Why Is My Sonic Doing This?

[nellyp]

Hi, I am fed up of my sonic. It is about 10 years old now, and I had and engine rebuild last year (up to 150cc) but I cannot understand this. She will do 100km/h in 3rd gear but if I change to 4th she goes no faster. If I change to 5th she will slow down to about 80-85km/h. I have a bit of oil blowing through the head (before and after rebuild) and maybe a bit blowing through the exhaust. Would this cause the lack of power when using the lower gears? Could it be tuned wrong? I am at a loss so any help would be great. I am located in a town called Kaset Wisai in Roiet so if anybody knows a good bike mechanic in the area that could be a help too.

I don't use these speeds very often, apart from to give it a blowout now and again, but I'm sure this is not right and would like to correct it. I just think it lacks power to rev high

Cheers

[Kilgore Trout]

I suggest replace engine with used spec 125

[VocalNeal]

Could be a lot of things.

Lean mixture being one. So as the carburetor is vacuum operated you could look at the rubber diaphragm inside the top of the carburetor it may have a hole in it. Either that or the needle in the slide has been set too low.

Try a new spark plug first as that is simple and cheap.

I suggest a weekend ride to Roi Et and a visit to a Honda main dealer's workshop. If you do the diaphragm is on page E-19 of the parts book , item number 16.

Oh and use 20/50 oil it is a bit thicker so won't leak as much.

Edited February 15, 2013 by VocalNeal

[nellyp]

Could be a lot of things.

Lean mixture being one. So as the carburetor is vacuum operated you could look at the rubber diaphragm inside the top of the carburetor it may have a hole in it. Either that or the needle in the slide has been set too low.

Try a new spark plug first as that is simple and cheap.

I suggest a weekend ride to Roi Et and a visit to a Honda main dealer's workshop. If you do the diaphragm is on page E-19 of the parts book , item number 16.

Oh and use 20/50 oil it is a bit thicker so won't leak as much.

Cheers, i'll replace the plug tomorrow.

i know they will be a main dealer but do you think they will understand about the lean mixture and the diaphragm? Also I'm not too sure they will know how to set the needle. What do you think about taking it to one of these garages that do up Sonics as racers etc? Do you think they will have a better idea of how to set a carb properly?

Nice tip about the oil. Some thing I've wondered about my sonic is whether I should read the oil with the stick screwed in or with it resting in the plug hole. Any ideas???? Oh how i would love to have a manual for tis bike so I could just do everything myself (including the head gasket...out with the hermatite)

[dave_boo]

Blowing through the head? As in the rings are shot and you're loosing compression? Have you ran a compression check?

[BSJ]

Blowing through the head? As in the rings are shot and you're loosing compression? Have you ran a compression check?

Seems like a likely scenario. But it would be burning a bit of oil, not spitting it out un-burned.

My take is they bored it out and fitted a new piston and rings but didn't increase the valve size or open up the inlet and exhaust passages....or rejet the carby for 150cc. You may need some head work and a bigger carby.

[VocalNeal]

Could be a lot of things.

Lean mixture being one. So as the carburetor is vacuum operated you could look at the rubber diaphragm inside the top of the carburetor it may have a hole in it. Either that or the needle in the slide has been set too low.

Try a new spark plug first as that is simple and cheap.

I suggest a weekend ride to Roi Et and a visit to a Honda main dealer's workshop. If you do the diaphragm is on page E-19 of the parts book , item number 16.

Oh and use 20/50 oil it is a bit thicker so won't leak as much.

Cheers, i'll replace the plug tomorrow.

i know they will be a main dealer but do you think they will understand about the lean mixture and the diaphragm? Also I'm not too sure they will know how to set the needle. What do you think about taking it to one of these garages that do up Sonics as racers etc? Do you think they will have a better idea of how to set a carb properly?

Nice tip about the oil. Some thing I've wondered about my sonic is whether I should read the oil with the stick screwed in or with it resting in the plug hole. Any ideas???? Oh how i would love to have a manual for tis bike so I could just do everything myself (including the head gasket...out with the hermatite)

Sure the dealer will know. give it a good clean first to remove the oil.

