JeremyD615
Well-Known Member
Hey guys, I'm a long time lurker, but first time poster here, so I'll try not to ask any of the questions that have been answered a thousand times.
I've had a 95 Speedster with twin 657X's that I've been slowly restoring for the past two years. The port side motor has one season on it, and seems to be running pretty smoothly with a top end RPM of about 6800. The starboard side motor is a fresh SBT rebuild that has been properly broken in and now has about 10 hours on it. It tops out at about 6600, for a top speed on the GPS of 50.5mph. Strangely, this new motor is the one I don't trust yet.
The motor starts up fairly easily with a little choke, and then revs up to 3500 and bounces off of the limiter for a few seconds when on the trailer. If I leave it alone, it will eventually settle down to 3k and idle well, or I can give it a bit of choke while it's bouncing off the limiter and it will settle right in as soon as I let off of the choke handle. That part doesn't really worry me too much, as the port motor behaves the same way. What has me questioning the new motor is its tendency to randomly drop the idle down to 1100 or so after about an hour on the water. When the rpm drops, it obviously idles rough, and seems to smoke more than usual. If I crack the throttle and bring it back to 1500, it feels normal, but drops again as soon as I pull the throttle back. At anything more than idle, it seems to run fine, although I sometimes feel a very slight miss if I hold the revs right around 4000. I did a plug chop after running at that throttle setting, and the plugs were a nice even brown, so I don't think it's a lean spot. Any ideas what could be causing this? I keep thinking plugs, but they don't look fouled, and I've gone through a few sets.
So far this is what I've done:
- Fresh SBT rebuild.
- Rebuilt carbs with OEM kits and new N/S.
- Double and triple checked pop-off pressure of 24lbs plus or minus 1psi.
- Set LS screw to 1-1/4 turns out and HS screws to barely cracked open.
- Bypassed fuel selector valve.
- Pressure tested the carbs, fuel pump, and fuel tank.
- Blown out all fuel hoses that are of the black automotive type.
- Clipped plug wires back.
- Confirmed oil pump arm is adjusted to spec.
When the problem first surfaced, I pulled the air box and found that the oil pump cable had flipped over 180 degrees on me, but I fixed that and it ran fine for another hour or so before the idle dropped again. This time all the linkage was fine. Any help from the experts would be much appreciated. Thanks!
I've had a 95 Speedster with twin 657X's that I've been slowly restoring for the past two years. The port side motor has one season on it, and seems to be running pretty smoothly with a top end RPM of about 6800. The starboard side motor is a fresh SBT rebuild that has been properly broken in and now has about 10 hours on it. It tops out at about 6600, for a top speed on the GPS of 50.5mph. Strangely, this new motor is the one I don't trust yet.
The motor starts up fairly easily with a little choke, and then revs up to 3500 and bounces off of the limiter for a few seconds when on the trailer. If I leave it alone, it will eventually settle down to 3k and idle well, or I can give it a bit of choke while it's bouncing off the limiter and it will settle right in as soon as I let off of the choke handle. That part doesn't really worry me too much, as the port motor behaves the same way. What has me questioning the new motor is its tendency to randomly drop the idle down to 1100 or so after about an hour on the water. When the rpm drops, it obviously idles rough, and seems to smoke more than usual. If I crack the throttle and bring it back to 1500, it feels normal, but drops again as soon as I pull the throttle back. At anything more than idle, it seems to run fine, although I sometimes feel a very slight miss if I hold the revs right around 4000. I did a plug chop after running at that throttle setting, and the plugs were a nice even brown, so I don't think it's a lean spot. Any ideas what could be causing this? I keep thinking plugs, but they don't look fouled, and I've gone through a few sets.
So far this is what I've done:
- Fresh SBT rebuild.
- Rebuilt carbs with OEM kits and new N/S.
- Double and triple checked pop-off pressure of 24lbs plus or minus 1psi.
- Set LS screw to 1-1/4 turns out and HS screws to barely cracked open.
- Bypassed fuel selector valve.
- Pressure tested the carbs, fuel pump, and fuel tank.
- Blown out all fuel hoses that are of the black automotive type.
- Clipped plug wires back.
- Confirmed oil pump arm is adjusted to spec.
When the problem first surfaced, I pulled the air box and found that the oil pump cable had flipped over 180 degrees on me, but I fixed that and it ran fine for another hour or so before the idle dropped again. This time all the linkage was fine. Any help from the experts would be much appreciated. Thanks!