Fouling plugs with FCR41's?

[671M900]

I've noticed that my bike will run great with new plugs, but will foul quickly. Like every 300-400 miles!

It's a 1999 M900 with no engine modifications, but FCR41's with Dyna coils and wires from CA-cycleworks. I have a set of DCPR9E's. I cleaned a plug with my pneumatic cleaner, and put a DCPR9E in the vertical cylinder to see if it'll make any difference. I know it's one range hotter, but I'm hoping it'll help. So far, it starts and idles smoother, but haven't taken her out for a ride.

Anything to look for to diagnose? It might be a plug issue, gap issue, jet issue, but don't know where to start or which to eliminate one by one.

Thanks again DMF!

[Langanobob]

With an older bike and assuming lots of miles, my first thought is that it might be oil fouling rather than a fuel issue.  Is there any oily residue on the plugs at all?  Can you post a close-up photo?  That might help some of the plug guru's with a diagnosis.

Also, what kind of gas are you running?  I've had trouble in the past with residue from additives  in the fuel building up on plugs in short order. 

I think its not easy to foul plugs every few hundred mile with Dyna coils.

[671M900]

Not oil, very dry, sooty, definitely from fuel. However, I haven't gapped the set of plugs yet, just did a quick google-fu for the gap and will install. Perhaps the gap is just not right/ too small?

I would post a photo, but I've already hit the last set of plugs with the cleaner.

Running regular ol' 87 octane.

[ducpainter]

I'm guessing you don't have it jetted right.

[Cloner]

I'm guessing you don't have it jetted right.

That's where I was going.

Lots of folks with FCRs (myself included) intentionally jet their bikes a bit fat on the bottom end to assist in starting since there's no choke.  However, you'll want to make sure everything "north" of idle is pretty close to correct.  Main jets, pilot jets, needles and needle jets are easy to come by at Sudco.

[duczilla]

DCPR9E is a colder plug than a DCPR8E which is the stock heat range

[64duc]

DCPR9E is a colder plug than a DCPR8E which is the stock heat range

Which means it will foul quicker.

[671M900]

Which means it will foul quicker.

My mistake, I read the .pdf of the NGK part number decoder wrong!

Anyways, the bike is supposed to take D8EA's stock, so I'll pick up a box tomorrow.

I'll attempt to do some plug chops tomorrow to see where it's too rich. I'm usually in half throttle in most of my riding (commuting), so I'm considering dropping the needle a notch. (FCR's are adjustable needles, right?) At that position it's the jet needle/needle jet, where the main jet is supposed to be WOT?

Any specific areas that are more likely than not to foul the plugs? (mains/needles/needlejets)

Thanks guys!

[ducpainter]

Chances are that you are rich in either the pilot or needle.

Dropping the needle would be a good start, as well as turning the idle mixture screw to a bit leaner.

Do you have banked FCR's or split singles?

[671M900]

Chances are that you are rich in either the pilot or needle.

Dropping the needle would be a good start, as well as turning the idle mixture screw to a bit leaner.

Do you have banked FCR's or split singles?

Banked, using the stock manifolds.

Got a box of D8EA's, will do some plugchops after the local traffic dies out.

[ducpainter]

Banked, using the stock manifolds.

Got a box of D8EA's, will do some plugchops after the local traffic dies out.

I hope you left out some characters from the plug # you bought.

You're looking for DCPR8E

[671M900]

D8EA's are what Chris Kelley sent me with the dyna's and FCR's. The only difference would be the larger hex size "C" denotes 5/16", "P" protected insulator, "R" Resistor. Otherwise, I believe they are the same heat range, and the resistors were meant for FI monsters.

However, if that's what causing the problems, then I'll pick up a box of those, or the champions the Haynes manual says is stock.

[brad black]

i always use dcpr8e in them.

i doubt you're anywhere near half throttle when commuting, usually eigth to quarter at most i'd think.

i'd go down on pilot - 60 is what they come with, i'd try 52.  i try to leave the mixture and slow air screws pretty close to where they are std and fix the richness using pilot jets.

[koko64]

+1