Jet experts please help with problem

[Cole Trickle]

http://www2.***boat.com/image_center/data/520/2491cole.JPG I own a 21' 1987 Cole Jet boat.
Here is the problem:
Boat runs and idles awesome.
Hooked up to a hose out of the water the boat will dry rev to 5K no problem but under load at about 3800-4000 rpm's the motor starts to sputter and back fire.(This is preventing us from hitting max mph)
The old motor used to get up to 5'000 rpms
Here is what we have done to the boat in the last year and a half.
We replaced the Berkley with a brand new unit.
We replaced the tired 454 with a 450- 500hp 496 BBC
New Plugs,Distributor,coil, plugs,etc...
Here is what various experts have guessed at:
We replaced the standard alternator with a higher output unit.(I want to say we went from 40-100?)
I thought that maybe it was a lean pop that was causing the limited RPM but the boat is just killing gas.(We have rebuilt the carb but can only marginally tune away the problem.before the rebuild we saw 3700 rpms and now we can see 3900-4000 with jet tuning.)
I have heard that maybe we have a flattend lobe on our cam causing the issue?
I recently heard that we need to change out the impeller on our jet because it's cavatating and putting a load on the motor.(I believe it's a standard impeller set up for approx 300hp)
Could the added HP be the culprit to our problems or do you think it could be something else?
Any help would be greatly appreciated!!
Thank
Brandin

[Hardin18 II]

I own a 21' 1987 Cole Jet boat.
Here is the problem:
Boat runs and idles awesome.
Hooked up to a hose out of the water the boat will dry rev to 5K no problem but under load at about 3800-4000 rpm's the motor starts to sputter and back fire.(This is preventing us from hitting max mph)
The old motor used to get up to 5'000 rpms
Here is what we have done to the boat in the last year and a half.
We replaced the Berkley with a brand new unit.
We replaced the tired 454 with a 450- 500hp 496 BBC
New Plugs,Distributor,coil, plugs,etc...
Here is what various experts have guessed at:
We replaced the standard alternator with a higher output unit.(I want to say we went from 40-100?)
I thought that maybe it was a lean pop that was causing the limited RPM but the boat is just killing gas.(We have rebuilt the carb but can only marginally tune away the problem.before the rebuild we saw 3700 rpms and now we can see 3900-4000 with jet tuning.)
I have heard that maybe we have a flattend lobe on our cam causing the issue?
I recently heard that we need to change out the impeller on our jet because it's cavatating and putting a load on the motor.(I believe it's a standard impeller set up for approx 300hp)
Could the added HP be the culprit to our problems or do you think it could be something else?
Any help would be greatly appreciated!!
Thank
Brandin
Not an expert by far but I had a problem simular to yours, It ended up being a vacume leak. I put hose clamps on every hose made sure they were all in good shape and made sure my carb was on tight. The problem was fixed.

[Squirtin Thunder]

I recently heard that we need to change out the impeller on our jet because it's cavatating and putting a load on the motor.(I believe it's a standard impeller set up for approx 300hp)
OK if it is cavitating the load is greatly reduced. Which would mean RPM would not be a problem !!!
Jim
I would look at Valve adjustment and carb more, change it to a bigger one just for the hell of it. Also check ign timing and amount of advance.

[Cole Trickle]

I recently heard that we need to change out the impeller on our jet because it's cavatating and putting a load on the motor.(I believe it's a standard impeller set up for approx 300hp)
OK if it is cavitating the load is greatly reduced. Which would mean RPM would not be a problem !!!
Jim
I would look at Valve adjustment and carb more, change it to a bigger one just for the hell of it. Also check ign timing and amount of advance.
Maybe I don't know what Cavitation means and am using the word incorrectly? :frown:
All I know is that at 3800rpms I have to let off the gas or it starts popping :cool:

[PipesClean]

I had the exact same problem before. The boat would idle and rev fine on the trailer, but when you put it in the water, it wouldn't go over 3500 without sputtering and making a complete fool out of me. Sounds rediculous, but it finally came down to not having enough fuel pressure at load! Check your pressure under load and see what it is. :cool:

[Lightning]

I would recommend you give Tom Papp a call in Corona, he'll know what the problem is.

