What would make Carb overflow when hot?
 

Its an HP500 carb, we have already rebuilt it, set the float levels multiple times and it keeps doing same thing,
once you have been out running for a while and idle down to dock it will sputter and be way rich, as you look down carb bores you can actually see fuel trickling out of tubes. Makes it a scary propisition to dock.
When its cold it does not do this, idles perfect , nice 13.9-14.1 AFR , no fuel dripping.
Driving me bonkers..
Its sitting on a Ebrock Victor Jr with no heat passges so intake stays relatively cool.

Replace the needle and seat. If it is a brass float be sure it has no fluid inside.

How much fuel pressure when this happens?

I had a Holley 800 do the same thing this spring. You could look down it and see gas pouring out. I just took the one bowl off cleaned it, set the level while the engine was running and never another issue.

Check the floats to make sure they are not filled with fuel.Also have you replaced the fuel pump with a higher volume. Those needle an seat cant take any more than 7 lbs .

Yep what he said !!! Even if they look good , which they will replace them .

not the vent tubes, it leaks out the venturi where fuel normally comes out when it is running.
Stock fuel pump.
Only does it after it warms up so if it is the float wouldnt it do it all the time?
Thanks!!

Bad Power valve? Idle not adjusted properly so that low idle vacuum lets the power valve open??

replaced power valve
good idle until it heats up and good vacuum.
Frustrating.

Try calling the Holley tech line

The only thing that will make fuel trickle out of the boost venturi at idle is the fuel level is too high in the fuel well. Why it only does it when warm is the mystery. Are the carb bowls properly vented?

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?

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?

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....

Fresh/correct metering plate gaskets?

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.

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.

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????

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.

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?

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. :grinser010:

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

I have a vacuum/boost gauge but Vic Jr doesnt have any vacuum ports so I have to drill and tap for one. Guess thats my next weekend project ..

power valve would have no effect on gas leaking in thru tubes, has to be fuel level rising after shut down, either fuel pressure, needle/seats, floats, etc..power would leak thru baseplate....Rob

thanks Rob..

My 850s both had the black floats and the epoxy that holds the weights in came off and the nedel and seat got cloged this year put metal floats in I beleve it was a fuel problem.
Rich

Rich,before rebuild we did pull some unexplained crap out of needle and seat which was weird considering fuel filter was clean.