Can Not Figure It Out,,Please Help
 

I have a Z33 W/twin 7.4 LX MPI W/bravo 1s. The problem that I can not figure out is that the rpm's do not match at all. At cruising speeds the starboard side runs about 300-400 less rpm's. and at wot about 500-600 less rpm's. So I read up on the forum about such problems and these are the things I have tried. both accelerator cables are in the WOT postion when throttle levers are maxed. next I switch props to see if its the props were it.where it would be in reverse and go forward etc etc.the rpms were right on the money and the sound of the engines was in sync. the props are 23p one is a quicksilver mirage and the other just says quicksilver both are 23p, not sure if that mattered or not. I have only had the boat for about a month and trying to figure this out. thanks for any help and suggestions

Re: Can Not Figure It Out,,Please Help
 

Check your tach's, then maybe a compression check?

Re: Can Not Figure It Out,,Please Help
 

Did the tachs read the same when you synched the engines by ear?

Re: Can Not Figure It Out,,Please Help
 

yes when I reveresed the props the tachs read the same and were in sync

Re: Can Not Figure It Out,,Please Help
 

its when I put them back like they are suppose to be the rpms are off and the sounds are out of sync only when i reverse them its all ok. does not make any sence to me at all could the props be mismatch or something they appear to be in perfect shape all except one is a quicksilver mirage and the other is just a quicksilver both are 23 pitch.its blowing my mind while it runs in sync reversed,and all out of wack when the props are on the right sides.

Re: Can Not Figure It Out,,Please Help
 

One has more cup than the other? If your ear says in sync the tach must be right. Have you opened throttles to 3/4 and take off the flame arrester if carbed to see that the throttle position is the same? I guess you can do that on FI too.

Re: Can Not Figure It Out,,Please Help
 

if one has more cup than the other how come they are in sync when i switch props from one side to the other. I am all confused

Re: Can Not Figure It Out,,Please Help
 

Has this problem been there since you have owned the boat?

If so,, verify drive gear ratios are the same.

Re: Can Not Figure It Out,,Please Help
 

Odd.

It is possible that one of your drives has bad thrust bearings for one set of gears. Not likely, but possible.

Mirage and Mirage Plus props say it on the hub. Mirage props are DIFFERENT than non-Mirage Quicksilver props. You may also have a trim issue where your indicators are not properly reading the same.

you SHOULD be running the same style of prop on both sides.

I say first thing to do is to make SURE both props have the same blade style. Do that before looking any further.

Re: Can Not Figure It Out,,Please Help
 

Not to sound like a dumb ass but when you say you swap props R to L you put the drives in reverse to go forward? Isn't that real tough on the upper bearings

Re: Can Not Figure It Out,,Please Help
 

Andy,on a bravo it should make no difference as the upper and lower thrust bearings on the gears are identical. Before he switched sides one drive was running on the upper thrust bearing,after switching the opposite side was running on the upper,Years ago there were some small blocks in boats that were lefthand rotation but that is a thing of the past,Smitty

Re: Can Not Figure It Out,,Please Help
 

OK I will try props first then, yes the boat has been doing it since ive had it. the only thing that has thrown me off about the props is that when i switch it straigtens out the problem. I figured if i switched then the port side would have been lower rpms and vice versa.

Re: Can Not Figure It Out,,Please Help
 

here is the exact rpms
when props are turned out starboard side is at 4500 rpm's and port side 5100

when props are turned in both are at 4800 rpm's and they sound in sync

one is a quicksilver mirage23p and the other is a quicksilver non-mirage
and thanks again for any help at all

Re: Can Not Figure It Out,,Please Help
 

I had a similar problem, when I discovered I had a 25p Mirage and a 25pMirage Plus. I was 400 rpms dif at WOT. Maybe when you reverse the props it evens back out because your making your hull act different and the one prop is slipping a little more to make it seem right. I would take the props to a prop shop and let them check to see if there is a diffence.
If there is a diffence between a Quicksilver and a Mirage, then I bet that is your trouble.

Re: Can Not Figure It Out,,Please Help
 

The easiest thing to do is to try another set of props or have your props checked out. After the props are matched then go from there. You may have several problems going on but start with the easiest one and then on to the next one.
Even if they are the same props it sounds like one was replaced for whatever reason. If the old prop has been worked or reconditioned it may not run the same as the newer prop.

Matt

Re: Can Not Figure It Out,,Please Help
 

thanks alot for all the info, I will check into getting a set of props to try out

Re: Can Not Figure It Out,,Please Help
 

You need to have the same type of prop on both drives.

You say 7.4 lx mpi ( the old 330's with port injection)
The rev limiters on those are set at 4700 rpm,
and one tach is saying 5100 ?

So....... the tach's don't appear to be accurate.

You need to check rpm's against a hand held tach.

Once you have a "matched" set (same model/pitch) of
props, and you can verify the true rpm, you have a
baseline to work with.

jt

Re: Can Not Figure It Out,,Please Help
 

thanks I will check the tachs. But it does show 5100 on the one engine when maxed trim. But I can here the engines are not in sync at all unless I turn the props inward

Re: Can Not Figure It Out,,Please Help
 

Do you think the owner could have changed the rev limiter by chance, Not sure if possible on these engines. Was just curious

Re: Can Not Figure It Out,,Please Help
 

On MPI engines, the rev limiter is in the ECM.

