Spitting back through carbs

[Mr_Rusty]

Hi all,

What exactly do the little secondary filters in the airbox do?

As far as I can see they have absolutely no effect on mixture as they are blanked off from the air box, am I right in thinking this?

If I am, then running with or without them should have no effect on the mixture at all, correct?


Next question, what effect should the intake horn have on the Firestorm (apart from stopping water entering in a deluge as we have had recently )?

I am battling with low speed backfire through the carbs at the moment and starting to get annoyed.

I have 3 air filters and 2 airbox tops to play with.
The air filters are standard (a little dirty but should be serviceable), what looks like a K&N, and a Pipercross. One airbox top has the air intake horn fitted the other does not.

My setup at the moment is almost standard Dynojet setup; 180 mains, needle in recommended groove with washer under the clip, Pipercross filter, and ART ProII cans with baffles fitted (like to keep baffles fitted if possible as its just too loud without them).

The bike runs superb at anything above about 4k rpm so this leads me to believe that main jets and needles are ok, however below this it will spitback through carb, getting worse as the revs get lower, making town and slow riding (esp in wet) hard to dangerous.
If I run with choke out at low speeds it is a LOT better, useable to be honest, but I dont always remember to shut it off when I open up and to be honest I should not have to do this.
Is it purely a case of tweaking the idle screws, if so whats recommended (please don't suggest a lot of fiddling with the screw as I have to take the carbs off to do it and am getting far too good at doing that ;) )

Also why if the filters and intake horn really should not have that much an effect does my bike run so bad when I install them?

Taking my base set up as above and changing only the airfilter/secondary filter/airbox top all jet/needle/exhausts remain same:

1. Standard air filter + secondary air filter + top with intake horn.
Good low speed, no back fires. Will not pull at anything more than about 4500 rpm just shuts down until I back off.

2. Pipercross air filter + secondary air filters + top with intake horn.
Almost exactly the same as above maybe a bit higher revs but not much.

Why should this be?

The only reason i can see for number 2 is that with the intake horn fitted its a bitch to get the airbox top on and the filter is being displaced somehow.

Note that to change the filters i am not removing the tank only pivoting it.

I do have more trying to do (for instance using the K&N rather than Pipercross but would like some comments first.

Sorry for the rather massive rambling post but I am getting disenchanted with these bikes atm due to this spitback problem.

Your thought, comments, insults happily received.

Cheers

Chris

[storminateacup]

Sounds like it's running weak. A lot of people have problems with K&Ns.

[Beamish]

A common problem. Its definately a card filter can combo that is causing it but I dont think you completely erradicate it with the best set up. ut back to standard inc can then sort the lack of revs. One by one introduce other combos after getting a smooth run with standard.

[kevg]

if you do a search you should find a few topics on this, i had a K&N on mine with a dynojet kit plus blu flame end cans and the fueling was spot on, the guy at the dyno took out the frame spacers either side of the head stock and this gave an instant 1hp gain, the bike ran like sh1t at below 3.5k revs, would try to stall, wouldn't pick up when you opened the throttle, backfired through carbs etc when trying to manouver slowly.
a good few people on here (myself included) have gone back to the standard filter and it almost completely cured the problem.
i'd like to get it back on a dyno with someone who knows storms and get it set up right eg jets, pilot, K&N but that won't be this year i think.

the K&N comes with caps to block off the two smaller sub filter ports below the main filter, i can't remember what they are supposed to be for, i think its some form of breather.

[Mr_Rusty]

Thanks for replies so far.

I can't go all the way back to standard as all slides I have are drilled as both sets seem to have been dynojetted so I have no standard parts at all.

I have tried a standard filter but it just made things worse for some reason, was ok around town but as soon as throttle was opened nothing.

I have tried a search but the php:bb search facility is not the best in the world as the logic does not work (same prob on my own forums so its common).

I am not actually running the K&N atm but the Pipercross which I thought were supposed to be better.

What I want to know is do those silly little filters actually effect carburation (cant seem how myself as there is no link to airbox from them)

Cheers

Chris

[yellowstorm]

I had exactly the same problem (see carb issues top of pg 2 under Bike Chat on this forum)
Although putting a standard filter made the bike run much better, it never really solved the problem.
Ended up flogging the bike and buyin another storm (chepaer than getting a dealer to sort it and I lost no money).
Save alot of time and effort by grabbing some used carbs off flebay (bout £30 - £40), strip em, clean em and whack em on. At least then you will have a standard benchmark to work from as it appears your carbs have had a bit of fettling. You can always flog them again afterwards

[Max]

My storm has almost the same setup as you.

I have a dynojet kit fitted a K+N filter the same cans as you and I run usually with the baffles in as its still sounds good. I run 2 small stacks in the air box instead of one of each. I still have the inlet thingy as well as I was told not to remove it. It runs super sweet from tick over and pulls all the way to the rev limiter. On Rogers dyno a couple of years ago it was giving 104 at the back wheel and the graph was very flat the usual storm dip was gone completely. I do run lower gearing which would help disguise things but i also weigh about 20 stone which wouldn't. The only time it runs rough and spits is when the carbs need balancing which is fairly regular but easy to do.
Sorry this has probably not been of much use, when I first strated balancing the carbs I was using cheap vacuum gauges and they were little use. I have expensive ones now and you do notice the difference.

[sirch345]

Iirc Stormin Ben had a Pipercross air filter on his Storm, he said it was not the easiest filter to get the fueling right . Once it was set-up properly on the dyno it was very good but took a fair few runs to get it right

Chris.

[Mr_Rusty]

Glad to say its almost completely sorted as far as I am concerned

All I did was take the mixture screw out to 2 1/2 turns.

I still get the odd fart through carbs but its definately rideable in town town now (and mosoons like we been having lately )

Possibly running a bit rich on idle but that I can put up with. Only problem now is my fuel consumption is going to get a lot worse now as I also fiited new chain and sprokets and new rear tyre and along with the improved ride I can start to really have fun .

Thanks for all the replies as well.

Chris