Post Number: 1
|Posted on Tuesday, August 25, 2009 - 01:13 pm: ||
I have a 1950 chris craft sportsman and it has developed a miss only from 2,000 to 2,500 rpm on both sides of this it runs like it always has. DOes anyone have a suggestion?
Post Number: 31
|Posted on Wednesday, August 26, 2009 - 08:29 am: ||
Most likely muck in the carburetor
Post Number: 7
|Posted on Thursday, August 27, 2009 - 09:57 am: ||
This could be caused by many different things, do you have electronic ignition? The first place I would check is your spark plugs and wires to make sure all is well with those. You can also check the phase of ignition points in relation to the camshaft. Let us all know how the process of elimination goes, good luck!
Post Number: 12
|Posted on Sunday, August 30, 2009 - 09:06 pm: ||
In my opinion if you know that the plugs/wires/points/condenser/cap/rotor are clean and not fowled I would set the plug gaps to the tightest side of the tolerance/spec. If you have a plug that is fowled I would replace it and check the cap rotor and wire for corrosion. If none is found continue on. I would then check/set the dwell and timing to spec. The mark should be fairly stable at all RPM’s but still advance with RPM’s. Sometimes the distributor can walk around and retard them selves so make sure you can’t move it by hand after you have tightened it down. I would then get a suitable container and drain the sediment bowl on the fuel filter, fuel pump and especially the carb float bowl taking note if you get dirt or water from either. Next put a fuel pressure gauge inline and check for good steady pressure above a minimum of 2.5 PSI at all RPM’s.
Next find a friend/captain that you trust to operate the vessel, bring her up to her normal operating temp and go to a suitable place that you can safely run the boat at the speeds you are having trouble. If you have solved your problem you don’t need to do the rest.
If the problem is still present get the boat RPM as stable as you can and then turn the high speed jet (small T handle at the bottom of the fuel bowl/air horn) out counter clockwise very slowly and see if the miss clears up, if it does I would then run her wide open and see if she achieves her max RPM you are accustomed to. If she does or runs better I would make note of that position and see if any more slight adjustments net you more RPM. If it does I would add/open the valve until no higher RPM is achieved. At this point you have peaked her out. Now this is the important part, don’t leave it adjusted this way, open the hi speed jet a little more so the RPM's drop slightly. In this day and age of fuel blends you don’t want to leave her at her peaked setting because it will be slightly lean and could cause engine trouble like valves burning, detonation scorched cylinders or rings. Next bring her back to the troubled area and see if the problem is still gone. If it is brake her back to idle in gear and see if she is smooth and crisp. If you think her idle is a little off, set the idle speed jet in this same manner.
If none of the above has fixed your problem, I would check the valve clearance of all the valves. I would set them to their highest lash setting spec. If there is only a single spec for each I would set the valves .002” wider than the noted spec. This will help keep the valves from burning from poor fuel quality control. This would be additives they don’t put in the fuel any more like lead.
Note: for some unknown reason I have found that Herc’s run better with A/C Delco or Autolite or MotorCraft plugs than they do with Champions. Even NGK plugs work better than champions but are more expensive.
Also the engine secondary electrical system was designed to run on solid core wires. For some reason carbon core/nylon core wires just don’t cut the mustard.
These are just my opinions. Hope this helps.