VMax 150 TRP drops power

[ghind]

Hello All,<br /><br />I have a '97 model Vmax 150 trp. My surfing so far tells me that the 97 model motor actually puts out 189hp (at the props I think) - so it is very nearly a Vmax 200 with a different leg.<br /><br />I use the boat for waterskiing and am finding it drops power sometimes under load. I can run at top speed all day and it doesn't worry it. If I do a fair bit of barefooting, after a while it will drop about 400rpm. It doesn't run rough - it is like a cylinder drops off. I don't know if my boat has an overheat alarm or if it is overheating.<br /><br />I ran with the cowl off trying to diagnose the problem and was able to tow two barefooters for ages at full throttle (50mph with a bit of trim). It didn't fault. A week later, I had a lot of people in the boat, one footer, cowl on and it did its old trick.<br /><br />A while back when I was having this problem, we found the fuel bulb was going soft. I have now put in an inline fuel pump and got rid of a couple of small but in the way kinks in the fuel hose. I have also replaced all the fuel hose except the bit from the filter into the motor, put a fuel strainer (for big chunks) in before the fuel pump and replaced the fuel filter. It is a full water seperating CAV type. I run Australian Premium Unleaded Petrol (95-96RON the supplier web site says)<br /><br />I'm finding this to be a big hassle. Any suggestions please? I just don't know if it is electrical, fuel, overheat or whatever<br /><br />Maybe answers to the following questions might help:<br /><br />* How can I tell if there is some kind of overheat alarm<br />* How can I test the alarm<br />* Should I avoid the premium fuel (I switched to it after a bad batch of standard gummed up my carbies really badly)<br />* Is there some kind of cutout that could do this<br />* Any ideas on what could give these kinds of symptoms?<br /><br />Thanks<br /><br />Greg

 

[Bob Kimber]

Re: VMax 150 TRP drops power

Hi Greg,<br />Just a comment on a couple of your questions, the general opinion in my area is to use the premium unleaded for the same reason you tried it. It has more addittives to stop fuel problems as well as storing slightly better, does not seem to attack plastic and rubber hoses and fuel parts as much as straight unleaded, I'm told by dealers and others that most unleaded is imported and is blended with other items which react with hoses and other parts.<br /><br />One query relating to your CAV filter, did your problem exist before it was fitted? I also use a similar filter, prior to my replacing motor 2 years ago, it was a sedimentation filter only (no filter element) as the element can remove oil from premix fuel. I modified filter to take element when I replaced with new oil injected motor (needed O ring on centre outlet to seal filter element). <br /><br />The only problem with the CAV filter is fuel flow, probably around 10 gls/hr (45 litres)which for your motor with a load at high speed could be a little low. If you use CAV fittings 1/2" UNF with tail for 3/8" hose the inside bore of the fitting is only about 7/32 which is too small to give you enough fuel. I carefully drilled out inlet & outlet fittings to 5/16 diameter, also the inlet/outlet passages inside the filter head to same size, I then drilled centre outlet to 1/2 because of housing bolt passing through outlet (be carefull not to drill centre outlet past discharge passage in filter head otherwise will weaken centre bolt housing)<br /><br />These modifications have almost doubled fuel flow through filter which is now more than adequate for my motor (3cyl 90hp merc), hose fittings to filters now require a sealing washer and sealant to threads as chamfer to fitting end and filter head are partialy removed by drilling larger bore.<br /><br />This may not be your problem but may be worth looking at, a lot of fittings have restricted bores regardless of outside diameter.<br /><br />Bob