It's possible they could have been "modified",
or maybe swapped for ECM's out of a 454 mag MPI ???

I think the ECM's are labeled, though.

jt

Re: Can Not Figure It Out,,Please Help
 

what props do you think would be best to start with. And where from and thanks again

Re: Can Not Figure It Out,,Please Help
 

I'm assuming the boat's a Donzi Z33 right ?

That boat and that power, I would think that
the 23's would be about right, (they just need to be the same)

Start with a set of 23 mirages.

I've had good luck with Houston prop ( He's also a board member)

jt

Re: Can Not Figure It Out,,Please Help
 

All else being equal, if you still have the problem after getting props, i would suggest you check the hull. If switching prop rotation made a drastic effect, you could have a hull problem that interferes with clean water flow to the props when turning the correct rotation that is less drastic when spinning them opposite.

Re: Can Not Figure It Out,,Please Help
 

Well today I did a compression check on both engines and are 100% good. also checked the tachs and they are 100% accurate. So we are down to props and still can not figure the rev limit thing now. anyway of checking the ecu etc etc to see if anyone has tampered with it. And thanks again for all the help

Re: Can Not Figure It Out,,Please Help
 

Try hooking up a vacuum gauge & check the reading at idle & blip the throttle.
If the slower engine has less overall vac, it may indicate an exhaust restriction.

Cool forum BTW

Re: Can Not Figure It Out,,Please Help
 

Have you considered trying swapping the ECUs and see if the problems reverse, that would indicate one was tampered with. Now the $100 question how hard is it to swap them, think just a matter of unplugging and swapping but someone with more smarts will hopefully know..

Re: Can Not Figure It Out,,Please Help
 

Ok heres what has been done and still a problem exists.
1.bought new matching props and went with 25p mirage plus.
2.changed plugs, cap and rotor to be safe.
3.changed fuel/water filter and didnt have a drop of water in them.
4. cleaned out the flame arrestors and cleaned the intake.
5. checked fuel presure (not running the boat) and both read stb side 36psi and port side 34 psi and they hold presure for a good long while.
6. found one problem and had a bent shaft on stb side and rebulit the lower foot w/ a new shaft.
7. changed both fluids in drives and both showed very very little signs on metal if any at all.
8. checked trim, and both trim exactly the same when cruising.
9. checked timing at 3k rpms and both show 30 deg, and 8 deg idle.
10. checked compression all are within 10 pounds of each other.

so all in all the problem still exist. now with the bigger props the stb engine runs at 3000 rpms and port engine runs 3300 rpms at midrange. at WOT the stb runs 4100 and port runs 4700. what should I try next. and the P/S pump is on the port side.(the one that runs higher rpms).
please if anyone has a clue.

Re: Can Not Figure It Out,,Please Help
 

Are you sure both motors are the same? I have seen people throw motors together and put different cam shafts in them. Also, have you checked plugs and wires? Usually a 3-400 rpm difference is one cylinder.

Re: Can Not Figure It Out,,Please Help
 

changed the plugs with the same affect havent changed the wires yet but will do.
And the motors looked untouched totally factory, so I would have to say nothing has been done the factory paint on the timing cover etc etc havent been touched.

Re: Can Not Figure It Out,,Please Help
 

Also forgot to mention I dont hear one single miss in either engine.

Re: Can Not Figure It Out,,Please Help
 

Are you certain the drives are trimming evenly? One higher than the other will have this affect. Also, you may want to take measurements on the toe in/ toe out setting of the two drives.

BT :cool:

Re: Can Not Figure It Out,,Please Help
 

yes checked the trim on them and even played with just one trim at a time while cruising the only way I could get the stb side to match the rpms if it comes close to cavitating(not sure if its called that or not)

Re: Can Not Figure It Out,,Please Help
 

also not sure about the toe in toe out thing at all. not sure how to check or set it

Re: Can Not Figure It Out,,Please Help
 

Do you spin the props in or out?

Re: Can Not Figure It Out,,Please Help
 

props spin out

Re: Can Not Figure It Out,,Please Help
 

This is checked by measuring the distance between the leading edge of the drive (edge closest to the boat) and the distance between the exact center of the prop shafts. Toe in is the leading edge measurement is closer than the measurement of the prop shaft. Normally, you want these to be exact, unless you want to play with it some to see what makes the most speed. For troubleshooting your problem it would be recommended to get them to match. Please note this measurement needs to be done as exactly as possible as small differences make significant differences in performance.

Re: Can Not Figure It Out,,Please Help
 

With the drives straight ahead, use a tape measure to get the measurement between the drives at the front of the bullet. Then measure center to center between the ends of the prop shalf centers. For spinning out I would have the prop shaft centers further apart than the front of the bullet by about 1/8". This is at least a good starting point. You adjust the tie bar.

BT :cool:

Re: Can Not Figure It Out,,Please Help
 

just checked the toe in toe out thing and it is dead on the money both are exactly 35 inches

Re: Can Not Figure It Out,,Please Help
 

How tight are the drive hinge pins and gimble pin? Any noticable slop up/down left or right? Are there any sea water pickups, transducers, trim tabs or anything else that may be causing turbulation on that side?

Re: Can Not Figure It Out,,Please Help
 

everything is tight I checked all that when the foot was rebuilt. nothing loose or any play.