I've been lurking in the shadows for a year or so enjoying the pics and posts but have had to stretch the grey matter a bit when I decided to repair a cracked cover on my Pro 550's carby (after reading on here how an air leak can make the mower rev too hard which it certainly did). A quick ebay purchase ensued.
Pretty straight forward you would think but after it wouldn't continue to run after installing I had to resort to the forums many valuable posts to help sort me out and a good thing too as I found the lifter installed incorrectly and the rubber boot completely worn through on one of the wires used to stop the mower (although it still functioned correctly). Anyway, mower up and running again and not revving quite as hard which is a good thing as it is easier to keep up with and it's cutting a treat so thanks to all those who give up their time and info here.
Hi JRC and welcome to the forum. Yes, the info on here is invaluable and it's always good to see people having a go. There's lots of good stuff here, so feel free to look around and post any questions of anything you may be having trouble with. Cheers, Ted
The over revving situation had got the better of me so I decided to do the NormK carby modification minus the idle adjustment but I still have the problem although it starts perfectly.
What happens is that when I increase throttle position and the engine revs up, it gets to a certain point where it takes over and opens up the throttle fully and excessively by itself.
At the moment I have cut a thin piece of angle iron to the precise length and pop it in the slot the throttle slides in to stop it pulling itself open any further but I'm sure there is another way to fix this.
I also have had this problem with my Victa Powertorque. It is still there, but it is very minor rev, I think I need a new throttle kill wire rubber, and governor diaphragm as one edge is a little squashed.
Here is what I did:
Clean carby (especially main jet), and add 2 brass washers under the throttle cam (3 too many for me, but maybe not in your case). Much better.
Turned poppet valve in carby, so the B is where the C was � this makes it richer (refer manuals section), but the change wasn�t that noticeable. It did pick up rpm better though.
Then I replaced the o ring on each end of the plastic intake manifold, and the one under the starter mechanism.
I also stuck a piece of wire down the port the vac hose attaches to (on the block next to the flywheel). I thought it might have clogged up and changed how the governor works.
I then took the exhaust off and cleaned carbon out of the exhaust port � I thought it was worth a shot if it was stuffing up back pressure.
I did the last few things all at the same time, so I don�t know which one made the most difference.
As far as I know, the governor works by pulling the throttle closed � that is, it�s making sure the poppet valve doesn�t fall all the way open. When the motor slows down (heavy grass), less vacuum is created, and this allows the poppet to drop and rev it up again. If you have a vac leak (eg split diaphragm) or insufficient vacuum signal (blocked vacuum port), then maybe there isn�t enough vacuum at high rpm when the engine is drawing the mixture hard (and pulling the poppet valve open by itself).
Checking this is probably the quickest � just don�t snap off the plastic connector on the carby.
Hi JRC, it is something you have done or something you haven't done. I have done in excess of a hundred of these and can't say I have come across the problem you describe. I have had the occasional carby body that caused problems but if I have problems I just swap it out. The only reason it can go full throttle without control is because the poppet is opening too far, there must be something wrong with the cam or lifter for this to happen. As for swapping the "O" rings out I find that I probably only have to one in maybe twenty so they are very rarely an issue.From memory I have replaced only 2 "O" rings on the inlet manifold (I have never bought any) and I replace the pull start "O" ring only when I change pull starts. The primer cap "O" ring change is a must but that is an obvious one
NormK, It was doing this before I did your carby modifications so I don't think there is a problem there, in fact throttle control is very smooth through the range now, I just can't let go of the handle as it will slowly pull itself open and really rev the guts out of it.
The little spring is underneath the diaphragm.
I have changed the primer cap as well to no avail although that was a necessity as the plastic around the bulb was failing.
Tyler, thanks for the info some of which I have already done. Maybe I need to to do the rest of the o'rings I haven't done.
After all the seals have been replaced and the carby is correct, then the only thing left is the dreaded bottom seal. I've had a couple (maybe 4 or 5) out of the hundreds i've repaired where the bottom seal is the culprit. If this is the case then a complete tear down is required to replace the bottom bearing and seal. If you're going to that effort, then a complete once over is recommended, both bearings, a light hone and new rings at a minimum.
Ok so now I understand, the problem is in the cable not the carby. If it is the actual throttle lever that is moving fully open, usually the cables have enough resistance in them to prevent the cable moving. You may be able to tighten the screw through the throttle control lever to increase the resistance on it
Holy crap, don't tell me I've overthought the problem. I've assumed there was an issue due to the fact that the engine revved so hard at full throttle.
My old man bought a Victa Silver Streak in 1980 (I think) and I just used it as a comparison. That old beast is always used at full throttle and doesn't rev as hard as this one.
I'm not entirely sure I haven't already tried that but will get onto it when this bloody weather improves a bit.
JRC, if you are concerned that it may be revving too hard you can fit one of the lifters with a shoulder on it that prevents it dropping fully down the cam,not sure why Victa fitted these to some of them, it may have been because of this problem. Not having had this problem because you can usually control the revs with the throttle control, so I cut the shoulder off.
Yesterday I thought I might mow some of my lawns, (takes an hour and a half on my 48" Husqvarna rider but far too soft under foot at the moment) as they are looking a bit rough, and then I'd have another look at the throttle.
After about an hour and a half or so the mower started to bog down so I eased it back and turned it off. I don't know what has happened (or what I've done), but I've managed to seize it. Ah well, no more over revving issues.
Too pissed off to think about repair etc. at the moment.
Apologies to those on the mainland suffering through the drought.
JRC, sorry to hear about this, any idea what might have caused it to happen? I don't want to state the obvious but the bogging down like that sounds like a shortage of oil.
I bought a new mixing bottle from supercheap as my old one had a badly leaking lid. It was also twice the size. I have used it a few times but I suspect I have been sloppy with my oil addition and under done it, but not by much so I don't really know. The oil I'm using is the red Stihl 2 stroke oil.
Hi JRC, all should not be lost, just look around and pick up a Powertorque mower and swap the motor over. I will fit, I'm just not sure if it runs a longer shaft. If you can pull the motor off and then I can check the measurement for you. I do have one of those here but it has a full crank motor on it. I can check that one tomorrow to see if the shaft is any longer than a normal full crank, but I think they would probably be the same. You should be able to pick up a Powertorque for free/$10/$15 at least that's what they are in Melb if you scratch around
I thought that's what I might do but in Tassie there just doesn't seem to be that many mowers about and what is, is on gumtree usually for too much or some other savvy "mower hunter" has already snavelled them up lol.
Another problem I have is a lack of workshop space and a buggered back (a couple of surgeries) which is a bad combination for working on mowers but I will tackle this when the weather warms up a bit.
I am just wondering if anybody has any knowledge on the drive on these mowers, it appears like some cone sort of setup, when you pull the lever it seems to rotate and twist in and this seems to lock the drive. I haven't pulled the box out but I have to do this because the cable is not connected and I am not sure if something is broken on the lever and why the cable has come out
I am just wondering if anybody has any knowledge on the drive on these mowers, it appears like some cone sort of setup, when you pull the lever it seems to rotate and twist in and this seems to lock the drive.
G'day Norm The drive is of similar design to the first Autodrives of the 1970s. It uses worm gear reduction to an output shaft where coil springs grab the drive sleeves leading to the LH and RH wheel pinions.
The double advantage is that loosening of the spring when a wheel pinion would exceed the speed of the final drive shaft [when turning, the outside wheel speed would exceed the drive speed] meant that differential action could be achieved.
Thanks Jack, that gives me something to work with, it seems a fairly robust design. I will pull it out a bit later, I have to get back to some other projects at the moment
