Gsxr1100 with b12 carbs

[wraith]

I know this would have been asked before, but I can't find anything.

So got a gsxr1100k (1127cc) with b12 bst 36 carbs on it with k&n filters and a Cobra zorst and qa throttle. I am currently running 144 main jets, needles set as standard and the pilot screws set at 2 1/3.

Seems to start and run well, but a bit gritty on acceleration and back pops a lot on shut off even at low speeds, as soon as gets warm (5 mins to 15, depending). 

Tried 160 jets and also 150s, both with pilot screws at 2 turns out. Maybe smoother and crisper throttle response throughout the range but still lots of popping and popping was a lot worse on the 150s - but then got better again once dropped to 144s but with screws bit further out.

On 144s at 2 turns out it flamed and popped a lot and was quite rough when revving through. Got better when turned pilot screws a bit further out.

It's really hard to get the same test ride conditions given weather/temp and road/traffic conditions, and don't have a local dyno. Plug chop also difficult to do around home or by roadside (tank & fuel lines off).

So, any ideas on a better setup? Anyone else running similar set up? Particularly want to minimise the back pop - bike's always bumbled & grumbled (nicely) on shut off once warm, but seems worse this year somehow.

Cheers

[fatblokeonbandit]

Standard mains are 122.5's, with and air filter and exhaust Id go 10% up first, so around 135's.

[wraith]

14 hours ago, fatblokeonbandit said:

Standard mains are 122.5's, with and air filter and exhaust Id go 10% up first, so around 135's.

That's the main jet setting for the bst36ss carbs on a GSXR1100K - these are bst36ss from a Bandit 1200 (I've stripped and checked part numbers just to be sure!), which have some internal differences and run as standard (on the slightly bigger but differently tuned B12 bore) 102.5...

I had the bike Dyno'd and set up by a reputable tuner a few years back and they put the 144s in, but that was on standard GSXR k carbs. They did tell me that a 4:1 exhaust (which I forget to say) is always going to be hard if not impossible to set up.

Logic says that I should go down main jet sizes on the B12 carbs as opposed to the GSXR ones, but I've also heard of people recommending 150-160 main jets on this set up, so I'm well confused now! Also, it was running very nice on 160 and 150 mains, perhps slightly better tan on 144s, so I'm already worried that 144s could be too lean. Some say that the back popping is a sign of it running lean, and turning out the pilot screw makes it richer at bottom end and I'm often told that contrary to theory the main jet does have some impact on 0-1/4+ throttle, not just pilot screw/jet settings (and vice versa at higher throttle), so maybe I actually ned to run bigger jets again along with richer bottom throttle (pilot)???

If only it was a damn sight easier to get carbs  on and off and even just to adjust the fiddly pilot screw (especially when engine's warm).

Aaaaagh.......

 

[fatblokeonbandit]

ive got b12 carbs on my 1216 big bore lumpy cammed 150 rwhp and it was set up on a dyno 5 years ago and has 145 mains, IIRC, so just a pipe and filter wouldn't need so much main jet, perhaps, mabey????

 

do you mean long pilot screws like these??? I keep meaning to get  a set..............

http://www.factorypro.com/Prod_Pages/prods09.html

 

[fatblokeonbandit]

just had a thought, 144 is a dynojet size isn't it, that's equivalent to 135 mikuni I think??

 

[wraith]

15 minutes ago, fatblokeonbandit said:

just had a thought, 144 is a dynojet size isn't it, that's equivalent to 135 mikuni I think??

 

Good point. Forgotten that. So it makes the comparison with the manual's standard specs a little more 'sensible'.

However, the 144 and also 150 and 160 jets which I've used are all Dynajet kit ones (= 135, 140 and 150 Mikuni equivalent per your table).  I bought the 150s recently as part of a dynajet kit for another 1127 motor (F on 750 38mm carbs) that I have, also on filters and reasonably unrestricted zorst, but actually ended running that currently on 155 main jets and it's running and acelerating very nicely (though maybe it's running a tad rich?) and not having anywhere near as much popping or similar issues (well, the odd flame......   ;-) ).

Equating 144 Dynajet to 135 Mikuni is in line with your original suggestion and is what the bike was set up with several years ago, but on standard GSXR K carbs; I just wonder what difference the Bandit 12 carb internals might make.

