B&S Newbie having issues with engine refresh, governor and throttle return issues

M

MtGoat

Forum Newbie
Hi All,
My kidlet was interested in getting our 2000 era Yard Machines riding mower running properly so we started in on it last week. He's fascinated by engines and I've been training him up on our Datsun fleet, which is pretty good for learning the basics. Neither one of us had ever messed with a single cylinder, magneto fired engine before, but I figured this must be pretty simple...LOL.

Anyway, we decided to attack the compression release issue. (And the fuel tank flooding the system if you let it sit deal as well.) I have *never* been able to start this mower without starter fluid and hand spinning the engine to just after TDC. After reading here and some YouTube university, decided it must be the compression release thing.

Ordered an aftermarket cam. Went to look for float bowl components and found aftermarket carbs were only a few bucks more than parts for them, so picked up a carb too. And the magneto was out of spec for resistance, so that as well. All in all about 60 bucks worth of parts. Carb, magneto, cam, all new.

Removed the engine, cleaned it up, got it on the bench. Pulled the sump and to my dismay the CR mechanism looked OK. Weight moved ok, little tab went up and down on the cam. Still, I got a new part so I wasn't going to not install it. Put in the new lifters, new cam, sealed it up. Put the steel pushrod on the exhaust, aluminum on the intake, gapped the valves, no big deal so far. One video said I should even hear a click when the lifter passed the tab when rotated by hand. I have never heard this with either cam in it.

My next issue showed up when I attempted to reassemble the throttle plate. I *know* there was only one spring in there (aside from the one sleeved onto the throttle pushrod), and I swear one end went on the short end of the governor bellcrank, and the other on a tang off the slider the throttle cable actuates. I can see the wear marks on the holes at both ends. Yet...the darned throttle does not want to return when let off. This would be the long arm of the governor bellcrank with the actual pushrod to the throttle shaft.

Working the slider where the cable goes in, as noted, the throttle will advance yet will not return, it simply stays open. I know the small long spring from shaft to gov arm is installed correctly. I have no idea what I did wrong.

This frustrated the crap out of me, but I decided to reinstall the engine and see if I could get her fired up, even if I had to poke at the throttle with my fingers.

That's when I discovered to my horror that I still had the compression release issue. I tightened the EX clearances, hoping to get it to ride the darned bump properly with lower clearances. I set it to .004 and it was still not great. I then, with the valve cover off and ignition disabled, would run the starter and tighten the valve just a skosh, and repeat until the CR appeared to be kind of working. I'm fearing having it too tight and burning a valve, but if it won't even start I'm screwed already.

I finally get it running and I have multiple issues....
1) Throttle arm (governor long arm) will not return on it's own, which I already knew
2) RPM too high. Ordered a tach. (amazon sale; 3$! life is crazy!)
3) Engine is surging.

I think I may have wacked the two arms of the governor bellcrank out of relation to each other, for one thing. I may have done something to it while spinning and shifting it around on the bench as I worked. I remain mystified at what is supposed to provide the return function on the long bellcrank arm, even with engine off. I know it worked before! I figured this small engine would be a piece of cake after decades of wrenching cars. NOT!! ;)

Anyway, this looked like a useful forum with knowledgeable people, thanks for reading my post. Sorry for it's length!
 
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Just DL the Briggs 276781 service manual and read it completely, just not scan over it. As for you have screwed up the adjustments. Most likely that mower has a Briggs Single Intek engine. The ACR is not on the exhaust valve but is on the intake which the rocker farthermost from the flywheel. These engine uses a cross flow head design.

Now as for the carburetor throttle lever it is suppose to be at wide open until the engine is running then governor pushes it back toward close. how much depend on the throttle setting. You may have destroyed the governor by setting it incorrectly.
 
Thanks for the response.

The ACR was on the lobe closest to the cam gear, which when I think about it means it's on the bottom, and I was adjusting the top valve which is clearly the exhaust, I can see that top valve (tube) in the exhaust port. It is the closest to the flywheel, not the farthest!

So I think you're right...I am probably adjusting the wrong valve. I'll give it another go!

I *thought* i saw the long arm (throttle) on the bell crank return on it's own when examining things before I removed that plate of sliding bits and springs. However, I am not certain so again you may be correct. I'll check into that...

I was uncertain how to set the mixture on the new carb, so I used interwebs instructions...turned it closed, then backed off 1.5 turns.

Thank you again for your input! I'll try to find that manual.
 
Got the manual off the web. I have all the numbers off the valve cover, which is good. Worked their decoder ring for 31C707..but I don't see a cross reference to the model numbers they use in the book (91000, 97700, etc) so that is irritating. Winging it from the pictures.

