mattg 2 #1 Posted September 1 Good Morning, Hope everyone is enjoying the holiday! So i have a 414-8 with the magnum kohler, thing ran flawlessly until a few weeks ago. It started to have a misfire and i noticed when i hold hand in front of exhaust it does not have the normal pressure, so i assumed the exhaust valve was sticking. I removed the cover plate and turned engine over by hand and it appeared that they both seemed to move. I did go in there and work them with a screwdriver and they seem to snap ok. Before I dig into it any farther any suggestions? have a good day! Share this post Link to post Share on other sites
gwest_ca-(File Mod) 11,612 #2 Posted September 1 Try it with the muffler removed. 1 1 Share this post Link to post Share on other sites
ri702bill 9,698 #3 Posted September 1 (edited) And perform a cylinder leak-down test. Air coming out of the exhaust when both valves are closed confirms it. How long since the last head removal and de-carboning??? A stray chunk of carbon when stuck between the valve & its seat will act the same way..... Edited September 1 by ri702bill Share this post Link to post Share on other sites
peter lena 9,358 #4 Posted September 1 @mattg , been using this for years now , rislone zinc zddp additive , add 4 oz to every oil change , the cleaning factor alone , is worth its use , its the very smooth running that you can sense , also the hot oil changes are very black oil and flushing , is showing you the varnish removal , another thing is the elimination of frequent , starting smoke . realise this is a touchy issue , but I experiment with any issue , and improve the original failure point , no smokey starts , easy running . couple hrs , of hot varnish break down , would not hurt . pete Share this post Link to post Share on other sites
wallfish 18,467 #5 Posted September 1 The internals of the muffler rust and rot which can come loose and block the air flow. 1 1 Share this post Link to post Share on other sites
mattg 2 #6 Posted September 2 Hello, Haven't ever had had head off to clean, just oil changes every season for the last 20yrs. I did try some marvel mystery oil, no luck. I will put valve cover back on, need a new gasket now, any chance someone has the part # for that?. then I will check the muffler and head and maybe try the suggested additive see what happens. Thank you for all the suggestions, greatly appreciated! Matt Share this post Link to post Share on other sites
Sparky-(Admin) 23,531 #7 Posted September 7 Exact same issue I had with a Magnum 14. Turned out part of the baffle inside the muffler had rotted or broke off and would get itself in front of the muffler output. Real easy to remove, then shake it, you’ll know if there’s a loose piece inside right away. 1 Share this post Link to post Share on other sites
8ntruck 8,041 #8 Posted September 7 Just opinion here. Additives are not a sure fire fix. Sometimes they help, other times, they don't. Whatever issue you have, it took some time to develop. With this in mind, it will likely take an additive some time to work. Good luck. Share this post Link to post Share on other sites
mattg 2 #9 Posted September 7 Thank you! Going to remove muffler, hopefully today Share this post Link to post Share on other sites
