Thread: Runs great for ten minutes then dies

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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 ..

..

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

Originally Posted by Jasonmreiss

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

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??