boat just wont run right in water, all out of ideas

[mr 88]

Not going to argue.The engine rebuilder that does them for 100 -180 mph boats also does there carbs. As I said we were yapping it up Monday and he was telling me about his customers that have money,but no clue on how they are to be setup Someone tells them to go buy a big cfm Holley and it will go faster,WRONG. A marine carb is not the same and you have a marine engine, NOT a auto engine,there is a difference in the cams,how they breathe,the load there pushing ,overflow vents, how the plates open up etc. I am not a carb guru so I cannot give specific info but you get the idea. You capitalized ONLY under load,a marine carb is always under load when pushing a boat and that is why there different than the auto. Like I said I would find a" MERCRUISER " carb or even borrow one if need be from a 350 and slap it on. Thats my 2 cents and I am done.

 

[NHGuy]

Non marine carbs are bad in boats any way. If it pukes the fuel sits in the bilge evaporating off and just waiting for any spark. Marine carbs have fail safes for that and for if the fuel pump diaphragm fails. You gotta use one or you can easily become a statistic.

 

[Scott Danforth]

A marine holley has a lower power valve, a lower preasure vac secondary spring, and the j tubes. The j tubes are required for marine compliance. The lower power valve is required to run correctly, the lower pressure spring is required to get the secondaries to open. You should have about #72 primary jets, #85 secondary jets.

 

[Shea_G]

Not going to argue.The engine rebuilder that does them for 100 -180 mph boats also does there carbs. As I said we were yapping it up Monday and he was telling me about his customers that have money,but no clue on how they are to be setup Someone tells them to go buy a big cfm Holley and it will go faster,WRONG. A marine carb is not the same and you have a marine engine, NOT a auto engine,there is a difference in the cams,how they breathe,the load there pushing ,overflow vents, how the plates open up etc. I am not a carb guru so I cannot give specific info but you get the idea. You capitalized ONLY under load,a marine carb is always under load when pushing a boat and that is why there different than the auto. Like I said I would find a" MERCRUISER " carb or even borrow one if need be from a 350 and slap it on. Thats my 2 cents and I am done.

You aren't understanding me correctly I think. I don't have a marine engine. Unless the previous owner of the 1995 suburban I took it from threw a couple ski's under the front tires and some paddle tires on the back.

 

[Shea_G]

Non marine carbs are bad in boats any way. If it pukes the fuel sits in the bilge evaporating off and just waiting for any spark. Marine carbs have fail safes for that and for if the fuel pump diaphragm fails. You gotta use one or you can easily become a statistic.

Yes I fully understand that. I'm just trying to get out on the water this year. I can fine tune it over the winter.

And like I said I was using a mercruiser carb and I had the exact same issue. Completely different Marine carb and when I swapped them the problem did not get any better or worse leading me to believe it's most likely not the carb.

 

[NHGuy]

Well be safe and use a marine carb.

 

[mr 88]

You said you had a marine carb that was a 750 cfm and too big and not the correct unit for your engine Then you went to a 660 Holley,which seems to have issues new out of the box. Just because it came out of a car does not mean a car carb will perform correctly on a boat. You need three things for it to perform correctly AIR which you have,Spark and correct timing which you said you have and proper fuel delivery, which IMHO you do not have.

 

[Scott Danforth]

You aren't understanding me correctly I think. I don't have a marine engine. Unless the previous owner of the 1995 suburban I took it from threw a couple ski's under the front tires and some paddle tires on the back.

You have a gm 350 mounted in a boat. Boat motor long blocks differ from truck motor long blocks only in the brass core plugs, stainless head gaskets, slightly different cam.

The ignition system, rotating electrics, exhaust systems, cooling systems, and specifically the fuel system are marine only items

 

[mr 88]

BTW I have a 91 regal 22' bowrider with a 8' 6'' beam powered by a 350 magnum and run a 19" pitch prop that still ends up a couple hundred under the redline in a empty boat. So in my case a 21" would be way overpropped even more so once I get a few people on board , 60 gallons of fuel and then do some water sports..

 

[Shea_G]

BTW I have a 91 regal 22' bowrider with a 8' 6'' beam powered by a 350 magnum and run a 19" pitch prop that still ends up a couple hundred under the redline in a empty boat. So in my case a 21" would be way overpropped even more so once I get a few people on board , 60 gallons of fuel and then do some water sports..

You're probably running 1.50 gear ratio though? I have 1.84

 

[Shea_G]

You said you had a marine carb that was a 750 cfm and too big and not the correct unit for your engine Then you went to a 660 Holley,which seems to have issues new out of the box. Just because it came out of a car does not mean a car carb will perform correctly on a boat. You need three things for it to perform correctly AIR which you have,Spark and correct timing which you said you have and proper fuel delivery, which IMHO you do not have.

Yea Imy pretty sure it's fuel delivery aswell. I guess I'll work my way back from the fuel tank to the carb and try another carb again if I can't find anything.

I'm hitting a wall at about half throttle and when I give it more nothing happens so it definitely sounds like a fuel issue to me.

 

[Watermann]

Usually what I've experienced when there's a lack f fuel flow and you open up the butterflies the increased air and lack of fuel fuel causes a loss of RPMs and bogging or stuttering until the throttle is decreased. There are a bunch of differences going on for your motor situation from when it was in the Burb vs a rock stock MC motor. The exhaust manifolds, Y pipe to bellows, intake, carb and ignition. So your motor could react very differently than most would expect since we work on our craft with pretty much stock MC motors. I do agree that it sounds fuel related and having 2 different carbs react the same makes one think it's upstream from there.

How about a couple of pics of your set up? We all love to see what others have going on with their boats. A video on the water with the boat acting out is always good too!

 

[Shea_G]

Usually what I've experienced when there's a lack f fuel flow and you open up the butterflies the increased air and lack of fuel fuel causes a loss of RPMs and bogging or stuttering until the throttle is decreased. There are a bunch of differences going on for your motor situation from when it was in the Burb vs a rock stock MC motor. The exhaust manifolds, Y pipe to bellows, intake, carb and ignition. So your motor could react very differently than most would expect since we work on our craft with pretty much stock MC motors. I do agree that it sounds fuel related and having 2 different carbs react the same makes one think it's upstream from there.

How about a couple of pics of your set up? We all love to see what others have going on with their boats. A video on the water with the boat acting out is always good too!

What you describe is exactly what happens. It starts to bog a bit as soon as I press the throttle too much and it slows down so I back it off. Wasn't sure how much the rpms are dropping because I don't have a dash tach (it's mounted in the back)

 

[Chad Flaugher]

Check your fuel pressure under load... With a dirty fuel filter, your pressure will read fine until you ask it for more G.P.H. buy pouring the power to it. I'd check your fuel line for kinks, and replace your filter with a high flow filter. And yes, running a non-marine carb in an enclosed area is an explosion waiting to happen.