Modifications - Performance Discuss aftermarket and DIY performance modifications

Fine tuning last tweeks necessary

Old 01-19-2019, 12:17 AM
  #1  
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Fine tuning last tweeks necessary

I AM SO CLOSE TO RUNNING PERFECT. I have two questions. My machine is running better than ever before!
The only issue I have is what seems to be a slight lean stumble around 3500 to 4000 rpm in 2nd and 3rd gear cruising.
I say lean stumble because, it seems to get better as I turn my A/F screws out.
I can't seem to get rid of it at 4 and 4. 5 turns out on the A/F screws. but it gets better when richer with the choke or A/F screws
I dont think I need/want bigger slow jets.

what is the best course of action?
  1. Rase the needles one 20 mil shim each needle, or one notch up on each needle.
  2. Plug the second hole on both my slides?

I have a 1998 VTR 1000F run @ sea level
Stock Honda air filter
Stock slides 2 stock holes
Dr. Honda Velocity Stacks
TPS = 506 OHMS
Flow Commander set to 3 turns = neutral
175 Front main 178 Rear Main
48 Slow Jets
Front A/F screw 2 1/4 turns out, Rear A/F screw 2 1/2 turns out
Factory Pro Front Needle 2nd clip from the top with 20 mil shim
Factory Pro Rear Needle 2nd clip from the top with 40 mil shim

Thanks for all your collective help and insight!


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Old 01-20-2019, 11:21 AM
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Originally Posted by black ops View Post
I AM SO CLOSE TO RUNNING PERFECT. I have two questions. My machine is running better than ever before!
The only issue I have is what seems to be a slight lean stumble around 3500 to 4000 rpm in 2nd and 3rd gear cruising.
I say lean stumble because, it seems to get better as I turn my A/F screws out.
I can't seem to get rid of it at 4 and 4. 5 turns out on the A/F screws. but it gets better when richer with the choke or A/F screws
I dont think I need/want bigger slow jets.

what is the best course of action?
  1. Rase the needles one 20 mil shim each needle, or one notch up on each needle.
  2. Plug the second hole on both my slides?

I have a 1998 VTR 1000F run @ sea level
Stock Honda air filter
Stock slides 2 stock holes
Dr. Honda Velocity Stacks
TPS = 506 OHMS
Flow Commander set to 3 turns = neutral
175 Front main 178 Rear Main
48 Slow Jets
Front A/F screw 2 1/4 turns out, Rear A/F screw 2 1/2 turns out
Factory Pro Front Needle 2nd clip from the top with 20 mil shim
Factory Pro Rear Needle 2nd clip from the top with 40 mil shim

Thanks for all your collective help and insight!
Well this is just my opinion but here are my thoughts.

First I am a bit confused with the shims you are using. You list 20 & 40 mil though I will assume you mean .020" & .040".
This can cause some of your issues. You really need proper .5 mil or .010 washers to get a good tune.
As I stated somewhere in the carb set up thread, that is one thing I would change....any mention of using #4 washers. .020" is just too big of a step with these carbs.

Then with pilots, anything over 3 turns out really doesn't do much and if everything else is correct is also a sign to go to a larger pilot.
Also the RPM range you are listing is right when the slides are starting to open.

Another point that seems to cause some confusion is the lift hole configuration. You only run a single lift hole if you are running a short stack.
Since the Dr Honda stacks are, for all intents and purposes, a set of aftermarket long stacks you run 2 lift holes in both slides for best performance.

So with all that, what I would do is:
Set the pilot screws at 2.5 turns out.
Remove the second shim from the rear needle and raise both needles 1 clip position.

Then go from there.

Last edited by 8541Hawk; 01-20-2019 at 11:26 AM.
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Old 01-20-2019, 12:05 PM
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Hawk, Good to see you on here again. But, now I'm confused! The last paragraph in the original "Carb Setup" post states a single lift hole is what is needed with Dr. Honda Stacks as they lift to quickly. So, should I be running 1 or 2 lift holes with Dr. Honda Stacks?
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Old 01-20-2019, 12:47 PM
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AWESOME!!! Thank YOU!
Thank you for responding!! I was about to PM you. My bike is aligning itself to your base line almost exactly!
I had to go up and down a size in mains just to be sure. The Flo commander really helped me guarantee the right main jet was in play.
Because of this forum and gentlemen such as yourself I have had shining success with this otherwise daunting task!
FYI...My carbs have been removed and reinstalled 14 times and counting... with a little assistance from quick disconnect fuel lines and Jack Flash's brass choke fittings. The performance gains are WELL worth the $, blood, sweat, and tears, in my book Thank you! again!

