Jetting advice: CPR air filter on 950

[randel]

I placed an order for CPR dome filter for 950SE and would like to have some advice regarding jetting.
I know that some information is in general CPR air filter thread, but it's quite difficult to find from several pages and hopefully there is also some new information since then.
Located at sea level and using 2-1 Acra exhaust with insert, I assume I would start from
main jets 175front/180rear
stock needle 3rd clip
what about IAJ etc?
I currently have H2W kit installed.

[Stumpalump]

How is it running with your current jets?

[blublapp]

If you are running a CPR/ITG Filter, you don't need different main jets for front and back cylinder.

[Vassily28]

Are you using an UNI prefilter with H2W kit? If yes and you remove it, you'll have to change the main cause you're probably have somthing like 148-152.

Even with the CPR, i think 175-180 is way too lagre mostly cause of you're 2-1. When you Akra 2-1 do you talk about a complete Akra header 2-1 system or only a standard 2-1 with an Akra exhaust.

The standard 2-1 with an AKRA will be the most restrictive part of your system, not the air intake just like with the UNI prefilter. So maybe you'll have to use 155-160 or 160-165 main but probably not bugger than that. Somebody with a 2-1 and an OEM or DNA filter can lead you on that.

I think that most of your gain will be in the LOW to LOW MIDDLE rev. cause the back pressure in the exhaust will raise faster. You're gonna have to adjust IMS, stock IAJ and maybe clip on needle.

My 2 cents.

[Navin]

Check my thread on CV carbs with K&Ns, I left my H2W jetting and went up on the main to 170 sumthing as I recall. I had a 2-1 with Q4. Picked up power everywhere.

[mousitsas]

Originally Posted by blublapp

If you are running a CPR/ITG Filter, you don't need different main jets for front and back cylinder.

Why?

[randel]

I have original header converted to left side 2-1 with Acra exhaust.
Currently I run H2W with prefilter, main jets 148/152. I know it's way to lean for CPR filter.

[blublapp]

Originally Posted by mousitsas

Why?

An austrian tuner tested this out on the dyno. It's necessary because of the construction form of the original airbox in which the rear cylinder gets more air, so more fuel is needed too.

he sells open airboxes too and gives out this information.

my setup with an ITG filter (same as CPR) is 155/155 mains at present.

[mountain eagle]

I'm in Denver, 5280', and was running 155/160 and am about to put 165/165 in for a test.

At least it only takes me 30-40 minutes to do the job now

[Balsta]

About same main jets front and rear when using CPR (or other similar concepts),

Originally Posted by blublapp

An austrian tuner tested this out on the dyno. It's necessary because of the construction form of the original airbox in which the rear cylinder gets more air, so more fuel is needed too. He sells open airboxes too and gives out this information. My setup with an ITG filter (same as CPR) is 155/155 mains at present.

This is interesting stuff if correct and perhaps there are other inmates with skills to approve/disapprove on this.

Actually, I have an oval K&N (similar concept with respect to air flows) with 175/180 on the SDR motor since 35000 kms. Exactly same nice light brown color on both plugs.

[mountain eagle]

Originally Posted by Balsta

About same main jets front and rear when using CPR (or other similar concepts),


This is interesting stuff if correct and perhaps there are other inmates with skills to approve/disapprove on this.

True I'd love to get that from multiple sources or someone I already trust. In the meantime I just dropped the 165's in and will ride it for a few miles and see how things feel, then see how the plugs look.

[mousitsas]

Originally Posted by blublapp

An austrian tuner tested this out on the dyno. It's necessary because of the construction form of the original airbox in which the rear cylinder gets more air, so more fuel is needed too.

he sells open airboxes too and gives out this information.

my setup with an ITG filter (same as CPR) is 155/155 mains at present.

I did suspect that the rear larger main has nothing to do with operating temperatures, but its airbox/exhaust related....Thanks!

