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| the95th |
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the95th
Nitrous Nuisance
Joined: 15 Dec 2010
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 Posted: 13:46 - 22 Jul 2011  Post subject: CB125 mpg? |
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Hi,
My 1982 CB125 TDC has a few holes in the exhaust, its a bit tatty overall. But i havnt got the cash to give it the love it needs nor the time. However the fuel economy keeps going down and down.
When i first got it, on a full tank it would do just under 200 miles. ( which is about 70 miles to the gallon)
now, 6 months later. Its doing 120 Miles to the tank. For a 125 4 stroke commuter bike, thats quite rubbish and is costing me about £40 a week on fuel 0.0 which is almost 3 times what my CM125 used to cost.
Is this because im using BP? high grade fuel + Old engine = crap economy?
As my mate who has a CG125 1886 or 4? uses his local garage which has shite fuel really, and can do 150 miles to the gallon.
So im thinking of filling up there for a change.
Or is it because of dodgy exhaust thats been welded and patched to no end, because the replacement exhausts are £120.
*cash strapped student*
Anyway, how to make the bike more economical? some websites say it should be doing two or 3 times as more as it is.
____________________
2004 Rieju Rs2 Matrix 50cc, 1982 Honda CG125, 1986 Honda Cm125, 1982 Honda Cb125..... I kill a lot of 125's |
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| Teflon-Mike |
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Teflon-Mike
tl;dr
Joined: 01 Jun 2010
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| Posted: 14:27 - 22 Jul 2011 Post subject: |
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Holes in exhaust wont be helping.
fuel grade shouldn't make much odds. These things will run hapily enough on 95RON.
Biggest killer of ecconomy on them is fuel leakage.
Float needles don't always seal 'the best' and fuel taps can 'drip' even in 'off' possition.
ALWAYS turn fuel 'off' when you stop.
Hot engine, fuel will evaporoate from the float bowl, and float will drop to let it refill.....
Next, if you have hole in the exhaust, motor will tend to run 'weak', if the mixture screw has been wound too far out (& I may have given erroneous advice recently that stock setting is 3 1/2 turns 'out'.... not 1&1/4 {doubled up my own 'half turns' maths!}) wont run great & ecconomy will be down, ditto lifting the needle; eitheer of which may be necssary to compensate if exhaust holed.
OH! Add on Ed:
Just thought, bottom corner of the fuel tank, on or other side, where the side panel meets tank. Two distinct 'corners' in the metal pressing. Nib a little paint off the lower one, either side, and se if petrol starts peeing out of a pin hole!
They have a habbit of rotting through at that point; seems to b a thin area of the metal pressing, plus where water collects in the bottom of the tank, and they rust through from the inside.
BUT, paint keps the petrol 'in' so you dont see the leak, and it just weeps out along the seam, and vaporates, so you dont gt any 'tell' of lost fuel.
____________________
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?' |
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| koolio |
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koolio
Spanner Monkey
Joined: 08 Apr 2011
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| Posted: 17:32 - 22 Jul 2011 Post subject: |
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Could be so many things.
I would probably do it in this order though maybe wrong.
Basics- check if brakes are binding, check and adjust valve clearances, new spark plug & then check the spark (cheap and worth it just to be sure), oil change maybe (although I would do this at the end).
Air filter - Check it is clean. Replace/Clean if necessary, better to replace regardless imo, (if the problem turns out not to be the air filter you can always replace the old one, and use the new one at a later date).
Carb - Inspection and complete clean.
Engine - Check compression, if low you have spotted the problem.
Once you've done that and all is ok, you'll have to sort out the mixture on the carb and the idling, do it by the book.
If you are still having trouble check the electrical system, check the spark strength and gap and for incorrect timing.
Can't think of anything else at the moment. |
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| Teflon-Mike |
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Teflon-Mike
tl;dr
Joined: 01 Jun 2010
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| Posted: 19:04 - 22 Jul 2011 Post subject: |
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| koolio wrote: | check if brakes are binding |
Always a good thing to check.
 Check where you are resting your FEET!
Had a niggly one like this before, after much muggring with the bike, went out and followed the lad while riding, and noticed his brake light was constantly on, but KNEW is was properly adjusted. he was resting his to on the brake pedal, and constantly riding the back brake!
| koolio wrote: | check and adjust valve clearances |
Always good on Benley engines, do CCT at the same time.
As cam chain stretches, retards the cam. May be worth while you have the cam cover off to do tappets, winding crank round to TDC and checking cam alignment. If it is 'off' thn you have a lot of cam chain stretch. real 'fix' is a new camchain. You REALLY don't want on braking on you... I know what it looks like and it ENT pretty... BUT slacking off the camchain tensionr, removing cam sproket and retiming the cam, advancing it inside the camchain one or two teeth can bring timing and performance back up markedly.
| koolio wrote: | new spark plug & then check the spark |
There's two of them, and thy are Honda sizes, so not THAT chap, about £3 each. But worth while, none the less.
| koolio wrote: | Air filter - Check it is clean. Replace/Clean if necessary, better to replace regardless imo, (if the problem turns out not to be the air filter you can always replace the old one, and use the new one at a later date) |
Superdream had twin carbs, with curiouse twin air box and twin filter arrangement. Filters ar horndously expensive; From Honda they are about £25 each, and you need two of them!
