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midrange needle differences?

  • Thread starter Thread starter RHODESIA SMITH
  • Start date Start date
R

RHODESIA SMITH

Guest
Hello all you clever chaps aka carb gurus out there?

perhaps one or two of you might be able to help with an answer to my question?

Back round-Just finished doing a base gasket on my 850G , did not change rings, but did a hone, a head and barrel skim , valves seats ect done, and valve clearances, and cam timing done nicely.

The bike runs well and so far no more leaks that I can see? I have done about 200km since the rebuild, but I am now trying to get rid of a slight hesitation that occurs in the midrange rev range. All I can think of is that the engine now breathes slightly better, following the rebuild.

I have made sure that the ignition side of things are all well. New intakes boots and O-rings, standard airbox sealed up , the works.

I have the carbs apart and I have noticed for the first time the needles are not all the same! I have 3 of 5C 32 and 1 of 5D 57. Dont know how I missed this before?

anyway - I have measured where I can like for like and cannot find a difference between the two types? (granted I have a normal vernier and not a digital one at hand to use)

there must be a difference, but could maybe one of you maybe tell me what they are?

why I am thinking the needles are the reason for the hesitation is that they control the midrange and this is the reason why I am looking in this area?

thanks all
 
sorry forgot to mention - the carbs are the CV type.
bike is 1981 GS850G (X)- UK?? SPEC?
 
The needles don't really cover "mid-range", what they cover is "mid-throttle". :o

Here is a chart from Sudco that might help a bit.

Neither one of your needles is listed there, but I certainly give a bit of insight on the numbering and measurments.

.
 
All 4 jet needles should be the same but if it woks. You do remember which carb the odd needle came from? It could be a match to an odd needle jet.

As for the hesitation, I put 1mm thick washers under the needle and give it a try. It works most of the time with CV carbs. Are you sure it is a mid-range (:rolleyes:mid-throttle:rolleyes:) hesitation and not more of a just off idle hesitation. Older CV carbs suffer from a lean spot at the change over from idle circuit to the needle jet circuit. Anyway if the washers don?t work you haven?t lost anything.
 
Yes the key here is to forget anything to do with the amount of revs yore turning when you have this hesitation. Pay more attention to the throttle position. Part throttle? 1/4? 1/2? If you're just cruising...that's generally the pilot, or pilot needle transition stage. Try opening your mix adjustment screws another half turn.

And see what you can do about finding a matching needle, just to eliminate that possibility from the equation.
 
Thanks all for the replies.

if I pull away hard in 1st gear-full throttle and bang the revs right to the redline- no hesitation just pulling strong all the way.

What is occuring if for example , I am in 5th say doing approx 50-70km/h and I change down a gear or two and and roll the throttle smoothly open to about 1/2 to 3/4 it begins to pull fine and then at the approx 4500-6000 rpm I expereince the hesitation that does clear quite quickly ,but is defineatly there, and then pulls again strongly all the way through to 8000+

( havent pulled away strongly to the red line in 4th as not enough road to do it in yet!).

I am currently looking around for the some 5d needles, but yes I may need to get a needle and jet set as they could be different.

thanks all - will do some reading on the sudoco stuff as well.

Do any of you guys live at high altitude and run 850's with standard airbox, 4 into 1 pipe.? That is the set up on my bike and we are at approx 1750m above sea level here. just to get an idea of what carb set up you blokes may have in this instance.


thanks
 
sounds like it's a little weak there.... like's been mentioned.... stick a thin washer under the needle to raise it a touch and see if it smooths things out
 
Graham said:
As for the hesitation, I put 1mm thick washers under the needle and give it a try.
Click to expand...

sparki said:
.... like's been mentioned.... stick a thin washer under the needle to raise it a touch and see if it smooths things out
Click to expand...
Simply inserting a washer "under the needle" (probably under the clip?) only adds preload to the spring. It does NOTHING to change the needle position.

What you need to to is to remove the thick nylon spacer above the clip on the needle and replace it with a shorter stack of thin washers. It usually takes about 4 washers to equal the nylon spacer, so try 2 or 3 washers, instead.

.
 
Steve said:
Simply inserting a washer "under the needle" (probably under the clip?) only adds preload to the spring. It does NOTHING to change the needle position.

What you need to to is to remove the thick nylon spacer above the clip on the needle and replace it with a shorter stack of thin washers. It usually takes about 4 washers to equal the nylon spacer, so try 2 or 3 washers, instead.

.
Click to expand...

Your right about the spring is under the clip on the GS850 carbs unlike most other CV carbs. Anyway the point is to raise the needles about 1mm should solve the hesitation issues.
 
Never saw that chart, will check that with my needles as maybe it will help my issue... do they have a stamp on the side or something that says the number? Also does the book say what is supposed to be stock on my bike? its an 80 850G.

Sorry of highjack, just looking to learn a bit more on this stuff to get my lean issue fixed.
 
Skateguy50 said:
Never saw that chart, will check that with my needles as maybe it will help my issue... do they have a stamp on the side or something that says the number? Also does the book say what is supposed to be stock on my bike? its an 80 850G.

Sorry of highjack, just looking to learn a bit more on this stuff to get my lean issue fixed.
Click to expand...

Your needles should be 5D50
 
Thanks, I checked and that is what I have... so my mystery continues.
 
yes according to my Haynes manual it says 5D57- 3rd.
3rd being the position that the circlip should be placed.

still looking might have a lead that I can follow up next week.

when i get the needles i will try the option of fitting the 1mm washer scenario.

any of you guys live at Altitude? if so how have you tuned? ie I have a 4 into with standard airbox. Just an idea so I have a datum point.

thanks
 
Ahh. Should have figured being you're not a Seppo that your bike would have adjustable needles.
In that case, ignore the "shim the needle" suggestions and simply move the clip down one notch (toward the pointy end) and see if it helps.
 
RHODESIA SMITH said:
Do any of you guys live at high altitude and run 850's with standard airbox, 4 into 1 pipe.? That is the set up on my bike and we are at approx 1750m above sea level here. just to get an idea of what carb set up you blokes may have in this instance.

thanks
Click to expand...

I ride at 4,000 and up feet of elevation. (10,000 ft. max.)
My '80 850 only had oval pod filters and factory pipes.
It was smooth to about 5,000 rpm then kind of slowed down.
In that application, at my altitudes, all that I had to do to cure it was change the main jets from 115's to 117.5's.
With the stock air box and filter (or is it K & N? Does it still have the snorkel?) with 4-into-1 pipes, have you tried going with 120 or 122.5 main jets?

Daniel
 
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