Runs great for ten minutes then dies

First time on this forum so if I'm in the wrong Place I'm sorry.

My mid 70's 355 has been built pretty good. Trw 11/1 pistons, wiend dual quad intake, dual edelbrock 600's which have been rebuilt by me so I'm 60% sure they are right. Unknown cast heads, Mallory fuel pump, Mallory dual point distributor, unknown coil, crane 6.1 roller rockers. Unknown bottom end, unknown cam

Anyway this is in a boat but no marine parts to my knowledge. I inherited it from my step dad and unfortunately can't ask him questions about it. I've replaced the head gaskets and one rocker stud, I adjusted all the rockers (which may be wrong), I set the timing by ear (which may be wrong), Fuel pressure seems right, oil pressure seems right, water temp seems right

Since I did that stuff it seems to run great for about ten minutes, then begins to stutter, then dies and won't restart. (leaving me in the middle of the lake) the next day it will start on the first crank

My question is why?
Old coil?
Misadjusted valves?
Flooding?

What water pump???is it runing backwards??? overheating will stop it from runin.

Check your fuel tank vent ..

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Welcome to CHR. Both good suggestions to check. What's your ignition system? Sounds like it could be the electronics in the distributor or ignition module getting hot? Also when it dies do you have good fuel pressure? Is you electric fuel pump working right after it heat up?

While those are reasonable suggestions, I'd start with fuel system too. Sounds like classic fuel being starved.

put it on a differant sized lake--that way you can either be farther out or closer to shore------------------

being a boat, with a full lake of cool water--overheating shouldn't be a problem--however----as said--water pump-- what is the cooling system like--the automotive water pump or an external pump???? it could be seizing up from overheating--the coil could be bad--is it mounted vertical or sideways--if vertical, the internal oil could be low and coil shorting out when it gets hot--

so---most likely you have a temperature problem or a fuel supply problem------

Well the pump is a cam driven water pump, I have a water temp guage that doesn't read hot, but since it's pulling water out of the lake I don't really know what it should read, I don't think it's overheating.
As far as the fuel tanks go, I could understand fuel starvation, but after it dies it will NOT restart, even though is can see the accelerator pumps working. That should be enough raw gas to at least get it to start for a second.
Which leaves the coil (others that I've asked said this as well)
Or I messed up the valve lash
I have bought a new coil so we'll have to see, thanks for the feedback

Some how you need to find out what cam is in it. Do you even know if it is hydraulic or solid? How did you adjust the lifters (explain roughly step by step). Even this really does not matter if you do not know what cam it is.

I'm pretty sure they're hydraulic flat tappet lifters. I rotated the engine until each lifter was on the base circle, I tightened
The rockers until the push rod barely stopped spinning then went 1/4 turn or so tighter, then locked them with the lock screw. I tried 3/4 turn first but then had no compression so it mustve been too far.

What kind of boat? If it's an IO with an engine cover and the coil is mounted on top of the engine, the top of the engine heat soaks terribly because of little if any air circulation over the top of the engine....Hmmm, the dreaded old dual point distributor, try a new condenser, too.

When it is warm and quits running, does it spin faster than when it is cold when cranking it?

Get a compression tester (if you do not already have one) and tools to remove a spark plug. Check the compression with the motor cold and then take it out & run it until it quits. Pull a plug and check the compression again (in the same cylinder of course) and see if there is a notable difference. That will tell you at least if there is something in the valve train that could be miss-adjusted.

The reason for this is if you have a solid lifter cam and are adjusting the lifters as a hydraulic you could have everything too tight and once the motor warms up and everything expands you could/might lose compression. Un-fortunately if you have a solid lifter cam you might have already damaged some lobes.

Also check for spark at the plugs and from the coil to be sure you are ok there. Of course be careful when checking the spark from the coil wire. They actually have spark testers that you install inline so you can see it without getting shocked.

Just some random thoughts. I might be full if El Torro CACA.

Another Random thought. There should be a place on the boat to hook up water to run through the motor to keep it cool while running in your driveway. Does this do the same thing then or is this only when you only take in out and run it for the 10 min.

