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DrHonda velocity stack re-jetting?

Old 07-21-2010, 11:08 AM
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DrHonda velocity stack re-jetting?

I will be installing the velocity stacks this weekend and have read that sometimes it causes the main jet to become too rich. I have a flo commander to help with that but have any of you who have installed it had to also make any needle height, pilot jet, or pilot screw adjustments as well? thanks for your help! Mort
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Old 07-21-2010, 11:30 AM
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velocity stacks have the potential to create positive pressure (boost) in the intake tract so I would be the least surprised if you needed to up the main jets. you may get away with just adjusting your needle height.
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Old 07-21-2010, 04:06 PM
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I have bolted mine in. No changes to jetting, I was impatient. No problems created by the change. It is a lot smoother at low rpm than previous.
I am doing some more longer runs to decide about jetting changes.

Previous history by those that have done it and are **** about correct jetting shows that installation of the stacks will usually result in having to go down by 1 size on the main jets. (Assuming that the jetting was spot on beforehand)

Last edited by revhead1957; 07-21-2010 at 04:07 PM. Reason: spelling
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Old 07-21-2010, 04:32 PM
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Interesting.
After installing new V-Stacks on a stock 05' with no pipe or jetting changes, I really didn't notice any differance good or bad, except for a very slight stumble when rolling W.O. from 3500 RPM at about 4000-4500. (Although I do not run WOT as a rule at this low of RPM). I then purchased the flo-commander and installed it and tried it at 3 turns out as suggested, no change good or bad. I have had little time to tune with the flo-commander but have tried various settings from 2 - 4 turns out from closed with little differance.
Could be that to really see the benifits of the stacks & FC, either a full system or less restrictive slip-ons, and or spot on jetting changes are necessary. Not disapointed as I do plan on Staintunes some time in the future, and more tinkering with the carbs. It's fun regardless.
BTW, synced carbs best for idle & 4K RPM FWIW.
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Old 07-21-2010, 04:49 PM
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I installed my V-Stacks and developed a low speed stumble at about 3000 RPM. When accelerating the RPMs would build until 2750 - 3000 then start to fall off until more throttle was given then it would pick up immediately. Since I have never made any jetting changes or tuned the carbs, I took the opportunity to do a little tuning. Found the pilot jets at 1.75 turns out and adjusted those to 2.5 turns out and synch'd the carbs. Found front carb was pulling 10hg more vacuum than rear, adjusted to spot on. Previously set TPS to 570 ohms.

Low speed stumble was nearly gone at this time but I continued my experiments by blocking off half of the K&N filter and found stumble went away. Now I have to find that OEM filter to put back in.

By the way, the new V-Stacks make a really cool grumbling noise!

