Jet needle circlip position on BDS28 mikuni '98 Royal Star

[Royal Star Ronnie]

Question #1:

What is the default position (of the 6 available positions) for the circlip on the jet needle of a stock original BDS28 Mikuni from a '98 Royal Star?

 

Bike:

1. Original owner of '98 Royal Star with 9,000 pampered miles. (Kept fully covered in an air conditioned garage. Oils and plugs changed yearly along with Sta-bil, etc.)

 

2. Ten years ago aftermarket mufflers were installed by a dealer and (as best I can recall) the dealer said he richen the carb to compensate for increased exhaust flow. He did not remove the carbs, therefore he must have richened by adjusting the pilot fuel screws and/or the circlips on the jet needles. (Hmmm, or maybe the jet needles were replaced.)

 

Story:

1. Bike has seemed to run rich with 30 mpg, but has run well and started easily.

 

2. Rebuilding all four carbs due to afterfire from right rear cylinder believed to be carburetor related. Right rear carb was indeed dirty(er) within float bowl, and had a slightly sticky jet needle slide as well.

 

3. All four carbs are fully cleaned and ready to reassemble with new o-rings and new float valves and needles.

 

4. Spark plugs are all equally colored with clean white insulator, sooty plaque on threads, and light brown electrodes. (Thoughts?)

 

Naturally, I will resync carbs as well as adjust the pilot fuel screws, but I'm wondering if I should alter the circlips position on the jet needles. Current circlip positions are #3 (down from the top clip end).

 

Question #2:

What are your thoughts about leaning it out a bit by installing the circlips at position #2?

 

Thanks.

Edited October 29, 2013 by Royal Star Ronnie
spelling

[Hucklecatt]

Unless I am mistaken, the 1998 used a Mikuni 95 main and 20 pilot jet. I also seem to recall that the original needle was not adjustable - it simply used a shim.

 

What numbers did you read off your jets when you removed/cleaned them? If the needles are adjustable, you may have an aftermarket kit installed (DynoJet; Barons). If so, you may be reading jet sizes of 110 - 117.5, with a 22.5 to even 25 pilot.

 

If you can get those numbers to us, along with your pipe brand name and airbox mods if any that would help. But from the hip? Yes, go with the 2nd position and try the throttle on/off method to determine if you are running too lean.

[Royal Star Ronnie]

Unless I am mistaken, the 1998 used a Mikuni 95 main and 20 pilot jet. I also seem to recall that the original needle was not adjustable - it simply used a shim.

 

What numbers did you read off your jets when you removed/cleaned them? If the needles are adjustable, you may have an aftermarket kit installed (DynoJet; Barons). If so, you may be reading jet sizes of 110 - 117.5, with a 22.5 to even 25 pilot.

 

If you can get those numbers to us, along with your pipe brand name and airbox mods if any that would help. But from the hip? Yes, go with the 2nd position and try the throttle on/off method to determine if you are running too lean.

 

 

Additional info:

1. Yes, main jet is #95 and pilot jet is #20. This is the first time carbs have been removed, so the inaccessible internals were original.

 

2. I have installed new float valves and needles, and needed to (slightly) level two of the floats to match the other two.

 

3. NOTE: I just found my original paperwork from the 2002 aftermarket muffler install and it shows a DynoJet kit #4148 was installed. The jet needles are DNO470 with instruction to set E-clip at #3. (The original jet needles were not given back to me.)

 

4. Jardine slash-cut mufflers, which are the same length as the original mufflers.

 

5. K&N air filter.

 

 

Thanks for assistance.

Edited October 29, 2013 by Royal Star Ronnie
new info discovered after post

[Hucklecatt]

Ah-ha! The hunt is on!

 

The shop that did this removed the airbox, then removed the carb covers, ditched the old needles, original springs, and should have removed the brass blocking items that cover your idle screws. They have installed the DynoJet kit's adjustable needles and longer springs and put in a K&N. Your Jardines flow a LOT of air, so it is not surprising you would set that needle at position #3. (Instructions at http://www.dynojet.com/pdf/4148.pdf).

 

From the description, your plugs sound very good. I do a lot of plug reading via plug chops and if you are not seeing "white hot" (all white; small dots showing heat damage from lean condtion) and not all sooty from a rich mixture, you are in the sweet spot. Most important is not to stray too far into a lean condition - a rich mixture may soot up everything, but a lean condition causes seizures in the worst case scenario. Stray/expermiment into a lean condition with your eyes wide open!

 

So I would go/stay with position #3. However, you should closely follow advice on http://www.mrlarsson.com/pdf/files/dynojet-troubleshoot.pdf, especially the section on Acceleration Problems with an eye to how the bike responds at steady cruising (my ref. above to the "twist grip" evaluation).

 

Really sounds like you are in good shape all around. At this point, proper idle adjustment and a spot-on synch should be job 1, after which you can safely run the bike and evaluate its performance. TIP: Get a VERY long screwdriver to perform your synch adjustments - trust me! I bought one of about 8" in length to reach in to the screws.

[Royal Star Ronnie]

Ah-ha! The hunt is on!

 

The shop that did this removed the airbox, then removed the carb covers, ditched the old needles, original springs, and should have removed the brass blocking items that cover your idle screws. They have installed the DynoJet kit's adjustable needles and longer springs and put in a K&N. Your Jardines flow a LOT of air, so it is not surprising you would set that needle at position #3. (Instructions at http://www.dynojet.com/pdf/4148.pdf).

 

From the description, your plugs sound very good. I do a lot of plug reading via plug chops and if you are not seeing "white hot" (all white; small dots showing heat damage from lean condtion) and not all sooty from a rich mixture, you are in the sweet spot. Most important is not to stray too far into a lean condition - a rich mixture may soot up everything, but a lean condition causes seizures in the worst case scenario. Stray/expermiment into a lean condition with your eyes wide open!

 

So I would go/stay with position #3. However, you should closely follow advice on http://www.mrlarsson.com/pdf/files/dynojet-troubleshoot.pdf, especially the section on Acceleration Problems with an eye to how the bike responds at steady cruising (my ref. above to the "twist grip" evaluation).

 

Really sounds like you are in good shape all around. At this point, proper idle adjustment and a spot-on synch should be job 1, after which you can safely run the bike and evaluate its performance. TIP: Get a VERY long screwdriver to perform your synch adjustments - trust me! I bought one of about 8" in length to reach in to the screws.

 

Hucklecatt, your advice is logical, and after reviewing your links, I agree.

 

My bike has always run well, except for this year's "popping" issue.

 

I've reassembled the carbs with jet needle E-clips at #3.

 

I'll remount the quad within a few weeks, but since local temps are ~40*F and rainy, I'll likely wait until spring to gas-up and sync.

 

DynoJet indicates the pilot fuel screw has an unusually large impact on mileage with BDS28 carb, so after syncing, I plan to adjust the pilot fuel screws to the leanest position which allows smooth idle in hopes that my milelage will improve.

 

Also, I wonder if Gunson's Colortune ($64) is worth it for optimizing the pilot fuel screw setting.

 

Thanks again, and I'll repost with my final results.