Lazey Johnson, why?

[Wynand N]

Took the boat out Thursday after work to test new prop with slightly different (1/2" more) pitch that the one I destroyed, and she went like crackers with 3 persons on board. Took it to the shop and left it until today and took it out again for some fishing.

She started at the touch of the button, idled nicely, in gear and slowly crept out through the reeds to open water. However when I opened the throttle what a disappointment - it refuses to rev up and get onto a plane. It sounds like the engine labors and turning about half its normal rpm with a slight miss under load.
Stopped, put it in neutral and revved it up, again not revving high and I would say half its full throttle rpm, again with a slight offbeat at revs. Turned the lean/rich screw slightly but to no avail. At low revs in displacement mode she runs like a charm until I feed some throttle. From half throttle to max no difference in sound, output.

What can be wrong - 2 days ago excellent?
The motor is a two stroke older Johnson 40Hp two cylinder (1973 with only 140 true hours used) and like new. After 30 years of storage the engine received a precautionary reconditioning about 45 hours ago.

[Fanie]

Can your fuel tank breathe ?

[Guest625101138]

If it was fuel related you would expect it would rev out under no load. The initial problem sounds like the high speed butterfly in the carby is not opening. Do 40HP have twin butterfly valves? I have seen these gum up after sitting for long periods without fuel being drained but you would expect this to have shown up first time not second time.

Seems more likely to be ignition. Maybe arcing across a coil. Could possibly see an arc in the dark. Can sometimes hear the arc crack above engine noise at idle with the cover off. Was it a cold damp morning? Was the engine damp after the initial use?

Rick W

[waikikin]

Wynand, I had a similar issue with an outboard, turned out it was some "fluff" partially blocking a needle & seat arrangement in the fuel supply/carby, hope you get it sorted & regards from Jeff.

[Wynand N]

Fanie, first thing I did after it refuses to rev up high in neutral, was to open the tank and checked out the breather and also the fuel filter.

Rick, The boat & engine had covers on and sat in my workshop since Thursday after the test run with new prop. We actual launched at around 13h00 - midday for some fly fishing and it was hot and slightly windy. Will check out the ignition tomorrow, but the engine is completely dry under the covers.

Thanks for that tip Waikikin, will check it out tomorrow as well - btw, I did not burn/drained the fuel in the carb off when switching her off before loading on trailer.

[Guest625101138]

The sort of gumming up I am referring to does not happen overnight. I have only seen it occur when the outboard has been stored for months without running. That said I always ran the fuel out if the outboard was going to be stored for a few weeks and never had the problem.

I would not get anal about emptying the carby unless it was going to be stored for a while. The problem I saw may have occurred due to the fuel being left connected and continuing to feed the carby over a long time from a pressurising tank. It took quite a few hours to free it up.

Rick W

[Manie B]

Hi Wynand

my experience over the years has shown that 90% of these problems are carburettor - 10% spark

many of these two stroke engines were fitted a Tillotson carb or something similar - basic principals

they work well for long periods of time but i have come to the conclusion that the alcohol in our fuel is not good for the diaphrams

i have repaired many many of these carbs and the most important thing is to try and get a new carb kit. They are cheap. Next important is i always run the carb dry after usage - even on the compaction machines

herewith the Tillotson manual - save it - you may need it on a rainy day

[Wynand N]

Found the culprit.
When I opened the engine cover I noticed some suspicious oily substance on the cylinder head. It turned out one of the spark plugs came loose and I removed it by hand! Replace both spark plugs, cleaned the carb, jets and put it all together and off 2km down the road to the local dam for a test run and some carb adjustment.

She went like clappers again Tomorrow is a PPH and Im of to hurt the catfish /bass at the dam where one can only get to by boat.

[Guest625101138]

Wynand
Appreciate the feedback. Something to put in the memory bank.

Wasn't too far wrong with it being ignition.

Like I said, a fuel problem should not prevent it from revving out under no load.

Rick W

[Boatpride]

Carb kits are extremely useful and as fuel delivery is such a penicaty (excuse spelling) part of the engine even more so. Interesting thread to learn from - thanks guys.