125cc seems underpowered, smaller sprocket?

[EazyDuz]

Its a GZ125, i know they arent quick anyway, but it should hit 60 without having to be going downhill...

I normally ride like:

1st up to 10ish
2nd up to 25ish
3rd up to 40
4th from there on, as said the needle usually stops at 50mph.
5th only maintains what speed im at as long as its flat ground

Its had:

2 brand new tyres
tappets done a few days ago (Thanks Tef for the lesson )
Recent oil change
Chain lubed and in good condition, as are sprockets, could do with tightening slightly so i am doing that in a minute
Air filter is clean

Im only 12 stone!
Its a 55 plate and done 15k, i only want another 5-8mph extra just so i dont hold traffic up on main roads.

So i was wondering, would it help to get a smaller front sprocket, or a larger rear one, are there any negative affects?
Will also put some Redex (snake oil) in the tank just because ive got some knocking about and i cant hurt,.

[nop]

A smaller front sprocket will make it go slower. If you want to go faster you want a bigger one!

The cheapest way to go is to increase the front sprocket by 1 or 2 teeth. This means you may get away with not needing to change chain length. You must realise though that this will come at the expense of acceleration.

However you ARE riding a 125 and 125s ARE utterly gutless. You simply have to accept it.

[EazyDuz]

well the way i saw it is that i havnt redlined 4th or 5th, so a smaller front sprocket will make it easier to redline therefore making it faster, a larger front sprocket will just make it struggle even more to reach redline...

[Kickstart]

Hi

Smaller front sprocket might make 5th gear usable, but doubt it will make any real difference to top speed (you might get another 1~2mph from it by 5th becoming usable,as though it were 4th with very slightly raised gearing).

But ~55 doesn't take that much power. Suggest you have quite a bit under 10hp.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[SnowTigeress]

well the other day when you was here you seen me changing my sprocket back to the bigger 15 tooth as the pup was slower in first,as the CB125 will do 30mph in first,The only reason i changed the sprocket to a 14 tooth was for mod 1 so i had to change gear..

But then again could you be changing gears to early?

With the smaller sprocket the pup was only getting to 25mph in first

Make the engine work for you not the other way round,thats what i was told by hinckley
____________________
Real bikers build their own Renovated and Riding a 1986 Honda CB125TD-C called the Pup. Full Licence 13/09/2012, 1994 Moto Guzzi 750 Strada
Can-Do Girl that does spanners TOO!
TheSmiler: binning it is better than going around a roundabout the wrong way

[EazyDuz]

i dont know snowie, because its my first bike, i dont know how much i should give the little engine, considering it has no rev counter either i dont want to stress it too much.

But it sounds a bit revvy in 3rd at 40mph...

front sprocket is stock 15 tooth, rear is 45 tooth. Would changing the front sprocket mean i need to cut the chain down slightly or will it be ok on the adjusters?

Like i was saying to mike i would be happy with maybe 3mph faster, i normally average around 50mph, so 53 or more would be better, ideally 60, which i thought it should do.

[SnowTigeress]

As for the other question you asked

do you think the bikes running lean or weak then check he spark plug...

that tells you a hell of a lot...

In the manual theres a page on the different colours and what it means
____________________
Real bikers build their own Renovated and Riding a 1986 Honda CB125TD-C called the Pup. Full Licence 13/09/2012, 1994 Moto Guzzi 750 Strada
Can-Do Girl that does spanners TOO!
TheSmiler: binning it is better than going around a roundabout the wrong way

[SnowTigeress]

[EazyDuz]

Since i cleaned it its slightly sooted again. Ordered a new one though, i dont think it has been changed in a while and im hoping that will improve the speed as well.

Is changing the mixture just a case of slight adjustments to the mixture screw? Like ive done so many times on my nitro RC cars lol

[EazyDuz]

[SnowTigeress]

[EazyDuz]

[SnowTigeress]

[SnowTigeress]

[Kickstart]

[EazyDuz]

Just tightened the chain as it was a bit loose, put quite a bit of snake oil in the tank, hope its not too much. Also the air filter scoop was facing the rear of the bike, surely it should face the front where all the oncoming wind will be flowing straight in? So i put it facing the front as well.
Tightened the throttle cable a tad, clutching at straws i know but it might help...

