2018 Aprilia RS4 50 Euro 4 Upgrade Project

[Berkeley]

So last week of inspecting the head, although there were no major score marks , it did look like scorch marks. I recall the first time it happened and how hard the bike was to start. I was nearly going to buy a new head at around 250 euros. Then i thought what if it were just the piston and or rings, so waited until now.
I took it apart today and found the piston in gorgeous shape. So with this in mind because of the scorching of the piston ill buy a new head.. If anyone thinks I can get away with a new piston and ring then pls let me know, otherwise its a new head.

[Berkeley]

Was looking at possible upgrade options , but realistically the bike needs to get back on the road as soon as possible.

some options:

1. stay with the same head as before but will it last? im running a 19mm carb will I see any performance change changing to a 21 or 24mm carb?

https://www.maxiscoot.com/en/product/me ... 50b0-37836

2. upgrade to the pro 70cc series but some questions.. Does this have the same conrod length as the standard.. trying to find out. It also suggests a 24 to 28mm carb, any preference? Also it suggests using a reinforced crankshaft. is it necessary as im ruining a standard one on 70cc top end at the moment . If I change then hopefully should see this one last a bit longer???

https://www.scootfast.net/metrakit-cyli ... and-4.html

3.Upgrading to a Pro Race 77cc, with 7 cc more will the crank shaft and clutch plates need to be upgraded or can run standard? If so 28mm carb is needed but any other parts need changing out? ie new chain and sprocket set to get the performance?

https://www.scooter-attack.com/en/produ ... uro4-80942

thanks

[Jaxx]

Thats seized piston for sure. I'm not sure if you can just replace piston, you probably need to replate and rehone cylinder but I don't think it's worth to bother with this. Just buy another kit.

Stock crankshaft will handle everything up to 50mm bore (78cc) if you keep revs low (<12000) and have good lubrication. And there is another limitiation - stock flywheel ingnition. It's rotating mass will progressivelly stress crank at higher rpms. I've read once that stock derbi crank is at least as good if not better quality as cheap race cranks.

So I think you guys should definitelly go for internal rotor (racing) ignition kit. In combination with 50mm bore, 77-78cc racing cylinder and some good flat slide 24mm carb. 28mm would probably give even more peak power, but it would be pain to set up properly and use anywhere but on racetrack.

Clutch springs should be upgraded with stiffer ones with anything bigger than stock 50cc. For this^ setup you should add racing clutch to your shopping list too.

[Berkeley]

Thanks jaxx,

With that piston the bike still ran but stopped idling .. so not sure that it seized. Im scratching my head as to why the bike is hard to start and wont idle. Even if I turn the idle screw all the way in it doesnt make any difference ... i have to hold the throttle open to keep it running then it does and a pain to start up again.

As far as i can tell theres nothing wrong with the air box, carb, reed valves, cdi unit, spark plug . This week I bought a replacement kit. Fitted it tonight and still the same issue ahhhhhhhhhhhhhh. I wondering if its an air leak in the carb boot like you had.
carb dismantled and jets cleaned out looked fine
cdi changed to old one and still the same problem
no missing parts in the reed valve.
I must admit i didnt do a compression check but assumed it was the piston so replaced the kit..

Anyone with any ideas?

thanks

[Jaxx]

As I understand, you did replace complete top end (cylinder and piston)? And you still have this idle problems?

[Berkeley]

As I understand, you did replace complete top end (cylinder and piston)? And you still have this idle problems?

All good now.. thanks jaxx!!! a lot of ups and downs but finally there ))))))))))))))))))))))))

[Berkeley]

So all finally sorted thanks jaxx!!!

My carb has always been in the same position, ie not fully wedged into the boot.. Had no problems before so kind of dismissed this as the cause. I think this was the issue and maybe wouldn't had needed to change the top end( cylinder and piston).. but maybe for the best that i did.

Here it is fully wedged in. i took the carb and the boot off. fitted the boot to the carb, then bolted the boot in.. a bit laborious but seemed to work



The boot connection had a small split. it doesnt appear to go all the way through but will get a new one anyway



So after I put it all together the things didnt even want to turn over.. even worse than before.. then i Bumped it down my steep drive and nothing.. completely dead.. pushed it up,
again scratched my head, thought it was the spark plug so changed it and it fired up and it got going.. enough for it to spew out all the gunk allowing me to adjust the idle and to keep it running.. whoop whoop

[Berkeley]

Whilst I was going to work on the top end change it out id thought id give her a proper service, new oils, rear tail lights, refurb pads and fluid, new paint for parts and exhaust. got the temp sensor working and a dam good clean!!

Im still not sure about why oil/water was coming out of the bleed hole . I assume that extra petrol was seeping down into the oil via the worn piston causing it to bleed out near the water pump.. lets see if the new cylinder head fixes this problem.

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[Berkeley]

No more oil juice leaking from the water pump weep hole. The damaged piston I assume the cause of it . Bikes not 100% on form.. needs some carb tuning .. will try with the carb spray to see if the boot is leaking.

[Rj_666]

You might care to search the forums for 'leak down tester', and use something of that nature rather than checking with carb cleaner / whatever...