New 1GM RPM Woes

[jddj]

I installed a new 1GM10 in my CD25D last year and reduced the prop pitch: 3x12”RH9" . I was getting 3400 rpms wide open throttle in forward and about 3600 in reverse (for short bursts) either free or tied to the dock. I just started the engine for this season tied to the dock and can only get 2400 in forward open throttle and 3200 in reverse. Engine starts immediately, idles smoothly, and reaches max rpm in neutral and full throttle. The only changes were a new Racor filter - 2 microns like last year - and Zinc Barrier coat spray on the prop. I usually just wax the prop and the grey stuff is not super smooth.

Any ideas?

[Boyd]

I assume the rpms you gave are per your onboard insturment's tach. If so is your alternator belt slipping? On my engine the alternator drives the tach.

You can verify its accuracy with an optical tach.

Other than that I am stumped.

Boyd
s/v Tern
CD30 MkII
Fort Lauderdale, Fla.

[Dean Abramson]

Could the prop be fouled with something already? It is conceivable that that would effect the revs in one direction more than the other.

By the way: I built a scope out of PVC pipe with plexiglass on the end (it's weighted with lead flashing) which enables me to inspect underwater things from above the water.

Keep us posted on the outcome. Good luck!

Dean

[seadawg]

I gained 300 rpm on my 1GM just by draining old fuel and replacing it with fresh!

[bobdugan]

I had a similar mysterious problem at the beginning of the sailing season a couple of years ago. After much experimentation and advice from the board I finally ended up replacing BOTH the primary (the tiny one on the engine) fuel filter and the secondary fuel filter. That did the trick!

Bad fuel/clogged fuel filters and fouled props (barnacles or seaweed) have been the cause of low RPM problems on Cricket.

Hope this helps!

[rtbates]

I gained over 1k rpms at the top end by simply running Seraph's 1GM for a few hours at 2k rpm while I motor sailed. They really need to be run at load from time to time to stay at top form.

[M. R. Bober]

...
By the way: I built a scope out of PVC pipe with plexiglass on the end (it's weighted with lead flashing) which enables me to inspect underwater things from above the water.
...

Dean

What a great idea!

Mitchell Bober
Sunny Annapolis (where we just hatched this year's crop of Ensigns--and a few 2nd Lt types) MD

[Dean Abramson]

Mitchell,

I'd like to take credit, but I think I got the idea years ago from an article in Cruising World. The thing lives in my cockpit locker and has proven to be wicked handy, either from a dock or the dinghy. It's about five feet long, and was actually built when I had my 25D, and now I may make a longer one. It's just a piece of (I am guessing now) 4" PVC pipe. I cut a round piece of plexi and cemented it to the underwater end only. I wrapped lead flashing around it, and secured that with hose clamps. If you play with the weight of the flashing, you can find the sweet spot where it just barely floats, so that when it's mostly submerged, you don't have to rassle with it trying to float up or sink. You look in the open end, and it's amazing how clear a view you can get. It takes a little patience to find the right spot on the boat, as the angle of view is quite small. But if, say, you zero in on your prop (actually, part of it at a time), you will KNOW if there is kelp there or not. I avoid diving in these cold Maine waters at all cost!

Dean