What is wrong with my 455???

[dgie]

I took my boat out today and the engine runs fine up to 3800 rpms then starts to pop and cutting out. I changed out the distributor cap, rotor, and points. I am running a Mallory single point distributor. I checked the timing with a timing light and it within specs. I made sure it was advancing via timing light and all looked well. Now for the fuel system I am running a Holley Red electric pump. I am running a Holley 750 Marine carb. I pulling fuel from side tanks and running through a fuel/water separator and an electric fuel selector valve from a Chevy pickup. I am running 5/16" line for the fuel system. The exhaust headers are black inside and on tips at the end of the day. Anyone have any Ideas on this one??

[Rexone]

Is this a setup that has run good above that rpm before or is it a new combination in any way. In other words is this a new problem that just started on an old setup? or a problem with a new setup you haven't run successfully before?

[Wet Dream]

You should be able to spin that engine up to 4500 or more. My guess would be that your carb isn't opening up on the secondaries or it might be out of adjustment. I like to run my 455 a little on the fat (rich) side, but if you are getting alot of black buildup, you might have a secondary float problem. Mine did the same thing last weekend. Set the floats and change the fuel filter.

[dgie]

I bought this boat last summer and completly rebuilt everything including fiberglassing in a new transom. I guess you could say that this is a new problem and this is only the seconds time I have had this boat on the water and it did the same thing last time. I do not know how to adjust a carb.

[Wet Dream]

Tear one apart and you'll learn quickly. :D They really aren't that bad.

[dgie]

Do you think it is only a float problem? how do you adjust them?

[Rexone]

dgie:
I took my boat out today and the engine runs fine up to 3800 rpms then starts to pop and cutting out. I changed out the distributor cap, rotor, and points. I am running a Mallory single point distributor. I checked the timing with a timing light and it within specs. I made sure it was advancing via timing light and all looked well. Now for the fuel system I am running a Holley Red electric pump. I am running a Holley 750 Marine carb. I pulling fuel from side tanks and running through a fuel/water separator and an electric fuel selector valve from a Chevy pickup. I am running 5/16" line for the fuel system. The exhaust headers are black inside and on tips at the end of the day. Anyone have any Ideas on this one?? Here's some possibilities. I'd recommend you take it to a shop capable of diagnosing this kind of thing rather than trial and error though if you don't have this capability yourself. You'll probably end up money ahead with much less frustration and time invested in it.
Some possible problems.
Bad Plug wire or wires
Bad coil
Fuel filter clogged or other obstruction in fuel lines limiting flow including too small fuel supply line or too small orifice in fuel selector valve for max flow.
Weak fuel pump that can't keep up
Carburetor problem (could be many things here)
This is all assuming the distributor is adjusted correctly.
Tough to diagnose something like this without having it to test things.
:)
[ June 01, 2003, 10:43 PM: Message edited by: Rexone ]

[dgie]

What size fuel line others are running on big blocks would 5/16" be too small?

[75_Elim]

dgie:
I took my boat out today and the engine runs fine up to 3800 rpms then starts to pop and cutting out. I changed out the distributor cap, rotor, and points. I am running a Mallory single point distributor. I checked the timing with a timing light and it within specs. I made sure it was advancing via timing light and all looked well. Now for the fuel system I am running a Holley Red electric pump. I am running a Holley 750 Marine carb. I pulling fuel from side tanks and running through a fuel/water separator and an electric fuel selector valve from a Chevy pickup. I am running 5/16" line for the fuel system. The exhaust headers are black inside and on tips at the end of the day. Anyone have any Ideas on this one?? I never post advice, just problems and resolutions I've had personally.... With that said, I can tell you this. If the cutting out happens during hard acceleration ie..you're getting into your secondaries it may be a float bowl issue. Unscrew the site window screw and see if the bowl is full. The fuel should just be to the bottom of the screw hole. If that's good, you may have a vapor lock issue with the gas tanks. At speed on the water pop up the cap and see if that resolves the problem. If so, replace your caps.
I would also add a fuel pressure gauge infront of the carb to be sure you have good gas flow pressure at the higher RPM's. Have someone watch it when you run and see if it cuts out at speed.
Like I said, this is not advice... Just what I did and it worked for me. Good Luck

[Rexone]

dgie:
What size fuel line others are running on big blocks would 5/16" be too small? It could be but not necessarily. Normally 3/8 or larger is pretty standard as a minimum. A fuel pressure reading at the rpm you're having the problem at would go a long way in telling you if you had a fuel supply issue. Just because it's black in the exhaust does not mean you're not running out of fuel on the top. It only means that it may be too fat in the cruise and lower range.
My gut feeling because of the popping and misfiring is that you're either going dead lean, (lack of fuel) or you have an ignition problem under max load. Again these are guesses, nothing more. :)
[ June 01, 2003, 10:44 PM: Message edited by: Rexone ]

[dgie]

Believe me at this point I am open to all suggestions.

