I have had this kick back on starting with a number of these silly little sprinter mowers, when they decide they don't want to go over compression they can nearly break your fingers. I should have weighed the blade bar the other day when I had one off but they are so light, probably 100 grams and my belief is this is no different than trying to start a motor with the blade carrier missing or loose. I wanted to see if I could add some weight to it to see what it would do but the bloke wanted to pick it up so I just left it and warned him of the problem. I am thinking of adding some weight above the blade bar to see if this helps solve the problem. I'm also thinking that increased spinning mass weight may also help with some of these Briggs that have hunting issues . Anybody have any thoughts?
I am still annoyed at the guy who said his centura (tecumseh) engined edger was 'hard to start'). I pulled the cord half leant over the handle, it kicked back and I did my back.
I haven't had a problem with my sprinter with 450 flat head briggs. But the blade on mine is near new as it never did much work.
Would one of the sanli blades for that small deck type model fit the existing boss - they have a big back of the blade - more weight, better catcher flow.
Hi Tyler, I must have had at least half a dozen of these Sprinters over the time and they have all had this problem. Some I just binned, some I fitted the motors on bigger chassis and I can't recall them still having the problem. Usually with these Sprinters I don't get a catcher so I don't bother with them but I do want to see if it is the lack of weight that causes the problem with these. I still have a couple of them here I can play with, just have to remove the blade boss and fit one that fits a decent type of blade carrier. Another issue with no weight in the spinning mass of the blade carrier is the fact that all the impact load required to cut the grass is being delivered directly by the crank shaft
Hi Norm and Tyler, I have had this kick back problem on a few mowers,as long as the blade is not slipping on the crank boss and the boss is not slipping on the crankshaft and the flywheel key has not sheared.
I would check the air gap on the coil to flywheel,by increasing the gap the timing is retarded.
When mowers have too much advance they kick back.
I've increased the air gap on a few mowers with this problem and it's worked to stop kick back.
I've also found a light bar blade doesn't cut as well as a heavier blade plate ,I have added weight to a light bar blade and in my opinion the mower cut a lot better and did not stall in long grass.
A boss cut in half then added to the crank should be enough to notice a difference you can also use a half inch piece of flat steel between the boss and the bar blade,the engine would need spacing up 1/2 an inch to compensate , this adding of weight needs to be professionally done for safety and durability reasons .
Hi Norm With the surging, I did have a slight surging issue. It required a tachometer to fix - couldn't do it by ear. I didn't know the top speed, so went with 3100. With the engine going, bend the little spring tab to make sure no tension, then get 2900rpm by tensioning the big spring (or 200rpm below top speed), then tension the little spring to get 3100rpm.
But I do think you have a really good point with it having stuff all reciprocal mass. I have just weighed one of the blades off a parts victa vantage 16in. it weighs 225 grams - but the back up lifts are worn flat, so 300g is probably about right
it has to be that the blade carrier is too light because of the number of these I have come across that have this problem. These motors fitted on Rovers etc don't kick back like this.
There's about 5 Sprinter mowers here Norm ,I will get one running and see if it kicks back,I have a Tiger mower that I have used for years and I think the bar blade is very similar to the Sprinter blade ,the Tiger has not kicked back.
I don't think it's a blade weight issue but bolting the Sprinter blade onto a good Rover for testing would prove the point one way or the other.
Max, is the Tiger an OHV Chonda? I have not had an issue with any of those kicking back, seems to be a Briggs SV issue. I have a Sprinter here with an OHV Briggs on it but I haven't looked at that one yet
I reckon the flywheel is somewhat heavy on those chonda's, just like the real thing, and prevents the problem. But then the cheap and nasty briggs is too light and kicks.
Yes Tyler, I am pretty sure that is what it is, the Briggs would be fine with a decent blade carrier and it is not for Briggs to know what a manufacturer is going to swing off the end of the shaft. When I get a chance I will see if I can set one up and try it.
Hello Gents, kickback is almost always a sheared flywheel key, creating spark well before TDC. First thing i check on any machine with a bar blade is the key to ensure it hasn't sheared. I also agree that the heavier blade mass produces more power simply due to the greater spinning mass.
Hi Max and BT, The sheared key can be directly related to the fact that the mower is relying on the spinning weight of the fly/fan wheel instead of having a good blade carrier to do this work.You only have to look at a Victa F/C on an 18 inch base and the same motor on a 24 inch machine, the big 24 inch blade carrier is doing most of the work making it a far more powerful machine
This Sprinter below was ripping the starter cord from my hand when I first tried to start the mower, the engine had oil in the combustion chamber and exhaust so I removed the spark plug and turned the motor over to remove the oil.
Dismantled the carby gave it a clean out reassembled the carby ,replaced the spark plug and I could not get it to kickback,started it at least 20 times.
The only other issue that may cause a problem is if the carby was over fueling or the valve guides or rings are worn which may cause the engine to hydraulic lock when starting, too much fuel or oil in the cylinder .
Hi Max, I have had a few Sprinters that have been fine, no sign of kick back but why is it that the only Briggs I have had with this severe kick back is the ones on the Sprinters. I'm thinking that with the heavier blade carrier they are more forgiving with the extra bit of weight.
Hi Norm, I've had a lot of mowers that had the kick back problem on starting ,the shear key on the flywheel is designed to break when the bar blade hits an unforeseen obstacle so the crank is not damaged .
It would be easy just to bolt one extra bar blade onto the Sprinter and see if the extra weight helps. I would try a heavier blade plate if all else failed to fix the kick back problem,old coils can give a weak spark and cause backfiring and old spark plugs can cause backfiring.
