Rough Idle

[ianyoung77]

I have a 1990 50DETO Yamaha. It is not idling well. I have cleaned the carbies, replaced the fuel pump, replaced the fuel tank and cleaned the filter. The motor runs intermittently well and then will not idle or accelerate properly. 10 minutes later it runs well again.<br /><br />I decided to check the CDI was functioning ok by checking with a timing light. I found it worked fine on all cylinders. I found that on full advance I was at 25BTDC. On the midlle retard mark I was at 5ATDC which is correct according to my Clymer manual<br /><br />I am having trouble getting any sort of smooth idle after 2ATDC. At 5ATDC it will idle fine for a few minutes and then miss, catch itself, idle again then gradually it will miss more often then stall.<br /><br />I have tried adjusting the pilot screw out by 1/8th turns from the manual setting of 1 3/4 turns but found no change through to 2 3/4 turns.<br /><br />Any suggestions where I should go from here? Do I do a top to bottom fuel system clean again?

 

[ianyoung77]

Re: Rough Idle

I decided to make sure the electricals were ok as well. I took the caps off the spark plugs and measured the resistance. On the top plug the resistance varied and there seemed to be a poor contact between the wire and spring. I cleaned it and made the wire contact better and the engine seems to idle a bit better but I have yet to do a water test.<br /><br />Would this connection make much difference. I would have thought the discharge voltage would overcome any such poor contact resistance.