Hello guys

I've got a 4700 - 5000 rpm weird flat spot on my storm. It has devil cans, some after market air filter and factory kit. It was home jetted without a dyno. We tried 180 - 182 jets, 45 pilots and gradually raised the needles up to one position down from maximum to make it work.
The results were good - the bike opening up really nice after 5500 revs and running very clearly at 1500 - 3000 rpm at town speeds. This particular hesitation appeared in 6th gear (thus lots of wind resistance). It feels like a slight stuttering on constant speed and grabbing full throttle at that time makes it hick up and then clear off when it reaches ~5100 rpm.

We played with the needle position a little but it rather made it a bit worse. Any ideas what to try next?

 

Put the stock airfilter in there and consider trying one size larger mains... You are most likely gettin to much air in the midband and the needle can't make enough of a difference to compensate... You could just increas the mains, but it's likely you will need two sizes with an aftermarket filter (or more) and then you end up rich in other areas...

 

Sounds reasonable..
On the other hand, is there a chance that it gets a little too rich instead of lean at those revs?

 

I'd say it's unlikely (but not impossible) since the classic problem with whatever aftermarket filters is that they increase airflow... Something that according to all the makers including but not exclusively to K&N produces "free power for your bike"...

That's complete bullshit, but on some engine's it cures a flow problem... On the VTR however the engine doesn't respond well to getting to much airflow unless you start swapping out internal parts to take advantage of it...

The end result is a big hole in the middle of the revband, just as you have described... This is a classic problem with aftermarket filters on the VTR, and it have been discussed extensively on the board, search for K&N and jetting problems and you will find an encyclopedia...

 

So if I want to avoid tuning issues when my bike gets together, I should find an OEM filter? Mine came with a K&M one...

Also, are these an item I can purchase used, or should I order a new one from Honda?

 

Try it first. Yruyur's bike runs great with a K&N & no engine mods (just exhaust), mine doesn't. But if it doesn't run right after putting the bike together and syncing the carbs then get a OEM one. (I'd go new, unless you can find a very low miles one, filters get dirty by design)

 

Here are the hickups and hesitations I experienced on my bike, nothing close to what Gaz experienced however some of the things I found may help some of you improve cold air delivery.

I had a very nasty flat spot anytime I went more than half throttle to wide open throttle at any rpm. My bike ended up falling off my truck while I was transporting it and getting damaged on the front and left hand side. I figured while I am disassembling and repairing the bike, I'll fix the flat spot too since it will be down from riding for a while.

I removed the gas tank and top of the airbox to find a bunch of insulation and mouse turds. Would you believe our motorcycles make a perfect winter home for mice? What has seemed to do the trick for my bike was to first evict the mouse home to the circular file, the stock airfilter was filled with lots of insulation and mouse droppings so I replaced it with the K&N.

While I was looking at the airbox assembly, I observed how little air gets to the twin small nostril looking openings to the airbox. Everywhere around the airbox openings were restricted by plastic covers.

I removed the screws holding them there and now there is lots of cold air coming to the intake of the airbox. I also removed those restrictive nostril looking airbox openings by simply pulling it off since it was a pressed in rubber piece.

After that, I could look right at the aircleaner through the open airway after removing that restrictive device(gas tank removed).

I purchased my bike used 6 months ago and aside from the visible aftermarket exhaust pipes, could not tell what mods had been done to the engine aside from the mouse house...

While the top of the airbox was removed I drilled 3/4 sized holes on the entire top of it to even let in more air to the filter and engine. After starting my engine it was rough for the first few minutes while warming up but after it reached operating temp, I went from idle to W.O.T and it screamed up a fury, and throws a couple fire ***** when I return back to just above idle. A huge improvement from before, then again how many bikes become a mouse house...

It seems the factory blocked every possible way to get air to the airbox inlet except from drawing hot air from the engine. After looking at the blocked off design, that seemed to be the only way air gets in.

My conclusion to the issues my bike had (aside from the mice) after looking at and correcting the restrictive airbox assembly, any modifications to the exhaust, airfilter, jets and such will not deliver improved power due to the effort required to get the air to the airfilter. Our Superhawk V-twin engines are indeed a unique animal and mods that work for most bikes, only work for ours after lots of other modifications just like Tweety mentioned above.

 

The first one is a judgement call, lazn's suggestion is a good one... The amount of threads on these specific question give a hint about the most likely outcome though...

The second... Well... Some people buy their underwear used, so I can't tell you for 100% sure... But I'd never ever even consider a used filter...

 

Well... That might work for you... But as advice for anyone else tuning a VTR it's not a good thing... You post reads like a list of things not to do...

The holes in the airbox is 99% of the time a bad thing on a VTR... Same goes for making the inlet to the airbox larger in any respect...

Go read up on the forum and you will find out...

My advice, leave the airbox and filter stock unless you have already thrown a substantial amount on your bike in terms of swapped engine parts... You will not get any measurable gains in performance...

You will however get a changed character like madmatt describes... Lean in someplaces, and rich in others... Spits flames and feels to the buttdyno as an improvement since the hit comes at high RPM's after a thing midband... Not really optimal, and compared to a good tune his bike will be down on usable power...

Sorry madmatt... But your description is classic... That discussion is old news...

 

pull the crappy filter, go with a stock one, and sync the carbs. i had a similar problem that we threw tons of fuel at cause it felt like a lean issue, carbs were way out to lunch, synced them, removed fuel via needles, re synced and she runs awsome now. i only get an occasional sputter when its really cold out.

 

Fitted a stock-like airfilter and went for a ride. The problem is not cured - maybe got a little worse. It is now evident in lower gears also. At 4.5 to 5 k rpm grabbing the throttle hard and it stumbles before accelerating. On constant throttle at those revs it's terrible...

 

Well... Stock-like isn't stock... But that distinction only matters to you wallet right? Wrong!

Since you obviously have no idea if that filter flows more or less air than an OEM filter, I just have to ask... What was the point of that swap?

And since I have found no aftermarket filter, OEM copy or not that flows less, than OEM, I'm willing to bet it's still flowing too much...

As for advice on getting the bike going rigth... Start fresh, mains one size up from the equivalent to stock... My guess 182/185 or 185/190 and the needle somewhere mid-range... It will probably be better, but not perfect... There is no doubt in my mind that you are now feeding that engine more air and fuel than it can effectively use...

 

The filter I replaced looks like K&N. Not paper - Cleanable. Flat in shape. Can post pics if you think is necessary. The idea was that the cheapo paper copy filter now installed, flows less so maybe help understand if I have a lean or rich problem...