Jet boat holly carb question

[bearphoto]

For all you big holly carb fans, maybe you can help me out. I've got a Carerra Jet boat with a chev 454 and a holly 850 double pump carb. I seem to constantly smell gas when out running the boat but it also seems to be flooding to some extent (might be the gas smell issue). Anyway, when pulling the kids on a tube, first the boat does not seem to have the power and once last year I thought the choke was stuck as I could only do 1 or 2 mph. Took the air cleaner off and the choke was wide open. It finally cleared up while trying to limp back to the dock 10 miles away.

This boat did come from Az and the colorado river area and I now have it at Big Bear Lake at 7000 ft. It has not been rejetted for the altitude. Should I drop to a smaller carb, do I have a power valve that is stuck or bad and should i then rejet the carb for the altitude. most of the time the boat will stay at big bear and once or twice a year go to the river.

[Scott Liggett]

Re: Jet boat holly carb question

Check the power valve. Could've popped or gone bad. While the bowls are off, spray out the air bleed holes in the main body. Next, check the float level. If it's high, it can cause the engine to run rich.

Lastly, is it a marine version or a standard car carb? A marine version has the vent tubes connected with a vented tube to keep gas from sloshing out. If it's a car style just run a rubber between the two vents. Cut small holes in the rubber hose to allow it to breathe.

[fabricatordave]

Re: Jet boat holly carb question

if the power valve is bad it will drip fuel out of the boosters at idle will also do it if floats are to high and make it run like poop!

[Mr4Speed]

Re: Jet boat holly carb question

While you have it apart check the floats to make sure they aren't heavy-full or saturated with fuel. Don't bother checking the power valves or the needle and seats-just replace them. Also check to see if it has the right jets in it now-someone may have been fooling around with it before you got it. Put it all back to the stock tuning spec with the new parts in it before trying to compensate for the altitude change-it should run a lot better. If you feel it then needs to be tuned for the altitude difference make SMALL changes in the jetting. On a car I would say don't go more that 2 jet sizes at a time but on a boat I would only go one at a time (erring on the side of caution). A lean boat motor can hurt itself pretty quickly.

[shaun callaway]

Re: Jet boat holly carb question

when you take the carb off replace it with an efi system and you will be happier. lol (no offense)

do you have any pics of this boat sound nice.

[Monster]

Re: Jet boat holly carb question

Maybe Detroit Jim could help out ??

Here's his introduction to the site:

Jim from the Detroit area, never lived more than a few miles from Woodward avenue! Raced there back in the late 70's. The gearhead life around here is great. Had many Firebirds, GTO's, and a Cougar Eliminator. Went from cars to boats for a long time, raced drag boats since 2002. Finally have a car again, dragged home a numbers matching Firebird 400 for Christmas. Restoring that one, also looking seriously at land speed racing next! It's all Frieburger's fault. If only I hadn't started reading car magazines again...
DJ

[Bamfster]

Re: Jet boat holly carb question

Another thing to think about is the quality of fuel you're running. This junk pump gas nowdays seems to boil at lower temps. My DP, granted on a car not a boat, tends to boil over w/pump gas and flood. The bowl vent extensions seem to help.

[bearphoto]

Re: Jet boat holly carb question

Awesome info guys, thanks. The engine does run poorly in my opinion but the 454 is so strong its still got alot of power. I would love to go to an efi system so I dont have to worry about the altitude issues but I seem to recall someone telling me I would then have to put some type of sensor into the exhaust system. Is that right?

[milner351]

Re: Jet boat holly carb question

I have a ski boat - not exactly the same but I know where you are coming from.

For the safety of you and your family - if the carb on the engine now is not marine spec
(the fuel vents are J shaped to direct liquid fuel into the venturi's in the event of a stuck open needle / seat)

I would put it on ebay and buy yourself a genuine marine carb.

The vents are not the only change - marine carbs also have seals around the throttle blades in the throttle plate.
There are other differences - but I don't recall them all at this point.

I would say you'd be better off with an edlebrock 750 marine - they don't have gaskets below the fuel level and don't have the power valve to deal with. Most 454 marine engines were equiped with 750 - I'm betting the 850 on your boat was added by a previous owner.

However you go, good luck with it.

[Bamfster]

Re: Jet boat holly carb question

Milner brings up a very good point....in the confines of an engine compartment on a boat, fuel vapor/fumes can be very dangerous.

[70.5CAMARO]

Re: Jet boat holly carb question

i have built quite a few of olds jet boats, 455's, 403's, i use a standard old's carb with no problems what so ever, generally i set the float a little low, not much but like 1/16 of an inche. I am in michigan, no real need for altitude adjustment. the boats i work with, are installed with a engine compartment evacuation fan. they recomend that you use it when ever you are startig or running the engine, to eliminate any explosion issues. as for the fuel boiling the engine is cooled by he lake water, heated in the exhaust riser, even then not very hot. i dont even run a thermostat.

[milner351]

Re: Jet boat holly carb question

every boat I've ever seen with an inboard or I/O has the vent fan and a note on the dash to run it for 5 minutes before starting the engine.

Most of the time on my boat I just open the engine cover when I start it the first time for the day - just to give a visual check and air things out.

Only marine approved carbs are legal on a boat - if you have sharp coast gaurd or local authorities on a boat on your lake - some will catch car parts on a boat, and ticket accordingly - most don't know the difference.

On most "jet boats" the engine is exposed anyway - so I suppose it makes no difference in that case - vapors aren't trapped and won't explode.

I have a marine holley spec'd for my engine - so far so good.

[70.5CAMARO]

Re: Jet boat holly carb question

thats the one thing i have never been ticketed about on the water, my engines are usually enclose, generally first of the day i start with the lid open just to check for leaks and such, but after that its all closed up, just because its loud and i have people on the boat. 1st of the day i am generally by myself