Honda sky 50

I have recently purchased a honda sky 50, not working. I have checked compression which seems good, it has a great blue spark, I have also cleaned the carb and yet it still doesn't want to start. I believe it is not creating the suction to draw down the fuel, but does anyone else have any ideas, any would be useful.
Thanks

 

Does it turn over but just not fire or is it not turning over at all?
Kick start or electric starter?
If it’s turning over but not firing then carry out basic checks.
Usual checks : is fuel entering the carburettor? If no then check fuel tap and vacuum system . To check this simply remove the fuel pipe from the carb and turn the engine over, if fuel comes out then all good to that point. Next check the carb is clean , jets clear and air/fuel settings are all set to base point. Usually about 2 1/4 turns out is a good place to start.
Check plug is getting fuel to it. Turn bike over, quickly remove plug and see if end is wet.
Next, remove air filter and whilst turning bike over spray starter fluid gently into the carb inlet. If the bike fires with sure-start spray then it’s a fuel issue with the carb.
If it’s electric start then also check the battery level. A low battery will stop the engine from building sufficient spark/ compression to start the engine.
If it’s turning over but not firing then my first check would be the sure start in the air filter.

 

Okay so, the bike turns over fine and I have cleaned carb already, a couple of times, I don't get fuel out fuel pipe when turning engine over, however I can suck on the suction pipe and fuel comes out easily? I sprayed some carb cleaner into the carb while turning over and it was firing which means it's not spark. Any idea about why the suction isn't good enough to suck the fuel down?
Thanks

 

What type of fuel tap do you have? There are free flow which is a fuel pipe running directly to the carb from the tank. You may have an inline filter part way along or you may have a metal tap attachment with a turn lever. Check the lever is in the on position and if you have a filter then check it is not blocked and is fitted the right way round.
You might have a vacuum tap. Under the fuel tap is a metal unit with small metal spigots. Usually two pipes run from this, one is the fuel pipe which goes to the carb inlet and the second is a vacuum pipe. This attaches to the fuel tap and then the other end feeds to the engine where the carb enters the main engine. When the engine turns over then a vacuum is caused at this inlet manifold area and sucks up this pipe causing a small rubber diaphragm to open in the metal tap allowing fuel to run. If you have this type then check the pipes are attached to the correct spigot. Check YouTube but one is fuel and one is vacuum but get it wrong and the engine sucks in fuel instead of going to the carb. If in doubt suck on the one not attached to the carb and fuel should run down the fuel line. Suck in short pulses not one single suck.
So, if vacuum type tap you have two hoses coming off, check they are fitted correctly and suck the vacuum one. If manual tap then check it’s on and allowing fuel to flow.
Check you have fuel in the tank of course?! Also make sure any tank breather pipes are clear and not blocked. If in doubt then remove fuel cap while testing the flow.
If you are sucking the vacuum pipe and fuel flows down the fuel pipe but doesn’t work when all is connected up then you may have a vacuum leak causing low pressure in the vacuum system. Attach the pipes turn the engine over, check the carb float bowl to see if fuel is entering. Just undo the drain screw to test. If no fuel then you have an issue in fuel reaching the carb but if it has fuel then it’s a carb issue.

 

Okay, so the tap is a vacuum tap and yes the pipes are connected the right way as I can suck on the suction pipe and fuel will flow out of the fuel pipe, however when I reconnect to the manifold and the carb and turn the engine over, I don't get any fuel out of the fuel pipe? So I know nothing is wrong with the tap and nothing is wrong with the pipes either as they work when not connected, it just when connected it doesn't seem to work......

 

Okay, I would be looking at the vacuum side of things then. Trace the vacuum pipe as best you can. It will do one of two things, either connect directly to the inlet where the carb joins the engine or attach to a T connector where it branches off to the carb and the engine. Check the lines for splits and holes, check the T piece if used and check its connected to the engine spigot. If all good and secure then check the carb connection to the engine. If its a rubber boot then look for leaks. Sounds like low vacuum pressure might be the issue.
Another thing to try is to disconnect the vacuum pipe from the engine end, block the hole then suck it to fill the carb float bowl, get the bike running and reconnect the pipe, see if it draws a vacuum. A carb float bowl should hold enough fuel for a minute or so.
Yet another option is rig up a makeshift fuel tank using a jar with a hole and fuel pipe rigged up and feed the carb directly, see if you can get the engine running. At least then you know for definite that its a vacuum issue and not carb related.

