How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Curtis B. Your Own Question
Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 28683
Experience:  have worked on and around most engine models for 35 yrs./Polaris ATV expert
Type Your Small Engine Question Here...
Curtis B. is online now
A new question is answered every 9 seconds

Regarding a 21 HP Briggs and Stratton motor model #331977:

Customer Question

Regarding a 21 HP Briggs and Stratton motor model #331977: My motor is backfiring. I have changed the spark plug, rebuild the Nikki carb, and changed the gas. The backfiring is almost rhythmic and I am at a loss. Help!
Submitted: 2 years ago.
Category: Small Engine
Expert:  Curtis B. replied 2 years ago.
Have you checked the valve lash? If a valve is not fully closed when the spark occurs, you get a backfire. Valves set .003 to .005 on intake, and .004 to .006 inch on exhaust. Or just set both on .005 inch! That is the place to start!
Customer: replied 2 years ago.
I have not checked this yet. Do you have a link to instructions?Also, I guess I am not sure if it is backfiring or misfiring... Not sure if this can make a difference.
Expert:  Curtis B. replied 2 years ago.
Same difference. There are U tube videos, Here is link to one.-----------------------------------------------------------------------------------------------------;_ylt=AhWMFmDVwwgGpNhDdYH8K6.bvZx4?fr=yfp-t-700-s&toggle=1&fp=1&cop=mss&ei=UTF-8&p=briggs%20intech%20valve%20adjustment
Customer: replied 2 years ago.
THanks, ***** ***** link did not post. I can search myself.One thing I noticed is that if I turn the flywheel by hand, air is pushed back through the carb air intake, which smells of fuel. Is this normal?
Expert:  Curtis B. replied 2 years ago.
It would seem to be normal. Just do a search for Briggs Intec valve adjustment.
Customer: replied 2 years ago.
That didn't help. Please view my video of the issue.
Expert:  Curtis B. replied 2 years ago.
I see and hear the video. Very strange one! What did you find with the valves? Go back and remove the valve cover, and turn the engine by hand ans see if the valve movement is erratic. Briggs is using a camshaft that has pressed on cam lobes, I wonder if one of the cam lobes is slipping, and causing the erratic operation.??
Customer: replied 2 years ago.
The valves seem fine. Could the fly wheel key cause an issue like this? I have not hit anything however, so I am not sure it would be sheared.
Expert:  Curtis B. replied 2 years ago.
Sheared key would cause hard start or no start. I don't see this as a key sheared. But there is something abnormal here. That is why I think the camshaft needs to be checked.
Customer: replied 2 years ago.
Okay, thanks for the replies. I am still under warranty and scheduled a service appointment. That should fix it!
Expert:  Curtis B. replied 2 years ago.
!! If under warranty I would certainly do that! Thanks for the reply. But I sure would like to know what the outcome is!