fastestbowtie

I am not familiar with the HP500 carb so lets start with the basics. What size is it, is it mech or vac secondary, if mech does it use progressive linkage, and do you know what size acc pumps it has, also does it have any sort of choke, etc.? Are you positive no fuel is coming from the squirters?

HTRDLNCN

hp500 carb from what I know is a Holley marine double pumper 850
with staggered jetting with 50cc primary and 30cc secondary pump
but I am sure someone on here knows more than I do about them.
Oh yeah,they come in blue Merc racing paint which adds another 10-15hp...

and yeah pretty positive it leaks out venturi..
Could the fuel be boiling out? What temp does gas boil?

ezstriper

ok, a HP500 carb is a 800DP, now I did have a weird deal on a carb a while back...had a race prepped 850 that had the bowls powder coated blue, had it on a street/stripe car worked great, put it on my boat and would flood everythime coming off plane. changed everthing twice, never stopped..new floats, hangers, needle/seats, etc....figure it had to do something with the powder coating and sticking the floats..did it bad enough to kill the bearings and the crank quick !!! a lot quicker than I would have believed....

Thunderstruck

Fresh/correct metering plate gaskets?

fastestbowtie

Did not get an answer on whether it had a choke or not? You mentioned the boat runs good when it is cold, but not when it is hot. If it does not have a choke, then it is jetted too fat. If it does not have a choke then you should have a hard time keeping it running (having to work the accelerator pumps a bit to fatten it up) when it is cold but then will run well with some temp in the motor. Also if you do not have any clearance in the accelerator pump linkage, just a slightly lopey idle could be causing the linkage to barely hit the pumps and shoot small squirts of extra fuel into the motor. Lastly, the carb actually mixes some air with the fuel before it ever gets to the venturi. If your air bleeds are clogged this could cause the problem you are having. Good Luck.

HTRDLNCN

no choke.
Used it all day yesterday and it didnt do it until the very end of the day as I was pulling back to my marina.
Guess I will just have to pull it off again and go thru everything again
and see if anything is plugged up.

Griff

Have you checked the adjustment of the floats/needle seat assembly with the boat sitting at rest in the water????

Does it happen when coming off plane quick????

BadDog

Fresh rebuild on my Blue HP 500 carb doing same thing. Checked all things recommended except the linkage for accelerator pump. If I let it idle for a bit and cool off it will idle just fine again. Funny thing is the engine does not seem to be hot at all after a hard run. Oil at 210 and water only rises 10 degrees over normal cruise. Time to pull it off and 3x check thing again.

HTRDLNCN

Installed fuel pressure gauge, pressure stays steady at 7lbs,
no clogged anything and have reset levels 3 times already..
My cam is slightly bigger than HP500 cam, could the power valve be acting funky because of this and causing the problem?

Thunderstruck

Of Course it could. I guess you did say in your first post that you had a 500 HP carb and not a carbed 500 HP.

See post #8 but look at vacuum at idle vs power valve opening vacuum.