View Full Version : Plugs fouled, consuming oil

04-26-2003, 08:02 PM
Has anybody run into this or have tips on troubleshooting? I have an Aprilia RS250 Challenge Cup, 1998. I recently replaced the cylindar base and head gaskets because the previous ones had at 4 years on them.

Afterward, I noticed that my plugs get fouled with a black, wet-looking coating on the side oposite the electrode and around the perimeter. This happens after just one race weekend. Also, it's consuming a _lot_ more oil. Just guessing at the amount, but it's using up about twice as much as usual.

I had noticed that my mixer pump cable jacket was stuck and had artificially extended the cable. So I put that back in place, and adjusted the oil mixer pump pulley according to the guidelines per the manual. I expected that this would have fixed the plug fouling problem, but it didn't.

If the mixer pump were injecting too much oil, would that foul the plugs? The manual says that the pump would push X amount of oil per minute. However, it doesn't say anything about the benchmark throttle position. Anybody know how this is measured?

Thanks very much for your time. I hope someboyd has some tips. Replacing plugs is pretty expensive.

Nicolas Romero
home.attbi.com/~sandcastleimages (http://home.attbi.com/~sandcastleimages)

04-28-2003, 01:47 AM
Firstly check the obvious - you did have the trottle part open (lining up the bottom of the gate in the flat-slides with the line maked on the carb bore), when you calibrated the oil injector pump. If not the injector will pump too much oil for the throttle position. Infact thats the only ting I can think of ... if the drive gear (in the gearbox) were damaged it would pump less oil ... If the pipes were damaged, there would be less oil to the engine. Its possible one of the oil metering valves are damaged, but as they are inside the crank it's hard to see how the damage could have occured - also they tend to jam shut when an engine is left dry, rather than open.:rolleyes:

05-10-2003, 06:42 PM
Hey, thanks very much for the reply. (Sorry I didn't say that sooner. Work has kept me away from the bike for a while. Uggh.)

I've check the pump guides again. They guidelines on the pulley are matching as described in the manual at throttle full close, half open, and full open. ?? Baffling.

I did find in the manual the method for measuring oil consumption. "Holding engine speed at the same 2.000 rpm move the pump lever up to the fully open position and hold for 2 minutes. In these conditions, the quantity of oil extracted from the milimetre-gauged container should be 4,8 - 6,0 ml."

Do you think it's possible that the oil pump valve is stuck open? Can the pulley become decoupled from the valve?

I'm looking for schematics of the pump so that I can understand the mechanism and make some guesses. Anybody know of any diagrams of the oil pump?

Thanks again for any tips you can share.

Nic Romero
See my 2001 attempt at racing here: home.attbi.com/~sandcastleimages (http://home.attbi.com/~sandcastleimages)

05-11-2003, 10:49 AM
It could be as simple as too rich a mixture, as this will take more oil from the crank to the cylinder with it. This is especially likely if the weather is hot where you are...

I have not seen a schematic of the pump - I do have one out of an engine (an ex-bottom crank case) that I could look at if you needed.

A tip for recycling plugs is to burn off the excess oil on a gas burner (a kitchen hob will do), then brush with a brass wire brush to remove carbon deposits, finally a squirt of brake dust remover to get rid of loosened carbon should let you re-use the plugs. An NGK rep told me that you shouldn't do this too often as the plugs have a special coating that will be worn off eventually, but then he was trying to sell more spark-plugs so who knows if thats true...