Have new 5.7L longblock with original Merc 2bbl & cast manifold. Been having issues with the acceleration from idle since installing the motor 30 hours ago. Motor runs good although plugs are blacker than they should be; (all plugs look identical.) Compression check is between 165 and 174 with most cylinders being right at 170. Vacuum gauge connected to the upper plenum on the intake near #8 cylinder jumps around a little bit at idle and at revs. Had a vacuum leak on the EGR block off plate that I believe I fixed a while back.
Knew the carb was "dirty" besides the fact that the gas down here is terrible. Add to that the spring was on the wrong side of the screen filter so that the filter was doing nothing. Carb sat for three weeks while I was out of town with the float bowl empty. Pulled all the fuel lines and reinstalled since i was having a problem with leakdown and priming and that solved that issue. Unfortunately, shortly after the motor started, fuel started pumping through the overflow into the horn. Shut it down, rapped lightly on the float bowl with the plastic part of a screwdriver and that fixed it good. Now the motor was running out of gas even at idle. Good excuse to rebuild the carb since I had a GLM kit for that carb lying around. Although I hate rebuilding carbs due to the fact that clean in my garage is not the same as clean in a rebuilding shop. Regardless, I've always been pretty successful at it.
First off, the carb in the diagram from the kit matches my Merc manual exactly. Also, my carb looks just like the exploded view of the two except that my carb is a two piece but both the manual and kit instruction sheet show a three piece where the throttle body separates from the float bowl assembly.
Which carb do I have then since it's obviously not what should have come on a 97 motor?
Another funny one is that the instruction sheet shows the filter going into the carb before the spring which is how it was assembled before. The manual shows the spring first, then the filter which is how it needs to be assembled for gas to be forced through the filter.
Rebuilt the carb; it was pretty gummed up inside along with the bowl being full of sediment. Put the carb back on the motor and it fired right up and sounded good. Attempted to get the idle speed setting close using a tach and vacuum gauge before putting the boat in the water for final settings and still have the same issues as before. Hitting the gas from idle even being nice to the throttle and the engine stumbles before bringing the revs up. Once revs come up, it runs smooth. Old accelerator pump looked new, replaced it anyways with the new one. Get a good stream of gas down both sides of the carb when hitting the throttle.
Another thing is that running the idle mixture screw in or out has little effect until it's practically all the way in or all the way out. Also, while I'm monkeying around with idle / mixture, the motor will be running smooth. I step back for 30 seconds or so and it will start running terrible and/or stall. It's like any change that's made takes a while to be felt. Never had a motor act like this before.
Have to believe I've narrowed it down to a vacuum leak, but I can't get a set of intake manifold gaskets nor carb to manifold gasket down here to try replacing. Sprayed carb cleaner around the edges of the intake manifold, base of the carb, around the EGR block off and don't hear any change in the engine. (That's how I found the original EGR leak.)
I have been thinking about just replacing the intake and carb for a 4bbl anyways, maybe that's the easy way out.
Anybody have any ideas besides setting the idle at 1k and practicing my docking at high speeds?
Knew the carb was "dirty" besides the fact that the gas down here is terrible. Add to that the spring was on the wrong side of the screen filter so that the filter was doing nothing. Carb sat for three weeks while I was out of town with the float bowl empty. Pulled all the fuel lines and reinstalled since i was having a problem with leakdown and priming and that solved that issue. Unfortunately, shortly after the motor started, fuel started pumping through the overflow into the horn. Shut it down, rapped lightly on the float bowl with the plastic part of a screwdriver and that fixed it good. Now the motor was running out of gas even at idle. Good excuse to rebuild the carb since I had a GLM kit for that carb lying around. Although I hate rebuilding carbs due to the fact that clean in my garage is not the same as clean in a rebuilding shop. Regardless, I've always been pretty successful at it.
First off, the carb in the diagram from the kit matches my Merc manual exactly. Also, my carb looks just like the exploded view of the two except that my carb is a two piece but both the manual and kit instruction sheet show a three piece where the throttle body separates from the float bowl assembly.
Which carb do I have then since it's obviously not what should have come on a 97 motor?
Another funny one is that the instruction sheet shows the filter going into the carb before the spring which is how it was assembled before. The manual shows the spring first, then the filter which is how it needs to be assembled for gas to be forced through the filter.
Rebuilt the carb; it was pretty gummed up inside along with the bowl being full of sediment. Put the carb back on the motor and it fired right up and sounded good. Attempted to get the idle speed setting close using a tach and vacuum gauge before putting the boat in the water for final settings and still have the same issues as before. Hitting the gas from idle even being nice to the throttle and the engine stumbles before bringing the revs up. Once revs come up, it runs smooth. Old accelerator pump looked new, replaced it anyways with the new one. Get a good stream of gas down both sides of the carb when hitting the throttle.
Another thing is that running the idle mixture screw in or out has little effect until it's practically all the way in or all the way out. Also, while I'm monkeying around with idle / mixture, the motor will be running smooth. I step back for 30 seconds or so and it will start running terrible and/or stall. It's like any change that's made takes a while to be felt. Never had a motor act like this before.
Have to believe I've narrowed it down to a vacuum leak, but I can't get a set of intake manifold gaskets nor carb to manifold gasket down here to try replacing. Sprayed carb cleaner around the edges of the intake manifold, base of the carb, around the EGR block off and don't hear any change in the engine. (That's how I found the original EGR leak.)
I have been thinking about just replacing the intake and carb for a 4bbl anyways, maybe that's the easy way out.
Anybody have any ideas besides setting the idle at 1k and practicing my docking at high speeds?
