1982 140 Johnson running lean

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scbljr

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I just melted a piston after the break in period of a fresh rebuild. I ran the motor with double oil for ten hours at different speeds,I checked the plugs often during this period no signs of running lean. The timing and linkage is adjusted properly. I am running Boeyesen Reeds though, I changed the idle jets like they recommended, Do I need to change the main jets also or go back to the stock reeds. The motor ran better than ever till the melt down.
 
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emdsapmgr

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Re: 1982 140 Johnson running lean

Did you overhaul the carbs? After the piston melted, did you take the carb apart that feeds that bad cylinder and inspect the jets that feed that cyl? Did you reset the timing after the overhaul? How did you set it? Did you time it on both #1 and #2 cyls, then set it correctly on the higher of the two? Engines will tend to run very well if they are lean, they just don't run very long that way. Did you replace the water diverters in the powerhead? It is possible for a single piston to overheat in a cool powerhead if the cooling water is blocked from flowing in the correct pattern aroung the cylinders.
 
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scbljr

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Re: 1982 140 Johnson running lean

I rebuilt the carbs, installed new water diverters, but only set the timing on #1.
The other cylinders are very dry, my plan is to retard the timing 2-4 degrees, go back to the surface gap plugs they seem to run cooler, and drill out the main jets, My question is what size to drill them? Do I drill the intermediate jets as well? I had been cruising between 3500 and 4000 rpm then ran the motor for the first time at 5500 rpm for about 100 yards then the melt down happened.
 
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emdsapmgr

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Re: 1982 140 Johnson running lean

Certainly, an unfortunate turn of events. There is some logical reason for the failure. Did you set the max timing when the engine was running at 5000 rpm? It makes a difference. I'm not a fan of drilling jets. They come from the factory specially drilled to flow maximum fuel and drilling them in the shop is not the same as a factory drill. If you want bigger jets, buy them from the dealer. What did you find when you inspected the jets of the carb that feeds the bad cyl?
 
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scbljr

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Re: 1982 140 Johnson running lean

I haven't inspected the carb yet. The timing was set at cranking speed with the plugs out and at 24 degrees the same as it was before the rebuild. The piston is burned in the center as well as the plug melted, the other pistons show no signs of damage. I will try to pull the carb tomorrow and report what I find.
 
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emdsapmgr

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Re: 1982 140 Johnson running lean

Setting the timing at 24 the way you did it should be ok. At that setting it may be as much as 4 degrees below the factory recommended setting.
 
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scbljr

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Re: 1982 140 Johnson running lean

My carbs look good. I spoke with a local guy who rebuilds a lot of old cross flows, he said to use a low compression head gasket and to drill the main jets ten percent larger, he burnt several pistons himself before he figured it out. All that we have here in Texas is ten percent ethenol fuel and that is the problem, I have a 1986 Mercury 115 that runs good on the stuff.
 
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emdsapmgr

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Re: 1982 140 Johnson running lean

If you need larger jets, it is better to buy new-larger ones instead of drilling the old ones. Bombardier sells them in many sizes.
 
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scbljr

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Re: 1982 140 Johnson running lean

I will check in to that, I don't like the idea of drilling them either. Thank you for all your help.
 
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scbljr

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Re: 1982 140 Johnson running lean update

Re: 1982 140 Johnson running lean update

I finally got the 140 running again. I checked the compression with the original heads, 155 on all 4 which I think is too high. I decided to go with a set of 115 heads which lowers compression to 125, go back to the surface gap plugs and leave the carb jets alone. I hope this works.
 
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scbljr

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Re: 1982 140 Johnson running lean

Well it is December motor is running great. Thanks for everyone's help!
 
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emdsapmgr

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Re: 1982 140 Johnson running lean

I've not heard of any stock crossflow with 155 compression. Maybe a prior owner cut the heads. Many early 140's of your vintage would normally run in the 125-130 range. Certainly at 155 premium fuel would be a must. I am suprised that just one piston went bad during the break in. Something is unusual for that type of failure. Glad it's working fine now.
 
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scbljr

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Re: 1982 140 Johnson running lean

The heads were shaved on two different occasions, that and the wrong spark plugs is what I believe caused all my problems.
 
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