Dyno Testing the VTR

Mikuni use flow rate, but I'm not sure what Keihan use. Sorry.

It should be interesting. It is a pity you have ground the exhaust out. I would love to see some dyno charts on this mod. I was discussing it with Keith from Honda MPE a couple of years ago. He offered to do a before and after run on Honda's dyno, they just had to be in the Melbourne area. Unfortunately at the time no one was doing it.

Factory and Keihin use the same numbering system (unlike DynoJet, for example)

As I stated elsewhere, I think this will be interesting.

I do not know how much reading you have done on the VTR, but there is plenty on the net. Lots of people have tried this stuff before, and there have been lots of hours spent on the dyno trying different things.

No doubt because you can, you are going to do your own experiments. Lucky you! Plenty of us would like the same opportunity. It will be interesting to see if you can break new ground, or if you end up at the same conclusions as those that have gone before you.

I would like to tell you a couple of things though, just to keep in the back of your mind while you experiment.

Main jet sizes - you think they can be smaller, but nobody else has got this to work with the standard intake. I have 170 main jets, but I have different velocity stacks. Another guy with a dyno said exactly what you did, and he tried smaller mains to get the AFR right, but the bike ran like a pig when he rode it. The only way he got it sorted was to go back to the larger main sizes. His bike was stock like yours.

Snorkel - one squillion people (approx) have tried removing it to get more power. You may get more power on the dyno, but when you ride it you will get flat spots. Same thing with opening up the airbox in other ways, or putting in a larger filter like the Unifilter (K&N, BMC etc are all ok). The carby slides don't like it (personal theory). I had to go back to a more normal intake design to get a smooth power curve. It never showed up on the dyno run though. I can give you a set-up that will run 205 mains, 50 pilots, and will pull your arms out when you crack the throttle. But it has flat spots. The only way to get rid of the flat spots was to reduce the airflow. Now it rides nicely, but with less power.

So while you are have a go at it keep these points in mind. It might save you a bit of time while you are stuffing about. Keep us posted on what you come up with. With any luck you may figure something out that has not been tried before.

One last thing. I tried everything I could think of to get rid of those flat spots. Every jetting combo possible, including some impossible to find HRC carby components which I borrowed. So I came to the conclusion that it was the carby slides being effected by the airflow, and not operating smoothly. So I then tried to change things to see if it could be fixed. Changing the slide holes either way made no difference. The next experiment was the spring rates, but I never got there. I had just had enough of working on it, and after a few months I gave it away. I reduced the airflow a bit, went back down in my jet sizes and just started thinking about EFI instead. So maybe the slide springs can be changed to help with this problem. You have a Factory kit, which will not have replacement springs unless you bought the top line race kit. Dyno Jets kits have new springs as well. I had DJ springs in my bike, so maybe stock springs could work better, or some other springs from something else.

Good luck.

Here is the sheet. I think the printout is a little messy and I will make sure the next runs are better laid out. I would normally re-scale the power and AFR axis a little better but it was out of my control at the time. Having a better look now I can see the AFR is richer than 11.5, more like 11.0 for a while leaning back to maybe 11.4 up top. These are the sort of mixtures you would run with 20psi of boost in it! I remember reading Hymey's info in another thread regarding his work on injecting and turbocharging and he mentioned the same thing with the mixtures.

I am actually looking forward to running into issues with the jetting. It is all part of the fun of seeing how things interact and it keeps me busy on the weekends. I have read just about every thread on all of the forums regarding the tuning of these bikes, but if there is one thing I have learned over the years it is to never trust another mans work. If I dont do it for myself, then I cant trust anyone elses ideas and work.

Riding the bike as it is now, there are no flatspots or roughness. It rides quite well so long as I dont crack it open below 3000rpm. I did not notice any difference with the snorkel out, and I am tempted to put it back in but for now it stays out to keep the testing all under the same conditions.

Oh yeah, I removed the inlet restrictors too. I forgot to mention that earlier in the thread.

As for any flatspots that show up, I am more than prepared to carve my own needles if need be. But doing that will require running without the airbox to monitor the slide position. We will see. I may end up going the way you have said Shayne, and detune it slightly to keep things happy, but that is what adds to the enjoyment.

I don't know for sure, but mine had a K & N and it wouldn't run right (others have not had that problem), but with a jet kit and stock filter tuning was better.
Now it has a stock filter with the 'wall' removed and it was fine with debaffled OEM cans.
Since putting the custom exhaust on things have changed a bit, but the most noticeable changes are above 7000 rpm and I don't get up there much . . .
Cannot remember jetting and clip position - sorry.

Got the other jet today, and just spent a little time in the garage installing them. I found it not too difficult, with it easy to just lay the carbs on their side and do the swap in the bike. Then in typical Murphy's Law fashion, as I was opening the garage door to go for a test ride the heavens opened up and it came down cats and dogs. Damn it! It will have to wait until tomorrow if the rain clears up, and if so I might head to the dyno again.

Does anyone on here have a spare long velocity stack they are willing to sell, or donate to science. :-) I may target more bottom and midrange as I dont often rev the engine out anyway. I tried ordering one today but was told Honda are out of stock and I need to wait a few weeks.

I don't think it makes it any leaner. I have the stock filter with the baffle removed and my Storm is still very heavy on fuel (stock jets too).
Mine also had no velocity stacks at all in it for about 2 years before I realised they should have been there. Went out and purchased a set from Honda and didn't notice any difference on the road at all.

Same happened to me with Stage 1 Jet kit and High Rise Staintunes.
Went back to the stock filter and it was rideable again. Others have not had the same issue though so I dunno what else to add.

I should add that I used Factory Pro Jets, not Dyno Jet.
Perhaps that makes a difference?

With the FP needles anything richer than the 3rd slot from the bottom is too rich.

When fitting a K&N filter with stock jetting, shimming the needles usually does the job.

Any updates?

Some thoughts on the effects of the snorkel.

From my experience here, removing it has the effect of making the fuel mixtures richer. I would dare say that anyone that has jetted richer than stock, then tried removing it, would find the mixtures far too rich and power would be lost. It may be that I am still using the stock filter that stops any weirdo things happening too. I cant see any benefit at all for running an aftermarket air filter at this point.

One small thing we found on the dyno is that we had a hard time trying to get an AFR reading at low rpm from the RHS muffler. Moving to the LHS gave a clean signal. From my experience when this happens with the cars it is from reversion on one side of the pipe and we simply pivot the probe around 180deg and it cleans up the signal. On a bike the pipe diameter is small so this has little effect. It may be that the LHS still flows better than the RHS even though it has been cleaned up with the die grinder. So my advice if you go to a dyno is to make sure the AFR probe is placed in the LHS pipe to get correct readings.



Thoughts on how the bike is running now vs stock.

We even held the throttle wide open below 2000rpm and the motor was still smooth with solid 13.0:1 mixtures. On the road it pulls clean from any revs without chugging, and feels to rev out very cleanly. Stock it would occasionally lean misfire at low rpm if you opened the throttle too quickly. Even the exhaust noise has cleaned up and sounds alot smoother. But these are points that anyone that has jetted their VTR correctly will report.

Oh, I should put a shout out to S&R Pro whose dyno I have been using. Both times I have needed to use it I just dropped in and he did it immediately.

There was some part throttle running for short periods up to 6000 with AFRs in the mid 13s but I was not going to waste too much time doing half throttle runs to redline. The airbox is untouched and air filter completely stock because a can't see a restriction there IMHO at the power level I am at.