1975 Mercruiser 140 Wont start I have tried...

[Mr.Outdoors]

I am hoping someone can help me. I have used this boat 6 times already this year with no problems. Last Friday I had the boat running about an hour when it jerked once. It then went back to running good. About five minutes later it started jerking real bad and finally quit running. I just had the points and condenser replaced 2 weeks ago during the spring tune up. On Sunday I replaced the coil and it started right up at home. I went to the lake and it started right up and ran good for about five minutes then jerked a couple of times then died. I checked the carburetor is getting fuel. I have spark at the coil and all four plugs. Today I checked the neutral safety switch behind the motor and it is working. I am really stumped. Any suggestions on what to try or test for next?
Thanks for anyone's suggestions!!

 

[Bt Doctur]

cracked dist cap or a bad rotor?

 

[Mr.Outdoors]

cracked dist cap or a bad rotor?

Nope. I checked them both and they are free of cracks and any discoloration.

 

[Eric 3.7LX Alpha 1]

Well it's either fuel or spark.

Check for spark at the plugs. Either with an inline spark tester like this one from Lisle for $12.00:
http://www.sears.com/lisle-inline-sp...&mktRedirect=y

or you can put the timing light on it and see if it senses spark.

If you have good spark then it's on to fuel,

Here are two good troubleshooting reads from the "sticky" at the beginning of this forum.

How To: Troubleshoot a Points Ignition System

http://forums.iboats.com/forum/engin...ystem?t=335407

HOW TO: Testing your boats fuel system.

http://forums.iboats.com/forum/engin...ystem?t=283269

 

[Boat Doctor1]

When you replaced the coil?? why?? also did you install the small wiring to thye coil in proper location on coil?? Did you use a new?? coil.or?? Now- if thats all good- id go get another set of points (only quality / heavy duty!!)from a quality parts store. NAPA!=some sell points that are cheap to buy & wont last or do the job needed-same for cap & rotor!! Copper -contacts -NOT ALUNIMUM looking contacts!! Then set points with a "Dwell " meter ONLY @ spec listed!! Not with a feeler gague!! retest & check crank timing!! then test in lake. also can check existing cap center carbon area for a small crack or worn area / missing a smooth rounded area.

 

[marky48170]

My son had a similar problem but this was with a car. It turned out to be one of his spark plug wire was bad. The wire would ground out and kill the engine. The only way we found out that it was a plug wire was to watch it at night, and believe me there was a light show. Just something to look for.

 

[Mr.Outdoors]

When you replaced the coil?? why?? also did you install the small wiring to thye coil in proper location on coil?? Did you use a new?? coil.or?? Now- if thats all good- id go get another set of points (only quality / heavy duty!!)from a quality parts store. NAPA!=some sell points that are cheap to buy & wont last or do the job needed-same for cap & rotor!! Copper -contacts -NOT ALUNIMUM looking contacts!! Then set points with a "Dwell " meter ONLY @ spec listed!! Not with a feeler gague!! retest & check crank timing!! then test in lake. also can check existing cap center carbon area for a small crack or worn area / missing a smooth rounded area.

I replaced the coil based on the problem I had and the condition of the old coil. It was leaking a little and the posts were corroded. I figured even if it was not the problem it would be soon in the future. The coil did come from NAPA. The points and condenser were Quicksilver brand replaced 2 weeks ago. I am going to replace the cap and rotor and see if it makes a difference. I will also replace the plug wires. Is the Sierra brand a quality brand? I did check each plug and I am getting spark at each one. That is why I was wondering it the boat had a second safety devise besides the neutral safety switch that would prevent the engine from running. This all started when the motor did a jerk then ran well for a few minutes then stopped running while making a jerking motion.

 

[Mr.Outdoors]

OK update for what I did tonight. I performed all of the tests in the How To: Troubleshoot a Points Ignition System link Eric 3.7LX Alpha 1 suggested. Based on all the tests the ignition works. I then moved over to the fuel. I did not have all the tools recommended so I did what I could. I removed the fuel line at the carb. I turned over the engine and I caught fuel in a clear jug. The fuel flow seemed good. The color of the fuel was not clear but more like a light apple juice. Based on the color I removed the tank and drained out all the fuel. I then added fresh fuel. Still does not want to start......I will pick up a new cap and rotor tomorrow. Any other suggestions??

 

[NHGuy]

How do the spark plugs look? When you crank the engine does it have normal seeming compression cycling, like any engine. It doesn't just spin freely or have uneven cycling? You could shoot a little burst of carb cleaner in the throat and see if that makes it fire.

 

[fishrdan]

I may be way off base here, but I'm thinking ignition switch... bad or a loose wire.

 

[Mr.Outdoors]

Update. Tonight I installed a new condenser, cap, and rotor. Still wont start. Plugs are new and look wet when I remove them. It turns over like a normal engine. I tried carb cleaner in the carb and it does nothing....Just wont start. Any other ideas for me to try????

 

[NHGuy]

Hmm, plugs wet, are you getting spark at the plugs? You could ground a plug that's attached to it's wire, crank and watch for spark.

 

[Mr.Outdoors]

I tested the plugs and they are getting spark. I have checked the coil wire and all plug wires also. Everything is getting spark. That is why I don't understand why it wont start.

 

[Mr.Outdoors]

Update. I went and bought a gauge to check compression. I took out all the spark plugs but the tester did not have any adaptors that would work. I turned the engine over a couple of times. I put three plugs back in and left the last one out so when it was at top dead center I could check under the cap to see if the rotor was pointing at that cylinder. While I was tapping the key to get the piston in the right spot the engine tried to start. I put the plug back in and engine started right up. Although this is a good thing I am nervous to take it to the lake since I am not sure what fixed it. Any ideas?????