Tach issues

[further]

Just want to say first how thankful I am for all the advice I have gotten over the past few months. Due to the great knowledge of several of you I was able to get my 1988 Force 85 HP to run and run great. However, I've been trying to figure out which prop to go with and getting my tach to work. First time out was last week and my stock tach didn't work, so I ordered a Tiny Tach, installed it this weekend and took it out. Stock tach miraculously started working again. At WOT I was reading 4400 rpm on the stock tach and 6800 rpm on the tiny tach??? with a top speed of 27 mph read on a gps. I'm using a 13.75 x 15 pitch. Btw its a 17' maxum. Seems like with this setup I should be close to 5000 rpm and seems like the tiny tach is out of wack. THe motor doesn't seem like its over revving when i'm cruising but not sure since this is my first boat and second time out on it. Trying a 13 x 17 pitch tomorrow but from what I understand this supposedly is going to lower my rpms? Not sure if this post was better suited for the prop forum, if so let me know and I"ll move it.
Thanks again.

 

[jerryjerry05]

Re: Tach issues

Gotta figure out which tach is working.I'd go with the tiny tach since it's new.
A 19 pitch prop is probably what you need.The 17 you are putting on will bring the rpm's down but not enough.Post what happens today,Good luck,J

 

[john from md]

Re: Tach issues

It is better suited for the prop forum.

That said, let me tell you my tiny tac experience. Those little tachs are not all the same. They are made for different applications because not all engines, especially CDI types, produce the same spark impulses.

I always recommend that people buy an inductive tach from Sears or ebay to verify their actual rpm.

Regards,

John

 

[further]

Re: Tach issues

Ugghh! the rain!! Anyway the reason why I question the tiny tach is the idle rpm reads around 1700 which is way off. John, I searched inductive tach on ebay and tiny tach came up. Any other specific ones you can recommend?
Thanks

 

[john from md]

Re: Tach issues

Try searching for Sears, craftsman, Mac, Snap-on and suntune. Use searches like dwell meter, tach and dwell, tune up meter.

John

 

[walk-on]

Re: Tach issues

On the Tiny Tach issue, did you call the guys at Tiny Tach to make sure you got the correct tach? Like John said, there are different models of that tach depending on the motor. Whoever you speak to at Tinytach will ask your model of outboard and make sure you get the correct unit.

 

[further]

Re: Tach issues

Well called the guys at tiny tach this morning. They said that I should coil the red wire around the bottom cylinder plug wire and to coil it 3 times not 4. I coiled it around the middle wire. They said this may be causing too much noise?? Will try this weekend. Hope it works. Odd though if my stock tach is working reading 4400 rpm at WOT and my prop is 13.75x15 I can't go any lower on the pitch to increase the rpms? what else could be done to get it to approx. 5000?

 

[john from md]

Re: Tach issues

Are you postive you don't have a dead cylinder? If not sure, pull a wire off each cylinder in turn. If one does not affect the engine operation, it is not working.

John

 

[further]

Re: Tach issues

Please don't go there - man that would suck.. Boat is running great otherwise. No issues at all, starts right up and cruises along great.

 

[john from md]

Re: Tach issues

Mine will do that and get 37 mph at 5000 RPM but the number two cylinder is only partially working because of bent reed valves. If you pull the plug or turn the mixture screw, it has no effect on the engine. As it uses alot more gas like this, I plan to fix it as soon as parts get in.

John

 

[walk-on]

Re: Tach issues

Further,
I'm curious how your stock tach reading compares to the Tiny Tach. My readings are different by a couple hundred rpms. I trust the Tiny Tach not the stock tach.

 

[further]

Re: Tach issues

I was getting a large variation so I called Tiny Tach directly. They told me to wrap the red wire on the bottom cylinder closer to the plug fairly tightly wound only 3 times. I originally had it on the center wire and 4 times. Well tried this this weekend and it worked. RPM readout matches stock tach spot on. I've had a post going in the prop forum http://forums.iboats.com/showthread.php?t=341055 because now that I have my tach situation worked out, can't get my motor to go any higher than 4500 rpm and 30mph no matter what pitch prop I use (tried 15 and 17 and no change in rpm). Everyone is leaning towards issue with carbs or timing. So now I need to decide whether to rebuild carbs myself or drop it at the marina and let them do it?