Got an ole Tecumseh (ohv155 204508d h) Have tried everything I can think of except a coil and still it backfires through the carb and sounds like in the muffler as well. Mostly at lower speeds. At full throttle it seems like its misfiring. While running I can spray carb clean in the intake and it will rev and run smooth. Key ways good, valves lapped and adjusted propper, new carb, new spark plug. Ive had the motor for years but never heard it run. The original carb was so bad it had to be replaced. Cant find a reasonable priced oem so the replacement is aftermarket. Tried drilling the jet with no change. Im sure this has been dealt with elsewhere in the forums but I never see any solutions. Thoughts
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155OHV backfires through the carb and muffler
- Thread starter CaptFerd
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Export threadThe carb for your engine should be Tecumseh part number 640330A. I have found this part, Tecumseh branded, on Amazon for $14.00. What was the brand and part number for the carb you got. Second, what did you set the coil gap at and each of the valve clearances? If you got a off brand carb with a jet too large and then you drilled it even larger, could also be your problem. To me I would be looking at a sticking valve or incorrect valve clearance, but with an aftermarket carb I can’t rule that out. Did your replace the head gasket when you pulled the head, I would never reuse a head gasket on an OHV engine.
Here is a service manual for your engine. Use spec listed under OHV11-17. https://www.mymowerparts.com/pdf/Te...-OVRM120-OVXLC120-OVXL120-OVXL125-695244A.pdf
That is a sweet manual. Thank you. Gona start digging through it.Here is a service manual for your engine. Use spec listed under OHV11-17. https://www.mymowerparts.com/pdf/Te...-OVRM120-OVXLC120-OVXL120-OVXL125-695244A.pdf
Yes it was an aftermarket carb and i did drill out the jet with no good results. I've sent it back and am trying a different one plus a new coil. The coil was set with a business card. Im guessing around .010. Not thinking the coil is the problem but at this point who knows. Ill try the carb first. Is it possible to solder the jet and redrill it if the new carb is the same? Ill get back to it around Wednesday. and post what happens.The carb for your engine should be Tecumseh part number 640330A. I have found this part, Tecumseh branded, on Amazon for $14.00. What was the brand and part number for the carb you got. Second, what did you set the coil gap at and each of the valve clearances? If you got a off brand carb with a jet too large and then you drilled it even larger, could also be your problem. To me I would be looking at a sticking valve or incorrect valve clearance, but with an aftermarket carb I can’t rule that out. Did your replace the head gasket when you pulled the head, I would never reuse a head gasket on an OHV engine.
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Solved. 2nd new carb and first coil and still backfiring. Went through the manual Rivets hooked me up with and I kept seeing governor over and over. so I focused on that. Replaced the rusty rod that goes from the carb to the lever, very thin and bent easily. Adjusted the Rpms to 3400 high and 2200 low and it runs strong and smooth no spitin back through the carb.
Im with you on that. The old gov rod was real flexible. Ive seen these motors purr like a kitten at a lower rpm but this one just refused. My thinking is that by the manual that the real problem was the rpm. 2200 seems higher than most engine idle rpms but thats the specs. Big help to me thanks again. Has been gone 2 months now with no complaints.Glad she is fixed.
Very unusual fix I must say.
Run her at 3600 and never look back. Briggs states that you get max engine life at max revs. All due to best engine air cooling and oil slinging away at full slosh. Not recommended to idle an air cooled mower engine.