Minor "kick" after hard throttle opening..

[damo the onion]

Ok, one for the real GS Master Mechanics.

Scenario:
Ride a while at a set throttle opening (say a mile or so at 90+) you roll off, drop a gear, and go to roll on...

and you get a small "kick", it feels like the shaft jumps a spline.

The shaft is fine both ends.
The Final Drive has been replaced.
Zero=Zero TPS has been set.
Throttle Cables have been sync'd
Throttle Butterflies have been sync'd ( time and time again)
Mixture has been checked (1.9 on the CO meter) and verified by colour tune as far as I can tell..



Am out of idea's now, it's not dangerous, just annoying . Apart from that the Motor is very good for its 70K miles. ...

Any Idea's?

 

[Big Lad]

My old 1100GS had gearbox probs. Symptoms were... as I went through the gears when it hit third, there was a momentary pause in the drive, this felt like a rear end twitch. It felt like the rear end was breaking away and the shock would squat and then it would be fine one sec later. This is the gearbox. It's 3rd gear jumping out and re-engaging in a split second and as such you lose drive for a sec.

There are two ways out. A new gearbox ( £1100 plus ) a recon or used box, or re-build the old one. You are looking at £500 min whatever happens. Good luck. Hopefully I'm taking bollocks and you have a different problem.

 

[CoolCarbon]

Myy 1150 does something similar....

I put it down to the 'Slack' being taken up....

I'll live with it, I've ridden dozens of BMs and most have had some 'latitude' within the transmission...

CC

 

[Steptoe]

just like big lad said - i take it your bike is an 1100 -

the earlier the model ( i think pre 97 bikes do it), the more likely to be the gearbox

 

[damo the onion]

Thanks for the idea's guy's, but in the nicest possible way i hope the Gearbox Theory is wrong , the bike is only worth about 3k and the idea of spending upwards of 500-1100 of our great british pounds on anything but tyres is not pleasant.

However, another idea came to me overnight (as they do) which i'll share for confirmation/denial/scrutiny/ridicule as appropriate.

I was thinking about the nasty little things that all managers never have time for.. Details.
Bear with me here, it's a little tedious to explain.. feel free to bugger off for something more interesting, say putting a running powerfile down your trousers....

The Bike suffered from bad carburation when I got it. (hoooge cloud of soot when throttled hard, on or off load)
It also Vibed like a badly balanced Rampant Rabbit on 3phase.
Have done all the things to sort this out, performed with the anal pricision born of years if practice (TPS/Sync/cables/valve clearance/plugs)-You get the picture.
It now is as close to perfect (engine mixture wise) as I can get it. With no soot and it runs at about 1.9% CO on the meter, which is slightly high although within range (book says 1.5-2.0%), but is still *slightly* rich when cranked on. However it pulls like a train (way more balls than the 3kmile 1150GS i test rode a while back) and gets about 140miles to a tank fuel.
So, I was wondering if the lump is just "Burping off" a small amount of excess fuel from overun and causing that "kick" through the tranny. It only does it when the oil temp is at about 5 or 6 bars AND you've been set at a constant (highish) throttle for while say coming off a carriageway to a roundabout, then roll off sharply and roll back on again sharply. (Am not the smoothest operator so this happens roughly all the time)

I've got all day on it today so i'll pull the air filter out and see if that helps....


If all else fails, i'll try to ignore it... but thats gonna be hard as it's driving me nuts at a cellular level. It's the only problem left on what would otherwise be a cracking example of an old bike come good.

Feel free to chuck rotten egg's/old fruit/large denomination notes at this whole thing 'cos, on re-reading, it sounds like the ravings of loony.....

 

[Pukmeister]

It sounds like it is combustion related to me, pre-ignition perhaps when fuelling up again from closed/part throttle? From your symptoms described it sounds like the mixture is igniting suddenly at the wrong point in the cycle giving you a bad knock. If this is the case, you could end up causing piston/conrod damage (worst case scenario).

Even if the plugs arent fouled, perhaps the ports and valves/piston crowns could have carbon build up like glowing cornflakes, you never know?

Maybe you could try changing the plugs for new or else changing the heat range of them slightly?

