Fuel Pump? 1988 Johnson 48 SPL

I finally took the boat out yesterday for the maiden voyage yesterday. Almost lost my antique truck in the lake while launching but thats another story

We went out twice yesterday. First time the 48 Spl motor ran fine the 40 minutes we were out on the lake and cruised around nicely. However when we got back to the dock I cut it off and it wouldn't start....checked and the starter bolts had come loose (maybe were never tightened)

So fixed that and when the wife came home we went out again, using her van to launch this time, and had a blast.

However after about 20 minutes of cruising at about 1/2 - 3/4 WOT all of a sudden she started surging, then slowing down until we were cruising at about 1/4 throttle even though the throttle lever was at WOT

Seemed the best we could get was a slow cruise out of it but she didn't sputter and didn't die. I could shut it off and restart and she idles fine.

Just before we made it back to the ramp I happened to push in the key (the "cold start" button) and she lept out of the water and took off (remember that throttle lever still at WOT)

If I held the key pushed in she ran like a champ. Soon as I released the cold start button she was back to only 1/4 throttle

I thought at first fuel pump, but wonder why it runs great with the cold start lever pushed in?? On this motor it's not a choke assembly, but more of an injector according to tashas D that squirts some fuel directly into the cylinder for a cold start.



Any suggestions?

One thing I will say for this motor is it DID NOT leave us stranded and kept on chugging.

Re: Fuel Pump? 1988 Johnson 48 SPL

was the vent open on the fuel tank? if it was it sounds like you need a carb cleaning and rebuild kits. these carbs are just like yours. http://forums.iboats.com/showthread.php?t=244013

also in that motor if the fuel line have not been changed.
Ethanol and fuel lines
replace all fuel line with Alcohol resistant lines. Ethanol deteriorates, the rubber lines, then they start to sluff off on the inside, going directly to the carbs. Settling to the bottom of the bowl. Contaminating the carbs high speed jets. clean a rebuild carbs, flushing fuel line before connecting to carbs.

Re: Fuel Pump? 1988 Johnson 48 SPL

Sounds like a boring case of the carb needing a clean.
Turning the manual lever on the priming pump to the start position should have had the same effect as holding the key in.

Now tell us the more interesting tale of how you nearly lost your truck. Any pictures?

Re: Fuel Pump? 1988 Johnson 48 SPL

Yeah thats about what I figured, carb clean.

However the puzzling thing was how great it ran with the key in. If I have a fuel line, bowl, or jet blockage how is it that just the little cold start squirt could make it run so well, and for so long. We motored back to the ramps with the key in (about 8 minutes worth)

I'll pull the carbs later today I hope. Gotta Subaru CV axle to change first.

So you asked for it.....the truck story. I own (#9) a 1968 International Scout 800 with 3spd, 152 4 banger (2.4 liters), and manual Drum Brakes all round

So here's the "rest of the story"

I loaded up my son (11yrs) into the scout and headed to the lake

1st problem: The boat is WAY heavier with motor and gear than when she was empty at purchase and towed home with scout. But we made it....The scout doesn't like the hills but chugged along....everyone behind us hated me but @#$@ em

2nd problem: The boat ramps are MUCH steeper than I remember (been a while since I've been there with a boat) The scout is 41 years old, and has MANUAL DRUM brakes all 4 tires. Backing down the ramp was fun, and just as the trailer touched water the brakes gave out (master cylinder) and I damn near lost the whole truck into the lake.
Saved it at the nick of time, Spun rubber on the boat ramp, Got the brakes pumped back up again and shut it off in gear. OK we're stopped now....whew!! Boat and trailer are in the water. No choice now, GOT to unload the boat to get the truck out. Managed to do so without much more incident, and didn't lose the truck (she's an antique you know). I sunk the back tires halfway in the water.

Park the truck and back to the boat. Up goes the bimini and tried the engine. Starts right up Me and the kid head out onto the lake and motor around for about 40 minutes and have No issues so far

Call the Wife who luckily works a few miles from the ramp, tell her to come rescue us as I am NOT trying to back down the ramp again in the scout until I overhaul the brakes (and probably not then either).

She shows up with her minivan, swap trailer over, yank out the boat, switch back, and annoy traffic again with a slow 10 mile drive home.

It was a close call, when the brakes gave I had about 2 seconds to "do something" before she went in the water to the roof

Ahhh, memories ya know



As far as the carb, I checked Iboat store and they only show a carb kit for 48 special 1992 - 1997....I was told mine is an 88 (or 87) year

Same kit?


Think I will break them down first, might not need a kit (probably will) but these carbs look even simpler than lawnmower carbs and I have "rebuilt" quite a few without a kit. Hopefully I can get her going enough for one more weekend (the 4th) and order the kits as well, then completely rebuild them later


Hope you enjoyed the truck story, I didn't lol

Re: Fuel Pump? 1988 Johnson 48 SPL

Scary isn't it when brakes fail. Closest I've come was when a vacuum valve on a servo stuck and I had no servo assist. Fortunately only travelling slowly and was able to pull up on the hand brake anyway.
Good job it did not fail on you doing an emergency stop in heavy traffic. That could really have been nasty.

Your carb kit. I make the original OMC part number 398729 but replaced by 396701.
Also Sierra kit with float 18-7222. or 18-7042 without the float

All three in stock at, dare I say it, MarineEngine.com
The Sierra kits are listed on iBoats for a whole load of models


At the boat yard we use an old tractor/digger for launching boats. Its brakes did not work at one time although they do now ... sort of. We always attach a wire to the trolley or trailer so that the digger never goes onto the slip way.