COBRA 6-6 On a UK Spec Bike

[Valklee]

Firstly my bike is a 97 and relatively new to me, only had it a few weeks

In the UK we apparently have a different spec, on the carbs we have Heaters, and the Main jet is 78 and slow 35

Currently I have the OEM exhaust on, but on the left side is a US silencer (larger piggies) and on the right an EU silencer ( smaller piggies)
I can only assume that internally the baffles etc may be different also, and the back pressure probably is as well !

Having removed the Carbs I checked the Jets, they all had 78's & 35's, but the pilot screw settings were set differently
on the left is a US Silencer and the pilots are set at 2 -1/2 turns out, and on the right side (EU Silencer) 3 - 1/4 turns out.

Does this sound right to you?  . . . do the EU / UK exhausts need to be set at 3 - 1/4 turns out ?

It has been running OK, no complaints there, starts straight away, no apparent problems apart from the throttle response is a little sluggish until it warms up

I have a brand new set of COBRA 6-6 to go on early next year, Can any one who has successfully fit a COBRA 6-6 in the UK, tell me

1 how many turns out to set the pilot screw ?
2 is the jetting as stated OK to use ?
3 Does adding an extra shim on the needle make any changes ?

using the Carb Jet Kits online Calculator, they say I should be using - six Main jets size 105 , six Pilot jets size 38 and 2 shims for each Slide Needle ?

Any other help or advice will be very much appreciated

[Bagger John - #3785]

The one thing I'd check is the cam profiles between U.S. and UK-spec bikes.

Tuning parameters for my '99 CA-model Tourer w/ 6x6 Cobras: Cobra jet kit (38 slows; 105 mains); needle clip 2nd notch from top (their adjustable needles were used) and idle screws were 2 1/2 turns out and stock air filter. The bike was running optimally with this setup.

I wanted quiet and went back to the stock exhaust. Jetting was not changed and the bike runs exactly as it should.

[steveB (VRCC UK)]

USA and UK both 2.25 turns (as workshop manual).
USA 48 state and UK use same camshafts. (14120-MZ0-670 left & 14110-MZ0-670 right)
Cobra's lose about 6 to 10 hp. Best tune on a dyno.
Lot of Valks in UK and Euroland drop by our FaceBook site.

[steveB (VRCC UK)]

As you have a UK bike, I take it you've checked the pre-filter is intact in the airbox lid. Runs super lean without it. Cured by gluing a piece of air filter foam (100x100x10 mm) back in or a piece of bath sponge if you're cheap. BTW 38 pilots way rich with shimmed needles.

[Valklee]

I take it you've checked the pre-filter is intact in the airbox lid. Runs super lean without it.

Well it was partially intact until I gave it a poke with a finger and it totally disintegrated into a powder, so removed the whole thing, have replaced as you suggested with a 10mm filter foam

[Valklee]

I take it you've checked the pre-filter is intact in the airbox lid. Runs super lean without it.

Yes I added the filter as shown below, the engine did not like it . . . . It started OK, but once it began to warm up and turn off enricher, it ran very sick with clouds of smoke. Removed it and was back to normal running, so can only assume it made it far too rich ?

[-mike-]

That's WAY too much filter foam.

You have to use closed cell foam in dimensions 10x90x110mm



If you want to use the Cobras, you have to remove this foam and rejet to US specs(keeping the 35 slow, some say 38 and 100-105 Main jets)

Running Cobras  on EU stock carb and foam in air filter lid will be way too lean.

As you told you have two different exhausts, I'd recommend removing the smaller piggies on the EU silencer and rebuild it to the US pendant on the other side.
35 slow,100 main, no foam in lids and you'll get the best performance achievable, hands down.

Cobras will loose 6HP at least., You may not notice as your setup ist not Optimum ATM (to be polite...)

-mike-

[steveB (VRCC UK)]

Whoa - that looks like 30mm thick. Slice it down with a bread knife job done.

[Valklee]

So its not acting as a filter it's basically restricting/reducing the intakes air flow ?

[steveB (VRCC UK)]

Yep restricts amount of air entering airbox. Allows leaner main jets. Most deteriorate in a couple of years keep an eye on it. Usual sign - bits of foam on top the air filter.

[Valklee]

OK, so I added some 10mm foam, will see how that runs now !

[Valklee]

Just goes to show just how much a difference changing the airflow into the airbox can make to the running of the engine

Thought I had it all running well with the tank off, as soon as I replaced the tank, 1, 3 and 5 started to play up and missing which required all pilot screws to be taken out by a further half turn, this now matches the pilot screw settings i wrote down before I took the carbs off for a good clean.

Going to check today all 6 cylinders with a gunson colortune to see how far out I am, will then have to do another Carb Sync if I need to make any changes to the pilot screws.

So far the new digisync appears to be worth the money in getting the carbs in balance, makes setting up much easier, the results achieved can be seen below.



It's nice to get it all running so smoothly now, but i know once i put the Cobra's back on I'll have to do it all again . . . . Oh Well it's all a learning curve !!!!

UPDATE 17:30
Checked it with the gunson colortune and it all seamed OK, will take it out if it stops raining ?

[Valklee]

Thought I would add a video showing how well it is now running
Throttle response is great and the idle is superb, well worth all the effort to get it running as best I can
look forward to some better weather to ride, and change the exhaust back over to the Cobra again after the winter

is there a way to upload a video to this forum ?