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Post by simonlc on Nov 13, 2022 19:47:08 GMT 1
I am sure there has been loads of threads on this but I will ask all the same. Running 31K carbs with standard jets and old style microns. Got a massive flat spot at 5/6k revs which can be ridden through in 1st and 2nd but other gears it’s impossible and have to knock it down a gear or slip clutch to get out of it. Bigger main jets first or raise needles?...
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Post by zig on Nov 13, 2022 19:53:57 GMT 1
i am running a 31k with small can Micron's standard jetting and plugs but Ram Air pod filters
pulls fantastic through the gears apart from top gear which i experience the flat spot and have to drop a gear
thinking i need to go a size up which i have not got around to doing as yet
ZiG
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Post by simonlc on Nov 13, 2022 20:02:44 GMT 1
Yep that sounds almost identical to me. Forgot to mention I am also running a premix in the tank as well as running the pump at the moment because can’t be 100% pump is working correctly so belt and braces. Don’t know wether over oiled will cause these symptoms
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Post by midlifecrisisrd on Nov 13, 2022 20:25:02 GMT 1
Pop the filter out and try it
If worse it's lean, if better it's rich
Don't thrash it as top end will be weak
My 31k wasn't too bad back in the day with microns. 250 mains but dropped needle. Had a bit of 5k stutter which I thought was rich but would pull through
Steve
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Post by bare on Mar 3, 2023 4:41:24 GMT 1
Sigh.. MY 1ua with pwks and (condor) Microns, mit Zeel has ZERO flat spots / stumbles... anywhere.
Pulling cleanly, WOT from 3000 rpms on up, with throttle cranked Wide open .. Regardless of Gear... right up to the rev limiter at 9500 rpms.
Did take some experimenting with the PV settings to get there tho.
Factory settings are simply Sad / Laughable.
As are 'Internet wisdom' suggestions :-)
My pve are programmed to open at 5k rpms and are wide open by 6K rpms. Heresy !!
All I know... is that THIS setting produces; Happy results / perfect miss /stumble free power delivery, WOT throttle to rev limiter.
every single time .
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Post by dusty350 on Mar 3, 2023 20:09:38 GMT 1
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Post by bare on Mar 4, 2023 4:13:03 GMT 1
Yuck it up :-) After 15 yrs of observing here... the seemingly unending and clearly Stoopid suggestions/advise.
Really are! tiresome.
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Post by dusty350 on Mar 4, 2023 8:47:29 GMT 1
Oh dear, have you got the painters in this week ?  |
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Post by beardy on Mar 4, 2023 9:47:30 GMT 1
Yuck it up :-) After 15 yrs of observing here... the seemingly unending and clearly Stoopid suggestions/advise. Really are! tiresome. Not “tiresome” enough as you keep coming back 😂 And I’m glad you do with your knowledge 👍🏻 |
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Post by jon on Mar 4, 2023 10:06:40 GMT 1
Sigh.. MY 1ua with pwks and (condor) Microns, mit Zeel has ZERO flat spots / stumbles... anywhere. Pulling cleanly, WOT from 3000 rpms on up, with throttle cranked Wide open .. Regardless of Gear... right up to the rev limiter at 9500 rpms. Did take some experimenting with the PV settings to get there tho. Factory settings are simply Sad / Laughable. As are 'Internet wisdom' suggestions :-) My pve are programmed to open at 5k rpms and are wide open by 6K rpms. Heresy !! All I know... is that THIS setting produces; Happy results / perfect miss /stumble free power delivery, WOT throttle to rev limiter. every single time . You mention the above bare, and then post the following: Yuck it up :-) After 15 yrs of observing here... the seemingly unending and clearly Stoopid suggestions/advise.
Really are! tiresome.I assume you’re not classing your posted quote above as stupid? Can you explain the reason you posted that your particular setup works well? How will that help the OP with their question? From the username of simonlc I assume he has an LC? Now I get it if your setup was a dead cert he could buy some PWKs and Zeel (at expense they may not want/have presently, just wanting to work with what they’ve got?) but obviously PV settings are completely irrelevant to him. Also your cylinders are tuned aren’t they? So a completely different and unachievable setup for him. Jon |
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Post by rigga on Mar 17, 2023 20:45:52 GMT 1
Bare always posts his perfect set up on his bike , failing to notice multiple times, his bike bears no resemblance to the person with the issue.
Now that does get tiresome.
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Post by 4l04ever on Mar 18, 2023 0:55:04 GMT 1
I thought Bare could see no reason to change from OEM Spec from Yamaha san...then has binned the carbs for PWKs???
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Post by simonlc on Apr 23, 2023 15:49:34 GMT 1
I am just looking for an answer to my set up not to admit defeat and swop carbs and other things to achieve a result. I’d rather learn than change bits 👍
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Post by Chewie01 on Apr 23, 2023 16:08:26 GMT 1
I had the same issue with my F2 when I first got it. I used to have to rag the hell out of it to keep it out the flat spot and if I did drop in to it the bike would slow down.
I tried all the jetting and needle fettling to no effect. It turned out to just be a worn out bore. So after a rebore, new pistons, rings and a crank rebuild it's all good now.
I suppose you can check the compression as a starting point.
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Post by simonlc on Apr 23, 2023 17:05:30 GMT 1
Well I’ve just tried it with no air filter in and it’s perfect. But I am confused because I am running 210 main jets as it is so I am scratching my head now lol
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Post by midlifecrisisrd on Apr 23, 2023 17:39:29 GMT 1
Think that's the problem
It is too rich at 5-6k but fine up top
Removing the filter has leaned it out so the splutter is gone but I'd like to see it on a dyno to see how lean it is up top
Steve
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Post by simonlc on Apr 23, 2023 18:32:26 GMT 1
Yeh that’s my thinking but didn’t make sense with such a small main jet.
