oldslowandugly
Petty Officer 3rd Class
- Joined
- May 12, 2010
- Messages
- 98
Hi, I've been reading all the topics on sync and link, jetting, carb cleaning, timing, etc, and still have a problem. Over the winter I tore down a 1980 Johnson 35 hp w/remote and an Evinrude 1985 30 hp tiller and built one motor. I used the 30 hp powerhead and compression is 150 psi on both cylinders. I used the 35 hp midsection as it was straighter and for remote control. I used the 30 hp lower unit for the better gear ratio. I used the 35 hp complete electrical system as the tach would not work with the 30 hp system, even though it charged fine. The spark is perfect, and would stun an elephant. Fuel pump and lines are new. The motor runs great except for the carbs. Both have been thoroughly cleaned and rebuilt. The 30 hp carb was 1/8" larger bore and had a 63D jet and would bog then rev to 5500 but was a bit rough at that speed, even surging a bit. The 35 hp carb had a 59D jet and would only run to 4500 rpm, but acceleration was very smooth. I preferred the 35 hp carb as it had an electric/manual choke as opposed to the primer on the 30 hp. I figured a 61D jet was right in the middle so I used it in the 35 hp carb and the WOT was outstanding, revving to 5800 rpm and sounding like a champ. Here's the problem. If I adjust for a smooth idle, the midrange gets rough and shakey. If I lean out the idle screw, the midrange improves, but then the idle sputters and dies. All the while, the WOT is great. My questions are- would the 61D jet change upset the midrange? I did the synchronisation, but when the roller and cam line up, then the carb gets to WOT at exactly the same time the spark gets to full advance. It should be later, right, so should I back off the carb opening a bit? What are the symptoms of the carb/timing being off? Would the carb opening too soon cause the rough midrange? I plan on adjusting the sync to see what affect the carb opening earlier/later has as soon as the raining cats and dogs stops, but I wanted some input first. This motor is on a 1969 Lund 18' aluminum skiff, not very heavy. I realise it's a Frankenstien motor, but any input would be appreciated.