 

[wraith]

1 hour ago, fatblokeonbandit said:

ive got b12 carbs on my 1216 big bore lumpy cammed 150 rwhp and it was set up on a dyno 5 years ago and has 145 mains, IIRC, so just a pipe and filter wouldn't need so much main jet, perhaps, mabey????

 

do you mean long pilot screws like these??? I keep meaning to get  a set..............

http://www.factorypro.com/Prod_Pages/prods09.html

 

Are those Mikuni or DJ main sizes, then?

Those long screws look rather useful! Do they still work with DJ components (emulsion tubes & jets etc?).

 

[fatblokeonbandit]

Mine has mikuni jets, not sure about the differences between gsxr and b12 36mm mikeys???

 

the screw's should be fine as they are a direct replacement  for the standard ones..i must get some one day..

[t3rse]

Excessively rich will pop too.  Lean pops are very sharp, and rich pops are more of a gurgle.

[wraith]

OK, update after some more test riding and a few chats with a very helpful guy at Dyna UK (thanks, Richard).

Apparently stage 3 Dyna kits for GSXR K (BST36SS) include 136, 140 and 144 main jets. Standard stage 3 kits for Bandit 12 same carbs, but some different internals, include 150 and 155 jets. For a 30cc bigger bore, it's likely that the main difference here is to do with carb design - so around 155 is what's been recommended to me (DJ jet size).

Rode it last night on 144 mains and with the pilots out to 3 turns. Originally tried them at under 2 and was not at all keen to rev through smoothly; at 2 1/3rd didn't seem too bad though 'gritty' feel on opening it up (from bottom to near top) though is pulling well and no flat spots; at 3 turns out is a bit more gritty though still accelerating well, but is a noticeable small flat spot at very bottom end.

On all pilot settings it was still popping quite loudly at low end whether running at slow speed (20-35mph) or decelerating from higher speeds - maybe a bit less on 3 turns out but not cured by any means.

Then experimented with turning idle screw in and out whilst riding and found that I could just about stop the popping if I ran the idle screw all the way out (i.e. butterfly near closed). If I turned it in the poppping and banging got considerably worse - but the overall gritty engine feel got a bit better. As I understand it, turing the idle all the way out makes the bottom end (and maybe all the way through?) a bit richer, but then again so does pulling out the pilot screws... Don't quite unerstand what's going on here, but it definitely does something!

So that's some kind of progress, I guess - and we're in the ball park and it's rideable under various combinations. I'm told that the popping isn't going to cause damage, just annoy the neighbours et al somewhat!

I'm now going to try the 155 jets as it seems that I'm going to be better going for a B12 Dyna set up jetting, as above. Also, when I tried it on 1602 and 150s it did seem to have a crisper, less 'gritty' feel to overall aceleration. Bit more messing with pilots and also now it seems trying combinations of pilot adn idle settings, and we'll see how it goes.

Oh, and the main advice was don't run a 4:1 exhaust and you'll never get it set up rigt and running really nice (for the road) with one on!!!

[jonny1bump]

You not mentioned needles theses are most important bit main jet for full throttle openings. Adjust these and check difference.

Sounds like dyno time needed.

[wraith]

13 hours ago, jonny1bump said:

You not mentioned needles theses are most important bit main jet for full throttle openings. Adjust these and check difference.

Sounds like dyno time needed.

 

Yes: but problem isn't at full throttle but mid to low down... Frankly, given the (rural) roads and traffic around here, never mind speed limits (!) it's never going to get anywhere near fully open throttle - but it does do a lot of quick on and off work in mid range or ave to bumble along at low speeds. Also, it is already running dyna B12 kit needles. Might finesse the needle position at some point, but really it seems OK as it is and I'm not keen on playing on and off with the carbs any more than I already am!

Access to a dyno would be really helpful; trouble is, there isn't one around here as far as I know, and certainly not one where I'd trust the operator to know what they're really doing as regards interpreting  mixtures thrughout the range and giving apropriate advice (sorry, but experience shows that to be true ata lot of places). I had planned to take it and several other of my bikes to a dyno which had opened up pretty locally by someone who works for race teams, but I can't get hold of him any more by phone so don't know if he's gone out of business or not - a trip down that way at some point will be in order. In the past I have had the bike set up by a reputable dyna place (now no longer), though on GSXR bst36 carbs, and that's where I got the current set up from. They also said that with a 4:1 exhaust on, I was never going to get it spot on throughout the range for road use.

