74 johnson 4 hp

aloha
just picked up an old 4hp motor fairly good running shape
was wondering if you master techs can educate me on the finer points
to get her running smooth on low speed it wants to die out some times
just wondering what my mix ratio should be for optimum running
and what octane gas we should run and how to properly tune
the slow and fast rich and lean controls?
mahalo

Re: 74 johnson 4 hp

Has it been running recently or has it been sitting for some time? Great little motors for sure. I would start by doing a compression test and writing down the numbers. From there it depends on how much you want to spend with both money and time. I would clean and rebuild the carb., check the points and coils, plug wires, replace the impeller and gear oil, etc., but only after I checked the compression. You can get a factory service manual (Johnson or Evinrude) for your specific year. The gas oil mix is 50/1 and just regular unleaded gas. Best of luck. Rick.

Re: 74 johnson 4 hp

Do not use 50:1 in that engine it will cook it. Use 24:1 16oz of TC-W3 oil to 3 gallons of fuel. Your engine does not have needle bearings. The book says 50:1 but that engine really needs to have 24:1. If your engine hasn't had any maintenance to it then it will need the following.

1 New fuel lines under the cowl the large one is 5/16 the small one is 5/32.
2 A new gas line from the tank to the engine.
3 Carb rebuild kit
4 Fuel pump rebuild
5 water pump impeller
6 Change the gear lube 80W90

The fuel lines and rubber gaskets and diaphragms are not compatible with fuel that contains ethanol. The alcohol will break down the rubber. The water pump you want to change out just because you don't know when it was last changed.

The following is a very good resource to use http://www.sschapterpsa.com/ramblings/OMC/OMC info.htm

He has great instructions on rebuilding the fuel pump and tune up. The 6 horse instructions work well but so well the 9 and 15 instructions for the ignition system.

Use the parts schematics to help you take it a part and put back together.

http://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1974&hp=4&model=4436R

Re: 74 johnson 4 hp

aloha
thank you for the replys and advice it has been sitting few months,i dont have a compression tester but local mech does hes good and nice so ill prob
hire his professional help as i dont want to mess it up and rebuy parts,runs nice when open but when slow she sputters at times i think its the pressure but im
not sure,i bought it from a old timer who had it for a few years and used it often.ill ask the mec to do a comp test and ill probably purchase complete tune up kit
and do the 1-6 like you advised hidef,unfortunately i believe with the use of ethanol(damn corn) it has worn down some rubber as my bubble on fuel line wont
get too hard so maybe a fuel pressure or air issue but fairly small just making it run wonky on low speed,thats some serious cash to throw down to get it right
so ill have to save a little and do it right thanks for the help guys
and as for mixture i went to 40 to 1 last fill up i didnt want to jump to 32 to 1 as chinewalker advised someone else, i wasnt sure if it would flood or foul it up,
i used to ride dirt bikes some and understand 2 strokes a little but am no mechanic my roommate and best friend was so he educated me a little,he was an amazing
mechanic,and passed away in a motorbike accident so i havent rode since and lost touch with tinkering with motors,ill go to 24 to 1 as you advise and see if that helps and check
fuel lines to make sure pressure is good,then ill start the tune up it prob need it done anyways.
lastly anyone have experience with stich and glue boats im planning to build my first 16ft boat from spira int. to learn and maybe step up to a 24-28 ft one day
mahalo