Non-starter 250 V-Twin - Help please

[Dan505]

Hi,

Bike won't start off ignition button and when bumped idles at 3K, but can hunt when accelerating. Have checked the following and all tested ok
Coil packs
Injectors
air sensor on throttle body
battery
sensor on air box
spark plugs
HT leads
valve clearance (all within spec)

compression on front cylinder is 120, rear is 110. Service limit is 146 so i know it is low. Cam chain tensioner is slack on the spring (ordered, waiting to fit). after pushing it home tonight for 3 miles I need to sort it. could this be an earth fault?

Any help/tips (yes it has fuel) very much appreciated as it very nearly got rolled into a ditch tonight.......

[Hondafan]

Have you got a spark WHILE it is cranking over on the button?
?

[Dan505]

Yeah it sparks off the button, started stripping it last but nothing looks amiss so far

[Dan505]

no one got any ideas?

[Hondafan]

If it is fuel injected and hunts when it does start I would check for

An Air leak into the inlet, allowing unmetered air past the throttle body.
there should be a crank and or cam position sensor which tells the ECU the engine speed and position to decide the correct time to inject and spark.

If one of these is faulty or is not getting a good connection you will get all sorts of running issues.

Is there a side stand switch to prevent the engine starting with the stand down?

Check the switch and any connections to the switch for corrosion etc.

Where is the bike and exactly what make/model is it?


Mark

[Dan505]

side stand switch removed last year, i'll check the inlet, do you mean between air filter and throttle body?

its a GT250R EFI

[Hondafan]

leak will be between the throttle body and the engine.
This will allow ait into the engine that the engine hasn't measured or accounted for.

There might be flanges where the inlet tract bolts to the head, these are sometimes rubber which is bonded to a metal piece which the bolts pass through.
The bonding can give out in time allowing the rubber inlet to become detached and let air in.

When you removed the side stand switch , what did you do with the wiring?
Has it corroded?

I had a bike where the wiring to the SS switch was under the engine and completely open to muck off the road.

If you can get it running, try spraying WD40 or similar around the inlets, see if this makes a difference to the running.

[Dan505]

my S/S wiring is high up under the fairing although i think the connector is exposed :/

[Hondafan]

did you look at the inlets?

[Dan505]

Not yet, plan to later