Twin KAD 300 poor acceleration any ideas

[nautical norman]

June started well with Steve from Mendez Marine putting myself and two budding skippers though our paces on the day skipper practical course on our twin kad 300 powered targa 34 in glorious weather around the solent, happy days and beginning to enjoy boating again

And then July comes in and one day acceleration is great and top speed is pushing 40 knots, then two weeks later I fill her up at the local marina prior to taking her out a further two weeks later with the family on board ......and wow what a difference acceleration is best what I can describe as pathetic and top speed is around 25 knots ...eventually

So after two scrubs ( yes two because it must be a growth problem ) the local vp dealer taker her out for a trial and engine under load test providing a very impressive print out that tell them all parameters are ok....and they need to scratch heads to think of what next. Acceleration is still poor but at least top speed is around 35 on a good day

No signs of clutch or prop slip as revs match speed

Could bad fuel have such an effect? The fuel flow rte is as expected and the fuel and tanks were polished last year and all new filters

Three weeks later and I'm still waiting for light bulb moment to come on

Any ideas appreciated

 

[Portofino]

Weight and or --

Turbo,s vanes burnt tips -they do that -Cos of excessive EGT trying to go fast with dirty bottom /props before scrub

-long shot - Trim -your flaps or drive trim wrong -unknowingly

 

[KevB]

Are the superchargers working? They're the bit's that get you out the water sharpish. They work on electric relay. On my boat I can stop them working by turning the ignition keys back to 0 position and would have the same effect you're having.

When you're accelerating hard do you get much black smoke?

 

[Momac]

I fill her up at the local marina prior to taking her out a further two weeks later with the family on board ......and wow what a difference acceleration is best what I can describe as pathetic and top speed is around 25 knots ...eventually

Sudden development of fault after refuelling might suggest the new fuel is a cause. Perhaps change the fuel filters and test again.

 

[aquatom]

What are the max revs you are getting for each engine?

 

[nautical norman]

Thanks for replies

Superchargers are kicking in and out at the right revs not sure how you would check they are delivering additional air flow, the problem with acceleration is from low revs all the way through the range so doesn't suggest high end turbos. No obvious black smoke and trims working ok. The engines will get to full revs....just takes a lot longer than it used to.

According to vp agent fuel rate delivery is fine but I'm grasping at straws so might go for new filters ....and new fuel.