Max tachometer RPM of Universal M-35BC / prop upgrade

[Ron Hill]

Guys : I always found the best RPM for idle was just over 1000rpm- so that it was smooth and the alternator was charging!!

A thought

[Dale Stone]

Hi Mick,
Is your flexifiold a 2 blader? I have a Gori 2 blader 15X12. I just got it in the water a week ago and have little experience. My gauge was reading around 1600 RPM and my knot meter was reading 6.5 knots. RPMs seemed too low for making 6.5 knots. Think I'll get one of those tachometers to check it.

[Bobg]

Dale, I have a similar problem, using a strobe hand held tack, my panel mounted tack was off about 200 rpm, all that said, my boat has slowed down too.  at 2300 rpm I used to get around 5.5 knots with a 15/9 prop, had it repitched to 15/10, I increased the speed at 2300 rpm to about 5.9 knots, was happy, but then the boat started slowing down, I am now around 4.8-5 knots at 2300 rpm, getting used to it, the tranny has passed all the tests I have been advised to check.  prop shaft rpm is is about 50 rpm below half of engine rpm.  can't turn prop by hand when in gear and on hard, clean bottom, calm seas, no weight on boat to speak of. Tranny flushed and new fluid every spring, clean filters clean screen on facet pump, learning to just live with it,  although someone said may have a vacuum leak in fuel line, (my next check) or injector pump may be wore, (don't know how to check that)I can get 3000 rpm at dock, and can achieve 6 knots at full throttle (3000 rpm), (hand held strobe) panel tack reads 3200, briefly when at sea.  None of this probably helps you but when I see another cruiser talk about boat slowing down I respond.  Good luck, I have the 25xp in a 1988

[Dale Stone]

Hi Bob,
Is your prop a 3 blade? I know a '88 34 with a 3 blade and will ask him. I bought the 2001 MKII in late 2016 and it had a 3 blade 15X9. It didn't launch in 2017 as I tore lots (more than I should have) apart. The survey indicated the bronze shaft was corroding from the inside out so I replaced it with SS. Decided to go with the GORI folding 2 blade at the same time and GORI specified the 15X12. 

I just launched almost 2 weeks ago and was very surprised I was making 6.5 knots at 1600 RPM. The sea was flat but didn't seem right. I figure either the RPM gauge was off or the knot meter, the knot meter is new too.

Doesn't make sense to me that you are slowing down while the RPMs seem unchanged. And you checked everything I could think of.
Do you have a chart plotter and does it agree with your knot meter?

I'll get back about the other '88 with the 3 blade.

[Bobg]

Yes my prop is a 3 blade, I have checked my speed with my handheld gps, phone app, boats moving along side me and everyone has same speed.  I do think your tack is probably off, my hand held strobe rpm checker was fairly cheap, under 20 bucks amazon and real easy to use.  I would definitely start with that.  Let me know what your buddy with the 88 says.  This board has been very helpful helping me figure out why the boat is slowing down and I have checked a number of suggested items it may be, but it still runs about a knot slower than it used to 2 years ago at same rpm.  Didn't mean to hijack your thread about my problem.. Good luck Dale

[Dale Stone]

Hi Bob
The guy with the '88 C34 has a tach that is not working. I spent the weekend on my boat and used the laser tach. I was reading about 200 RPM more than the panel and thus lowered the RPM a bit.
Another issue is I cannot increase RPM (whether in gear or not) more that 1500. I give more throttle and within seconds, the RPMs lower to about 1500 again.
I have a call in to the universal service and they believe it is a governor/ injection type issue. I expect a call back for T/S or having someone get on the boat for service.

Talk later
Dale

[Geoffreykwright]

I've long suspected my tach is off.  I've a good gori folding prop but I am doing 6.5 knots at 1200 RPM (sometimes slightly more if I've engaged the overdrive feature).  I know my speed is right - always assumed the tach is off.  Did not know the laser tachs were so cheap ($25 on Amazon).  Question - where I am measuring the RPM?  (i.e. what am I pointing the laser at).  Can't be the coupling on from the engine to the prop-shaft since I want to check the speed in neutral.  (Might sound like a silly question - but thanks in advance).

[Craig Illman]

Measure the crankshaft pully at the lower front of the motor. When you measure the output shaft, you're getting the result of the transmission reduction ratio (around 2:1, depending....)

Craig

[Geoffreykwright]

Thanks Craig!

[Dale Stone]

Yep, That is how I did it, pulley at center and another at the pulley edge for repeatably. Placement of the reflective tape and black tape covering painted surfaces was key. The laser tach worked but took a while to get a stable reading. Had to be patient with it.

Update on the limited RPMs. The throttle lever is returning by itself. If I hold the throttle at max the RPMs are 2800 and stable.

I need a throttle cable brake.

My Gori prop is 2 blade 15X12. At 1500RPM and small chop I was making 5 knots SOG read from the chart plotter.

[Craig Illman]

Dale - In your Edson pedestal, where the throttle hand passes through, there's a Delrin bushing. Inside the pedestal is a little bolt that squeezes against that bushing. You'll need to remove your compass to access it. You might need a 7/16" crowfoot to tighten it to increase the friction.

Hope this helps.

Craig

[Stu Jackson]

Craig's right, Dale.  If you don't have an Edson manual, you can most likely find one at www.edsonmarine.com.

[Mick Laver]

Dale
Sorry for the delay. My prop's a 15x9 3-blade Flex-o-fold. I usually run 2400-2500 rpm (calibrated) for a cruising speed of 6.5-6.8 kts. I have a friend with the same prop but a 15x10 and it seems to work OK, same SOG and slightly lower rpm. At 15x12 you might be a bit over pitched and maybe that's why you can't get the rpms up.