Well as always you are exactly spot on, the shims I use are .020" one in front and two .020" in back.
​​​​​​To confirm: your suggestion: raise the needles one notch richer which in my case will end up 3 notches from the top.
also I will leave a single spacer .020" on both needles making them identically configured

I thought I had digested all the threads correctly, NO slide mod needed when Dr. honda stacks are used.
I needed to be certain my slides were best left factory 2 hole stock. Sincerely... Many Thanks for the peace of mind!!
Because my bike, pulls so well everywhere else on the power band I didn't want to go to 50 slow jets.

MY Black Widow Exhaust is almost a straight pipe with a bit of baffle at the end. Its basically a GP track pipe. They sound SOOoo Good!
I am considering installing the baffles, if they would provide some needed back pressure for optimal scavenging effect.
I'm not sure how to measure that modification for analysis. Your thoughts would be very welcome!




this picture was taken before leaning it out and dialing it in. yes its too rich in this pic

Last edited by black ops; 01-21-2019 at 03:16 AM. Reason: mis quote
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Old 01-21-2019, 01:00 AM
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My bike is running like a scalded dog. Butt Dyno says its dialed in!! after 15 carb removals/reinstals

175 Front main 178 Rear Main
48 Slow Jets
Front A/F screw 2 1/4 turns out, Rear A/F screw 2 1/4 turns out
Factory Pro Front Needle 3rd clip from the top with 0.020" shim
Factory Pro Rear Needle 3rd clip from the top with 0.020" shim

WOW feels good knowing the bike is optimized to the best of my ability anyway.
Special thanks to 8541Hawk for keeping me on track, saving me tons of time, frustration, and uncertainty.
I would encourage anyone with the time and patience to invest in your ride getting the most out of it!
I would highly recommend buying jack flash's AF screws and brass choke fittings before attempting this process.
https://www.superhawkforum.com/forums/modifications-performance-29/choke-fitting-replacement-brass-made-33364/

https://www.superhawkforum.com/forums/modifications-performance-29/thumb-fuel-screw-31449/


Maybe some quick disconnect fuel line fittings. 11.8MM SAE 3/8" 10MM Nylon Fuel Line Quick Release Hose Elbow Straight Connector

https://www.ebay.com/itm/372086516841?var=&hash=item56a215ac69

Last edited by black ops; 01-21-2019 at 03:11 AM. Reason: mis quote
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Old 01-21-2019, 01:49 PM
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I am still having trouble verifying the AF screws are optimised.
I have used the manual idle drop procedure at 1200 rpm
I have tried the fast idle drop procedure at 1800 rpm
Both procedures seem to take me farther away from a snappy blip test.
my problem is the rpm only shows up as a subtle increase or drop and then a blip test seems to indicate indicate popping or hanging when it should be improving.
What's the magic sauce for this operation?

Has anyone used the COLOR TUNE visible spark plug product or method.
Motorcycle Colortune Kit 12mm | Part No. G4171 | Part of the Colortune range from Gunson
This seems to be a fairly certain and definite visible result but they do not offer a long reach 12mm spark plug.
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Old 01-24-2019, 02:05 PM
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Originally Posted by CaryDG View Post
Hawk, Good to see you on here again. But, now I'm confused! The last paragraph in the original "Carb Setup" post states a single lift hole is what is needed with Dr. Honda Stacks as they lift to quickly. So, should I be running 1 or 2 lift holes with Dr. Honda Stacks?
I guess I had forgotten to update that thread. After more testing I have found the Dr Honda stacks actually like 2 lift holes.
Sorry for the confusion and I'll try to remember to update the other thread.
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Old 01-24-2019, 02:14 PM
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Originally Posted by black ops View Post

MY Black Widow Exhaust is almost a straight pipe with a bit of baffle at the end. Its basically a GP track pipe. They sound SOOoo Good!
I am considering installing the baffles, if they would provide some needed back pressure for optimal scavenging effect.
I'm not sure how to measure that modification for analysis. Your thoughts would be very welcome!
The no baffles might be the cause to the issues you are still having. If you do install them you might need to drop the mains down one size.
This is typical with the Dr Honda stacks.
As for the idle drop test, it is kind of tough to do unless you have a good tach and even then it can be tough. I always end up doing the blip test and adjust from there as needed.

