jets troubles?

Sideshow bob · 07-28-2009, 4:51 PM

... Put new jets in the gixxer at the weekend...

bike starts fine....

but wont accelerate...
if you gently roll the throttle it's fine but try and crank it open at some speed and it just stutters/stumbles and dies?

radiobloke · 07-28-2009, 5:03 PM

i never f£ck around with jetting...drilling jets etc scares the cr4p outa me...could end up with junked carbs.

I'd stop...cal someone who knows carbs and set up ( dyno place) and take it there. go any further and you at best not get the best out of the crabs, and at worse need a new set of carbs.

just my 2 penneth!

Twincam · 07-28-2009, 8:21 PM

Have you still got the old jets or are they what you drilled?

Sideshow bob · 07-29-2009, 2:38 AM

Quote:

Originally Posted by radiobloke

i never f£ck around with jetting...drilling jets etc scares the cr4p outa me...could end up with junked carbs.

me too... although...
when i've fitted them in the past they always been pretty good...
fitt, ballance and ride jods a good un!......

but not this time???

Quote:

Originally Posted by Twincam

Have you still got the old jets or are they what you drilled?

yeah... gunna try a couple of things later and if still buggering about I'll go back to stock

Kelv · 07-29-2009, 4:18 AM

Thinking out loud, ... it might help...
Did you end up drilling the pilots?
..again from memory which is getting less and less reliable these days..
They have you drill the pilots because the new needles are a different shape which means the pilots have to cover till a bit further up the rev range, so the simple answer is to lift the needles a notch at a time till it transitions from one jet to the other smoothly.. If you havent already drilled don't....
Or take it to a dyno and get them to do it, its a bit of cash but its worth it.
The problem with the slab/sling/bandit engines is once you remove ugly airbox you've shafted the fuelling as the carbs are no longer getting a relative high pressure so the mixture is stuffed hense them always running a little rich.
My answer to it was to FI the little beasty, Check out mega-squirt, I never did check but I was looking at the 929 injector mechanism as being a possible pop on, but never did the maths/ measuring.

OSS has some good info on the BST38's and I'm pretty sure if you dig around there is something on the 36's.

Todays random babblings over... enjoy carb exploring

bladeracer · 07-29-2009, 5:02 AM

Quote:

Originally Posted by Sideshow bob

... Put new jets in the gixxer at the weekend...

bike starts fine....

but wont accelerate...
if you gently roll the throttle it's fine but try and crank it open at some speed and it just stutters/stumbles and dies?

My first question has to be, why did you put new jets in?
Was there a problem you were trying to fix? Was it running fine before this?
How much mileage is on the carbs?
Early GSXR carbs are reknown for ovaling the emulsion tubes.
The usual symptoms are similar to your description above - starts and idles fine but won't pull throttle.

Westers · 07-30-2009, 5:43 PM

I'd go as far as to say it's a fuelling issue - either too much or not enough. Is that sat on the fence enough?

However, I agree with RB (as much as it pains me

) and get down to a dyno man. Otherwise you'll end up like a dog, forever chasing your arse around in circles, but getting nowhere.

Sideshow bob · 08-01-2009, 5:24 AM

Quote:

Originally Posted by bladeracer

My first question has to be, why did you put new jets in?
Was there a problem you were trying to fix? Was it running fine before this?
How much mileage is on the carbs?
Early GSXR carbs are reknown for ovaling the emulsion tubes.
The usual symptoms are similar to your description above - starts and idles fine but won't pull throttle.

she was running and throttling up okish... but there was a flat spot between about 4-6000.. then she would get fuel starvation right at the top of the rev range....

know i can get plenty of fuel through as I already got high flow valve fitted.. figured if i could get rid of the flat spot... i would either cure the top end issue also... if not, was thinking about reinstating the mikuni' redundant pressure drop feeds*

*or whatever they called... the line that runs from the bottom of the fuel bowl to the bell mouth.. that drops aditional fuel into the carbs at top end

Quote:

Originally Posted by Kelv

Thinking out loud, ... it might help...
Did you end up drilling the pilots?
..again from memory which is getting less and less reliable these days..
They have you drill the pilots because the new needles are a different shape which means the pilots have to cover till a bit further up the rev range, so the simple answer is to lift the needles a notch at a time till it transitions from one jet to the other smoothly.. If you havent already drilled don't....

