GSF1200S Weird AFR with dynojet stage 3 and KN - Suzuki GSX-R Motorcycle Forums Gixxer.com

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post #1 of 10 (permalink) Old 06-01-2019, 05:25 PM Thread Starter
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GSF1200S Weird AFR with dynojet stage 3 and KN

Hi,

I have 2005 gsf1200s bandit, europe version. I've removed system that injects air into exhaust (plugged holes on engine block with special kit), installed aftermarket muffler, K&N air filters (RU-2922), Dynojet stage 3 jets spring and needle kit (E3351). I had to play around with needle setting and idle adjustment screw in order to get it working normally, first it was done according to Dynojet manual and it was awful because it had no thrust and was terribly firing (i.e. with real fire) from exhaust pipe...

I had different feeling compared to what it was before, however I considered everything was ok. I had to make myself confident about opening full throttle very fast - it was not working good, I've found a solution for rapid bike acceleration by opening throttle bit by bit relative to speed, full throttle result in not good thrust and opening it as RPM are growing allowed faster accelaerations that it was before.

This week I've installed Haltech WBC1 wideband O2 kit with gauge. I've calibrated it on open air as per instructions.

Now the problem is that with warmed up engine I'm getting 11:1 AFR while crouising (<4000rpm), then it gets to 14.1 at 6000rpm and then rapidly falls to 17:1-18:1 above 7000rpm.

I would expect bad tuned carb to be rich only or lean only througout the rpm range and there are methodics described over the web on how to deal with that, however I can not find information on how to deal with part rich part lean operation. Could someone give me a link on how to tune carbs in this situation?

Thank you.
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post #2 of 10 (permalink) Old 06-01-2019, 09:14 PM
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Re: GSF1200S Weird AFR with dynojet stage 3 and KN

CV Carb Tuning Procedures
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post #3 of 10 (permalink) Old 06-03-2019, 11:21 AM
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Re: GSF1200S Weird AFR with dynojet stage 3 and KN

pilot jet/needle position is too rich, main jet too lean. refer to the hyperlink mark_E provided
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post #4 of 10 (permalink) Old 06-06-2019, 11:00 AM
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Re: GSF1200S Weird AFR with dynojet stage 3 and KN

Throw away the Dynojet kit and use one from Dale Walker's Holeshot Performance, or from Factory Pro. Personally, I'd also run the stock airbox and a Suzuki filter.
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post #5 of 10 (permalink) Old 06-06-2019, 12:23 PM
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Re: GSF1200S Weird AFR with dynojet stage 3 and KN

Quote:
Originally Posted by javadog View Post
Throw away the Dynojet kit and use one from Dale Walker's Holeshot Performance, or from Factory Pro. Personally, I'd also run the stock airbox and a Suzuki filter.

+1 that's what I'm running, with a K&N filter and a 2" hole in the airbox lid
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post #6 of 10 (permalink) Old 06-22-2019, 07:18 AM Thread Starter
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Re: GSF1200S Weird AFR with dynojet stage 3 and KN

Quote:
Originally Posted by mark_E View Post
CV Carb Tuning Procedures
Thank you, this helped a lot. I was able to get more or less constant AFR of 13.7, however it seems to be impossible to get it through entire RPM range as it always goes bad either mid or high rpm range, when it is good up to 6k+ rpm then it is lean from 7k, when it is ~14 from 7k rpm then it is rich(afr~10.9) before 6k... I've done a lot of job and tried all 4 main jets from dynojet kit as well as all 5 position of needle on each jet, and can not find setup that will allow normal operation both high and mid range... Very disappointed with this kit!

I suppose supplied needles are very thin for my carbs (compared to stock ones) as main jets heavily affects AFR during idle.

I've bought dynojet kit as I've read that it is only bad for old bandits before 2000', and it was available at local shop.

It seems I will have to order Holeshot kit from USA.

By the way, there are suggests to install stock air filter box with large hole, then what is the point of everybody installing K&N filters? They are supposed to be installed on heavily modified engine only?
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post #7 of 10 (permalink) Old 06-26-2019, 12:30 PM
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Re: GSF1200S Weird AFR with dynojet stage 3 and KN

Get some proper BST SS 36 ....
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post #8 of 10 (permalink) Old 06-27-2019, 08:30 AM Thread Starter
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Re: GSF1200S Weird AFR with dynojet stage 3 and KN

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Originally Posted by ghostrider.1127 View Post
Get some proper BST SS 36 ....
I thought that is exact model of stock carbs...

BTW What are the benefits of slide carbs compared to CV carbs? Do slide carbs provide something good on stock B12 engine (with modified exhaust and intake)?
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post #9 of 10 (permalink) Old 06-27-2019, 02:22 PM
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Re: GSF1200S Weird AFR with dynojet stage 3 and KN

think in 05 they used keihin , but if i“m wrong check for worn/oval emulsion tubes
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post #10 of 10 (permalink) Old 06-29-2019, 10:38 AM
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Re: GSF1200S Weird AFR with dynojet stage 3 and KN

Quote:
Originally Posted by awpe View Post
By the way, there are suggests to install stock air filter box with large hole, then what is the point of everybody installing K&N filters? They are supposed to be installed on heavily modified engine only?
K&N filters don't filter the air very well. They are used by people that remove the stock airbox and want something as a filter, even if the filtration isn't as effective as the stock filter, or because they just don't know any better. The engine usually breathes a little better, which might make a few horsepower difference, if you can get it jetted properly. Removing the airbox and adding the K&N filters (which have a blocked end opposite the carb inlet) changes the flow characteristics and pulse reflections experienced by the intake. You might see better peak power, but may also have a torque and power curve that are less smooth. Most bike engines will have a dip in the power curve somewhere between 4,000 and 7,000 revs from a too rich mixture caused by carb reversion. I have found that the Dynojet stage 3 kits I have used on similar carbs make this quite a bit worse, once you get the mixture right for high rpm.

I've had a second generation Bandit and used the Holeshot kit, a modified airbox running a stock filter and a Yoshimura slip on muffler and had good results.
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