Carb; fine tuning question

[Tywaugh]

Hi Guys,

Spent many, many hours, getting my bike to this point. It is near perfect except for a small inconsistency that I can not isolate and hoping someone with more experience knows. Sorry for the long post, I am a bit of a perfectionist so I give as many details as possible.

Bike:
2003 SH with 12k miles (20k kms)
Yoshimura slip-ons
Elevation is sea level

Current setup:
Front carb;
- 45 pilot (fuel screw 2 1/4 turns out)
- 180 Dynojet main
- Dynojet needle 4th clip from top
- Brand new OE diaphram spring
- 1 lift hole on slide

Rear carb;
- 45 pilot (fuel screw 2 1/2 turns out)
- 185 Dynojet main
- Dynojet needle 4th clip from top + shimmed 0.020"
- Brand new OE diaphram spring
- 2 lift holes on slide

Misc:
TPS set to 435ish ohms
K&N air filter

I must also say I've tested this bike with approx 20 different carb configurations over the last 6k miles, everything from bone stock, stock needles, shimmed, stock air filter, stock mains, etc and slowly but surely made small changes, getting better each time until this configuration. This setup feels the strongest yet, and is near perfect. The last symptoms I fixed was a fairly noticeable flat spot in the mid-range when rolling on throttle aggressively, but pulled strong with slow throttle input. I plugged a lift hole in the front slide and installed brand new OE diaphram springs and this made a huge difference. It felt like everything came together and started working in sync, the bike pulls noticeably harder over stock configuration.


Last nagging issue:
Scenario 1; If you ride the bike for 10mins cruising at 3-4k rpm and you jump on the throttle; Ex. to pass a car, the bike pulls firm but not hard almost like it's a tad rich, however....

Scenario 2; If you are riding spiritedly with rpms always in the range of 4k - 8k on the regular like a curvy back road, the thing pulls very hard, it just wants to get up and go no matter the gear or rpm.

Scenario 3; There is a connection between the bike at cruising speed for long periods of time and not wanting to get up and "dance" right away so-to-speak when you get on it. If you roll the throttle on and off once or twice it almost feels like the thing is charged up and raring to go, then it's game on.


Final thoughts:
When there is a steady heavy flow of fuel and air in the carb there is an increase in performance. I am reluctant to adjust, fuel screw, jets, etc because it works so well any other time. What kind of symptom is this? I feel like if it wasn't dialed in well it wouldn't work as well as it does in Scenario 2. I don't even know what you would call a symptom like this.

I obviously want it to pull hard all the time whenever I want it to, and maybe that's asking too much from two very large, finicky CV carbs. Maybe this is a normal trait and something I need to learn to live with. I am curious if other riders know what I am talking about and have experienced/fixed it themselves. I can't remember if mine did this in stock form but I have ridden two other stock VTR's and they have similar symptoms, they only work their best when they are in "spirited" mode.

Thanks for reading!

-Ty

[Wicky]

Scenario 1; If you ride the bike for 10mins cruising at 3-4k rpm

What gear 6th? As that's an overdrive gear. Try changing down a gear to help it fill its lungs quickly and cleanly for overtakes


K&N air filter

Tricky to set up without repeated dyno runs by someone who knows the VTR - and while giving a boost at top end can cause a dip lower down.

viewtopic.php?f=36&t=28029

[Tywaugh]

Scenario 1; If you ride the bike for 10mins cruising at 3-4k rpm

What gear 6th? As that's an overdrive gear. Try changing down a gear to help it fill its lungs quickly and cleanly for overtakes


K&N air filter

Tricky to set up without repeated dyno runs by someone who knows the VTR - and while giving a boost at top end can cause a dip lower down.

viewtopic.php?f=36&t=28029

Hey Wicky,

Thanks for your reply. That's a good way to word it "Filling its lungs" that's kind of exactly how it feels.

Also not only in 6th gear, happens in any gear when cruising for a while. Could be in 4th gear for 5 mins and then roll the throttle aggressively and it will pull firm but not hard, but then you lean off the throttle then roll back on aggressively and there is an increase in pull. Like you say feels like its filling it lungs.

