setting carbs

martin · Post by **martin** » Mon Jul 23, 2007 1:15 pm

hi all, can anybody help me. i am now putting back together my kr1 after many years, the engine has had a complete strip rebuild and 300cc conversion by stan stevens, the carbs have standard jets in them, i have heard that using bigger pilot jets is the way to go and one size smaller on the main jet as they run rich at the top end,i have set up the carbs correctly and it seems to run best with the pilot screws threequaters of a turn out and not one and a half what it should be, i am a bit stuck, will it start to run better once i start riding it, thank you

rc46 · Post by **rc46** » Mon Jul 23, 2007 2:05 pm

STOP!

If the bike has a 300cc conversion. I would think standard jetting is very unlikely to give you best results. could even kill your engine.

Where in the country are you.. I would seriously think ablut spending a little bit of cash on some dyno work.

For safe jetting just now, get some bigger main jets in there, a pilot jet should be 40# but i have a 45# seems to work fine this way. your air screw should be 1.5 turns, mines at 1.75 and runs rich at tick over and the revs hang a little but as its pre mix and a track bike i dont mind the bottom end being rich.

Youll need to set the carbs up as well, get them ballanced. If you want to PM me your number ill be happy to talk you through this bit, But DONT run your bike on the road untill you have increased your jetting, runnning rich will preserve the engine and then once your there you can work down on jet size. Take your time and youll have a serious weapon.

Are you running premix or oil pump?

Cheers

martin · Post by **martin** » Mon Jul 23, 2007 2:28 pm

thanks for reply,i am near luton,what size jets would you reccomend,the bike is running on the oil pump,not premix,the pump is set standard,would nt be able to dyno as the bike has nt been on the road or run in yet,do kr1 s need running in.is it because the pilot jets are standard size that is causing the pilot screws having to be turned in so much,the needles are on stock settings,

rc46 · Post by **rc46** » Mon Jul 23, 2007 3:10 pm

Have you tried taking them out to 1.5 What happens, Are the carbs ballanced? At the rear of the carb the Slide should be ABOUT 0.7 - 0.8mm (thats rough as i cant remeber off hand) they should also open together and have some slack in the cable.

Losen off the cables then use the idel screw adjusters on each carb to get a base of 0.7 or 0.8 there abouts you can adjust from there. then using the brass screws on top of the carbs, look down the mouth of the carb and slowly open the carbs with the grip, you want them to start openning together, Once thats done use the adjuster near the bars to take up the slack, that should be you, you may need to adjust the idel scrws again once running if revs are to low or to high. once youve done this set your air mix to 1.5 and try again.

Thats base

I dont think your pilot jet will affect it to much at the moment as long as its standard size, there is guys on here running the standard 40# with a high state of tune. Hang back there will be someone along who can recomend jets, but id say start big and work down, 155 on mains then try a 145, The main thing once you have the bike ideling well is start big and go small.

If it was my bike id want to increas the oil pump flow but for now to get it running stick with standard and just make sure oil is getting in (smoke from both pipes even and heavy from cold) check end of cans and plugs for a rich bike you want it a bit wet looking.

When you get a chance and its running it might be worth taking her to a GOOD dyno center to get it set up right. Your far away but i would recomend BDK, there in Norwich wich is miles away but atleast itll get done right! If you have use of a Van or trailer its the best way.

Cheers

By the way Wellcome!

the-elf · Post by **the-elf** » Mon Jul 23, 2007 5:13 pm

Welcome mate,

RC46 is right here, get the carbs balanced and the slides opening together to start with. If your un-sure of the jetting give Stan Stephens a ring and ask him. I know he is very busy ATM as his wife has been ill recently but he'll give you some advice of what to use as a starter point.

the-elf · Post by **the-elf** » Mon Jul 23, 2007 5:13 pm

Welcome mate,

RC46 is right here, get the carbs balanced and the slides opening together to start with. If your un-sure of the jetting give Stan Stephens a ring and ask him. I know he is very busy ATM as his wife has been ill recently but he'll give you some advice of what to use as a starter point.

martin · Post by **martin** » Mon Jul 23, 2007 5:24 pm

thanks to all of you for the advise,i will phone stan stevens and ask him about jet sizes,and will set the carbs up like you all have said,you say the standard pilot jet is 40 , in the manual and in the bike it is 35, the main jet is standard 135. when i get the right jets and set the carbs up,i will let you all know how i get on as i am not giving up on my stroker. thanks again

the-elf · Post by **the-elf** » Mon Jul 23, 2007 5:46 pm

From memory the pilot jetting is a 38 on a KR1 and a 40 on a KR1s or is it the other way round

.