Last edited by RWhisen; 07-21-2010 at 05:37 PM.
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Old 07-21-2010, 05:06 PM
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I'm pretty sure that the stacks will cause a lean condition, not a rich condition. I upped my mains one size before I installed my stacks, and I think I need to raise my needles one clip as well.
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Old 07-21-2010, 10:17 PM
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+1. Agree that a lean condition would be the result.
I thought the flo-commander would help more with richening up the main air jets, but I don't think they are made to substitute proper jetting, moreso just to give you an idea of where you are at. ( And isolation of the air jets for less turbulance.) I plan on shimming the stock needles .020 and see how that works.
I will also check the mixture screws as mentioned above.
Anyone else install stacks and flo-commander with stock pipes and jetting? Just curious if your results were the same? Thanks
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Old 07-22-2010, 07:01 AM
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I installed mine on the weekend. My experience was like revhead1957's. Throttle response is smoother below 4,000 rpm. The motor feels stronger above 4,000 rpm. I took it around a 120 kph. corner I know well. It went about 20 kph faster around the corner in the same gear and at the same throttle opening I used previously. Woo hoo! I recognize that a dyno run is necessary to establish an improvement and that my subjective assessment could be coloured by my reluctance to admit I threw money away by buying them. I can say with certainty that I encountered no carburettion problems as a result of installing the velocity stacks.
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Old 07-22-2010, 01:51 PM
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Originally Posted by Upland111 View Post
+1. Agree that a lean condition would be the result.
I thought the flo-commander would help more with richening up the main air jets, but I don't think they are made to substitute proper jetting, moreso just to give you an idea of where you are at. ( And isolation of the air jets for less turbulance.) I plan on shimming the stock needles .020 and see how that works.
I will also check the mixture screws as mentioned above.
Anyone else install stacks and flo-commander with stock pipes and jetting? Just curious if your results were the same? Thanks
That's exactly what the FC is for... Essentially it's about the equivalent of one jetsize larger or smaller at the very end positions on the adjustment screw... So No i won't really "solve" a jetting problem... It can fine tune what you have got, and it's a good "telltale" to see where you should go...
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Old 07-22-2010, 04:30 PM
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Appreciate the reply Tweety. I have not had the chance to give the flo-commander the full testing it deserves yet, and I am hopeful that further testing will help.
I think the stock mufflers are pretty restrictive, so my expectations are not grand. Eventually I will be able to afford some slip-ons which will then necessitate some minor carb tweeking, (shimming, bigger pilots, etc.) I feel having the V-stacks and flo-commander in place will be of greater benifit once this is complete.
As others have suggested the only real way to tell is a dyno run if you want to get close to spot on, it is tough for me to tell by seat of the pants.
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Old 07-22-2010, 11:00 PM
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I will be taking the hawk in on Monday for a dyno run and rejet I have before runs from the same dyno so should have some for you guys. before it goes in im going to check the tps adjustment and syn the carbs with the new VS installed the old runs are from two years ago but no new parts have been installed so we should get a good comparison. I am also going to have it weighed so i can find out the weight bias looking for 51% on the front
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Old 07-26-2010, 07:02 PM
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Just saw info on the DrHonda velocity stacks. Beside the fact that they look really cool and make a neat grumbling sound, what's the performance benefit supposed to be? I've got a full Moriwaki exhaust, DynoJet Kit, K&N on now and it runs fine (except for cooling problems I mention in another post).
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Old 07-27-2010, 06:19 AM
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The consensus is that there is a performance benefit. If you do a search using "velocity" and "stack" as key words in "titles only" and "at least 10 replies", you'll find a great deal of information.
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Old 07-27-2010, 08:39 AM
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Originally Posted by Stumpy View Post
I will be taking the hawk in on Monday for a dyno run and rejet I have before runs from the same dyno so should have some for you guys.
Any news on this? I'm curious to see a dyno charts before and after the velocity stacks.
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Old 07-28-2010, 12:51 AM
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Well got it their late on monday and they called today about something did not say it was done. I work nights and was already sleeping and it was closed when I seen they called. will call tomarrow but I dont like not knowing what they wanted. GF did not understand when i looked at her and said not now hun my hawk might be sick give me a few. just got that stuped look back. LOL will let you know what is up when I find out ok. if they tell me something when I talk to them I will post but wont have the sheets until I pick it up.
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Old 07-28-2010, 05:30 AM
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how could something go wrong with it? they better fix it is there actually is a problem that wasn't there before.
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Old 07-28-2010, 07:29 AM
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All they have done is put it on the dyno. I put the stacks on and the bike has been sitting for sometime. but I did store it right. Ran 4 tanks of fuel before i took it in.I just talked to them and they want the old stacks back so they can make a run and see if it is something on the bike or the stacks. Its down 7 hp and running rich. I know that some of you are going down a jet size witch makes sense but I want to make sure of the bike before so I can have a good evaluation of the stacks so off to Madison I go. I plan on rebuilding an engine had my heads done on a flow bench. Here is the place doing the work. http://motorcycleperf.com/ let you know what up when I do.

Last edited by Stumpy; 07-28-2010 at 07:31 AM.
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Old 07-28-2010, 07:35 AM
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too rich will for sure kill your HP, most car tuners I know try to ride right on that edge of below stoich to almost lean for the most power, not sure if it's different on carb'd bikes. good luck with figuring it out, jets are your main suspect!
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Old 07-28-2010, 10:40 AM
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Exclamation

Yep I agree so I drooped the old stacks off with an extra set of carbs in case I have a bad diaphragm or something. you can see running rich at almost all rpm range so maybe just a rejet will work time will tell.

