1972 F-36 port motor problems

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fdean396
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1972 F-36 port motor problems

Post by fdean396 » Sat Dec 23, 2017 9:49 am

I have posted about what I believe are fuel problems affecting our port motor. The boat is powered with Marine Power 454's. About 2 years ago I began have some intermittent stalling problems typically after a short shut down and then restarting. Initially the boat would stall and shut down. After restarting it would run fine. Then the problem started occurring more frequently after shutting down for a half hour or so and when I'd try to restart the motor it would not start. For a while once it cooled down the motor would start again and run fine. The problem got worse over time to the point the motor would not start until we'd get back to the dock or sometimes it would not restart until the next morning.

My mechanic initially suspected an electrical issue and we replaced the distributor. That didn't fix the problem. Then we started looking at the fuel system and found when the motor was hot no fuel was getting past the primer pump which had not been working for a couple years. My mechanic bi-passed the priming pump and that fixed the starting problem when the boat was hot but a new problem then started happening. Now when underway and throttling up or down in the 900 to 1100 rpm range the motor stalls and the rpms drop to zero and they jump back up. This happens repeatedly until I power down a couple hundred rpms, or powering up a couple hundred RPMs when powering up. The boat runs great outside of 300 RMP range when powering up or down. The problem only happens in the same 300 or so RPM range. The boat runs great at higher and lower speeds. Yesterday the same problem happened at the dock while we were not underway. After revving the boat up and down it would run rough and stall. Restart and the problem would repeat. This time my mechanic was on the boat to witness the problem under power and at the dock. We just rebuilt the carbuerator thinking that would finally fix the problem but it did not.

My mechanic is convinced there is still a fuel problem. Could running the boat with the priming pump bipassed becausing the RPM and stalling problem? This problem newest problem started after the priming pump was bipassed. When we were checking the fuel system a few months ago we pulled the motors fuel seperator filter and there was a little water and debris in the fuel. Could this be the problem? If it is, is there something that can remove the water and any debris that may be in the port fuel tanks? Should the fuel be polished to remove the water and sediment?

My new concern now is the port fuel tanks. If there's sediment and rust in the tanks should the tanks be replaced? I'm sure replacing the fuel tanks will be very expensive since the motor will need to be removed to replace the port motor saddle tank and the rear transom deck will need to be removed to replace the stern reserve tank. Has anyone replaced their fuel tanks? If so how much did it cost?

Any ideas on what may be causing the problem and possible solution would be greatly appreciated. This problem has been happenning for over two years in varying degrees. I really want to get it fixed once and for all so I can confidenatlly run the motor. Right now its running very erratically and you never know what's going to happen next.

Thanks,
Frank

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1972 F-36
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1972 - F36

mikeandanne
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Re: 1972 F-36 port motor problems

Post by mikeandanne » Sat Dec 23, 2017 10:40 am

Unless I missed it, what kind of carb you got and has your mechanic opened it up again to check for debris.
78 F 32

fdean396
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Re: 1972 F-36 port motor problems

Post by fdean396 » Sat Dec 23, 2017 11:10 am

Thank you Mike. I do not know what type of carb is on the boat but will find out. We have not checked the new carb for sediment but will. There's never been sediment in the filter on the fuel filter just prior to the carb. I didn't get any feedback on the condition of the carb when it was being rebuilt but will ask my mechanic to ask the company that rebuilt it.

Never have had any problems with the starboard motor. It runs great!
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1972 - F36

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bjanakos
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Re: 1972 F-36 port motor problems

Post by bjanakos » Sat Dec 23, 2017 4:32 pm

If you noticed the problem after the primer pump was bypassed, than there is a high probability this may be related to you issue. I imagine you only really need it for starting, however, it could be also acting as a surge valve delivering more fuel when needed.

My only question is why was it bypassed and not replaced?

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prowlersfish
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Re: 1972 F-36 port motor problems

Post by prowlersfish » Sat Dec 23, 2017 6:03 pm

Priming pump ?? Is this by chance a added on elc fuel pump ? Can you find out what carb you have ? I suspect a Q-jet
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fdean396
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Re: 1972 F-36 port motor problems

Post by fdean396 » Sat Jan 06, 2018 11:59 am

Thanks everyone for the replies and suggestions. I'm going to try reconnecting the port motor's priming pump to see if the current problem stops when accelerating and decelerating in the 1500 to 2000 rpm range. It almost sounds like running without the priming pump is causing some kind of back flow problem. Never had this problem prior to the priming pump being bypassed and I suspect as one poster stated the problem may be happening now that the priming pump is bypassed. Thinking back i think the hot starting problem we were originally trying to resolve started when the priming pump stopped failed a couple of years ago. After the motor had been run and then shut down after a half hour or so it would not restart while hot and we found there was no fuel flowing past the priming pump. Let the motor cool and fuel would flow again and motor would start and run great. Removed the priming pump and the hot starting problem was resolved but the new accelerating and decelerating problem started. I agree a new priming pump may be needed and may resolve the old and new fuel issues. I suppose we could try bypassing the starboard motor priming pump to see if doing so creates a similar accelerating and decelerating problem for the starboard motor. I have never had any fuel problems with the starboard motor.

Will also open the rebuilt carb to see if there is debris in it and check the Q jet.

Thanks again! Hopefully my next post will be one that states problem resolved and what fixed theproblems.
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1972 - F36

mikeandanne
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Re: 1972 F-36 port motor problems

Post by mikeandanne » Sat Jan 06, 2018 5:17 pm

So after reading the latest, do you still have the mechanical fuel pump on the engine as well as an electric pump ? These pumps do get tired and the pump rod inside that drives the pump sometimes wears down , reducing the pumps ability to keep up.A little more info for you.
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tpd777
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Re: 1972 F-36 port motor problems

Post by tpd777 » Tue Jan 16, 2018 1:02 am

I had similar problem/symptoms in my 1985 Tri-cabin and it was water in the fuel. replaced engine fuel filters and added water remover to fuel tank. I did not think to check filters at first as I had recently replaced them. Problem started when fuel tank quantity was low and power requirement was high, coming up on plane. Bow rise caused water in tank to collect at fuel pickup point in tank. Probably not causing your issue but worth checking out your water separators if you haven't already.
1985 36 Tri Cabin

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