Flapper removal; effects of

[MikeScoot]

Is anyone running a flapper motor without the flapper? If so, what is the effect?
The actuating mechanism on mine interferes with fitment of a common air filter so I'm wondering what the effect of removing it might be.
I'm surmising that it (absence of flapper) would reduce the fuel richness when the throttle is opened from idle, but am interested to know the REAL effect.
Thanks in advance.
Mike

[Walt_M.]

The real effect would be the worsening of 'Vision stumble', the condition for which the flapper added to cure. I do not have a flapper on mine but I don't have stock carbs either.

[The Prophet of Doom]

There's no such thing as a "flapper motor".  The early 82s had a gravity flapper, and the vacuum mechanism was released as a mid-year modification. You can see what's different in the booklet "XZ550 (11J) Intake and Carburetor Modification Kit 1982 Models".  Same motor though, and essentially the same carbs, but with a different top.

You can definitely go flapperless.  #3 came with no flapper at all.  It howled like a banshee on full accell, growled like a lion on decell.  Only suitable for hooligans, but goes like a scalded cat.   It took a lot of pissing about to re-jet and set the accelerator pump properly.

I dabbled with the vacuum flapper, but I'm going back to flapperless on the super-mod. 

[MikeScoot]

... Only suitable for hooligans, but goes like a scalded cat ...

:P So then, might it be said that real men don't have flappers?  :P

Sounds like just my cup of tea! Just what the doctor ordered! Right up my alley. A match made in heaven! Would suit me down to the ground.
Thanks for the info.

[Walt_M.]

And, while you are sorting your jetting, you can get rid of the YICS. It is there to improve low rpm rideability due to the lean mixture settings. Quick question though, do you have to pass emissions testing? If you do these mods, it won't.

[MikeScoot]

YICS is gone already as is vacuum fuel pump, and it will be with GREAT pleasure that I remove the flapper too.
Emissions test? Last time I did one of those was at the doctor's. The nurse, who had to stand there and make sure I didn't pull a swifty with the sample, laughed her head off when I asked her to help out a bit. But seriously, na - no problem here with that sort of thing :-)

[fret not]

I suspect the flapper was added by the factory to cut down the intake noise.  These days we wear ear plugs to prevent hearing damage from the wind noise in our helmets.  It is amazing any of us survived all that noise.  I have had several bikes over the years that made more noise from the intake than exhaust.

[The Prophet of Doom]

As an added bonus, when the popo pull you over for a loud exhaust, you say nah mate, the exhaust is extra quiet - that's my highly modified super noisy intake and there are NO standards for intake noise.  They won't know what to make of that and will wander off in bewilderment looking for easier targets - like fully patched Harley riders who don't even do their own maintenance.  No impounding for you!

[MikeScoot]

...  It is amazing any of us survived all that noise. ...

What's that, Mike? Can't quite hear what you're saying. Lousy audio on this forum.

[MikeScoot]

... when the popo pull you over for a loud exhaust, ...

What? You mean stop? lolololol Surely you jest!  :P

[Walt_M.]

When I was doing my carb swap, I briefly tried a set of pod filters with no airbox. Not only did it run poorly, the intake roar was unpleasant at best. Kind of like riding an industrial shop vac, and not in a good way.

[MikeScoot]

When I was doing my carb swap, I briefly tried a set of pod filters with no airbox. Not only did it run poorly, the intake roar was unpleasant at best. Kind of like riding an industrial shop vac, and not in a good way.

lololol That conjures up a few really weird, but very funny,  mental images! :-) And disturbing noises!
I've always believed, rightly or wrongly, that the engineers at the factory put a fair bit of effort into ensuring their air inlet tracts and exhausts have pretty damned good fluid-dynamic characteristcs. That's not to say that removing some of the odd add-on afterthought bits is a bad idea.
Pod filters have always seemed a bad idea to me. The main reason is that they greatly reduce the volume between the filter element and the valve/s to about as low as it could possibly be. This would surely cause HUGE fluctuations in pressure, wouldn't it? Greater volume in this area would, I think,  enable more constant pressure which would, to my mind, be much more desirable. I may well be entirely wrong about all this though - just as I was about making an excellent and luxuriously appointed spacecraft from the tin-foil lids from milk bottles when I was a kid.