[Sporting Wood]

The restriction in the airbox is the snorkel at high rpms. Bigger mains fix this, and are absolutely necessary using the airbox and even more so without. The first jet you set in tuning is the main, and its done at wide open max rpm. All the others are adjusted down to accept the larger main...This the difference between properly tuning the carbs and not.

My experience with the 950, which is extensive, indicates there is absolutely no difference between front and back, temperature, egt, o2, etc... I have ran 170 mains front and rear in the box for 5 years. My bike is jetted near perfectly, outruns every other buddy with a 950, and returns 40mpg. o2 from either cylinder always registers between 14 and 17.

I just made a filter like these, not the cpr, but the same filter element on an aluminum baseplate, and am starting with 175 mains, tweeking the bowls a touch leaner by lowering the floats. These carbs tend to have an annoying tendency to suck fuel from the main when it should be drawing off the slow, so compensating adjustments must be made with the float and the screws. My floats are already a mm leaner and my screws are at 2 turns. Another half mm and a half turn in might do it but I'm running it to evaluate first.

To the op, if your swapping from the h2w prefilter jet setup to this, don't forget to swap your airjets back to stock!

[mousitsas]

Originally Posted by Sporting Wood

The restriction in the airbox is the snorkel at high rpms. Bigger mains fix this, and are absolutely necessary using the airbox and even more so without. The first jet you set in tuning is the main, and its done at wide open max rpm. All the others are adjusted down to accept the larger main...This the difference between properly tuning the carbs and not.

My experience with the 950, which is extensive, indicates there is absolutely no difference between front and back, temperature, egt, o2, etc... I have ran 170 mains front and rear in the box for 5 years. My bike is jetted near perfectly, outruns every other buddy with a 950, and returns 40mpg. o2 from either cylinder always registers between 14 and 17.

I just made a filter like these, not the cpr, but the same filter element on an aluminum baseplate, and am starting with 175 mains, tweeking the bowls a touch leaner by lowering the floats. These carbs tend to have an annoying tendency to suck fuel from the main when it should be drawing off the slow, so compensating adjustments must be made with the float and the screws. My floats are already a mm leaner and my screws are at 2 turns. Another half mm and a half turn in might do it but I'm running it to evaluate first.

To the op, if your swapping from the h2w prefilter jet setup to this, don't forget to swap your airjets back to stock!

Interesting thoughts....but why do you say that the snorkel restricts the airbox? The inlet snorkel surface area is clearly larger than each individual carb inlet. Also, the 990R can happily put down 110+bhp with an identical airbox-snorkel.
Also, what problems do you expect if the H2W base jetting (plus larger mains) is used with a CPR filter?

[Sporting Wood]

Originally Posted by mousitsas

Interesting thoughts....but why do you say that the snorkel restricts the airbox? The inlet snorkel surface area is clearly larger than each individual carb inlet. Also, the 990R can happily put down 110+bhp with an identical airbox-snorkel.
Also, what problems do you expect if the H2W base jetting (plus larger mains) is used with a CPR filter?

From lots of dyno time, the snorkle restricts airflow into the box. Simply taking it off makes a huge difference in top end, this after upsizing mains. In stock condition, the first thing to run out are the mains. Factory mains are still lean even with the snorkle on. I assume the 990R makes its higher top hp numbers from either/ or both more fuel flow through the injectors or higher rev limit, greater displacement...dunno. I have a 950. Simply put, an airbox equipped 950 benefits from a bigger main, its smaller fueling ability being the top end restriction in stock form, a 950 without an airbox benefits far more, as the next restriction caused by the snorkle is eliminated.

In regards to using h2w's kit intended for the prefilter, this would be a total donkey show. That system relies on greater vacuum and less atomization. The airjets will be way off, really way off, and the mains beyond dangerously small and lean. I'd not be at all surprised to see a seized motor as a result! I'm certain Ken has warned against this, repeatedly. Shifting to a tune with greater airflow, less vacuum and better atomization is totally, completely different, and require totally different settings.

Also, the stock needle has to go!