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Garden Tractors Discussion Forum

Briggs Straton Ignition Timing

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wsmm

12-28-2018 14:52:10




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I have an 11 hp Briggs and Straton Model 252707-0622-02 engine. Just had to lap the intake valve due to it not sealing completely. Also that exhaust valve stem had too little clearance so I fixed that while I was at it. Had originally run a compression and leak down test. Low compression 70 psi and failed leak down test, could hear it exiting the intake valve through the carb. After lapping the valve and adjusting valve stem clearance leak down test passed and compression was 125 psi. Tried starting it and it would not start, did not detect any gas blowing back out of the carb and was getting puffs of smoke out of the exhaust. Did have what appeared to be one or two backfires through the carb though. I have an ignition tester for small engines it has an approximate 1/4" spark gap inside of a hollow tube into which you insert a solid tube to raise the pressure on the gauge into the green range to simulate the condition in a cylinder. Bright blue consistent spark. When I was working on the valves I had the cover and screens off of the flywheel enclosure and looked at what I could see of the flywheel key. It did not locked sheared or broken. I did not however take off the flywheel to confirm it. When I pulled the plug it appeared to have some gas on it, not a lot. Any ideas of my next steps to get this monster to run or do I just out it out of its misery.

Thanks for any ideas or help,
Bill

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kevinstuff

01-10-2019 23:24:55




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 Re: Briggs Straton Ignition Timing in reply to wsmm, 12-28-2018 14:52:10  
My Briggs model 19 after many years Of faithful service , one day trying to start It had no compression ! So it was a piece Of carbon stuck between valve seat and valve But the old Briggs had a compression resale built into the cam , they have a spring on cam sprocket , So if yours was working good before lapping the valve , then it could be hard starting due to excess valve clearance
and if it is like my old model 19 , i had to grind the valve stems down . To get clearance Or there is a chance the compression realease spring is broken , and if the valve was leaking you wound not have hard starting . Now that the valves are seating and high compression is making it turn over slower. Try to locate parts list for engine , and identify that compression release . And. change the oil as it may be diluted with gasoline

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Bob

12-30-2018 15:37:54




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 Re: Briggs Straton Ignition Timing in reply to wsmm, 12-28-2018 14:52:10  
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Valve clearance "specs" for your engine... Intake .005" - .007", Exhaust .009" to .011"



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wsmm

12-30-2018 15:15:25




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 Re: Briggs Straton Ignition Timing in reply to wsmm, 12-28-2018 14:52:10  
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Just read a post says all Briggs and Straton engines have a compression release. My book does not give any information on the way to set the valves, only gives the clearance specs. Guess I'll have to do some research and see if I can find what I need.



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Texasmark1

01-02-2019 05:48:35




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 Re: Briggs Straton Ignition Timing in reply to wsmm, 12-30-2018 15:15:25  
One form of BS compression release is a hump on the camshaft preceding the regular valve lifting cam lobe. I forget which valve it cracks but there is a little ridge that lifts one of the valves off the seat just enough to let off some compression yet have enough compression to get started.

As the rpms increase, as the engine comes online, the speed of the camshaft rotating, exceeds the physical ability of the gas to leak out and the easy start function ceases to be a viable part of the combustion cycle. Pretty simple, reliable, handy way of providing easier starting if you ask me.

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Bob

12-30-2018 15:02:51




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 Re: Briggs Straton Ignition Timing in reply to wsmm, 12-28-2018 14:52:10  
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"It is an overhear 11hp old Briggs and Straton with electric start."

Did you set the valves according to the shop manual so the compression release function is working as it's supposed to?

You didn't post the model number, but the procedure MAY involve bringing the piston up to TDC at the end of the compression stroke, then continuing to rotate the crankshaft 'til the piston drops 0.25", then set the valves (and to rather "tight tolerances").

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wsmm

12-30-2018 15:09:09




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 Re: Briggs Straton Ignition Timing in reply to Bob, 12-30-2018 15:02:51  
Model number is 252707-0622-02. I don't believe it has a compression release feature. I have a general Briggs manual and not a service manual to this specific engine.



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wsmm

12-30-2018 14:33:27




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 Re: Briggs Straton Ignition Timing in reply to wsmm, 12-28-2018 14:52:10  
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It is an overhear 11hp old Briggs and Straton with electric start.



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Mule Meat

12-30-2018 11:41:49




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 Re: Briggs Straton Ignition Timing in reply to wsmm, 12-28-2018 14:52:10  
Overhead engine? Sounds like the valves are to tight.

If flywheel key is ok. Check the coil if you had it iff. Could be on upside down.



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wsmm

12-30-2018 14:31:42




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 Re: Briggs Straton Ignition Timing in reply to Mule Meat, 12-30-2018 11:41:49  
Did not have coil off. Valves did not have proper clearance, when I checked them with feeler gauges. Had to take a little off and set them at the minimum clearance according to the manual. Believe my initial problem was with an intake valve that would not close completely allow blow back through the carburetor.