 

[colinworth79]

cant believe someone has said you cant get it running right with a 4 into 1 . Is a stock bandit 1200 not a 4 into 1 ???? Carbs are a quite simple way of metering the fuel into an engine but when you start changing parts its quite easy to get into a muddle and Change the wrong part . Main jet does do the top end of the fueling but does have nock on affect with the lower down fueling . As mentioned above needle is doing the main metering when used on the road but you have still got to have a main jet close to being the right size if not your not going to get the needle part right . Dyno time or invest In something to monitor the air fuel ratio. Other wise you will spend years and it still wont be right . Most AFR gauges now a days have recording options that you can then download onto a lap top .

looking at plug colour is another waste of time for a 4 stroke road bike , this may have been the way to see if some pile of scrap that rev'ed to 2000rpm was running but things have moved on since 1950.

[jonny1bump]

Dude you really need to sort your needles and pilot settings out, main jet hardly coming into play in your rev range.

[clivegto]

Have just spent a lot of hours playing around with b12 carbs on a 1127 power screen engine with a full yoshimura system, might not be the same for all, but I ended up with standard b12 carbs apart from having dynojet stage 3 needles and springs with needles on top notch 2 1/2 turns out on mixture screws 160 main jets. Runs really good, my needles were second hand so may have been a little worn, polished them up with some scotch brite which made it run a lot better mid range. Made just over 125hp on the dyno but that was with 155 mains and it was flating of at the top end hence the 160 jets.

[wraith]

On 06/08/2016 at 6:02 PM, colinworth79 said:

cant believe someone has said you cant get it running right with a 4 into 1 .

 

Surprises me too, but since one lot who said this were V&M Racing and it's also been said several times by Dyna UK, I tend to bow to thier superior knowledge.

I think they mean a 4: 1 race-type exhaust (as opposed to standard OEMs perhaps?) - especially for lower down road use perfomance.

[wraith]

So it got a run out again yesterday, though sadly mostly at very bottom end (blinking traffic!)

It's now on 155 mains (Dyna size) and pilots at 2 1/2 out. Balanced the carbs again after re-setting, though they weren't out by much, surprisingly.

Though it still feels maybe a tad not 'free' yet, it's accellerating very well (when I got the chance!) and running very smooth all the way through as soon as the throttle's  more than a few degrees/mm open (I guess from previous marking/testing and feel, that's as soon as the needle starts to lift at all - running a very QA throttle and no rev counter so hard to say more than that). No flat spots or other problems, and have lost the 'bogging' at bottom end which I had with the 144s and pilots at 3 turns out (which seemed to be a pilot mixture issue).

Still popping & gurgling at bottom end, sometimes not much and sometimes quite a lot (can't work out when/why), much worse when coming downhill (which with hindsight I realise has always been the case) especially on tickover or very low revs. Idle/tickover screw adjustment definitley has an effect on the popping. Some still on over run but not as bad. Some tinkering with idle screw (throttle stop screw) still required and will continue to play with pilot screw/mixture to get the best we can at very bottom end. I am wondering if a 160 main jet would be worth a go again, and ideally testing different needle positons would be good, but maybe it'll have to do for now; more riding, less faffing!  It's running, seemingly well enough for the roads around here. Not enough dry, never mind sunny days (with unbusy roads) to ride the thing as it is!

[Del]

 

On 06/08/2016 at 6:02 PM, colinworth79 said:

cant believe someone has said you cant get it running right with a 4 into 1 .

Same here 
I'm using a micron 4-1 with harpoon can(and a one off can)system on my  11k  and it is spot-on(I was using a 4-2-1 and the 4-2-2).I  have no flat spots,which is usually a problem with 4-1 systems(I had a 750h that I couldn't get rid of the 3.5-4k flat spot.That was a yoshi 4-1).On my brothers slabby(fitted with a powerscreen 1127)we are using a v&h sport 4-1 system(this is going on the dyno,so we'll see if there is any problems).
Also PDF Paul was running a Yoshi full 4-1 system on his 1100L,that was also spot-on(sounds luverly as well) 
http://vid276.photobucket.com/albums/kk10/gsxrdel/MOV00169.mp4

 

Edited August 8, 2016 by Del

[Del]

Can you not junk the dynojet kit and go back to stock jets,etc? Airbox with K&N insert would also help