Back to BM's yet again...:) And carb question...

[Wrigsby1]

So I tried to get rid of the 11GS and the guy pissed me off so I kept it... Then I realised having any of the new stuff wasn't the be all and end all so I sold my CT DCT and ended up with this... A US import with a very long history and good range of mods and fetching paintjob... 32mm carbs which I had on my Mono 100RT and then I went and bought some 40mms that were on the Bay...

Do I just rejet them to UK standard settings...? Seems the logical starting point and see what else I need to fit them on... The 32mm's seem set up fine but it needs a bit of winding up and I wonder if the 40mms will potentially give the bike a bit more low down torque...

All good fun and now with a scruffy but great running 11GS and the R100R I am happy happy...

 

[Schtum]

The 32mm's seem set up fine but it needs a bit of winding up and I wonder if the 40mms will potentially give the bike a bit more low down torque...

I'd have thought it would be the other way round and the 40 mm carbs will give more top end power at the expense of bottom end and mid range torque.

 

[Beemerboff]

In theory Schtum is correct, and if you had the perfect set up on each bike it would probably be the case.
But perfect set ups are rare and in reality it is a bit pot luck - my R100 GS has 40 's , my 1000 cc R80G/S 32 's and there is nothing between them in normal riding.
Try a few things too, a few people like lean / small main jets, my bikes seem to prefer at least a 150 and a 2.68 needle jet.
A bit rich keeps things cooler too, which is a major factor in this part of Oz.

 

[solidstate100]

32's better for low/midrange, less of a stumble off idle, better MPG, suit the GS and its gearing better than the 40's which only really come into their own at much higher revs

IME.

 

[Wrigsby1]

Thanks for the replies so far... Lots of useful feedback... I thought it would have been the other way round but that's 'cos I'm relearning carbology... It runs fine on the 32's with fine mpg... I'm messing with things that can be easily reversed I suppose...

I nearly/should have bought a previous 100r and then a mystic... They were uk bike which seemed to have 40mm carbs... The mystic sticks in my mind as a very sweet running bike but that might have been the owner being really fussy...

Stupidly my last 11gs was a good one for a carb mod but this one runs really well as it is...!

 

[Rob Farmer]

32mm for me every time ��


looks like you have a crappy keihin y piece. This will be messing things up big time.
Is there a balance pipe on your downpipes?

 

[Wrigsby1]

On no, curse of the crappy Y piece... No balance pipe and I was wondering where they came from as they are non BM but stainless... I will investigate... Makes me laugh as I remember you or someone else saying about R100RT monos being crappy after the early 80's ones but I thought you meant the 32mm set up... it might have just been the mono rear end...

 

[Rob Farmer]

They'll be keihin as well. Having the crappy y piece isn't as bad if you have the balance pipe on your downpipes (still crap though) unfortunately you have the worst setup possible. Boxer supplies do a really nice stainless pair with a balance pipe.The r100 engine in the mono is very nice. I really don't like the mono chassis but some of the guys rate them so you pays your money...You'll be amazed at the improvement if you change that exhaust setup. Put the 32mm back on and it'll fly.

 

[Schtum]

Thanks for the replies so far... Lots of useful feedback... I thought it would have been the other way round but that's 'cos I'm relearning carbology...

Basic fluid dynamics and the works of that nice Mr Bernouilli is what you need.

 

[Wrigsby1]

I may just visit...

https://upload.wikimedia.org/wikipedia/commons/7/78/VenturiFlow.png

 

[Wrigsby1]

Also apologies to Rob as it was the R80RT Mono that you once said was weak and not as good a handling bike as the earlier R80's... Don't know for the life of me where I thought I read 40mm's were better than 32's...

The downpipe issue is being looked into as we speak... I "tuned" the R100's carbs in a carpark in 5 minutes or so as they were a bit rough for settings... I love that sort of stuff... no tools bar a spanner, screwdriver and working hearing and feel... My 11GS was set up like that along with a TPS mV adjust... That was Sept 2014 and I have hardly touched it since...

Apart from a rough spot around 3k revs the bike runs pretty well...

 

[Rob Farmer]

Go and put it on a dyno and then see how it compares to how well it could run.

 

[Wrigsby1]

Tough but fair... will ask you re the downpipes tomorrow...

 

[Posh Pete]

Also apologies to Rob as it was the R80RT Mono that you once said was weak and not as good a handling bike as the earlier R80's... Don't know for the life of me where I thought I read 40mm's were better than 32's...

The downpipe issue is being looked into as we speak... I "tuned" the R100's carbs in a carpark in 5 minutes or so as they were a bit rough for settings... I love that sort of stuff... no tools bar a spanner, screwdriver and working hearing and feel... My 11GS was set up like that along with a TPS mV adjust... That was Sept 2014 and I have hardly touched it since...

Apart from a rough spot around 3k revs the bike runs pretty well...

Mine has some vibes around 3k also. Handy to know it's not unique.

 

[Rob Farmer]

Tough but fair... will ask you re the downpipes tomorrow...

This was exactly the same exhaust setup and 40mm carbs on the dyno.

 

[Wrigsby1]

Even to my untrained eye that looks a bit wafty, especially the Air/fuel... The honesty box of hp readings on airheads is a leveller and this is pretty

I always respect your input and now know the 32's are to stay... Re the downpipes and Y piece on Boxer Supplies, what I am seeing is the downpipes with crossover and a R100R only Y piece... Is that right...? Then onto orig silencer... I don't like too much noise...

The 40mm's came originally off a 79/80 100S or 100T... I can save them for a rainy day of if my 11GS ever gets carbed... The only "problem" is after 4 11GS's and riding many other 11/1150 bikes, this is the sweetest and most free revving 11 I have ridden... It was like a 600 sports bike with thin midrange and off after 4/4.5k then I added a "John fae Greece" chip and it has a very good low midrange to complement it... Just as good as the dynode and rechipped one I had in the early 2000's... And that on a standard set up... If it aint broke etc...

Your input is greatly appreciated and I look forward to a better running R100... I've wanted an 100R model for over 10 years and I will be keeping this for the foreseeable...

 

[Rob Farmer]

If you have one local it's well worth spending £25/£30 on a dyno run. It saves all the guesswork.

I wasnt trying to suggest that you have to make those changes but having had a bike with the same setup as yours I know how much better it ran by junking the keihin parts.

 

[Wrigsby1]

Sadly no local dyno as 60N is Shetland but there are some good ones in NE Scotland...

You guys have said about the importance of the balance pipe a few times before... If it works well then I'll give it a try... I'll check what's in the carbs as well...

 

[Wrigsby1]

There's no balance pipe and now I see what you mean about the Y piece... It runs back on itself...! Looks a shite design and seen as the gasses a trying to get out, the LH pipe is going to have a far more difficult job than the straight piece RH...

I've measure the header pipes and they are 38mm dia...

PS I know its cracked at the join (top and bottom...) ) and I need to sort the hole for the emissions thing that the PO -2 removed... I was looking at it the other night and the 3 layers gaffa is a temporary job...

 

[solidstate100]

If you run the system with a y piece and not the collector box you may well find that the baffles in the oem exhaust get knocked out (and another tuning headache can be casued...)