Baffle causing leaness?

[Dudeofrude]

I removed my baffle earlier just to see what it sounded like and decided to leave it out for the day but while out riding I seemed to notice signs of lean running again? Pops on deceleration, revs hanging slightly and smells rather hot around the downpipes?
I'm just wondering if removing the baffle can make that much difference or is it just a more noticeable underlying condition?

It's a 2007 fz1n with all the mods except flies (they are still standard)

[pilninggas]

Very much doubt it will be making it leaner. On a carbed bike fuelling relates to flow rate (bernoullis) and flow rate through the engine can be effected by the exhaust. On an EFI bike fuelling is either the alpha-N or Speed Density, both of which will take data on inlet temp/pressure and therefore inlet massflow, TPS and revs. The inlet parameters don't change if the baffle is pulled (in my experience the FZ1 doesn't even notice the decat), so the algorithm for the EFI is unaffected and the engine runs the same. The only exhaust measure is lambda, but on the FZ1 that only occurs in a small rev range on very small, steady throttle openings and has quite limited effect (mainly emissions appeasement). Potentially decel pops may be more noticeable sans baffle due to the obvious reduction in noise suppression (or increase in noise production).

Potentially you could do back to back runs with and without and look at coolant temp or better still use an IR thermometer and read the downpipe temps (how I do carb tweaks on my fzr and rg these days).

[Dudeofrude]

OK cheers for the advice. I didn't think it could make that much difference. I'll have to try a richer map and see what that does?

[darrsi]

Carb balance will get rid of popping, just make sure your air filter is good before doing it.

[Dudeofrude]

Carb balance will get rid of popping, just make sure your air filter is good before doing it.

It's a gen2, none of them pita carb thingys 😉 haha

[Dudeofrude]

Well seems like my initial concerns were on the right track, Ilive out the baffle back in and been for a ride and it's sweet as a nut? Haven't got a clue why but idles better (still has a sporadic fluctuation but I think that's due to the plugs needing changing) didn't have any popping on decel and ran at normal temperature.
So guess it's a case of best left alone. Was too noisy without the baffle anyway haha

[darrsi]

Carb balance will get rid of popping, just make sure your air filter is good before doing it.

It's a gen2, none of them pita carb thingys 😉 haha

Haha, my bad.
Isn't that where a power commander comes into play?

[pilninggas]

Well seems like my initial concerns were on the right track, Ilive out the baffle back in and been for a ride and it's sweet as a nut? Haven't got a clue why but idles better (still has a sporadic fluctuation but I think that's due to the plugs needing changing) didn't have any popping on decel and ran at normal temperature.
So guess it's a case of best left alone. Was too noisy without the baffle anyway haha

Genuinely surprised that the baffle is having any effect. Must be allowing the pressure in the downpipes to drop much quicker.

As for sporadic fluctuations, a lot of bikes with very big throttle bodies seem to do this. The engine tries to hunt, but the ECU reins it in quickly.

[slappy]

With the baffle out would it not decrease the back pressure? And if the back pressure is not within a certain range would it not affect how the engine runs?
Or am I talking nonsense?

[tommyardin]

Hi Slappy,
My understanding is that it is not so crucial on a 4 stroke, but, on a 2 stroke removing all the baffles is the kiss of death because the 2 stroke does not have exhaust valves and relys on the restriction of a baffled exhaust to retain back pressure, I know that there are very noisy expansion boxes for strokers but their design/shape helps retain the back pressure.

As back pressure is not so important on a 4 stroke because of the exhaust valves doing the job I would think that it would do very little to the mixture to Petrol/Air ratio. I know with my race can (PipeWerks) it says in the bumph that come with it, that no mixture adjustments is necessary with or without the baffle in. The only real difference then if that is true is the sound and maybe, just maybe, the exhaust gasses clear the system a tad quicker, where or not that would impact on power I don't know if it did it would be for the positive i would imagine.

If anyone knows different to that please do say as I am only going on what I have heard and read and not through any real knowledge or experience.

Other than removing the baffles with a 2 foot long piece of galvanised water pipe and a club hammer many many years ago on a 250cc Ambassador Villier 2 stroke twin, it made a huge difference to the way the bike performed, with baffles in 82 mph with baffles out 72 and absolutely gutless, reverse tuning I believe its called.
Anyway Miniear & Bruce of Guildford ordered me to new silencers that cost me 23 quid, it don't sound much I know but it was in the late 60's.

[Dudeofrude]

Well seems like my initial concerns were on the right track, Ilive out the baffle back in and been for a ride and it's sweet as a nut? Haven't got a clue why but idles better (still has a sporadic fluctuation but I think that's due to the plugs needing changing) didn't have any popping on decel and ran at normal temperature.
So guess it's a case of best left alone. Was too noisy without the baffle anyway haha

Genuinely surprised that the baffle is having any effect. Must be allowing the pressure in the downpipes to drop much quicker.

As for sporadic fluctuations, a lot of bikes with very big throttle bodies seem to do this. The engine tries to hunt, but the ECU reins it in quickly.

Ah that's a relief then. I just assumed with it being FI that it would idle on a cats whisker. I may wait till the 12000 mile service to get the plugs done then 🤔

[pilninggas]

Well seems like my initial concerns were on the right track, Ilive out the baffle back in and been for a ride and it's sweet as a nut? Haven't got a clue why but idles better (still has a sporadic fluctuation but I think that's due to the plugs needing changing) didn't have any popping on decel and ran at normal temperature.
So guess it's a case of best left alone. Was too noisy without the baffle anyway haha

Genuinely surprised that the baffle is having any effect. Must be allowing the pressure in the downpipes to drop much quicker.

As for sporadic fluctuations, a lot of bikes with very big throttle bodies seem to do this. The engine tries to hunt, but the ECU reins it in quickly.

Ah that's a relief then. I just assumed with it being FI that it would idle on a cats whisker. I may wait till the 12000 mile service to get the plugs done then 🤔

It's in a high state of tune with a relatively light flywheel. At idle the system is almost on a hair trigger, particularly with 45mm throttle bodies.

[Fazafou]

With the baffle out would it not decrease the back pressure? And if the back pressure is not within a certain range would it not affect how the engine runs?
Or am I talking nonsense?

You don't want any "back pressure" at all, it's a completely misunderstood concept.


The sizes of exhausts etc are not about maintaining pressure but more to do with getting exit velocity correct.  If you put massive pipes on, it slows down the gases (think of 2 rivers with the same volume of water, a deep one will be slow running compared to a fast flowing shallow one).  If the gases can't exit quick enough it hinders the engine.  So basically the pipes need to be 'tuned' to the engine to get the most out of them.


Too small and they restrict the flow, too large and the gases can't exit fast enough.  So people put massive pipes on, suffer problems and then say "I've not got enough back pressure now".

[Oldgit]

Yes I always lean when Baffled

[Dudeofrude]

Yes I always lean when Baffled

I didn't think they let you out for Xmas anymore? 😉😋