20hp Briggs Loses power under load.

[Dowd_Elwood_P]

I have a 20hp Twin Briggs Model 461707 Type 0143 E1 Code 9911295B that's in a 13A6699H192 1997 LTD Yard Machines lawn mower. It's slow to throttle up & loses power when it's under a load. I've cleaned the carb, new spark plugs, checked the coil, checked good fuel supply & no black smoke when it starts to lose power. It does have a lot of fuel sprayed out of the intake in just a few minutes of run time. Any help would be appreciated. Thanks.

 

[bertsmobile1]

If the plugs are not oiling up and it is just loosing power and not missing or stopping then it is most likely either valves or overheating.

To check the valves you have to remove the cowl and to clean the fins you have yo do the same thing so may as well do both.

If you don't have a manual you can download one from the B & S web site

 

[ILENGINE]

I think it is running on one cylinder. Make sure you have spark on both cylinders, and then if possibly do a compression check.

 

[motoman]

You know immediately if only one cylinder, right? If the guys' suggestions are implemented and still problem are the plugs "lean looking?" (no deposits or very light). How about fuel starvation on power demand? (Plugged main jet, bad float level, stuck inlet valve). Just ideas.

 

[ILENGINE]

Some people don't know they are running on one cylinder. Heard of a Briggs Opposed several years ago in my region that broke a rod when new, and the guy ran it 4 years before it went to a repair shop, and the tech found the one cylinder problem. Briggs gave the guy a new engine even after 4 years.

 

[Dowd_Elwood_P]

Thanks for the replies! I checked spark, it has spark on both cylinders so I started it & pulled the left wire & it died. Started it & pulled the right & no change. Changed the plugs to different sides, same result & the right one was white with gas on it, left was blackened a bit. I rechecked spark with it running & the right one is quite a bit dimmer than the left. Compression was 33 on the left & 60 on the right, cold. I'll pull the plug out and ground it to see if it's getting enough to actually spark and report back. Thanks

 

[Dowd_Elwood_P]

The spark on the right plug looks sporadic and weak compared to the other side so I guess I'll try a new coil.

 

[mechanic mark]

Results engine manual & parts list, check air filter for replacement, adjust valves engine cold, always use B&S OEM parts.

http://www.globalsoftware-inc.com/c...er L-Head repair manual BRIGGS & STRATTON.pdf your engine repair manual online

 

[bertsmobile1]

Thanks for the replies! I checked spark, it has spark on both cylinders so I started it & pulled the left wire & it died. Started it & pulled the right & no change. Changed the plugs to different sides, same result & the right one was white with gas on it, left was blackened a bit. I rechecked spark with it running & the right one is quite a bit dimmer than the left. Compression was 33 on the left & 60 on the right, cold. I'll pull the plug out and ground it to see if it's getting enough to actually spark and report back. Thanks

With the left being 1/2 the compression of the right you have a compression problem, not a spark problem and it ain't going to work no matter how big the spark is.
SO it will be a valve / gasket / ring problem.
So as the Queen of Spades said to Alice "OFF WITH YOUR HEAD"

 

[Dowd_Elwood_P]

I put the new coil on and its running on both cylinders now. The right cylinder smoked like crazy burning off a bunch of oil build up so it looks like the previous owner had been running it like that for a while. It has plenty of power to mow now.

Bert, I noticed after cranking it for a while it actually dripped gas from the bottom of the left cylinder head which has the lower compression. I'm new to small engine repair but I don't think its supposed to do that I think you're right, I need to pull and inspect that head.