i need a lesson in jetting
 

got the dyno graphs and they are posted below.

the dyno showed that my 2000 hawk is running terribly lean between 2500rpm and 5500rpm.

here are the readings:
2250 14.63
2500 18.77
2750 18.77
3000 18.77
3250 18.78
3500 18.79
3750 18.77
4000 18.78
4250 18.77
4500 18.79
4750 18.52
5000 17.93
5250 15.73
5500 15.24
5750 14.56
6000 14.14
6227 14.01
6250 13.94
6500 13.83
6750 13.88
7000 13.82
7250 14.10
7500 13.98
7750 13.93
8000 13.80
8250 14.09
8500 13.84
8744 14.06
8750 14.12
9000 13.92
9250 13.96
9500 13.67
9750 13.63

the bike came with yosh slip ons. i had a mechanic do some maintenance including a honda oem air filter and new plugs. he didn't mention the plugs looking bad and unfortunately i don't know what the plugs looked like, i bet they were white!

i will post the graph as soon as it's emailed to me.

so, what do i need to do to bring things into line?

Go one size up on the pilot jet or try raising the needles

i need to read up on this jetting bsiness. i don't even know what the pilot jet is.

where is there an article discussing the basics? "jetting for dummies" or "jetting 101"?

Well it's kind of old and for Mikuni carbs but it's a start
http://www.carlsalter.com/aaman/Miku...ing-manual.pdf

Go to www.factorypro.com, click on technical support, click on motorcycle tuning, click on CV carb tuning. It's very helpful.

Do you know what jets or jet kit are in it now? Do you have the HP graph in addition to A/F?

Rule of thumb -

Pilot jets affect zero throttle to ,maybe 1/4 throttle.
Needle profile ( the shape ) determines opening up to around Half throttle.
Needle hight ( clip position ) affects this same range +plus the region up to about 75% throttle
Mains of course overlap everything from about 65% throttle up to full throttle.

This is a generic description but holds true on most bikes , CV carbed and non CV.

Heres a crude but effective visual aide to jetting ranges .

This is a chart of a dyno pull. It should be all main jet, and therefore should need changes to fuel flow that comes through that jet. 3 things affect this flow, needle profile, needle height, and main jet size.

for the profile of the needle you have, you should have a larger main, and a raised needle. Two positions would be probably be on the border of getting close. This thing needs more fuel!

more fuel for sure!

thanks for the input fellas. please keep it coming.

so it's throttle position, not engine rpm, that dictates what needles and jets are working. the dyno operator did a partial throttle opening too, 1/3 to 1/2 throttle. it showed similar a/f ratios. he took it through the gears too. everything showed lean at 2500rpm to 5500rpm.

hp was 104.0
torque was 67.7
should have the graph emailed to me tonight.

it doesn't have to be highly tuned. i just want it close enough to not blow up the motor.

But on a CV carb the slide, which opens the main needle, is controlled by engine vacuum, so rpm does play a part.

you're one hp and one torque number lower than mine...

yes, definitively looks like you need a bigger pilot jet in there.

The only time the CV plunger offers adjustment is when they drill a little hole on the slide. Some do it some dont.
So its not a solid formula to even consider.
Jet ranges are solidly connected to throttle openings, not engine speed.
Its pretty easy for someone to see the RPM playing a role though.

everyone is talking pilot jet... the research continues

Pilot jet is only for slight throttle openings.
Think "pilot light" same concept.
If you plug the pilot jet the bike dies at idle.
Any throttle opening over 1/4 , the pilot means nothing at all.

well, with the throttle wide open, the a/f is lean between 2500 and 5500rpm.
at 1/3 to 1/2 throttle it was lean in that same rpm range.
it always seemed to be lean in that rpm range.

+1 main size, maybe +2 needle position
 

What he said is exactly what you need to do first. You are looking to get the A/F ratio, at full throttle, as close to 13.0 as possible.
Judging from your numbers I would assume that the carbs are in stock form?... as in, no jetting changes to the mains/needles?

bought bike used but i too am assuming the carbs are stock.

i just talked to my mechanic. he says up on size, maybe two on the pilot. i mentioned putting a k&n in and he said that would be up two on the pilot for starters.

he also mentioned possibly shimming the needle. this would be after doing the pilot and seeing the dyno results.

I cannot agree on the pilot adjustment only because I cannot see what the idle a/f mixture even is in your graph. If it pops on deceleration with the pair blocked off, then yes. If it has poor response off idle, then yes. If you do not have a k&n in yet, and you are going to jetting, then you probably will have to go up on the main by two. If you are not going to replace the stock needles with a dynojet or factory pro jet kit, i would stay away from the air filter. This will only exacerbate the problem. If you can get into the carbs yourself, it will be easy to determine if you have either or neither. If there are no grooves and a snap ring on the needle, it is stock. I would, in mine opinion, replace this immediately. They will give you pretty close jetting specs for what you are trying to do. Just a thought.

