Hp 500 carb setup help
09-02-2014, 07:59 PM
#1
Gold Member
Hp 500 carb setup help
Have a brand new carb on my hp 500 model year 1999. It is a Holley 850 marine carb. Having some trouble getting it set up right it's surging around 3500 rpm down a few hundred and back up. It came with 88 in front and 98 in rear I changed to what the old carb had 77 and 88. Brand new 850 had a power valve in the secondary. I changed it out to the old non power valve secondary metering block. So my questions are what is the jetting to run? should I leave what it came with it? Power valve secondary metering block or no. If so what size valves? Thanks for the help Also it starts right up cold. After sitting for ten mins once hot it cranks for 10 seconds or so before starting. I noticed with the arrester off a small amount of fuel coming in down by where the throttle plate is and running into the carb. Maybe the old metering block I had on there is a problem. ??
09-02-2014, 11:37 PM
#2
Registered
iTrader: (3)
Put it back to how it was shipped. It should have had 96 jets in secondary? Your old carbs were smaller and therefore won't meter fuel like the new ones. Smaller carbs like smaller jets. As for the fuel leaking, loose bowl screws can lead to a carb leaking internally. If you want to block the rear pv on the 850 marine carb you'd want to jet up about 6 sizes in the rear. Put it back to how it was shipped , go run it, and report back.
09-03-2014, 07:37 AM
#6
Registered
iTrader: (3)
I am assuming they are the R80443 marine 850 carb?
I have these carbs on my engines, but with roots blowers. Two of them per engine. As of right now, they have 88P/96S, with 10.5PV in front, 2.5PV in rear. (blower deal). I too thought the stock jetting was way too much, but the wideband told me otherwise. I have buddys with similiar roots blown setups, running way less jet in their carbs, but making more power than me and bigger cubic inches, etc, but different carbs.
Mine are blown 468's. When I bought these carbs, they had came off of a blown 572. I took them apart to rebuild, and saw they had 96P/96S, with 6.5PV front and rear. I thought "geez, thats a ton of fuel, guy who set these up must be silly". But in reality, they were prob right on. I jetted them 84/92 with a pv just in the primary for my engines. They were simply too lean.
I am not surprised, that taking 20 jet sizes out from stock, plus blocking the rear powervalve, is making them lean for you, which is probably causing the surging condition you are seeing.
I have these carbs on my engines, but with roots blowers. Two of them per engine. As of right now, they have 88P/96S, with 10.5PV in front, 2.5PV in rear. (blower deal). I too thought the stock jetting was way too much, but the wideband told me otherwise. I have buddys with similiar roots blown setups, running way less jet in their carbs, but making more power than me and bigger cubic inches, etc, but different carbs.
Mine are blown 468's. When I bought these carbs, they had came off of a blown 572. I took them apart to rebuild, and saw they had 96P/96S, with 6.5PV front and rear. I thought "geez, thats a ton of fuel, guy who set these up must be silly". But in reality, they were prob right on. I jetted them 84/92 with a pv just in the primary for my engines. They were simply too lean.
I am not surprised, that taking 20 jet sizes out from stock, plus blocking the rear powervalve, is making them lean for you, which is probably causing the surging condition you are seeing.
09-03-2014, 07:46 AM
#7
Registered
iTrader: (1)
Wholly schit !
Jetting is not the same from carb to carb so get those jet's you swapped out of there !
Surging could possibly be lean surging.
If you do not want the PV in the rear, put a power valve plug in there , jet the secondaries a few, but do not change the metering block.
Oh my gosh.
Jetting is not the same from carb to carb so get those jet's you swapped out of there !
Surging could possibly be lean surging.
If you do not want the PV in the rear, put a power valve plug in there , jet the secondaries a few, but do not change the metering block.
Oh my gosh.
Last edited by SB; 09-03-2014 at 07:53 AM.
09-03-2014, 08:03 AM
#9
Registered
Wholly schit !
Jetting is not the same from carb to carb so get those jet's you swapped out of there !
Surging could possibly be lean surging.
If you do not want the PV in the rear, put a power valve plug in there , jet the secondaries a few, but do not change the metering block.
Oh my gosh.
Jetting is not the same from carb to carb so get those jet's you swapped out of there !
Surging could possibly be lean surging.
If you do not want the PV in the rear, put a power valve plug in there , jet the secondaries a few, but do not change the metering block.
Oh my gosh.
09-03-2014, 08:32 AM
#10
What power valve do you have in the primary side? My first guess on the fuel dribbling issue would be that you have the wrong PV in there, and it is opening at idle and dumping fuel. That would explain why it runs fine when cold, because then it would actually need a little extra fuel until it reaches temperature.
As other said, put it back to box stock and run it, and then report back to us. Honestly, you are flying blind on this deal without any kind of wideband O2 sensor to tell you if you are lean or rich. It is very hard to get any decent plug readings with all of the ethanol and oxygenators in today's fuel blends, and even then, it takes someone with some experience to read plugs correctly. Be very careful, because you could be treading on some thin ice here. If in doubt, always jet on the rich side for a marine application. Lean kills!
As other said, put it back to box stock and run it, and then report back to us. Honestly, you are flying blind on this deal without any kind of wideband O2 sensor to tell you if you are lean or rich. It is very hard to get any decent plug readings with all of the ethanol and oxygenators in today's fuel blends, and even then, it takes someone with some experience to read plugs correctly. Be very careful, because you could be treading on some thin ice here. If in doubt, always jet on the rich side for a marine application. Lean kills!
