Suzuki ay50 overheating

If they are all failing in exactly the same place, then the head is most likely warped and where they keep failing is where the warpage is. Most plate glass is float glass these days and it's the best true flat surface you'll lay hands on quickly. I've even used a glass topped coffee table in the past (shhh - don't tell the missus!)

Stevep said:

"Breaking"?
Do they have a black or burnt mark around the break?

That's my thoughts - overheat - head warped - causes burn-through on the head gasket.

This is what they look like

I had a lucky purchase on ebay won a brand new bigbore kit for 99p got delivered today should I replace the whole lot or just use the head and gasket?

I'd replace the whole lot. That will get the bike running then you can work on the old head. Those pictures show severe burn-through of the gasket by combustion gases so it's definitely warped and needs lapping back to being flat. It can be saved.

We have developed a new issue. Got it all up and running took it for a test ride and it started dying and at full throttle it was just ticking over. Cleaned the carb but will only start at full throttle

You may need to go up one size of the main in jet the carb as a result of the bigger bore kit. I'd also recommend adding 1 or 2% 2T oil to the petrol as you will need a little more oil to lubricate the larger surface area of the big bore kit. Try the extra oil and see if that helps while you order a jet kit.

I have a set of jets tried a few of them. If I take the air filter off and kick it over it will start and tick over but as soon as you puLloyd the throttle it spits petrol out the carb and dies

You may have burned the new piston rings out from lack of oil, broken a piston ring or scored the bore. You need to take it apart and look at the piston rings and cylinder bore. The only way that petrol would get blown back past the carburettor is if the crankcase is over-pressuring as a result of blow-by of the compression past the rings or the bore being scored.

New bores need to be carefully broken in and closing the throttle after a long run at full throttle (when the piston is hottest), coupled with a lack of fuel and oil to coll the piston when still running at high revs on the over-run with the transmission driving the engine, can cause the piston to heat seize. Using engine braking is bad on new cylinders.

I never put the new barrel and piston on just the head and gasket I will check the piston and rings tomorrow. I did a compression tester and it was just over 100 psi

Also it will only start and tick over with the air filter off

Bigger bore kits normally need a larger carburettor and larger carbs usually have smaller jets. The fuel/air mix may be too rich and the increased flow of air being drawn in by the larger bore might be causing it. Add 2% oil to the petrol to ensure lubrication of the bearings and bore and try going down one size with the jet to see if that helps. DON'T ride it for now, this is just troubleshooting.

It's had a bigbore kit on since I got it and I put a bigger jet in to try stop it over heating but I will put the smaller one in to try it. My son told me when he was riding it it was spluttering then picking back up then it conked and wouldn't start so he had to push it home. I just thought the head gasket had gone but when I checked it this morning no water in the barrel and started first kick. I just changed the head and gasket incase the other one had warped. So the issue I'm having now might have been the problem he had a couple of days ago not sure if I've disrupted the floats when I've been changing the jet? When I'm kicking it over it tries to fire every kick

start it up on the rear patio and leave it running while you sit and drink coffee and read paper/watch tv . leave it for a good 20-40 mins see if its stalls over . if not get son to ride it up n down road a good few times see if you can force it to stutter and failover again.

possible your tinkering has unstuck a sticky float and now its just wanting to fire up, but when the new kit comes fit it and grab some plate glass sheet that top end head can be reworked , like merlin and guys say, just tape the paper to the glass on each side run a drizzle of oil onto the paper then use a figure 8 motion to lap the head surface flat , dont push down on it just let the weight of the head slowly lap itself.

keep lifting head and checking for lap misses. where one part is shining up but another looks untouched, that untouched area is the warped side ......... its how we lap computer CPU heatsinks and the cpus when we go hardcore overclocking
if you take your time and do it right you can end up with a mirror finish lapping

I've fitted a brand new head today. I've had it ticking over for ages and as soon as you touch the throttle it dies. But will only start with the air filter off as as soon as you go to put it back on whilst it's running it dies

Check the plug colour. You want a mid to dark brown colour. If the needle on the throttle slide has more than one groove, move the circlip up one notch and see if that helps. If it gets worse, go down one notch. If it still dies with the needle in the bottom notch, jet up one size, put the needle circlip in the top notch and try again. Obviously, keep checking the plug and if it goes sooty and black, you are going the wrong way, the mix is too rich so you need a smaller jet. Your problem appears to be the mid-range mixture that is controlled by the needle and main jet.

Seriously, it's worth you spending £15 on a Colourtune spark plug kit from Halfords. Using this, you can see the colour of the combustion as you open the throttle and the kit comes with a colour guide as to what colour flame you need. You'll be able to see straight away what the problem is. Make sure that you get the size of kit that matches your spark plug thread.

I'll try it tomorrow took a day off it today was doing my head in haha

Ok tried moving the needle with no joy so checked the reeds and low and behold they are damaged