These guys are good have no worries that it will get sorted out. Just hope I don't have to pay to much. Here is the dyno sheet with just adding the stacks. the only thing they don't have on the sheet is that I have a dyno jet kit installed with K&N air filter. I also adjusted the cam chain so maybe its to tight. adjusted so the noise stops when running - cleaned and re-oiled the k&n maybe to much oil restricting air flow ? told them what I did will know more later time for night night.
Attached Thumbnails DrHonda velocity stack re-jetting?-dyno-run.jpg  
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Old 07-28-2010, 10:53 AM
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holy snoop dogg is your midrange rich!
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Old 07-28-2010, 10:59 AM
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Originally Posted by nothing View Post
too rich will for sure kill your HP, most car tuners I know try to ride right on that edge of below stoich to almost lean for the most power, not sure if it's different on carb'd bikes. good luck with figuring it out, jets are your main suspect!
And that is where most folks go wrong with these bikes. They like to be a touch on the rich side. Tune for torque, not top end HP numbers and you will be much happier with the results...... but of course YMMV
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Old 07-28-2010, 11:03 AM
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WOW!!!! dropping below 10:1. There has to be something other than just the stacks there.

On the first and second runs... did you also change the exhaust?
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Old 07-28-2010, 11:04 AM
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Well that makes sense, never actually tuned the bike so I wouldn't know. I have mine a bit rich because I do a lot of hot weather riding, and the bike just loves it so I can see what you mean.
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Old 07-28-2010, 06:07 PM
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No the only change was the stacks. have not heard back anything today they might not look at it until tomorrow or they did and just don't know yet. But when I get the facts I will let everyone know what is up.

imho we will not see any improvement until the rejeting. Just ruling out any other problems form storage but don't think that was the case.
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Old 07-28-2010, 06:16 PM
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And when I (and others) told people that the velocity stacks would make it run rich people said it was impossible... I have seen that result before... Down one ot two sizes on the mains is the cure...
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Old 07-28-2010, 06:57 PM
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Originally Posted by Tweety View Post
And when I (and others) told people that the velocity stacks would make it run rich people said it was impossible... I have seen that result before... Down one ot two sizes on the mains is the cure...
It is funny how some folks just won't listen or think you make things up........lol
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Old 07-28-2010, 07:06 PM
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Uhum... That's right... I have a vivid imagination...
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Old 07-28-2010, 07:14 PM
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Originally Posted by Upland111 View Post
Interesting.
After installing new V-Stacks on a stock 05' with no pipe or jetting changes, I really didn't notice any differance good or bad, except for a very slight stumble when rolling W.O. from 3500 RPM at about 4000-4500. (Although I do not run WOT as a rule at this low of RPM). I then purchased the flo-commander and installed it and tried it at 3 turns out as suggested, no change good or bad. I have had little time to tune with the flo-commander but have tried various settings from 2 - 4 turns out from closed with little differance.
Could be that to really see the benifits of the stacks & FC, either a full system or less restrictive slip-ons, and or spot on jetting changes are necessary. Not disapointed as I do plan on Staintunes some time in the future, and more tinkering with the carbs. It's fun regardless.
BTW, synced carbs best for idle & 4K RPM FWIW.
Try a half-step washer on the needles. The stacks are a handful - forget fuel mileage - at least around town. The improved air volume leans the mix out when you install. Not a great amount but it's still there.

I had the same hesitation at 3500-4k until we installed the washers.
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Old 07-29-2010, 09:18 AM
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So I just talked to them for a sec as they are still working on it. but I was right with the K&N to much red oil they cleaned it and put a light coat of oil on it and it jumped up 7hp so much for doing it in the dark with my brother helping should always check someone else work but in the end its my fault for being in a hurry and not doing it my self. Blocked air flow makes it rich good slap to the back of my head would help. LOL will tell more tomorrow should pick it up then I hope.
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Old 08-03-2010, 08:45 AM
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Here is some stuff to look at They did a lot of work to the carbs 28 runs. The tech was not there when I stopped to pick it up I still need the hp / torque comparisons form 2006 until now. remember its had a lot of track days so have to take that into account. but something to look at. I think they will benefit my new motor much more as it will have the head work , higher compression pistons. I want to see how the torque curve pans out as i was thinking that would see the most gains. my best run that I know of was 103.8 hp but don't know about the torque. will let you know. calling them now.
Attached Thumbnails DrHonda velocity stack re-jetting?-dyno-runs-2005.jpg   DrHonda velocity stack re-jetting?-dyno-runs-2010.jpg  
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