I just can't find the problem.

[klicky96]

Alright guys, I have a 13.5HP Briggs I/C engine. It is spittin' and sputterin' really bad. Its not missin though. Its hard to explain. Sometimes, it blows flames back through my carb.

Now I've checked the valves, they are going through there cycle fine. Compression is fine. Key on my flywheel is fine. Coil is fine. Sparkplug is fine.

I just dont understand. It kinda sounds like the timing is off. When I do get it started, I can punch it full throttle and then it'll miss.

Does anyone have any ideas?

 

[souperman000]

maybe its the mixture

 

[Doc Sprocket]

Replace the spark plug in case the old one is faulty. Make sure new plug is gapped to spec (0.030 is a safe bet). Make sure fuel is NEW. Check that valve lash is set to spec, using a feeler gauge. Check coil air gap against specs with above gauge. Remove flywheel to check key.

 

[Doc Sprocket]

Sorry- had to make up a SPAM sandwich. Anyways-

Clean your carb and make sure you have the spec baseline settings. Also, coil/CDI could be defective. Just because it's producing spark doesn't mean it's strong, consistent, or well-timed.
In addition, make sure the spark plug lead is not cracked or abraded, and is well-routed. Check the ignition/kill circuit too. I recently came across a mis-wiring that caused very similar symptoms. Some idiot (me, in a hurry) accisentally tied the charging circuit into the kill circuit. Look for cracked or abraded insulation on the wired, tight and proper connections, and that they go where they're supposed to (duh!)

 

[klicky96]

Well the coil is giving a really strong spark. Im not too smart and grabbed the wire. It lit me up pretty good. The flywheel key is fine. Spark plug is new, pre gapped to .020. It is a flatty so it doesnt have a valve lash like the hondas. I pulled tghe head and checked the valves, they are opening up fine. I did see a little bit of oil around the piston, kinda a little more than usual, but the rings aren't shot. Im just really really confused. It is bone stock. When It started to do this, I gave it a good tuneup. Cleaned the exhaust port, new sparkplug, new oil, etc. But that did nothing.

 

[Doc Sprocket]

Please note, I edited my above post for more info.

Also- check spec, but plug gap should be more like 0.030", IIRC.

Flatty? I saw I/C and thought OHC. Fine- Check points and condenser too, if so equipped. AND- if grabbing the "wire" lit you up, insulation may well be bad.

 

[klicky96]

I will, its kinda late and I got school in the morning. Thanks for the help.

 

[Doc Sprocket]

No sweat- don't overlook souperman's comment either. I had an engine behave similarly stupidly when it was just a bit too rich.

 

[klicky96]

I didn't. I'm gonna my carb out also.

 

[OzFab]

These guys may be right, it may be something simple but, if all that fails...
Have you had the engine apart recently? Valves may be working correctly, but are the working at the right time?

 

[klicky96]

I have never taken this engine apart prior to this. It is still the factory-built engine. I just took the head off to check the valves.

 

[klicky96]

Well guys, I doodles with the engine today. Cleaned the carb, checked the spark, got a new plug, tried to fire her up. She will crank over, backfire, blow some exhaust back through the carb, and then it'll do nothing. I try again, she does the same. I'm thinking maybe the valve springs are worn and its not opening the exhaust valve up right. Now I've heard that even though the exhaust valve is opening, it doesn't mean it is opening when the engine fires over and gives more pressure. What do you guys think?

 

[Jake.B]

Yeah take of your valve cover, check for any thing out of the ususall then replace the springs check your valves why your at it for any warps or problems.