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I'm hoping for a... most likely cause I guess. Got an older Murray Lawn Tractor this summer. 20hp B&S twin. It runs terrific but has a problem when turning over to start. It acts like the timing is off or at least that's what it reminds me of. Like when you advance the timing too far in a car and try to start it. It turns over and kinda hangs up in between each cylinder. Which of course is the spark plugs firing too soon. Now this engine runs off a magneto (right?) so I figured I'd check the flywheel and see if the shear key had broke maybe. Pulled off the big nut and looked but it was OK. So... anybody have a guess?

info. new battery this summer. Starter was froze from sitting (4 yrs) but after cleaning worked well. Could it still be bad? Maybe drawing too many amps? How would you check that? Ummm, battery cables?

Thanks

You are going to have to adjust the valves. Post all the engine numbers and I should be able to find you a service manual.

as rivets said adjust the valves

If its vtwin briggs then manual part number is 273521. If its a Lhead twin then manual part number is 271172.

Rivets said:

You are going to have to adjust the valves. Post all the engine numbers and I should be able to find you a service manual.

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Adjust the valves. Super, I can do that. :smile: OK, I looked that up on youtube.com and the guy said to pretty much set all V-Twins to .004 thousandths. Does that sound right to you?

Here's the info. you requested:
Model 460777 25C
Type 1277 01
Code 9601155B
Briggs Diamond I/C
20 hp

Brads said:

Adjust the valves. Super, I can do that. :smile: OK, I looked that up on youtube.com and the guy said to pretty much set all V-Twins to .004 thousandths. Does that sound right to you?

Here's the info. you requested:
Model 460777 25C
Type 1277 01
Code 9601155B
Briggs Diamond I/C
20 hp

Click to expand...

No, My briggs vtwin manual says .004-.006 for intake valve and .007-.009 for exhaust valve. Thats not a vtwin its Lhead twin.

Here is a good guide to go by

Carscw said:

Here is a good guide to go by

View attachment 18262

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cool link :thumbsup:

Carscw said:

Here is a good guide to go by

View attachment 18262

Click to expand...

briggs said:

cool link :thumbsup:

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But some of the info on there is not correct when comparing it to the Briggs manual for Lhead twins.

Here's link to the Lhead twin shop manual. http://dl.dropbox.com/u/12502267/B&S Service Manuals/02_271172TwinCylinderLHead.pdf

davbell22602 said:

But some of the info on there is not correct when comparing it to the Briggs manual for Lhead twins.

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i see i have the book at the shop ...Should mark that one as a bad link

OK, so is this a great place or what!?! Thanks to everyone. :laughing: You guys are the best!

Brads said:

OK, so is this a great place or what!?! Thanks to everyone. :laughing: You guys are the best!

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SHH DONT TELL ANYONE lol

It is a common problem on the old L-head twins. Also another problem that can add to it is the starter's top bushing being worn out, while the top is off, grab the starter
gear and wiggle, see how much slop is there.

But the most likely cause of your symptoms is excessive carbon buildup in the combustion chamber, so you need to pull both heads and scrape/buff/etc.........
It doesn't take much carbon to be a problem.

Update: Well, spring is almost here so I finally got around to filing/adjusting the valves. Cheated a little (a lot) and just pulled the side covers off, stuck a file in there and went for it. Not the best way I know but it worked. Filed the intakes to .006 and exhaust to .009. Took care of the starter problem and runs way smoother. Thanks again :smile: