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Cold Start 1983 Johnson 7.5hp 2cyl

T

tsam

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Engine starts with one or two pulls, normally. Unless it has been sitting for for more than 4 or 5 days. Then can take 5 to 7 pulls to start. Once started it will start on 1 or 2 pulls every time. Compression 75 on both cylinders. Good sparks. Engine runs well at all speeds and idle.
My thinking is that the gas fumes in the crankcase and combustion chambers dissipate in a couple of days and it takes more pulls to drawn enough fresh gas fumes through the system to the firing chambers. Compression is not high so it takes more pulls to charge the system with fumes. Once the system is recharged with fumes it is ready to fire with one pull.
Is this normal operation for this old engine?
Or should I consider new rings and/or reed valves?
 
75 is decent compression for this motor....I don't think it's the problem. Make sure the choke is closing fully, there is a small port in the butterfly to help it get air when it first fires....this is normal. If you learn the right sqweezing pressure on the bulb, you can be sure that the carburator is ready to "spill in" right on your first pull when cold with choke on. Perhaps your not pumping "quite" enough pressure when starting after full resting time....over3 days. In this resting time, is the hose always connected, and do you pump up the squeeze bulb until solid? Another trick that works sometimes is this: When you are shutting down the motor and don't expect to use it for a few days, then pull the choke when it's idling and let it "flood" to a stop. Then when next outing, there is already a little fuel in the crankcase and cylinders that's ready to fire off right away.
 
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Are you priming the fuel system by pumping the priming ball until it is firm.

Are you closing the choke fully? Does the flap close properly?

How much throttle opening are you using? As much as the interlock with the starter will allow?

How good are the sparks? How large an air gap will they jump?

I think my '84 6 hp is the same motor, just with the power measured in a different way. I did check its compression once. I forget the exact figure but I am sure it was higher than 75 .
It takes several pulls to start when cold but I can't say I've ever bothered to count.
 
tsam said:
Engine starts with one or two pulls, normally. Unless it has been sitting for for more than 4 or 5 days. Then can take 5 to 7 pulls to start. Once started it will start on 1 or 2 pulls every time. Compression 75 on both cylinders. Good sparks. Engine runs well at all speeds and idle.
My thinking is that the gas fumes in the crankcase and combustion chambers dissipate in a couple of days and it takes more pulls to drawn enough fresh gas fumes through the system to the firing chambers. Compression is not high so it takes more pulls to charge the system with fumes. Once the system is recharged with fumes it is ready to fire with one pull.
Is this normal operation for this old engine?
Or should I consider new rings and/or reed valves?
Click to expand...

I applaud your thinking on the "fumes" idea. It simply takes more fuel to start a cold engine. That's why they have a choke in the first place. And also why they later went to a primer instead of a choke on many models.

In any case, I consider your motor "normal" and doesn't need fixing.
 
With the correct starting procedure a motor in good condition should start up the same.----Sitting for 1 day or 2 weeks !
 
Agreed....key words here, "correct starting proceedure"......and "good condition".
All great points, Sir Vic.....thanks and take care.
Yes, Gator..... proper priming gives instant starts when cold....great system. Those 30's in Avatar never ever crank more than a few revolutions. The starters will likely NEVER wear out. Notice rope start too, why? Sometimes no battery around.....even had a battery stolen from our boat once. So sad what some will do. Eventually one of the 30's was stolen from the storage shed during wintertime. The other 30 is looking for another mate....they were consecutive serial numbers.
 
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Point is, the '83 has a choke, not a primer, right? So how's it going to get a rich starting mixture through the crankcase and into the cylinders without cranking it over a few revolutions?

Guy said 5-7 pulls. That might be a couple more than expected, but I still don't think there is anything wrong with it.
 
Thanks - will try the “choke it to stop it” and “open throttle while choking to start it” methods.
Curious about installing a primer. Could I find one on a later engine same model?
 
Yes, but not sure if the fitting is on your carburator or intake area in order to plumb it in. Then you will need to tap into your fuel supply hose with a "t"....somewhere before the carb. The "t", or "y" can go either side of your fuel pump, so the hose size will vary. Here is the manual primer unit.....not sure what route to use is best, see next post.
 

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Will need a nipple like this to tap into carb float base and main jet area.Screenshot_20201227-184824.jpg

Probably looking at $140 in parts, if all new stuff.
 
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