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  #1  
Old 3 Oct 2009
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How much noise to be blamed on Poor fuel?

I am in Bangladesh, on my 1988 R100GS. I am not sure of fuel quality here but I think it is reasonably safe to say that it's not great. Since Pakistan I have been hearing a few noises on ignition of bike that I have put down to fuel quality but now it seems to be getting a lot worse. Is it possible the fuel in Bangladesh is that much worse than in India, Nepal and Pakistan that I am getting the new symptoms or should I be concerned that there is something else at play?

Symptoms:
Frequently getting pinking noises on ignition of bike from cold and when warm, by frequently I mean 95% of time. When accelerating from low rpm bike has started to make some loud rattling noises, not all the time but enough to worry me. RPM at idle is a little rough. Choke requires to be left on for longer than now before it can be trusted not to stall, the bike seems happier if choke is left on just a little for in city driving - (running lean? but see below)


Possibly connected but not sure:
At even low altitudes, less than 2000meters I start to get problems with stalling, suggesting I need to lean out the mixture, I would assume that since stalling is beginning to happen at such a low altitude I am running slightly rich all the time and could do with adjusting slightly anyway.

I am appalling with bikes, this may be clear to anyone from reading ths if I have got everything confused. If anyone out there could reassure me that all this is caused by poor fuel and the Bangladesh fuel is the worst of all, that would be great. If its not could you please le me know what you think the bad new could be.
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Old 3 Oct 2009
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http://www.horizonsunlimited.com/hub...-head-bmw-8348

or... you could...:
* change to 8.2:1 pistons instead of the 9.5:1...
* modify a cylinder base gasket to do the same as changing pistons...
* add octane booster into the petrol...
* polish/grind all surfaces in the heads and on the piston tops "smooth as a babies bottom"...
* test other plugs (1 degree warmer and multi electrodes)
* get well working ear-plugs...

Your problem is the one that sparked the dual-pluggings back in the 1970:ties. You have some material on: Airheads Beemer Club - Home
Here are some other links:
twin plug timing question. - BMW MOA
Dual Plugging BMW Motorcycles
http://rubberchickenracinggarage.com...ugIgnition.pdf
Dual Plugging the R100GS
But you will need to do it this way on a post braker-point beemer:
Daniel Dicke: Doppelz├╝ndung


These are the causes that afflicts your engine = what you need to adress:
- compression ratio too high for the petrol
- hot-spots; poorly finnished combustion chamber
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Old 4 Oct 2009
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I'm off into Thailand soon and I have hopes the fuel quality may increase there. Dual plugging isnt an option for me, I'm cash-strapped and in Bangladesh. I will have a read of your links though, try another plug type and get some ear protection!

Is the pinking causing any long term problems? Would raising the carb needles be of any use?

Thanks for help
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Old 4 Oct 2009
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Pinking can result in blowing a hole in your piston so, yes, it could cause problems.

If this problem is due to pre-detonation of the air-fuel mixture, sounds to me like an octane booster is the way forward: easiest to implement, and the cheapest too. I have no experience of octane boosters, so I can't sayhow good they are but if they do as they say, and if the problem is due to poor fuel, it should get you to Thailand.

Just my thoughts...
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Old 4 Oct 2009
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Just some generic advice ,--retarding the ignition will help ,but I'm not sure you can do that on your bike .
Octane booster may help ,but you'll need a lot ,use toluene instead .It's a fairly common paint thinner ,[but make sure it's actually toluene and not regular paint thinner ] .Up to 30% max - google it .
Pull out the spark plugs and look at the colour ,white is lean , brown is good , black is too rich .Check their condition and check the gap .
Adjust carburation as necessary .Raising the needle will richen the mixture in the mid throttle range .
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Old 4 Oct 2009
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Good suggestion Dodger.

Pull back the timing by 1-2' (1.78mm/degree on the flywheel). I think the single plug can cope with that.

Octane booster is a real need in this case since the options of lowering the compresstion rate and/or dual-plugging is not available.

Rising the needles will not help - it will only cause more problems with more hotspots and sooth.

The problem is too high compression - that is what is needed to accomodate for... think that the most important recommendation will be to try to avoid pressing the engine, to let it use as light load as possible (=rather shift down a gear) and to try to keep the revs below 4000.

When I accidentally poured 80% caroseen into my R80 I could run up to about 3000rpm before the spiking, not just pinging, got too bad - and as long as I kept the engine under light load it also stayed "acceptable". Just... do not copy my silly misstake - the beemer engines do not like to run on caroseen!

