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21 Posts
Discussion Starter · #1 ·
Hello everyone i don't like to ask for help very much.....but i really need some help with my old Mtd gt, aka " Betsey" I just cant seem to get her running right.
She's got a 18.5 b/s model 42a707 type 1238 01, 1997 code, twin opposed i/c engine, The problem is when i mow with it, Does fine for the first 5-10 min,
then i bring it down to about 1/2 throttle or less and it starts to hunt up and down up and down, i can make it stop by pulling the choke out a bit and it will run fine,But when i try to adjust the low speed mixture nothing,Next morning
i go out start her up all is well Intel i start working here a Lil.
Things i have tried to resolve the problem...

Rebuilt carb "new gaskets,cleaned,new pump,etc"
New inline fuel-filter
New fuel lines
Cleaned and flushed gas tank
New fuel cap "vent work's fine no vapor lock there"
I put a new ignition on it for a separate problem.
I have checked the crank-case for air leaks around manifold flanges, manifold,
Cleaned and checked for free movement of the governor and linkages.

Is it possible that a sticking valve can cause this problem,resulting in not enough vacuum to draw in the correct air/fuel ratio? the reason i ask is because i have noticed a lil tick tick tick in the motor, experience tells me thats a clearance issue with the valve and tappet.
But wouldn't the good cylinder make up for that?

Any help would be appreciated, Thanks in advance.


Senior MTF Poster
13,263 Posts
Not likely to be ignition.

" it starts to hunt up and down up and down, i can make it stop by pulling the choke out a bit and it will run fine,"

That pretty well says lean mixture.

"when i try to adjust the low speed mixture nothing"

And that pretty well says that when you cleaned the carb., you did not get the low speed circuit clean. Low speed mixture screw MUST make a difference. Did you run "tag wire" thru the orifices when you cleaned, especially the brass one in the top surface of the lower carb casting, accessible when the carb top is removed?

Walt Conner

21 Posts
Discussion Starter · #4 ·
Thanks for the reply Walt, no i didn't run any "tag wire" Thru the passages in the carb.
But before i put the carb back together i did make sure that carb cleaner shot thru all the passages, but of course that does not say that the flow is 100%.
I just really hate to have to tear it back down again, I'm thinking of maybe just getting a new bowl for it, cause the last time i tore it down i do remember white crusty deposits in the bowl. So whose to say the same thing is int in the passageways? I would use tag wire but...never liked how thin it was especially for an idle circuit (afraid of it breaking).
What about that seafoam stuff everyones talking about?
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