# 1985 (?) Johnson 120 hp low end power sagging



## 1Chief101 (Aug 7, 2010)

Hi all,

New to this forum, but not new to boating. Been struggling with an outboard motor problem for quiet a while and a fellow boater (and PFF member) suggested that I join and lay out my problem. 

I apologize in advance for the lengthy dissertation that follows, but I thought that it would be best to give out all the information on what had been done up to now and to better enable anyone to advise me. 

Subject: 1985 (?) Johnson 120 mounted on a 16’ Bonito bass pro style boat. Motor # on the motor clamp is J 120 ? L C O S. The motor # on the "freeze plug" on the block reads J 140 T L C O S.

History: Bought the boat “used” in Feb 1997, with the motor newly rebuilt. Ran fine from the get-go with WOT RPMs at about 5200.

During the last few years, idle has become increasingly unreliable (I have to input a bit of throttle to keep it running), and it was getting harder and harder to transition from idle to getting on step (at about 2600 RPM). After that speed, it was no problem getting it to transition to WOT.

Last year, decided to have the water pump replaced by a local mobile marine guy. After doing the work, we took it out for a test run. It checked out OK, but as we headed back in at WOT, it suddenly lost a little over 1000 RPM, but continued to run steadily. (I thought that it had dropped a cylinder.) 

After getting it home and finding that the compression checked out ok, he checked the reeds, gaskets, and rebuilt the 4 carburetors. Launched and tested again with no change in performance. Then while checking out the ignition system he pointed out that the epoxy encasing the power pack was soft and spongy. Replaced it and water tested again with no change in performance. However, he noticed that while running at WOT if he held in the choke button, that the RPMs would increase. He naturally suspected the fuel pump and substituted mine with one that he had. We water tested it again and it performed pretty much the same as with my fuel pump. 

Since that time, I have had to be away to deal with the loss of a couple of family members and have just now started back working this problem.

I started by dismantling and cleaning the fuel pump. Found that the little “flapper valve” inside the inlet nozzle was not sealing completely. After much cleaning and flushing, got it sealing properly. Replaced the large fuel diaphragm and ensured that the unused VRO section of the pump was properly sealed off. (Have always premixed oil and gas at 50:1 in the tank). Have replaced the fuel bulb and all gas lines in the system, from the tank to each carburetor. I then removed the drain plug on each carburetor and liberally sprayed the OMC (foaming) Carburetor Cleaner into each fuel bowl, flushing through the high speed jet and out all associated ports. I removed the low and midrange jets and did the same thing. I then flushed the carbs with gas, connected everything up started the motor on the “ear muffs”. After letting it warm up a bit, I then used the OMC Engine Tune, injecting it through the choke shrader valve and let it set overnight as the directions indicated. In the morning, I started the motor again on the “ear muffs” then took it to the water for another test run. 

On this trip, I took along a friend and his portable gas tank with fresh gas in it to eliminate problems with my tank, and to have him pump the fuel bulb while trying to get on step.. The idle was still unreliable at about 600 RPM and I had to have my friend pump the fuel bulb in order to transition from idle up to about mid-range. No pumping was ever needed to throttle up from mid-range to WOT. (I guess cleaning the carburetors helped, as now WOT RPMs were reading about 5500 with the motor trimmed up). Substituted the portable tank and got exactly the same performance and characteristics. 

I then thought that the water separator might be causing a heavy restriction to the fuel, so I bought a glass filter and substituted in place of the water separator. In order to really feel confident that there was no small air leak in the system, I also removed the quick disconnect fitting at the tank and replaced it with a 90 degree 3/8 brass fitting and connected the fuel line with a clamp.

Tested it again on the water and it seemed to perform a little better but still wanting to bog down and die transitioning from idle to mid-range without pumping the bulb. After getting to mid-range, it seems to have no trouble throttling up and down between there and full throttle. But slow down to under about 2300 RPM and just seems to loose power and die.

Well, I’m truly stumped! 

While not yet fully understanding what I’ve read on how the initial timing and throttle cam position is set, I’m beginning to think that the problem may lie in this area. 

Well folks, there’s the saga. I apologize again for the length of this correspondence, but I wanted to give as much info as possible. Should someone find it in their heart to venture some suggestions to me I surely would appreciate it. I am aware of how busy everyone is at this time of year and I want to thank you in advance for any time spent reading and evaluating this.

1Chief101


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## mt0264 (May 8, 2010)

your in luck. I had a friend that had the same problem with a smaller motor that old he added a cheep fuel pump in line that only put out about 2 psi or so and it smoothed right out.


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## 1Chief101 (Aug 7, 2010)

Hi mt0264

Thank you for taking the time to read that dissertation....... I really appreciate you taking the time to answer me personally. Interesting "fix" for your friends problem...I have often mused as to why even fool with crankcase pressure fuel pump....Why not just get an inexpensive electric fuel pump that puts out just about 3 psi and go with that? 

I'm willing to try what your friend did, but I am a little confused... Did he insert this fuel pump in addition to the on board fuel pump, and if that was the case, did he insert it before or after the on board pump? 

Or, did he just replace it completely? 

I have just recently found out that the marine shop here in Ft Walton Beach sells the old style (pre VRO days) fuel pump. The style that you see when you look at an exploded drawing of usually a 90 hp or smaller motor. I told the sales guy that I thought that that style of pump was only for the smaller motors, and he told me that they were used on the larger motors be for VRO came into being..... Cost is about $97. What do you think? 

Once again, my hartiest thanks, 1Chief101


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## jaster (Oct 7, 2007)

Any contact number or the shop in ft walton? I need a pump. my vro is disconected, bypassed, and my pump isnt pumping?


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## jaster (Oct 7, 2007)

, ha, found this post online and now that I am loged on I see it is a year old, dates threw me off. Any idea on where to find a non vro pump under $350?


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