Trying to figure out whats causeing engine to stumble passed mid throttle

Hi ,Its been awhile, but I need some more help with this 93 3.0lx. It's on a 25" pontoon and stubbles or misses when shifted passed mid throttle. Its got a rebuilt carb, new fuel pump, coil, plugs, wires rotor, and cap. Timings was checked three times and is correct. Checked all fuel filters (on pump and carb) and found no trash or water. Checked pick-up tube and anti- syphon valve, and breather tube on tank. Fuel line is clear and tight. Have no changed separator filter yet. Considering tearing into rebuilt carb o re-check float height and check for trash in jets. Plugs are NKG BPR6EFS, and where supposed to be a cross over to what I wanted. Al check's were this week, but boat has sat for almost year since all these parts were replaced and tried out on lake just last weekend. Compression was around 145 on all cylinders last fall if I remember correctly. Could these new parts have gone bad in less than a year? Engine will fire right up and idle great. Just Boggs when throttle is pushed passed mid way. Fixing to check pressure on pump next, and change water separator filter. Then open the carb up. Any idea's? Thanks for any help..



















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Boat sat for a year? Did you stabil the fuel? Sounds to me that you have a fuel issue...possibly the carb. The stumble and the bog would make me think that your running lean...float set to low, dirty power valve ( if its a Mercarb ), main jets partially clogged. Sounds to me like your on the right track....Let us know what the fix was. Good luck

















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Carb was nasty inside but water and fuel filters were all clean. How can that be? Also, several parts were missing on re-built carb. Clip that holds accelerator pump linkage,one jet gasket missing, baffle plate; and I thought there was suppose to be a spring from needle to float that wasn't there.On muff's it seems run better now, but all the sudden shifting to forward it clicks.Reverse seems good.Didn't mess with the shift adjustments,so I'm at a loss there.

Cant help from here with the carb issues...........I would suggest buying a replacement so you are using a GOOD carb to start with...


As far as your shifting issue follow these directions for adjusting the cables........

This procedure is typically used when replacing the short shift cable so most of the procedure may not be needed.

Trim out drive up 2 inches from all the way down.
Take keys out of ignition!!!!!!!!!!!
Have a second person stand at the prop.
You, remove the short shift cable from the shift bracket.
After the cable has been removed, push the plastic cable end all the way in and hold in place while prop is being spun C’Clockwise..
Have second person rotate prop counter clock wise until the prop is fully engaged and wont turn anymore. Maintain light effort on shift cable plastic end pushing it to keep forward engaged.

Measure the distance from the center of the brass trunion to the center of the round mounting hole in the plastic end. Adjust trunion to make that distance 6 inches. no more no less! In cases where the shift cable is old but still works well you can adjust this dimension to 5 15/16”. NO MORE.

Put shift control handle in forward FULL wide open throttle position.
Remove the control shift cable from shift bracket at this time.

Install short shift cable back onto bracket at this time.

Take the shift control cable and adjust the trunion so it fits perfectly back into the shift bracket.
Before installing it turn the brass trunion 4 complete turns away from the plastic end and reinstall into shift bracket.

Now put shift control handle in the neutral position.
Have second person spin prop, it should spin freely.
Put shift control into the forward detent position at ~ 10:00 position. NO FUTHER.
Have the second person rotate the prop counter clockwise. You should have solid engagement with no ability to continue to turn the prop.

Now shift back into neutral. Prop should spin freely with no clacking or clunking.

Now shift to reverse to the 2:00 o’clock position detent NO FURTHER!!

Have the second person spin the prop clockwise.

If you have positive engagement with no clunking or jumping out of engagement, you are done.

If it does not fully engage into reverse than look at the shift bracket where the short shift cable mounts and there is a slot. Loosen the 7/16 hex nut/screw that is touching the bracket and move the stud so you are pulling the short cable.

Try this and retest in water under load.

Anyway there are tests that would tell you if the cable is bad but to difficult to type out here but in general if you remove the shift control cable from the shift bracket, shift the control handle to full forward/wide open throttle and make a mark on the cable end, now go full reverse and repeat. Measure distance between marks, (2 7/8" to 3 1/8") any more and replace the control cable.

Short cable measurement test, remove short cable from shift bracket, push all the way in and spin prop by hand until full forward is made. Make a mark on shift cable end where the plastic stops over the metal.
Now with someone holding the prop from spinning pull the cable end out with two fingers, as soon as resistance is felt mark the inner cable where the plastic cable end ends. Now measure between the marks,
The measurement should be if I remember correctly 1/2 " to 9/16". anymore and the cable or linkage is bad.

Thanks Kghost, Will get my son to help adjust it again. Shift cable and all bellows were replaced a year ago when I replaced the upper unit. You helped me a lot during that time, and its great to see your still here for us.I bet I can still see those sharpee marks from where we checked play back then on the cable.Thanks again.