01 Diablo Power
 

The 3.0 L4 is not a powerhouse I know but has been just fine for us even with 6 adults or 4 adults and 4 kids onboard. We do a little tubing and mainly cruise along just above plane or maybe 25-30 mph no problem. Last time out with just 3 of us was the first time in a while I even let it run WOT. It seemed a little down on rpm and speed, maybe about 4200 at 37mph (indicated) with 19P prop. So after about 18 years and nothing but oil & filter changes I am wondering if it is finally time for a tune up or maybe look for other issues.

My point of reference (memory) says I should see 4500+ rpm and solid 40 mph with light load. OH and while Smarttabs have been great on our boat I did try putting them on the lowest setting (least pressure) to minimize their impact which made no difference.

Any suggestions for maintenance and things to look for. I'm familiar with old school motors like this so for example I would start with...
Plugs
Cap
Rotor
Check Timing and ignition module( need to read up on this one)
Clean the arrestor well

After that I really don't know what others have experienced and did not find a lot of useful information but things like:
Rebuild carb & check float level
Check fuel filter (I did replace that a few years back)
Check fuel lines for swelling from ethanol gas
Polish the hull, hah, mine is still almost like new
There were some other crazy things I found

Some of the reason for asking for a little detail and ideas is I have a friend with a 'new to him' boat that is trying to sort out an even greater low power issue. He has done some of the above but I think he may also be over propped and since I have a 19 and 21 we might try those on his boat next.

Thanks in advance for any ideas.

Re: 01 Diablo Power
 

Sounds like your engine is simply getting a bit 'tired'. WOT operating range is 4400 - 4800 rpms and a well-tuned 3.0 should touch on 40 - 42 mph with 2 persons and a half tank of fuel. A good thorough tune-up is in order and there are a number of on-line videos that would assist you with that job.

As for your friend, if he's a bit 'low on power' and has done the work you mentioned, i dont think a 21 pitch prop will help him as it will struggle a bit more to get him going. Try your 19 pitch though if his looks a 'bit rough'.

Re: 01 Diablo Power
 

Thanks mikeyt... I hope a basic tune-up is all it really needs but I haven't even looked at a plug or anything in 18 years. I'm usually more pro-active but the thing has just worked all these years and doesn't have big number of hours on the motor. It appears the parts are not crazy expensive like some 'marine' stuff can be so I will start there with basic tune up.

To be a little more clear about my friends boat it is bigger and heavier deck boat with a carbureted 4.3. He has improved idle and throttle input with a carb rebuild and adjusting float but it was still struggling just to get on plane. I suggested looking at the timing which he found way off and after doing that it helped a lot and gets on plane but still won't come close to WOT. He doesn't know what prop he has but the OE has been replaced so maybe it's a 23P. Sounds like his boat should run a 19 or 21 max like mine but his Alpha is probably also different gearing than mine. I have not seen it yet but plan to go with him soon and take the two props I have.

He also complains that when it does get up on plane it porpoises a lot. i think there is a whale tail on the lower unit also :shakehead: I told him to get Smarttabs but he doesn't want to do that until he gets the engine sorted.

Re: 01 Diablo Power
 

First thing i would do is get rid of that dammed (and ridiculously ugly) 'whale tail'. :thumbdown:

If he isn't getting any where near WOT rpms then he is over-propped assuming that the engine is running fine. That 4.3 should run between 4400 - 4800 rpms at WOT. A larger boat with a 4.3 likely should be running a 19 or 20 pitch prop at most. Try the 19p but an 18p or 20p 4 blade would likely help too.