Engine dies after starting

[Boater Bill]

Short Story ? had the 4 cyl engine in my 86 Merc 140 rebuilt. Got it back together and it will start for about 2 secs then it dies. Any suggestions would be a huge help! Thanks!

Long Story and details: not sure how much of this is pertinent, but thought I?d lay it all out there in case something that doesn?t seem important to me is the smoking gun to my issue. The engine doesn?t stay on long enough to get a good long term trusty read on the timing light, but it?s close and the 6 before mark (like my manual says). And that position lets it ?run? the longest. If I spin the cap slightly one way or the other the mark jumps off out of sight and the engine doesn?t stay going as long. When I put the cap and shaft back in the first time, I had it 180 degrees out and it just would backfire thru the carb (dog didn?t like that at all either).

Engine was a full rebuild by a boat and high performance car machine shop, so I have to trust that he did it right. I Siphoned the gas out before the rebuild since I knew it was going to be a while. New gas I put in was 91 Octane (thought it would be better than 87, maybe I was wrong). Fuel pump pumps gas when turned over (I took the hard line off and the pump shot gas into the air ? I hear that I have the early model pump since it has the filter on TOP instead of on bottom). I have fuel in my filter, and fuel in my stiff line (not sure what that?s called) that goes to the carb, but no fuel in the flexible line that goes to the carb (what does that flexible line do anyway?). I get fuel pumping into the carb when I pump the throttle. Not sure if this is just coincidence but I have some fuel that drops about once every 3 seconds out of ONE of the venturi tubes. No new points yet (local boat guys gets more on the shelf in a few days). New plugs with proper gap, wires are in good shape. I?m pumping the throttle 2 or 3 times (and getting gas to squirt) then trying to start, it goes for about 2 seconds. If I spray carb cleaner in the cab (what I used to do to help it start when it was cold and sitting for a few weeks) then it will run a bit longer, maybe 3 seconds. I?ve been told it?s a Rochester carb.

Sounds to me like I?m not getting continued fuel, Maybe? Issue with choke maybe?

Any help is greatly appreciated!
Thanks!
Bill

 

[flintcam]

Re: Engine dies after starting

The first thing I would do is clean out the carburetor while making sure the center venturi bolt is tight and has a gasket then adjust the float level. Rust in the fuel system can cause all sorts of problems with a Rochester carburetor.

 

[uaw9fan]

Re: Engine dies after starting

The first thing I would do is verify the lanyard switch is in the run position. Sounds like it's only running as long as the starter is spinning.

The clear line from the fuel pump to the carb is a safety in case you fuel pump diaphragm ruptures. In the event of a rupture excess fuel will be routed into the carb causing the engine to stall from too rich running leading you to check the engine.

 

[achris]

Re: Engine dies after starting

Sounds like a dead resistance wire (akin to a ballast resistor in a car system) in the circuit between the key and the coil. Hook a temporary wire from the battery positive to the coil + and start the engine. If it continues to run, you found the problem. Remove the wire and the engine will stop.

Chris...

 

[Boater Bill]

Re: Engine dies after starting

Thanks guys, huge help! I've got a couple things to try now this afternoon, i'll try them all and get back with ya. Thanks agian!

 

[Boater Bill]

Re: Engine dies after starting

So the pos coil to the pos bat terminal didnt help. Checked the The engine starts and tries to go after the starter is turned off, but only briefly.
My boat place doent have the carb re-build kit so i'll have to order one. Anthing else that it might be anyone can think of? Thanks all for your help!

 

[mpdive]

Re: Engine dies after starting

Have someone stand there and sqirt a couple of shots of carb cleaner down the carb as you crank it. If your able to nurse it and keep it running then it's fuel related. Verify you have enough fuel making it to the carb before doing a rebuild.

 

[Boater Bill]

Re: Engine dies after starting

Thanks MP, the Carb nursing didnt work either...is there a cut out switch that might be the issue maybe? The engine gets up to about idle and then just dies...
There is the electric choke and its getting hot since i'm was leaving the key in accessory while i was tinkering (is that normal), also the butterfly is normally staying open, is that normal either?

From looking at the wiring diagram, looks like the purple thats connected to the choke connects to the pos coil terminal (the resistance wire that Chris metioned above) and connects to the alternator, then into the wiring harness, then it LOOKS like (anyone feel free to correct me on this one) looks like it it feeds power to each of the gauges? anything with that have anything to do maybe?