Read about setting the mixture. Closed the screw, then out 1 1/4 turns.

Set exhaust valve back to .004. Adjusted intake valve, set it to .004. ACR still fails. That was my smallest gap on the set. Loosened set screw, tightened just a little. Success! Replaced valve cover.

Started right up. No backfiring. Throttle does return to home/idle now, when running. Surges at full, but the comment about the governor splodin' worried me, so I didn't run it at full for more than a few seconds. Now reading up on setting up the governor. I'll mess with that tomorrow when my magical chinazon 3 dollar tach shows up. Sounds above 3400 or whatever to me, when I did manage to start it in the past I don't recall it sounding as fast as it does now.

Again, thanks for the help so far!! :)
 
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I guess I'll need to open up the exhaust clearance a bit more, I still can't tell which 'model' I have other than it's a vertical drive, and get it to .005-.007 which looks common across vertical shaft engines.
 
it's true there is no substitute for reading the manual. i think it's a 310000 series. I searched the number and looked at all the associated pics.

having never dealt with a governor before I was mystified. I think I get it now. It's an analog cruise control of sorts. The g shaft is trying to turn to push the g arm towards closed (idle). the bellcrank transmits this via a spring to the throttle slider. The spring buffers the throttle cable slider from the bellcrank arm, and the system exists in tension, spring is trying to hold the throttle where it wants while the governor tries to slow the system down. since I have a new carb, a reasonable assumption is surges are caused by a mismatch in the system, resulting in oscillation.

the throttle return action of the g arm has nothing to do with the governor spring, the g arm returns to idle position via the natural tendency of the g shaft to want to slow things down

this is why the max throttle is set by the tension on the g spring, and the ritual bending of the tang to hit a max rpm? the higher the tension the more the current throttle setting resists being slowed down. set too high, the gov has to run higher to force it back, and the result will be rpm which are too high because the governor had to spin that fast to turn the shaft against the tight spring?
 
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MtGoat said:
I guess I'll need to open up the exhaust clearance a bit more, I still can't tell which 'model' I have other than it's a vertical drive, and get it to .005-.007 which looks common across vertical shaft engines.
Click to expand...
For 31/33 Cu In OHV engines the valves are set at .003-.005 for the intake and the exhaust at .005-.007.

This should be in the manual I sent along with a few added notes. I still haven't added the new flywheel and cylinder head torque values. Still learning how to modify the PDF. Some these PDFs are password protected which has to be stripped out to edit them.

And for parts you do need use the numbers on the rocker cover as Briggs have made changes to the engine based on the date code.

With you having most likely a Nikki clone carb the high idle jet maybe too lean causing the lean burn surging. The solution is to enlarge the jet a frog hair so the mixture screw becomes more in play. Just got be very carefully as you can over it very easily and the mixture screw can't the too rich mixture.
 
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I’ve found many aftermarket Briggs carburetors often surge and need the main jet opened up a bit.
I have a jewelry drill bit set and welding tip cleaners. On size up on the drill bit at a time. These bits are super tiny.

I believe you have the governor linkage setup wrong unless you installed it incorrectly?

So far you have received excellent advice above.

The final question is “What have you learned from this?”
 
Ok, it starts and runs now. I followed the procedures step by step from the manual. I need to get a better tach, the one from chinazon is a piece of junk. readings all over the map. I should have paid attention to the fact that it has only the plug wire pickup and no ground. It's probably ground bouncing all over the place.

It turns out I've been fighting a couple other things. The anti diesel solenoid wire to the carb keeps coming loose but not falling off. That was fun to debug. Then I found that the foot brake pedal does not hit the safety switch properly without your foot literally on it, and that comes and goes. I'll get under there and screw with the switch some. Prior, once it was set with the parking brake on, and mower deck retracted, it would start. Now it requires a little pressure on the pedal.

The throttle response is now fairly linear to the lever motion, so I think I got the springs in the right holes. Before, it did basically nothing until 2/3s of the way to full. Now, I get a smooth transition.

It's still surging, but I can drive it and the surging quells a little once it's warm. Doesn't occur until above half throttle.

Another not great thing...what looks like burning oil (whitish blue smoke) belches out when I change throttle or the load on the motor increases. I took it for a spin and mowed a patch, when it hits thick grass a thick puff emerges, clears up, and runs OK until the next thick patch. I wonder if the rings are going.

What have I learned? A one lung engine is not a simple beast, read the damned manual, and my this is tedious!
 
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