At Wit's End on Johnson 40 1987?

[mmarino]

JTLCUD. I just rebuilt both carbs, and my fuel pump. When I fired it up in the driveway with the water earmuffs, it idled like a champ in and out gear and ran in gear at high rps really well. I took it out on Lake Mead to give it the final test, and wummph! It idles in gear better than before the rebuilds. It would then run at about 2000 rpms rather well, but after that when I tried to give it full throttle, gradually or quickly, it completely bogged down and would die unless I would quickly back down on the throttle. But if I held in the electric choke at the key and didn't let it out, it would take off like a jet and run really well at the higher rpms and full throttle. It would run like a champ for as long as I would hold the choke button in. AS soon as I would release the choke it would run a second or two longer then die completely unless I would again back down on the throttle quickly. I'm frustrated and not sure what to do next. Any ideas would be greatly appreciated. I feel like I'm going backwards. Followed directions from the manual for the rebuilds and used some prior advice from Iboats to verify. VRO has been disconnected running oil and gas mixed. New plugs.

 

[1946Zephyr]

Re: At Wit's End on Johnson 40 1987?

It sounds to me, like your fuel pump is not keeping up with demand. You have two carbs on a 40? WOW! You'll need a very good fuel pump to keep up with that kind of demand and if it's a little weak, you'll have issues like this. You also might check the fuel flow and make sure all the lines are flowing fuel freely. Any restrictions can cause fuel starvation too.

 

[HybridMX6]

Re: At Wit's End on Johnson 40 1987?

Honestly it sounds like the high speed jets need more attention. I don't see how the fuel pump would be the problem seeing as he just rebuilt it, and since choking it won't matter if the pump was bad because the fuel still has to go through the pump and filter first, at least it does on my 60hp.
Are you sure you cleaned the high speed jets out as best you could? I've heard you really have to clean them very well, even to the extent of using wire to run through them to get everything out.

 

[1946Zephyr]

Re: At Wit's End on Johnson 40 1987?

Well, that may be true, but it's always worth the effort of testing the fuel pump. New ones have been known to fail too, in my recent experience.

 

[tashasdaddy]

Re: At Wit's End on Johnson 40 1987?

did you do the link n sinc, after carb rebuild? as said the high speed jets may need more attention.
http://forums.iboats.com/showthread.php?t=244013

 

[mmarino]

Re: At Wit's End on Johnson 40 1987?

I read your link on the steps to rebuild. Unsure of the lync n sync suggestion. Could you explain? Thanks to all who are trying to help.
I'll look at the high speed jets again. From what I remember, I had them both out and cleaned and air compressed blow outs, and visually could look through them.

 

[Bear 45/70]

Re: At Wit's End on Johnson 40 1987?

Your choke test tells me the fuel pump is fine. The carbs are too lean. Could be the float levels are too low and/or you need to change the main jets. If it ran OK before, then you need to make sure all the passages in the carb are clean. I prefer to use WD-40 or BrakeKleen to spray thru the passages. FYI, OMC always warns to never use high pressure air to blow thru carb passages. They say 35 PSI or less only. The fuel pump on the 40hp is the same pump the the 3 cylinder, 3 carb engines run.

 

[mikesea]

Re: At Wit's End on Johnson 40 1987?

I would bet the carb body has a clog somewhere,its always best to soak in a carb cleaner and then rinse with warm soapy water,blow dry with air or get a can of spray carb cleaner for FINAL clensing.The choke is the key answer to the prob being in the carb,you know your getting the fuel to the carb,just not from the carb at high speed

 

[mmarino]

Re: At Wit's End on Johnson 40 1987?

Thanks a lot to everyone who has helped. I'll follow up on the carb restriction and see if I can't get some results. Get back with the Forum, hopefully with good news. You guys are great for giving of your time and expertise.

 

[Boatdood]

Re: At Wit's End on Johnson 40 1987?

One more thing it could be is that you missed the gaskets that slide over the high speed tubes leading to the throat of the carbs. You've got to have that passage sealed or the gasoline that flows through the orifices you just cleaned cannot get to the throats. Look for the brass tubes which extend to the lower regions of the bowl of the carb. They are about 1/4" diameter. At the base of those tubes where they are pressed into the carb body there should be a gasket slightly smaller in diameter than a dime, round on the outside and with three triangular shaped retaining tabs on the inside.

 

[HybridMX6]

Re: At Wit's End on Johnson 40 1987?

I read your link on the steps to rebuild. Unsure of the lync n sync suggestion. Could you explain? Thanks to all who are trying to help.
I'll look at the high speed jets again. From what I remember, I had them both out and cleaned and air compressed blow outs, and visually could look through them.

I'm about as clueless about the "linc n sync" as you. I've searched around some, nothing helped explain it. Just referals to do it.

 

[Bear 45/70]

Re: At Wit's End on Johnson 40 1987?

"Link and sync" or Sync and Link" refers the doing the tuning procedure where you adjust the linkages to put the idle timing, carb pick, max timing and WOT for the carb in synchronization. So the motor will idle, accelerate ans run at WOT properly and everywhere in between.