250cc does not go over 35 mph

[toppetsaha]

Another problem with my Honda CB250N 1995...

When riding the bike seems to be stuck at 30mph uphill, 35mph on flat and 40mph down hill. However there does not seem to be any lag within the rev range.

I have already established that it is not a fuel breather problem or a problem with fuel leaving the tank.

My only guess is some sort of carburetor restrictor is blocking the flow.

Thanks in advance for relpys.

[Copycat73]

what are the valve clearances like ?
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[toppetsaha]

[suzukirider19...]

have you checked the clutch might be slipping as this would cause the speed issue
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[numpty2]

There is a fuel filter in the petrol tap. Have you checked this?
Switch the fuel to OFF. Then unscrew the big nut at the bottom of the fuel tap - gently it's only soft aluminium. Make sure you remember how it fits in place. Check the filter.
Gently re-fit, being careful to get it back in properly.

These bikes can get to 80mph, but they are happier at 60-65.

I've owned 2 of these in the last 10 years, so I know my way round them. I might be able to help if you are anywhere near Rugby.

Is this the same bike with poor electrics? Could that be the problem (weak spark)?

If you do check the valves be very careful when refitting the cylinder head cover as the threads strip very very easily.

[toppetsaha]

[numpty2]

It is number 6 on this drawing:

https://www.ronayers.com/Fiche/TypeID/26/Type/FUEL_TANK/MakeID/1/Make/Honda/YearID/42/Year/2001/ModelID/7336/Model/CB250/GroupID/320086/Group/FUEL_TANK

Be gentle!


And of course there is the air filter. This is a big papery thing. You can get replacements, but often it can benefit from blasting back though with compressed air, or maybe even hoovering. It might be worth changing if it is of unknown age:

https://www.wemoto.com/bikes/honda/cb_250_m_n_p_r_t_w_x_y_1_two_fifty_mc26/91-03/picture/air_filter_honda_oem/


What do the spark plugs look like?

[toppetsaha]

[Howling TerrorOutOfOffice]

Just a thought.

Might be worth checking the choke mechanism is working. Reason being, I had the choke on my 250 working its way from the off position to the half-choke position. It's the plunger type. Took me a minute to suss what had happened. Similar results to what you are experiencing.
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[toppetsaha]

[toppetsaha]

[numpty2]

The choke cables on these can cause problems. Cable routing is a bit tight and some people have issues with the engine cutting out on full steering lock (when this pulls the choke cable and the choke goes on).
Check that the choke outer sleeve is properly seated at the carb.

But I'd check the fuel filter first, it is easy & quick to do.

If you do decide to strip the carb down, this might help:
https://www.youtube.com/watch?v=RIa23_0Hn9I
But this will be the USA version, and the UK one has some differences, perhaps just the jet sizes.

[toppetsaha]

[numpty2]

I agree with you. I have only had to strip a carb once, about 20 years ago. They are full of delicate little bits unsuited to my hamfisted mitts. Stripping a carb is a last resort as far as I am concerned. There is a high probability of losing bits or having bits left over.

You could try a carb cleaner first anyway:
https://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_202903_langId_-1_categoryId_255221

or the USA guys like Seafoam, but I don't know where you would get this in the UK:
https://www.ehow.co.uk/how_8685128_use-seafoam-motorcycles.html

[toppetsaha]

i did give it a go before on a moped... didnt go very well...

I have considered the carburetor cleaner, will check the free options first tho

That sea foam stuff looks like a mix between fuel conditioner and 2 stroke! trust the yanks...