... welllll! I had drilled... but looks like i didn't go all the way?
looks like a bit more needs doing

fingers crossed*

*oh and its not the jets that are drilled.... its the air correctionholes

Quote:

Originally Posted by Kelv

Todays random babblings over... enjoy carb exploring

to be honest.... I've always been a bit scared of f##kin around with carbs....
but i'm over that now....

may never get it right and it may turn out to be an expensive error....

but if its cured my carbaphobia

Quote:

Originally Posted by Westers

However, I agree with RB (as much as it pains me ) and get down to a dyno man. Otherwise you'll end up like a dog, forever chasing your arse around in circles, but getting nowhere.

.... but that's the easy way out...

much prefer fidling* then I might accidently learn something

*until i lose my rag, kick the sh!t out of the things, and buy a new set before pretending i never touched them

Twincam · 08-01-2009, 8:10 AM

Quote:

Originally Posted by Sideshow bob

much prefer fidling* then I might accidently learn something

*until i lose my rag, kick the sh!t out of the things, and buy a new set before pretending i never touched them

The last line sounds a bit like me!

Sideshow bob · 08-01-2009, 10:55 AM

Quote:

Originally Posted by Twincam

The last line sounds a bit like me!

shall we start a club

BTW... finaly seem to be getting somewhere* now running smaller main, and stronger springs after blocking one of the slide holes...

she now accelerates with a slight stumble but each time i raised the needle now its reducing it.....

... oh well... time for next set of adjustment

MCR001 · 08-01-2009, 11:12 AM

have fun there sideshow...I did on my CBR900RR and it took forever to balance them, but now its a piece of cake to work on them.

Sideshow bob · 08-01-2009, 11:52 AM

Quote:

Originally Posted by MCR001

have fun there sideshow...I did on my CBR900RR and it took forever to balance them, but now its a piece of cake to work on them.

tell me about it...... can strip um in seconds now

....last adjustment to neeedles coming up.. but it looks like i gunna have to go back to the bigger main

shoulda left it in when i changed the spring and slide hole.. oh well! you live and learn*

*sometimes slowly with the aid of labelled diagramsfor the terminaly hard of thinking

Sideshow bob · 08-01-2009, 3:51 PM

sorted

Sideshow bob · 08-02-2009, 10:13 AM

Quote:

Originally Posted by Sideshow bob

sorted

spoke too soon...... runs well at low speeds.... goes flat after 7-8000 damn

bladeracer · 08-02-2009, 1:51 PM

Quote:

Originally Posted by Sideshow bob

spoke too soon...... runs well at low speeds.... goes flat after 7-8000 damn

At cruise as well as full throttle?
Any difference if you give it light throttle rather than whacking it open?
When I dyno-jetted my '90 I plugged one slide orifice and drilled the other a little larger. What have you done to yours?
Have you checked the emulsion tubes for ovaling? If they are, there isn't an effective way of jetting around them - you have to replace them.

Sideshow bob · 08-02-2009, 2:13 PM

Quote:

Originally Posted by bladeracer

At cruise as well as full throttle?
Any difference if you give it light throttle rather than whacking it open?
When I dyno-jetted my '90 I plugged one slide orifice and drilled the other a little larger. What have you done to yours?
Have you checked the emulsion tubes for ovaling? If they are, there isn't an effective way of jetting around them - you have to replace them.

yeah at both cruise and full throttle....

the emulsion tubes are new,
and after hours of p!ssing around yesterday...
she's running great with good throttle response, quick exceleration.. till she hits about 8000 then flat.. even with gentle throttle she struggles at the top end..

i too have had to plug one slide orrifice and use stronger springs

& to get her to run -throttle up smoothly without a stutter/pause the needle as had to be lifted to the last notch..

radiobloke · 08-03-2009, 12:41 PM

take it to a dyono/carb specialist...

Sideshow bob · 08-03-2009, 2:16 PM

Quote:

Originally Posted by radiobloke

take it to a dyono/carb specialist...

