'73 Johnson 115hp hard to start.

[flykr2s]

I have recently purchased a boat with a 1973 Johnson 115hp. The engine is hard to start. Sometimes it takes ten to fifteen minutes of working with it to get it to start and sometimes it will not start. But, once started and warmed up, she purrs like a kitten. She will even restart with the bump of the switch. I have done the following: replaced fuel lines and bulb, new fuel pump, rebuilt carbs, checked timing, new plugs, checked sparks for firing, checked neutural position switches, checked carb linkages and checked choke operation. All this and she is still hard to start. The battery is strong and spins the motor good. Any suggestions would be greatly appreciated.

 

[clanton]

Re: '73 Johnson 115hp hard to start.

Check the timing sensor air gap.

 

[ledgefinder]

Re: '73 Johnson 115hp hard to start.

Check to be sure your choke flaps are COMPLETELY closed (slammed shut hard) when you cold start. Its very common on the older V4s for them to be 99.94% closed - which isn't enough.<br /><br />To test this, you can put some premix in a spray bottle. Spray a little in the carb throats (Warning - fire hazard!), then try to cold start it. Starts right up now? OK, work on the choke flaps issue. Still doesn't start? Work on the imer base issue.

 

[SCO]

Re: '73 Johnson 115hp hard to start.

Ive got the identical motor, but mine is the 135 hp. I had the same problem, and have solved it. Can you indulge me and describe your start procedure? You should put on full choke and have the neutral throttle lever all the way up. Do this with the cover off and the carb cover off too. Identify the choke flapper and the throttle flapper and their linkages. When you lift the throttle lever check to make sure the throttle flaper linkage moves enough to open it significantly. <br />If you crank for some 5 seconds with full choke, the fuel will pour out the front of the carbs or at least soak the barrels of the carbs.Check for this and get back to us. Ditto on the premix test. Point here is to rule in/out a fuel delivery problem, the problem I had that was vexing me.<br /><br />You might have a procedure prob. 1st pump primer bulb till hard. 2nd apply full throttle with neutral throttle lever, put on full choke. If you dont do both (choke and throttle), if you do one or the other, you will crank all day to start. You must choke a load of fuel from the carbs and the throttle must be open to let the fuel you just pulled in and air into the engine at first startup.<br /><br />On my engine, the main problem was that the throttle cable from the control box was screwed too tight against the idle stop. When I lifted the neutral throttle lever to start, the throttle would barely move off the idle stop, leaving the carb throttle flapper almost all the way closed. Though choke was working, the closed throttle flapper blocked the fuel air's entry into the engine.

 

[blueboat1]

Re: '73 Johnson 115hp hard to start.

My 74 70hp was not shutting the choke butterflies all the way and you could wear a battery down. I popped out one of the plastic caps off the carb cover and pushed it shut with my finger. It fired right up. I adjusted that linkage and now she fires each time the choke is engaged.<br />Good luck

 

[flykr2s]

Re: '73 Johnson 115hp hard to start.

You guys ROCK.....I tried all everyone said so far and I found my start lever was barely opening the butterfly on the carbs. Adjusted that and she started right up. Then she started idling rough like all plugs were not firing. I felt #4 and #3 were not getting warm so as the engine was running I unplugged #4, no change...I then unplugged #3, no change....unplugged #1, engine died. She was running on #1 and #2 only. I pulled the plugs and had spark in #1 and #2. None in #3 and #4. I tried #3 and #4 again and then there was spark. I started engine and she was hitting on all four then all of a sudden she was running rough and hitting on #1 and #2 only. What would cause intermittent spark plug firing?

 

[ledgefinder]

Re: '73 Johnson 115hp hard to start.

That sounds like a timer base. (Right? I think there are two sensors, and 1&2 are on one sensor, 3&4 on the other.) Timer bases can be intermittent so that they only act up at low rpms. They generate a signal from a magnet on the inner flywheel passing by the sensor coil, & when the magnets going faster they'll work fine. Does it run OK if you rev it up a bit? <br /><br />Ideally you want to measure the output of the sensor coils with an oscilloscope, or a peak-reading-voltmeter. If you don't have one, you can measure the resistance of the sensor coils, & compare versus the expected resistance in the shop manual. Beware, though, sometimes sensors will have good resistance, but still not be putting out enough signal.<br /><br />Adjusting the sensor gap may help, but it's not guaranteed to work, and it's tricky on the 1973+ motors. You need a gauge that mimics the diameter of the inner part of the flywheel (Rapair sells one). OMC wants a fair amount of money for a new one (I think around $200). They go on eBay quite a bit cheaper.

 

[flykr2s]

Re: '73 Johnson 115hp hard to start.

Actually, the sensor coils are 1&3 and 2&4 according to my service manual. That is what is puzzeling since it is 3&4 that fire intermittantly. I will have to check for spark at higher rpm and let you know. Thanks

 

[clanton]

Re: '73 Johnson 115hp hard to start.

The Rapair pn for sensor adjusting tool 553-9702, price 2002 cat. 10.00. The wiring diagram I have is unreadable, but I think this engine has 1 charge coil, 2 sensors 1 power pack. Two cylinders<br />misfiring should only be pack, sensor, wires. You should be able to tell something with a multimeter AC scale, all of the termials are easy to get to after you remove the pack cover.

 

[flykr2s]

Re: '73 Johnson 115hp hard to start.

Well I just got back from the lake. Engine started fairly easy but everytime I would put it in gear it would die. The engine still ran rough at idle so I know cylinders 3&4 were not firing. Sure did want to be on the lake this weekend.