I'll try the compression test, good tip

It's a v-drive so the engine is open

How do you set solid lifter lash? I can imagine it'd be any looser than a 1/4 turn. Hope I didn't damage anything

It did run fine on land with the hose, but in the water this happens

I did order cap, points, rotor, capacitor and coil, they come in tomorrow

Quote:

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Originally Posted by Jasonmreiss

It did run fine on land with the hose, but in the water this happens

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Now it realy sounds like water pump. or blocked entry or exit of water.

is it possible your water intake is out of the water when runing the boat (Like wide open???) Someone once told me of a check valve in the watercooled exhaust is that backwards??

It does sound related, but I really don't think it is...I've been a gear head and Chevy 350 guy for a long time and it just doesn't seem like its overheating, maybe I'm wrong though

The only other difference between the land and water runs were the land run was idling for 30 minutes, the water run it was at 4k for ten minutes

I'll do the ignition stuff this weekend, if it doesn't work I'll look into valve stuff and overheating stuff

Solid lifter lash is set with a feeler gauge. You need to know the cam to set the specs. I am sure there is a rough standard but I cant remember what it is. It has been 30+ years since I built a motor with a solid lifter cam. Maybe Jerry, Pat or ? can chime in on that.

If it runs fine though with the hose hooked up then it seems likely that the issue is maybe too much water going into the motor when out boating. Or maybe not enough like Charlie mentioned. Check the water intake area on the hull to see if it is plugged.

Last though is to contact a boat place and run it by them. They might know right off the top of their head.

Delete, I re-read your first post and got my answer.

Points for a dual point Mallory----do you know how to install them????? is it a 4 lobe distributor?????

No idea, how hard can it be though? It's an 8 lobe with tach drive

I would keep looking into other things before you start changing out the points and other items. If it runs fine in your drive way and at the lake up to 4K for 10 min then points, plugs, rotor cap, distributor cap & wires should not be the problem. You could just manifest the issue throwing parts at it.

It seems to me (like was mentioned before in the posts) something is either getting heat soaked (condenser, coil, ect) or it could have something to do with the water flow while out boating.

As I mentioned in a previous post, check with a place that works on boats. I think that it is BOAT related. You might have something hooked up incorrectly (hope that is all it is).

Yeah that makes total sense, I think I'll just replace the coil then check it. If that doesn't fix it I'll check the other suggestions I've gotten here. Cuz I know the points cap and rotor aren't the problem. They are about 10 years old though so were due for replacement anyway

Just a thought, does it have a ignition coil ballast resistor? A weak resistor (12 volt side) will lose value when it gets hot (go high) and shut the coil off until it cools. Also a resistor coil wire (high voltage side) will do this.

The condenser (capacitor) stores voltage, momentarily pushing the current ahead of the voltage, this reduces metal transfer and the points last longer (without the condenser the points burn rapidly). A bad rotor or cap usually causes miss fires caused by contacts arching due to wear, or back fires due to carbon tracks conducting to the wrong cylinders.

My thinking is a bad coil as I had two Accell super coils do the same thing in my 66 Mustang which is also running a Mallory dual point distributor. I changed the distributor to Petronix as I grew tired of setting the points.

If it was a old ford from the 70's, I would ask if the same brain was in the boat like in the old LTD's that used to over heat and not start till they cooled down.
I don't know if anywater can get around your engine, But after it dies on the lake I would say to pull the distributor cap and look for water or condensation in the cap.
That will cause it not to start till that dries up.
Kurt

sure sounds like a heat problem to me - - - - - seems like the temp is the "only" thing that would change the performance after 10 minutes of operation - - - -don't some marine engine set-ups have an automatic shut down when the temps get excessive???

be sure and let us know what you find out about this, OK?

meller

Water in the cap is the first thing I checked, bone dry.

It isn't a marine engine so wouldn't shut down from heat

I got all the new ignition parts, just gotta find the time to install em
I will definitely let you all know what fixed it, thanks for all the help

Water in the cap....What cap. Do you have a radiator on there?????

Distributor cap ;)

I would bet good money your coil is bad. Had a boat do the exact thing. Ran great, got hot, would not run...I tried everything...A buddy said he thought it could be the coil and happened to have one...Been fishing every since...