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Old 03-09-2011, 08:36 PM   post #1 of 25
wolf-head
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Default 18 hp b&s twin problem

Hey guys I have a MTD GT1846 with the 18 hp opposed twin briggs & stratton engine. I'll start at the beginning of the story so you get an idea. A while back when this lawn mower had the muffler on it, it was having some power troubles. Half the time it was only running on one cylinder (later found out it was the right cylinder) When I rev'd it up from just about any idle, it would only idle up on one cylinder then eventually the other one would kick in. When you engaged the mower, like any other lawn mower, it bogged down a bit but of course came back up to high idle with one cylinder firing then soon the other. So any time the engine would get bogged down some how, it would only run on that one cylinder. So a month or 2 ago, I decided to take the muffler off and put custom pipes on it so i could 1. Find which cylinder it was and 2. Because I didn't use the mower much so wanted it to sound "unique" So sure enough it was the right cylinder not firing half the time. I cleaned the spark plugs up and it was a little better. But when i was mowing last night, the spark plug wire on the left side (the side that ran OK) popped off and it was running on only the right cylinder and the pipe on the right side (i put duals on it), which was the only cylinder running, was shooting out flames like crazy. Pretty much every time it fired it shot out a flame. But it did not do this when i left the left wire plugged in and unplugged the right one. It shot no flames whatsoever. So it is the right side cylinder is the one with all the problems. Sorry for the long story but does anyone have an idea of what it might be? Any help would be appreciated. Thanks!
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Old 03-09-2011, 08:55 PM   post #2 of 25
larrybl
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Default Re: 18 hp b&s twin problem

First off I'll welcome a fellow Texan. It really sounds like you have an exaust valve issue on that cyl. At low idle there is not enough compression to fire the cyl. At higher rpm the flames from the exaust are from the cyl firing and blowing by the exaust valve.
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Old 03-09-2011, 09:05 PM   post #3 of 25
wolf-head
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Default Re: 18 hp b&s twin problem

Thanks for the welcome. I will continue to look up on the issue and thanks for the info. What area of texas are you from?
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Old 03-09-2011, 09:08 PM   post #4 of 25
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Default Re: 18 hp b&s twin problem

Might be as simple as adjusting the valve clearance. Lots of threads on that procedure on here if you do a search.
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Old 03-09-2011, 09:10 PM   post #5 of 25
monteman_73
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Default Re: 18 hp b&s twin problem

Sounds like the right hand cylinder is running lean. Start it up and let it idle, and spray WD 40 around the intake gasket at the right hand cylinder and see if the idle changes. If the idle does change, you may need to replace the intake gaskets. If that is ok, spray the intake runner from the right cylinder to the carb. Maybe the intake runner is cracked. Good luck in your venture.
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Old 03-09-2011, 09:34 PM   post #6 of 25
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Default Re: 18 hp b&s twin problem

try this......take out both plugs....do a compression check on each cyl.....this will let u know if a valve is leakin...or maybe the rings r gettin bad...
does this engine burn any oil...(can b seen by a slightly blue tinted exhaust).. if it is usin oil....the weaker cyl rings may b bad....
then again...if it does use oil... i can also b seen on ur spark plugs too.....bad cyl will b blacker color on plug...may also have some deposits built uo on ur valvees & seats....not lettin them close tight
my guess ....10 to 1 that u got deposits built up on ur exhaust valve.....& it not closin right....remendy....remove valve.....clean to shiny look....clean seat too.....then do a LAP grind in seat...(this all requires removin the head) .... aftyergrindins....clean real good.....replace valve.....check valve LASH....& adjust if needed....replace head & restart engine when all put back togather
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Old 03-09-2011, 09:39 PM   post #7 of 25
wolf-head
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Default Re: 18 hp b&s twin problem

here is a video of it shooting the flames and a picture of my set up.
http://www.youtube.com/watch?v=fg4id4mq_TM
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Old 03-09-2011, 09:50 PM   post #8 of 25
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Default Re: 18 hp b&s twin problem

Dang, I need to remember to turn the sound DOWN before clicking on a link of a running B/S Ran all the cats out of the shop, and I think I poped a speaker.

You know those straight pipes may be causing your problem. The engine needs some back pressure from the muffler to work properly.

Turn your sound down before viewing mine.
http://www.youtube.com/watch?v=VGe-z6GaZ34

I'm pretty sure if I turned off the lights, and with straight pipes I would see flames.

Last edited by larrybl; 03-09-2011 at 09:55 PM. Reason: need to add the link
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Old 03-09-2011, 09:53 PM   post #9 of 25
Walt 2002
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Default Re: 18 hp b&s twin problem

It is fairly common for the valve seat to come loose in these engine if the cooling shroud and or cooling fins are dirty. IF the valve seat is coming out and you continue to run it, it will wallow out the block until it is not repairable.

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Old 03-09-2011, 09:58 PM   post #10 of 25
larrybl
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Default Re: 18 hp b&s twin problem

Quote:
Originally Posted by Walt 2002 View Post
It is fairly common for the valve seat to come loose in these engine if the cooling shroud and or cooling fins are dirty. IF the valve seat is coming out and you continue to run it, it will wallow out the block until it is not repairable.

Walt Conner
Walt knows a lot, he helped me on mine greatly. Much appricated Walt.
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Old 03-09-2011, 10:00 PM   post #11 of 25
wolf-head
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Default Re: 18 hp b&s twin problem

Thanks for all the comments i will start with the valves. And Larrybl it was running bad like this before i took the muffler off. Actually i think taking it off made it a little better lol. And when I check the spark plug it is always black, every time. Am I also having piston problems?
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Old 03-09-2011, 10:10 PM   post #12 of 25
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Default Re: 18 hp b&s twin problem

I had (I think) rite side cyl issues with both of my opposed twins. Ended up boring both to .020 over and replaceing pistons rings and valves. Not sure if you want to go that far, or spend that much, about $350 per engine.

Here is the link to one of the builds, and a picture of what the Cyl looked like before.
http://www.mytractorforum.com/showth...hlight=hulk+ii
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Old 03-09-2011, 10:27 PM   post #13 of 25
wolf-head
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Default Re: 18 hp b&s twin problem

here is a video (in the light ) of the engine running. You can hear it hesitate when i rev it up. TO NOTE: the flames in this video are NOT the ones i'm talking about, these are just back fire flames
http://www.youtube.com/watch?v=C2DdxnR0Dsw
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Old 03-09-2011, 10:28 PM   post #14 of 25
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Default Re: 18 hp b&s twin problem

I went back and looked at the thread I posted about my 18HP rebuild, and relized why I did two of them. I really enjoyed rebuilding those motors. I hope yours turns into an enjoyable and learing experiance.

Good luck, and remember
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Old 03-09-2011, 10:33 PM   post #15 of 25
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Default Re: 18 hp b&s twin problem

That actually looked and sounded pretty normal. I didn't see any smoke (a good thing). Start simple, Plugs, Clean and adjust the carb, And put a couple cheep bullet mufflers on.
Good luck, and keep us posted
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