F36 440's running weird

stevocom · Post by **stevocom** » Mon Jul 12, 2010 4:12 pm

Just picked up my first go slo boat In Lake St Clair Mi and brought it back home to Fairport harbor Oh and so far im loving it, except I am having a problem with the Starboard 440.
When I bought the boat it had old varnished fuel in it and no idea how long it had sat my guess would be a couple years, old owner added lots of chemicals to help with the varnish. Seemed to run ok with 3/4 tank of gas so I had filled it up with 89 and proceeded to head home at approx 80 miles into the trip or at a 1/2 tank of fuel it started acting up horribly, I wasnt not able to run up past 15-1700, back firing with no power and would hardly stay running. I was able to keep it running at about 1200. I made it to the closest marina which took about an hour. We did another complete tune up, cap,rotor,plugs,cleaned out the carb and changed all fuel filters again. filled it up with more fresh gas and away we went again heading towards Cleveland ran great at 3k. So about another 80 miles and/or half tank of fuel the same excat thing happend. Starved for fuel, back firing, stalling, no power, but would run at high idle. I am not at all familiar with the F36 Please help any and all suggestions are greatly appreciated. Steve

Stripermann2 · Post by **Stripermann2** » Mon Jul 12, 2010 4:43 pm

Knowing what year and model would help...it does sound like a fuel issue, lean condition, only from your description.

Could be a rusted hole in the fuel pick-up, mid tank. You can't pump fuel if it's sucking air. This would explain why at 1/2 tank, you have this issue.

Do you have another onboard tank you can draw from? If so, your issue would lie with the fuel supply from the offending tank.

k9th · Post by **k9th** » Mon Jul 12, 2010 5:09 pm

Welcome to the forum, and I agree that it sounds like a fuel issue more than anything. A hole in the pick up line a ways from the bottom would certainly explain the same conditions happening irregardless of the age or condition of the ignition components.

Hopefully it will be something simple.

turtlem1969 · Post by **turtlem1969** » Mon Jul 12, 2010 5:34 pm

when you changed the fuel filters did you by chance empty them into a clear clean glass to see how much trash was in them? If they were relatively clean then it is more then likely what the others have said, a hole in the pickup tube. Also if you filled up with e10 gas then it could be cleaning all that varnish in the tanks out and sending it thru the system, either way it is definitely a fuel problem.

stevocom · Post by **stevocom** » Mon Jul 12, 2010 6:43 pm

1978 F36 T 440's. I had tried swapping tank's although been unsuccessful due to lack of knowledge which valve shuts which line etc, I am sure it's quit easy, just havnt investigated as of yet.. I have 6 different filter on this boat. 3 per side. A steel canister down low off the fuel pump and a disposable water serporator up top off the main 5 valves and a disposable off the carb. I had changed all at the begining of my trip. No water and/or dirt in any of them. Has anyone seen holes half way up the pick up? Is this pick up easy to inspect/replace? Would air foul plugs? If not a hole in the pickup could this be water that I am picking up at half tank?

Stripermann2 · Post by **Stripermann2** » Mon Jul 12, 2010 8:41 pm

It wouldn't be water at half tank. Water is heavier than fuel and sits on the bottom, the pickup goes mostly to the bottom. If it were picking up water,a full or half tank wouldn't make a difference. As far the tanks go, follow the 4 lines from the fuel shut off valves to each tank, then mark them. When running each motor from either two respective tanks,( one for each engine), or both engines from one tank, keep the valves to the remaining tanks closed.you need to try running from another tank first and see...

Danny Bailey · Post by **Danny Bailey** » Mon Jul 12, 2010 9:23 pm

Could be picking up sediment out of the tank, plugging the anti-siphon valve, and then the sediment is flushed back in the tank when the engine quits and the suction on the fuel line dissipates.

Paul · Post by **Paul** » Tue Jul 13, 2010 8:06 am

I agree with Dan. I've had this exact same problem with my boat with the anti-syphon valve. The engine would run great for quite a while then stall & backfire then only run OK at a fast idle. Turned out to be a piece of debris in the anti-syphon that would block the flow of fuel. If the engine was then shut down for a while, the debris would float off and it would start right back up and run fine again for a while.

