1972 F-36 Port Motor Problem

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fdean396
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1972 F-36 Port Motor Problem

Post by fdean396 »

I have been intending to send an update to an going post about a recurring problem with my port motor (454 Marine Power engines with 1000 hrs). Someone said it was best to start a new post and not go back and add to an old post so here we go. Unfortunately the problem I have been experiencing for almost 2 years is still ongoing and has now dramatically changed after I thought it was finally fixed about a month ago. I suspect the problem is really a fuel or carburetor problem but its now happening under different operating conditions. Previously the motor would not start when it was hot. Let it cool off sometimes for a short period or occasionally as long as over night and it would start and run great. This cycle repeated itself for over a year. My mechanic initially thought it was an electrical problem and installed a new distributor and spark plug wires but that didn't solve the problem. I was finally able to get the problem to occur with my mechanic at the boat when the motor was hot. Checked fuel lines all the way back to the engine priming pump (which stopped working sometime ago) and that was where the fuel stoppage was. Pulled the priming pump out and the boat ran great again, started while hot, etc..... Changed the fuel/water separator filter and there was some water in the fuel and a little debris. The 2nd filter was fine. Mechanic inspected the small filter prior to the carb and said it was fine too.

We just took our boat out on a ten day cruise in the Washington San Juan Islands. Boat ran great and we cruised at about 3000 RMP for a couple hours to each location. However each time we powered down from cruising speed to about 1500 RMP the port motor would shutter and lurch, the RMPs would drop to almost zero, go up slightly and the motor would run rough for a couple seconds and each time I thought it was going to die it returned to a lower RPM as I lowered and raised the throttle. In total this situation would last for about 10 to 15 seconds. The motor would reset and run great at lower RPM while we docked or run at lower RPM if we needed to travel slowly. Powering back up and at higher RPM cruising speeds the motor ran great. This occurred multiple times as we cruised to each new location. On our return trip one morning it was difficult starting the port motor when it was cold. The motor turned over but ran rough, misfired, backfired and died. After a couple attempts it started and ran great until we were powering down again. The same starting issue happened an hour later at the fuel dock while the motor was still hot. After a couple minutes the boat finally started and ran great but we had the same problem while powering down on the last leg of our trip.

Does this sound like a carburetor problem? Prior messages in this thread have discussed rebuilding the carb.
Fuel line problem?
The small filter prior to the carb was not replaced. Could this be a factor?

I'm also a little concerned about the water and small amount of debris we saw in the fuel. I do run on ethanol free fuel. I have four fuel tanks and they are original. I always add StarTron gasoline additive each time we fill up or add fuel. I also make sure all four gas tanks are at least 3/4 full or more over the winter (our boat is docked under covered moorage year round and has been for 14 yrs since we purchased it). Someone in a previous thread recommended to only run the boat on two tanks at a time and to shut off the other two tanks. Someone also said to leave the rear tanks dry and only run off the forward tanks. I have always maintained fuel in all four tanks and run the fuel down in all four tanks before we refilling for the winter. Also when we go on long trips I fill all four tanks and I also add fresh fuel to all four tanks once or twice during the summer.

--How should I be managing and using the four fuel tanks?
--Should i be concerned about my fuel tanks and their age? (I can only imagine what would be involved and what it would cost to remove and
replace them - especially the saddle gas tanks in the salon next to the motors)
--Should the fuel tanks be replaced at a certain age?
--Is there anything that can be done to reline the fuel tanks?

I've never had any problems with the boats port motor's electrical or fuel system. I appreciate everyone's comments and expertise and am looking forward to finally resolving this nearly two year ever changing problem. Once its fixed I will happily post the final solution!

Frank

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prowlersfish
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Re: 1972 F-36 Port Motor Problem

Post by prowlersfish »

Try swapping Carps side to side .
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Re: 1972 F-36 Port Motor Problem

Post by P-Dogg »

prowlersfish wrote:Try swapping Carps side to side .
I keep spare gaskets on hand just for this eventuality.

