Carb confusion

[firemink]

Hi, I have a 2003 storm. Completely standard apart from CCT stopper mod which I did before Christmas.Bike runs fine. Recently I have noticed carb cough and stumbling at around 2000rpm. Read the threads re carbs had carbs balanced. New air filter, plugs, checked all pipe work on air box. If anything the new air filter honda one made it worse especially in this cold weather. Did a blip test and see that the revs hang at precisely 2000 rpm so I am sure it is running lean. Having read the carb guides it appears to me that tuning carbs is a black art so I am a bit nervous about messing with the fuel mixture. Questions the fuel mixture is set a factory so why would it change. Does the TPS mod apply to my model F3 model. Any help and suggestions would be appreciated. There is a dyno at Bude Ace motors but I do not know if they are any good. Could live with it I suppose and hope warm weather will improve things. Thing goes like a rocket from midrange! Thanks..

[Wicky]

You could raise the idle to 12-12500 to lessen the chance of stalling cos of carb fart. And then look at correcting the TPS.

[VTRDark]

If anything the new air filter honda one made it worse

First off you can't just go and change an airfilter from a more free flowing filter or more restrictive filter and not expect to have to make any changes to the jetting/mixture. There is the off chance you could improve things without changes if the jetting was not accurate to begin with. ie you start off with an overly rich setup, then go and put a more free flowing filter in which then leans it off to a more balanced mixture and improves performance. The opposite if putting a less restrictive filter in, if the setup is overly lean to begin with then, putting a less restrictive filter will richen it up and balance things out.

If anything the new air filter honda one made it worse especially in this cold weather.

What filter did you have previously. Have just changed an old dirty standard filter for a new clean one or changed from an aftermarket filter like a K&N or something? If you had an old clogged up standard filter and put a new clean one in then you have slightly more airflow which will lean it off a tad. If you had a more free flowing filter then you have richened it up by putting the less restrictive standard filter in.

So from your statement above putting the standard filter in has leaned it off more, so I'm guessing you had an older clogged up/dirty standard filter in and have just replaced it. Which coincides with the rev needle hanging. Can be tricky sometimes to determine whether it is lean or rich so you may want to pull the choke out a fraction 1/8 to 1/4 out. The chocke is actually an enricher and adds fuel to the mix, so if things improve then you are running lean, it things get worse then it's either OK or running rich. Best to do this once the bike is at it's full operating temperature.

Did a blip test and see that the revs hang at precisely 2000 rpm so I am sure it is running lean

This suggests that the mixture is not right. By turning the mixture screw, which technically is a fuel screw as it controls fuel flow like the choke, out (anticlockwise) it enriches the pilot circuit, and by turning inwards (anti-clockwise) it leans out. This not only works on the pilot circuit but throughout the range but less so. It's mainly for the pilot circuit.

if you are indeed running lean and there is a very noticeable hanging before it drops down to idle then 1/2 turn out on the mixture screws should fix fix this. And also compensate for the new airfilter that has leaned it off.

Questions the fuel mixture is set a factory so why would it change. Does the TPS mod apply to my model F3 model

Everything at the factory is set for best emissions and not performance with the standard factory setup. As soon as you change things like aftermarket airfilters or exhaust then this is going to alter things. Not to mention changes in weather, altitude or wear and tear. The TPS yet again is set accordingly to best emissions. Adjusting this will improve things also and will help the low speed running and idle. The TPS is the same no matter what year the bike is.
http://www.vtr1000.org/phpBB3/viewtopic ... or#p222504

Remember that none of these changes are destructive and you can always go back and set things as they where previously if you wished to do so. Just make a note of what the TPS is set to originally before making any adjustments. The same with the mixture screws, make a note of how many turns your adjusting by.

I would suggest turning your mixture screws 1/2 turn out and see if this improves things. The problem is, to adjust them is tricky without the right screwdriver and even then very fiddly with the carbs still attached to the bike. So far more easy and more accurate to remove the carbs. While the carbs are off, one may as well set the TPS.

Sounds scary but in reality it is really easy. If one is capable of doing a stopper mod then one is more than capable of removing carbs or stripping them down to clean. The TPS can be a little fiddly but is not difficult, just time consuming trying to get it as accurate as possible. The problem is one loosens the screws to adjust, and when you tighten them back up it moves. So you have to find the point for example 487 (I just picked a random number there) so that when you tighten the screws it moves +13 to within spec of 500 plus or minus 10.

Me personally once the carbs are off would also strip the carbs down and see what the jetting set up is and what exactly is in there. Is it as standard? is it an aftermaket jet kit or a mix of both? etc and while in there give all the passageways a blast out with some carb cleaning spray.
http://www.vtr1000.org/phpBB3/viewtopic ... 77#p214203

A couple of other things to check which I forgot to mention in another post yesterday that can cause bad running and carb farts. Make sure you have no intake leaks either around the rubber seals that attach the carbs to the inlets and where the airbox sits on the carbs. You may also want to check that all the breather hoses are attached correctly to the airbox. The front ones can be a bit awkward. You should be able to just get you finger underneath the round bar that runs across the frame and feel the hoses underneath the airbox.

If you have the later updated model VTR then you may also want to consider doing a pair removal. There is a link here somewhere. Sorry I haven't the time to search for it right now, but I will find it later and post here for you. There's also lots of info on the Superhawk site regarding PAIR removal. The PAIR system is just an added restrictive emission control that was added to later models. There's no harm in removing it.

Hope that helps.

So what filter did you have before putting the standard one in? And what exhaust are you running and with or without baffles?

Dam that took ages. Got stuff to do now

(:-})

[firemink]

Wow thanks for prompt and detailed reply. The bike is completely standard, standard pipes air filter etc. all I can think has caused this is changing from old dirty standard filter running rich to a new clean standard filter causing it to run lean. Will a dyno run help determine exact diagnosis. Do I have to buy a special tool to adjust fuel pilot or is there something else I can use. Don't really want to strip off everything to get at carb unless I really have to. Thanks again for all your help and advice.

[VTRDark]

I've just PM's you. But in answer to your questions here yes a dyn run will tell you what's going on whether it's rich or lean and whereabouts in the carb circuit it is. It wont tell anything to do with the TPS. As you have everything as standard and I'm presuming it has the standard jetting as well. I would suggest adjusting the TPS and just turn the mixture screw out 1/4 to 1/2 turn out. There are specialist carb mixture adjusting screwdrivers but it's still fiddly.

Removing the carbs is dead simple it should take you no longer than 20-30 mins for the first time. After you have done it a few time it would only take 10-15 mins. The worst bit is undoing all the screws in the airbox.

http://www.vtr1000.org/phpBB3/viewtopic ... 22#p223894



(:-})

[firemink]

Thanks for all your help! TPS mod next on the list, then off to the dyno!

[BigVeeGrin]

Go for it - carl is king of carbs and previously from his advice I had mine out, stripped and cleaned, and if I can then anyone can

[VTRDark]

Carlos Carbs it's only 2 CC's I wouldn't call me king of carbs but I have a fair bit of theatrical knowledge. they still mystify (I think that's the word) me a bit at times and I'm persistent. It's definitely an area I take an interest in.

Here's the link to PAIR removal http://www.vtr1000.org/phpBB3/viewtopic ... ir+removal IIRC There should be an extra hose from the carbs and attached under the airbox that I have not mentioned in my carb removal.

(:-})

[lloydie]

I like Carlos the hippy more :-)

[VTRDark]

So do I, it's more realistic, just leave out the X in front of hippy. eh, hold on, once a hippy always a hippy at heart. Well, new age hippy, I'm not that old.

Peace brother

(:-})