I guess it depends if you have an alternative means of transport but you could look at the diaphragm yourself. Take the carb off and undo the screws on the cover on the top, remove the top and pull out the diaphragm and slide. Then inspect the diaphragm.

Sonic racing shops might offer to replace the carb. probably with a Keihin PE28 which is a "conventional" carb but will it be correctly jetted. You could ask? I bought one once in Rayong market for 500B. Not for a Sonic.

Surf for < Honda Sonic RS 125 2003 service manual in English anyone >

pick the first on the list

at the bottom of that forum thread you will find an .RAR file with parts diagrams. OK not a manual but...

Edited February 15, 2013 by VocalNeal

[nellyp]

Blowing through the head? As in the rings are shot and you're loosing compression? Have you ran a compression check?

I'm not blowing out the exhaust so I have kind of dismissed this as being the rings that are shot, it's only a bit of oil. How can I do a compression test without taking it back to a garage?

[nellyp]

Blowing through the head? As in the rings are shot and you're loosing compression? Have you ran a compression check?

Seems like a likely scenario. But it would be burning a bit of oil, not spitting it out un-burned.

My take is they bored it out and fitted a new piston and rings but didn't increase the valve size or open up the inlet and exhaust passages....or rejet the carby for 150cc. You may need some head work and a bigger carby.

My take has always been that they bored it out but neglected to do something else as well

. I have often wondered about the way the carb is set up. Are you saying that the should have increased the size of other parts at the same time. A bigger carb or resetting it seems the best way to go about it first. Remember this is a 10 year old sonic and not worth a lot. How much do you think the work would cost? Or should I forget about it.

[nellyp]

Could be a lot of things.

Lean mixture being one. So as the carburetor is vacuum operated you could look at the rubber diaphragm inside the top of the carburetor it may have a hole in it. Either that or the needle in the slide has been set too low.

Try a new spark plug first as that is simple and cheap.

I suggest a weekend ride to Roi Et and a visit to a Honda main dealer's workshop. If you do the diaphragm is on page E-19 of the parts book , item number 16.

Oh and use 20/50 oil it is a bit thicker so won't leak as much.

Cheers, i'll replace the plug tomorrow.

i know they will be a main dealer but do you think they will understand about the lean mixture and the diaphragm? Also I'm not too sure they will know how to set the needle. What do you think about taking it to one of these garages that do up Sonics as racers etc? Do you think they will have a better idea of how to set a carb properly?

Nice tip about the oil. Some thing I've wondered about my sonic is whether I should read the oil with the stick screwed in or with it resting in the plug hole. Any ideas???? Oh how i would love to have a manual for tis bike so I could just do everything myself (including the head gasket...out with the hermatite)

Sure the dealer will know. give it a good clean first to remove the oil.

I guess it depends if you have an alternative means of transport but you could look at the diaphragm yourself. Take the carb off and undo the screws on the cover on the top, remove the top and pull out the diaphragm and slide. Then inspect the diaphragm.

Sonic racing shops might offer to replace the carb. probably with a Keihin PE28 which is a "conventional" carb but will it be correctly jetted. You could ask? I bought one once in Rayong market for 500B. Not for a Sonic.

Surf for < Honda Sonic RS 125 2003 service manual in English anyone >

pick the first on the list

at the bottom of that forum thread you will find an .RAR file with parts diagrams. OK not a manual but...

I would attack the carb but am worried that something will fall out that I can't replace, I've never been much good with carbs or electrics once past the basics

[VocalNeal]

It is very basic you just take the top off and look at the diaphragm. Take the carburettor off and do it on some newspaper.

Some lateral/obvious thinking? Same engine as CBR125 R so surf for < honda cbr 125 r service manual download >

Edited February 15, 2013 by VocalNeal

[karlos]

Blowing through the head? As in the rings are shot and you're loosing compression? Have you ran a compression check?

I'm not blowing out the exhaust so I have kind of dismissed this as being the rings that are shot, it's only a bit of oil. How can I do a compression test without taking it back to a garage?

How is oil blowing through the head?

Do you mean up into the airbox? If so it could very well be the piston rings, too much crankcase pressure will force an excessive quantity of oil up to the airbox.

You may also be burning oil and not noticing it, having worn piston rings doesn't necessarily mean you'll see an oily residue on the exhaust's outlet.