 

The suction pipe leads to the inlet manifold that connects the carb to the cylinder, how could I tests to test the vacuum pressure?

 

I was writing while you were, try the direct fuel feed idea to check that the bike runs. That at least eliminates everything else.

 

Okay well I have tried applying suction to the pipe while fuel pipe connected to the carb which gets the fuel into the carb but i don't think it is drawing the fuel out of the carb very well as it seems to fire but never actually start idling ?

 

Are you testing this with the air filter attached or off. Try restricting the airflow into the carb a little. If it’s open then it will run lean and there won’t be enough vacuum pressure to draw air across the carb Venturi to suck up fuel from the idle jet. Ensure the filter is attached.
Key is making sure you have a good flow of fuel into the carb floatbowl. Bypass the fuel valve system by rigging a bottle of fuel to flow directly into the carb fuel inlet. Once you have unrestricted fuel flow then try to run it. If it’s not running then there’s a good chance it’s the carb settings.
If it runs with a free flow of fuel to the carb then go back to checking the vacuum system.
To make a temporary fuel tank for testing get a glass drinks bottle, drill a hole in the lid which will allow a short length of fuel pipe to slip in. Seal around the pipe / hole with sealant or tape (doesn’t need to last long, just enough to stop it pouring out around the pipe), fill bottle with fresh fuel and attach lid so fuel pipe sits a cm in. Turn it upside down and fuel should flow out of the pipe. Attach pipe to carb fuel inlet. There you have a simple fuel tank for testing the carb.

 

Okay I had the air filter off however I did cover the end of the carb to pull the fuel through which still doesn't work very well, I will try using the bottle in a moment but I think the problem is the fuel is not being sucked from the carb into the cylinder?

 

Put filter on and rig up the fuel bottle direct to carb ensuring it’s actually entering the floatbowl. If you get no start then remove air filter and spray sure- start again keeping the fuel bottle rigged up. If it still won’t run then This eliminates the fuel delivery system as being the issue. That leaves carb settings and compression I reckon.
If electric start then make sure battery is fully charged as low battery can prevent firing.

 

Okay I have tried with air filter on and still the same , and I kept the fuel coming and sprayed carb cleaner straight through the carb, this seemed to try and start but not quite like u could hear it firing? Any ideas why?

 

So you are confident that fuel is reaching the carburettor, you have spark. When you spray carb cleaner then you get a slight attempt at firing but not great. This attempt suggests the spark is present.
Having never used carb cleaner for this purpose then I can’t comment on its effectiveness, I always use a starter fluid like sure-start which is designed to replace the petrol on start up for damp engines and poor starting. Might be worth buying some. Keep the air filter on and spray a fine mist into the box whilst trying the starter. Just a mist is needed, not a good soaking.
Try compression.
Remove spark plug and place thumb or finger tightly over the hole then crank the engine. This should force your finger off completely. If it’s a light puff then spray a little wd40 or small drop of oil into the plug hole and try again. If this results in a stronger pressure then it indicates a compression leak. If you can get hold of a compression gauge then even better.
So this really suggests that the carb is not set up correctly or compression is low. Both will need rechecking fully. Beyond that I’m not sure.

 

Pretty sure fuel is getting into carb and yes definitely have a spark, carb cleaner is flammable and will usually start or attempt to start the engine when sprayed in, and I started with compression as have a compression gauge and it reads a pretty solid 75 not sure how it compares but I recently put a new cylinder into another bike and the reading straight out was 75 so I assume it has enough, and okay I was looking around and it says it could be the crankcase seals leaking which wouldn't give enough suction to drag the fuel into the cylinder? But I want to make sure before I open up the engine. Thanks for the help