honda crm engine problem

[pecka2491]

i have a honda crm 125 1989 (i know its not a 250 but i cant find anywhere else on the net that can help me with my problem) it has a honda nsr 125 engine fitted which is meant to be pretty much the same as the original crm 125 engine i have just finally managed to get the bike running after buying it as spares and rebuilding the top end but when testing it once the engine reaches the 5/6 on the rpm counter it just seems to crackle and not want to go over this i have fiddled with the mixture screw and have had no joy but when i rev the bike in neutral it runs fine right round the rpm counter with powervalve kicking in at about 6 nd a half ish as it should if someone could help me out it would be greatly appreciated.
p.s. the carb on it is a big kehin one off a 1989 honda cr 125 could this also be a problem should i get a standard nsr carb or not?
thanks.

[fallenmikethebike]

Hi there, I fear you may have read somewhere that the bike should be good for about 100mph +.
The reality is, it's probably nearly 20 years old and many variables are connected to the ultimate top speed available, such as, carburation, gearing, condition of the engine, maintenance schedules, all of which need checking.
It is more than likely from your description that carburation is the problem here, albeit the jets within the carb are unknown, as is the needle position.
The fact that the bike will rev out cleanly stationary may also hint at gearing issues, BUT, the plug should be checked to ensure that a chronic weak mixture is not the issue, as this will kill the engine PDQ, [ it arrived with you as a box of bits after a previous top end problem], BE AWARE. It's probably best to run the poor little bugger in for a while if a new top end has been fitted, this will ensure mechanical longevity.
Good luck.
Mike

[pecka2491]

hi thanks for your reply believe me im not interested in claims that these would do 100mph+ i would not even want to try that on a 24 year old bike what do i look for on the plug and what sort of jets should i try in the carb and how do i solve gearing issues could you give me a step by step of things to do to cancel each problem out sorry i'm new to tinkering on with bikes and learning as i go along, thanks.

[fallenmikethebike]

The plug should be a tan/ biscuit colour, if it's lighter than that the engine is running seriously weakened mixture.
Start there first.
Ideally a plug chop test should be carried out at the offending RPM range, to find out exactly what's happening.
You will need to do some reading in the search area for " plug chop test".
Yes being 24 years old, many other things could also be adding to the bikes unwillingness to rev out, but start with the plug.
That should reveal where to go next to resolve the problem.
Mike

[knackeredMk1]

There is no way that a CRM125 would cope with the jetting of a CR125 carb. If you get the jetting right you will have increased top end by a very small amount over standard but taken away a large section of bottom/mid range power. CRM125s already lack low/mid range so it will become more difficult to ride for the sake of a very small gain in top end.

Go back to the original carb.

When you have it running correctly and if you really feel the need then get one that is say 2mm larger for that tiny top end performance gain.

The 125 has very odd gearing as it is based on the road bike so for decent off road performance and practicality you need to drop the gearing. Take one off the front and add 5 to the back to start with.

[pecka2491]

thanks for the replies i will try and sort it when i get time and a hold of an original carb also does anybody know of other exhausts that would fit a crm 125 don't want to pay £300 for a dep one lol or a place in the north east what can restore an exhaust cheaply the old owner of mine cut the exhaust to remove the cat apparantly and welded it back up badly thanks again.

[knackeredMk1]

There is no cat in a CRM125 exhaust.

DEP is your only option unless you can find a Honda original.

[Mudfacetony]

thanks for the replies i will try and sort it when i get time and a hold of an original carb also does anybody know of other exhausts that would fit a crm 125 don't want to pay £300 for a dep one lol or a place in the north east what can restore an exhaust cheaply the old owner of mine cut the exhaust to remove the cat apparantly and welded it back up badly thanks again.

If you want exhausts welding I know of two options, first is Armstrong's on Westgate Road, the second is a small bike shop on Hobson industrial estate (back end of Stanley/Burnopfield)

[pecka2491]

thanks wil try the stanley place as i live 5 mins from there