These 150cc upgrade kits i have seen for various bikes have questionable build quality.

If it is your rings, i'd go for another stock engine or find a reputable manufacture who does oversized kits and pay a decent mechanic to get it done right.

Regarding the compression check, you will have to buy a compression tester, or you can just take the bike to any main dealer that has one (alot easier if you have one nearby)

If all else fails, try feeding Sonic a few gold rings and he should spring back into life.

[Briggsy]

100 km/h in 3rd gear? With standard sprockets and standard gearing ratio?? I don't think that is possible.

(I have owned a Sonic since they came out over 12 years ago.)

Edited February 15, 2013 by Briggsy

[karlos]

That speed in 3rd seems far too high. It seems like someone has been toying with the gear ratios / sprockets, which would explain why the bike isn't able to pull 4th and 5th.

When i say 'far too high' i mean the bike's speed should be spread out over 4th and 5th a little better, ie; 85kmh in 3rd, 110kmh in 4th, 130kmh+ in 5th with the 150 kit you have.

But you should still be investigating the oil issue also

Edited February 15, 2013 by karlos

[nellyp]

Blowing through the head? As in the rings are shot and you're loosing compression? Have you ran a compression check?

I'm not blowing out the exhaust so I have kind of dismissed this as being the rings that are shot, it's only a bit of oil. How can I do a compression test without taking it back to a garage?

How is oil blowing through the head?

Do you mean up into the airbox? If so it could very well be the piston rings, too much crankcase pressure will force an excessive quantity of oil up to the airbox.

You may also be burning oil and not noticing it, having worn piston rings doesn't necessarily mean you'll see an oily residue on the exhaust's outlet.

These 150cc upgrade kits i have seen for various bikes have questionable build quality.

If it is your rings, i'd go for another stock engine or find a reputable manufacture who does oversized kits and pay a decent mechanic to get it done right.

Regarding the compression check, you will have to buy a compression tester, or you can just take the bike to any main dealer that has one (alot easier if you have one nearby)

If all else fails, try feeding Sonic a few gold rings and he should spring back into life.

The oil is around the head joint, if this was on a car I would say the head gasket was gone. It could be coming from the exhaust manifold but i thought that unlikely. The airfilter box is too far away from the site of the oil for it to be that. The amount of oil loss is minimal and I have not topped it up since the rebuild, which was apparently a year ago (though I don't think it was that long, I'm going by my misses' memory). Any idea how to ask for a compression test in Thai? I really can't justify spending a load of money on the bike, especially as I was offered 10k on a part exchange for a scoopy for the wife. I just can't face riding a full scooter everywhere so if I can get this done cheap I will. In a perfect world I want a 1980s scrambler

[nellyp]

100 km/h in 3rd gear? With standard sprockets and standard gearing ratio?? I don't think that is possible.

(I have owned a Sonic since they came out over 12 years ago.)

I have never had anything done to the sprockets or gears, though like I said it has been upped a bit in the cc department. I was back home in the Uk for 6 years when the bike was on the family farm. No way would they pay to have the gearing altered. A sprocket replacement could have been possible though. It's something I'll check on. You seem to be the man on Sonic stuff, do you have any idea how many teeth the sprockets should have? A question about the oil stick too. Do you screw it all the way back in to check the oil? I am, but some bikes just have the stick pushed up to the threads. How fast does yours go in #rd and what does it top out at. I have nothing to guage my bike to, and can't remember what it was like when new It's a sonic RS

Cheers for your input

[nellyp]

That speed in 3rd seems far too high. It seems like someone has been toying with the gear ratios / sprockets, which would explain why the bike isn't able to pull 4th and 5th.

When i say 'far too high' i mean the bike's speed should be spread out over 4th and 5th a little better, ie; 85kmh in 3rd, 110kmh in 4th, 130kmh+ in 5th with the 150 kit you have.

But you should still be investigating the oil issue also

I can get way over 3rd, it'll stay at 98 in 4th and will get nowhere near 130. It'll go over 100 in forth but it is a long pull and loses speed as soon as I go to 5th. I take it you are suggesting going back to standard sprockets.

