Scorpions and Fuel

[Mick B]

Well I put my lovely Scorpion road legal cans on and they look so much better and sound amazing But my fuelling around 3-6000 rpm is poor .Any type of cruising in traffic is totally unbearable as it nudges back all the time or surges .Giving it a bit of throttle and all my power is there . I have whipped the plugs out and they look more grey than tan so I guess its running lean(any advice taken). I didn't want to spend extra money on jet kits but obviously my bike needs to be spot on and not surging etc. I have spoke to a few bike garages and they say it will be running lean but Scorpion say it shouldn't need dyno jetting.
I have been put in touch with a bike garage called dynobike in Maldon North Yorkshire and he said it will be lean in the midrange.He comes highly recommended and can fit a full dyno kit and rolling road the bike for £200 all in(book it in for 4 hrs).Does this sound like a good price.

Also has anyone overcome the same fuel issues and also heard of dynobike ?

Cheers
Chaps

[benny hedges]

i'd take a chance and say the mains will be ok as they're too big anyway std.
but try another 1/4 turn out on the idle jet and put another shim or 2 under the needles to raise them a bit.
should richen it up in the mid range.
a dynojet kit will set you back 70-80 quid unless you get one from jcmotors.com in the states, but you have to wait 2wks for delivery.
try lifting the needles first & see how smooth it is.
ive got round this before by sticking the needles in the chuck of my cordless and reprofiling them with wet & dry, but it's very trial & error and no going back once it's done.

out of interest, do you have a k&n filter on as well???
if you're thinking of getting one, look for a bmc 144/04 race filter instead
but then it will most definately want dynojetting.

*carb balance might be out a bit as well if it's uppy & downy & lurchy - worth doing anyway.

[Mick B]

The bike will be running on a stock filter not that bothered about changing it. To shim the needles basicaly adding extra washers to lift the needles ? If so where do you get them from. I don't mind paying for the dynoJet kit and rolling road session if my bike is then spot on.Plus local it's £50 just to balance my carbs. So paying for the kit set up rolling road session looks good at £200 all in. But I always like cheaper options :-)

[Stratman]

I have Scorpions on mine (with the removable baffles) and didn't need to do anything, even with the baffles out (which they always are, except 1 day of the year), so maybe it was running a bit lean already?

[benny hedges]

To shim the needles basicaly adding extra washers to lift the needles ?
yes m8


If so where do you get them from.
i would suggest taking the needles out, have a look at the outside and inside diameter of the shims fitted now, and go b&q and get some washers to suit - from them little pre-pack brass nut&bolt packs down the hardware aisle)


I don't mind paying for the dynoJet kit
make sure everything else is spot on before fitting a dynojet kit otherwise you're just adding to your problems by making it non-standard.


Plus local it's £50 just to balance my carbs.
probably better off buying your own set off ebay for like £20 and learn to do them yourself - from the info here it's a doddle.


So paying for the kit set up rolling road session looks good at £200 all in. But I always like cheaper options :-)

im(h)o you would be as well getting the bike near as damn it before going near a dynamometer otherwise it will end up costing you a small fortune and also piss everyone else off who's waiting to get on the deck lol.

might be something and nothing - try new plugs, check the air filter is good and clean, if it's a k&n wash and oil it, run the tank dry and try it on super unleaded ;)
and check back here in a bit when all the boffins are back from work lol, i haven't done a lot on my storm apart from smash it up and put it back together (twice lol) - just going off general tampering over the last 30yrs, but others here know these bikes inside out, far better than i do.

[Mick B]

This problem first appeared when the bike was standard when I drilled x4 holes in the end of the stock cans. The flat spot was a pain so I welded the holes back up and the problem went. Since putting the scorpions on and just a new clean stock filter the problem is back but a little worse With a lot more carb farts so it must have been very lean as standard.

[benny hedges]

are you sure its the carb popping and not a link pipe air leak???
worth having a 2nd look before you have to take the tank & airbox off to mess with the carbs.

those washers (shims) are 6mm OD and 3mm ID and approx 1/2mm thick.
so if you get some m3 nuts bolts & washers, they should be bob on.

put a diaphragm cap screw in the top of the needle retaining tube to pull it out.
check the diaphragms while youve got at them and be carefull you dont nip them when you put it back together - if they tear you're fkt lol!

good luck getting the standard spring back in

[Mick B]

are you sure its the carb popping and not a link pipe air leak???
worth having a 2nd look before you have to take the tank & airbox off to mess with the carbs.

those washers (shims) are 6mm OD and 3mm ID and approx 1/2mm thick.
so if you get some m3 nuts bolts & washers, they should be bob on.

put a diaphragm cap screw in the top of the needle retaining tube to pull it out.
check the diaphragms while youve got at them and be carefull you dont nip them when you put it back together - if they tear you're fkt lol!

good luck getting the standard spring back in

Deffo from the carbs as they are under the tank .Always had them with the twin just having a few more recently.Plus if it was just the exhaust joints it would cause the jerkyness on steady throttle. Do the washers need to be stainless and is it best to remove the carbs from the bike.