Or throw some redex or similar through her then try a good old 'Italian tune-up' on a straight road ? Worse case, pull the heads and do a proper decoke the old fashioned way.

I know I am clutching at straws, but it sounds like you've done everything else possible apart from a proper dyno run with a professional gas analyser to check mixture settings through the entire rev/load cycle. Thats the other option I would consider (assuming the CO check you mention is with a DIY unit). A dyno run could be money well spent on giving a detailed diagnosis and ruling out combustion faults.

 

[Mouse]

If it only does it after a while on a constant throttle, I'd say it's something to do with the fuel injection, so I think you may be on to something with the "burp" theory

I'm not an expert, buyt I do remember Spout telling me about all his FI woes, mainly concerned with the system's inability to run correctly on a constant throttle opening. You could ask him if he ever got his bike sorted correctly, I am not sure what result he had in the end.

 

[Big Lad]

Still think it's the gearbox. The symptons are exactly the same as mine. You should feel the rear shock take the strain as the bike jumps out and then back on the 3rd gear cog. If you can isolate it to 3rd gear only, when under hard throttle, then it's the box. Where in Herts are you?. If you want, I could take it for a quick spin and see if it's the same.

I bought an 1150 in the end because a pre 97 1100 was too much a gamble and post 97 1100s were the same as the early 1150 price wise. I've now got an 1150 and love it.

 

[Taipan]

Has its got a techlusion on it per chance? If it has an R259 try backing the red pot back a .2v or so. If it doesn't have a techlusion, ignore me.

 

[Steptoe]

it still sounds like the gearbox -

it happens all the time on the early models ( what year is your bike ), thats why BMW changed the bearings/internals on the later 1100

 

[damo the onion]

just got into the office after a morning banging up and down the A1/414/M10/etc paying attention to whats going on....

The results just in (although the Russian Judge is late),

It seems to happen in any of the gears, although its hard to say about 1st and 2nd because they dont get used much once rolling. Certainly happening in 3rd 4th and 5th. (to lesser effect in top as the torque multiplier up there smooths it out out somewhat) but its still *just about* detectable.
I must admit that having checked the FD Pivot bearings this morning, i've discovered that they need doing, and have picked up a new set for this (just need to remember where I put the heat gun).

removing the air filter makes no difference at all, which could mean one of two things, a) it was stoopid idea and doomed not to make a difference, or b) I'm not sensitive enough to feel any...

Got to say, the only other indicator that the tranny may be duff is that it's occationally difficult to drop through the 'box at low rev's. Not very, just enough to need a "clutch up" in order to make it blow through to 1st or 2nd. However most bikes i've had do this to some extent so I wrote the idea off. Unless this problem is indicative of other nasties waiting to pounce.

Watch this space......

P.s its an "N" plater, 1995.....

 

[damo the onion]

After the first "Friday Ace-to-Bridge Night" i've been to in years, I've got good news and bad news..

good news: tagged onto the back of a group of London Headcases, the old girl aquitted herself very well indeed. Trouble is, in the process of doing this the bad news introduced itself...

bad news:
I can safely say that my "burp" theory was complete and total wishful thinking. AR$E. The gearbox is leaping in and out of 5th gear on a randon basis.....


I can see my future, and it involves lots of Cogs and Springs...



You may now "I Told you so" at will......

 

[Deleted account 220427002]

it still sounds like the gearbox -

it happens all the time on the early models ( what year is your bike ), thats why BMW changed the bearings/internals on the later 1100

He knows you know

 

[Wizard]

You may now "I Told you so" at will......

Steptoe told you so

 

[(RIP) Kaister]

The gearbox is leaping in and out of 5th gear on a randon basis.....

used to happen to a 1978 xs750 i had, but in 2nd gear only.
had to hold my foot under the lever while accelerating.

its due to gear side face dog wear - can be cured by undercutting the drive dogs by 5 degrees.

Once the top corners of the dogs go, then they're toast.

I used to rebuild Jean Alesi's race 'boxes at Tyrrell's - surprised they even managed to stay in gear

 

[damo the onion]

I know, I know...

Keep it coming, i can take it.. (humiliation is supposed to be good for me)