[Beardog]

All the waves I've had & 1 Yamaha Nuovo the way to check the oil was to just push the stick to the threads, not screw it back in & then check. I change bikes every year or so. Easier for me to trade the small bike in for a new one or one with 5000 kilos or less. 10,000 on a trade in for your ride sounds fair.

I don't think I would sink another 1000 baht on that old of a bike if it won't bring back any more return.....but I never get married to vehicles. A better one is right around the corner. Got rid of the sucky Boss & picked up a ER6N. Best choice I made in a long time

[nellyp]

100 km/h in 3rd gear? With standard sprockets and standard gearing ratio?? I don't think that is possible.

(I have owned a Sonic since they came out over 12 years ago.)

I have never had anything done to the sprockets or gears, though like I said it has been upped a bit in the cc department. I was back home in the Uk for 6 years when the bike was on the family farm. No way would they pay to have the gearing altered. A sprocket replacement could have been possible though. It's something I'll check on. You seem to be the man on Sonic stuff, do you have any idea how many teeth the sprockets should have? A question about the oil stick too. Do you screw it all the way back in to check the oil? I am, but some bikes just have the stick pushed up to the threads. How fast does yours go in #rd and what does it top out at. I have nothing to guage my bike to, and can't remember what it was like when new It's a sonic RS

Cheers for your input

OOpps just read this again and realised it's wrong. I check the oil both ways to be safe. At the moment it's on th elower limit when screwed in, and upper limit when not. Lucky it does this as it could get confusing

[nellyp]

All the waves I've had & 1 Yamaha Nuovo the way to check the oil was to just push the stick to the threads, not screw it back in & then check. I change bikes every year or so. Easier for me to trade the small bike in for a new one or one with 5000 kilos or less. 10,000 on a trade in for your ride sounds fair.

I don't think I would sink another 1000 baht on that old of a bike if it won't bring back any more return.....but I never get married to vehicles. A better one is right around the corner. Got rid of the sucky Boss & picked up a ER6N. Best choice I made in a long time

I don't mind 1000 baht if it gets me feeling better about the bike. It starts ok i'm checking mpg at the moment but it looks much better than a mates mio amor. Only thing is it smells because of the oil burning on the engine. If I can get the carb sorted for 1000 I'd be happy. Thing is i would then be thinking about the valves etc. Oh i don't know

[KRS1]

That speed in 3rd seems far too high. It seems like someone has been toying with the gear ratios / sprockets, which would explain why the bike isn't able to pull 4th and 5th.

When i say 'far too high' i mean the bike's speed should be spread out over 4th and 5th a little better, ie; 85kmh in 3rd, 110kmh in 4th, 130kmh+ in 5th with the 150 kit you have.

But you should still be investigating the oil issue also

Listen to this man.

sprockets should be around 15 front 44 rear...if you have a 16 on front its too big, if you have less than 42 rear its too small.

valve clearances are also suspect, this is a dealer only repair, don't trust somchai.

report back.

[nellyp]

That speed in 3rd seems far too high. It seems like someone has been toying with the gear ratios / sprockets, which would explain why the bike isn't able to pull 4th and 5th.

When i say 'far too high' i mean the bike's speed should be spread out over 4th and 5th a little better, ie; 85kmh in 3rd, 110kmh in 4th, 130kmh+ in 5th with the 150 kit you have.

But you should still be investigating the oil issue also

Listen to this man.

sprockets should be around 15 front 44 rear...if you have a 16 on front its too big, if you have less than 42 rear its too small.

valve clearances are also suspect, this is a dealer only repair, don't trust somchai.

report back.

OK I'll check the teeth today. I hope it is this as it's an easy fix (don't know the cost) I would also like to check the carb though

[nellyp]

That speed in 3rd seems far too high. It seems like someone has been toying with the gear ratios / sprockets, which would explain why the bike isn't able to pull 4th and 5th.

When i say 'far too high' i mean the bike's speed should be spread out over 4th and 5th a little better, ie; 85kmh in 3rd, 110kmh in 4th, 130kmh+ in 5th with the 150 kit you have.

But you should still be investigating the oil issue also

Listen to this man.

sprockets should be around 15 front 44 rear...if you have a 16 on front its too big, if you have less than 42 rear its too small.

valve clearances are also suspect, this is a dealer only repair, don't trust somchai.

report back.