While I was taking the trash out tonight, I pulled the spark plug and the engine turned over freely. Put the plug back in finger tight only and the engine would turn over, hesitate, and then turn over again and hesitate. Not sure if my battery is up to snuff or not. Going to put one of my batter battery charges on it, let it take a good charge and then switch the charger to the boost start position and try it.

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jeffcat

12-30-2018 15:58:40




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 Re: Briggs Straton Ignition Timing in reply to wsmm, 12-30-2018 14:31:42  
No that sounds like the release is not working. Classic description. Set the valves correctly should fix it. If not then you might have the little cam thingy broken on the camshaft.



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t.r.k.

12-28-2018 18:27:12




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 Re: Briggs Straton Ignition Timing in reply to wsmm, 12-28-2018 14:52:10  
A little back story may be helpful. Why were you working on it? What was it doing before or when it quit? etc.

I have measured 60 psi compression on a new Briggs engine, so your compression is very good.

Is the starter having a hard time spinning it over compression stroke? I mean, does it stall or slow down at some point when its turning over?

How is your spark plug? You didn't mention it. (Sometimes its the little things that get you.) If its got grey glaze on the insulator, its time for a new one whether that fixes it or not.

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wsmm

12-29-2018 08:49:26




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 Re: Briggs Straton Ignition Timing in reply to t.r.k., 12-28-2018 18:27:12  
It stopped after I was using it and went to adjust the carb, because I had to keep the choke partially on it to run. It just stopped as if out of gas and wouldn't start again. As I was turning it over after this I noticed it was spitting gas out of the carb. Now that you mention. Now that you mention it when turning it over now it will hesitate at a point and stall and then catch and turn over again. I thought it maybe was that the battery was low, turned over a bit better, but not right,when I but my old battery charger on it. Will try again with one of my two newer and better battery charged with boost start. I did notice last night that the oil looked a little overfilled, drew some off and it looks thin, wondering if somehow some gas got in the oil and diluted it. This is an old Briggs and Straton and has never been taken apart to my knowledge. Thanks you for all of you help, questions and advice. I'm open to any ideas you might have as I don't normally do much work on small engines and this one has me baffled. I'm wondering if the compression I now have of 125psi is an indication of any problem and if so what. Spark plug is a new RJ19LM gaped at .025, it appeared to be slightly wet when removed. When turning over I will get a puff of white exhaust gas out of the muffler as it turns over, like it is trying to start. If you need further information let me know and I'll rack my brain for the correct answer or go back out an try to start it again to see what happens. I'll probably wait until tomorrow when it warms up to 35 to try it again, it's 22 and my old body can't seem to deal with the cold. Could even be Tuesday until I get to it, as Church is this after noon, Grocery shopping tomorrow and Monday taking our God Daughter, who is also our foster daughter out for a Birthday lunch.

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Russ from MN

12-28-2018 16:52:17




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 Re: Briggs Straton Ignition Timing in reply to wsmm, 12-28-2018 14:52:10  
On the ones I have worked on you can take the nut and washer off and then see the key. If it's even partially sheared it's obvious.



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jeffcat

12-28-2018 15:11:55




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 Re: Briggs Straton Ignition Timing in reply to wsmm, 12-28-2018 14:52:10  
Not going to stick my toe too far into this one. Backfire through carb most times is timing problem. Partialy sheared key will drive you buggy. They are only aluminum. Hanging intake valve too. You didn't take this engine apart and didn't get the little punch marks back together? Just throwing a coulpe of ideas. One that really threw me for a while was on a Mc Culloch chainsaw. Guy I know has a pretty large repair and service shop. They had this Timber wolf that they just couldn't get to fire. The customer said heck with it. I walked in the next day and he gave it to me for parts cause he was so discusted with it. About ten minutes at home I had it running like a jazzed kitten. The flywheel that is cast pot metal. In that flywheel is a metal nut that is keyed and goes onto the crank shaft. The flywheel was defective and that nut had spun partially in the cast flywheel. No I never said anything to him because it was so stupid but i did have a Briggs Vtwin that the wafer washer was weak and would allow the flywheel to slip and shear the key. Put a big lock washer on it. You'll find the problem sooner or later. Let us know.

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wsmm

12-28-2018 15:40:06




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 Re: Briggs Straton Ignition Timing in reply to jeffcat, 12-28-2018 15:11:55  
Will pull flywheel and replace the key. I think some in my parts drawer. Intake shouldn't be hanging, when I had it out to lap I cleaned the shaft on it and the exhaust valve real good. Then turned the engine over by hand to insure they went up and down with no problem. Depending on the weather and what else comes up it maybe a few days before I get back to it. Due to being a young 75 and major surgery and infection last year I'm not at my best and tire and get real sore easily. Will keep you all posted on wht I find and if I get it running or swap it with another engine, newer 14.5 hp briggs, from my ewer lawn tractor that blew the forward clutch gear assembly again.

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