a/f ratio and jetting question

a/f ratio and jetting question

Postby super jim » Mon Oct 07, 2019 7:14 pm

Is there a way to add fuel in the 4.5-6k range without going too rich on the upper end on a 1980? I have 120 mains now. I'm just a little lean on top but it goes way lean in the 4.5-6 range when going full throttle. see graph. If I go up a couple sizes on the mains to help the midrange I may be too rich in the upper range. And raising the needle would also affect the upper end. thoughts?
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Re: a/f ratio and jetting question

Postby Rick Pope » Mon Oct 07, 2019 11:39 pm

Don't different needle have different tapers? For instance, stock v. K&N stage 1 or 3? I'm no carb guru, but just thinking out loud........
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Re: a/f ratio and jetting question

Postby super jim » Tue Oct 08, 2019 9:21 am

Rick Pope wrote:Don't different needle have different tapers? For instance, stock v. K&N stage 1 or 3? I'm no carb guru, but just thinking out loud........


That is correct. However I have no idea if that would help or which ones to try.

I"m thinking this is just due to the lag time from when the slides open and the fuel starts getting sucked in. I guess that's what the accelerator pump is supposed to help with but not able to provide enough fuel instantly???

Have others seen this same lean condition when the throttle is first turned wide open?
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Re: a/f ratio and jetting question

Postby daves79x » Wed Oct 09, 2019 7:57 am

So I assume you are talking about your bike with the 'custom' intakes and DG exhaust (DG header with Kerker can)? This is an almost universal complaint with this combo. CV carbs are not really designed for pods, no matter what the configuration. But you know this and we've been through this before. Some guys have had good luck with the Dyna Stage 3 kit, I have not. You can richen it up with the Dyna kit, but if you can live with 20mpg and black soot everywhere, you can try that.

As you know, i'm not a fan of either of the mods you did (pods and DG). Obviously, the flat spot will disappear with the stock airbox and ANY other pipe.

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Re: a/f ratio and jetting question

Postby super jim » Wed Oct 09, 2019 11:03 am

Yes and No. The a/f curve with that brief lean spot was present with the K&N pods and DG/Kerker 6-1. It is the same with my new individual intake runners and filters with the Pipemaster 6-6. I would like to see an a/f ratio curve from a stock bike for comparison.

You are correct also on the Dynojet stage 3. WAY too rich and ran like crap. Also agree the short K&N pods with the flat metal back don't play well with CV carbs either.

But I'm guessing the instantaneous and momentary lean condition upon going full throttle is inherent even in the stock configuration. I have not yet seen an a/f ration curve from a dyno run that does not go lean in that area for a moment, but that's why I'm asking.
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Re: a/f ratio and jetting question

Postby Gearheadgregg » Wed Oct 09, 2019 4:43 pm

Looks like your Idle circuit is lean looking at your AFR graph , I dont see anywhere here what slow jet your using , I have countless hrs on the Dyno with tuning my bikes , Nothing bothers me more than a week part throttle FLAT SPOT...,Have you tried One Step larger Slow jet ? I am 2 Steps up on the Slow with 120 mains with PODS Free flowing RC Race exhaust and have Stage 3 needles , I have absolutely NO Midrange Flatspot and Nice easy Cold Start . Not sure why everybody goes right to the Main jet ? I have completely removed my Main jet and test rode my other bike to check Idle circuit and you would not known it was out unless you twisted the throttle past half way.. That flat spot haunted me for 5 years on one of my bikes , Ended up being the Emulsion tube needed to be enlarged... Needles ,Larger slow jet Main jet and larger accelerator pump nozzle could not get it out ..But finally got rid of it !!! Dave is right my fuel mileage dropped about 5 mpg ! But cooler cylinder temps and PUNCH at 4000 rpm is amazing , even a different lower tone exhaust .. put your headphones on and hear ..Light on the throttle here https://www.youtube.com/watch?v=L9Y-CvWRw1Q
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Re: a/f ratio and jetting question

Postby super jim » Thu Oct 10, 2019 7:53 am

That sounds nice and crisp on the low end with snappy throttle response. I like it. I think you may be right on the slow speed jetting. Mine is very lean on cold start and hard to warm up. That is where I was headed next. I'm not sure what slow speed jets are in but will check. What size is stock?

I also have ordered an handheld exhaust gas analyzer to help determine my a/f at each level of throttle including idle. And with 6 pipes I can check each carb individually.
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Re: a/f ratio and jetting question

Postby EMS » Thu Oct 10, 2019 8:16 am

What 6-6 do you have? Some have a collector and are not really true 6 into 6.
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Re: a/f ratio and jetting question

Postby Gearheadgregg » Thu Oct 10, 2019 8:23 am

Think Stock pilot jet is # 35 the 38 jets worked very nice ,I put # 40 in this last 90 days and they worked out really nice . But i have racing lowered gear ratio and Ported heads Racing Cams and so on . Try the #38 and enjoy your ride also helps Pipe Bluing https://www.ebay.com/itm/HONDA-CBX-1000 ... 1594878970
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Re: a/f ratio and jetting question

Postby super jim » Thu Oct 10, 2019 9:31 am

EMS wrote:What 6-6 do you have? Some have a collector and are not really true 6 into 6.


pipemaster. true 6 individual pipes
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Re: a/f ratio and jetting question

Postby super jim » Thu Oct 10, 2019 9:35 am

Ordered. Thanks. I believe that is headed down the right path.
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Re: a/f ratio and jetting question

Postby EMS » Sun Oct 13, 2019 12:10 pm

super jim wrote:
EMS wrote:What 6-6 do you have? Some have a collector and are not really true 6 into 6.


pipemaster. true 6 individual pipes



Not that it matters, but if you have a true 6-6 they are most likely not Pipemasters. My Pipemasters have a collector. You may have Dencos.
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