... will do if I can't figure it out ... but wanna keep trying at the moment.....

especially as I've learnt more about carbs this week than i have in the last 20 years

Twincam · 08-03-2009, 6:23 PM

SSB, I'll probs make a right fool of myself but I couldn't help but think about the "mikuni' redundant pressure drop feeds" you removed - wouldn't that "restrict" fuel flow at high RPM if they were not fitted or have you put them back on?

radiobloke · 08-04-2009, 5:19 AM

Quote:

Originally Posted by Sideshow bob

... will do if I can't figure it out ... but wanna keep trying at the moment.....

especially as I've learnt more about carbs this week than i have in the last 20 years

depends if you wanna learn how to rebuild an engine when it leans out too much at the top end once you get the midrange sorted!!

bladeracer · 08-04-2009, 6:30 AM

Quote:

Originally Posted by radiobloke

depends if you wanna learn how to rebuild an engine when it leans out too much at the top end once you get the midrange sorted!!

To damage the engine it would have to be so lean as to be very obviously not right.

Sideshow bob · 08-04-2009, 5:57 PM

Quote:

Originally Posted by Twincam

SSB, I'll probs make a right fool of myself but I couldn't help but think about the "mikuni' redundant pressure drop feeds" you removed - wouldn't that "restrict" fuel flow at high RPM if they were not fitted or have you put them back on?

I Didn't remove it Twin...... Its blanked as standard..... i'm thinking of reinstating it

Quote:

Originally Posted by radiobloke

depends if you wanna learn how to rebuild an engine when it leans out too much at the top end once you get the midrange sorted!!

......you trying to scare me Radiobloke

radiobloke · 08-04-2009, 6:15 PM

Quote:

Originally Posted by bladeracer

To damage the engine it would have to be so lean as to be very obviously not right.

we are talking about SSBob here remember!!

bladeracer · 08-05-2009, 3:14 AM

Quote:

Originally Posted by Sideshow bob

I Didn't remove it Twin...... Its blanked as standard..... i'm thinking of reinstating it

......you trying to scare me Radiobloke

If you mean the blank jets in the float bowls, I drilled mine but it was nineteen years ago so I don't know what size I did. They were _very_ small though :-)
If you drill them and don't like the effect just drop a blob of solder in them to block them again.

Sideshow bob · 08-05-2009, 3:21 AM

Quote:

Originally Posted by bladeracer

If you mean the blank jets in the float bowls, I drilled mine but it was nineteen years ago so I don't know what size I did. They were _very_ small though :-)
If you drill them and don't like the effect just drop a blob of solder in them to block them again.

that's the ones!!! and that's what i planning to do once she running properly..... drill then fill if rubbish

how did it affect yours?

bladeracer · 08-05-2009, 3:24 AM

Quote:

Originally Posted by Sideshow bob

that's the ones!!! and that's what i planning to do once she running properly..... drill then fill if rubbish

how did it affect yours?

I don't recall any noticeable difference but it was a very long time ago :-)
I wasn't rushing around telling others to do the same so it probably didn't impress me very much :-)
Have you considered trying some much younger Bandit 1200 carbs?
Or some nice big flatslides :-)

Sideshow bob · 08-05-2009, 2:30 PM

Quote:

Originally Posted by bladeracer

I don't recall any noticeable difference but it was a very long time ago :-)
I wasn't rushing around telling others to do the same so it probably didn't impress me very much :-)

was hoping you'd say it caused it to fly...... but from what i've read it only comes into play right at the top of the revs so possibly wouldn't even be noticable the way i ride most of the time.. but might still give it a go*

* even if it's pure curiosity or just to say i have and it's not worth it!!!

Quote:

Originally Posted by bladeracer

Have you considered trying some much younger Bandit 1200 carbs?
Or some nice big flatslides :-)

yeah I'm considering it......

but I'm also hoping to fit a 11 lump at some stage* (possibly a newer bandit twelve**)

so may need to go through the whole process again

must admit: I'm quite enjoying the learning how carbs work....
previously.. any jetting i've done has been simply bolting in the new recomended bits, adjusting needle either up or down and job was sorted.
I never understood how carbs actually worked other than the basic "they mix air/fuel and dump it into the engine when you turn the twisty hand grippy thing***" now after a week of plundering the T'internet i'm starting to understand how jets, needles etc interact. weather i can put this new found knowledge to good use is another matter... but gotta try

especially as another kind member**** sent me some bits and the best set of instructions i've ever seen