[GlastronGuy]

Rexone:
My gut feeling because of the popping and misfiring is that you're either going dead lean, (lack of fuel) or you have an ignition problem under max load. Again these are guesses, nothing more. :) Lean is bad in a jet boat.

[Squirtcha?]

For what it's worth, I agree with all the above. Especially the fuel pressure deal. Those Holley red fuel pumps only put out about 5 psi max pressure. I'd say invest the twenty some bucks on a fuel pressure gauge (like the others said). I'm betting you'll find the problem.

[Rexone]

GlastronGuy:
Rexone:
My gut feeling because of the popping and misfiring is that you're either going dead lean, (lack of fuel) or you have an ignition problem under max load. Again these are guesses, nothing more. :) Lean is bad in a jet boat. Jets really don't have the exclusive on this badness, lol.
the only good thing is that when it runs completely out of fuel and pops maybe you have enough warning to shut off before piston damage. It's those ones that just surge almost unnoticeably and kind of go flat on power that really burn em down because you're more likely to keep your foot in it not recognizing the problem. That's been my experience anyway.
[ June 01, 2003, 11:02 PM: Message edited by: Rexone ]

[SeaSlut]

I just need to share, the SeaSlut (455) did the same thing. The plug wires were only a year old, so I KNEW they were good. We checked everything twice! It was frustrating because everything check out. Then just as a lark, I swapped those plug wires out for a new set I had fopr another project and VIOLA' the old ***** is ripping it up and letting everyone ride her!

[75_Elim]

SeaSlut:
the old ***** is ripping it up and letting everyone ride her! God Bless Her :D :D :D

[DansBlown73Nordic]

Dgie, where are you from? Maybe someone could take a look at it for you. idea

[skeepwerkzaz]

Did you just overhaul the engine yourself? If you installed the camshaft, did you use a straight edge? It may be a tooth off.

[dgie]

I am from Texas Dallas area, and I did not do the rebuild it was done for me.

[victorfb]

you can take this with a grain of salt, but i would look further into the cam and installation. a "tooth off" is easily and commonly done. another thing comes to mind is the cam may be going flat.(lobes worn down) was the cam new? new lifters? broken in correctly? you said the engine was reciently rebuilt. did your builder fire it up before you recieved it? and did he intruct you on cam break in? ( normally 2500 rpm for 20 minutes min.) at firt fire. very important!!!
Also, OLDs heads have a tendancy of "tulipping" the intake valves. meaning the valve stems get pulled from the face of the valve, causeing them to look like dished valves from the chamber view. one way to get an idea is to remove the valve cover and rocker arms. allowing the springs to completely close all the valves. then take a straight edge (metal ruler or ?)and hold it on the valve tips. they all SHOULD be the same hieght. if the valves tulipped, the stems will be much higher, and not all the same hieght.
with tulipped valves, or a flat cam, your engine would run very similar to what you described.
just my oppinion and two cents. though that might be 2 cents over payed.
good luck and please let us know what you come up with.
... victor

[dgie]

Thanks Victor (you are the second person to tell me this and I will check it out) also everyone else who has responded thank you also. Great advice and things to help me narrow down the problem. Anyone who has not responded yet please do so now, thanks again.

[HavasuBarney]

Personally, I'd scrap the whole car motor thing and strap on an outboard! :D
But that's just my opinion, I could be wrong! wink
[ June 05, 2003, 10:54 PM: Message edited by: HavasuBarney ]

[dgie]

better yet how about a trolling motor? idea

[victorfb]

hey dgie. i hope it all works out well for ya.
also let me know what the outcome is. i know olds heads are hard to find so if it IS your valves i may be able to help. i have a couple pairs of olds heads ive been keeping for just that reason. also edelbrock has a nice set but pricey.
good luck... and lets get that boat back on the water.

[dgie]

Thanks, I have a second set of heads also from the first motor that was blown up (not by me).I will hold off with the trolling motor as a last resort :D

[TX Daytona]

I've had the same engine in a jet boat and live in yout area. I'm familiar with Holley carbs. I have a good 750 you could bolt on and see if thats the problem. If your still having trouble let me know if you want to try that. jw@jwbowman.com