jet needle profile options

[tirebiter]

Can anyone direct me to sources for an optional carb jet needle to use instead of the stock 5D50 in my 1980 GS850L ?

Been having a dickens of a time remedying a subtle problem I'm experincing, during light throttle, steady speed cruise.

Check this other thread if you want more details :
http://www.thegsresources.com/_foru...e-the-CV-carbs-good-for&p=2141844#post2141844

 

[Dave8338]

What is your problem and how can I help ?

Just read through your link. Two things come to mind.

1) are your compressions numbers even across all four?
2) have you adjusted the valves so that they are all even and within spec ?

 

[JJ]

When was the last time you synched your carbs?

 

[tirebiter]

Dave, I checked compression and all was even although low, when I first got the bike in August. The whole story including electrical work, ignition timing and other mechanical issues are all listed as they occurred in another thread, if you want to wade through it. All the numbers, valve clearances, compression readings, cylinder leakage, carb jetting and more are included :

http://www.thegsresources.com/_forum/showthread.php?225303-Just-bought-non-running-GS850

Valve clearances were tight so I did the adjustment and afterwards a cylinder leakage test. All good. Major difference for the better in idle stability. Runs about the same otherwise, good to excellent until it got really cold out, lately. I have never seen smoke from the exhaust and the bike runs well except for this currently occuring symptom, which I am trying to sort out without running the mixture screws out to compensate. I do not want to have a bike that cannot idle indefinitly, when neccesary.

Johnny, I bench-synched the carbs way back at the beginning. I do not own a manometer setup to do a vacuum synch at idle and I have not been able to figure out a workaround. I assume the engine will not idle if I remove the air filter housing so I cannot use a listening device to hear the balance between the carbs - typically I do this with a rubber tube with other multi-carb setups.

At this point I am thinking I may want to try raising the needle even more than it was before I relocated the nylon spacer to above the circlip. Only reason I have not yet is because the engine seems to take initial throttle opening just off idle, better than before the nylon spacer got relocated. It acts like it was maybe going a little too rich when the air piston began moving but now is leaner under that condition - just barely opening the throttle - liking it more. A better transition now, from idle to extremely slight application of throttle opening.

The nylon spacer is about 3mm thick so the needle moved a little over 6mm downwards in the piston, by relocating the spacer. At the previous setting, the jet needle taper started about 3 mm below the bottom of the piston. Now the taper is about 9 mm below the bottom of the air piston/diaphragm piston/slide (whatever it's called). The lean surge (symptom) occurs more noticeably now and at a larger range of RPM than before but the throttle "takeup" just coming off idle ( term used for a quicker description) seems much smoother.

For what it's worth, my driving style and traffic in general, dictate that I am doing a lot of riding with extremly small throttle openings. For much of my riding, I am constantly going from closed throttle to barely open throttle and then closed again and then maybe a little more throttle. Much of it at very low RPM and sometimes pulling the RPM to sub idle speeds in 1st gear, creeping along in stop and go traffic. Last thing I want to do is to slip the clutch almsot constantly which seems to be the only other option.

I'm thinking a jet needle profile that starts to taper farther up, closer to the bottom of the piston would work better than the stock jet needle. I know the 1980s were a bad time for all vehicle manufactureres as they all floundered around to meet ever stricter emissions standards. Not that I think it was bad idea but at this point I am willing to compromise emissions for better running and so I'm thinking a different jet needle profile is in order. I'm hoping someone here has done the same thing already and may have some recommendations as to which jet needles I might try.

 

[GSX1000E]

The nylon spacer is about 3mm thick so the needle moved a little over 6mm downwards in the piston,

What are you using for a measuring device??? Those spacers are 2.5mm

 

[JTGS850GL]

Before messing with new needles, I would remove the plastic spacers and replace them with 3 metal washers per needle. You can pick up a kit of assorted washers at Radio Shack. It should contain 16 or so of the exact washer you need plus a few other sizes. Stack 3 of the correct sized washers above the E-clip in place of the plastic washer. That would raise the needle just a little under 1mm from stock. The plastic spacer should never have been located below the E-clip. That's a PO's hack. From top to bottom the order on the needle should be plastic spacer, E-clip, 1 OEM washer and then the spring. In the new arrangement you simply replace the plastic spacer with 3 metal washers.

Here's a pic of what I'm talking about:

 

[tirebiter]

GSX1000E, I measured the spacer by eye. It was a pretty close estimate.

JTGS850GL, OK, I can try the setup you mentioned. I've seen it on other threads but must have misread the distance it would lower the jet needle. I figured I would try the stock location and work from there. Yes, the PO - or somebody - must have swapped the nylon spacer position, before I bought this 850.

So just to get this straight, in other words you are saying I need a 1.5 mm spacer instead of the stock 2.5 mm (GSX1000E pointed out) spacer. Apparently what you are telling me is that the Radio Shack washers are 0.5 mm thick. I'll give it a try because I am still not 100% satisfied that I have corrected the lean surge although the symptom seems to have all but disappeared.

For the record, I went out last night in 18F degree weather, the coldest yet encountered this season. I had adjusted the mixture screws to lean-drop best idle and then 1/2 turn richer, the other day when it was about 40 out after relocating the nylon spacer and a couple of test drives. Last night when using "Little Suzy" the idle was ok at stop lights etc. Stable enough and returning to 1000 RPM every time but only after the engine warmed up, which is fine by me.

The only thing I can say about the lean surge is it seems to be almost 100% gone. Better (I think) than it was, at steady cruise speeds up to 55 MPH. Did not go out on the highway to see if the 60-65 and up range was as good.

I noticed a few times when taking off from a standstill a little faster than normal - slightly more throttle than my usual "little old lady" style - I got a small cough or hiccup from the engine. I think most of the time I'm normally operating below the (idle fueling circuit to intermediate fueling circuit) transition point and maybe not even causing the piston to lift at all considering how light I am on the throttle, when leaving a stop light. I'm thinking this cough or hiccup must be the stumble everyone talks about and raises the jet needle to remedy.

I only got a similar cough or hiccup in a super heavy downpour ONCE in the nearly 3000 miles I've ridden her since August, before putting the nylon spacer in the stock location. Before and afetr that one rain-soaked occurance, regardless how fast I would take off from a stop (there have been several occasions where the power this thing has was VERY useful) she never skipped a beat starting off. Now, I feel I can make the stumble occur at will.

I realize tiny increments can make all the difference. I'll defintiely be raising the needle as suggested.

The one thing I'm wondering though is that the needle taper starts very, very far down the shaft of the jet needle. It doesn't seem posible that it will make a difference but I have seen what (corrected-thank you GSX1000E) a 5 mm change can do. According to my measurments with a micrometer, with the carb piston sitting down all the way, the beginning of the taper would be at the top of the mainjet holder/emulsion tube if I were to raise the needle even more than it was when at the 5 mm higher (nylon under circlip) position. Does the tip of the jet needle actually go through the opening of the screw-in mainjet orifice ? Is the needle long enough to do that ? I didn't think to look at that when I had the carbs off, previously.

What I'm used to with various other carb makes (that use a vacuum controlled piston and needle arrangement) is that in 99.9% of them, the needle taper starts right at the bottom of the piston. This is what I'd like to find but in the meantime, I'll give your experience (and that of others on this forum) the nod, and see how rasing the jet needle 1 mm from the stock position, works for me.