4500 Max RPM on Rotax 657

4500 Max RPM on Rotax 657 Full RPM's Not Realized Rate Topic:

#1 mase

Novice

Group: Members
Posts: 11
Joined: 24-April 06
Year of DOO:1995
Model of DOO:Speedster
Engine in DOO:Twin 85hp Rotax (720)

Posted 06 June 2006 - 08:43 AM

My 95 Speedster with Twin 85HP engines has one engine that starts and runs great until it goes past 4,500 RPM. It just hangs at 4500.

The compression is 120 for each cylindar.

I have adjusted both the high and low speed jets to 1 turn H and 1 Turn low. The engine has twin carbs and seem to be syncronized based on throttle opening.

Changed out the plugs which looked fouled and reset the oil pump setting which was way to rich. After new plugs the RPM's went higher but then the engine surged between 4500 and 5500 RPM.

Now the engine just hangs at 4500 when given full throttle.

Does anyone have any ideas?

My thoughts are the fuel filter (I have not checked the in line filter) or the fuel pump?

My other thought would be since it was running rich on oil maybe the exaust ports are restricted? Is this a possibility?

Just need some guidance as my lower back is sun burned from leaning over the back seat to adjust the engine.

Let me know your thoughts.

Mase

#2 mase

Novice

Group: Members
Posts: 11
Joined: 24-April 06
Year of DOO:1995
Model of DOO:Speedster
Engine in DOO:Twin 85hp Rotax (720)

Posted 23 June 2006 - 04:08 PM

Just to update what I found durning the carb rebuild. There was a sand like substance blocking 80% of the fuel filters in the carbs.

Did the rebuild and all works but have the final water test this weekend.

Mase :blue_bandana:

#3 mase

Novice

Group: Members
Posts: 11
Joined: 24-April 06
Year of DOO:1995
Model of DOO:Speedster
Engine in DOO:Twin 85hp Rotax (720)

Posted 05 July 2006 - 12:17 PM

mase, on Jun 23 2006, 04:08 PM, said:

Just a post to let anyone know the final resolution.

The Carb rebuild took care of the problem and now the engine will go to 6,000 rpm without any problem.

Have 10 hours on the rebuild and no fouled plugs!!!

#4 foundation

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Group: Members
Posts: 6
Joined: 14-July 06
Year of DOO:1997
Model of DOO:Speedster
Engine in DOO:Twin 85hp Rotax (720)

Posted 16 July 2006 - 03:37 AM

mase, on Jul 5 2006, 12:17 PM, said:

mase, on Jun 23 2006, 04:08 PM, said:

Hello,
I am glad to hear of your success with the engine.
I think I am having the same problem with a newly purchase used 1997 speedster (twin engines).
The starboard engine with up to a certain RPM even at full throttle.
Did you use an overhaul kit to fix your carbs.
Any help will be greatly appreciated.
Bob on Kauai