Sorry, but it's carbs and Cobras....

[tmfp]

I'm a new Valkyrie owner, three months and 5000 miles on my 97 red and white Standard. Stock exhaust system with 4" truck tips.
It starts and runs faultlessly, 12.5 sec 1/4 mile, 140 mph top with a slight incline, around 32 mpg, no flat spots, beautiful.

I like it so much I bought 'Pinhead' last week, 97 Standard with Cobra boulevard 6/6 exhaust with baffles in. Lumpy low tickover, little effect from choke on or off. Pulls well till around 4500 then goes 'flat' unless I roll off from WOT and roll on again. Flat out barely 110 mph. Around 28 mpg.
An ad hoc road test confirms the top end is the problem on Pinhead. WOT from 30 mph in top over the same distance saw both bikes 'crossing the line' about 90 mph.
A standing start, changing up at 6000, saw 100 mph on the red and white, 88 on Pinhead.
Both bikes have genuine 35000ish miles and Pair systems and are ridden just above sea level.
I have tightened the carb boot jubilee clips, both bikes took a couple of turns.

I have used the 'Search' extensively before posting this, as I'm sure you guys are pretty much sick of the topic, and now have brain overload, so......

1)   Ignoring the different exhaust for the moment, please advise on the 'usual subject' check list, vacuum lines etc.
Once I have completed these checks, I will re test both bikes and if the difference is still noticeable, then suspicion will fall on the exhaust.

2)   Regarding the Cobras, 115 mains and 38 slows seemed to be a concensus from search.
What is the best way to buy these?  Where does a DynoJet stg 1 fit in the picture? Shimming? I/S springs?

PS Please don't recommend a K&N, I have a mental blank about their products.

Thank you very much.

[Blackduck]

First pull the plugs and see what colour they are. Really need a new/clean set in there and run hard at the top end and shut the motor off and coast to a stop then check the colour.
Most likely be too much or not enough fuel. Any idea of the jets and needles in it now?
Has the air box been played with and does it have a standard air filter.
Standard or aftermarket triiger wheel.
There is also a possiblilty of a bad coil
Cheers Steve

[EDDIE SPAGHETTI]

i HAVE A 2003 VALK STD W/LOW MILEAGE. lOOKED INTO STOCK EXHAUST CHANGE TO COBRA 6 IN 6, WHICH I HAVE ON THE LIVING ROOM FLOOR.  WITH BAFFLES INSTALLED, THERE HAS TO BE A NEEDLE AND SPRING KIT INSTALLED, PART #92-1269.  POSSIBLY THIS WAS NEVER INSTALLED.  ALSO LOOK AT THE COLOR OF THE PIPES COMING OFF THE ENGINE FOR EXCESSIVE COLOR CHANGE, BLUING.

WITHOUT THE BAFFLES, THE CARBS HAD TO BE REJETTED.

LOOKING FOR A SET OF BAFFLES, IN CASE YOU DECIDE TO REMOVE THE ONES THAT ARE IN THE 6 IN 6.

ES

[Ricky-D]

It sounds to me that there have already been some changes made to the carburetion.

Stock has been the usual end result when talking about carburetor changes with aftermarket pipes, when looking to improve performance.

I guess the best course of action would be to look and see what you have there now!

***

[tmfp]

Pulled the plugs today after a sedate 25 mile ride keeping below 4000, they were quite sooty, but pale on the electrode.
I had time to take the tops off the carbs and found needles with 5 notches, set on the middle one, presumably these are the Cobra needles from the kit that EDDIE refers to.
The plugs indicated over fuelling in mid range so I moved the clips up a notch and removed the small shim washer, equivalent to half a notch.
She pulled cleaner and sharper up to about 5000 rpm. but then started struggling as before, the very blue pipes also making me think this is underfuelling due to an undersized main jet.
I haven't had the tank off yet to check the airbox/filter (or checked for a trigger wheel), so will potter around until I have the time and facilities to do the job properly.

My pipes have baffles, I can''t imagine how loud they would be without!
The 'quiet' option suits me when needed, due to cops and neighbours 

[Blackduck]

As you have found improvement by raising the needles I would try raising them to the maximum. Easier than pulling the carbs.
The Cobra needle taper is closer to stock on the first 1/3 to half then go very rich in the last half.
I have measured early and late Honda needles, Factory Pro and Cobra. Both the aftermarket go very rich on the lower half of the needle.
Cheers Steve

[Ricky-D]

Pulled the plugs today after a sedate 25 mile ride keeping below 4000, they were quite sooty, but pale on the electrode.

Here's a link you may find helpful.

http://www.4secondsflat.com/Spark_plug_reading.html

As you have found improvement by raising the needles I would try raising them to the maximum.

Actually he lowered the needles. Please don't construe this as criticism.

***

[Blackduck]

Not often I agree with Ricky but he is right, I meant raise the E cilp to the upper groove which lowers the needle.
Apologies for miss information
Cheers Steve

[tmfp]

Pulled the plugs today after a sedate 25 mile ride keeping below 4000, they were quite sooty, but pale on the electrode.

Here's a link you may find helpful.

http://www.4secondsflat.com/Spark_plug_reading.html

As you have found improvement by raising the needles I would try raising them to the maximum.

Actually he lowered the needles. Please don't construe this as criticism.

***

Thanks for the very helpful link 

I thought my phrasing might cause confusion, sorry.
I raised the clips, lowering the needles, and found the improvement.
I'll re-post when I pull the carbs and airbox and find further info about the state of affairs.
Thanks for the help, everyone. Also, just to double clarify, the pipes are baffled and will remain so.

PS
Also replacing the buttonhead M5's with A4 stainless, the originals appear to be made of very soft material.