[TBONE1904]

Maybe I don't know what Cavitation means and am using the word incorrectly? :frown:
All I know is that at 3800rpms I have to let off the gas or it starts popping :cool:
Are you referring to detenating or pinging? Basically that means the combustion chamber is getting way to hot, various reasons such as carb to lean, not enough octane for the engine, too much timing, etc and under load it sometimes makes a popping type noise. It depends what kind of popping
your speaking of.

[cave]

I had a problem like that and change a bunch of parts. Turned out it was water in my fuel. my motor would also run good at idle and on the trailer but once in the water and I punched it the fuel flow increased and my water separator couldn't separate. Hopefully its that simple for you too.
I bought a new MSD distributor, new MSD box, new coil, new alternator, rebuilt the carb twice & new floats. Then my bro asked if I check the fuel for water. :hammerhea I totally forgot to check this. It wasn't very much either.

[Flip]

What are you running for a carb and fuel pump? I'm guessing you don't rev it up to 5k on the trailer (which can't be very good for that new pump without a jet-away) and holding it there. Which would explain why you're not able to notice that it's probably sucking the fuel bowls dry and maybe even leaning out the mix cause your backfire. You gotta feed that big bad 496!
Just a guess though..... :rollside:

[sleekvino]

i had the same problem as cave "water in the fuel"

[Floored]

just for grins :) check the plug wires to see you dont have 2 of them crossed, only takes a minute.easy to do and drives you nuts. :cry:

[GasGuzzler]

If you have a cheap-ass electric tachometer.....unhook it and try it. Had one to go bad last year and done the same thing, made it pop and crack. Also had one go bad on a racecar and did the same thing under load, so give it a shot, cost nothing to check it......and stop running the pump out of the water :frown: or you going to have a big repair bill. (just my 2 cents)

[Any&All'sgirl]

My hubbys told me to tell you;
It's hard for any of us to answer your problem in a quick solution without being there and hearing it for ourselves. I think everybody has good ideas, it's a hard problem to cure because it may be 1 of 1000 little things. We had same problem with 454, couldn't get it over 4000rpms without popping thru the exhaust. Our problem was cured, the distributer baring was bad, a stock HEI fixed our problem. Good luck and we hope u find the problem!!! :jawdrop:

[NELSON#109]

Just As Floored Said, Double Check The Firing Order. Done It , And Seen Many Others Do It.. That Has Stumped Many Of The Best Many Times. Could Be A Vacuum Leak To, Check The Intake Gasket For Leaks. U Can Spray Carb Cleaner Along The Surface, Where The Intake Meets The Heads. If U Have A Leak, The Carb Cleaner Will Get Sucked In At The Leak.

[MudPumper]

I would recommend you give Tom Papp a call in Corona, he'll know what the problem is.
Probably the best advice so far, could be any thing. Tom can find it quick and easy.

[MarKist]

What are you running for a carb and fuel pump? I'm guessing you don't rev it up to 5k on the trailer (which can't be very good for that new pump without a jet-away) and holding it there. Which would explain why you're not able to notice that it's probably sucking the fuel bowls dry and maybe even leaning out the mix cause your backfire. You gotta feed that big bad 496!
Just a guess though..... :rollside:
WE experienced this same problem Sunday ,If I was you! first, I would make sure that the fuel pressure stays the same at WOT,second I would check your float levels,WE had the same pressure at WOT ,so WE adjusted the float levels. Actally turned them all one turn out and she was a patch of hell then,maybe this could be a quick fix ,it sounds like the bowls are getting dry like Flip said!good luck!..oh yeah! I wouldn't start that thing out of the water!that's a NO NO, unless you have a Jet-a-way!!just my O2
Markist

[bakerjet]

i had the same problem, it was low fuel psi.

[lilrick]

i say that you should sell that troublesome 496 to me and the problema is solved!!!!!!!!!!

[JESSE]

make sure nothing is up in your jet like a rope.

