backfires while being started!

[redrigger]

I recently purchased a johnson 20hp,seahorse model#20r73a Serial# 26555.First of all I figured out the 20r73 relates to the yr and hp of the motor what does the "A" represent.Secondly the engine backfires while I attempt to start it.Is this normal?Is this engine a reliable model?I only ask because I am having a hard time finding out any info on this make and model.Any info related to this motor or where to find it would be greatly appreaciated.This is my first boat and motor and I wanted more info than the seller was able to provide. thanx

 

[orca]

Re: backfires while being started!

G'day. Always willing to try and help out a Pom. Will your motor actually start? If it only backfires but will not start then the plug leads may be crossed. may also be poor fuel or carby problems. <br />These motors were preety good when they were built but getting a bit long in the tooth now.

 

[Bear]

Re: backfires while being started!

1973 it is. 20HP @ 4500 RPM. Fuel mix 50:1.<br /><br />Check the ignition. Get new spark plugs. Do you have a spark on both plugs?<br /><br />Later: Change the oil in the lower unit. Maybe a new impeller too.<br /> <br />Search this forum. Get a manual for it. Check the link below.

 

[G DANE]

Re: backfires while being started!

Hi Redrigger<br /><br />I owned a motor like yours, both 20 and 25 model. The link between the little roller following the cam on the startorplate ( turning when you move trottle ) and the carbureator, should be set so the trottle does not open at all, before the roller is between or passed the two marks om the cam. Trottle at low rpm is given only by advancing ignition timing. If trottle is opened before ignition advances, it backfires immediately. Its a great and economic motor. Only weakness is a tendency to corrode at block side of headgasket, when run in saltwater. You can adjust the link, by loosening a little screw at trottle axel end or changing length or lever ( depending of year )<br />Keep me posted if further problems.

 

[redrigger]

Re: backfires while being started!

It apparently backfires while being started, but once started and warmed up runs great.A friend of mine who has been boating for a few years recomended an out fit that loos like a big U with two suction cups one on each end,you put these over the water intake and attach a garden hose.I think I may try to find one.Are they engine specific or do you just buy a universal one for the size of the engine? I guess this way i will know for sure without having to tinker on the water(it does not look fun to me)or maybe just try the good old barrel.Thanks for all the info and the site for the manual.I will let you know what happens when I can get it in some water and get it going.The guy that sold it to me had it on a little home made baot designed for a 9.9 and said he was selling this one because it was to powerful,would almost flip the boat over even at low speedsif he was not easy on the steering, whatever thas good for.Any way be back real soon,thanx again.

 

[orca]

Re: backfires while being started!

G'day. Your friend is referring to flushers or Ear muffs. Generally they are universal but they do not fit some motors. Guess what? Yep. the motor you have is one that the ear muffs do not fit. Fear not, there is a flusher designed for your motor however I only Know of an Australian brand, probebly not for sale in pommyland, but Im sure that something will be availabe locally. Try your Marine shop. You can test run your motor on the flusher but you cannot load up the motor, A bit like test running your car with the wheels off the ground. The only real test is on the water.

 

[fireman 757]

Re: backfires while being started!

put it in a garbage can filled with water.