Airhead

This might be a difficult one to solve, Firstly, have you got a haynes manual or another manual, that will tell you how to set up the ignition timing, it does however requre a dial test indicator and spark plug adapter to set it to the required 2mm BTDC. I'm a bit confused about this though because you say you checked it with a strobe and it was spot on, so in suspecting the timing you may be barking up the wrong tree. It might be a missfire at 3500/4000 rpm and that could be caused by almost anything, could be an air leak somewhere someting blocked or dirty in the carb faulty CDI faulty spark plug worn piston rings / bore not sure about the air gap you mention, I wouldnt have thought this is an adjustable setting, but if it is then yes maybe its even this, to what extent did you strip and clean the carb if you screw the mixture screw in and out does it have an affect on the idle speed?

Nice Who did it?

Here

Might take you a couple of hours longer Steve

This could be caused by several things Loose Cylinder head bolts Loose Cylinder to Crankcase Loose connection on carb to reed block connections

The 125's had a smaller venturi carb, you are looking for a mikuni VM24 for the 175, it will have an ID mark of 2H500 on it I wouldnt bother about the exhaust if you cannot see the restriction in the header pipe I dont think there will be one, the 125's didnt need restricting as the would barely put out more than 12 BHP anyhow, the 175's are only 15 / 16 BHP as standard.

Why not just strip the caliper and fit new seals, do you have to keep topping up the reservoir? I'm surprised it passes an MOT test like this!

Try it again, give it a good blast, seems you may have some oil in your crank cases What was the extent of your strip & clean, why did you do it, lets have some detail

Poke the hole through with a pin or something

Wipe off what you can, then hold the end with pliers and if you have a gas hob, burn off the excess oil, watch you dont burn yourself!!!...Then have another go

pull the cap off remove the plug from the head re fit the cap rest the metal side of the plug on the cyl head turn on ignition watch for spark as you either kickstart or electric start the motor

Have you checked for spark?

Next time you do an oil change, get yourself a spare gasket and remove the case, then use some T - Cut on the glass to clean it

Thats correct, as the fuel from the tank is used up it needs to be replaced with air or a vacuum will be developed in the tank, this vacuum would overcome the gravity feed to the carb of fuel pump. Open the cap and have a good look at it underneath, see if you can see any little holes that might be blocked up (Vent holes)

What the heck does "Not turning over" mean, do you mean its seized up now?

I ve been watching this thread and like you I have heard that the 125 barrel head and piston...and carb, can be swapped for the 175 versions, it seemed to me that the only thing to check is the part numbers for the crank cases, if the cases are the same, and as you have stated before the crank / con rod are the same, then this would be a good proposition, a quick look on Bike Bandit site confirms that both engine sizes use the same crank cases, therfore, theres nothing stopping you from putting the 175 barrel and carb on to your 125...is there? you can see the part numbers below. ...Paul

Dont be so soft, I've done 125 miles os a bloody pushbike in a day!!

Did you clean the screen in the fuel tap bowl, I know you said the flow is OK, but with rust particles you should have done this anyhow.

Torquey and rugged, heres one to consider.

Its either running out of fuel because the carb is only filling slowly......Or running out of sparks You need to find out which is the case, next time it conks out, pull the spark plug and test for sparks, it might be the pickup coil breaking down as the engine warms up, then as it cools a little works again...and so on and so on, you say you flushed out the tank...what was it like?

does it have a CDI ignition?

Try pulling the fuel feed pipe off the carb, open the fuel tap and run fuel into a container, you should have a healthy flow rate, check this first

+1^^^^^^^^^^^^^^^^^^^^^^ Check and adjust chain slack as per spec for your bike, and give the chain a good lube

Sorry i dont but I found This, perhaps the link will be a good place to ask

Hi Carole, you can find out if your old fizz is still around (but not the address) on the DVLA vehicle tax site, enter the registration number there we have a member Deenjay who is big into these small yams, look his posts up on the search feature