And no my insurance doesnt cover me for that unfortunately.

[nop]

Iridium spark plug!

Did you buy an iridium plug yet?

[EazyDuz]

nope, research tells me its the biggest scam going... its a 125 not a high powered race bike.

[Kickstart]

[EazyDuz]

Ok so put it back how it was is what you are saying, fair enough

[Kickstart]

Hi

Airbox is meant to give a supply of smooth air (smooth is the wrong word, but my brain isn't cooperating). You might disrupt this as well.

However at 60mph I suspect the effects either way will be nil.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[EazyDuz]

Put the filter back how it was, i swear the exhaust seems louder since i put redex in but thats probably just me going nuts.

Wind seems to be the biggest problem, just did 65 down a slight hill with wind going my way, coming back up the road i was stuck at 40!

[SnowTigeress]

[EazyDuz]

I swear i did in another thread? I start on Monday, i said i paid upfront ans they owe me a fiver, they couldnt let me start without proof of cbt etc so ive got all that and filler their form in.

Fit a 12v socket to my bike yesterday to charge the nav first mod on the bike.

[Teflon-Mike]

I think I ought o leave this one to Snowie!
She obviousely HAS learned something, despite all her protestations!

Right; said after we did the tappets (BTW looked at vid... and err, no cant tell if its tappety by the sound!) To check the plug. Would have taken it abouty two three miles to burn off any old deposits then brought it back, coming 'in' up the street so I could 'nail it' to the stop from the roundabout on the corner in second to put it under load, then drag in clutch and kill the ignition, to stop the engine as it's running under full throttle... to coast to my drive way, where I can then pull the plug and look at colour. Called a 'Plug-Chop'.
If you carry plug spanner & spare you can do it on a long straight bit of road from real speed; swap plug, pop it in your pocket and then check when you get home.

Taking the plug out on your drive, after its been allowed to idle, tells you only how its running at idle; not under load.

I couldn't see a choke on your bike; and you started it without choke every time.

I would suspect its ritch at idle; hence black sooty plug; when you check without doing an 'on-load' chop.

As for fine adjustment:!?!

CHECK THE BOOK

Basic low speed mixure is set by the idle jet, then 'adjusted' on the idle air screw. There's usually a pipe or port through the carb body from intake to outlet, joining the emulsion galleries above the main-jets together; and it 'usually' lets more vacuum from the outlet end to the emulsion tubes by opening the tap, letting more air get sucked through the emulsion galleries, hence making the mixture weaker, lowering pressure difference over the jet.... hence out often means lean, not ritch... BUT not always so. Super-Dream carbs, its out for rich in for lean, AND book often doesn't tell you this 'simple' fact, just says 'adjust' for best running!

ANYWAY: starting point is to do tappets and cam-chain adjuster - DONE. Next up you do the air-filter (done?!) then 'ignition'.

Ignition on your bike I THINK is fixed timed CDI system that's in effect non user adjustable. BUT CHECK THE BOOK. So all you reallyt have in there is the spark plug to clean (or replace) GAP (dont rely on brand new one being correctly gapped for your engine!) and the spark plug leads to clean and check for splits or cracks.

BUT; the googlie on your bike is the throttle possition sensor on the carb-butterfly. I suspect, as I spotted no other leads on the carb, that it is purelky a sensor for a more evolved CDI ignition to more critically adjust timing according to engine 'load' as well as revs, so that it can run more advance and leaner mixture for ecconomy & emmissions...... but I am guessing. There MAY be a mechanism in there to modify the slide bahaviour.... CHECK THE BOOK

So, last thing on the ignition system will be to check that TPS. Two 'things' first the adjustment. You may be lucky and the book will tell you what resistance it should give at fullt closed and full open possitions; or maybe voltage on one of the wires; In which case you can slack the two screws holding it to the carb body, put multi meter on the wires to read volts or ohms depending what book values you have; and with the air-box out of the way, so you can see the throttle butterfly..... 'SET' to the open possition, by getting the butterfly exactly horezontal in the carb bore, then twisting the TPS on its screws until you get correct reading, nip screws, then back butterfly to closed and check reading again for closed possition.

