Engine runs for ~30sec, coughs, then quits

[tuanp]

Last year I bought an '85 Searay with a Merc 470 engine (model 170MR). The boat sat for 5 years when I bought it so I've been spending time fixing the floors, etc. I just recently started working on the engine in earnest. I've done the following work on it:<br />- installed new raw water pump<br />- changed engine oil, filter, and coolant<br />- installed new fuel pump filter, inspected carburetor inlet filter (looks clean)<br />- put in new plugs, breaker points and condenser<br />- drained fuel tank and put in new gas<br />- fed cylinders some Marvel Mystery oil and let soak for a couple days.<br /><br />When I fired it up on muffs, it started and idled well, then I shut her off after a few seconds so I can pull the raw water hose and make sure I'm drawing in water. I was. So I fired it up again, it idled smoothly for about 30 seconds, then it started to misfire and run rough; it ran rougher and rougher until it quits about 30 seconds later. After that, I could not start it again.<br /><br />I checked and got spark from all four plugs, although the sparks are bright yellow/white, not the ideal blue. I disconnected the fuel pump line at the carb and got good squirts of fuel when I cranked; so pump is working. When I pulled the plugs, they were also wet so I believe I'm getting fuel to the cylinders. On my subsequent attempts to start it, it would act like it's just about to turn over, but would stop when I stop cranking and doesn't turn over.<br /><br />My Clymers manual says to check this and that but not much specifics. I checked the distibutor cap and rotor, looked good. Got 11.x volts at the coil. I also disconnected and cleaned the wires and connections at the battery, starter solenoid and coil, etc.<br /><br />So I'm looking at two problems:<br />1. Starts but begins to misfire and quits after a minute.<br />2. Could not start afterwards even with spark and fuel in cylinders (wet plugs).<br /><br />Do you guys have any ideas or advice about these problem? (My guess on #2 is that it maybe caused by fouled plugs or flooded cylinders from all the cranking attempts.) Any help would be appreciated. Thanks in advance.<br /><br />tuan

 

[TwoBallScrewBall]

Re: Engine runs for ~30sec, coughs, then quits

If it's running or trying to run when you have the key in "start" but then dies as soon as you let it go, it might be the ignition switch. Make sure you have 12V at the coil when the key is "on". Happened to me. The ignition would have power when the starter was cranking, but when they key was released the ignition went dead. Bad ignition switch. I just took it out and installed a on/off ignition switch and pushbutton starter switch. Didn't ever lose those keys again!

 

[tuanp]

Re: Engine runs for ~30sec, coughs, then quits

Hi huminski,<br /><br />I did check the voltage at the coil with switch "ON" and got about 11.7 volts, on both + and - terminals. Instrument panel also shows 12 volts when I switch key to "ON". Thanks,<br /><br />tuan

 

[flashback]

Re: Engine runs for ~30sec, coughs, then quits

Taun, this sounds like it could be a carb problem, may be some trash in the idle circuit of the carb, may be a bad float, about the only thing you can do is rebuild/replace the carb. sounds like you checked everything else.....but I am sure there could be many other things....good luck

 

[tuanp]

Re: Engine runs for ~30sec, coughs, then quits

Ok. Sounds like another learning experience is waiting for me. So I'll need a carb rebuild kits, right?. Saw them at theshadconnection; I need to get the number from my carb to find the right kit. Do I need anything else for the rebuild? or are these kits complete?<br /><br />Can't wait to get this thing running as the wife's patience (and boat-fix allowance) is wearing thin. Thank you.<br /><br />tuan

 

[kcole683]

Re: Engine runs for ~30sec, coughs, then quits

Is the choke stuck in the closed position causing it to flood? Does the choke move freely?<br /><br />My MCM 170 (1985 3.7 4 cyl Merc) will flood itself out if you don't clear it's throat shortly after a cold start. I have to let it idle at 1200-1300 rpm for a minute or so. Sometimes it loads up and tries to flood out.<br /><br />just a thought.

 

[tuanp]

Re: Engine runs for ~30sec, coughs, then quits

I'll check the choke plate when I get home. I know it's not really "stuck" stuck because I can move it with my fingers to spray some starting fluid down there; but it isn't completely freely moving though. I thought it's spring loaded right? it felt like it was when I try to open the throat. Anyway, I'll try to get it started again and open the throat like you did.<br /><br />By the way, should I bother trying carb cleaners also? Maybe it'll clear something up? Thanks,<br /><br />tuan

 

[TwoBallScrewBall]

Re: Engine runs for ~30sec, coughs, then quits

11.7 is low but it should start. Good luck tracking it down!

 

[tuanp]

Re: Engine runs for ~30sec, coughs, then quits

Hi folks,<br /><br />Just want to report back that my engine fires and runs well now. I believe the starting problems were due to water in the gas. After I added some fuel drier to the gas and waited a day, the thing fired up and ran like a champ. All my belly-aching was fixed with a $1.09 bottle of dry gas. Go figure. Anyway, thanks to everyone for your help.<br /><br />tuan