DynoJet Stage 3 recommendations RICH??

[Darin Jordan]

Hi Guys....

Well, after riding and tuning and tweaking, I'm coming to the conclusion that the DynoJet Stage 3 recommendations for jetting on my GS850 may be simply too rich in the main circuit.

The original setup recommended (K&N Pods and 4-1) the 165 mains, 4.5 turns out on the pilots (kit adds a smaller ID plug into the pilot jet hole... ), and the new DynoJet needles in the middle hole (3rd hole) with the extra washer under the clip.

That proved to be WAY too rich above 6000RPM and would stumble roughly at WOT when it hit 6000-6500.

I reduced the mains to 160s and it got better, but still a stumble up top and the high-altitude (above 4000ft) riding was very "stumbly".

I have dropped the needed down 1-notch to the 2nd groove from the top, and it's a little better. Weather is still cool around here, though, and I'm STILL getting a bit of the "rich" stumble right at WOT and 6000.

Also, I ended up riding about 55-miles in the pouring rain yesterday, temp around 55 or so, and the stumble was a bit worse.

I'm thinking of maybe doing one the following:

1) Dropping the mains down to the DynoJet 155 size, and moving the needle back to the 3rd slot (raising the needle up 1-slot from where it is now)
2) Dropping the Needles down 1 more notch, placing the clip in the 1st slot
3) Removing the additional washer/spacer that the DynoJet kit supplied from under the clip (lowering the needle down slightly.
​

I'm honing in on an excellent tune. The bike feels just a tad rich off the line, but rolls out smoothly right up the 6000RPM point, where it gets that stumble. It pulls though it now, however, and clears up around 7000-7500 or so, and pulls pretty hard to the top, though not as consistently when it's warmer out.

I just feel, based on my past experience with the 165's and also the 160s riding at altitude, that it's still a bit on the rich side, and might benefit from an overall leaning out of the main circuit?

Would love to hear some experienced thoughts on this.

Thanks...

 

[koolaid_kid]

What do the plugs look like? Sounds like you need smaller main jets. I had to go 2 sizes down on the mains from what they supplied. Do some plug chops at WOT first, then check your needle by doing plug chops at less than full throttle. The mains need to be dialed in first before you start adjusting the needle, since the size of the mains have a direct effect on the needle position.

 

[Darin Jordan]

I had to go 2 sizes down on the mains from what they supplied.

That would sound about right... the 165s (their recommendation) was clearly WAY too rich... The 160s are close... Lowering the needle down 1-notch with the 160s in place had a slight affect, but my experience thus far is leading me to think it's still 1-jet size too rich on the mains. This may have been further supported by the recent "maintenance" I did to the K&N Pods... I got a tad too much oil on them and the stumble got worse...

I need to try to get a set of the DynoJet 155 mains, and I'll install those and see how they feel.

Will do the plug chops as well, once the weather around here stabilizes...

 

[tkent02]

They have to make their kits rich enough that the dumbest moron won't go too lean and burn up his engine. They are rich. If you want it right, you have a lot of tuning to do.

 

[Guest]

Did you tap in the brass restrictors into the main air jet?

 

[Darin Jordan]

Did you tap in the brass restrictors into the main air jet?

Certainly. The kit is installed exactly as instructed and adjusted as recommended. I have my own CarbTune Syncronizer and the carbs are beautifully sync'd... almost perfectly, based on their recommended tolerances.

The only deviations I've made at this point is:

1) 160's on the mains (DJ recommended was 165)
2) Needles on 2nd hole (Lowered needles compared to the DJ recommended was 3rd)
3) Pilot screws (Idle-Air??) turned out 4.75 turns (DJ recommended was 4.5)
​

#3 is because it was doing a lot of popping on deceleration, which is supposedly indicative of the screws being too lean still. The additional 1/4 turn seemed to help.

 

[Guest]

I'd go up one on your pilot jet.
You leaned the needle then and are still rich at full throttle? Have you done a plug chop at full throttle?
You can not get the needle tuned properly without having the main dialed in first. You are compensating for a rich main leaning the needle.
You can use mikuni mains in place of the DJ. I have some jets that should work for you.

 

[Katarat]

I know chef1366 knows this but 160 DJs are = to 150 Mikunis, just in case Darin doesnt. Good luck with it

 

[Darin Jordan]

Quick follow-up question. I think Bill is out of town, but he's been helping me via PM this week!

Have new mains on the way... But would like to get another set of Pilots to see if I can perfect that circuit as well...

I haven't torn them apart again, but assuming that my carbs are stock, or at least that the pilots are stock, the manual says they are sized "40".