[injuhneer]

Well the flap changes the velocity of the incoming air. Why? Given that it is above the air filter and that the air filter will laminate most of the airflow it has to be about the box volume above the filter.

I added a second flap to my bike's air box. At the rear with a half-dozen 8mm holes. The flap is EPDM and acts like a check valve. The big flap really could help the lower-mid -> mid but really kills any resonant behavior because of its mass. I added the second flapper to allow the air in pulses at low speed then acting as a check against the air-box to prevent any rebound from low to mid-range.

With no jetting change there is a little flat spot about 2400rpm and it is only there is a slow throttle roll-on. Roll it quickly and there is no hesitation.

Given that I live in an area about 4500ft in elevation the jetting could use a tweak to cure that flat spot and give a little better pull above mid-range but with the helper flap added I see no reason to remove the main flap. I used a bit of the same EDPM to fix the flapper hinge.

I may change my mind later but that is my current rationalization.  ;D

Also consider that the YICS box is a rudimentary resonator. That too has its effect but is limited in frequency/range (like a Helmholtz resonator).

[fret not]

So, what RPM range do you think the YICS system should resonate?

[MikeScoot]

Well the flap changes the velocity of the incoming air. Why? Given that it is above the air filter and that the air filter will laminate most of the airflow it has to be about the box volume above the filter.

Yes. The velocity past the flapper would increase the more it were closed (assuming revs were the same). It would also cause a reduction in both pressure and (therefore) flow (through the carbs), wouldn't it? The reduction in pressure would cause more fuel to be issued into the airstream due to the increased imbalance on either side of the jets/nozzles.

I too have been considering 'opening up' the inlet/s to the airbox and am interested in what you mean by "rebound". Also interested in why you went with a fairly modest increase in intake opening to the box.

Cheers

Ps I'm not sure that chasing beneficial resonance from the YICS would be fruitful. The condition of the hoses and a few other variables would make any benefit fairly unpredictable. If indeed there was a benefit it would only affect a fairly narrow rev/load range and, potentially, have a detrimental effect at other revs/loads, wouldn't it?

Cheers again,
Mike

[injuhneer]

So, what RPM range do you think the YICS system should resonate?

All the Yamaha YICs implementations were targeting improved VE. I'd need to take some measurements to calculate the resonant frequency.

Right after I typed that comment I had a thought of making a variable resonator using a sensor and an Arduino controller. LOL!

[injuhneer]

Yes. The velocity past the flapper would increase the more it were closed (assuming revs were the same). It would also cause a reduction in both pressure and (therefore) flow (through the carbs), wouldn't it? The reduction in pressure would cause more fuel to be issued into the airstream due to the increased imbalance on either side of the jets/nozzles.

I admit to experimenting. The consequent observations are incomplete but I agree. The flap would change the pressure above the throttle plates during the transition. These carbs need the velocity of air to work. The stumble is in the transition. The flap would change the air behavior to compensate for the momentary pressure change. Jetting can hide the stumble by compensating for air or fuel but that moment between slower moving air on pilot with the throttle plates closed (or nearly) and the rush of accelerating air through the venturi is still there. It is how air behaves, right? The rapid change in pressure in the venturi means air density drops for a moment as the air behind accelerates and the air in front (engine facing) gets sucked in.

