to remember that the CFM rating is WOT, and that is the amount of air it will flow. The necessary fuel for the 850 CF of air will vary with conditions, but I don't think hard starting is related to the size of the carb, and I doubt the main jets are flowing while cranking to start. Sounds like high floats, or leaky needle seat assemblies.......MP

[GofastRacer]

Ok first of all jetting has nothing to do with starting or dying when you come to an idle. As far as a starting point you start with stock out of the box jets and go from there. Your problem is beyond jetting, is this a fresh carb or is it an old one, several things can cuase this like an internal leak, bad P/V, bowls loose,old gaskets, metering blocks warped, etc!. Maybe all you need is to do a good rebuild on it!..

[OMEGA_BUBBLE_JET]

check for vacuum leaks. I also think you are a bit over carbed but I have said that all before. I think you are more than likely getting a weak vacuum signal at idle conditions causing your hard starts and stalls.
If you want to check your jetting run it wide open and cut it off before idling back down and pull your plugs. You want them to be carmel colored. black is rich....white is lean.
Omega

[058]

Those jets would work good in a 650 Holley but are way lean for the 850. Factory jetting for a typical 850 d/p [4781] is 80s pri and 80s sec with sec powervalve. On a typical BBF the engine seems to like 81-82s pri and 83s-84s sec with p/v or 88s-90s without.

[oldbuck40]

check your float level! if its too high while you have it parked and the waves are moving it around the extra fuel will spill over in the intake and when you try to start it it gives the impression of being flooded,which it is! same as when you slow down to a crawl after a fast run. quick way to check this is IF its a regular 850 and not a marine type it will have straight vent tubes on the carb. take a piece of fuel line and slide it over the rear vent tube and make a small curve up to the front vent tube,slide it on the front tube. then in the middle of the hose at the top of the curve cut the hose half way thru making a vent. this will keep the extra fuel from running over in the engine and it will tell you if that is the problem. all it takes is time to check this and about 5 inches of fuel line...oh yea and the 850 is no way too big for that motor.

[Greaser]

Thanks for the advice guys. So do you guys think that starting with 71's and 74's will be to lean for that carb?

[Greaser]

check for vacuum leaks. I also think you are a bit over carbed but I have said that all before. I think you are more than likely getting a weak vacuum signal at idle conditions causing your hard starts and stalls.
If you want to check your jetting run it wide open and cut it off before idling back down and pull your plugs. You want them to be carmel colored. black is rich....white is lean.
Omega
Thanks, I will check into that......... Hey, when will you be coming back out to Somerville? We miss you out there. Everyone is wanting to watch some more xtreme tubing. :supp:

[SmokinLowriderSS]

Most of the 4150 style double pumpers (you didn't post the list #) are stock fitted with 80's square & sometimes 78's in the rear with double #65 power valves. Knowing that, I'd tend to think 71/72 may be too lean. I think I'd look at the other problems posted here fiirst, especially high float levels. That'll cause all manner of richness/slosh/flooding troubles. Maybe just too high, maybe needles not closing off properly. Also, if you don't have a marine carb, there are a small set of flat tubes to go horizontally in the holley bowl vents inside the bowls attatched to the metering blocks that help keep fuel from sloshing out the top vents under normal float height conditions.