[benny hedges]

should be nice and dry in there bud - the original one looks like steel tbh or possible ally.
there won't be any corrosion in there so anything will do as long as it's right size.

unless you are extremely dexterous i would say remove the carbs - at least pull the tubes off and heater pipes so you can twist them round.
might need a stubby number 2 phillips.
the front diaphragm cap is hard to get at imo and you need to know you have sat the diaphragm down right without nipping it - making sure the lip goes in the recess proper.

i turned my diaphragms upwards and wedged the slider with a clean screwy handle so the slide doesnt go all the way down whey you pop the spring back in, otherwise it goes all the way down and the diaphragm comes out of it's groove.

you'll see what i mean when you're putting it back together!!

[Pete.L]

I had the same problem when the mid pipe gasket by the rear shock went.
Check that and the other joints for leaks first, it makes a big difference. 3-5 k is the start of your needle range. Do not go near them with emery cloth They are a little bit special on the twin. A 0.6mm washer to raise them a bit however is a good idea if you don't have an exhaust leak.
IMPO I'd steer away from a Dynojet kit if you can, they are pretty abrasive on the emulsion tubes and can shag your carbs prematurely. Also make sure everything has been put back together correctly around the air box/carbs. The VTR is normally quite good with an original filter.

Pete.l

[Mick B]

I had the same problem when the mid pipe gasket by the rear shock went.
Check that and the other joints for leaks first, it makes a big difference. 3-5 k is the start of your needle range. Do not go near them with emery cloth They are a little bit special on the twin. A 0.6mm washer to raise them a bit however is a good idea if you don't have an exhaust leak.
IMPO I'd steer away from a Dynojet kit if you can, they are pretty abrasive on the emulsion tubes and can shag your carbs prematurely. Also make sure everything has been put back together correctly around the air box/carbs. The VTR is normally quite good with an original filter.

Pete.l

Cheers Benny for the tips fella :-)


Pete

I didnt think exhaust joints would cause uneven running on a steady throttle If so I will check them first tomorrow morning and go from there.

Also I thought the dyno route was good as the bike would be set up on the rollers getting fuelling throughout the range.

[tony.mon]

Rolling road is definitely the best way to get your fuelling spot on, and a good operator will get every last little BHP from the engine.

But then if you change anything- ft a better air filter; change cans, add a full system- you really need to get it re-Dyno'd.

[sirch345]

This problem first appeared when the bike was standard when I drilled x4 holes in the end of the stock cans. The flat spot was a pain so I welded the holes back up and the problem went. Since putting the scorpions on and just a new clean stock filter the problem is back but a little worse With a lot more carb farts so it must have been very lean as standard.

Mick,
That is not normally the case, if anything Firestorms are set up on the rich side from the factory, not the other way around.

I fitted Scorpions to my Storm. Like Paul (Stratman) my bike has not suffered any flats spots and that's with standard jetting and standard air filter. Also as you say Scorpion say no re-jetting is required for a standard bike, so either a previous owner has re-jetted the bike or something else is not right IMHO.

Chris.

[Pete.L]

Mick said

I didnt think exhaust joints would cause uneven running on a steady throttle If so I will check them first tomorrow morning and go from there.

Oh yes!
I tried running on some 175's instead of the 180 and even though it went like sh!t off a shovelon the gas at steady revs it was surging everywhere.
Like Chris said, make sure eveything is correct before you start making any changes.
Oh and I haven't got a problem with Dyno tuning, it's just the shite Dyno jet needles I don't like

Pete.l

[tony.mon]

Slightly off-topic, but if a bike's had a DJ kit fitted to suit race cans and then the cans are removed from the bike before the sale, then sometimes the DJ kit's been removed too.

So far so good, you might think, but when the kit's installed you have to drill two small holes in the bottom of the carb slide, and those extra holes would make a difference to throttle response, even with standard cans and jets back in.

Wonder what difference it would make to the way a standard bike runs?

(The Factory Pro kit option doesn't need holes drilling, though, so no worries with that jet kit).