Oh yeah, check out my signature. I have a custom exhaust. Very true one of a kind. The exhaust flow is nasty, and that means more air in. I would almost wager to say I have the biggest jets(or close to it), and when I went to NC last year and hit clingmans, it wasn't even an issue. It's definitely a fun ride.

Best power is around 12.5 to 13 the A/F is critical on a big bore high reving engine so the flame speed is high enough to burn all the charge.
I agree on the needles too low, pull them a notch or two and go from there, one change at the time, one size main jets will help too.
The CV slide is controlled by two ports one before, one after it will open depending of the airflow, it's opening is depending of the volume of air flowing trough the carbs witch is related to throttle opening and vacuum (RPM related)

i took a photo of the two dyno chart print outs. hopefully you guys can read them and let me know what you think.

the first graph is full throttle, second is 25-50% throttle.

2.25 turns on the mixture screws and one size larger main will get you where you need to be.

any more thoughts after seeing the graphs?

what if i add a k&n?

i got the actual dyno graph emailed to me. any comments?

Needle is fine adjustment. Mains is the biggest factor. Go 1-2 up on the mains. Then fine tune with needle height. my 2cents:) That's what I have found when using our dyno. Mains plays a huge role in the whole rpm range more then u think in a CV carb esp hawks. Usually cures all low speed surging to if the main is correct. If its to fat up top just lower the needle. I have not played with my hawk for 12 months now. As mostly with carburetors I use main jet for top end only and needles play more role down low, until another tuner said to me that hawks are a pita to tune due to the fact they have twin 50mm cv on a tame 1000 twin. Now with efi no problems with 50mm TBs as u have precise control. With 42mm flatslides also tunable as they have more airspeed going thru also more precise control thru needle jet. But with 50mm CVs airspeed is less yet they require lots of suction to open the slides. I forgot everything I knew and took his advice "with cv's on hawks, you tune mid range with main jets and fine tune topend with needles, a motor will draw fuel from a cv from mains from even low end as the main is the main fuel supply, the needle can fine tune topend". Any funny low end issues points to the main jet size if you have 4000rpm lean surge that is fixed by going to extremeties with needle adjustment. It normally means the main jet is to small. Step up 1 size to fix the problem and then the needle can be adjusted correctly to get best mixture at peak torque. The pilot does idle only. Stick a w.b on and see for yourself. I have never looked back since learning this technique.

And if anyone has experienced the 1500rpm stutter/surge on overrun from being lean. ie in neutral when engine is hot rev it and it occurs as revs drops at 1500rpm it will stuble then return to idle. This problem is solved by correct main jet aswell. Lifting the needle up to compensate to fix lean holes on transition is due to incorrect main jet selection. Once the main is right you can go up or down without any running issues, in our case its a fine adjustment.

Every carb has its quirks, The Honda pollution CV is basic in its design incorrectly sized for the application, Hence crude metering is a result and slightly different methods are required to get the engine running nicely with cans/filter etc. Had we had a smaller carb it would have been more simple to jet and normal methods due to higher velocity could have been exercised.

If you tune as a job full time like me. You would see the good and bad points of the setup and weigh up the costs of setting up a better system, ie 42mm flatslides or better again twin 50mm TB with ram tubes, foam filters, and a couple of 42lb injectors with fuel only ecu. Looking at the plugs the timing looks pretty well close at WOT. So a fuel only would suffice for simplicity.

wow. i'm gonna have to read hymey's post a few times to get it to sink in!

I feel robbed...
 

My S'Hawk only came w/ 48mm... You Aussie's get bigger ones? :rolleyes:

Must have mate. Not sure on what u have exactly even jetting wise and ours is also called a VTR1000 firestorm, what there is exactly in differences I am unaware.

I know this is an old ass thread but I have decided to revive it.

I had my bike on a dyno today following my HC piston install. My EGA readings are nearly exactly the same as mentioned in the first post. I am just slightly leaner throughout the second half of the rev range. Right around 15 between 6k and 10k rpm.

It was very hot here today (90+ degrees and humid) and there is some off-idle hesitation when the engine was hot in slow traffic.

I am wondering what, if any, the resolution was. I have no problems at all tinkering with the carbs. It would just be nice to know the right direction to go and maybe only have to go in there once this time.

My current settings:

FP 182 front, 185 rear, 48 pilot
2 1/4 out on fuel screws
FP needles (I think they are at the second highest setting)
BMC street filter
Shorted Jardine slip-ons


My first thought was to raise the needle. My second was to go up on the mains. My third was both thoughts one and two.

Opinions please.

Do you have stock needles? If so, that may need to change.

Man it looks like I missed a lot of this thread..... so much mis-information and I missed out on trying to clear things up.....