The thought about replacing the air filter back to stock crossed my mind. Through testing on my own I did notice an increase on the top end with the K&N filter and obviously I am trying to retain that but I will try the stock filter and test it again.

I also may try adjusting the fuel screw a little. I did notice after I plugged one of the lift holes in the front slide it took noticeable more force to push the slide manually by finger. You could feel the difference in vacuum. It greatly improved the flat spot mid-range issue, but now I am wondering if it went too far the opposite and maybe it's now too lean on the front cylinder, or still too rich. I will try tuning with the fuel screw a bit more.

[kenmoore]

I have a set up much like yours and experienced a similar problem that became worse over time.

It turned out to be the fuel tap diaphragm .

Just a thought.

[fabiostar]

bring it to a good dyno shop and they will save you months of heartbreak

[tony.mon]

I can't think of any advantage in having two holes in one slide and one in the other, as that will ensure they're out of synch when you open the throttle after cruising, until they settle back to slide lift under the new conditions.

[8541Hawk]

I can't think of any advantage in having two holes in one slide and one in the other, as that will ensure they're out of synch when you open the throttle after cruising, until they settle back to slide lift under the new conditions.

It's the way HRC set the carbs up. it has to do with the length of the velocity stacks.

[jchesshyre]

It's quite common to have slight oval wear to the needle jet, causing a 'wet' mixture just as the slide starts to lift, i.e. at 3–4k rpm. If cruising in this range for a while this could cause the symptoms you mention.

http://www.factorypro.com/tech/needle_jet_wear.html

and see the bullet-point just before section 4 in this http://www.factorypro.com/tech/tech_tun ... gines.html

[Tywaugh]

Hey Guys, thanks so much for the pointers. Gives me a lot more to look into which is promising. Some of the stuff I would never have though to check.

Scenario 1; If you ride the bike for 10mins cruising at 3-4k rpm

K&N air filter

Tricky to set up without repeated dyno runs by someone who knows the VTR - and while giving a boost at top end can cause a dip lower down.

viewtopic.php?f=36&t=28029

Tested the bike last night with the stock OE filter and it ran worse in all aspects of the rev range. More sluggish, didn't pull as hard, felt soggy. My bike definitely feels setup to run the K&N better. I've always felt the stock filter addresses the low range flat-ness because the bike is known to run lean on the low end and the stock filter would create more suction through less flow therefore increasing more fuel draw to fatten up the bottom end where needed. Just a theory...

I have a set up much like yours and experienced a similar problem that became worse over time.

It turned out to be the fuel tap diaphragm .

Just a thought.

Never would have thought that! but it makes sense and I am going to investigate. Also I do kind of sort of remember seeing some seepage around the 8mm fuel shut off last time I had the tank off. I really think you could be onto something. I had the fuel turned off and on 25 or so times and It feels tight and squeaky every time I do it. Not sure if that's normal but that info is helpful. Thank you!

bring it to a good dyno shop and they will save you months of heartbreak

I agree! I am looking into that now.

I can't think of any advantage in having two holes in one slide and one in the other, as that will ensure they're out of synch when you open the throttle after cruising, until they settle back to slide lift under the new conditions.

It's the way HRC set the carbs up. it has to do with the length of the velocity stacks.

And I learned that from your post on carb setup. Very informative and helpful! Plugging one lift hole on the front carb with new diaphram springs is still one of the most noticeable improvements I have made to my bike.

It's quite common to have slight oval wear to the needle jet, causing a 'wet' mixture just as the slide starts to lift, i.e. at 3–4k rpm. If cruising in this range for a while this could cause the symptoms you mention.

http://www.factorypro.com/tech/needle_jet_wear.html

and see the bullet-point just before section 4 in this http://www.factorypro.com/tech/tech_tun ... gines.html

This is terrific information! Thank you! My bike is fairly low kms I am hoping nothing is too worn yet but I will look more carefully next time they are apart. I don't know how I haven't found that info before. It's some of the best I have seen yet in regards to CV carbs.

[VTRDark]

First off what a really well written and explained post.

