I always try Seafoam first. I love that stuff. Once a year, half a can down it's throat thru the master cyl. vacuum line, 1/4 can in the crank, the rest in the fuel. I have someone turn it off while putting a healthy dose of it in the vac. line and let it marinate for 15 minutes. Lite her back off and make sure it's not in the garage
I change the oil after running it for a bit. Remember to change the plugs after the Seafoam cause it can foul them.
Good luck. Hope it's something simple.
