1990 90 HP Merc Fuel Issue?

[69 Alumacraft]

Posting for a buddy. : Problem started when he ran out one portable tank and switched to another. Engine would not go above slow idle without cutting out. He then dumped out in line external fuel pump and filled it with clean gas and it seemed to fix the problem for about 15 minutes. Next he changed the external and internal fuel filters, used fresh new gas. It was fine for a while but went back to 1/2 throttle only with his buddy squeezing the bulb. I am thinking the fuel pump is gone. Also heard anti- siphon valve and check valve could be the culprit. Gas that was in the filter seemed to be water free. Boat is used several times a week without issues this season. How hard is it to drain carbs or is that pointless? Thinking of changing the fuel pump and testing it out. Any advice appreciated.

 

[Bill kubiak]

The ethanol gas we have nowadays is hell on those old motors, anything rubber can and will go bad. Most carbs I have seen have a drain plug on the bottom of the fuel bowl. If you let that e gas sit for 6 most or more it turns to crap, gotta keep sea foam or stabile in there, if you put a bottle of seafoam or stabile in for every 10-15 gallons you buy it will help, but at 8.99 a bottle it really raises the price of your gas per gallon. I now use only ethanol free gas, it costs more but in the long run it works out cheaper then adding stuff. For some really good gas visit your local small airport with some metal containers and get some 100LL av gas to mix with your gas, will give you a good boost and they will not fill plastic gas tanks

 

[roscoe]

Fuel pump rebuilds are cheap, and easy to install.

If he ran it out of fuel, the diaphragm very easily could have ruptured.

 

[69 Alumacraft]

Ok thanks guys I will pass on the advice and report back after we change the fuel pump

 

[Bill kubiak]

The ethanol gas we have nowadays is hell on those old motors, anything rubber can and will go bad. Most carbs I have seen have a drain plug on the bottom of the fuel bowl. If you let that e gas sit for 6 most or more it turns to crap, gotta keep sea foam or stabile in there, if you put a bottle of seafoam or stabile in for every 10-15 gallons you buy it will help, but at 8.99 a bottle it really raises the price of your gas per gallon. I now use only ethanol free gas, it costs more but in the long run it works out cheaper then adding stuff. For some really good gas visit your local small airport with some metal containers and get some 100LL av gas to mix with your gas, will give you a good boost and they will not fill plastic gas tanks

For you non aviator guys 100LL means 100 0ctane with a Low Lead content, and it will give you a power boost, they cannot put av gas in plastic cans, per FAA rules it can only be put into metal cans so they can ground the fuel nozzle to the can before squirting the gas to prevent a static spark, which can ruin your whole day.
All the guys you see running those really fancy Hi speed boats use av. gas or even something even more powerful like the drag race cars use

When I was still flying on the few days prior to big boat races in Miami we used to see dozens of those mega race boats coming to the airport to get gassed up and many of them had plenty of those military style metal Jerry cans that they filled also.

 

[Silvertip]

Octane alone does not make more power. The "high speed guys" you mention have their engines modified and "tuned" with far more spark advance than the everyday boater can use. Higher octane fuel allows increased spark advance which can increase power. Octane retards pre-ignition (spark knock). Any "perceived" power increase from higher octane fuel is just that -- perceived. Non-ECU controlled engines have no way of automatically advancing and retarding spark. If however, the engine was previously tuned (ages ago) for a higher octane fuel but has been burning a lower octane fuel for a long period, then yes -- you might see slightly increased performance. But since outboard engines typically run in the 7:1 compression ratio, high octane fuel is not needed and is a waste of money. This is why today's cars and trucks have one or more knock sensors on them. To run at optimum performance the ECU advances timing until such time as the knock sensor says, you reached the limit. And just so you know -- ethanol has 104 octane. On older engines, change the fuel line and fuel pump parts to ethanol tolerant varieties and go boating using E-10. The conversion is simple and cheap (all things considered). The 6 months to trash philosophy is no longer worth discussing and a waste of keystrokes.

 

[ondarvr]

^^ agree. I'll save the key strokes by not rehashing an old topic like this.