800GS misfiring (bad, but at least it sounds nice :)

[cbutler]

Hi all. Not posted properly in sometime, good to be back...

On the A3 a couple of days ago I applied full throttle as someone moved out of the outside lane, and the bike didn't respond positively but instead lost speed. This is only the case on about 90%+ throttle. However the throttle didnt seem to respond as normal at any amount.

When I left the A3, at lower speeds and less revs, 2800rpm > it seems as if it was misfiring or as it was very burbly exhaust and very bad throttle response. It would also stall easily.

No warning lights, and it starts without issue although idles rough. Been using the bike plenty and fitted new battery a couple of weeks ago (with plenty of ride outs since then).

I've seen many YouTube videos about 800-engined bikes and their problems, although mine didn't seem that bad - just less power.

Friends have said to change the plugs, which I will be doing this Saturday. Does anyone have suggestions, heard of this before perhaps?

 

[harry the cat]

Rough Running

My 800 started doing that a few years ago and went on to full scale stalling. Turned out in my case to be a fuel pump/fuel pump controller issue but there are a number of other options.

I've hopefully attached an article from a guy on the Adventure Rider Forum which helped me. Its saved as an image so if it's too small to read p.m. me with an email address and I'll send it on to you.

 

[Nick V]

There is another possibility not mentioned on that list: the throttle-position sensor may be making intermittent contact or have water in it.

I wrote a tech article on how to run diagnostic checks and fix this problem (if indeed this is the problem in this case).
The article is at http://www.ukgser.com/technical/index.htm?.

Best of luck! Let us know how it goes.

 

[cbutler]

Thanks for the advice guys.

I dismantled the fairing quite easily, was good fun actually - first time I've ever done such a thing. Anyway, battery compartment out, airbox and hoses off and I get to the coils.

Coils were tricky to take off, but didn't require the special tool plug thing BMW offer.

However... trying to get the plugs out, blimey never had such an issue with mechanical things before. The standard spark plug sockets you get with any decent mechanics set are WAY to chunky to fit in, I then bought a spark plug removal tool from screwfix but it was a bunch of rubbish as even though it slid down to the plug, it was too small round the nut. A second slightly bigger tool and that was just too wide to fit in at all.

The two I bought were:
http://www.screwfix.com/p/laser-spark-plug-spanner-16-21mm/12571 (too small)
http://www.ebay.co.uk/itm/351009306450 (too big)

To top everything off, I had bought the wrong plugs (somehow managed to get the 650GS ones instead of 800GS).

So... yeah, not best pleased its SO difficult.

Needless to say, I have ordered this:
http://www.motorworks.co.uk/vlive/Shop/Parts.php?T=4&NU=15&M=72&Ct=WA&spPage=2 (down the page, "spark plug spanner tool").

 

[Nick V]

To top everything off, I had bought the wrong plugs (somehow managed to get the 650GS ones instead of 800GS).

Which plugs did you buy?
All 798 cm3 F-series of all years, without exception, use NGK DCPR8E.

 

[cbutler]

I originally bought DR8EIX, but need DCR8EIX (iridium version) instead.

 

[Nick V]

I originally bought DR8EIX, but need DCR8EIX (iridium version) instead.

If you're using DCR plugs and not DCPR, you may run into troubles with fuel consumption and power delivery.
The 'P' signifies a projected centre electrode (for NGK, usually by 1.0 to 1.5mm). That projection gives better combustion in the F-series engine's combustion chambers by putting the spark closer to the epicentre of each combustion. What you really need are DCPR8EIX.

If you want to keep head temperatures a little lower and fight the possibility of detonation (especially if you ever have to run lower-octane fuel), you may even want to try DCPR9EIX. It's exactly the same plug, just one heat range colder. I've successfully run DCPR9EVX and DCPR9EIX in an F800S, ST and GS with no problems whatsoever. (Because the F-series engines run so lean, even the 9s run slightly too hot. At each service, I see a virtually clean firing end, with no deposits at all. When I used to run DCPR8Es, I used to see accelerated electrode erosion if I ran the bikes very hard for long periods.)

In this case, the NGK plug code means:
DC: 12mm plug body, 16mm hex to remove.
P: Projected firing end.
R: 5 Kiloohm resistor.
9: Heat range number. For NGK, the larger the number, the colder the plug.
E: 19mm plug-body reach.
IX: Iridium centre electrode. (The earlier spec, which IX plugs replaced, is VX - for Platinum centre electrode).

As a side note, you can also use DCPR9EIX to replace KR9CI in 1 157 cm3 and 1 293 cm3 K-series, and you can use DCPR8EIX or DCPR9EIX to replace DCPR8EKC in '04-'09 R-series.