Also are you running the standard air box or has it been modified or air ramed? This will make a big difference to the correct jetting.

martin · Post by **martin** » Mon Jul 23, 2007 7:23 pm

the air box has had two holes[around the size of a 10p] cut either side on the lid. and at the bottom by the brake lever the bit that sticks out at the bottom has a hole,it was like it when i bought it, with the pilot screws 1 and half out,the bike dies when you realy yank the throttle, but 3quaters out,its no where near as bad,not sure if because of the 300cc conversion is causing it or its the air box,i know i set the carbs right,both throttle bodies at bottom them take up free play[twisting the throttle, both bodies are level] then set idle screws level,same pressure out of each pipe and both pipes same temperature. its doing my head in, i am an expert at taking the fuel tank on and off now

mgtkr1 · Post by **mgtkr1** » Mon Jul 23, 2007 7:58 pm

martin, after rebuilding my bike i had a similar problem with poor idling and extreme changes in the idle screw settings caused little improvement although they did improve marginally. after swapping carbs for a known good set it improved things no end and turned out the floa height was the culprit not to mention the blocked pilot that caused a hurrendous flat spot at 6k ish. check the float height and also the pilot jets arnet blocked before yo go out and give it a hand full though i reccomend you alter the main jet and needle clip(richer one groove from middle) to start with and work from there doing a plug chop if a dyno is out the question. i would start with a 145 minimum on main jet as this should be in the right range but if you have access to 155,150, and then 145 possibly 140 then try the biggest and work down. if your limited with what jets you can get then try a 145 and keep an eye on things. i would also junk the oil pump as i hate autolube systems but thats just a prefference. as for running in i would give it a few heat cycles, ensuring its warmed thoroughlyu each time and err on the rich side. dont rev the nuts of it for the first 50-100 mile but more importantly dont load the engine for as long as possible, i know its not always easy on a road bike but it will improve engine life if you avoid doing so. revs arent really that much of a problem, on the race bikes just heat cycle em a few times and a few laps before you nail it but a roadie needs to do more miles between service intervals aswell as having twice as many rings to take the wear(assuming the 300 retains the use of a lower ring)? anyway, im sure stan or bdk will put you right as both know there stuff. all the best matt

rc46 · Post by **rc46** » Mon Jul 23, 2007 9:11 pm

Martin, good to talk to you..

I was mistaken My Air screw is 1.25 turns out Not 1.5.

Get the 2 carbs ballanced nice first, then start her up, If you get any difficulty dont worry just come back here and let us know whats going on, Worse case i could swing past at somepoint and have a look. I work in london and could detour off to Luton either on way home or early doors one morning on the way in.

The 2 holes i would either leave em for now (you only want it to run first) or tape em up,

Get her to idel first and then concentrate on needle postion and main jet.

Elf, mgtkr1 and others all know there stuff and may not be here straight away with an answer but a bit of time and someone will come and help..

From what you said it sounds like you have a nice engine build there, take yer time now, as it wont be long before you can thrash the arse off it. Youll be grinning from ear to ear!

mgtkr1 · Post by **mgtkr1** » Mon Jul 23, 2007 9:34 pm

as f250 states 250cc max or whatever manufacture reccomends as max o/s on bikes with iron liners the 300 is something im unlikely to experience but i would be very intrested to hear how it goes, bet its a devastating little track tool with plenty of grunt and a right hoot. heard a lot of debate on the nsr forum regarding 250vs300 but in my opinion each to there own and on the road i would consider it although i love the way the 250 screams. anyone else have any experience of the kr300?

the-elf · Post by **the-elf** » Tue Jul 24, 2007 12:23 am

So its a slightly modded air box

Any efforts I've seen on incresing the airflow into the engine has resulted in more power but results in it running rich and appearing to have little increase in power until rejetted (this is on my tuned engines so it may well be different on your's). The airbox is a big restriction to performance on the Kr. Fitting a decent air ram system will improve it no end but this will also upset the jetting quite a bit.
My bike with air ram fitted on the old 28mm carbs, the engine ran very rich and I ended up running a 135 main on premix (guess at about a 130 on autolub) this is at 20C 1000Mb pressure and 50% humidity I ran a 140 before the air ram was fitted. But this is a race bike and so was jetted on the edge.

Just thinking out load and hopeing to give you a bit of info on how my bike was jetted. This may not work on your bike so be warned (but the air ram system is nice

)

mgtkr1 · Post by **mgtkr1** » Tue Jul 24, 2007 6:43 pm

with a fully pssurised system fitted and bike rebuilt i ran the bike on 135's and it was crisp with linear pull up to about 8grand when things start happening faster than i can keep up! the plugs were a nice light tan and like you say elf, this is on a tuned motor, im of the opinion that the more efficent flowed cases distribute the mixture much more effectively thus allowing a leaner mixture than you would guess. im almost certain the ss 300 is ported as per f250 but not sure how the boost in volume (bore) will affect fueling, think dropping the clip can be a possible improvement but cant be certain. martin, do you have flowed cases? i must also add that i have a rad that has approx twice as much volume as a std rad therefore allowing jetting to be that bit more on the edge.

martin · Post by **martin** » Tue Jul 24, 2007 8:17 pm

thanks guys for all your help, and thanks to rc46 for phoning me and giving me advise, i phoned stan stevens today, he says standard jetting is fine, 38pilot,135main,he says lean the clip up to the 2nd from the top[leaner]. i have tried that with the pilot screws at all different amounts and it seems worse, above 4000 its fine,but below 4000 its fluffy,if the throttle is pulled hard from tickover,it dies,i balanced the carbs as rc46 said,so am pretty sure carbs are near on balanced, tomorrow i will drop the clip on the needle to the bottom[richest setting]and play with the tickover screws to see if that helps,surly the extra 50cc would mean it would need more fuel.

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