Any Volvo Penta duoprop experts here?

Hey guys. I've got a 1987 Volvo Penta AQ271A (275 HP, 350 cu in, Holley 850 DP) with a Volvo Penta DP290. The boat (87 Sunray Mirage, 25ft, approx 4500 lbs loaded, fuel and water)got it pretty much as a wreck and I've been rebuilding it gradually over the last 3 years. <br /><br />Problem is with performance. I have to go full down on the trim tabs (which by the way were just stolen, looking for a used set of 24X9's), shift passengers forward and nurse it to get it to come out of the hole. It'll rev to about 2900 and its like hitting a wall. WOT is only 4000 Seloc manual says it should be 4400. I've rebuilt the entire fuel and ignition system as well as the entire top end of the engine so I don't think I'm underpowered. Boat cruises at 25Kts @ 3000 RPM and tops out at over 42Kts @ 4000 RPM.<br /><br />My intuition is telling me I've overpropped. The current set is B6. I have no idea what the pitch or diameter of the individual props are. What I was wondering is approx. how many RPM would I pick up by taking some pitch out? The Volvo Penta info I have doesn't give me any ideas. I can only afford to buy one set of screws this year and need to make an educated decision on getting the proper set. I'm guessing but by going down a set (ie. B6 to B5) I'm taking about 2" of pitch off the set.<br /><br />There aren't any dealers around here that have test props I can use to dial in the boat.<br /><br />I'm guessing that a B4 set would do the trick. Any help you Volvo Penta guys could offer would be greatly appreciated.

Re: Any Volvo Penta duoprop experts here?

Your problem could be carburation. Why such a large carburator? 650 to 700 cfm should be plenty for that engine. Ignition timing (slow or no advance) and valve adjustment (valves to tight) can cause this also. Before you change or work on props be sure the engine is in proper tune.

Re: Any Volvo Penta duoprop experts here?

Hi Reel Poor<br /><br />Thanks for the thoughts.<br /><br />I think I've pretty much eliminated those faults. The mechanic (old time race car builder) who rebuilt the carb, distributor and heads tuned the engine once I put it all back together. Timing is spot on. Carb is working perfectly. I adjusted the valves myself and will again before it goes back in the water this spring. <br /><br />As far as I can tell, by the Seloc manual and what little I can get from VP the Holley 850 DP is the standard carb for this engine. The AQ271 seems to be a bit of an oddball model. Most 350 cu in engines I've seen are all 650 or 680 single pumpers. When I had Holley size a ProJection fuel injection for this engine it sized out at about 600 CFM.<br /><br />Fuel consumption isn't outrageous at cruising speed so the carb is probably not too oversized.

Re: Any Volvo Penta duoprop experts here?

You might want to post this in the Prop Topics and Questions. Lots of prop knowledge over there. Give it a different title so it doesnt look like a duplicate post.<br /><br /> Click here for short cut.

Re: Any Volvo Penta duoprop experts here?

Could not find post in the prop section so will post here. Not close to an expert on 290DP but have been up close and personal in the last 2 years trying to fix the same problem you are having. Had the same problem, turns out someone replaced the lower gear box with props which were B-5 or 6. Way overproped for the 305. With the help of a prop shop tweeked it in to a set of B-3s Were no test props available so friend had to get it right the first time at $600 plus for a set of aluminum. Info is out there but hull manuf. and volvo did not want to comitt themselves on what to use. Hopefully someone with more knowledge will come along. In the mean time will find out and pass along where the ultimate good info came from. regards fred

Re: Any Volvo Penta duoprop experts here?

If I had to wing it I would say that the B-4s would be correct. But damn its not my money. Stand by, hopefully more expert help is on the way. fred

Re: Any Volvo Penta duoprop experts here?

check exhaust for a restriction specically on cav plate flap

Re: Any Volvo Penta duoprop experts here?

Hi Guys<br /><br />Thanks for the tips. I'm sorry, newbie to this board, didn't see the prop topic. A little overwhelmed at the vast volume of info on here. I'll take this one over to the prop questions.