Mag drop 350 on each side

by Paul Hamilton in 912 / 914 Technical Questions 6 years ago

During 4000 RPM runup, what is the most probable cause of a consistent 350 mag drop with rough running on each side (both consistant rough and consistant drop) but super smooth running great on both mags. 10 year old 80 HP engine, dry climate, about 400 hours. Have never had this situation with many years of carbed 912's. Most common situations/fixes for this?

Re: Mag drop 350 on each side

by Roger Lee » 6 years ago

Roger Lee

126 5.13k 4.55k

Most common and might as well start easy and simple.
The 300-350 mag drop many times is one plug or firing in one cylinder not doing well. If it were me I would start with new plugs whether you think they are good or not (gap between .023 - .027). Unscrew the plug caps and trim each plug wire back 1/4" - 3/8" for fresh plug wire ends. Apply a tad of dielectric grease to each wire end and screw the caps all the way back on until they seat all the way in. Many times this will take care of this 300 rpm loss.

Carb sync?

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Mag drop 350 on each side

by James Ott » 6 years ago

James Ott

22 322 358

Why would you put "dielectric" grease on the wire ends? The definition of "dielectric" means that it is an insulator and does not pass electricity easily.

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Re: Mag drop 350 on each side

by Dennis Richardson » 6 years ago

Dennis Richardson

1 153 169

Dielectric grease is electrically insulating and does not break down when high voltage is applied. It is often applied to electrical connectors, particularly those containing rubber gaskets, as a means of lubricating and sealing rubber portions of the connector without arcing.

A common use of dielectric grease is in high-voltage connections associated with gasoline engine spark plugs. The grease is applied to the rubber boot of the plug wire. This helps the rubber boot slide onto the ceramic insulator of the plug. The grease also acts to seal the rubber boot, while at the same time preventing the rubber from becoming stuck to the ceramic. Generally, spark plugs are located in areas of high temperature and the grease is formulated to withstand the temperature range expected. It can be applied to the actual contact as well, because the contact pressure is sufficient to penetrate the grease film. Doing so on such high pressure contact surfaces between different metals has the advantage of sealing the contact area against electrolytes that might cause rapid deterioration from galvanic corrosion.

Thank you said by: David HEAL, Garrett Wysocki

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Re: Mag drop 350 on each side

by Roger Lee » 6 years ago

Roger Lee

126 5.13k 4.55k

What Dennis said. (Good explanation, That's worth a Karma for sure :))
It's a very acceptable practice and helps keep corrosion at bay..

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Mag drop 350 on each side

by Paul Hamilton » 6 years ago

Paul Hamilton

30 145 298

OK thanks Roger. Back to the basics. 1. plugs 2. plug connections 3. Carb Sync will by my priority order for this. Nice to do it in steps of possible to see what has the best effect. Just wanted to use some common practices/experience. Greatly appreciated. Yes Dennis very helpful.

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Mag drop 350 on each side

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