I know this is a hoary old subject but...last year after reading Norm K's fix for the plastic carbies and deciding it was out of my skill level, I got the pictured mower running at one speed (a bit fast) with no throttle control whatsoever.
Anyway it was usable although using a bit too much fuel. It stopped dead the other day while I was emptying the catcher, no cough or splutter just cut out. I determined no spark so put a brand new(ish) CJ8 plug in. It starts but immediately continues to rev to the point of self destruction if not shut down.
I remembered afterwards that I had tried this same plug last year and the same thing happened and had used the plug that died the other day. This plug was new from Mitre10 last September and has only been used to start the mower a couple of times with the above result! I can't understand why it would run so differently just because of the plug. Any ideas appreciated.
I had a powertorque screamer that defied me to no end.
I changed the crankcase ring, two manifold rings, rebuilt the carby and popped in a brass washer and new diaphragm, checked the hoses, and even replaced the head gasket. Still a screaming. I then got some whipper snipper cord, and cleaned out the venturi pipe on the engine block base, that the hose going from the carby fits in to. I also changed the front plate on the carby, with a new ring and a metal needle. After that, she started and ran fine with no screaming, and always started first go until I passed her on to the new owner.
Another thing, make sure the rubber boot for the kill switch, that fits into the back of the carby, hasn't perished. I have found this to be another airleak area.
Failing all the above, that leaves the bottom seal/bearing I guess, but you would have to love your mower to go all the way for that.
Maybe too much effort, but I am just a hobbyist that does it as I find machines, more to learn and have fun, so I don't make much money off the ones I sell. The ones I don't get too attached to anyway haha.
I may have also changed the poppet valve to "A" as well, as I read in some old manual that this certain model of powertorque use this setting. Or maybe I am getting this mixed up with another PT I did this to.
Changing the sparkplug with a new will likely shows noticeable difference on revs especially when the governor is not working properly. You mentioned that the plug that just died, the revs is a bit too high and the new plug revs the engine to the point it almost self destruct. Obvious reason is because the plug is new and has stronger spark and strong ignition. But still that doesn't address the main issue and only the difference between plugs.
Possible solution: 1. Clean the governor air venturi with wire and carby cleaner. This air venturi is located on the base of the mower in-line with the flywheel with nozzle connected to the carburetor diaphragm cap. 2. Change the diaphragm. The diaphragm might be getting hardened and stiffer or you might have the aftermarket diaphragm which is hard, thicker and stiff. 3. Change the long spring or return spring with a lower weigh or grams (weight is measured by grams per displacement) e.g. the clear color one. 4. Change the main jet with lower flow rate e.g. 2-rings. 5. Adjust poppet valve setting to low or more restricted when fully closed.
Yes Norm but a spark plug change can't do that unless there is a problem somewhere else.
There are a lot of things you can check and adjust ,clean etc but sometimes if you don't replace the main crank bearing nothing will stop the over revving.
Thanks all for your contributions, looks like I'm back to square one with this machine, Last year September I pulled the carb and fitted it with Joel's (CM) SS needle & return spring with modified cap to suit,plus diaphragm. When it was over revving I pulled the carby off to discover that there was actually a chunk missing out of the bayonet type fitting where it fits to the manifold.
I stole a carb off a mower I had with a dodgy frame (Victa Rapier) and swapped the new bits into it but used the original poppet as the rapier one appeared different...only 2 settings but a nifty little peg which would have made it easier to change settings, I renewed the O rings to carby, manifold &starter but not the lower bearing one. I was sure this was going to solve all but not so! I'm not sure which needle is in it but I'm a bit suspicious of the thread where that goes in so don't want to interfere too much with it ffor the time being.
I had a poke around with the air diaphragm but wasn't sure whether to poke the wire right through it...thought it might have a mesh or something in there. @Sapper, is this what you refer to (Engine Venturi pipe) having been cleaned out with whipper snipper line?
EDIT. Just remembered I did put a shorter spring in the diaphragm cap, just for the heck of it!
I never have a problem with high revving motors once I modify the carby, by lifting the cam with 3 washers under it. A couple of times I have had to put 4 washers under the cam to bring the revs down and then adjust my idle screw up to open the poppet to a nice idle
Hi Danny, Yes the higher you lift the cam the more difficult it becomes to fit the cable without bending it and creating another issue. I have a small round file and I file in the slot the cable comes through on an angle so that the cable has a more friendly entrance so you can easily clip the outer cable in its locating slot. I fit a 6mm screw in the cap so I can adjust the idle or if you have a G4 cap you can use the idler screw Victa fitted to those carbies
Thanks all for your contributions, looks like I'm back to square one with this machine, Last year September I pulled the carb and fitted it with Joel's (CM) SS needle & return spring with modified cap to suit,plus diaphragm. When it was over revving I pulled the carby off to discover that there was actually a chunk missing out of the bayonet type fitting where it fits to the manifold.