You still are in deep water... the risk to blow holes in the piston heads is acute... be -very- careful.
What you can do - as a acute temporary solution, is to install double head-gastkets. It works if you use new once (done that by misstake as well). That will lower the compression ratio from 9.5:1 to about 9:1 something and that will lower the risks considerably.
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Old 5 Oct 2009
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Thanks for the replies. I was hoping that I can just ignore it and get to Thailand where I might be able to purchase some better fuel but it sounds more serious than I thought. I haven't ridden it since arriving in Dhaka, but on the way here it was not good. I will try to find some decent octane booster, sure there must be some somewhere around here. I did think of bringing some but Haynes manual advises against using it, they probably weren't anticipating the bike being ridden in Bangladesh though.

The spark plugs are fairly new so there is not much wear on them, the last were too black, suggesting rich. A couple of drops of water were in the float bowls. As I have one more days ride before I ship to Thailand I left the 20ltrs fuel in the tank and will clean it out at the port. Is it worth adjusting needles to lean out mixture or should I leave alone, needles are on Haynes settings at the moment (3rd from top I think).

Thanks for advice, I am on going on a 2 day boat trip today but will check back asap.
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Old 5 Oct 2009
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Adjusting needles:

If the bike was fine before Bangladesh, I see no reason to touch the needles, until symptoms suggest a mixture problem.

The pinking you've been hearing, if it is a result of bad fuel, is the petrol igniting, spontaneously, in the cylinder due to heat and pressure, but before and without the spark from the plug.

So you have a flame front hitting the piston as it is still travelling up to top dead centre, sooner than expected and this violence is what can hole the piston....( as far as I understand it).

So it is not a different amount of fuel that will change things, but the fuel's stability in hot and high pressure conditions...

I am no mechanic, so others can advise you better, but I would suggest trying to look at a piston surface when you arrive in Thailand.
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Old 5 Oct 2009
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Quote:
Originally Posted by nico-la-vo View Post
Thanks for the replies.

The spark plugs are fairly new so there is not much wear on them, the last were too black, suggesting rich. A couple of drops of water were in the float bowls. As I have one more days ride before I ship to Thailand I left the 20ltrs fuel in the tank and will clean it out at the port. Is it worth adjusting needles to lean out mixture or should I leave alone, needles are on Haynes settings at the moment (3rd from top I think).
Your welcome -


* Which plugs were installed when they were soothy?
* Do not mess with jetting and needleposition (yet)
* Have you checked the jettings and current needle position - if so; please state findings.
* Which carbs are you using? 94/40/... or 64/32/... or ?

Reason for black soothy plugs:
- too low octane => can be compensated just a little bit by using 1 degree hotter plugs
- too hot plugs => change to correct plugs, or swap to multy-electrode plugs
- too low rev and to high gear => shift down a gear.
- clogged air-filter => clean or renew
- incorrectly jetted carbs => install correct jettings
BING POWER SYSTEMS GmbH
BING POWER SYSTEMS GmbH
BING POWER SYSTEMS GmbH - Tuning manuals

Please to not cause yourself more problems than you already have.
* octane booster *
Then:
1 - check the timing; where is the spark at idle and where is it at full advance (3000-4000rpm it does vary from engine to engine).
2 - pull back the timing to 1-2' retarded (above "S" and "F"); if that cures the worst problems; leave it at that.
3 -if 2 does not have enough effect => swap plugs to 1' hotter.
4 - if 2 and 3 does not have enough effect... and installing dual head-gaskets is not an option... and octane booster is not available... drive with great care not to strain the engine and see to that is runs as cold as possible (you do have an oilcooled installed?!...) - and "pray".

The beemer engine can take quite a beating, but it is wise to avoid testing how much one can punish it...

You could test a controversial method... 1-3% diesel. Diesel burns more slowly and spreads the time of the burning thus reducing the peak heat that causes the pistonhead damamges... in theory i.e. ... my very humble non-scientific "tests" have indicated to me with my engines that it have indeed had this effect; however... my engines are tuned, i.e. non-stock...
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Old 8 Oct 2009
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I had NGK Iridium plugs in when sooty. Now Bosch.
I had a look at jets and needles, jet is 150, all clean, needle position is 3rd from top (think).
Not so technical to know what carbs I have, they are whatever came with the r100gs in 1988, sorry!

I will add the octane booster and see how I get on. Unless Burma change there minds and let me through (in contact with the Junta now!) I only have one more days driving to Chittagong, tomorrow, where I will empty tank and send the bike on its way to Thailand. Hopefully fuel will be better there and all problems solved. If not expect to hear more from me!

Thanks again
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Old 12 Oct 2009
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Just to say that the octane booster made a hell of a difference, its not perfect yet but it improved massively. Shipping to Thailand soon I hope.
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Old 12 Oct 2009
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Great!
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