However, simple carbon track resistor; common problem is that the tracks wear, and on a little bike like yours, where they are cracked wide open often, likely that there is a wear 'furrow' with pronounced ramp at the ends which likely to send readings wampy either lifting contact off the track or going 'low' depending how sensor is arranged.

Here book may not be too helpful; but TPS is like the volume control knob on a cheap radio; and you know how if its a radio you turn 'off' with the same knob, so the tracks wiped every time you switch it on, it can ear out and go a bit 'funny' volume going loud or quiet as it wipes over crud or nicks 'stop' furrows.... or like on a radio that turns off on a button and rarely has volume adjusted, when you do, it crackles becouse the contacts are dirty.... it's possibly a sealed for life unit you cant clean, and its worn out beyond, so check prices. BUT you may be able to open it and simply clean the tracks....

And for what it's likely to do.... may be possible to ditch the thing all together and simply hard wire the sensor with a plain resistor to mimick perhaps 2/3 throttle!

Anyway; THAT one needs investigating; THEN you can look at the carb. AND first thing is to make sure jets are clean and your diagphram not perished. Which is a carb off job.

Cleaned & serviced; then you can put it back on; make sure choke mechanism 'set up' so it is fully open when it ought to be and not fluttering about ritchening mixture; then base settings for mixture screw; best idle on the idle screw; set TPS as book, THEN start mucking with the idle air for 'best running' and plug colour at idle..

THEN on load plug-chop; which, as its a CV carb, if its out, may not be much you can do; as I suspect that the needle is fixed.

Meanwhile NOTHING you can bludy do NOW until you have run that tank of REDEX adulterated fuel through the engine... and then a couple more tank fulls to 'wash'......

And chalk it up to 'Learning'...... Redex is an oxidising agent; it grabs oxygen out of your charge to burn off carbon deposits; so until the stuff has all 'gone' you are never going to know whats base setting and whats an effect of the REDEX.....

Meanwhile any effect it has of de gunking yoru carb, is negligible..... its diluted with petrol; I have FILLED a float bowl with neat redex to see what effect it has, and still had to scrape chillac.... its not very effective! And doing the job properly as you should have to begin with; stripping and cleaning, will do far more good.

Redex is for folk that prefer to use thier credit card than spanners, and don't realluy want to use either, and a £5 bottle of reddex seems like good 'ecconomy' compared to paying a mechanic £30 to ;have a look' and probably present them with an £80 bill for a full service and tune up! The difference it makes is negligible!

Though in its defense; FIFTY years ago, and I only know this because there were still people aroiund that swore by it, when I was a kid, and my local lap-board garage still offered a 'shot of redex' in your fill up! When cars were rather less precisely engineered as they are today, generally had points ignition, carburettors, low compression ratios and two push-rod valves per cylindxer, AND we had low octane, high volatility 'blended' petrol; engines DID 'coke up' and it was a regular service procedure, more soo on 'side valve' engines that some 'new' vehicles still used when I was a child STOP SCOFFING, I'm NOT that old! You did a De-Coke every year or 10K miles. And Redex DID, as an oxidising agent actually help keep the engine clean and prolong service intervals..... also reduced already low octane rating, reducing possible power, and throttle response, AND made the engine run weaker, both by its oxygen robbing AND by bunging a % of the stuff into the fuel so you got less petrol.... but most engines were set 'ritch' for safety in them days against the dreaded 'pinking'...... so it had SOME use..... but?!?!? Even then, when it might have done something useful, was still one for those happier rattling coins than spanners and want to spend them!
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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?'