Sluggish throttle response under 4000rpm

[Steve.Storm]

Can anyone help?

When up to temp, whether its in neutral at idle, pulling away or accelerating in any gear under 3-4000 rpm the throttle response is sluggish or very laboured, and the engine judders violently if I go to open it up quickly. I have to make very gradual throttle movements to pull away or accelerate. After 4000 the throttle is fine and accelerates normally. I also think the mixture might be a bit rich, as it smells like the choke is on when it isn't.

Could this be caused by having a too rich mixture?

Thanks

[VTRDark]

Have you recently over oiled an airfilter by any chance.

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[Steve.Storm]

Have you recently over oiled an airfilter by any chance.

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No I have vacuumed the dirt out of it a while ago but not oiled it, the 2 small odd shaped holes under the main filter are missing their mini filters, but I can't recall them ever being there.

[darkember]

If you are using a K&N then they should be blanked of with blanking plugs that come with the K&N filter

[Steve.Storm]

If you are using a K&N then they should be blanked of with blanking plugs that come with the K&N filter

I'm using standard filter.

[VTRDark]

OK so your using a standard filter if your giving it a hoover There should be foam filters in corners of the airbox as crap can get sucked into the carbs. Mostly behind the diaphragm but small particles can get through the slide lift holes and sucked into the engine.

You mentioned it smelt rich. Is you choke operating properly and not got stuck. Maybe it would be worth stripping the carbs and giving them a good clean out, especially as your missing the foam filters. It's also a lot easier to remove the choke cable with the carbs off and give the cable a good lube and the ends that go into the carbs. Be careful with the Black plastic nuts at the carb end as they break easily and have a very fine thread. I find it best to unclip the rubber elbow on the cable off them first before undoing.

Get some foam in the corners of the airbox. You can gett sheets of filter foam on EBay which you can cut bits out to fit. You will have loads left over for another day or some other purpose. Or pop into an aquarium shop and buy some small filter foam. It doesn't have to be anything special all they do is filter the ambient air to the back of the carb slides but they do stop crap getting into the carbs.

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[Steve.Storm]

Thanks for the info, is there a particular thickness of foam I should look for?

As for the carbs/choke, the choke seems nomal as there is an obvious difference when pulled out and put back in. I have stumbled accross your excellent thread on the fuel mixture screw, I have seen the tools etc for it, I was wondering what screw head it takes? I've a feeling it could be the problem.

Thanks

[VTRDark]

No particular thickness to the foam as long as it stops fine particles getting through and allows air through. Obviously you don't want something hugely thick as that would just be silly and could cause issues with the fit of the filter over the top. Try and get something as close to the original as possible give or take a bit. Anything is better than nothing.

Fuel mixture screws are a small flat head. Not easy getting access to them and takes a bit of practice, especially the rear as one af the carb coolant hoses gets in the way a bit there. The idle drop procedure also take some practise. If it's smelling rich and the choke is working fine then try turning the fuel mixture screw in a 1/4 turn at a time. If you want to verify if it's running rich or lean you can use the choke as a test. Pulling it out richens up the mix. Only pull it out ever so slightly though or it will just flood.

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[Steve.Storm]

Just to confirm they're the little brass screws pointing vertically down?

[VTRDark]

In the middle alongside the float bowl. Looks like a crosshead screw but is not.





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[Steve.Storm]

Thanks for your help on this, and the photos too. I managed to make my own tool from an old screwdriver and the vice, but I think I might invest in the real tool, as its still not quite right. I also worked out I'm running on about 25 mpg, so something isn't right.

[VTRDark]

Photo's courtesy of Seb
http://www.vtr1000.org/phpBB3/viewtopic.php?f=9&t=25177

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