CBF125 M-D after market exhaust.

[Davewins13]

Hi all,

Got me new (2nd hand) Honda CBF125 on Saturday and it came with an after market exhaust. It sounds great but feels down on power. It takes ages to get to 50mph and doesn’t feel very responsive when accelerating in mid range. Could this be because they didn’t deal with the ports etc when fitting the new exhaust?

If so how hard is it to put right (without reverting back to a stock exhaust)?

Cheers
Dave

[Rogerborg]

Against what are you comparing it?

Have you changed the oil and spark plug, and cleaned or replaced the air filter?
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Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[Davewins13]

[cb1rocket]

carry out the full service yourself. Do some checks, it probably wasn't done.
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Honda H100S2 Rebuild - https://www.bikechatforums.com/viewtopic.php?t=253852

[Davewins13]

[Teflon-Mike]

TOP bet on this one, is that there's little 'unusually' wrong with the bike. Topping out at 50-55mph is enormously co-incident with playing 'gears' and up-shifting too may, too soon.

Little 125's, have barely enough power to pull the skin of a rice pudding. With around 10 bhp at 'max' revs, they just about have enough power to achieve 70mph. Top gear is almost always an 'over-drive', and on a bike with a 5-Cog-Box you will almost always go just about as fast as the thing ever will, in 4th, where the lower gearing begs the motor rev-out to peak power, to let you get that top speed, and all top will do s hold road speed, to save some buziness, and 'maybe' help you find the last 5mph or so of ultimate top end on a flat or down hill road, if long enough....

Reving a little motor out in the lower gears, feels 'harsh' and sounds 'brutal' and is utterly alien to car-driver's taught to get up the gears asap, 'for ecconomy' rather than use the lower cogs for 'response'.

Rule of thumb for a 125; you use 1st only for 'launch' from a stand-still. It will run-out of revs pretty quick, maybe before you are dong 20mph, but let it get there! 2nd gear, should take you from about 15mph to about 30. Riding for response, this is the only gear you should need round the houses. 3rd, you wont need untl you are on a 30 road, and is the mother-of-all-work gear. Will take you from about 20mph up to about 50. Unless you are on a main 50 marked road, THIS is the gear to use! It gives you most speed and acceleration, around town, to let you ride for response. AND not to make life hard for yourself, doing more work than you need going 'up' gears, to do more work still,, coming back down them, usually in a rush, and not very smoothly, and making a complete arse of it slowing and braking for junctions. DONT go up.. o need come back down! all good! You shouldn't need 4th until you are on a 40+ marked road AND have enough of it you 'may' wind the bike up a bit, and NOT expect to have to come back down the box in a hurry. Ie more major town roads, and most 50/60-limit country roads. Now you may 'max-out' ad that lower gear will let you wind the thing up to peak-power revs and get at the little power the engine makes, that the bike needs to reach terminal velocity. Should take you up to well over 60mph, and only THEN, on a long straight open road with no junctions or hazards 'might' you snick that up-shift into 'over-drive 5th to 'hold' 60ish wthout the motor so frenetically buzzing, or to find those extra couple of mph, if the road long enough, straight enough and down-hill enough to find them.

Its little, low powered bike, to make progress, or something even vaguely resembling progress, you HAVE to THRASH IT!!! If the motor is in half decent fettle, t doesn't make enough power to do itself any harm; if it isn't? Well, it-gonna-break, sooner or later, regardles! Little bikes NEED to be revved! You shouldn't do it any damage by using them revs.

Incidentally, no engine failure I have EVER encountered has been from it being 'over-revved', opening the throttle..... if they go 'bang' t's usually on the 'over-run' the rider crashing down too many gears too fast, the back wheel driving the crank up to speeds that it simply cant achieve under its own steam.... and even then.... on a light wight bike, on public road macaddam, there's usually simply not enough 'grip' for the back-wheel to generate the kind of force needed to drive crank to them revs... it just 'skids'.

Oh-Kay.... having eliminated the silly/stupid first...

Next Best Bet, for ANY actual lack of power..... is NOT an after-market exhaust, but simple owner-Neglect/abuse.

Little bikes live hard lives. Little LEARNER bikes, in the hands of learners, even harder... 'Preventative-Maintenance is not something in the lexicon... thrash it till it breaks... then 'moan' about it is the more usual ways about!

Or they get 'killed with kindness' and chains tightened up until the out-put shaft starts weeping oil.. then a bit more, until the bearing starts whining! Spark-Plugs get tightened up until the (alloy) threads that hold the in to the head, pull out, this kind of thing, is 'typical'....