OK I'll check the teeth today. I hope it is this as it's an easy fix (don't know the cost) I would also like to check the carb though

Back sprocket has 36 teeth front 15. So what was the intesion of this? Acceleration aint that good (again nothing to compare it to) and top end is crap.

[nellyp]

looked at thegear of teeth and it looks like if I put a sprocket with 44 teeth on it my top speed will reduce, but I should rev higher in higher gears. Not too sure that will be a great idea. I'll get a sprcoket fitted though, as this on is obviously not meant for the bike. Looking at the engine now for blowing etc. I'm enjoying this now, good to get the hands dirty and show my sons how to work spanners

[KRS1]

looked at thegear of teeth and it looks like if I put a sprocket with 44 teeth on it my top speed will reduce, but I should rev higher in higher gears. Not too sure that will be a great idea. I'll get a sprocket fitted though, as this on is obviously not meant for the bike. Looking at the engine now for blowing etc. I'm enjoying this now, good to get the hands dirty and show my sons how to work spanners

That back sprocket is way too small, there is not enough power in that engine to allow the rpm's to climb higher...too much resistance. Your top speed will increase do to higher efficiency.

Its a common misconception that putting on a smaller rear sprocket or larger front sprocket will increase top end speed, you have to have the power to back it up first.

You will probably need a new chain too in order to fit the sprockets, unless the chain adjustment indicators are currently all the way back, then it may still fit.

The sonic and cbr 150 both consume oil its normal for the levels to recede. I bet the oil you see coming from the head, is actually from the valve cover which is also normal for a 10 year old bike with a reused gasket, not that its good but it happens and fairly usual. Dont screw the oil stick in when checking. Screwing it in will make it appear to have more oil than there really is.

Edited February 16, 2013 by KRS1

[Briggsy]

LOL 36 teeth on the back sprocket. Who da fok put that on? You gotta be kidding me. This was somebody's crazy idea du jour.

Measuring oil, do NOT screw the dipstick/lid combo back in. Simply firmly rest it in the hole.

[nellyp]

looked at thegear of teeth and it looks like if I put a sprocket with 44 teeth on it my top speed will reduce, but I should rev higher in higher gears. Not too sure that will be a great idea. I'll get a sprocket fitted though, as this on is obviously not meant for the bike. Looking at the engine now for blowing etc. I'm enjoying this now, good to get the hands dirty and show my sons how to work spanners

That back sprocket is way too small, there is not enough power in that engine to allow the rpm's to climb higher...too much resistance. Your top speed will increase do to higher efficiency.

Its a common misconception that putting on a smaller rear sprocket or larger front sprocket will increase top end speed, you have to have the power to back it up first.

You will probably need a new chain too in order to fit the sprockets, unless the chain adjustment indicators are currently all the way back, then it may still fit.

The sonic and cbr 150 both consume oil its normal for the levels to recede. I bet the oil you see coming from the head, is actually from the valve cover which is also normal for a 10 year old bike with a reused gasket, not that its good but it happens and fairly usual. Dont screw the oil stick in when checking. Screwing it in will make it appear to have more oil than there really is.

Brilliant

Cheers mate

[nellyp]

LOL 36 teeth on the back sprocket. Who da fok put that on? You gotta be kidding me. This was somebody's crazy idea du jour.

Measuring oil, do NOT screw the dipstick/lid combo back in. Simply firmly rest it in the hole.

It's funny that my brother in-law who was in charge of the bike while on the farm totally denies changing the sprocket. I suppose the fairies may have done it

[VocalNeal]

100 km/h in 3rd gear? With standard sprockets and standard gearing ratio?? I don't think that is possible.

(I have owned a Sonic since they came out over 12 years ago.)

Good call.

Stock is around 15/42 so at least the bike should be taken back to stock and start again Or put 14 on the front that gets it to roughly the same.

Edited February 16, 2013 by VocalNeal

[Briggsy]

P.s. Oil measurement should be done on the centre stand, not the side stand. Let bike warm up for a bit then turn it off and leave it for at least 3 mins to allow oil to run down.

You know all this already, why I am telling you this.