:confused: engine will fire but wont stay running?/?

[miahlloyd]

need some input please

This is my first post. This site is great I have looked at other post like this but nothing was quite like this from what I saw.

I have a gm 305 1977 mark twain mercruiser outdrive
I have been trying to get it to run correctly.
I finally have it timed right and idol at about 700 or so.
Then the PROBLEM...
I have started the engine just last week. It ran rough idol though, there was to much white smoke for me through the vent breather and pcv valve,. so I thought maybe water leak or blown head gasket, but it was a cold night and so I also checked to see if it may have been the water vapor or condensation whatever you may.
[exhaust manifolds are new]
I went through and checked the oil for leaks no milky oil at all I also looked at the top of one of the valve cover gaskets I have no peanut butter look or milky color at all just clean oil..? also the same amount.

I started it up today and it ran for about 10 sec and stopped, then again for 5seconds and stopped again.
Now it will fire perfectly but wont stay at a idol. I just get a good strong fire.

I can tell you I have all new components also new gas, including carb its a quadrajet.
I cant for the life of me understand what would case a engine not to keep the fire resistor wire maybe?
Any suggestions for troubleshooting.
I should say the ammeter was recently changed between the last time I ran it and now. I dont know if that could change anything.

Thank you all in advance for the help

 

[jtybt]

Re: engine will fire but wont stay running?/?

Doesn't sound like you're getting gas. Check filters. Water/fuel separator and the one in the carb.

 

[Apollo75]

Re: engine will fire but wont stay running?/?

Welcome;

Running rough and white smoke out of the crankcase calls for a compression check before you proceed much further ---- not a good sign.

If the engine runs at all after you turn the key back from the start position to the run position I would not suspect the ballast resistor / wire.

Please let us know everything that you have replaced.

How long have you owned the boat ?

When did run last and how good did it run ?

OFM

 

[bds85466]

Re: engine will fire but wont stay running?/?

besides filters, choke?

 

[Glastron_V210]

Re: engine will fire but wont stay running?/?

Gas, spark or worse really.

I'd start by getting a fuel pressure guage ahead of your carb. If that's ok, the next easiest is spark, but it sounds like you have been there already.

Do a compression test for sure with what you have described.

Also, be sure to check your ignition switch. There are three position...off, run and start. It could be that your run contact is on the way out, meaning you get voltage (And hense spark) in the start position, but none as you get back to the run position. To check this, hang a voltmeter from the + terminal on the ig coil to ground. Look for +12 or so with the switch in the run position. It hopefully is that easy.

Chay

 

[miahlloyd]

Re: engine will fire but wont stay running?/?

Thank you all.
I have had the boat for about 2 years but this is the first time I have tried to run the engine it didnt have one when we bought the boat.
Engine was running great before and after the boat was.
{dotn worry everything has been changed marine (fresh water)}

I will start with a compression test.

Engine ran great when the last time it was on idol was smooth,
that run position sure does sound good.
It really may be that? Ill have to check the + side of coil and the key in the run position for power.

also apolo I have replaced everything becasue we had nothing to start with but the mail wiring harness.
all accessoried the fuel is runing straight from a gas can to the pump to carb all filters are brand new.
The choke works the carb was rebuilt and tuned to the engine.
But I will recheck for blockage never know right,.
I do know the floats stay full of gas becasue I have tried to pump the carb a bit and see if I have gas pressure.

A BIG THANK YOU ALL.

I will be doing all of these test tomorrow.

 

[RinkerSteve]

Re: engine will fire but wont stay running?/?

Sounds like the ignition bypass resistor. I had one do that very thing. Fire but wont run.

 

[Jerseymk2]

Re: engine will fire but wont stay running?/?

I have seen similar issues i'm a mercruiser tech for a living i agree with all the posts so far compression test check fuel filter on the bottom of the fuel pump check the inline filter on the carb itself i would also look at ignition if all else checks out i have had problems were it will run for a few seconds and not stay running and has been due to moisture inside the distributor cap or carbon on the points etc... those are the first things i would look at personally

 

[miahlloyd]

Re: engine will fire but wont stay running?/?

So far so good i have done a few test I noticed now in the run position I had no hot wire at the + side of the coil.
Ill have to check the wire there and jump one from the starter to the coil and see if I am running right???

I have not found the smoke problem yet but I will do a compression test next
Thank you for all your help
O the distributor cap is new and points and capasitor.

More test this weekend

 

[fabrimacator21]

Re: engine will fire but wont stay running?/?

I have the same problem (sort of). I have a 1978 305 omc and it'll fire up and idle for about a minute then die. I pulled the fuel filter and it was UGLY. Hardened gas at the base of it and it looked to be clogged. I also found a stuck check ball/valve in the carb where the throttle return spring/plunger is. To me it sounds like a fuel problem.

If you don't want to buy a fuel pressure gauge, and easy way to check for blockage in the fuel system is to pull the fuel line from the carb and stick it in an old milk jug then crank the motor. You should see a good strong fuel pulse coming out of the line. If the pulses get weaker as it cranks then you most likely have some blockage or a bad fuel pump.

Good luck mang.

 

[miahlloyd]

Re: engine will fire but wont stay running?/?

Ill check that as well thanks for the inside trick

 

[capri_1850SS_lover]

Re: engine will fire but wont stay running?/?

I had a similar problem with my boat where it would run for a 10 to 20 second span and then die. Guys on the forum helped me diagnose it as a problem as a bad oil pressure switch. I had a broken terminal which was obvious, but there is a way to check it with a volt meter also.

Just my 2? worth... Good luck.