Perplexing RPM issue

[vranasaurus]

I have a 1989 90 hp Evinrude.<br /><br />I just rebuilt it, new carb kits, had a link & sync done by a shop(did good up to that point but couldn't figure it out by reading the manual.) Did a proper break in.<br /><br />When I get the motor to wide open throttle it will only pull 4200 RPM's.<br /><br />The current prop is a stainless steel 13-3/8" X 17.<br /><br />I went to my local shop and asked to borrow a prop to try to get my RPM's up. They had an aluminum 13-3/4" X 15. When I put it on I got the same 4200 RPM's.<br /><br />What is keeping my RPM's down?

 

[Basscat 1]

Re: Perplexing RPM issue

Make sure the butterflies on the carbs are open all the way and the timing linkage is up against the stop at wot. You can do this of course with the engine off at home.<br />Have you checked your timing at wot?

 

[vranasaurus]

Re: Perplexing RPM issue

I checked all of that and the timing was set at the shop.

 

[Dhadley]

Re: Perplexing RPM issue

Did it ever pull more than that?

 

[vranasaurus]

Re: Perplexing RPM issue

Not since it has been rebuilt. And since I got it in need of a rebuild I don't know before that.<br /><br />Also it makes no difference how much the boat is loaded. 5 guys or two guys same RPMs.

 

[Dhadley]

Re: Perplexing RPM issue

I think we should start by verifying the tach. (Sounds like we may have a 4200 tach) Ask the shop that did the sync & link and set the timing what tach they used. They should have used a shop tach. They can tell you what rpm the timing was set at.

 

[vranasaurus]

Re: Perplexing RPM issue

Honestly i may have to find someone near here to look at it. The mechanic from back home may not have timed it right because I don't think he timed it with a shop tach.

 

[Dhadley]

Re: Perplexing RPM issue

What kind (brand) of tach is it? Is it set on position 6?

 

[vranasaurus]

Re: Perplexing RPM issue

position 6, it's a teleflex tach

 

[Dhadley]

Re: Perplexing RPM issue

It really sounds like its not working properly. It didnt respond to change in load or pitch.

 

[vranasaurus]

Re: Perplexing RPM issue

Tell me if this sounds right:<br /><br />The idle timing screw is all the way in or advanced and it still idles a little low.<br /><br /><br />My thought is to mark where the timing is now and advance it a little to see if that affects the RPMs.<br /><br /><br />When I first put it back together I set the WOT with the starter. When it didn't run right I checked it again and it was off. I thought the fly wheel might have shifted but it hadn't TDC was TDC.<br /><br />Will it work to adavance the timing a little and see if that gets the RPMs up?

 

[Dhadley]

Re: Perplexing RPM issue

The idle screw in the throttle arm should be about halfway in. What "idle timing screw" are you refering to?<br /><br />Advancing the total timing may burn a piston if you go much past 28*. <br /><br />If the tach doesnt respond to changes in weight or pitch I would suspect a bad tach.

 

[vranasaurus]

Re: Perplexing RPM issue

The idle screw(idle timing screw as it adjusts the idle threw the timing)is all of the way in.<br /><br />I was reading the other thread where the guy is haveing a similar problem. I might try and check the timing again. I also may check to see if my tach is working properly.