Again, thanks guys, i'll keep posting as i find new things and def post when i find out what was wrong so someone else can find their answer in the archives.
Bill

 

[mpdive]

Re: Engine dies after starting

If the key is in run position I am almost sure the choke coil is energized. The choke will open and stay open while energized. Try wiggling the wires around on the ignition module if it's HEI.

 

[Don S]

Re: Engine dies after starting

Get yourself a jumper wire with alligator clips on each end, hook one end to the + terminal on the coil, the other end to the positive terminal of the battery and see if it stays running.
If it does, you have an electrical problem.
If nothing changes and you have the same problem, it's probably a fuel problem.

PS: if it does stay running, disconnect the jumper to shut it off.

 

[Boater Bill]

Thanks Don, the Jumper didnt work. So sounds like probably a fuel issue then.
Random question, would bad points have anything to do with it? old points, bad gap? since it tries to start, the point sound like they're good (at least for a few seconds, right?)

On the Carb - I get 2 good squirts when push the throttle, but one of the venturi tubes is dripping - I've always steared clear of carbs just because i dont really understand them.

Sounds like thats reason for a carb rebuild?

 

[mpdive]

Re: Engine dies after starting

I was assuming you had HEI. Points and the whole secondary ignition system will cause this. Don was on the right track here. For the small investment, I would be throwing new points condensor cap and rotor in it anyhow, especially if it has not been done recently. Good squirts down the carb rule out fuel issues although the drip means a rebuild is in order. That is not your problem right now though and is not causing your issue.

 

[Don S]

Re: Engine dies after starting

If it was points, it wouldn't start at all.

Pull the carb and disassemble. Could be full of corrosion.

 

[mpdive]

Re: Engine dies after starting

If it was points, it wouldn't start at all.

Pull the carb and disassemble. Could be full of corrosion.

I am under the impression it is firing slightly the way he is explaining it. When he said it gets to idle and dies, it sounds like it is getting spark momentarily. I was thinking on the lines of the condensor discharging prematurely. Did you interpret that the same way?

 

[Fishermark]

Re: Engine dies after starting

...is there a cut out switch that might be the issue maybe? The engine gets up to about idle and then just dies...

Check and ensure your shift interrupt switch is not engaging for whatever reason. You can simply disconnect it completely to make sure it isn't causing the problem.

 

[mpdive]

Re: Engine dies after starting

Good point Fishermark. Three things needed for combustion....fuel air combustion. You have fuel down the carb. Granted your carb may be dumping and overich, but unless you plugs are fuel fouled, it should start. Did you by any chance notice this happening after you put plugs in? Did you remove the coil plug wire? By Don having you apply 12 volts to the coil, we know the primary ignition is not the problem. Moving onto the secondary, there could be a breakdown somewhere. If you have a dwell meter, get a cranking dwell on the points. If all checks out there, check for spark on the coil wire. What color was it? Carefully inspect your rotor for burning through, pit marks, rotor button and your cap too. Something is wrotten in Denmark here and I don't see fuel as the issue. Dumping carb or not, it should at least start unless, like I said you plugs are fouled. Pull your shift interupt switch as Fishermark said before doing any of this.

 

[Boater Bill]

Re: Engine dies after starting

I have to thank everyone for all their comments and suggestions, my issue was part electrical and part clogged carb. (I'll leave some comments below for the future boaters looking for answers for what worked for me). The contacts on the choke were not as good as i thought they were, so a good cleaning helped that out a lot, then I had to take apart the carb and clean out all the seats, pick up tubes...just about everything. WD40 and Carb cleaner worked well with a dental pick (available at harbor frieght or home depot). The carb re-build kit I got from my boat dealer was not perfectly the correct one, i didnt have the model number from the carb, the tag had gone missing and nothing evident on the side - the carb i have has a larger barrel configuration into the manifold than the kit i got so the gasket didnt fit right, i had to use parts from the new gasket and parts from the old one that were still good to reseat it. Also the gasket below the venturi manifold wasnt right, but just by a little bit, a knife helped shape it right.

My suggestion for anyone with this issue (starts for a moment then dies) is to dump a little gas in the small tube in the carb that fills up the bowl, if that keeps it running longer, then you have a carb issue. If you're still not getting things running then check the cut out switches and be sure they are working right (bypass them if need be), check the wires from the ignition. An alligator wire (from Walmart) or just a length of spare wire will help out a lot in bypassing things. Good luck and thanks to all the experts that helped me.