If there has been one problem I have seen on this site way to often it is the mid 70's v4 idling rough, sneezing and stalling even though it runs great at every other speed. Last season I was given a 1975 starcraft with a 1975 evinrude 85hp and a 1975 rude 4hp kicker. The main engine ran fine but would idle like "crap". The first thing I did was completely clean the carbs including removing the welsh plugs and rodding the jets with wire. (no change)
I next replaced all the fuel lines under the cowl as well as the primer bulb, main line and fuel pump. (no change) I changed the plugs from ngk's to champion 77's. ( no change)
I pulled the carbs and removed and inspected the reed box, replaced one set that was out of spec. ( no change)
performed a link and sync with the clymers manual and set pickup timing ( no change)
Then tested impedance on all electrical components all were fine, spark test was good. (no change)
I then gave all connections and gaskets the torch test (an unlit propane torch with the fuel on will usually pinpoint a lean vaccuum leak through an increase in rpm's as the propane is sucked into the circuit.) no leaks were found.
Resorting to the "Joe Reeves" two finger test on all carb throats I found an increase in rpm's on the inductive tach at every cylinder. I pulled the idle mixture screws and found they were 027's, after ordering 4 new ones that were also 027's I put every thing back together. (no change)
I then bored the original jets to 028 engine ran better, bored them again to 031 engine was now showing signs of too much fuel. Bored the new jets to 029 and the engine runs perfect; no sputtering, no sneezing, no stalling.
It is amazing to me how such a small change in the idle orfices can make a huge difference. I wonder if changes in the fuel since the 1970's are making these engines require an increase in jetting, thanks to all who contributed advice on this problem.
I next replaced all the fuel lines under the cowl as well as the primer bulb, main line and fuel pump. (no change) I changed the plugs from ngk's to champion 77's. ( no change)
I pulled the carbs and removed and inspected the reed box, replaced one set that was out of spec. ( no change)
performed a link and sync with the clymers manual and set pickup timing ( no change)
Then tested impedance on all electrical components all were fine, spark test was good. (no change)
I then gave all connections and gaskets the torch test (an unlit propane torch with the fuel on will usually pinpoint a lean vaccuum leak through an increase in rpm's as the propane is sucked into the circuit.) no leaks were found.
Resorting to the "Joe Reeves" two finger test on all carb throats I found an increase in rpm's on the inductive tach at every cylinder. I pulled the idle mixture screws and found they were 027's, after ordering 4 new ones that were also 027's I put every thing back together. (no change)
I then bored the original jets to 028 engine ran better, bored them again to 031 engine was now showing signs of too much fuel. Bored the new jets to 029 and the engine runs perfect; no sputtering, no sneezing, no stalling.
It is amazing to me how such a small change in the idle orfices can make a huge difference. I wonder if changes in the fuel since the 1970's are making these engines require an increase in jetting, thanks to all who contributed advice on this problem.