This can also happen if the pick up tube gets blocked in the tank. To see if you have a restriction in or at the tank the next time this happens, slowly remove the spin on fuel filter. If you hear a sucking sound when the seal breaks on the filter & the filter is not full, you have a restriction.

alexander38 · Post by **alexander38** » Tue Jul 13, 2010 10:41 am

what type of carb ? does it have a in carb filter like a Q-jet ?

stevocom · Post by **stevocom** » Tue Jul 13, 2010 11:10 pm

well I shut off the starboard fuel valves and the motor runs fine off the port tank. So I guess I should first replace the anti syphon and then pull the fuel tank pickup and check for holes and/or debris at either end in the screen's. So where do i find this pickup and how hard is it to pull out?

Danny Bailey · Post by **Danny Bailey** » Thu Jul 15, 2010 2:13 pm

The access to the fwd tanks (my boat does not have aft tanks) is made by removing the outboard most strip of flooring in the salon. It's about 14 inches by 6 1/2 feet. The pick up fittings and the anti-siphon valve will be in the aft top of the tank. The anti-siphon valve is between the copper tubing and the brass elbow screwed into the top of the tank. The right tank has one engine pick-up and one generator pick-up. Trace out the copper tubing to see which one goes to the engine. Hold the valve with a wrench and screw off the copper tubing nut with another wrench. Then hold the elbow with a wrench and screw out the anti-siphon valve with another wrench. Try to blow through the valve both ways. If it is plugged, hold one end with a wrench and screw it apart by turning the other end. Remove the internal spring clip, the poppet, retainer and spring and clean all the parts. The pick up tube is removed by un-screwing the bushing that the elbow that you un-screwed the anti-siphon valve from is screwed into. If you try to screw the elbow out without the bushing you will destroy your pick up hose.

stevocom · Post by **stevocom** » Thu Jul 15, 2010 4:28 pm

Well thanks to all so far who have taken there time to help. So far I have not found anything wrong yet. I have pulled the elbow off the top of the tank and found NO anti syphon and/or NO tube. Seems as if this tube is internaly manufactured into the aluminum tank? How on earth can you inspect it or replace it if it's bad if thats the case? There was anti syphon's installed leading out of the water seporator's which I had temporarly removed due to the problem I am having (process of elimination) but doesnt seem to be the problem, should i re-install them off the top of the tank at this point?.

k9th · Post by **k9th** » Thu Jul 15, 2010 5:48 pm

I just replaced my original galvanized steel tanks with aluminum tanks this spring. Both sets of tanks have a fill tube which had an elbow right on top of the tank. But they all had tube connections a few inches in front of the fill tube that connected the pickup tube to the steel tube running to the fuel selector valves. Each also had an anti-siphon valve at that point also. My starboard side tanks, both new and old, also had an additional connection of pickup, anti-siphon, and steel supply tube for the generator.

There has to be a connection for the pickup somewhere on top of the tank that runs to your fuel selector valve or else you would never get fuel through it.

Danny Bailey · Post by **Danny Bailey** » Thu Jul 15, 2010 9:14 pm

Sounds like your original tanks may have been replaced. The custom built aluminum tanks I installed when I did my repower have pick-up tubes built in like you describe. It may help you to construct a test rig using an outboard motor squeeze bulb, some hose and fittings to adapt to your gas lines. You can use this to tap in at various points in the system to see where you have gas and where it stops. Just put the open end in an empty gas jug and see if you can pump gas.

Just in case you didn't see them....on the stock tanks there were four fittings on the aft end of the right tank. Two suction fittings (engine and genny), one vent (just about the same size as the suction fittings), and the fill fitting (1 1/2 inch galv pipe). Hope this helps

stevocom · Post by **stevocom** » Mon Jul 19, 2010 10:02 am

Well back to the drawing board. Was out over the weekend added another 30 gal of fresh fuel ran the boat 5 miles at 3k, ran great. Went to the beach for a few hours took off again 3k about a mile the starboard started choking down to 1500, sputtering stalling and would not run up over 1200. Im now thinking maybe either vapor locking,Fuel pump or ECU. Any thoughts?