R80GS Tuning probs
 

Just fitted new header pipes and new push rod tubes. Started up the bike and the bike sounded ok at idle but a blip of the throttle caused a slight mis-fire at higher revs. I noticed the right hand down-pipe was getting glowing red hot compared to the left which remained ok. The neutral light when at idle was ok but when i hit the revs it seemed to glow noticably brighter although the charging light itself went out as normal.
I ran out of daylight before I could balance the carbs so this will make some difference but the glowing header did concern me. Appreciate any words of wisdom before facing it again tomorrow. Cheers
Mark

Sounds to me like you have set the valves wrong to the timing - did you put everything back in the correct order and place it where it came from - pushrods back where they came from eg left exhaust to left exhaust etc if you have mixed things up it may cause problems, maybe the push rod have not been seated correctly or the barrel, heads or cams have not seated correctly when torqued down I would suggest you remove everything and re check your work and each component make sure you have not bent a pushrod or put anything back on in the wrong place. Then turn the engine over by hand slowly and watch that the whole sequence of tdc and valves opening closing is correct. This is not going to be a carb problem if you have not touched them - the flame front is burning in your exhaust making it glow. Did you check the condition of your valves and seats before re assembly.
Was the bike fine before you did the work ? have you altered anything else.
If not it seems simply that the exhaust valve is opening too soon or not closing properly for some reason.

I double checked everything before i put it back. I cleaned all valves and seats and piston and reset valves accordingly. The battery is dead, I was using a jump start to fire up which may allow for erratic misfire but i am not sure about the burning in the header pipe

Amazing!

I've tried to get my down-pipes to turn orange, but have faild to even with 1000cc system.
Let me know how you manage to do it!

What you have is way too hot exhaust fumes...
* timing off
* valveplay off
* jetting off
* air leakage (leaning the mixture to way off)
* jammed choke return
* spark problems
* changed back-pressure from exhaust system (ex., dual to single or vice versa)
* changed airfilter from stock paper to K&N or similar

Is your version equipped with the exhaust return system crap ? Those were said to cause weird phenomenas and overheating problems...

Hi
The main difference is that I changed from a fron balnce pipe set up to no balance pipe into a y-piece. I will balance the carbs tomorrow and re-check the valve clearences and see if it makes a difference

That's not good...

Alibaba what would you suggest as a rough basic idea of rejetting to when doing as Simplemind have done by chaning the back-pressure so radically as he have done?

Whould a lift of the needle (one or two notches) and a change to next larger main-jet be fairly ok guess work, or would you recommend as I would => workshop with proper tools to adjust the mixture correctly?

I've tested s/s "megaphone" (made in Australia sold by www.midland.se in Sweden) once on my R80. Loved the sound! But... lost all low rev torque => opted to stick with "stock" mufflers/silencers instead (have regretted that choice ever since -ROWL). My reason was that I was very concerned about what the effect would have on the exhaust fume temps, and rejettings were beyond my scope of knowledge back then.
Sounds very much like what Simplemind have done with his beemer , i.e. altering back-pressure way too much without rejetting the carbs accordingly...

Most interested to hear about your thoughts in/on the jetting theories/practicalities -:)

Albert thanks for the advice. The valve clearences are set OK and the bike actually idles pretty smoothly only gets a bit poppy higher up the revs. Whilst balnancing the carbs with a vacuum gauge is within my capability - adjustment of mixture is something i would try but needle adjustment is beyond my ability without extensive reading up first (dont want to make matters worse). I take it from all this is that the mixture is too weak thereby causing overheating in the header pipe?
I would be happy to get the bike on the road without causing any permanent engine damage and then take it to a bike shop for them to sort out.
Mark

Begin by checking the Bing site:
BING POWER SYSTEMS GmbH
BING POWER SYSTEMS GmbH - Einstellblätter

On the side of the carbs there is a number 32/64/xxx or 40/94/yyy - type that into the box at Bing site => then you get the original Bing jettings for your carbs (each carb have its specific jettings - BMW may have altered the jettings to suit different markets!).

My guess is that you have 145 main jets if in europe and 135 if in the US.
As an acute remedy you could get main 150-160 or 145-155 jets to test with - what you risk is too rich mixture => just cause a soothing which is far less damaging compared to overheating. (I've tested both duirng the 1990:ties...).

Best is however to have a workshop fix the situation for you - and you should look at a racing shop then... something like MOTOSPEED.se - Your Performance Partner or MODELBOUWWINKEL & WEBSHOP - LIMBURG - MBS-RACING guys that know how to jett and tune bikes - beemer shops very rarely do...


