Mercruiser 170 acting flaky when warm

david.gabhart

Recruit
Joined
Mar 29, 2004
Messages
3
I have an 86 22 foot Thompson 215 Carrera with a Mercruiser 170 (225 CI I/O) and the other day I was running about 3500 RPM for about 25 minutes when it suddenly acted like it had lost all power and started slowing down. Once I throttled back and sat tight idling for a minute it ran fine again and went on down river. About 2 hours later I left heading back up river, again, after 20 minutes or so at 3500 it died, restarted, died, etc. etc. et al. A buddy towed me and when we got into the marina (after 30 minutes) it fired and ran great for well over 15 minutes at idle speed. This is the second time out this season. First time no issues. I am wondering if it is possible it is a fuel related problem vice an electrical issue. Any thoughts would be appreciated as the local Marina has a 4 week wait...
 

airman

Petty Officer 1st Class
Joined
Aug 9, 2003
Messages
332
Re: Mercruiser 170 acting flaky when warm

Sounds like ignition to me, probably the coil. Scan through past posts and you'll definetly find your problem and several answers.
 
D

DJ

Guest
Re: Mercruiser 170 acting flaky when warm

It could be a coil, true. Or, it just as well could be fuel.<br /><br />As far as fuel goes, here is where I would start.<br /><br />1. Does the fuel tank have an anti siphon valve? This would be where the outlet leaves the tank. It is usually part of the outlet. I can be removed for testing.<br /><br />2. Is the fuel tank vent clogged?<br /><br />3. How old are the fuel filter(s)?
 

david.gabhart

Recruit
Joined
Mar 29, 2004
Messages
3
Re: Mercruiser 170 acting flaky when warm

Just bought the boat and have never had an I/O so most of this is all new. I have an access panel in the floor to the fuel tank so I will start looking there for the anti siphon valve. As far as the maintenance and fuel filters, the guy I bought it from as extremely Anal, so all the maintenance was done meticulously. I was just perplexed by it only stopping after it was warm and then running fine when it was cold. I plan to change the points, rotar, dist cap and wires this weekend, as well as checking the battery cable to ensure it is a 2.0 and to ensure the battery is at least 800 amps. Some posts have suggested that if the batt is only @ 550 it will cause issues. Thanks for your replies. Is there any way to Check the coil without changing it?
 

Boomyal

Supreme Mariner
Joined
Aug 16, 2003
Messages
12,072
Re: Mercruiser 170 acting flaky when warm

I strongly suspect the fuel pump. Your symptoms are classic for a failing fuel pump. After you check your anti-siphon valve (bad valves usually react quicker than 20-25 minutes) put a fuel pressure guage between the pump and carb. Have someone else watch it while you drive. Betcha that's your problem.<br /><br />If it is the pump, be sure to replace it with a marine pump.
 

david.gabhart

Recruit
Joined
Mar 29, 2004
Messages
3
Re: Mercruiser 170 acting flaky when warm

It has a mechanical pump on the side and I thought about that but I haven't dealt with a mechanical pump in years. I know the electronic in tank pumps start going out sporadically when they are warm but in my memory I seemed to recall that the mechanical pumps just went and then you were SOL. I guess I can check that next. Thanks!
 
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