engine surging and backfiring at wot

[Lanceer]

serial number OF071470. carbed 7.4 liter. I rebuilt the carb and did a tune up with new plugs, wires, coil and cleaned the fuel system and added a new fuel pump because of wot dying and hard starting. took the boat out yesterday and it was surging and occasionally backfiring and a less powerful hole shot. sounds like I didn't rebuild the carb correctly and have a lean condition. I didn't adjust the idol mixture screws but I thought they have nothing to do with wot.i thought I followed the rebuild procedure correctly but you never know. I starts great and idols perfect. my first question is what is the correct adjustments for the carb floats. it's a 700 cfm
I soaked and blew out everything. what could be wrong.

 

[achris]

From the serial number (and thank you ) it's a Bravo stern drive and has a Weber 9772 carb....

Float level on that carb should be set at 33mm (1-9/32")...

And you are correct, the idle mixtures don't have any effect on WOT. Have you put a vacuum gauge on the inlet side of the pump to make sure there's no restriction from the tank?

Chris.......

 

[Lanceer]

I used that measurement, which is basically level. and 2 inches for the drop measurement.( I think) I'm at work now but I'll look at the paperwork I used and post back. thanks

 

[achris]

2" is the right drop.

You could have an air leak in a manifold gasket or some such similar problem...

Chris......

 

[Lanceer]

all right. I was finally able to do some checking. pulled the water separator/ filter and no water in tank. when I was unscrewing it though, I heard air. dont know if it is vacuum or pressure. also, at what condition does the second aries come in. also could I have got the air horn( the weighted flap just below the second aries in wrong. it looked like it can only go in one way. I raved the engine up with no load and it ran perfect. I did it for only a romp and pulled the throttle back down. I know you really should not do this but I really want to get this fixed. maybe my next thing to do is to get it back to the lake and run it at wot and then pull some plugs and take a look at them and report back, but that may take a couple weeks.

 

[achris]

.... when I was unscrewing it though, I heard air. dont know if it is vacuum or pressure. ....

Likely vacuum. If it was pressure, fuel would have splashed out... Check your tank vent line/s, and the line between the tank and the filter housing for restrictions.

Revving on the flushers, as well and being very bad for the engine and water pump impeller, will not recreate a high load fuel problem.

Chris.....

 

[mr 88]

"New wires and plugs now it backfires " sounds like you crossed a plug wire. I would double check that ,then I would time it. Could be your carb rebuild as mentioned but the backfiring has me leaning towards timing and or a plug wire on the wrong plug.