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Post by simonlc on Apr 23, 2023 18:34:10 GMT 1
Maybe now start going up main jet sizes and seeing how far I can go before stutter comes back and then I know how far I can take it with jet size?
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Post by zed1015 on Apr 23, 2023 19:40:52 GMT 1
Forget the rpm range, you need to determine the throttle position that the flat spot occurs then address the associated part of the fueling curve that is responsible.
If dyno runs are not possible then do this by marking the travel on the throttle grip in to quarters ( 1/4, 1/2 ,3/4 and full throttle) and a mark or pointer on the switch gear to correlate with the closed position.
Then go do some loaded pulls through the gears and note the position on the throttle where the issue occurs.
This will take out the guesswork and vagueness of using rpms as they are not forced to follow throttle position in every gear.
If the cause is overfuelling then you will need to lean off the mix at that point.
This will likely be on the needle and not the mains.
Ideally you should do some full throttle plug chops to get the correct main jetting size first ( always starting large and working down) before sorting out the midrange.
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Post by simonlc on Apr 23, 2023 20:47:15 GMT 1
Useful advice there thank you. I was always lead to believe pilot jet took care over 1/4 throttle and mains then takes over from there. I will definitely try and settle for the biggest main jet I can fit before problems occur and then do a plug chop .
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Post by zed1015 on Apr 23, 2023 21:51:32 GMT 1
Pilot jet is for starting and idle only. this transitions (around 2k rpm-ish) to the emulsion tube, jet needle-needle jet then main jet.
Overall jetting is a stack up of all of these (really just the pilot mix and the main as the rest just meters the ratios in between).
Main jet needs sorting first and then the problem area.
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Post by midlifecrisisrd on Apr 23, 2023 22:05:16 GMT 1
Would be interesting to hear from someone using microns on an F2
My LC2 had its original 31k carbs and needed 250 mains for the top end but was rich and had the 5k stutter
Wonder if the 1ua carbs with the leaner needle and emulsion would help 🤔
Steve
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Post by Chewie01 on Apr 23, 2023 23:20:54 GMT 1
On my F2 I've used standard pipes, Micron side by sides, Micron GP style and Alonze all rounders. All with standard air box and filter.
When it comes to jetting I use standard with standard pipes, cos Yamaha probably know what they're doing. For the other 3 types I go with 190 or 195 mains and standard pilots. As for needles I think they are in the middle position, but I can't remember for sure.
As for the results, in general I would say that I'm on the rich side based on a couple of plug chops. I've not witnessed the dead mid range issue with any of these setups after the rebuild.
I need to add the disclaimer that I understand the principles and can nod along when someone talks about the subject, because it makes sense. However, in practice jetting's all a bit of the dark arts to me.
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Post by midlifecrisisrd on Apr 24, 2023 8:04:28 GMT 1
That's what I'd hoped the answer would be
The power jet carbs should be leaner on the needle, especially without WOT and the PJ'S working
It had popped into my head ad never heard any F2 owners complaining
Steve
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Post by JonW on Apr 25, 2023 1:40:38 GMT 1
cleaned behind yer balls?
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Post by simonlc on Apr 26, 2023 19:26:40 GMT 1
Not too keen on getting me balls out because the consequence of them falling out on full throttle don’t bear thinking about lol
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Post by simonlc on Apr 26, 2023 19:28:25 GMT 1
So since I’ve removed air filter element it’s running perfect on 210 mains and 27.5 pilot. I will try a few sizes up mains and see what happens
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Post by muttsnuts on Apr 27, 2023 14:30:28 GMT 1
well the question has to be asked, what air filter is it, genuine or a pattern?, or is it like alot I see, some foam from a settee or the likes ?
also stock jetting for 31K carbs is 240 main, so I'd be very worried if its on a 210 and no air filter, unless they aren't 31k carbs and are like 1UA carbs etc, which has a stock main of 185, which could explain the 210 main and it working better
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Post by tsa on Apr 27, 2023 14:58:11 GMT 1
Pilot jet is for starting and idle only. this transitions (around 2k rpm-ish) to the emulsion tube, jet needle-needle jet then main jet. Overall jetting is a stack up of all of these (really just the pilot mix and the main as the rest just meters the ratios in between). Main jet needs sorting first and then the problem area. Pilot jets are primarily for starting and just off idle but do flow fuel at all throttle positions all of the time. Its really noticable with PWK carbs that the pilot adds more fuel at the WOT position. He is correct that jetting is not rpm critical but throttle position critical. A good std 31K will be slightly rich on 240, if you then add premix you will be close on 240 maybe 250 but you have also leaned out the pilot too. leave the airbox lid off Go up on the pilot 1-2 size, jet to 290 and come down until correct. Also you may need to lift the needle 1 clip. This is only a guide as all engines will run right on what they require only this includes left and right cylinders, yes these can be different too. Check your reed valves too for warp or damage. Some warp of fibre reeds is ok but better if they are flat. Compression can affect how the engine runs too so check how balanced the 2 cylinders are for comp and over 100psi on both much lower will need re-boring. CHeck carb balance too engines hate an imbalance here and can make all kinds of weird problems/issues. You could also have a super rich mix because the air bleed is blocked in the carb that leads to the emulsion tube. Kenny |
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Post by simonlc on May 1, 2023 18:29:12 GMT 1
Well I’ve fitted ram air filters and 320 main jets and she’s running perfect. Nice good chocolate brown plug so might of found the sweet spot but will continue to go up some sizes on the main jet.
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