Small Engines (Lawn Mowers, etc.)/Ryobi 790r


QUESTION: My trimmer starts then stops after using prime fuel. I have changed the fuel lines, filter and carb. I took the muffler off to check the spark arrestor but there is no arrestor in the muffler unit. Any ideas?

ANSWER: Was the replacement carb a new carburetor?  Where did you get the carburetor?
Can you keep the engine running if you prime by hand?

---------- FOLLOW-UP ----------

QUESTION: I got the new carb from All Parts Direct and it is an MTD genuine spare.

No I can't keep it running with the primer.

That model is prone to some issues.

Have you checked the engine compression with a compression gauge?

Have you pressure tested the crankcase to see if a gasket or seal is leaking?

You will need to do a compression check to make sure the engine is capable of running.

Let me know what the compression is.

Small Engines (Lawn Mowers, etc.)

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Eric A. Jones


Lawnmower Repair . Certified Master Service Technician from B&S. Have 23 years experience on B&S, Lawn Chief, Weed Eater, Echo, Peerless, Wheel Horse, Snapper, Atlas, MTD, McCulloch, Homelite and many other numerous brands. Specialize in electrical repair.


Born and raised in the midwest. Started tinkering with engines when I was about 14 on my Suzuki RM-80. I began lawn mower repair at a small hardware store. I knew absolutely nothing. I read lots of repair manuals and met an older fellow who taught me many lessons. I continued working on small engines through high school and paid my way through college working on mowers at the same hardware store. Decided to get away from the midwest and mower repair so I joined the Air Force. I repaired air traffic control electronic equipment and ended up in Hawaii where I got a part time job at Small Engine Clinic. I gained a lot of experience from the Small Engine Clinic and had a blast repairing small engines. I then took the Briggs and Stratton Master Service Technician test and earned my MST. I then traveled to Wisconsin where I attended the factory update training seminar and received formal training. Continued working on mowers part time as I completed 20 years of military. Retired from the military on a Friday and continued in the lawn and garden industry the next Monday.

MAS Aerospace Operations BA Mathematics AAS Electronic Communications AAS Electronic Technology

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