Hi folks,
New member here but been riding a while. I've had my GS (2004) for about 4 years now and recently moved from pretty much sea level to around 1300 feet with runs up the local hills to around 3500 feet. When I rebuilt the carbs few years ago I noted the jets/needles sized etc but have lost that info (stupid stupid) but i think it was all stock. Previous owner put a K&N air filter on. Only using non-ethanol fuel and fuel is quite fresh, a couple of weeks at most. Riding around town the bike behaves perfectly but heading up the passes the engine gets quite lumpy on one or two occasions but not all the time (internet searching has indicated this is also called 8 stroking). The engine would seem to lose power in a rythmic way. It felt like i was losing every second or third power stroke (was probably around 5k rpm). Problem would partially dissapear if I downshifted but did not seem to be at 100% full power. This happend with a half tank and with a full tank.
I've poked around the forum a bit and there seems to be a general consensus that the GSs are jetted quite lean and I first thought that maybe I was having a lean condition problem. Then thinking about it, this should not be as I am climbing in altitude it should get richer as the air thins.
I checked plugs when I got home and they seem the usual light brown as they are supposed to be ( I know plug reading is not too valuable these days but I've been lead to beleive that if I am missing cycles due to over rich mixture the plugs will be rather sooted up). However this plug reading was done after 15 minutes of riding back home. Would this "overide" a sooty plug or would the sooty deposit hang around for this long?
So my current thinking is that it is running fine at some throttle positions and very rich at others. I plan to mark the throttle (1/4 1/2 3/4) and head back out to see if this happens at a repeatable throttle position. At that point I will try to pull over and check the plugs (not many places to do that on the passes though). If I see evidence of richness I guess I'll need to try and mess with the jets controlling that throttle opening
I just wanted to see if you folks have any advice or insights. Am I on the right path. Anyone experienced this before.
Valves are checked regularly and are quite stable. Last check/adjustment was 1000 miles ago.
Thanks
HNN
I haven't had exactly the same symptoms as you but I have found the engine reluctant to restart after a brief photo-stop at high altitude.
It gave symptoms of being flooded and did it twice on the same day.
It took two or three attempts to get it restarted which has NEVER happened before or since.
It was also noticeably down on power during the same period.
It was extremely cold (around freezing point or 0C here) and the bike was just switched off for about 3 minutes.
It has never done it before or since under "normal" conditions.
I put it down to "thin air" at altitude causing an over-rich mixture.
I don't believe that it had cooled down enough in 3 minutes to need choke to restart and the symptoms did not fit that as I had to give it throttle to get it going, not choke!
Macka
15 minutes riding back into town would definitely mean you're reading the plugs for in-town conditions. Ideally you do a plug read while up in the hills.
If previous owner put on a K&N they may have put in larger jets, especially if it's reading brown in town, since the air filter will typically lean it out even more.
You had it work fine on that same hill before ???
The part that is most likely to wear on this bike is the float. It drifts high, on the later models it happens a lot less, but still does happen.
That's my closest guess. You should check and diagnose it properly before starting any fixes.
You have K&N but stock pipe ?
Cool.
Buddha.
Hi Folks, thanks for the input.
Buddah, yes k&N filter with stock pipes. Been meaning to get original filter but have not gotten around to it yet. I have ridden the hill three times, first time was very slow as I did not know the pass and all seemed fine although maybe slightly underpowered - put it down to a 500cc on a steep pass. On the next week I did the road twice more and both times I had this problem. You have a point RE float height - It has been about three years since I checked float height and I've heard it should be almost a yearly maintenance procedure...
Would float height lead to constant rich condition or only at certain throttle openings? If the former should I see rich plugs even at lower altitude?
Float being high will affect you as you open the throttle typically from 1/4 throttle to 1/2 throttle. It would be there at all times but likely feel worse where you're constantly opening the throttle (like on a steep hill).
Also you could have fuel get into the air box, and maybe wet the filter - is it K&N in the airbox ? or Clamped on K&N ?
Cool.
Buddha.
Buddha, it is a drop in replacement for the standard air filter, in the original airbox. I'll check that at the she time as I check the plugs the next time it happens.
Those drop in's have a restrictor in them for allowing them to use stock jetting. Since a stock bike cant quite use the stock jetting in many cases, you may need to either go to the stock filter or probably rejet.
I think the K&N regardless of what their fitment is, is a bit dirty to the top end, and accelerates wear on it.
Cool.
Buddha.
Hi Folks,
Finally got to ride back up the hill and test it, first ride it was lumpy - similar to previous times. Plugs were quite lean- not rich looking as I expected.
Second time I decided to see if a bit richer might help and went up with the choke at around 25% and this seemed to improve it a bit.
Both times the plugs were quite "lean" looking. We dont have Ethenol fuel over here so I believe the plugs reads are more reliable. I only remembered to take photos of the plugs after the "choke run" but they still no sign of richness.
(http://i827.photobucket.com/albums/zz199/brettmarkfarrell/20170622_210619_zpsidmhrmhq.jpg)
(http://i827.photobucket.com/albums/zz199/brettmarkfarrell/20170622_205918_zpsbomrh6pb.jpg)
So it seems that I was totally off course assuming rich behaviour and the bike IS actually running lean wich is exacerbated with spirited mountain climbs at around 1/2 to 3/4 throttle openings.
Does that seem reasonable?
Next plan is to open the carbs to check all jet sizes and then to clean it, do a few more rides to check at which throttle opening the problem occurs which will identify which carb circuits need to be increased.
Does that plan of action sound right?
Thanks
HnN
I'd bump all (both... don't remember your year model) jets +1 size. Your plugs don't look that lean. Clean everything while the carbs are apart, verify no vacuum leaks, etc.
I'd check the float height, give the carbs a good cleaning and test that before changing any jets.
3500' isn't that high, the bike should run fine with stock jetting if the carbs are in good shape.
Both my 97 and 02 GSs running completely stock were up and down the Blue Ridge Parkway at altitudes of up to 6000 ft and I never did anything to the carbs except adjust the idle speed. My 97 with the old 2 circuit carbs was a bit too lean for winter riding here and having bought it new and living in NE Ohio I parked it winters and rode an old CM400A thru our salty winters. I rode my 02 GS year around for it's 100k miles and it looked like it.
(http://img.photobucket.com/albums/v443/jcp8832/GSsigpic4.jpg)