Stumble and Backfire during accel

I have a 92 Ski Nautique with a carbureted 351. Last season, it started hesitating intermittently under hard acceleration. Finally it got to where it would not pull up a skier - hesitation, loss of power and backfires. IT does this warm or cold. If I give it less throttle and ease my way up, it runs wide open just fine, which makes me think it's not fuel filter. I have rebuilt the carburetor with help from a friend. No effect. I just changed the fuel filter anyway, and have not had a chance to run it yet (other than idle - it still idles fine). The engine still has the Pro Tec ignition, which I know is very problematic, but it does not seem to fit what people describe as typical failures for that system. Any thoughts would be appreciated.

I had the exact same issue with our 96' and it turned out to be that the secondaries were not opening due to corrosion. Maybe check those and see if you can move them?

I don't think the timing is ajustable with a Pro-tec and they ARE problematic.
1) It could be a coil pack braking down.
2) Check the spark plugs and wires if there all firing tan in color thats good.   
3) Check for a vacuum leak by spraying wd 40 or carb cleaner LIGHTLY around the base of the carb and at the intake/head gaskets.

Easy to do and pretty much free.

tahoegaper:
Do you know what standard distributor system they installed and how they wired it? If they used the 12V wire coming from the dash it still may be a low voltage problem caused by the dash wiring issues associated with our boats ( I have a '92 also).

I forgot to mention that I have also replaced the water/fuel separator with a Racor system.

Like I said all of the major components that I can think of has been replaced.

Thanks,

TG

My first gut feeling is accelerator pump not working..

Disregard if too elementary.
Good day.

I agree with the accelerator pump for the first poster.

Keith, the key is not only that the accelerator pump is working, but that it's coming in immediately. Make sure adjust out any slop by using the adjuster but on the pump linkage arm. If there's any free play, you'll get that bog.

I have actuated the accelerator pump by hand, and watched the fuel streams into the primary venturis - seems ok, but I don't have much frame of reference. I'll check for slop. Will also look at the plugs. From everything I've read/seen on Youtube about Holleys, it seems more likely a problem with the secondaries. It picks up smoothly off idle, where the accelerator pump is supposed to add fuel. But when I try to open past say 60-70% throttle, that's when it sputters, backfires, etc.

Next steps: 1.) check plug condition; 2.) check accel pump linkage; 3.) check for vacuum leaks; 4.) check idle timing; 5.) try loosening fill cap.

desertskier: could you elaborate on what wiring you beefed up to the Protec?

Thanks for all your input, I hope to run the boat this week and get to the bottom of this.

A known problem with our boats is the dash wiring. CC wired the instruments in series (daisy chained) rather than using terminal blocks for power and ground and wiring in parallel. There are some very good posts that describe how to correct the dash wiring issues just search for dash wiring. The main symptom of the poor dash wiring is when you turn on your navigation lights the gauges jump or peg. But the daisy chains also affect the ProTec because it gets power from the key switch on the dash. The power (12Vdc Battery) starts at the 50 Amp breaker at the engine (point 22 on the schematic) it is then routed through the main connector back to the dash. It enters the dash at the ignition breaker switch on the right side of the dash. The output of the ignition breaker switch is then daisy chained through the dash wiring and ends up at the input to the key switch. From the key switch it is routed back to the engine 12.5 Amp breaker (point 41 on the schematic). Then the output of the 12.5 breaker is routed to the ProTec pin "P". The main problem is that because of IR voltage drops through the dash wiring the voltage is less than it should be by the time it gets back to the ProTec. I "beefed up" the dash wiring by adding a single wire that goes directly from the output of the ignition breaker to the input of the key switch. This increases the voltage at the key switch and ultimately the input to the ProTec. You can start by turning on the key and measuring the voltage at the 12.5 Amp breaker. It should be close to battery voltage. Mine reads about 11.5 volts after I fixed it. If it is low then there are several options depending on how comfortable you are with wiring. You can add the dash wire or a cleaner fix would be to install a relay at the input to the 12.5 breaker that is controlled by the key switch but gets battery voltage from the 50 Amp breaker and routes it to the ProTec. I guess the first question is do you have a voltmeter and know how to use it? If not they are pretty cheap to buy and easy to use. If you don't know how to use one there are posts with pictures that we can point to and help you through it.

Here's the thread where I added the dash ground and later added a new positive:
http://www.correctcraftfan.com/forum/forum_posts.asp?TID=21901&PN=1&title=added-new-dash-ground-to-93-with-pics
That fixed my gauge and perfect pass issues, so I stopped there.

It sounds like to get the Protec all the power it needs, you'd want to run a new ignition (Purple) along with the new ground and positive.

Might not be a bad idea to just totally replace the Dash to Engine Harness:
http://www.skidim.com/prodinfo.asp?number=R121014

Eddie,

It is one problem, not described very well on my part. If there's a dramatic change in throttle setting, the engine misses and backfires. If the throttle change is gradual enough, I can get to full throttle and run full speed. I actuated the secondaries, they don't appear to be stuck. I looked at the spark plugs, cyl 7 was definitely darker and wet when I pulled it out. The rest were light tan or almost white (fairly new plugs). I checked compression, 145-155 psi on all cylinders. I was thinking of putting the timing light on the cylinder 7 wire and just see if it's getting current at all.

Desertskier, thanks for the schematic, that really helps. I will check voltage at the 12.5 A breaker (good chance to use my new voltmeter!)

You could check it again with the engine running just to be sure but it looks good. If there is some resistance in the path it will drop more voltage as the current increases.

It's the front cylinders that are the problem. ProTec is a waste spark system, it fires 2 plugs at the same time, one is on the compression stroke and the othe is on the exhaust so it doesn't matter. There are plenty of coil packs around, Ford and Chrysler both used them, but there isn't any documentation that I've seen that explains the design enough to know what else might work.

Is it two sets of two? Is the brain box integrated or is it separate?

Someone on her once claimed they replaced them with a Cadillac Northstar coil pack set, but no details where ever given.

Ok, I finally isolated the problem to the Protec. I bought the conversion kit and have it installed. I plan to run it this evening, but am confused about setting the distributor. There is an ignition pulse every 90 degrees (45 cam angle degrees). I understand any location can be cyl #1, but I don't know how to get the rotor oriented so the timing will be close enough for the engine to run. It could be as much as 45 deg early or 45 deg late. Is there a way to get closer? Also, the PCM instructions call for 5 deg timing. Is there a reason it's later than the 10 deg recommendation with the Protec?