When you changed form dual balans pipes to a collecting Y you trade off low rev torque for high rev performance - you were aware of this, and that was your intension ?


Looking forward to hear how it goes -:)

How did it go?

How it went
 

Albert,
I took the bike to a BMW mechanic who stripped the carbs and found a blockage in one of the jets. The bike starts and idles smoothly but after 2000rpm the exhaust note is loud and raucous (banging noticably). I realise that the exhaust configuration will alter the exhaust note but the mechanic thinks that the baffles in the silencer (the 11yr old original) sound shot. I can pick up one for around £300 but want to make sure that it is the baffles. What is the life span of a silencer? I would imagine that if the mods to the exhaust were unsuitable I wouldnt have a smooth running accross the rev range particularlyat idle/low revs, any thoughts?
Mark

Great that your carb issue is solved!

Lifespan on chromed steel mufflers is -low-. A few years at most. I -have- seen what have been claimed to be the original mufflers some 30-40 years after the bike was sold... trick... not used and and inside of mufflers filled with used engine oil every winter.

You will find that s/s (all through) will be expensive, but they will last "for ever".

The mufflers on my R80 was original back in 1991 when I bought it. By 1995:ish I had to buy new... bought s/s from www.midland.se made in Australia - still have the same mufflers, 150 000km and >15 years later.

However, ... you -can- buy "any" mufflers just as long as you pay close attension to the effect on the mixture need. Your mechanic should be able to help you re-jet the carbs to fit whatever you buy.
I have seen standard car-mufflers (looks awfull!) being used on a R75 - and that works ok.

What do you want from the mufflers?
- K75 sound?
- best high-rev (most open and longest) power?
- the "correct" bike sound (original Bonneville 750cc like)?
- low power sound?
- snappy sharp banging sound?
- canned sound?
- open sound?
etc
Since you need new mufflers - why not get some that meets your requirements and wishes the best ?
4-stroke Performace Tuning, Haynes Books, Graham Bell, have a chapter on how to build/adapt exhausts and mufflers to fit the engine.

What you ask about is how to get low-rev smooth running and even power. Not so tricky - Yamaha had an exhaust with variable back-pressure from the exhaust system (forgotten which model it was, 1100cc?, racing, four).

It is more an issue of jetting than of mufflers.
You can affect a lot by changing carbs. Keihan 27mm from Suzuki GS750-850 will be better at low revs than bing 32 on a 750-800cc, but probably too small for a 1000-1100cc. Just (2010-09-03) got words from Motorworks that they have discontinued their dell'orto conversion kits that they had in the 90:ties (of which I have one set).
Throttle-carbs works far better at low-revs than CV (my experience only); Mikuni flat slide are really neat - makes a big deep whole in once wallet though.

Do you have the Y-section, or the pre-muffler, or do you have stock dual exhaust on your R80GS ?


beer

:scooter:

Thanks Albert, a lot to think about. I have the non original Y fitted and although it sounds good (not that that is a major issue) I have spoken to the people at Keihan and am at the moment toying with the idea of going back to a ss collector box / single balance pipe down pipe configuration (ie back to stock), I will have to save up some money first
Mark

I had a Keihan header and Y setup. I did not like the fit of the Y, nor the poor'ish running. I kept the headers, no balance pipe, and bought a BSM Power Pipe from BMWBoxerSupplies. Very nice and works very well with the standard jetting - More Changes....

John

Nice rockerarm-set-up Redboots!
Where did you buy it - Israel Motoren?

As for balance-pipe or not. I do not know how it affects the GS. On the street model you will hear a lot of opinions. My personal experience is that below 3000rpm is does play a significant role in back-pressure / low-rev torque. I have tested none, single and dual - only dual gives my bike the torque I want. On higher revs, 4000 and up, I can not say that I noticed any difference at all whilst driving.

Tested a K75 with motorcross muffler - it sure sounded a lot!
Now low-rev power at all!
But, as revs built up, so did power!!!
It was -fun- driving; no one asked the locals what they thought though...

Ok - issue here is funds.
Keihan s/s mufflers are ok, but the Aussie once are better.

Go to the scrap-yard and pick-up a nice muffler from a Nippion Rice Cooker (RR-bike); something that have a loose inner section around which you stuff insulation/silencing material.
You will need to re-jet the carbs though; a fair guess is 1 step up on the mainjet and perhaps 1 notch up with the needle - your mechanic can set it up. Motorworks have a good collection of jets and needles.

You will get a louder sound, loose a bit of low-rev torque, and save a bundle.

Size and weight is an issue on a GS, I know, but the scrap-yard will gladly help you find a suitable silencer/muffler.


Creativity at work is always apprechiated:
- Remember to post/send photos of the solution!