could this issue be the fuel pump

[rpatton]

Last weekend i took my johnson 70 which is a 1975 out for some fun and fishing and it ran great all weekend. This week i took it out and ran great on
Sat but when i took it out on sun it started surging like it was runing out of fuel so i pumped the ball but it was hard, then i backed the throttle to half and it ran fine. On the way back the rpm droped to a fast idle but smooth. Then as soon as i pulled the throttle back a little more it died and i am unable to start it now. i pulled the plugs and the top 2 are tan and clean but dry even after a lot of cranking. The bottom plug looked black and flooded.
Does this sound like a fuel pump or something else. Where do i start?

 

[fireman57]

Re: could this issue be the fuel pump

I would do a compression test first as it doesn't take much time. This will make sure that you aren't beating a dead horse. I suspect though you need to give you carbs a good cleaning as you probably picked up some trash in your tank.

 

[rpatton]

Re: could this issue be the fuel pump

Thanks for the reply. Compression is good and all three carbs where rebuilt at the beginging of the season. As far as dirt the screen isspotless at the pump

 

[pn]

Re: could this issue be the fuel pump

one thing at a time, lucky your compression is good. next is spark, but im jumpin to fuel because that's what i think it is...
to see if your floats are working correctly, you could pump the primer until it stops and then unscrew the drain plug from each carb. gas or no gas.

to check fuel flow, unhook the fuel line post fuel pump and crank, gas or no gas. there may be restriction in your fuel tank pick up, or in the vent pipe as well, blow some compressed air in the hose and the vent pipe. The last reccomendation i think is the best. good luck.

 

[sutor623]

Re: could this issue be the fuel pump

Thanks for the reply. Compression is good and all three carbs where rebuilt at the beginging of the season. As far as dirt the screen isspotless at the pump

If you did carbs without changing your inline fuel filter, or fuel pump, or fuel lines, yada yada, you could still have some dislodged varnish run into your carbs. Drives me nuts when people rebuild the carbs without cleaning and changing the fuel pump diaphragm. I hope this isnt the case, but it sounds like you got varnish into your jets. Running at WOT through an older fuel system is known to dislodge garbage upstream from the carbs.

 

[rpatton]

Re: could this issue be the fuel pump

Thanks i too thought it might be air locked tank but i am runing on fuel cells . When it started acting up i changed tanks and it still did it. I should add that this motor sat for probly 10 years or so. Thats why i rebuilt the cabs and it ran great untill this week. Im wondering if the pump gave out from age and lack of use. Can anyone tell me if this is a simtom of a pump

 

[sutor623]

Re: could this issue be the fuel pump

Thanks i too thought it might be air locked tank but i am runing on fuel cells . When it started acting up i changed tanks and it still did it. I should add that this motor sat for probly 10 years or so. Thats why i rebuilt the cabs and it ran great untill this week. Im wondering if the pump gave out from age and lack of use. Can anyone tell me if this is a simtom of a pump

Yes, when a fuel pump first begins to fail it typically will do so at WOT. That diaphragm is a simple piece of rubber. If it blows a hole in it or gets weaker, bye bye fuel pressure. This motor sat for 10 years and you didnt change out/clean the fuel pump???

 

[rpatton]

Re: could this issue be the fuel pump

Yea i know it was a bone head move .even worse i have a new to put in it. Guess ill start there and see . Fuel lines and screen where replaced . Dont have a inline filter

 

[sutor623]

Re: could this issue be the fuel pump

Okay, well go to auto parts store or walmart and get a 5-7$ inline fuel filter for your main tank line (which Id consider changing out if its been a while). Worth every penny. Then, check your compression if you have a tester. Make sure you didnt run lean and do any damage to cylinders. If I were you I'd change out the fuel pump, and fuel lines then put a heavy seafoam mix into the fuel tank and let it run for a while on muffs, monitoring temperature at each cylinder. If you have varnish in the carbs hopefully this will get it out. Just be aware that many outboard failures happen due to a very small piece of debris getting lodged into one of the main fuel jets in a carb.

If you were extremely paranoid as I am, you would take the three carbs off and drop the bowls, and spray a little carb cleaner through the main and idle jets. I have an '84 3 cylinder very similar to yours, and it really takes under an hour to get carbs off, check the jets, and then replace them. Some on here will tell you to swap the fuel pump out, and then gun it, but I wouldnt want a small piece of that blown fuel pump diaphragm running up into one of my jets, only to find out WOT 8 miles from the dock with my wife onboard. Either way, do whatever YOU feel necessary to have some peace of mind while on the water. Not sure about you, but when its 80 and sunny and I actually get a chance to be on the water, the LAST thing I want to worry about is having motor troubles....