[wet77]

i had the same problem as cave "water in the fuel"
Count me in on the water in the fuel problem :mad:
Put on a water fuel seperator and bingo no more popping :cool:

[BobS]

Here's a little tid bit that I saved from one of the jet gurus about fuel delivery.
********************************************
The 1/4 pipe fitting on the tank quite often has an even smaller pickup tube inside. That's ok for a stock engine but not for one that's modified. I'd change to a 3/8 pipe bung and a pickup tube with the same inside diameter as a #8 fitting. Then run #8 lines from tanks to the regulators and #6 from the regulators to the carbs. Also make sure that any filters or water separators have at least 3/8 pipe ports.
"Is 6an big enough for 2 600 Edelbrock, possibly two 750s?"
It's not the carb size that matters. It's the horsepower the engine makes at WOT. Multiply the Hp times the BSFC (brake specific fuel consumption), which might be about .5lbs/hp/hr. The result will be the lbs of fuel the engine will consume per hour at WOT. Now divide that number by the weight of one gallon of the fuel you run (maybe 6.5lbs/gal) and you'll have the gallons per hour that engine uses at WOT. Look in the fitting mfg's catalog for a chart that tells you the flow rate of the different AN hose sizes.
example: 600Hp X .5lbs/hp/hr = 300lbs/hr
300lbs/hr / 6.5lbs/gal = 46.2gal/hr
********************************************
Keep in mind, it doesn't take much HP (i.e., doesn't require a lot of fuel) to rev 5k with no load on the trailer so I'm not sure that will tell you much.

[kojac]

All of the above is good advice.
When I first got into boating I bought a used checkmate that did the same thing and after changing plugs, points,distributor springs,timing,carb floats,powervalves,check for vacuum leak,increased fuel lines sizes, changed fuel pumps, checked valve springs for breakage or weakness etc. finally put the fuel pressure guage on dash where I could see it and found it was running out of fuel pressure at wot. checked lines until I got to the tank and found the screens would clog up with debris while sucking hard. At idle and moderate speeds it would run fine.
Apparently I filled up with gas at the wrong station and put in a lot of small leaves.
After that I always mount fuel pressure gauges where I can moniter them.
Kojac

[R.A.D.man]

Happend to my dad when I was young and always ran great on the trailer and layed down at the lake. Turned out to be the flame arrestor had become clogged and only when at the lake for the third time (3 weekends and 400 miles later) did my uncle in from out of town say lets take off the flame arrestor and all of a sudden problem was fixed. Looking back, every time we ran it on the trailer and all seemed good, no flame arrestor was on it. Just another simple thing that can cause big problems.

[Hallett19]

Sounds like it has nothing to do with the jet and is probably not a vaccum leak which would not cause you any problems if any at wide open considering there is no vaccum at wot.
Simple Fixes
1. Water in gas or bad gas or clogged gas feeds. The higher the demand of the motor, its getting starved, but then it wouldnt be eating so much gas.
2. Ignition timing. A bad distributor or springs that might have gone bad would cause popping and stuttering.
3. A rich condition would cause the high gas consumption and stuttering. My secondaries would get clogged real easily when i had a rinky dink fuel filter on and would run like hell down low, pop, backfire, die, you name it. You could have a problem causing the carb to puke gas at high rpm's.
4.Crossed plug wires, bad coil...
Hard fixes..
1. Flat Cam
2. Bent Valve
3. Maybe a bad ring
4. Lifters collapsing
These are my best guesses :cool:

[Cole Trickle]

Thanks for all the help I really appreciate it!
Still looking for any and all input.
Brandin

[MarKist]

well, have you tried anything?
Markist

[pops1]

[QUOTE=Squirtin Thunder]I recently heard that we need to change out the impeller on our jet because it's cavatating and putting a load on the motor.(I believe it's a standard impeller set up for approx 300hp)
OK if it is cavitating the load is greatly reduced. Which would mean RPM would not be a problem !!!
Jim
QUOTE]You are right. Cav would increase you R's (less load)Its the motor side.