fuel pump question 68 merc, 20 hp

[JBK248]

My fuel pump is not working, I have replaced the diaphram and the hoses that go to the block. I checked all the fittings for blockages and so forth. I am really stumped on this one and could use some direction. oh yeah I also checked the fuel lines to and from. really have no idea what else to do on this one. thanks.

 

[JBK248]

Re: fuel pump question 68 merc, 20 hp

bump for help

 

[jtjt]

Re: fuel pump question 68 merc, 20 hp

do a compression test, if the cyl the pump runs off has low pressure it wont operate the pump properly. Also check the fittings at the tank, any leaks even on the smallest scale will render your pump useless, also make sure that when its flashed up that theres nothing shooting out the carb cause a bad reed sucks aswell.

 

[JBK248]

Re: fuel pump question 68 merc, 20 hp

do a compression test, if the cyl the pump runs off has low pressure it wont operate the pump properly. Also check the fittings at the tank, any leaks even on the smallest scale will render your pump useless, also make sure that when its flashed up that theres nothing shooting out the carb cause a bad reed sucks aswell.

Ok, 130# at each cylander. Triple checked all fittings. Maybe this reed valve you speak of. What, where is it and how do I check it? Thanks

 

[Wingedwheel]

Re: fuel pump question 68 merc, 20 hp

Double check your Diaphrams in the pump. I know that I've put one in backwards before and it wouldn't pump. I figured it out finally, but it was frustrating at first.

 

[JBK248]

Re: fuel pump question 68 merc, 20 hp

http://store.oldmercs.com/product_p/53245a1.htm

This is the diaphram i used. The exsisting set up only used the 3 parts on the right side. Do i need the piece on the left? if so where would it go? The diagram i have in my manual shows a different fuel pump all together. so, it is of no help. thanks if anybody knows the answer

 

[jtjt]

Re: fuel pump question 68 merc, 20 hp

The reed valve generally sits right on the other side of the intake, inside the block. You should be able to flash up your motor by pumping the bulb and to some extent keep it running, once its running look for gas spraying out the throat of the carb, the reed is a one way valve that seals when the piston is on its down stroke, if its not sealing youll notice it, pretty rare for the most part. Spray your fittings with soap and water and look for bubbling remember your not looking for fuel leaks your looking for vacuum leaks, it sounds strange but true where a fitting will hold fuel but as soon as suction is applied to it a small air leak will occur thats all it takes. If you cant get your engine to run by priming the bulb or supplying the carb with fuel by some other means you have other issues. also spray soapy water around the block area where the pump mounts to the block, check that area for leaks, always do those checks with the engine running.

 

[JBK248]

Re: fuel pump question 68 merc, 20 hp

Wow, great tips, thank you. Will update when done.

 

[JBK248]

Re: fuel pump question 68 merc, 20 hp

ok, i was able to do the soapy water test and didnt find any leaks around the fittings, hoses or fuel pump. I can keep the motor running with the primer bulb no problem. Sometimes, it will pump fuel without me pumping the bulb. I didnt notice any fuel dumping out of the carb when i tested it. where to go from here? reeds? would that be intermittent or is that something that is constant? thanks guys

 

[jtjt]

Re: fuel pump question 68 merc, 20 hp

Getting into swapping your reeds out is nothing short of a total tear down and a total pain in the *** and probably not your issue, the only other thing i can suggest is to make sure the pump was assembled properly, other than that im lost myself cause its all pretty straight forward from there, its kinda hard to help people over these forums without actually being there to look at it, sometimes you just gotta break down and take it to the local pro!

 

[JBK248]

Re: fuel pump question 68 merc, 20 hp

ok, looks like i am missing the spring loaded stem that goes into the reciever portion of the adapter to which the the fuel line from the tank goes to. I assume this device only prevents fuel from spilling out when the fuel line is removed?? or could this effect the fuel pump?

 

[jtjt]

Re: fuel pump question 68 merc, 20 hp

Your right i think it just prevents fuel from splashing out when you remove the fuel line but it wouldnt hurt to grab another one and give it a try. Also im not exactly sure how you have your engine set up wheather its on a boat or a stand but keep in mind that those little pumps will only pump uphill so far, so if your engine is up high on a stand/boat and your fuel tank is on the ground down below it could simply be struggling to pull the fuel up that far, i dont really have an answer for you im just throwing **** out there!

 

[JBK248]

Re: fuel pump question 68 merc, 20 hp

thanks for all the advice jtjt! I did some more testing and tinkering today. results are It will run all day at low rpms, circled the lake. Idles about as good as can be expected for being 44yrs old. Once i get into the throttle and open it up it runs out of fuel in a few seconds unless I pump the primer bulb. and even then it really doesnt run well. Not sure what the next step is besides calling for reinforcments or going another direction.

 

[JBK248]

Re: fuel pump question 68 merc, 20 hp

ok, after much tinkering and checking and rechecking It is my unproffesional opinion that the fuel pump is working just fine. However, I believe that the motor is sucking air between the intake and the cranckcase. Next question. Should I give up on this or attempt to fix.? Really, I dont think I have it in me. I have already spent too much time on this thing. I know it looks like the whole thing has to come apart to get to it. ugh..

 

[jtjt]

Re: fuel pump question 68 merc, 20 hp

If you think you have a vacuum leak somewhere try running the engine and take a propane bottle with a torch head on it (dont light it) turn it on and point it where you think its leaking, if it leaks you will find a sudden change in rpm as the engine sucks in the propane, try to keep it away from the throat of the carb though as it will naturally give you the same result. Other than that yes it will be a pain in the *** to do the job but not impossible and usually just a gasket so not terribly expensive, it never hurts to test yourself and while your in there clean your carb aswell and hopefully when your done you ll have a decent motor and literally know it by the back of your hand.