It seems that the engineers were looking to put a large carb on to ultimately feed the motor for higher HP. The problem then is low speed operation. CV carbs would be less susceptible. They resolved the problem in the V-Max with V-Boost and CV carbs: smaller carbs resulting in higher inlet velocity and CV to adapt to the demand. The passage between cylinder pairs in V-Boost to open pairs of carbs to pairs of cylinders at higher RPM solved the volume problem. And yes I have been contemplating fabricating a V-Boost for this engine with two smaller CV carbs and a controller operated passage between cylinders. Just for the fun of it (I am thinking two Venture carbs or smaller and a PIC or Arduino to count revs and modulate the stepper for the passage butterfly).

I too have been considering 'opening up' the inlet/s to the airbox and am interested in what you mean by "rebound". Also interested in why you went with a fairly modest increase in intake opening to the box.


Cheers

I wanted to observe the pulsations in the airbox with a simple mechanism. The small holes were to make it easily reversible with epoxy or a different airbox lid. I have been considering a couple of transducers to do logging. One on a YICS port, one in the airbox. I also wanted to observe if the volume of the airbox contributed to any reversion (bounce/rebound) of air at lower RPM or is adequate to absorb those pulsations.

Ps I'm not sure that chasing beneficial resonance from the YICS would be fruitful. The condition of the hoses and a few other variables would make any benefit fairly unpredictable. If indeed there was a benefit it would only affect a fairly narrow rev/load range and, potentially, have a detrimental effect at other revs/loads, wouldn't it?

True. It won't do a lot except in a specific RPM range. My thought was that the YICS passage and a correctly size chamber might be an answer to the stumble. Or not.

Cheers again,
Mike

I suppose that EFI is an alternative. I had been looking at the Speeduino project other applications. Looks like it might be a good option along with some other EFI bike bits. Ninja 650R throttle bodies look like a near dimensional match for the OEM carb.

Or just skip all that and buy an FJR1300.

Anyway...

[MikeScoot]

Or just skip all that and buy an FJR1300.

Anyway...

lololol That would be understandable. These things are blo0dy cantankerous!
I've had a bit of a break from doing anything with mine for the last few weeks while getting a few other things done. But I did get a few things done to the bike over the last couple of days. The most rewarding of which was refitting the ducktail and its Yamaha Badge. I spent a LOT of time on the badge and it has come up very nicely indeed.
Spring will be here soon and I'm looking forward to riding my decrappified Maxini in the better weather.
In the meantime, the next thing on the list for me is removal of the flapper and opening up the airbox a fair bit. I have another (airbox) here so there's nothing much to lose and, perhaps, a lot to gain - not the least of which will be an increase in that glorious intake roar!

Thanks for all the info in your last post and good luck if you decide to go ahead with the Arduino fun.

Cheers

[The Prophet of Doom]

The most rewarding of which was refitting the ducktail and its Yamaha Badge. I spent a LOT of time on the badge and it has come up very nicely indeed.

I've got that badge to do also.
Any pictures / methods to share?

[MikeScoot]

I've got that badge to do also.
Any pictures / methods to share?

Ah, yes. I'll write myself a note and endeavour to get some pics tomorrow. But in the meantime - I used traditional enamel paints. I did this mainly because of their high 'solids' content as I wanted to build a slightly rounded gold face on the lettering - also because of enamel's excellent flow and levelling. I should add that my first attempt, which was to roll the face of the letters on a flat plate coated in wet gold paint, was a disaster. So from there I resigned to doing it carefully using rather expensive long, soft-bristled brush. I had the gold enamel mixed to my liking by the kindly chaps at the local spraypainter's supply shop. The first attempt at this resulted in a bit of paint winding up on the flat surface below the lettering but I decided to press on and carefully overpaint it with black (again using a very fine brush and magnifying spectacles) after I was happy with the gold. I built several thick layers allowing a couple of weeks between each, then flattened the just the very tops with 1200 paper and added another thick coat of the gold. I gave it another couple of weeks sitting on top of an LED worklamp to harden more and ...  I'll post some pics within a day or two :-)

It might sound funny, but that one badge has been the most troublesome part of the whole bike project - including single-handed engine changing.