4hp 1973 Johnson-plz read

Discussion in 'Boats and Motors' started by NorthSouthOhioFisherman, Oct 18, 2007.

  1. NorthSouthOhioFisherman

    NorthSouthOhioFisherman The Young Outdoorsman

    This is a short shaft tiller good condition motor. It does not have handle controls they are on the side. When u go full speed it only goes about half of wat it normally does. Smells a little of oil. Brand new plugs. runs fine on idle and works fine just wont go fast. Wat is the prob any suggestions? carb? Thanks for any help!
  2. Wannabitawerm

    Wannabitawerm Flatulent Entreprenuer

    Sounds like a stuck float or a bad fuel pump, if it has one. I would pull the carb, blow it out real good with cleaner and try adjusting the needles to see if that helps.

  3. freyedknot

    freyedknot useless poster

    the fuel pump with screen will be on the side of the motor has a few screws in it. follow the gas line and you will find it. the cover will be a 1 inch square. i would also check for any air leaks(by listening ) to your hose connections for air leaks.
  4. Some of these smaller motors have a high speed mixture adjustment as well as the idle (main) mixture. The high speed circuit may need to be set richer.

    If the float in the carb is made of brass, a trick that cleans the carb passages without total disassembly is to put about 1/4 laquer thinner to 3/4 gasoline in the fuel tank. The laquer thinner eats any varnish out of passages. DO NOT use this trick if the carb has a cork float, as it will destroy the varnish sealing the float!!
  5. TMK


    Those little 4 horse motors have both low speed and high speed lean/rich adjustments. Low speed is on top and high is on the bottom.

    From the sounds of your problem, the motor is probably starved for fuel at higher rpms.

    I had the same problem with a 9.9hp evinrude two years ago. I completely cleand and rebuilt the carb (twice), and still had the high speed problem.

    The primer bulb ended up being the culprit. One of the check valves was blocking fuel flow through the bulb.

    I'd rule out the fuel hose + connections to the tank and motor (especially those little o-rings).

    Try to adjust the high speed lean/rich to solve the problem.

    Get a rebuild kit or at least a gasket set and clean out the carb as well as the screen at the fuel pump. Check the condition of the tip of the high speed adjustment needle.

    Some fuel tanks also have a screen at the bottom of the supply tube inside the tank.

  6. NorthSouthOhioFisherman

    NorthSouthOhioFisherman The Young Outdoorsman

    thanks for the tips. I've tried adjusting the lean/rich high to low and in-between but that doesnt work. So igeuss we'll just clean the carb and check the needles
  7. Got one of those myself. Sounds like your on the right track. Only thing you can try is choking the thing at half throttle and pumping the ball if not hard.
  8. First, check your primer bulb is it staying firm when the motor acts up in full throttle under load? If not then you should try to find your problem in the primer bulb or your fuel pump. Alot of times the fuel pump diaphram becomes stretched or punctured alowing the engine to starve for fuel at high rpms. By looking at your fish numbers I can see that this motor may be used ALOT and a stretched diaphram may well be your problem. You can purchase a rebuild kit for about $15-$23 or a new fuel pump for about $55-$70.
    Then, if this is not the problem check your spark! You can do this by pulling the plug and then insert the plug into the wire. Then with a pair of RUBBER HANDLED pliers hold the plug so that it touches the block with the threads or buisness end of the plug. Turn the key and try to start or have some one pull the rope if thats the case. You should see that your spark will be a brilliant blue or white. If the spark looks a little or alot orange then you may be dealing with a power pack or an ignition coil issue. Also make sure your plug is properly gapped at .035.
    Last, if none of these things are an issue then I would look at my carb. Check fuel lines going to carb to look for dry rot in the rubber which will lead to air leaks, it is not likely that you will hear an airleak without a trained ear. If nothing is detected then pull the carb apart,clean it, clean it and rebuild it! Rebuild kits for those are readily available and inexspensive.
    Make sure your fuel ratio is correct @ 50/1 this would be 1 pint to 6 gallons of fuel. Use good two stroke oil, don't cheap out on this part!!!!!!!! Mercury premium plus is the best I've seen. Have you changed your water pump impeller in the last 4 years??? If not, get it done, they're cheap and not hard to do yourself. All of this should save you some headaches in the long run. Good Luck
  9. NorthSouthOhioFisherman

    NorthSouthOhioFisherman The Young Outdoorsman

    Thanks for all that info!!!!! We did get her going great a loose gasket thing was the prob. somehow water was getting into there and leaking out? It has not been tried on a load but it runs better than ever in the bucket so well see wat happens on the water...thanks again
  10. NorthSouthOhioFisherman

    NorthSouthOhioFisherman The Young Outdoorsman

    I tried it on the water. Still not going full speed!!! it sometimes sounds like it on the border but not quite gettin there :( anymore suggestions???
  11. freyedknot

    freyedknot useless poster

    do you have new plugs in her? and do they look wet? and are you running 50:1 oil ratio?
  12. NorthSouthOhioFisherman

    NorthSouthOhioFisherman The Young Outdoorsman

    yeah new plugs not black-50:1?????should we take it in???
  13. K gonefishin

    K gonefishin Bit by Musky bug

    Some of those olders motors require a pressurized tank to keep the fuel flowing, I had a problem on a old motor that wouldn't go past half throttle. turned out I was trying to use the wrong kind of tank. Are you trying to run it with a tank that you know is proper for the motor? Could be a hairline crack in the fuel pump as well I had another motor that run but just died alot and that was the cause, it was pumping fuel just not all the way.
  14. NorthSouthOhioFisherman

    NorthSouthOhioFisherman The Young Outdoorsman

    yeah it has orginal tank but new pumpbulb and line so. must be carb or somewhere in the fuel line is wat we're thinkin...
  15. Only tell what I know from mine. If it run at low speeds only I lost a cly. Pull the plugs out and ground one at a time. Make sure you got it to both. Then go fuel and let know what ya find.
  16. freyedknot

    freyedknot useless poster

    try another tank and hose.50:1 is the oil mix ratio
  17. Is it a single or twin cylinder? I lost one coil on my Fisherman and it acted the same way. It would start and run but no power. I checked the plugs one nice and brown, the other wet and black.
  18. NorthSouthOhioFisherman

    NorthSouthOhioFisherman The Young Outdoorsman

    well finally went to work on it again turns out only one cyliner was working cuz the points were bad. Its great now-thanks to all