ron7000
Banned
- Joined
- Jul 10, 2004
- Messages
- 498
after going by the advice here about changing out the power valve on the mercarb, I still have a bog on acceleration between 2000 - 3000 rpms. Is there another cause, and fix, for this?<br /><br />Here's the rundown:<br />all last year and this year, engine would stumble or bog out on acceleration between 2k-3k rpms. It happens worse when it's the first acceleration for the day. If the boat's been running all day, it's less likely to do it. And sometimes it won't do it, but usually always does. Engine has less than 50hrs on it, I took possession of boat from original owner around 10 engine hours in 2002. To describe the stumble, it sounds like the engine is sucking air hard when it happens on a slow and easy acceleration. RPM's hold steady or drop a slight bit, then engine takes off and the boat hauls. It runs right up to 4800 rpms and sounds great.<br /><br />As of this weekend:<br />I've installed NEW 1.55mm stock main jets (3302-811853) and, a new .65 Power jet which is correct for that particular carb casting (807504N). I've also tried all three positions on the accelerator pump arm, with no luck. Engine also has new NGK TR5 (equivalent to BPR6EFS) plugs, which made no difference.<br />Upon taking the top half of the carb off to change out the pwr jet and main jets, I checked float level (I have spring loaded needle-seat) and that measured fine. I adjusted the float level a little higher even, still didn't fix the bog. The Accelerator pump (a simple design) seems to be in working order- the seal is good so I can't figure how that can be faulty at all.<br />I've also readjusted the valves, with engine running, to 3/4 turn down after zero lash per service manual, also had no effect. Checked timing too, that was at 0 deg and I moved it back to 2deg ATDC which is where it's supposed to be. Still no luck, and engine still hits top rpm even though I retarded timing 2deg.<br /><br />One thing I did notice, after checking the NGK plugs after running 20 minutes, is their electrodes are a little on the white side, which leads me to believe the motor is running lean. The AC-MR43LTS plugs that the boat came with from factory looked the same way too. So now I wonder if the main jets are too small. I placed an order for all the larger jets, 1.60mm to 1.90mm, so hopefully they'll come in quick. Other than rejetting, I can't think of what else to try. Any ideas, or TSB's on this?<br /><br />Is there a colder plug to AC-MR43LTS?<br /><br />Engine model 4111021N2<br />carb 807504N, 21, 1226