 

[fireman57]

Re: could this issue be the fuel pump

I always like the reply: Compression is good and I cleaned the carbs last year or whatever time frame it was. Any piece of junk screws it up. Have just been lurking to see what was going to happen here. You are right sutor, takes an hour to do the carbs again and cost absolutely nothing but your time. At worst it eliminates them from the equation if they are done right, at best, it solves the problem. Give me the willies when guys just want to throw parts at problem.

 

[rpatton]

Re: could this issue be the fuel pump

Just an fyi fireman the boat has exactly 6 hours on rebuilt correctly carbs . The only mistake i made was to not replace the fuel pump. Ipulled the bowls and checked them out and they are spotless. Put the new pump on and it fired right up. Pump was not ruptured but looked very stretched out. I was going to ask about changing the water pump . Especialy the linkage but dont want to get scolded again. But truly a thanks to have helped

 

[sutor623]

Re: could this issue be the fuel pump

Well Im glad to hear she runs after a fuel pump kit. That diaphragm can only last so long..... If that motor has sat for 10 years you NEED to change the water pump and thermostat. It will be flowing water fine, and then one day at high rpms, you never know what could happen to that 10+ year old piece of rubber.

Hahaha, and no scoldings here! We here just all understand how truly easy it is to torch one of these motors, just by simple neglect. Learn the ins and outs of your motor. That way if something were to pop up you'd know right where to start.

 

[rpatton]

Re: could this issue be the fuel pump

Thanks sutor no problems. I was just venting. Water pump is this weekend. Any tricks i should knowabout linkage. Im a merc guy and this is my first johnson

 

[sutor623]

Re: could this issue be the fuel pump

There is a screw up top you have to remove to drop the gearcase. Right under the starter. I just use an angle socket to get to it. DONT SPIN THIS ROD once the unit is dropped. There are threads at the bottom of it so if you spin it you can mess up the height. Other than that its all easy going.

 

[fireman57]

Re: could this issue be the fuel pump

rpatton sorry about my rant. It's that time of year I guess. Glad it's going better but YES YES YES on the water pump. If I remember correctly it is easier to get that bolt out with it in forward. Just make sure you have the shift rod in forward when you put it back up in there.

 

[rpatton]

Re: could this issue be the fuel pump

No problem fireman i to gave days like that. Just a thought , could a motor that is runing hot create the problem i had?? I would like to install a tell tail on it since there is not a factory one but all the service bulitins and info i have found are newer motors so i am afraid to drill into the motor. Anyone have any thoughts

 

[fireman57]

Re: could this issue be the fuel pump

running hot will slow and stop an engine. You can put a telltale on that engine. It goes on the very top of the head. If you do a search I know you will find it. We did it to a '77 70hp just to make sure that plenty of water was getting to the top of the heads to cool them and that there could not be an air pocket develop there. If you are wondering if your engine did overheat then pull your head and look for scoring in the cylinder. If you have plug that is clean and the other's are chocolate or darker then you have a bad head gasket and are burning water. You will need to buy a new head gasket if you do this because you should never reuse an old one.
The reason I wanted you to do a compression test right away is because it sounded like it overheated. You said the numbers were fine but don't know if that was before or after this happened.

 

[rpatton]

Re: could this issue be the fuel pump

thanks ill check it again since it was before the issue. iwill repost later with the numbers

 

[gm280]

Re: could this issue be the fuel pump

Just for the record, I had a 1976 40HP Johnson and was rebuilding the engine and wanted to check and verify everything. In doing so I cleaned and run a vacuum test on my fuel pump. And of course it worked and held vacuum fine. Then I run a pressure test on it as well, and again it help pressure just fine also. After a few days I had that gut feeling that I should completely disassemble it just to be absolutely certain. Well surprise, surprise! While it did test good with both vacuum and pressure, the diaphragm was completely hardened up and was as stiff as a piece of cardboard. So much for the testing. I bought this OB from a guy and didn't know if the fuel pump has ever been changed, so that was my reason for testing it. But I should have just bought a rebuild kit and be done with it...which I did anyway now... So even if a diaphragm is not cracked or split or has any hold in it, it still can be bad. Had the exact same issues with two pieces of yard equipment this season with hardened up diaphragms in the carbs as well... :joyous:

 

[rpatton]

Re: could this issue be the fuel pump

UPDATE I checked the compression. top cyl is 143 lbs middle is 140 lbs and bottom is 140 lbs so i am assumeing i fine . guess my next step is to put the water pump in it and see if it does it again.