I am lucky, my 98 has no pair rubbish to worry about!

I have dedicated this Sunday to further experimenting. If I can't get it right after that it's dyno time. I can get it to produce bulk power, but I end up with a spot about 6000 rpm where it runs rough. With WOT you don't notice it at all, you are too busy hanging on, but under VERY gentle acceleration you can feel it. It you sit exactly on that spot, and then try to accelerate slowly it runs rough. Go to WOT and you're away.

I am guessing that it is the needle to main transition, but I have tried all needle and main combos I have with no luck yet. My main jet sizes only go to 190/195 (Dynojet) so I haven't been able to try larger than that yet. Going leaner reduces power and the problem remains so that is not the answer.

With my engine specs being quite unusual it is difficult to use other bikes as a guide. The answer is yet to be found it seems!

 

No, it's not the needle to main transition, but it does have to do with the needles, whether it be height or profile, I'm not sure. Partial throttle, even up to redline is pretty much all needle metering of fuel. The only time the mains come into play is when the carb slides are almost all the way or more open, and this is based on throttle position.

Shayne, have you tried the choke test yet? Try to reproduce the condition both with choke and without. If the condition improves with choke then you're running lean and you need to raise your needles one notch. If it gets worse then lower them.

 

I was thinking exactly the same as you, however the needle clip position doesn't affect it. I can tune it for power of course, but the glitch remains at all positions. I have a DJ needle. Thinking that the needle profile was perhaps the culprit, I contacted the Keihin parts distributor who tells me that adjustable Keihin needles are not available. The ones in the HRC kit are special order for Honda only apparently. So my only option for another needle as far as I know is to buy a complete Factory jet kit I think. Factory make more than one kit, so I can possibly get one with a richer needle.

But all that got me thinking. I don't remember other people having a problem with DJ needles, so perhaps that wasn't it. That's what got me thinking abot main jets. Your argument for the needles makes good sense though Greg. I was going to try to get some bigger mains to try, but you have me thinking it may be a waste of money.

I have not gone down the traditional route of cams, ported heads and 11.5 compression. I wanted a nice street engine with good throttle respnse and a nice torque curve. To that end I have standard cams, ports & valves. I have 10.1 compression ratio, and have focussed my attention on airflow. I have Moriwaki Ti headers and Staintune mufflers. I have also paid a lot of attention to air intake, such as the snorkel, inlet manifolds and inlet runners/trumpets. The theory being to maximise airflow through having efficient components rather than "big" everything. Apart from this glitch at a particular spot, the engine has exceeded my expectations. It has more grunt than I shall need mostly. I realise I have a different engine combo to most, and that may need unusual fuelling.

I will try the choke trick, and see if it does anything.

Does anyone have any experience with bikes that may have needed a different needle profile?

Anyone used the Factory stage 2 or 3 type kits? (I forget the Factory numbering system)

Any random thoughts would be appreciated too. It all helps.

 

Shayne,

I think you could probably call Factory Pro and get just the needles. I guess if they give you a hard time you could tell them you bought their kit and the needles have now got some wear on them so you'd like to replace them. I don't think it'll be an issue though. They should sell you just the needles.

I'd like to know exactly what you've done with the intake components. I have a feeling that your flat spot is coming from those mods. In particular, if you've removed the rubber snorkel at the front of the airbox, I really think you should put it back on and see what happens.

 

I am going to send an email to Factory Pro actually and see what they recommend for my bike. I will ask them if they will sell me some indivdual components and see what they say. To buy a whole jet kit in Aus is about $170.00. Not cheap. To get stuff from the US means I have to wait though. Oh well....

The snorkel is in place. If you have a look inside it you will see it is not smooth, it has "casting" type ridges in it which cannot be good for airflow. I have filled in the divots to give the airflow a smooth run. I have also modded the inlet manifolds, which are smaller in diameter than the carb body. I have port matched these to the carb size and port size as best I can, paying attention to them not being oversize of course. I also have an Aussie made Unifilter. This is considerably larger than a K&N in it's surface area, maybe an extra 30-40% at a rough guess.

And the last mod you won't like I am sure! I am convinced that getting extra air into the airbox is worth pursuing at the moment. If I can't match fuel to it I will have to revert to stock, but at the moment I have two additional air intakes as well as the snorkel. These two intakes are a proper airbox part made by Unifilter. They are essentially a rubber grommet with some pre-filter type foam in them. Each one has an internal diameter of about your finger (technical measurement there I know!). They are positioned right beside the snorkel in the airbox lid.

