The Fuel Pump Diaphragm Blues !

1985 Force 85hp. I replaced the fuel pump diaphragm. It Ran before, up on plane and all, just not very well. When replacing the spark plugs the third cylinder, bottom one, always did not show ware/combustion. Spark was good so I asked on here and got the suggestion that the fuel pump diaphragm is leaking and flooding the lower cylinder.

I opened the fuel pump and the diaphragm had a tear. THERE YOU GO I SAY! I replaced the diaphragm and gasket. Now it starts fine but as soon as I try to launch it dies. ??? When I replaced the diaphragm, I tested at home first. Started fine then it blew the hose from the fuel pump to the carbs off. I thought, this is good! New diaphragm is working - more pressure. It idles okay, but dies when I put it in gear and try to give some throttle? Any help would be GREAT !!!!!!!!!!!

Re: The Fuel Pump Diaphragm Blues !

Do a compression test and then a spark test an all cylinders and report your findings,J

Re: The Fuel Pump Diaphragm Blues !

It blew the fuel lines off the inlet? Did you remember to clamp down the fuel lines tight to the inlets? It sounds like you might be having air leaking in.

Re: The Fuel Pump Diaphragm Blues !

jerryjerry05 said:

Do a compression test and then a spark test an all cylinders and report your findings,J

Click to expand...

Hey Jerry... Motor ran before the diaphragm change, just not well. I did a spart test on all three - Good. Have not done a compression check but don't know how changing the diaphragm would affect that.

Re: The Fuel Pump Diaphragm Blues !

erikpn said:

It blew the fuel lines off the inlet? Did you remember to clamp down the fuel lines tight to the inlets? It sounds like you might be having air leaking in.

Click to expand...

Fuel line from the pump to the carbs did not have any clamps on it. Guess it's been that way. I put clamps on both ends.

I took the fuel pump off again and the diaphragm looks fine.

?????

Re: The Fuel Pump Diaphragm Blues !

Rechecked the linkage, second time out and still.. Starts ok, needs some choke, then I put it in gear and chug chug die. A little throttle, a lot of throttle, it does not seem to matter. What can change just by putting in a new fuel pump diaphragm??? Appriciate the help.

Re: The Fuel Pump Diaphragm Blues !

Did you reassemble the pump right?Something as simple as a valve or diaphram in wrong will screw things.After the compression test and all is fine.Start it and spray starting fluid around the motor to see if anything either speeds up or slows down the motor.
Poor performance and good spark can mean a bad head gasket.
There are steps to diagnose a problem and a comp and spark test are the first things you do.J

Re: The Fuel Pump Diaphragm Blues !

Carbs could need cleaning..?? Carb kit possibly in order if it hasnt been done in a year or so.

Re: The Fuel Pump Diaphragm Blues !

Thanks Jerry and cbercaw,

I pulled one of the carbs less than 10 hours ago (motor hours). It was clean as whistle. I'll check again. I'm also rechecking the spark and doing a compression check. I'm still looking for what could have caused such a great difference when all that was changed was the diaphrgm. This should not have caused electrical, compression or other problems. I did not take the fuel pump apart, just pulled it from the block and replaced the diaphragm and gasket.

I do not see air or fuel leaking but perhaps the gasket is not sealing?

Re: The Fuel Pump Diaphragm Blues !

Try this.

1 Sorry, pull the pump off again.
2. Gently push the poppets of the check valves and see if they are sticking. Note their color. The ones that stick are a clear orange color, the new ones are charcoal grey.

Report your findings.

John

Re: The Fuel Pump Diaphragm Blues !

Pulled the pump again. The little dohickies are closed and open with a easy push. Perhaps the new diaphragm is pushing stronger and they are unable to close when required? Pics added...

Re: The Fuel Pump Diaphragm Blues !

The fuel pump is operated by the action of the pistons going up and down. Blow air through the holes at the base of the pump and make sure they are clear. They are shown in the second picture of your series.

When you start to advance the trottle, you start moving the trigger via the tower linkage. You may have a wire that has a bare spot and is contacting ground. It may just be a coincidence that it has happened now.

Will the engine idle at 1000 rpm or so with the trottle in neutral (not fast idle)?

If you advance to fast idle (not placing it in gear), will it advance to 1800-2000 rpm?

I need the info in order to troubleshoot your problem.

John

Re: The Fuel Pump Diaphragm Blues !

Hi John,

Thanks for the help. I don't think I have a wire grounding but I'll check. Motor need choke each time I start. When it dies it seems almost like it is flooding. Starts, fast idle okay, slow idle okay, put in gear at idle it keeps running but as soon as I advance it goes bad, chug chug for 2 to 3 seconds and dies. Small throttle, full throttle the same. I did try in reverse once and it ran. I should test that more.

Re: The Fuel Pump Diaphragm Blues !

Force engines are notoriously cold blooded and require more choke than other engines. That is of no concern.

Have you checked the carb/timing sync? Since you said that the engine ran in reverse, you may have a problem with the syncronization of the carbs and timing. If they are not sync's correctly, the timing will not advance as you are adding fuel and this will cause the engine to run poorly or not at all.

In order to do a sync check properly, you must start at the begining and do all the steps. Any shortcuts usually result in poor performance.

The Clymer and Seloc books both illustrate this procedure well enough. If you need assistance, just ask.

John

Re: The Fuel Pump Diaphragm Blues !

My Force 50 HP 507Y8C has similar symptoms. Few questions: Q1-My hose doesn't have clamps (picture#2) and the hose is stiff / spins easily - should have clamps correct? Q2-Per picture#4 the valve held down with 2 screws doesn't have a gasket - should have a gasket - correct? Q3-I am not sure how the valve operates - How do I know if the valve is bad? The diaphragm is not torn but seems stretched - will replace.

This is what led up to checking the fuel pump...
The motor ran fine up until this past season... I had changed to a different set of plugs and the speed went from 17 mph to 23 mph then the next time I went out the motor began running slow at full throttle. I am not sure if this was a coincidence or if the plugs caused the problem by running too hot or vice versa. A mechanic told me a cylinder was out so I decided to check the coil. I removed the coil and noticed the previous owner replaced the coils but the blue wire was pressed between the back of the coil and the housing bolt. The insulation was worn/burned off. I repaired the wire and remounted the coil. The engine fired right up and idled smooth. Took it out on the water it ran great the first 10 minutes then bogged down and eventually cutoff and wouldn't start.

I checked the fuel line and the bulb pumps fuel. I then removed the fuel pump and it appears ok. I will get a fuel pump repair kit and replace the fuel lines connecting to pump since they are not flexible (replace primer bulb).

Once the fuel lines from the tank to the fuel pump and the fuel pump is repaired I will fire it up. I will then check the carburetor... Does this sound like the right direction? Any feedback will be very helpful.