Bill gave me the link: https://www.denniskirk.com/vm22-210-pilot-jets.p176415.prd/176420.sku?_requestid=3183481

For the Pilots... But I'm wondering, just like with the Mains, if the sizes directly translate, or if there is another conversion from "stock" to these listed sizes??

In other words... to go up one size, do I order a set of "45" sized Pilots?

 

[koolaid_kid]

DJ does not supply the pilot jets. You need stock Mikuni parts, readily available from Z1 at less than $2 each. You will need larger. I purchased 2-3 sizes larger, since shipping was so high per set. You will need to go at least 1 size larger, I may have gone 2 (it's been a while). If you have 40s stock, I suggest purchasing at least 42.5 & 45.0. That should cover you. You won't know until the end, as the pilots are the last jets to tune.

 

[Darin Jordan]

DJ does not supply the pilot jets. You need stock Mikuni parts, readily available from Z1 at less than $2 each. You will need larger. I purchased 2-3 sizes larger, since shipping was so high per set. You will need to go at least 1 size larger, I may have gone 2 (it's been a while). If you have 40s stock, I suggest purchasing at least 42.5 & 45.0. That should cover you. You won't know until the end, as the pilots are the last jets to tune.

Thank you, Sir... that's what I was figuring would be the case... I'll get the mains installed, re-tune, then see where everything else is. I'd like to get it close, perhaps within the Pilot Jet change of being right, and then order some new float-bowl gaskets to go along with the Pilot Jet install. Then, hopefully, I'll have it about right and won't have to tinker with it for awhile. It feels so close now, I'm really hoping that these last couple of updates take care of it.

 

[Darin Jordan]

Well... I put in the new DynoJet 155 mains, and moved the needles back to the 3rd groove. DANG! What a difference! Feels much crisper, especially when accelerating from a cruising speed. Ripping through the gears is clean and smooth, and it pulls nice and solidly right on through the redline, which caught me a little by surprise the first couple of shifts!

Will ride it around this week and give it a solid evaluation, but I'm definitely in a better place than previously. We have some nice weather ahead of us this week, so I should be able to get some quality time in on the throttle and we'll see then if any further adjustments are needed.

 

[posplayr]

You will see my results from jetting a BS36 carb for my built 1166. My main is only 135 (down from 140-145's due to 4:2:1), but that is not that far from your 155 mains so the sensitivity to changes between step size and AFR should be reasonably close. This data was measured using an LM-2 Wideband O2 sensor pulling a long steep hill in first four gears.


http://www.thegsresources.com/_forum/showpost.php?p=1303763&postcount=12

As A guide, this is what I saw near my optimum tune point.

• At 1/2 throttle, each step on the needle was worth about 1 AFR about 13.So if you are at an AFR of 14.0 at 4 notches from the bottom, you can drop to AFR=13.0 at 3 notches from the bottom.
• A change in the Main by 1/2 a step (e.g. 140 to 135) makes the needle at 1/2 throttle move up 1 full point (e.g. 13.5 to 14.5)
• A change in main by 1/2 a step (e.g. 140 to 135) makes the AFR at WOT rise about 1/2 a point. For example from 11.0 to 11.5

Optimum tune (for my setup) seems to be about; In other words I'm not sure it will get any better than what it is :

WOT is AFR 11.5-12.5
1/2 throttle (high RPM) is AFR 13.5-14.5
1/8-1/4 throttle AFR is 11.5-12.5 (75 mph at 4500 RPM)
Idle AFR 13.5

 

[TheCafeKid]

Wow. This just impresses upon me even more that the 8v heads really didn't breathe nearly as well as the 16. Obviously a fact, but to what end I didn't know.
And that the 850 doesn't like pods and a pipe.

I've never messed with the 8v DJ kits, but they're obviously way more persnickety than the 16v stuff. The fact that the needles retain nearly a stock taper is a bit of a surprise considering this is generally where people have the most trouble when tuning for pods and pipe combos, and even stock bikes were lean on the needle.

Just because I am a glutton for punishment and like to tinker on carbs, I may take a set of 16v needles and play with an 8v bike and see what happens. I'm wondering if a set of 16v DJ needles would allow for less of a bump in the main size...

 

[Darin Jordan]

Just because I am a glutton for punishment and like to tinker on carbs, I may take a set of 16v needles and play with an 8v bike and see what happens. I'm wondering if a set of 16v DJ needles would allow for less of a bump in the main size...

I'm very much enjoying riding my bike these last couple of days, and am not sure I want to tinker with it too much more, HOWEVER...

I too am a glutton for punishment, disguised as an overwhelming desire to have everything tuned PERFECTLY... SSOOOOO... Please let us know what you find out!