Formula not up to speed. Help...
 

I have a 93 Formula 33 foot with twin 502's just recently rebuilt. The boat is not breaking the 40mph barrier @ 5000 rpm. Comes up on plane fairly easy. Port engine jumps from 3500 to 5000 rpm much faster than starboard engine. I was thinking that maybe the engine coupler may be slipping on port engine. Don't smell burning rubber but do feel some vibration with port side. Props are 23 pitch stainless with no visible signs of any damage. Engines are not overheating. Any Ideas?

Something is not correct for sure. You should be running about 60 or so with 23 pitch at 5 grand. What is the condition of your props? Check each blade very carefully for any cracks, flolded over blade, dings..... What kind of prop? If has a changeable hub make sure that is not messed up as well. I doubt it is your coupler as from what I have heard when they go they go. How much are you triming the boat? Are you trimming the same amount? On the motors are they carb or EFI? Have you checked your fuel filters and so on?

Check the hub in prop. If a coupler went it would free wheel. Been there, done that. Make sure you don't have one of the motors missfiring. That can be your vibration. Distributer cap and rotor are very prone to corrosion.

I have removed the prop and see no signs of damage to prop, washer or splines. They are Mirage props. I have not checked fuel filters, but the engine itself does not seem to be missing or any latency. Just HP reaching the prop on the port side.

Do the Mirage props have removable hubs? are they the plastic hubs? Plastic spin much easier than brass. If they spin there won't be any damage to the splines you need to pull the hubs out to inspect for damage.

Removed the distributor cap and everything looks good here. The Mirage props are one piece fixed.

Have you tried pulling back on 1 of the throttles at a time while running to see if the boat losses speed or stays the same? Is the bottom clean, free of algea and slime? That alone will keep a boat from going anywhere till it wears down.

Gotta be easy to diagnose if both motors are hitting 5000 and the props and couplers are good.

If you are hitting 5000 rpm's something is slipping. The rubber inside the prop hub is probably slipping. you visually will not be able to tell more than likely.

Bottom of boat is very clean. Up to about 4,000 rpm, throttle is in same position for both engines. When you push up on both throttle levers at same time the port engine revs up to about 5300 and starboard only to about 4700. So you have to back off the port engine throttle to bring it back to 4700 but does not seem like the boat slows down that much.

BTW, thanks for all the attempts so far.

Port engine jumps from 3500 to 5000 rpm much faster than starboard engine.


Have you checked the engine timing, sounds like maybe the timing on the starboard engine maybe retarded if it seems more sluggish that the port engine???

ohh and are ther carb or efi engies??

Regardless of how fast either motor gets to 5300/4700, still gotta be going faster than 40mph. Those props don't care what's turning them. If the hubs were bad, I'd think getting on plain would be impossible.
Are you sure the props are indeed 23"? Drive and tabs trimming up ok?

Did it run fine before the rebuild? new/different drives?

The Mirage props are one piece fixed.

he has solid props.....

The engines are carbed. And yes the props are 23. No problem with trimming at all. I just bought the boat and part of the deal was that the engines were to be rebuilt. There was low compression on the starboard engine and so the engines were rebuilt just before I took delivery. I re-checked compression after delivery and compression running at 165 on all cylinders. Fuel or ignition problems might cover the lack of power issues but not the over-revving of rpm's. Right?

Could the tach's be wrong?

Here's a long shot. Could the upper gears on the port side be worn to the point that they slip (or skip) under the high speed load?

Should not be the tach as these are brand new livorsi gauges. At this point I think I will yank the outdrive next weekend and do some further investigation. With good compression and the engine not missing, in my simple mind it has to be south of the flywheel.

your speedo could be wrong or plugged or is this gps reading, 600 rpm difference will slow you down a lot also

Check your timing before you pull the drive. In my mind your problem is in the motor. Check the simple stuff first. We had a guy on the board a few months back that had the throttle linkage hooked up wrong and his issues were almost the same. Take off your air cleaners and with the motors off see if the throttles are opening up all the way. If not look at the other motor and see what is different. After the rebuild did it run ok on the sea trial?

