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Discussion Starter #1
Ok, Z425 with Briggs 23HP OHV engine.

Checked keyway. ok
Replaced carb. ok
Checked coil gap. ok
Spark plugs. ok
Adjusted valves, 1/4 inch past TDC ok (twice)

Runs like a top when you can get it to run. pops and backfires through carb trying to start.
Checked compression in both cylinders today. 180 on one and 120 on the other.
I haven't been able to get it to run since the last time I mowed. Took an charger with lots of power and still the engine popped and backfires through carb until it finally started. Ran for an hour and never has started again.
I did all the things above and it still backfires through the carb when trying to start.
Before I rip into the low compression cylinder, is maybe the valves still out on the low compression cylinder?

Forgive me but it has been 50 years since I worked on these small engines at this level. HELP?

Thanks
 

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Does your throttle lever also include the choke? Or do you have a seperate choke cable?

Sent from my LGL52VL using Tapatalk
 

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My z445 has started hard since day one. They are famous for choke out of adjustment if you have the chock on the same lever as throttle. It back several times when new and would be fine for awhile. This year I went back to stock plugs, new fuel filter and seam to start better. It stills cranks a lot before it fires. Last year the battery would start to run down and I would give it a shot of starting fluid.
 

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Discussion Starter #4
Does your throttle lever also include the choke? Or do you have a seperate choke cable?

Sent from my LGL52VL using Tapatalk
Throttle cable is separate from the choke cable.
 

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I had one like this. If the fuel in the tank was below half it seldom would crank. The pump had to pull the fuel up and out of the top of the tank.
Not gravity flow. The choke had to be pulled before the key was turned also, very finicky..

I sold it and don't miss it for one second. Not because of the fuel issue either, I just didn't like the machine, but it was a grass cutting monster..
 

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Discussion Starter #6
I didn't have a lot of spare time today but I did go back and check the valves. Don't know where I went wrong. Brought up on TDC and then 1/4 inch past but the 180 compression cylinder way out of spec when I rechecked. I readjusted the valves and now I have reversed the compression. Now 180 is 120 and 120 is 180. Guess I am doing something wrong. Will look again tomorrow when I get time. I think both need to be in the 120 range for this engine.
 

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I didn't have a lot of spare time today but I did go back and check the valves. Don't know where I went wrong. Brought up on TDC and then 1/4 inch past but the 180 compression cylinder way out of spec when I rechecked. I readjusted the valves and now I have reversed the compression. Now 180 is 120 and 120 is 180. Guess I am doing something wrong. Will look again tomorrow when I get time. I think both need to be in the 120 range for this engine.
I recommend forgetting that silly 1/4-inch past TDC procedure. Rotate the engine to compress the exhaust valve completely and adjust the intake. Then rotate to compress the intake and adjust the exhaust. I've never had this procedure fail to achieve proper valve clearance adjustment.
 

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Discussion Starter #8
I recommend forgetting that silly 1/4-inch past TDC procedure. Rotate the engine to compress the exhaust valve completely and adjust the intake. Then rotate to compress the intake and adjust the exhaust. I've never had this procedure fail to achieve proper valve clearance adjustment.
Yeah, that is the way I remember doing it but I read the Briggs manual. lol I will try and give a try today. Thanks
 

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Discussion Starter #9
Ok, to close out this thread I will say it is up and running. I had a brain fart and was thinking when both valves were closed I was on the compression stroke. I forgot, both valves are closed on the power stroke also. I adjusted both on compression stroke and all is well.
 

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For a long time I had to use starting fluid on my 18 hp Kohler (my old Gravely ZTR) even after an ignition overhaul. When I was getting it ready to sell I removed the carb and cleaned it in my ultrasonic cleaner (with heated water). Then I had to tweak the idle fuel mixture so it wouldn't backfire on ignition shutoff.
 

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My Z445 was the hardest to start when I first got it. Simple choke adjustment and for 8 years it started first crank after that. The throttle cable design and placement could have been improved on but I believe my issue was mostly who did the PDI when it was new.
 
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