Briggs Lawnmower difficult start when hot

[Kristof_J]

Hey guys, I'm struggling with a B&S Lawnmower which 50% of the time has difficulties to start up again when it's hot. When the engine is cold, I prime 3 times and it starts fine. It also runs perfect and NEVER cuts out. But when you stop the engine, wait a few minutes and pull the cord, 50% of the time it fires up and 50% of the time, it won't...
I discovered, that it seems to help when I prime 1 time also when engine is hot... But this is not the "normal" course of events.
Weird thing is, when it won't start, I still have spark (checked with a spark-tester with adjustable gap) and sometimes it reacts on carb cleaner and sometimes it won't. Drives me crazy.
Fitted new spark plug and new gasoline, cleaned carb with a needle in all locations.

Should I try with a new coil?? Starting to think that the spark OUTSIDE the engine is ok, but maybe under load the spark is too weak for start-up??

Thx in advance!!

 

[bertsmobile1]

I would start by checking the valve lash, some thing that definately changes when hot
Second thing I would check is the inlet manifold for being loose or cracked , some thing that also changes when hot.

We could give ou specific information for some of the know hot start problems with various B & S engines but we have no idea which particular B & S engine you have and typing 2000 lines of text takes way too long .

 

[slomo]

Check for a sticking closed choke plate. Remove the air filter and see if choke is OPEN when the engine is hot and NOT running. Should be open. If closed, there's your dinner.

Does your engine have the air vane that controls the choke? And maybe that thermostatic muffler arm?

slomo

 

[Rivets]

OP says he has a primer, so no choke. Before you replace coil see if you have spark when trying to start unit when hot. As Bert said telling us the model, type and code numbers would help your cause.

 

[Scrubcadet10]

https://www.jackssmallengines.com/jacks-parts-lookup/briggs-stratton-model-locator.aspx

 

[Kristof_J]

Hey guys, busy weekend... Sorry for delay. Meanwhile I tried another coil, sold to me as a "known good used" one, but no difference...
But I must say, with the multimeter, I measure about 9k Ohms between the plug-cap and the body of the coil. On both the coils I have now. However, I read some stuff that the B&S coils normally are in a range of 2.5 - 5k Ohms... Can anyone confirm?
I've got 60PSI compression, cold and hot about the same.
No cracked or broken inlet-tube
Chassisnumber is 12H809-2108-B1

I'll try to post a little clip of it's behaviour

 

[Rivets]

Secondary coil resistance on coils should normally read 15K ohms or less. 60 psi is low, cause may be valves not seating, worn rings, bad head gasket or compression release not working properly. A leak down test is a better way to find the cause of low compression.

 

[slomo]

Most Briggs coils either work or they don't. Put the meters away in the drawer.

Don't forget the never decarbonizing the piston and head areas. Small chunks of ultra hard carbon get between the piston and rings. Those little guys gouge the snot out of the bore. Probably why the compression is low.

 

[Scrubcadet10]

pour a small amount of oil, like maybe a quarter or half a teaspoon in the plug hole into the cylinder, see if that raises your compression on your tester.

 

[SlopeMan2]

Hey Kris, my old stovebolt 7hp B&S was acting up, seems like after it would get warmed up. It would belch, miss, and quit. I thought it was the fuel supply. Before I got into the carb., I found that the spark did not look strong, and the plug was carboned up. I checked the coil field/crankshaft gap, and it looked very close on one side. I loosened it up, stuck a business card between them,tightened it up, and bingo, it has a hot spark again. This is on a very old Snapper. I use it to mow a very steep slope. I was so happy, when it never missed a lick after that. I had installed a pointless module coil a couple of years ago, and I guess I just didn't get it tightened down good enough. I hope your problem is as simple. Good luck.