Author Topic: 1991 36mm SP needles ?  (Read 138 times)

Andy Bush

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1991 36mm SP needles ?
« on: March 16, 2019, 03:14:00 PM »
Afternoon everyone

My 91 SP is progressing nicely.
Had it on the dyno last weekend, and ran in to an issue

As it pulls through the midrange it encounters a rich patch between 8,500 - 10,000



It?s got the 36mm SP carbs on it, with the 633 nozzle. Currently has a 6FI3-62 needle.

Does anyone know what needle the rc-sugo kit included? Or maybe one they have found to work ok .

I do have an 6FI90-62 needles, which will be my next trial. Not sure how to read the code, as to what difference in shape / taper this will have over the other one.

Any help appreciated 👍🏻😀

Thanks
Andy

vinny

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Re: 1991 36mm SP needles ?
« Reply #1 on: March 16, 2019, 03:37:56 PM »
Sorry for the stupid question but is it a 3xv or a 3ma you have  Andy ?

Andy Bush

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Re: 1991 36mm SP needles ?
« Reply #2 on: March 16, 2019, 06:21:54 PM »
It?s a 3xv mate

maccas

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Re: 1991 36mm SP needles ?
« Reply #3 on: March 16, 2019, 07:50:18 PM »
Sugo kit needle is the same as the 92 TZ 4DP so check the TZ manual for the number.

However, on the dyno  you'll already be full throttle there so i'm not sure changing the needle will change anything as you are already on the main jet.

What's going on with the air jets or power jets?

Dan

vinny

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Re: 1991 36mm SP needles ?
« Reply #4 on: March 16, 2019, 11:13:16 PM »
Ah ok it's a 3xv .
 you have the same carbs as me 36mm sp carbs.
Dan is on the money.
 I used  tz 4dp parts in mine they are pretty easy to find compared to sugo stuff .
I'm using race fuel so my jetting will probally be different .
What nozzles are you using .?

Andy Bush

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Re: 1991 36mm SP needles ?
« Reply #5 on: March 17, 2019, 12:29:49 AM »
Thanks guys

It had S0 nozzles in, with needle on the 4th clip from top. Was rich right up the 10k . Would just about pull through if you part throttled it.
Changed down to R5 nozzles which cleaned it up lots.
The tried the needle on 3rd from top . But this made it flat as a pancake off idle, to the point it wouldn?t pull away !
So back to 4th grove.
Down jetted the main, and lost power , and still had the flat spot.
So figured it might be the needle profile was all wrong.
I will try these other needles I have, and see if it helps.
Cheers
Andy

Warwick

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Re: 1991 36mm SP needles ?
« Reply #6 on: March 17, 2019, 01:12:46 AM »
I run 6FI80-61 needles in R3 633 needle jets, Andy. That's in 4DP TZ carbs, but it's in the ballpark for the 36s too I'd think as it's pretty much the recommended '91/92 Sugo base settings.

I think the 36s are a bit more of a challenge to set up if you block off the air jet completely as in the Sugo set-up. Doesn't the needle jet also sit at a slightly different height if using the 633s rather than the sugo type setters and the 610 type jet on top in the 36s? That might also be a factor if using the 633s? I remember with a mate's bike  some years ago that it was always a lot harder to get the jetting sweet with the oe 36s even using all the pukka Sugo jets and settings than the TZ carbs I was using. If you have access to a pair of 3YL or early 4DP 38s they might be worth trying as they seem a lot easier to set up in my experience.
« Last Edit: March 17, 2019, 02:00:05 AM by Warwick »
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Andy Bush

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Re: 1991 36mm SP needles ?
« Reply #7 on: March 17, 2019, 12:14:59 PM »
Thanks Warwick
I was reading some of the old posts in the archive, and it seams this is a common issue with these 36?s !

The fact the 633 nozzle sits at a different height probably affects things.

I have these other needles...let?s hope they give some good results 😀


Hoatso

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Re: 1991 36mm SP needles ?
« Reply #8 on: March 19, 2019, 06:10:27 PM »
It?s common to think the needle affects mid-rpm, but it actually affects mid-throttle. So, if there is a rich or lean spot, note the throttle opening.

If it is a problem with a certain rpm range during wide open throttle, this might be corrected by programming the vaj or power valve opening differently, as these change with rpm.

The emulsion tube in the carb also is rpm-dependent: as the rpm increases, the fuel level in the emulsion tube well lowers, exposing more air holes, and leaning the mixture. Folks don?t normally change this.

Scotty4321

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Re: 1991 36mm SP needles ?
« Reply #9 on: March 20, 2019, 08:29:36 PM »
Hi,
I managed to get reasonable results with a 91 SP on standard carbs and all std carb parts, bar the main jets.
I junked the VAJ blocks and the electronic power jets and simply tee'd together the pipes coming from the  carbs that went to the VAJ blocks. I bought a load of different sized air jets (the ones that fit the vaj blocks) and trialled them in the  end of the pipe.
Worked fine for me and I got the A/F ratio pretty good.
I did start playing with the duty cycle solenoids off an RGV. I'm convinced this offers the ultimate solution to mixture control across the rev range. Struggled with them though so didn't get them working You would need a zeel to try this though. Good luck Scotty