If I can't match fuel to my airflow I can simply plug these holes, but I would like to persist for the moment. I cannot see how a 1000cc engine can be fed by that snorkel. My Suzuki 650 has a snorkel not much smaller than it, and when you increase the size of it the performance increases dramatically. As the bike is injected it controlls the fuelling for you of course, wheres with the VTR it is up to me to get it right. My Suzuki now has an inlet larger than the VTR. Smaller inlet sizes reduce the performance. However I know you must compare apples with apples, and not oranges, so this must be proven to work on th VTR. Plenty of people have tried this before with recorded failures, however they have all been a bit rough in my opinion. Simply drilling holes in th lid or removing it entirely is not the right way to go in my opinion. I am happy to be proven wrong in due course. If I can find the answer then everyone will benefit. Ram air systems work, and they are simply a method of increasing airfow. Time will tell on this one of course, but I think if you are right and the needles are the problem, then it would seem that my mods are simply flowing more air than the current needles can keep up with. I would rather fix the problem with the needles if I can rather than reduce the air to match.

More experimenting!!!

 

Did you try the choke experiment yet?

Okay, this is what's on my mind.... I highly suspect the extra intake holes in the airbox are altering the airbox resonance enough to disprupt the airflow in this rpm range. The manifold porting and intake stacks will probably not affect the resonance, only the airflow. In concert with the choke experiment, try taping up the two additional holes in the airbox and see what happens. If this is a resonance issue then there's pretty much no way to tune it out with carburetion changes. Honda did a nice job on the airbox and in my many years of being active on this board or another I've not yet heard of any successful airbox mods on the VTR-F.

Additionally, if you're crafty, and have access to a lathe, you can machine the stock or DJ needles to suit your fancy. You just have to go a little bit at a time. Since you say this only occurs at part-throttle, I'd say if you determine that you're lean then taking off .5mm or so about 1.5cm up from the tip will help richen up that area. I'm not sure what the needle profile is for the DJ needles.

 

I have a few things to try actually. I haven't heard back from Factory Pro yet, but I have a friend who has a HRC jet kit which contains richer needles, so I shall try those out in conjunction with using drilled and undrilled slides and see what occurs. The HRC kit is interesting. The mains are very small, in the 140's & 150's in conjunction with closing the main air jet, and the neeedles are way richer, easily seen by the naked eye. They use one undrilled slide (factory holes filled) and one drilled one. My friend reports more power throughout the range, but less suitable to road use. More of a track mod he reckons.

As you sugest it is all too easy to close the extra intakes up if it is upsetting airflow. It is possible that the upset airflow is making it too rich, rather than lean as was my first thought, hence looking for other nedles. If it is the problem, at least I had a fair go at it!

Back to the shed for a few days it seems!

 

Well I have gone back to my best settings, and then tried the choke trick, which made no difference. So I blocked off the extra air intakes which also made no difference.

Got me stuffed if I know, and I have had enough of it, so it's off to the dyno I think!

As they say "you pay your money, you make your noise"

 

Wow! I'm really surprised that neither test resulted in any determination. That sucks, but it's always fun to go to the dyno. Make sure you find one with an exhaust gas analyzer, if available in your area. Good luck.

 

Part of the problem was trying to test it on the road. Under track conditions I may have made a better job of it. On my last test I had just slowed down from a roll-on test and went past a cop with a radar gun on me. With a bit of bad luck and a few more seconds on the throttle I would have lost my licence. Lucky!! That sealed it for me to go to the dyno. I have good guy near me so that is cool. Looks like he can do it next week.

 

well I adjusted the needles to 2 from the top and used the mity vac to approximately get the carbs synched... I believe they're still off and am thinking about buying some mercury gauges or finding someone real close with some... I appear to be running rich now though (or my synch is off enough to throw the bike out of wack). It is however running better then before and the wheelie test went pretty well.

I did finally do the smart thing and called and send in a question to erion racing requesting some recommended settings for my bike setup. I was told I'd get a call back once the tech's got a chance but figure what the hell it can't hurt to send it in electronically as well. Erion is a big enough company that I'd think they'd have a good idea as to what to use... I'd think... We'll see once I get a response