1 very loud pop in engine bay during holeshot or pulling ski

[schiffsnautique]

i have 93 closed bow with 420 hrs. i've had it for a year and has ran great. yesterday i heard a loud pop like metal being broken during a holeshot. i checked the motor mounts nad didn't see anything wrong. later the driver heard it when i was getting out on a slalom so i quit. the boat did it once out of 5 times when i was wakeboarding. the faster and smoother i got out of the water everyting was fine. it also did it once in 4 times on a kneeboard. the pop wasn't heard when i eased into the throttle to cruise but i did notice some quick revving at cruising at 2800 rpm. rpm's would go up really quick then go back to the original throttle position. could the knock sensor be the culprit? also, i noticed that the oil dipstick had been forced out slightly and i know that i had placed the entire way back in. any insight would be grealty appreciated.

[AuMDLST]

RE: 1 very loud pop in engine bay during holeshot or pulling

Potential Backfire?

[core-rider]

RE: 1 very loud pop in engine bay during holeshot or pulling

Is this a carburated engine? If so, it was probably a backfire through the carb. It could happen with FI, but not nearly as possible. Might just need a little tuneup or carb tuning/rebuild.

[schiffsnautique]

RE: 1 very loud pop in engine bay during holeshot or pulling

it is carburated. just thought of the fuel goin in under certain circumstances.. but why would their be a backfire only during more load to the engine and only once when pulling out or holeshots? and what about the rpm jumping from time-2-time when cruising?

[schiffsnautique]

RE: 1 very loud pop in engine bay during holeshot or pulling

i had a 91 wellcraft i/o and heard it backfire a couple of times under a strong load. the wellcraft was easy to tell of a backfire. i've had a few street 5.0 mustangs that had motor work and have heard the same backfire like the wellcraft. the nautique was much more of a distinguished sound that i've never heard. i'm aware that the i/o is placed further back and their is not a muffler/silencer like my nautique. just tryin to give as much info as possible to find the cause.

[81nautique]

RE: 1 very loud pop in engine bay during holeshot or pulling

power valve gone bad?

[schiffsnautique]

RE: 1 very loud pop in engine bay during holeshot or pulling

not aware of a power valve???? what is it?? is this something with a carb 5.8 pro boss?

[81nautique]

Re: RE: 1 very loud pop in engine bay during holeshot or pul

not aware of a power valve???? what is it?? is this something with a carb 5.8 pro boss?

Power valve is inside the primary side of the carb. It increases fuel flow +-20% under demand based on engine vacuum, if it is blown the engine will lean out and cause a backfire. you might want to post this question over on CCfan. and let the Holley gurus at it. If it is the PV it's a less than $10 part and a new gasket set for the bowl and block, inexpensive fix or just buy a kit and have the carb rebuilt.

[donjoz]

RE: Re: RE: 1 very loud pop in engine bay during holeshot or

I had a similar problem with my old '92. It sas backfiring under load. Ran fine anywhere else.

The fix was not so easy. It could be lots of things, but mine was a bad coil pack. A very, very good mechanic diagnosed it step by step for me.

Good luck. Have a look at your electronic ignition and connections.

Don

[81nautique]

Re: RE: Re: RE: 1 very loud pop in engine bay during holesho

I had a similar problem with my old '92. It sas backfiring under load. Ran fine anywhere else.

The fix was not so easy. It could be lots of things, but mine was a bad coil pack. A very, very good mechanic diagnosed it step by step for me.

Good luck. Have a look at your electronic ignition and connections.

Don

Good call, Protec ignition on it's way out maybe

[schiffsnautique]

RE: Re: RE: Re: RE: 1 very loud pop in engine bay during hol

thanks for the input. i was curious about the coil pack. talked to a friend that is an excellent mechanic and may have traced the problem to the number 6 plug. the ceramic had came loose. had the boat out last night and ran perfect. i think pro-tecs are good but had a car with a coil pack and wasn't very happy. hopefully the problem is cured. another question, i'm going to start using a set of old plugs during the fogging process and then put the good set back in after i've de-winterized it. i always put the fake-a lake on in the spring to check everything before launching. does anyone else do this. i believe that it offers some preventative maintainence. you guys?