And, oh yeah, kiddie-go-kwik-thinking. IF money gets spent on 'bits', and or time spent with spanners; much more likely to be spent on 'stuff' they 'think' will make it go faster.... not stuff that keeps it gong as slow as the factory intended! Which s usually faster than it would with ill-conceived 'mods' like loud exhaust pipes!

I am tempted to park the suggestion that there's anything necessarily wrong with the Aft-Mark exhaust, or its fitting.... first port of call would be to do a full and thorough 'service'. It's probably ever had one... even if a dealer has stamped the book beyond the first one!

With bikes, maintenance is needed on a little and often basis, where cars, due to the duplo scale of stuff, are, these days almost run until they are scrap! Bikes aren't! And ts a t of a shock t many! Especially to new owners of little bikes, where the 'little' is actually very little, but still more than they expect, but the 'often' is very much more than they 'maybe if the MOT Man Moans' a car may get!

Check the Owners-Book and or Haynes Manual. There's a whole list of things to do, and intervals they need doing... check the mileage... scratch your head and add a bit if you don't believe it, then look at the manual, look at everythg that should have been done from new, till that mileage, and presume you will have to do it all!!!

New oil, new filters, new spark plug. Tappets tickled.

DON'T dive in and pull the carburetor off, or to bits!
Oft done, for the sake of, and oft replaced with the old gaskets so they don't work... you ANY have to re-visit this one, but... you'll probably tell me its fuel-injected!!!! In which case Dirty Throttle Position sensors are the usual culprit, but still... dont touch it unless you have to... and the book says so!

Check the chain and lube it.Check the BRAKES... make sure that they are free and clean and not binding.. and back to top, Simple&Stupid.. lots of riders toe the back brake lever whilst riding,and don't realize that they are applying the brake whlst they do so... check your riding position, and adjust lever positions to suit.

BUT, all basic service operations 'done'... you have a bse line for any remaining 'problems'.

Back to that exhaust.... they often do very little to 'aid' performance.... just make more noise. And if the engine isn't set up for a 'free-flow' exhaust they can start to do damage, making bike run 'lean'. This can, in dire instances make valves burn out, or pistons melt.

If EFI, then the injection system 'aught' self tune, and correct the mixture for the changed exhaust. If Carburated, then not, and more worry-some that modern air-cooled bikes, are often leaned out before an after-market pipe is added to help with 'emmissions'.

Whether the 'ports have been matched' to the pipe?!?!?!?! I haven't heard of that one since the 1980's, and then by an old timer who told me it made SO much difference to his Matchless 350!!!!! It is NOT something that any-one tends to 'do' any more, or needs to be done!

Whether the conurbations been dicked with, IS something slightly more worry-some... a carburated engne should be 'jetted' to suit an alternative exhaust, and as after-market pipes tend to be less restrictive and make the engine run a bit weak, its common to up-jet them to run slightly rich to compensate..... this may or much more likely, not have been done; i anything, some-one may have dicked with the idle mixture screw on the carb.... and it could be anywhere! Set to the book.. and hope for the best, is my advice on that one. On an EFI engine, as said, system should self compensate... BUT if there's an Echaust-Gas-Recirculation system, and or a Lambda sensor in the collector... who knows what's still attached and functional, after mods! Like a carb, look at the book, put t back as close as you can to the book, and hope for the best! Work from there!

It's possible, that damage has already been done, IF the exhaust was at fault.. other-wise, that the exhaust ever was at fault... in which case, its not worth dicking with and risking making more problems than you have.

Hence, start with top bet, of rider error, and short-shifting, or ridng the brake.

May be little or nowt wrong with the bike; and these don't require ANY spanners or dirty hands to check and eliminate or even fix if needed.

Next; prevouse owner neglect/abuse. Do the proper servicing. Make sure it has all it should, and is doing what it should when it should. Eliminate posibilities and base line, the thing for further diagnostics.

The 'Zorst.. has a question-mark hanging over it... BUT it's not the first 'thing' to premsume fault with or start messing with. They are a common mod, and frequently not that great for either performance or economy, and meddle-mechanics give umpety extra chances for effup.. BUT, unless you are absolutely certain ts at fault, dont jump to conclusions!!! First make sure rider isn't to blame; then basic servicng. THEN you might stand a chance of fndng real fault else where.
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[Nobby the Bastard]

Jebus, mother of God!
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[Rogerborg]

[cb1rocket]

Don't take too much notice of Teflon mike. It's more general info on any bike but clearly doesnt know the specifics of the cbf125.

Carbs on an efi......come on Mike!
____________________
Honda H100S2 Rebuild - https://www.bikechatforums.com/viewtopic.php?t=253852

[Courier265]

[Davewins13]

Thanks for all your advice. Weekend of maintenance ahead I think.