I stole a carb off a mower I had with a dodgy frame (Victa Rapier) and swapped the new bits into it but used the original poppet as the rapier one appeared different...only 2 settings but a nifty little peg which would have made it easier to change settings, I renewed the O rings to carby, manifold &starter but not the lower bearing one. I was sure this was going to solve all but not so! I'm not sure which needle is in it but I'm a bit suspicious of the thread where that goes in so don't want to interfere too much with it ffor the time being.
I had a poke around with the air diaphragm but wasn't sure whether to poke the wire right through it...thought it might have a mesh or something in there. @Sapper, is this what you refer to (Engine Venturi pipe) having been cleaned out with whipper snipper line?
EDIT. Just remembered I did put a shorter spring in the diaphragm cap, just for the heck of it!
Danny
Hi Danny,
What I mean is the little stub that comes out of the engine block in front of the fly wheel. So, you have one hose coming out of the carby on the cap, this goes to the engine venturi stub in front of the fly wheel. Just gently take the hose off the stub. Sometimes this can be blocked with junk (somtimes even the hose can be), and cause the engine to scream uncontrollably, even for a while after you change the throttle down to lower revs. Push the wire/whipper snipper cord right through and back again, just in case it was blocked.
CM explains it better than me actually
Quote
Possible solution: 1. Clean the governor air venturi with wire and carby cleaner. This air venturi is located on the base of the mower in-line with the flywheel with nozzle connected to the carburetor diaphragm cap. 2. Change the diaphragm. The diaphragm might be getting hardened and stiffer or you might have the aftermarket diaphragm which is hard, thicker and stiff. 3. Change the long spring or return spring with a lower weigh or grams (weight is measured by grams per displacement) e.g. the clear color one. 4. Change the main jet with lower flow rate e.g. 2-rings. 5. Adjust poppet valve setting to low or more restricted when fully closed.
what I'm about to tell you must remain between us, no sniggering, no whispering behind my back.
I pulled the carby off and cleaned out the govenor orifice, I think it was clear anyway, then took the carby apart. I pondered on poppet valves for a while and decided that the carby that I used last year had the 2 position valve and at the time I swapped it for the one that was on the mower I I was working on...the 3 position one.
I thought today that maybe I should use the poppet that was originally in the carby...the 2 position.Did that, then took the diaphragm cap off and deemed that the diaphragm was good and after a clean up started to put it together. I then realised that I couldn't find the locking plate for the diaphragm. Thinking a magpie had pinched it I went to find the other one I knew I had and found 2 in a plastic tray in the shed...I've only ever had 2 of them apart.
Yup been running it since last September without that plate on the diaphragm! It started right up with the new spark plug and although not much response with the thottle control worked well...untill the fuel pipe came off the front plate. Oh well!
what I'm about to tell you must remain between us, no sniggering, no whispering behind my back.
I pulled the carby off and cleaned out the govenor orifice, I think it was clear anyway, then took the carby apart. I pondered on poppet valves for a while and decided that the carby that I used last year had the 2 position valve and at the time I swapped it for the one that was on the mower I I was working on...the 3 position one.
I thought today that maybe I should use the poppet that was originally in the carby...the 2 position.Did that, then took the diaphragm cap off and deemed that the diaphragm was good and after a clean up started to put it together. I then realised that I couldn't find the locking plate for the diaphragm. Thinking a magpie had pinched it I went to find the other one I knew I had and found 2 in a plastic tray in the shed...I've only ever had 2 of them apart.
Yup been running it since last September without that plate on the diaphragm! It started right up with the new spark plug and although not much response with the thottle control worked well...untill the fuel pipe came off the front plate. Oh well!
Danny
Don't worry, I won't tell the rest of the forum. Just between us.
Seriously though, all's well that ends well. I have done stuff like this before as well, but in the process, managed to learn about all the other things to look out for, how they work, etc, off the fine gents of this forum before stumbling upon my silly mistakes.
Did you put a full size spring in the carby this time?
I didn't interfere with the springs this time, when I realised the error with the diaphragm plateI just bunged it back together and hoped for the best.
I'd still like to understand why the throttle lever has little effect on play!
Danny, many reasons why it won't open the poppet , cable has popped out, springs preventing it from opening, so many variables. When I have these problems, and believe me I have buckets of problems with these [Censored] carbies I take the carby off and look down at the poppet and open and close the snorkel lever and see if the poppet is opening, doesn't open a lot but you can see it. If it isn't opening you then have to pull it apart and see if you can find the cause. They are a crap of a carby but we are stuck with them on these motors. Only good thing with them is they don't rust
