Peter_C
Petty Officer 2nd Class
- Joined
- Jun 7, 2009
- Messages
- 193
Engine runs great at idle, smooth up towards mid throttle, then falls flat on its face and starts misfiring. From an idle I can whack the throttle open and it jumps out of the water for about two seconds, then falls flat on its face. Pulling the choke out ever so slightly feeds it extra fuel and it runs like it should right up over 25mph. Push the choke in and it falls flat on its face. Pinch off one side of the choke to the carb and it misfires. Pinch off the other carb's choke line and it misfires. Definitely a lack of fuel to BOTH carbs.
So parts replaced for various reasons, stator, power pack, coils, spark plugs, which covers the ignition side, and it is not a timing issue. This is not an ignition problem. On the fuel side I rebuilt the fuel pump, which is pumping great! Fuel shoots out from the lines just on a hand crank. The priming pump gets hard and feeds fuel with no issues also. All fuel line connections are functioning with no fluid nor vacuum leaks. The carbs are getting all the fuel they need to run from the fuel pump as the choke is feed from the lower carb float bowl. I had recently rebuilt both carbs using Sierra rebuild kits and that seems to be when this problem occurred. The carbs were stripped put into my nice heated ultrasonic cleaner with Simple Green and came out spotless. Reassembled correctly as far as I can tell. Since then I have torn the carbs down twice more trying to find what could be the cause, including removing the jets and blowing them out, along with the rest of passages. Nothing is apparent. The jets can not be put in the wrong place and these are the simplest carbs in the world...well almost, there really is nothing to them. The gaskets appear to be correct for the application which I checked on assembly, but now unfortunately no longer have them to compare. I am considering buying 2 OE carb rebuild kits and starting over.
The reed valves shouldn't be the problem?? The boat runs like a champ when it is feed more fuel. Compression is good, and if I remember correctly around 145#'s cold (Of course every compression gauge will read different).
Both float bowls have enough fuel in them for the engine to run for a at least a minute at full throttle before running out of fuel, so even if it was a fuel pump issue, the primer bulb being pumped under way should keep the float bowls full. So back to just a minor lean condition, which is enough to cause a misfire in both cylinders. I can not find a vacuum leak since it goes reed block straight to the carb with only one gasket.
Anyone have a bad experience with Sierra carb rebuild kits? Any advice that doesn't involve gas and a match?
So parts replaced for various reasons, stator, power pack, coils, spark plugs, which covers the ignition side, and it is not a timing issue. This is not an ignition problem. On the fuel side I rebuilt the fuel pump, which is pumping great! Fuel shoots out from the lines just on a hand crank. The priming pump gets hard and feeds fuel with no issues also. All fuel line connections are functioning with no fluid nor vacuum leaks. The carbs are getting all the fuel they need to run from the fuel pump as the choke is feed from the lower carb float bowl. I had recently rebuilt both carbs using Sierra rebuild kits and that seems to be when this problem occurred. The carbs were stripped put into my nice heated ultrasonic cleaner with Simple Green and came out spotless. Reassembled correctly as far as I can tell. Since then I have torn the carbs down twice more trying to find what could be the cause, including removing the jets and blowing them out, along with the rest of passages. Nothing is apparent. The jets can not be put in the wrong place and these are the simplest carbs in the world...well almost, there really is nothing to them. The gaskets appear to be correct for the application which I checked on assembly, but now unfortunately no longer have them to compare. I am considering buying 2 OE carb rebuild kits and starting over.
The reed valves shouldn't be the problem?? The boat runs like a champ when it is feed more fuel. Compression is good, and if I remember correctly around 145#'s cold (Of course every compression gauge will read different).
Both float bowls have enough fuel in them for the engine to run for a at least a minute at full throttle before running out of fuel, so even if it was a fuel pump issue, the primer bulb being pumped under way should keep the float bowls full. So back to just a minor lean condition, which is enough to cause a misfire in both cylinders. I can not find a vacuum leak since it goes reed block straight to the carb with only one gasket.
Anyone have a bad experience with Sierra carb rebuild kits? Any advice that doesn't involve gas and a match?
