This is a continuation of sorts of my last thread from over a year ago.
My dad has a Tecumseh BVS 143 on a Mountfield Empress 16, we believe bought in the mid-80s. It gave very good service for about 30 years but missed several seasons over the past few years, predominantly because for a long time it was nigh on impossible to start, which several mechanics failed to resolve for any length of time.
Last year I committed to getting it running again as I've loved this mower through my childhood and it seems far too good to dispose of, as has come close to happening on a few occasions. Now, this year, I finally have a full toolkit so am able to do some work and implement suggestions.
With the help of this forum, we got it starting reliably - enthusiastically and every time. The hypothesis is excess oil always got into the cylinder on the car journey home from the various mechanics it went to, so it ran while away but performed poorly again at home. At least that's the explanation that appeals to me.
So we now have it starting although we do find there is a strange period of resistance - described in my older thread - when the cord will sometimes go completely stiff, and you end up yanking the mower off the ground. (The pull cord itself runs completely smoothly, the cord is new, and the mechanism has been sprayed with WD-40, so it is the engine/flywheel causing the tension.)
Now the problem is in running. It does run - it has done every cut of 2020 and 2021, but I believe it is running very rich with a constant misfire.
It has felt down on power, puffs blue smoke through tough patches of grass, and when increasing the throttle, and smells petrol-y in the air. Fuel has diminished at a rate far beyond what we think it used to use. I may be at fault as before really understanding the problem, or asking for help, I had already tried adjusting the mixture and idle screws, and now I really wish I'd left them alone. It's now set up per the Tecumseh operating instructions though, with the mixture screw tightened and backed off a turn and a half.
The running problems have got progressively worse until a few weeks ago when it was finally running really quite poorly and barely powerful enough to cut confidently.
This weekend I pulled the spark plug at last and found it absolutely disgusting. It was black and oily when it came out last year but went in reasonably clean. This year I am amazed it was still running, sadly I did not take a photo but there was hardened sludge all over it, even in the gap. I cleaned the plug as best I could and put it back in - I will be getting a new plug - and immediately it is running much better, of course, still puffing blue but not missing nearly so often.
Oil has been topped-up over the summer, Dad did it and I'm not sure what he added exactly, it has not been changed probably since 2019 when it was given a brief service by one of the mechanics. Oil has gone down again since it was topped-up and is maybe 2-3cm below the top of the filling hole now.
I wondered whether the flywheel key could be sheared and the culprit behind everything, so I got the flywheel nut off by jamming the blade against a wooden log. Am I correct in saying these photos suggest the flywheel key is in fact intact and not sheared? Do I need to take the flywheel off to confirm that? I do not have a knockoff tool yet.
I'm not really sure what to do now to be honest, I feel like there's too many variables to address here and as I have no experience I'm not sure which is the best thing to focus on.
I will get it a new spark plug, and intend to change the oil in the coming weeks, but this is not going to address the root of the issue so far as I can see. I will buy a couple of plugs as it seems certain it's going to ruin another one until we get it running properly. I was truly astonished on Sunday when that plug came out, it was just black muck caked all over it.
Any help appreciated.
Many thanks!
My dad has a Tecumseh BVS 143 on a Mountfield Empress 16, we believe bought in the mid-80s. It gave very good service for about 30 years but missed several seasons over the past few years, predominantly because for a long time it was nigh on impossible to start, which several mechanics failed to resolve for any length of time.
Last year I committed to getting it running again as I've loved this mower through my childhood and it seems far too good to dispose of, as has come close to happening on a few occasions. Now, this year, I finally have a full toolkit so am able to do some work and implement suggestions.
With the help of this forum, we got it starting reliably - enthusiastically and every time. The hypothesis is excess oil always got into the cylinder on the car journey home from the various mechanics it went to, so it ran while away but performed poorly again at home. At least that's the explanation that appeals to me.
So we now have it starting although we do find there is a strange period of resistance - described in my older thread - when the cord will sometimes go completely stiff, and you end up yanking the mower off the ground. (The pull cord itself runs completely smoothly, the cord is new, and the mechanism has been sprayed with WD-40, so it is the engine/flywheel causing the tension.)
Now the problem is in running. It does run - it has done every cut of 2020 and 2021, but I believe it is running very rich with a constant misfire.
It has felt down on power, puffs blue smoke through tough patches of grass, and when increasing the throttle, and smells petrol-y in the air. Fuel has diminished at a rate far beyond what we think it used to use. I may be at fault as before really understanding the problem, or asking for help, I had already tried adjusting the mixture and idle screws, and now I really wish I'd left them alone. It's now set up per the Tecumseh operating instructions though, with the mixture screw tightened and backed off a turn and a half.
The running problems have got progressively worse until a few weeks ago when it was finally running really quite poorly and barely powerful enough to cut confidently.
This weekend I pulled the spark plug at last and found it absolutely disgusting. It was black and oily when it came out last year but went in reasonably clean. This year I am amazed it was still running, sadly I did not take a photo but there was hardened sludge all over it, even in the gap. I cleaned the plug as best I could and put it back in - I will be getting a new plug - and immediately it is running much better, of course, still puffing blue but not missing nearly so often.
Oil has been topped-up over the summer, Dad did it and I'm not sure what he added exactly, it has not been changed probably since 2019 when it was given a brief service by one of the mechanics. Oil has gone down again since it was topped-up and is maybe 2-3cm below the top of the filling hole now.
I wondered whether the flywheel key could be sheared and the culprit behind everything, so I got the flywheel nut off by jamming the blade against a wooden log. Am I correct in saying these photos suggest the flywheel key is in fact intact and not sheared? Do I need to take the flywheel off to confirm that? I do not have a knockoff tool yet.
I'm not really sure what to do now to be honest, I feel like there's too many variables to address here and as I have no experience I'm not sure which is the best thing to focus on.
I will get it a new spark plug, and intend to change the oil in the coming weeks, but this is not going to address the root of the issue so far as I can see. I will buy a couple of plugs as it seems certain it's going to ruin another one until we get it running properly. I was truly astonished on Sunday when that plug came out, it was just black muck caked all over it.
Any help appreciated.
Many thanks!
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