johnson 8hp fuel trouble

[pinboy122]

Hi all, I have a 1985 johnson 8hp(model j8rcob) with a fuel issue.I just bought it and it really ran great as long as I pumped the primer ball.If I would forget,it would die.So I put on a new hose and primer ball and had the same trouble.So today I rebuilt the fuel pump and now it will only run with the choke on.It runs good and will idle nicely but when under power it wont get on plane.If I take the choke off it starts to run the rpms up but dies within 5sec.I dont know why before I rebuilt the pump it would run wide open throttle(when contiunously primed) and now with the rebuilt pump it will only run with the choke on and wont reach peak rpms at all.When I remove the fuel pump to carb hose it squirts out fuel.I guess the logical explanation woud be clean the carb but why did it run fine before?
I would have just pulled the carb but the recoil is in the way of 1 of the bolts and Im afraid to pull it off without a manual, things with springs scare me! What do you think???? thanks Al

 

[AlTn]

Re: johnson 8hp fuel trouble

how does it run now if you pump the primer bulb? does it run like it did before you rebuilt the fuel pump?

 

[pinboy122]

Re: johnson 8hp fuel trouble

pumping the ball doesnt seem to have any effect with or without choke.1 thing to note is that I dont have to pump to keep it running anymore

 

[AlTn]

Re: johnson 8hp fuel trouble

have you tried pumping the primer bulb when you go to wot with the choke off?...right now with only the fuel pump supplying fuel, it runs out of fuel in 5 secs. when going to wot?...my thoughts are these, your f/p isn't capable of supplying enough pressure/volume or a combination of the two to keep the bowl full. If you can squeeze the bulb and the engine with obtain wot, you may have to revisit the f/p rebuild. If pumping the bulb won't allow you to get to wot you've got air entering the system or something has gotten into the main jet or nozzle and is resticting fuel flow.
Things with springs scare you?...check out the price of a new spring at marineengine.com, boats.net, shop.evinrude.com, you have every right to be scared. A factory manual for you model year is available from outboardbooks.com, marineengine.com, or maybe one's available on ebay...it's worth every cent in my opinion.

 

[pinboy122]

Re: johnson 8hp fuel trouble

I started thinking air leak too,so im going to put the pump back on(I took it off again to be sure the springs were in place correctly)And make sure its not leaking air.I really dont think its the carb because it ran so well,but at this point anything goes.To answer your question pumping the ball doesnt make any difference at any speed or choke setting. thanks for the ideas,keep em rollin' Al

 

[pinboy122]

Re: johnson 8hp fuel trouble

I just put the pump back on,made sure the gasket surfaces were clean and same thing.I sprayed some starting fluid around but no rpm change.The ball is hard to squeeze,like I cant force gas into it too much.When i pull the carb feed hose from the pump I get gas shooting out.Also with the engine not running and the pump to carb hose off if I pump the ball,a full steam of gas comes out of the pump but more than when it is running.Im starting to think something in the pump is not 100% right.With the pump off the engine I can blow air through the pump inlet fitting but it seems a little restricted and makes a noise a little like a horn.I cant blow air into the pump discharge fitting.These pumps are a little of a pain to rebuild,I was tryin to be carefull of how it came apart but Im wonderin if I didnt mix something up.A couple more beers and this project is gonna have to wait!!!I just hate buyin a new pump when I already spent the money on the kit.One other thing,the engine starts to die right away when I try tio turn the choke off

 

[pinboy122]

Re: johnson 8hp fuel trouble

I rebuilt the fuel pump(the details are all in previous post)on my 8hp johnson.My question is acording to the instructions when the rebuild is complete you should be able to "blow into the inlet tube but not the outlet tube of the pump."When I do this I get some resistance and it sounds like your blowing into a kazoo or a horn.Is this normal???

 

[AlTn]

Re: johnson 8hp fuel trouble

it's been 2 years since I attempted to rebuild the little square pump on a '78 9.9...same effect you describe, kazoo...this rebuild < 4 hours of "education"> yielded a pump that was no better than what it replaced...found a new pump online $75, installed and it's working w/o problem today...if you want verification of the pump being bad, take it out of mix by covering the pulse hole on the rear of the pump and reattach it to the block, bypass the pump with a fuel line from the connector on the motor to the carb and use the primer ball as the pump. If you get normal operation now at wot as long as you keep it pumped up, then your pump or connections are suspect. That was my experience, fwiw.

 

[Tim Frank]

Re: johnson 8hp fuel trouble

The choke thing suggests to me that you may need to clean the carb.

 

[spunkyjr]

Re: johnson 8hp fuel trouble

Try here thttp://www.sschapterpsa.com/ramblings/OMC/OMC%20info.htm for the step by step instructions for a pump rebuild.

 

[pinboy122]

Re: johnson 8hp fuel trouble

Ok got it!!!It looks like a damn bug must have gotten into to pump to carb hose when i was rebuilding the pump.He was stuck in the needle seat,and now the rotten bastard is dead! Of all things......Thanks for all the help Al