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18 hp b&s twin problem

12K views 24 replies 8 participants last post by  dj722000 
#1 ·
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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#2 ·
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.
 
#5 ·
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.
 
#6 ·
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
 
#8 · (Edited)
Dang, I need to remember to turn the sound DOWN before clicking on a link of a running B/S :00000060: 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.
 
#11 ·
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?
 
#12 ·
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/showthread.php?t=160114&highlight=hulk+ii
 

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#14 ·
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 :wwp:
 
#15 ·
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
 
#16 ·
after you rev it up, when the right cylinder finally starts firing, it smokes but im guessing its just gas. It still has me scratching my head wondering why it does the flame thing and that hesitation at rev up. There is something fishy happening for sure..
 
#17 ·
OK I went back and lisestened to your vid again, Make sure you have two good matched plugs. I did have that problem once with HULK I and it turned out one of the plugs was weak / bad

PS, Speaker didn't blow, the connector plug was dirty.
 
#20 ·
i just fixed that problem with my pulling tractor it was the magneto was bad on the one side when it warmed up the number 1 cylinder would cut in and out real bad lucky for me I got about 4 of those motors in parts I can just dig through the box and find what I need if you eliminate everything else you might want to look there.
 
#21 ·
Do you have enough plug wire to swap plug wires? Unlike a car engine the plugs fire twice each cycle.
 
#23 ·
No, if the wires are long enough, put the L wire on the R plug and vice versa for the other plug.
 
#24 ·
ok now i get what your saying Larrybl guess i didnt read it right the first time....the wires are not long enough and the motor that the coil is on has been rebuilt once already plus when i got it the motor had sat for about 6 months in a barn before I got it(only paid $25 for it and it ran!!!!!! so i cant complain fixed the started and it fired right up I did have to fix the carburetor the float was stuck but that was an easy fix) for $25 I had bought it for parts but after finding out it was .20 over I decided to get it running I said well that is a new pulling motor now.
 
#25 ·
Take your old plug, cut the elctrode off and check for spark again. If it jumps the gap, its good to go. If it doesnt, may need a new coil. Also sounds a little like your carb is out of adjustment or maybe a little dirty.
 
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