JustinW.73 224 #1 Posted July 8, 2014 (edited) I have a k301 and when I'm mowing (having the idle up to its highest) and shut the mower off and idle down it makes this backfire noise through the muffler. Also, when going from a low idle to a fast idle it will puff a little black smoke and I know if its black its a gas/carb problem. Could the carb just need to be rebuilt and cleaned? Any help would be great, thanks. Edited July 8, 2014 by JustinW.73 Share this post Link to post Share on other sites
formariz 11,862 #2 Posted July 8, 2014 I am sure that experts will chime in but I think it is running rich at high throttle and unburned gases ignite in mufler when throttle is lowered. My Electro 12 does the same thing. If I shut it off right from high throttle it backfires really loud and shoots a long flame out of exhaust. I just lower throttle gradually and let it idle for a few seconds prior to shut off. 1 Share this post Link to post Share on other sites
Catmanii 36 #3 Posted July 9, 2014 My C-120 does the same. Like formariz says, I just lower slowly and let idle for a little bit and then shut it off. No backfire that way. Share this post Link to post Share on other sites
JustinW.73 224 #4 Posted July 9, 2014 Ok ya I do that now. I found that out a while back but i would think you could do something to fix it. Share this post Link to post Share on other sites
formariz 11,862 #5 Posted July 9, 2014 I tried several times to adjust fuel mixture so it would stop the backfiring but it did not run well with such a setting so I just went back to original setting with the backfire which is easily avoided. Share this post Link to post Share on other sites
Fordiesel69 214 #6 Posted July 9, 2014 Valves gapped wrong, or carb incorrectly adjusted. The other issue could be the carb cannot be adjusted properly because of throttle shaft wear, or it is dirty. Share this post Link to post Share on other sites
JustinW.73 224 #7 Posted July 9, 2014 Ya I think the valves (especially the exhaust) needs to be replaced. The exhaust valve is almost burnt to a crisp. Share this post Link to post Share on other sites
JustinW.73 224 #8 Posted July 18, 2014 Does anyone else have any ideas? Share this post Link to post Share on other sites
Geno 1,928 #9 Posted July 18, 2014 Weak spark can cause it also, Point gap, dirty points, a weak coil, plug wire or spark plug. If you dont get a good strong spark in the cylinder it can cause a lighter explosion leaving leftover fuel. Share this post Link to post Share on other sites
JustinW.73 224 #10 Posted July 23, 2014 (edited) It has strong blue/white spark. Edited July 23, 2014 by JustinW.73 Share this post Link to post Share on other sites
gwest_ca-(File Mod) 10,503 #11 Posted July 23, 2014 Is it possible the governor is setting the carb to wide open throttle once the engine starts to roll to a stop? I don't know if that is a normal condition or not. Garry Share this post Link to post Share on other sites
Geno 1,928 #12 Posted July 23, 2014 If we have plenty of fuel + spark next step would be a compression check. Share this post Link to post Share on other sites
JustinW.73 224 #13 Posted July 23, 2014 No i think the governor is fine. The compression is fine to. Share this post Link to post Share on other sites
JustinW.73 224 #14 Posted July 25, 2014 Hey I found out how you can solve or at least decrease the backfiring. Make your idle speed about a half to a full turn faster and lean the idle mixture screw an 1/8 to a 1/4 turn. It seems to be a lot better now. Share this post Link to post Share on other sites
Jparkes43 329 #15 Posted July 25, 2014 guys my horse backfires quite violently sometimes and could you help me out aswell. heres a video (skip to 0:07 for the backfire) sorry to join in someone elses page but it is easier than creating another james Share this post Link to post Share on other sites
JustinW.73 224 #16 Posted July 28, 2014 Thats odd. I couldn't tell but is it backfiring when slowing down or is it when it is just at a steady running idle. Share this post Link to post Share on other sites
