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justaguyntn · Jun 16, 2011, 08:35 PM

I recently acquired a 2004 model Murray rider with the afore mentioned engine.The problem is this, when idleing it runs snooth, advance the power and it backfires through the carb. I checked and changed the flywheel key( had the wrong key installed and was partially sheared), cleaned the carb, changed the plug, re-set coil to flywheel gap. I have been reading here and suspect the valves need adjusting. Anyone with other suggestions?

crigby · Jun 17, 2011, 12:42 PM

Hi,
You certainly could set the valves to 0.006" per the YouTube videoYouTube - ‪Lawn Mower Repair Valve Adjustment‬&rlm;
The wise thing is to rotate the engine and watch the rocker arms. They should move about the same. There were a bad batch of camshafts about that time.
Peace,
Clarke

justaguyntn · Jun 19, 2011, 01:12 PM

Thank you Clarke. So if I understand you correctly, excess valve lash can cause backfire through the carb?

crigby · Jun 19, 2011, 05:12 PM

Hi,
No the bad cam is more likely to do it because the exhaust lobe wears down and you get normal intake and reduced exhaust so that air/gas mix enters and but cannot leave well.
Peace,
Clarke