formula18

first the engine...1989 350 rebuilt to vortec engine with 330 hp. has a quadrajet that was rebuild last yearhorsepower...the boat as plenty of power and seems to run great....


only problem is when i go full throttle it kinda dies...it does bog or pop just seems to lose rpm...it is supposed to rev to 5200 but i cant get it above 4600. it will do it will coming up onto plane or while cruising...as i said its very strong up to about 7/8ths throttle and i know there is more...what should i start to look for...it has a fresh fuel filter with a high flow fuel pump as well. thanks for you help... Harry

spazboz

Anti-syphon valve on top of the gas tank???

formula18

i don't know what that means?? also im running 87 octane should i be running higher? its a 21 foot formula

spazboz

On top of the fuel cell in your boat, you should have what is called an anti-syphn valve. I believe what this does is prevent fuel from draining back into the tank when the negines arn't running. Sometimes they can get stuck halfway open and restrict fuel flow to the engine. Primarily this would be most evident when the motor is operating at WOT, obviously it would be using the most GPH at this point. A friend of mine was having the same problem in his 230 Conquest, and this was the issue I found in his boat. The other symptom he had from this issue was that if the baot sat for a while, it would start really hard, due to the fuel system being dry. No guarantee this is what it is, but its easy to check.

spazboz

Man, I had a lot of type-o's in that last post. BTW, it couldn't hurt to run a little higher octane fuel. Esp. if you have increased the compression ratio. Just curious, what kind of speed do you achieve with the 21 and 330 hp?

Hotdog1922

Had the same problem with my boat. Check the fuel pressure. Turned out my fuel pump had only half the pressure.

hoozeyurdaddy

sounds like it could be going lean at wot, or there is just not enough air getting in, Quadrajet's are not the best carb to have on a modified engine, if you went from a 260hp 5.7L to a 330 HP 5.7L more air has to come from some where, the 7.4L 330 HP engine's used a larger quad with larger jetting, It could be the anti-syphon valve, I would check it, but I would also check into if your carb is larg enough, the purpose of the anti-syphon valve is a safty thing, if you get a cut or hole in the fuel line before the filter assy, it is unable to just syphon all your fuel into the bilge and turning your boat into a bomb.
it has to have the vacuum of the fuel pump to open.
Larry

formula18

thanks for the input guys...the quadrajet was rebuilt knowing of the modifications to the engine...the jets were changed...i will look into that valve...as far as speeds I am see low 50's right now...boat is a formula 1989 so i know its pretty damn heavy...about 3200 lbs says the spec sheet...than with full fuel and 4 people including me im sure its over 4000lbs...im hoping it will run into the 60's because from the factory it was supposed to do 57 with the original 260 hp. anything else I should look for? i know this engine has more

stevesxm

the quadrajet is plenty big enough for that motor. jetting and float level are something else again and need to be correct as they would need to be in any instance... but as mentioned above, this sounds life fuel pressure and a gage is going to be essential to sorting this out. you need to hook that up and run your scenario and watch the gage. if it drops for any reason you are essentially running the motor out of gas under load. and i assume you have checked that you are actually GETTING full throttle at the carb. low float level or bad accelerator pump will give you that big hesitation.

98itrwhite

years ago had the same problom, it was the fuel pump. i put a new one on and its been great ever since.