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B&s won't start after heat soak


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#1 OLD HOUSEBOATER OFFLINE  

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Posted September 03, 2011 - 12:06 AM

42A707 B&S twin won't start hot. Has spark and carb has been overhauled.

Starts perfect and runs like new when cold. Can run all day and not miss a lick. Shut it down for 10 minutes and won't even cough.

#2 MH81 ONLINE  

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Posted September 03, 2011 - 07:14 AM

It turns over OK? No weird noises or labored sounds while turning it over?

Gotta be missing one of the big 3. Fuel, air or fire. I assume it's not air, unless it's got a sticky valve... But she wouldn't run right or at all once warm. I would pull the air cleaner and see if you can tell if the air is huffing in and out of the carb. That's the valve that has stuck for me in the past. We will assume it's OK, So that leaves fire or fuel. Have you tried giving it a snort of flammable carb cleaner while turning it over? I would try that first, then change the plug, then check for spark. I know that last sentence seems backwards, but I've had too many plugs show spark out of the engine and not spark in the compression. Champion plugs hate me.

#3 NUTNDUN OFFLINE  

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Posted September 03, 2011 - 07:45 AM

My vote is vapor lock. Is there plenty of room for air to get through and is the exhaust shielded from the carb area?

#4 NUTNDUN OFFLINE  

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Posted September 03, 2011 - 07:47 AM

Also, I don't know how the carb setup is on them but if you have a separate high speed needle adjustment you can try giving it an 1/8th of a turn counter clockwise to richen the top end a little. Might be just enough to get the motor to run a little cooler. If it is on the lean side it will run hotter then normal and if the problem is vapor lock then a couple of degrees cooler could be all you need.

#5 Sparky OFFLINE  

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Posted September 03, 2011 - 08:23 AM

How about this for an idea - you didn't say whether you shut it down outside ( normal ) 0r in shade or garage. Try parking inside and trying again after 10 minute shutdown. - Oxygen content factor.

#6 Tennblue59 OFFLINE  

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Posted September 03, 2011 - 01:19 PM

Does it have spark when hot and won't start? A coil going bad sometimes will work when cold, then act up once it gets hot and heat soaks for a while. Also, as stated before, there is a difference between open air spark and compresion chamber spark - is the spark bright, and strong?

Second, are the valves in adjustment? Clearance changes as dis-similar metals heat up - usually the exhaust valve clearance is out of spec

#7 Byron R OFFLINE  

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Posted September 03, 2011 - 04:49 PM

Does it have a Condensor?

#8 OLD HOUSEBOATER OFFLINE  

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Posted September 04, 2011 - 10:09 AM

No condensor. I ordered a new coil module, tried everything else. Will report back when I get it installed.

#9 Alc ONLINE  

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Posted September 04, 2011 - 11:57 AM

I'm guessing that when you pulled the plugs out when it didn't start they where wet ? I wonder if you stopped the engine by shutting the fuel off . Wait the amount of time your having problems , open the fuel and see if it starts then . Al

#10 OLD HOUSEBOATER OFFLINE  

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Posted September 05, 2011 - 10:32 AM

Nope, plugs were dry. An hour later 1 turn and it's happy time.

#11 JDBrian OFFLINE  

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Posted September 05, 2011 - 11:33 AM

It does sound like vapour lock. Good luck with getting it sorted out.

#12 OLD HOUSEBOATER OFFLINE  

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Posted September 09, 2011 - 09:00 PM

Was bad coil.

#13 DougT ONLINE  

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Posted September 10, 2011 - 08:56 AM

I've heard it recommended that you gap the plugs at .025 on the Briggs twins to help improve coil life. I went through 2 coils before I was told that and the 3rd coil outlasted the engine. Doug T




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