You can also troubleshoot fuel issues by swapping the fuel lines. Do so downstream of all of your filters etc. to the extent possible.
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Lance F28
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Re: 1972 F-36 Port Motor Problem

Post by Lance F28 »

It sounds like trash in one of the tanks being picked up from time to time. I like Prowler's suggestion to swap the carbs then you can work your way back towards the tank if the problem stays with the port motor. Probably should replace the inline filter when you replace the water separator just to remove all doubt and you may want to try that before swapping the carbs. If you do keep in mind there is probably a screen in the carburetor where the line enters the carb that you should remove and clean if necessary. And if the problem follows your carb to the starboard motor you know it's time to re-build it.

When your mechanic thought it could be an electrical issue did he replace the coil? If you can't find any more fuel issues you may want to swap the coils. A bad coil will act funny when it gets hot and then work fine after cooling off as well. Even if he replaced it you might try swapping it because I have bought bad coils brand new in the box.
fdean396
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Re: 1972 F-36 Port Motor Problem

Post by fdean396 »

Thank you for all the feedback and suggestions. My mechanic did replace the coil while replacing the distributor prior to starting our investigation of the fuel systems. Given the fact that the port carb has never been rebuilt since I've owner the oat (15 yrs) and that the problem has shown itself in four different ways Hot starting, cold starting, deceleration and at little on initial acceleration I'm leaning towards a carb issue. However I'm going to swap the fuel lines, replace all the filters and carb screen and try the other suggestions in the event the problem is something getting sucked up from one of the fuel tanks. I suppose I could also try shutting off the fuel supply from each of the two port tanks at different times and run the boat to see if I can isolate the problem to either the forward or aft port tank. Do the motors draw fuel off the forward tanks initially and then draw off the rear tanks when the fuel in the forward tanks drops to a certain level? I believe this is how the fuel draws based on looking at the two fuel gauges for each motor but someone with more experience probably knows more about this than I do. I'm somewhat mechanical on the basics but haven't ever dealt much with fuel systems.

One other thing I have noticed. The starboard motor seems to burn a lot more fuel than the port motor. The starboard motor has always burned a little more fuel which I was told is normal but recently it seems like it's burning a lot more fuel than it used to in comparison to the port motor. Could this somehow be tied to my port motor problem or be another possible carb issue with the starboard motor?
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mikeandanne
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Re: 1972 F-36 Port Motor Problem

Post by mikeandanne »

To give you an idea of how very small things can create a lot of the same thing you are describing,here is a little story. Years ago had an outboard that all of a sudden started the same sort of thing , it would run great for a while then act up, no particular pattern.We cleaned the carb, some crud and it ran great for a while then acted up again. Well after much removing carb and fooling around, got lucky and found something stuck in a jet, removed it and ran great again, then same thing. I know this is kinda long but turned out to be the gasket on the float bowl was cork and was breaking down, replaced gasket and no more problems, so I guess you really should have a look in that carb and see what is what....good luck with it .
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Re: 1972 F-36 Port Motor Problem

Post by mikeandanne »

double post
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Re: 1972 F-36 Port Motor Problem

Post by WayWeGo »

How do you know one engine is burning more fuel? Do you have fuel flow sensors or are you going by the amount being used out of each tank? If you are going by tank usage, it is only valid if you are running each engine off a separate tank and all crossover valves are closed. In other words, you might not be getting good data if you have the tanks connected and are going off of tank levels.
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daylategeorge
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Re: 1972 F-36 Port Motor Problem

Post by daylategeorge »

Just an FYI. I had a similar problem with my '78 F 32 with 360 Chryslers. Turned out it was water in the carb bowls. Port side was worse than starboard. Had a hard time getting carb apart but has been fine since being rebuilt. Good luck with finding out the problem.
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Re: 1972 F-36 Port Motor Problem

Post by WayWeGo »

Any progress?
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