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run-on engine?

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pchapman(at)ionsys.com
Guest

Posted: Tue Oct 10, 2006 7:58 pm Post subject: run-on engine?

In a Sept 20 posting I asked about a problem with a run-on engine, on 

a Rotax 912 UL.



As we had used good fuel, the plugs were showing the right colours, 

and the problem continued during cooler fall weather, we started to 

suspect the ignition system grounding more. We had tried the 

suggestion of using the choke when about to cut the engine, but it 

wasn't enough to stop the sputtering run-on.



The problem was solved by tightening a bolt on the engine, that 

connects an ignition electronics ground wire to the engine (actually 

to one intake manifold I think). The bolt wasn't obviously loose, or 

loose to the touch -- the bolt only tightened up an eighth of a turn 

or less. This minor change was clearly the solution, as the engine 

was run a couple times shortly before and shortly after. The run-on 

disappeared completely.

Peter Chapman

Toronto, ON           601 HDS  /  912  /  C-GZDC

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klaus(at)utdallas.edu
Guest

Posted: Wed Oct 11, 2006 12:18 pm Post subject: run-on engine?

Hi,



The run-on effect can become a nasty problem if not treated promptly,

due to the violent shaking of the engine before it finally stops.



The suggested cure, tightening of the bolt holding the grounding wires 

of the ignition

module, is a good idea. But the tightening may just scratch the surfaces

of the connectors a bit, thus re-establishing the desired grounding. But 

this

may fail again within a few weeks due to additional corrosion.  Rotax 

Canada suggested years ago

a permanent fix. The idea is to remove the bolt, clean the grounding 

connectors

and bolt carefully, and then reinstall everything with insulating 

silicon grease.

It may sound odd that insulating grease is used. But this works, since 

it keeps out the

moisture. There is also a silicon grease that conducts. That type should NOT

be used.



As for my case, even with the silicon grease, the problem kept on coming 

up. Eventually

I installed a separate grounding wire that connects the bolt of the 

grounding wires

with the firewall. That really solved the problem.



Best wishes,



Klaus



-- 

Klaus Truemper

Professor Emeritus of Computer Science

University of Texas at Dallas

Erik Jonsson School of Engineering and

  Computer Science EC31

P.O. Box 830688

Richardson, TX 75083-0688

(972) 883-2712

klaus(at)utdallas.edu

www.utdallas.edu/~klaus

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planejim(at)bellsouth.net
Guest

Posted: Thu Oct 12, 2006 3:59 pm Post subject: run-on engine?

Peter,



I ran into this same problem a while back. I have an item on my Annual 

Condition Check List to remove the bolt. clean all the wire terminals at 

that location every year. No continuing problems.



I did have a later problem where the engine would not shut down. After much 

trouble shooting, it was decided that the problem was an OPEN in the ground 

wire inside one of the very expensive Ignition Units. Kerry at Lockwood 

Aviation suggested breaking into one of the hot leads to the faulty ignition 

unit and run it through a switch in the cockpit. It worked great and 

continues to do so. Cheaper than buying one of those expensive Ign units.



Jim Hoak



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