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Old 01-24-2019, 04:07 PM
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Mike, No apology needed. I've been running 2 lift holes for a while as I hadn't had time (read too lazy) to fill one on each anyways since I picked up some Dr. Honda copies. I ended up dropping the OEM needles .010" and she runs great. As far as setting the fuel screws using the idle drop method. I have the tool for the OEM screws and found a cheap inductive tach that reads 4 x actual. So each 100 rpm is really only 25 rpm making it easier to see a 50 rpm drop while adjusting. I can only get it right if I do the front carb first. Who'd a thunk that the shop manual would be right when they state to do the front carb first followed by the rear.
Thank you for all the knowledge you impart on our fading forum. I hope you got good use out of the tank I dropped off a while ago.
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Old 01-25-2019, 08:10 AM
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Originally Posted by CaryDG View Post
Mike, No apology needed. I've been running 2 lift holes for a while as I hadn't had time (read too lazy) to fill one on each anyways since I picked up some Dr. Honda copies. I ended up dropping the OEM needles .010" and she runs great. As far as setting the fuel screws using the idle drop method. I have the tool for the OEM screws and found a cheap inductive tach that reads 4 x actual. So each 100 rpm is really only 25 rpm making it easier to see a 50 rpm drop while adjusting. I can only get it right if I do the front carb first. Who'd a thunk that the shop manual would be right when they state to do the front carb first followed by the rear.
Thank you for all the knowledge you impart on our fading forum. I hope you got good use out of the tank I dropped off a while ago.
I might have to see if I can find a tach like that one as I also have the factory tool for pilot adjustment.
Once again thanks for the tank. right now it is still waiting for me to get back to bike projects as I lost my place to live and have ended up back in New Mexico.
So after the dust settles I have a couple things in mind for the bike. =)

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Old 01-25-2019, 11:13 PM
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I'm saddened that you had to move as you had a great location and a good setup. hope it all works out. If I find another one I'll make a trip out this spring and bring it to you. What part of New Mexico?
I still search the globe for an HRC CDI Box as you gave me the part number. Maybe someday I'll come across one. What do they do besides advance the timing, and bypass the side stand safety?
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Old 01-26-2019, 07:36 AM
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Originally Posted by CaryDG View Post
I'm saddened that you had to move as you had a great location and a good setup. hope it all works out. If I find another one I'll make a trip out this spring and bring it to you. What part of New Mexico?
I still search the globe for an HRC CDI Box as you gave me the part number. Maybe someday I'll come across one. What do they do besides advance the timing, and bypass the side stand safety?
Yeah it was a good set up but I did have to deal with a lot of non-sense to stay there. I am in Bosque Farms or just outside of ABQ, so if nothing else there is a track close and have already have some ins with the local vintage racers.
As for the HRC box the big one to remember is it also deletes the rev limiter..... other than that they actually have a different advance curve, more advance down low and then it starts to back the timing off at high rpms.
Which makes the bike rev quicker though out the entire rev range. There are a good add, if you can find one at a reasonable price.
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Old 02-04-2019, 08:33 AM
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Gunson color tune! works for me!

I tuned the air mixture screws using the gunson color tune i was not far off using the blip test and a Fluke tach but it was out of wack 1/2 a turn in front. and 1/4 turn in back. i can finally understand what they mean when they say crisp exhaust notes
The main thing for me was being sure i have it optimised.

how can i obtain a HRC computer module? it sounds worth the effort.
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Old 02-04-2019, 08:52 AM
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Originally Posted by black ops View Post
how can i obtain a HRC computer module? it sounds worth the effort.
They show up used from time to time but can be hard to ID if the ink stamps have worn off.
Even then they are starting to command a steep price. I did see a new one listed a couple of years back from Aus.....but they wanted $1200 for it......
If you do find a used one, they normally go for $400-500.

There is an aftermarket option but you would need to figure out your own advance curve.

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