100gs carb problems at altitude???

[topher]

I am currently building a 100gs for a trip from Germany to Nepal (and back) starting in August - regulars might remember the posts a few weeks ago relating to the siebenrock 800 - 1000cc motor that I was considering. I decided to go for that option, due to the fact that my friend who currently owns it knows the motor and has recently inspected the pistons/rings/barrels and says that everything is A1. Other advice that I received and followed related to the potential drive-shaft problem - I have just received a modified shaft from Eric Demant which will be fitted at the weekend, hopefully laying this potential gremlin to rest. With the addition of a modified Nippon starter (from Motorrad Elektrik) and a Whitepower shock, I hope that the obvious weaknesses have been ironed out - although no matter how well you plan something always goes wrong!!!

My next concern is with the fuel system. Has anyone here had problems with the mixture at high altitude (over 3000m)? It has been suggested to me that it is better to go with the smaller carbs (32's) and maybe to think about taking different jets with me - just in case. Any suggestions/ information/ past experiences would be very welcome!!!

Thanks

Chris

 

[Redboots]

My next concern is with the fuel system. Has anyone here had problems with the mixture at high altitude (over 3000m)? It has been suggested to me that it is better to go with the smaller carbs (32's) and maybe to think about taking different jets with me - just in case. Any suggestions/ information/ past experiences would be very welcome!!!

Chris, I went to India via China over the Shengi pass in the Teng Shian mountains at 4280m, another in the Pamir range at 4260m and then the Karakoram's Kunjerap pass to Pakistan at 4760m on me 94 GS PD. A bit of pinking if you give it too much throttle so just use steady and gentle throttle openings.

I don't think its worth the effort to replace jets... you are only at the very high altitudes as you go aver the passes. Lots of the road in China/Pakistan was over 3000m, but so long as you are gentle with the twistgrip its not a problem.

The scenerey is too good for racing anyway and as there aint much air, you wont have much power

http://bikerbytes.com/txp but the site is dog slow at the moment... web hoster probs

DO replace your fork seals b4 you go!... and fit solid diode board mounts

John

 

[B Murr]

I did some of Nepal on my R100Gs in '94, two up fully loaded the only difference I noticed was a loss of power at altitude, still plenty of power left to get me up steep inclines. I presume she was running rich. I wouldn't bother modifying anything, just make sure the air filter doesn't get clogged with dust so as to give her plenty of breath.

 

[topher]

Thanks John and BMurr!!

Thanks for sharing your experiences and for the other tips! I'll leave everything as it is and accept the loss of power. It shouldn't be a problem for me as I am travelling alone, as lightly as possible and the machine shouldn't weigh too much - after much deliberation I have decided to stick with the original tank and carry two 5 litre petrol cans for when petrol is scarce. From what I have read on Horizonsunlimited recently, the main problems with fuel at the moment are Iran (the voucher system means that you can't buy so much fuel at once and often have to resort to hanging round petrol stations with a 5 litre can to get anything at all) and Nepal where fuel is very scarce at the moment. In both cases, having the 40+ litre tank wouldn't help much.

Cheers and thanks again!

Chris

 

[chasbmw]

Many years ago I went to South america where large parts of peru and bolivia are at over 13,000 ft, i did take some smaller jets and hotter plugs, seemed to work OK, bings do to some extent compensate for altitude, but you will feel loss of power from 8000 ft upwards and a real loss from 13,000, due to lack of oxygen.

Charles

 

[fritz]

I'll add another for 'leave alone'. Our leviathan was half metric tonne loaded with both on and it ran like sh*te on the near 5000m roads (above 4 basically). Sooted up, coughed and farted but never stopped Bloody strong - think a marathon runner on Players rather than a sprinter with asthma We have t' big tank and it's brilliant - but you can deffo manage without Envious

 

[Paul Rochdale]

My record is up Mount Evans, Colorado, in 2006 at 14,260ft, and Pike's Peak, a little lower at 14,110ft, on a Pan and she wouldn't tick over on the summits.

 

[NickC]

Another 'leave alone' - a week '2 up' at 4000m in boliva was no problem for my R100GS

 

[topher]

43l tank - Touratech or HPN??

Thanks for the info gentlemen!! I'll leave the carbs alone.

My bike is now almost finished and I am reconsidering the possibility of buying the big tank. Am I correct in thinking that the Touratech and HPN tanks are identical ? - I phoned Touratech in Germany this morning and they didn't know. If they are different, which is better? If they are identical does anyone have an opinion as to which firm is better to deal with? The prices are very similar - from Touratech you buy a complete kit with all mounting parts etc for 682€, from HPN you have to order the tank and fitments separately and that amounts to much the same price. I've also heard reports of dodgy threads where the petrol taps screw in - apparently they used to be cut directly into the plastic and were prone to stripping - is this true?

As ever, I'd be grateful to get any input on the above!!


Cheers

Chris