PS on my 311 with 23's that are beat up I can see 70 (speedo not gps) at about 5200 rpm's.

Easiest First!!!!! Change To Good Known Props!!!!!!!!!!

i would double check the timing, and if that is ok, try swaping carbs from one engine to another, to eliminate a carb issue..

sounds like prop slip

drive showers

ditto. I had a 21p mirage on my boat for a few minutes after i got my new power in it. the pvs caps were missing and it would get on plane and it would slip when i cracked power to it. it was the incorrect prop i just wanted to see what it would do. i woud switch to known good props and then if that does not work check timing and swap the carbs from engine to engin to eliminate that concern. the beauty of having two engines is that they are great for diagnostics. the ultimate donor.

We put the drive in forward gear and attempted to turn the prop ccw. Prop would not turn.

Unfortunately the boat is currently on the lift having some touchup paint work being done. And I cannot put it back on water until this weekend.

I have a boat mechanic from a local shop telling me that it is the engine coupler failing. He says that Friday he will pull the engine, replace the coupler and if it does not solve the problem, I owe him nothing. He is very confident in his ability so I guess we will see what happens this weekend.

I like his confidence.

If it's a bravo coupler they don't slip. It is a all or nothing. You would see some shavings around it. here's two pictures, one was trashed, prop won't turn at all. The second one is close to failing but you could not tell at all. Worked just like a new one, but not for long.
You can see if the shaft turns it will trash the coupler, no way could it turn the prop and grab at all.

NO. They are either good or trashed. You would here all sorts of grinding and the drive would not do a thing.

He may be confident, but not very smart. A coupler may let go slowly............ by slowly, that is a couple minutes at most at higher rpms.. Once it starts to go bad, it takes about 30 seconds before its completely trashed.

Things that need to be done.......................
Verify tach accuracy and speed accuracy
Check timing on both engines
Try a known good set of props
What are the drive gear ratios????

The boat should run about 40mph at around 3000 rpms

+2

If the coupler is bad at high rpm, how do you even get on plane?

He's right...just replaced two shot couplers. They were completely trashed and had no idea....I was one or two hole shots from roasting them. When they go...they apparently just go. No halfway there. BUT...if he's willing to give you a free coupler....TAKE IT!!!!

Ha... I was thinking the same thing!

Did you verify that both throttle linkages were giving you wide open throttle?

Make sure the slower engine is getting enough fuel. Check the fuel filter and water seperator, check for a plugged pick-up in the tank and make sure the fuel pump is working correctly.

I can easily reach the 5,000 rpm range on either engine without any hesitation (misfires, lack of fuel, etc). Seems like the power plants are generating the proper HP.

It almost feels like an automatic transmission in a car that is low on fluid(slippage). If the boat is running 35 and you back off the port side throttle you do not feel a loss of speed but if back off the starboard side you notice a drastic reduction of speed. On the other hand if you are running 4,000 rpms on both engines and push both throttles equally forward the starboard will move up to 4,500 while the port runs up to 5,200 so I have to back off the port to keep from red lining.
Hope that is as clear as mud...
Thanks guys

Make sure both drives are the same ratio.

Sounds like the port side is your problem, no speed loss and rpms raise faster.
I'd be looking for slippage somewhere. If the drives were a different ratio, I'd think the rpm difference would be across the board. But not sure if 1 would carry the other???

Try swapping the props.
Possibly try getting on plain with just 1 motor. Not actually doing that, but making 1 side work harder, so if there is something slipping, you'd think it would show up then.

When I had 4 blade bravo 1"s , I would have to stagger the throttles pretty far apart to run the same rpm above half throttle, went to 25 mirage"s and the problem went away.. Could be prop related.