Personally, on an older engine, that's likely to be rather tired anyway, I'd simply ditch them, and run the engine 'open' Long term wear wont be hugely effected, neither will the carburation, that on old PD is probably not the best to begin with.
| koolio wrote: | Carb - Inspection and complete clean. |
Again, there are two of them. And unfortunately, MANY old Supr Dreams suffer cronic carburation faults from cleaning 'damage'
They are prone to the float needles not always saling, though, as mentioned.
Something I FORGOT to mention, that IS worth checking, is the choke mechanism syncronisation. Another common fault, also exaserbated by carb removal for 'cleaning'.
Horible flex link between choke buttrfly spindls on two carbs. When fitted, link often doesn't get attachd, or attached properly, or falls off. Result choke on RH Carb flaps about of its own accord. OR, if th link isn't syncronisd, RH Choke doesn't fully close.
A snip of cable tie under flx link clip can help tightn up the link, twisting it to syncronise can help, but some times an elastic band between the bottom of the U of the flex link and a cable tie on th frame to positively hold the RH Choke open 'Off' is needed.
| koolio wrote: | Engine - Check compression, if low you have spotted the problem. |
Well, you have spotted a symptom. Low Comprssion could b a number of things; worn bore, worn or sticking rings, gummed or worn valves. And TBH on an old CB125 engine, unlikely it will have great compression. So many older bikes left derelict for many years, one or other valve left open, they corrode on the seats and dont seal so well. The Oil controll rings also tend to suffer clogging, and the bottom rings are more prone to sticking in their groove.
That, and hard valve stem seals are main causes of CB125 oil consumption; something which also hampers economy.
Its an engine tar down and top end rebuild 'fix' though, and you are looking at a £25 gasket set, and probably £90 for new barrel & piston, or re-bore and oversize pistons, plus any other work, such as valve grind or replacement, seat cutting, and while you are in there, further consideration of that camchain. BIG works. Enough to bring into question the economic viability of the fix, against value of bike, and putting repair cost to resale value towards another bike.
| koolio wrote: | Once you've done that and all is ok, you'll have to sort out the mixture on the carb and the idling, do it by the book.. |
Needle second notch from top, mixture screw one and a quarter turns from all the way in.
| koolio wrote: | If you are still having trouble check the electrical system, check the spark strength and gap and for incorrect timing. |
CB125 has self energsed CDi ignition. Quite common to gt a weak spark 'cranking' on the starter, because starters can be tired, battery powering them often tired, and the dog clutch to the crank can be 'sticky', giving low cranking RPM. As Sparks are self energised from the stator, low cranking revs give low energy to CDi hence weak spark; you wouldn't necsserily be able to tell from a poor cranking spark whether its the ignition system not doing its job, or the starter motor. Of the two, though, more likely to be weak cranking, CDi sparks on CB125 tend to b pretty good.
You cant adjust timing on them, its fixed by inductor triggers in the genrator casing, though if thy are dirty or the cover is misaligned, can give poor signal to the CDi.
The exhaust, is most likely his biggest problem; NOT having funds to sort that, he'll never get the carbs set up great.
Not getting carbs set up, running ritch is probably better than running lean, from holed pipe, means less likely to have motor overhating, and blow head gasket or siezure adding umpety cost to problem of replacing exhausts!
Check the bay, though 2nd hand pipes usually Micron or Motad pop up quite frequently for around £30.
Snowie has the £120 Pattern Twin pipes on the Pup. They are nice, but thy are also heavy, BUT you have to be careful when ordering; many of the cheaper ones are for earlier T-Shock model, and dont clear the starter motor and don't fit the hanger bracketry, and hang lower.
____________________
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?' |
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| lozza59 |
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lozza59
Nova Slayer
Joined: 19 May 2011
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| koolio |
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koolio
Spanner Monkey
Joined: 08 Apr 2011
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| Posted: 06:51 - 23 Jul 2011 Post subject: |
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???? Who gives a crap whether its two or one carb or two or one spark, same principle applies?
| Quote: | | Quote: |
new spark plug & then check the spark |
There's two of them, and thy are Honda sizes, so not THAT chap, about £3 each. But worth while, none the less. |
I'd say at £3 each thats piss cheap. Probably cheaper on ebay.
| Quote: | Something I FORGOT to mention, that IS worth checking, is the choke mechanism syncronisation. Another common fault, also exaserbated by carb removal for 'cleaning'.
Horible flex link between choke buttrfly spindls on two carbs. When fitted, link often doesn't get attachd, or attached properly, or falls off. Result choke on RH Carb flaps about of its own accord. OR, if th link isn't syncronisd, RH Choke doesn't fully close.
A snip of cable tie under flx link clip can help tightn up the link, twisting it to syncronise can help, but some times an elastic band between the bottom of the U of the flex link and a cable tie on th frame to positively hold the RH Choke open 'Off' is needed. |
???? Is the same as below really? On the whole choke is found on the carb????? Pick up the haynes or whatever and go through it "by the book".
| Quote: | Once you've done that and all is ok, you'll have to sort out the mixture on the carb and the idling, do it by the book.. |
Do the simple checks and overhauls that you should do on such an old bike and the problem should arise, most of them are in the without waffle list I wrote above. |
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Old Thread Alert!
The last post was made 14 years, 208 days ago. Instead of replying here, would creating a new thread be more useful? |
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