*if i can find one.....they getting scarce and expensive (or i'm just tight and not looking in the right places)
** am reliably told they will fit as original ones were only a modified 1100 but as yet this info is unconfimed
*** note the use of highly technical terms (radiobloke could be right about me)

****thank you skiddy (Sidmarklong)*****
***** oooops! I got a bit carried away with the foot notes

bladeracer · 08-06-2009, 1:15 AM

Quote:

Originally Posted by Sideshow bob

was hoping you'd say it caused it to fly...... but from what i've read it only comes into play right at the top of the revs so possibly wouldn't even be noticable the way i ride most of the time.. but might still give it a go*

* even if it's pure curiosity or just to say i have and it's not worth it!!!

yeah I'm considering it......

but I'm also hoping to fit a 11 lump at some stage* (possibly a newer bandit twelve**)

so may need to go through the whole process again

must admit: I'm quite enjoying the learning how carbs work....
previously.. any jetting i've done has been simply bolting in the new recomended bits, adjusting needle either up or down and job was sorted.
I never understood how carbs actually worked other than the basic "they mix air/fuel and dump it into the engine when you turn the twisty hand grippy thing***" now after a week of plundering the T'internet i'm starting to understand how jets, needles etc interact. weather i can put this new found knowledge to good use is another matter... but gotta try

especially as another kind member**** sent me some bits and the best set of instructions i've ever seen

*if i can find one.....they getting scarce and expensive (or i'm just tight and not looking in the right places)
** am reliably told they will fit as original ones were only a modified 1100 but as yet this info is unconfimed
*** note the use of highly technical terms (radiobloke could be right about me)

****thank you skiddy (Sidmarklong)*****
***** oooops! I got a bit carried away with the foot notes

When I drilled mine I believe Suzuki was calling them "high-speed jets"?
Bandit 1200 is the same as the 750/1100 oil-cooled engine. I can't recall if the 12 is the same deck height as the 11 but it'd be very close. I measured a 1200 (Robbie Bolger's bike actually) to be 12mm taller than the 750 but it was some years ago. The 11/12 cranks have the same main journals as the short-stroke 750 so you can drop them into the 750 cases.
I discovered this week that you can cut the GSXR head down and run it on the GS500 engine. So of course, I'm looking at fitting one to an old XS400 I'm building :-)
I'm looking for a set of late Bandit 1200 carbs myself to put on my car :-)

Sideshow bob · 08-06-2009, 3:28 AM

Quote:

Originally Posted by bladeracer

When I drilled mine I believe Suzuki was calling them "high-speed jets"?

they probley still are.... no one i asked knew what they were

Quote:

Originally Posted by bladeracer

Bandit 1200 is the same as the 750/1100 oil-cooled engine. I can't recall if the 12 is the same deck height as the 11 but it'd be very close. I measured a 1200 (Robbie Bolger's bike actually) to be 12mm taller than the 750 but it was some years ago. The 11/12 cranks have the same main journals as the short-stroke 750 so you can drop them into the 750 cases.

that's good

think it'll be easier to find a goodnick/low mile bandit1200 than a gsxr1100 one

Quote:

Originally Posted by bladeracer

I discovered this week that you can cut the GSXR head down and run it on the GS500 engine. So of course, I'm looking at fitting one to an old XS400 I'm building :-)
I'm looking for a set of late Bandit 1200 carbs myself to put on my car :-)

11 in a old XS?

sounds interesting! .....that needs a build tread

bladeracer · 08-06-2009, 4:20 AM

Quote:

Originally Posted by Sideshow bob

they probley still are.... no one i asked knew what they were

that's good

think it'll be easier to find a goodnick/low mile bandit1200 than a gsxr1100 one

11 in a old XS?

sounds interesting! .....that needs a build tread

No sorry, an XS400 _twin_ with a GSXR11 head :-)
Bandit motors are easier to find and are in better condition because they're tuned so low. The 1052/1127 are good for 130hp whereas the 1156 only pumps 100hp. From memory I think the Bandit runs about 9.5:1 compression?
Both the 11 and 12 are only five-speed boxes although you can put 750 boxes in them.