OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions on Other Engines Scott Bonnar SX4000 Starter mechanism

Hi, I have a Scott Bonnar SX4000 and the starter mechanism is sticking every odd pull. If I pull slowly when it is jammed I can go through the binding as if I have passed through the problem. I have checked the spring and the action of the pawls and it seems OK. I have adjusted the valves to specs. I was wondering if there was a compression relief valve somewhere on the mower that may need attention. Is there such a mechanism on an OHV mower like this? To test the pull starter I also removed the spark plug and there was no jamming at all with the pull start mechanism. That's what makes me think there must be a compression valve on it somewhere.

same as a honda still . try checking the blade plate or bladebar , from what i think your saying , might be a loose plate/bar . the do have a decomp' but if you have adjusted the tappets then should be allgood (if done correctly) ...

try that before it gets more involved then we go deeper into it


oops , it is a chonda too mate . but its ok , they are getting better

Thanks vccomm.I'll check the blades tomorrow. Time for a glass or two now. If that doesn't show anything I'll re-check the valve clearance.

only a glass or 2 ? hahaha does it sort of pull strange ...... like it tightens up then tries to pull the starter handle out of your hand ? if yes . loose blades or broken key in flywheel puts out the timing

Ended up having three. Anyway, I had the luxury of a second one of these and tried the pull start assembly on it and it was quite smooth. That means something on the original mower is wrong. I hadn't thought of the flywheel key, must be onset of alzheimers. That is a good suggestion as the symptoms are like that. Strange though that it starts and runs OK with a drill or the odd pull with the cord. I guess that could mean the key has only shifted marginally. Does that sound feasible? The original is on the right.

sounds like just a loose blade though , a sheared key will do almost the same thing and it don't take much of a tree root or the like to break one ....... but check blade or plate first its easier .

if it is a bar blade they dont act much like a flywheel , not enough weight and they are the main culprit for a busted key too . no give they just stop fast .
so just have a looksee if its nice n tight and go from there

Dave

They do have a decompresser built into the cam gear, i have seen one but can't remember right now. A troll through the forum should get you more info.

correct bigted , the same type of setup as briggs so depends on valve clearances , if you remove the cover you can see it rock a little on the exhuast stroke just before compression but im sure he said he has adjusted them already though ?

so mainly its just a good service is needed if its the problem

Well I have taken off the blade holder and it seems in good condition and the blades are fine too. The flywheel key appears to be in position but I couldn't get the flywheel off (I don't have a big enough puller) to really have a good inspection. I'm going to do the valves again as that seems to be the consensus. I adjusted the exhaust (top one) to 0.020mm and the inlet to 0.015mm. Is that correct?

You guys were right. The valves needed more attention. I checked them and the gaps were far too big. I went looking for the correct clearance and somebody recommended both at 0.004" so I did that and now it's as smooth as silk. Whenever I do this the clearances usually end up too tight and I have to do it 3 or 4 times before I get it right. This helped: Donyboy valve adjustment
Thanks for your help again.

I just did another chonda a Victa V40. Wouldn't start, plenty of spark, would not start even if fuel was squirted into spark plug hole. Checked the valve clearance and there was none and they were done up so tight I had to use a socket wrench to undo them. Reset the clearance and it started first pull. This is a crucial setting as others have said here.

Gday Sparker.

Good result here. I find a lot of these machines where the valves are closed up and if they are really bad like yours they eventually flog out the starter which makes things difficult unless you have another chonda starter to fit.

In the last week I have had a Sanli and a Gardeners Choice Chonda's with exactly the same problem as your Scott Bonnar.

I adjust them at inlet - .15mm and exhaust .20mm and I haven't had an issue yet. When these machines are well serviced they are always 1 pull starters.

I too like Donnyboys video's. He is a very good teacher.
Anyhow good work.