I obviously want it to pull hard all the time whenever I want it to, and maybe that's asking too much from two very large, finicky CV carbs. Maybe this is a normal trait and something I need to learn to live with. I am curious if other riders know what I am talking about and have experienced/fixed it themselves. I can't remember if mine did this in stock form but I have ridden two other stock VTR's and they have similar symptoms, they only work their best when they are in "spirited" mode.

There's is some logic to this. Usually getting one area perfect on these bikes is at the sacrifice of another. It's not like fuel injection where electronics can adapt to the surrounding environment and CV carbs are bit of a living beast that seem to have a mind of their own. You will probably notice slight differences in behaviour whether the bike is warm or cold, whether the weather is dry or wet, hot or cold. The 3-4k range could be a cause of the K&N and putting a standard filter in may help with that but then you may find this then affects the top end.

These bikes generally don't like to plod along at lower rev / speeds and are more comfortable cruising along at a slightly higher rev where things are more responsive. This doesn't mean you can't cruise along at lower revs and use the torque but don't expect it to be quite as responsive as it would be slightly higher up. Obviously which gear your in makes a difference to this too.

Sounds like you have done a pretty good job getting things running to your liking by feel. If you really want to know how good things are and where your at then as has been mentioned get it on a dyno run, see what the fuelling is doing. The problem is once one starts tinkering with carbs it can become an addiction and constant niggling trying reach ultimate perfection and one ends up chasing their tail. You change one thing and it ends up upsetting the balance requiring another change elsewhere. To get things running absolutely spot on throughout the complete rev range in any gear is like trying to reach nirvana. No easy task and then the weather changes and things start behaving slightly differently again. One could go out for a ride on a nice hot sunny day and things behave great but when riding back home in the evening when things are a little cooler you may find the bike runs even better or vica versa. It's one of the things that makes these bikes little more exciting. They are not a stagnant set it and be done with it and will stay that way, they change according to the surrounding conditions rather than adapt and work with them. That's carbs for you.

Something else to consider is when ones goal is more performance then things are a lot more temperamental and not as reliable. For everyday run of the mill riding then usually this requires a little softening and lack of performance with the advantage of not being as temperamental and more reliable. If that's what your after then put everything back to standard just as Mr Honda intended. If you going to chase performance then be prepared for it to have a knock on effect elsewhere and constantly making little changes here and there.

[Tywaugh]

The problem is once one starts tinkering with carbs it can become an addiction and constant niggling trying reach ultimate perfection and one ends up chasing their tail. You change one thing and it ends up upsetting the balance requiring another change elsewhere. To get things running absolutely spot on throughout the complete rev range in any gear is like trying to reach nirvana. No easy task and then the weather changes and things start behaving slightly differently again. One could go out for a ride on a nice hot sunny day and things behave great but when riding back home in the evening when things are a little cooler you may find the bike runs even better or vica versa. It's one of the things that makes these bikes little more exciting. They are not a stagnant set it and be done with it and will stay that way, they change according to the surrounding conditions rather than adapt and work with them. That's carbs for you.

Something else to consider is when ones goal is more performance then things are a lot more temperamental and not as reliable. For everyday run of the mill riding then usually this requires a little softening and lack of performance with the advantage of not being as temperamental and more reliable. If that's what your after then put everything back to standard just as Mr Honda intended. If you going to chase performance then be prepared for it to have a knock on effect elsewhere and constantly making little changes here and there.

I appreciate the feedback and I totally get what you're saying. My bike was so far off the mark when I first got it (K&N, jetted way rich) that I didn't know where to start and small changes seemingly made no difference at all. Once I got all the parts to return to stock form, it wasn't until then that I could start making changes and feeling positive results which led to the addiction of reaching ultimate perfection/performance, haha.

I also agree, tuning with high performance in mind can create a sensitive tipping point where one day or morning things work fantastic and the next day or afternoon things can work not as great. I feel it is expected when tuning for high performance you create higher maintenance but I do enjoy tinkering however it can become obsessive My last bike was an 05 600RR and fuel injected however really loving the v-twin now that it's coming together.

Take care,
Ty