boostedtoy13 1 #1 Posted June 25, 2017 I have a 520 with 800 hours. It's started surging all through out the rpm range. No load. Smokes a little at idle. I've cleaned carb many times, resealed the intake manifold, changed spark plugs, checked cylinder leak down and compression, adjusted valve clearance, being out of ideas I bought new ignition module, condenser, crank trigger. And still no change. Then i found the resistance specs for thr coil. Primary winding is 4.1 max is 3.6. Sencondary is 22000 max 19500. I have great spark. Could the coil being out of spec cause the ignition timing to be off. I don't want to buy a coil if I'm missing something else. HELP!!! Share this post Link to post Share on other sites
oldredrider 2,547 #2 Posted June 25, 2017 Surging is almost ALWAYS caused by carb/fuel delivery issues. IMO, the carb needs a really good cleaning. Share this post Link to post Share on other sites
N3PUY 1,031 #3 Posted June 25, 2017 does the surging go away if you pull out the choke a little bit? Share this post Link to post Share on other sites
Jerry77 1,218 #4 Posted June 25, 2017 My p216 had a surging problem until I put an electric fuel pump on it - your pump may be weak and if the tank isn't full, it will have a hard time picking up enough fuel causing it to surge and die back.. Share this post Link to post Share on other sites
boostedtoy13 1 #5 Posted June 25, 2017 No change with choke until it is running worse. Not fuel related with this one Share this post Link to post Share on other sites
boomers_influence 106 #6 Posted June 25, 2017 boostedtoy you do not state the coil # that you have?? the coil # will start with 166-0xxx. the replacement coil has different resistance values. AS A RULE, surging = to much air, or not enough fuel. you stated you cleaned the carb, did you remove it to clean it? did you remove the main jet and the idle jet tube to clean them? did you check the float level setting? did you check to see if the welch plug is in place at the rear of the carb? did you check the volume of the fuel pump output? thank you. boomer ( the used onan engine parts guy, also NOS and new ) 2 Share this post Link to post Share on other sites
boostedtoy13 1 #7 Posted June 26, 2017 I removed carb disassemble and used an ultrasonic cleaner with a simple green solution. Fuel pump flow looks very strong. Coil part number is 166-0820 1 Share this post Link to post Share on other sites
JeremyF 13 #8 Posted June 28, 2017 I had this same problem and tried everything you have tried, and finally gave up and took it to a shop. What they found was that there is a polymer piece pressed on top of the cam that holds ball bearings that work the governor and it was cracked. Luckily he had a parts motor and swapped it out, and the thing runs like a top. Hope this helps. Share this post Link to post Share on other sites
520HC 207 #9 Posted June 28, 2017 Yep I would say governor issue. Share this post Link to post Share on other sites
