2018 Aprilia RS4 50 Euro 4 Upgrade Project

[Berkeley]

Hi there,
Compression ratio ...not sure of the difference.

As soon as I let go of the throttle it dies.. no wind down.
Ill take vid and record a run. Then I'll remove the exhaust to see any scoring of cylinder and send pics. An endoscop would be easier!!
What's the remedy to tiiiiiiihgt rings??? Wearing them in or look to replace with new ones???

[kaldis12]

Im pretty sure its not the tight rings. They would propably catched by the ports. But not for sure tough. If they are too tight then you can just grind away the 2 ends and voila less tight rings. But you need to watch for the camfer if you are grinding it. Cant just grind it down. It needs a special shape. The user manual propably says it.

[toratora]

Eric Idle - The Patron saint of Idle
The only importance in the number of turns of the mixture screw is if there are no turns left to go in or out. If there is not then change the idle jet. Turns are not a decent metric to know if the mixture is set correctly, and although many people will toss out a number of turns as the holy grail of mixture setting, in general, those people are talking out of their incontinentia buttocks. They obviously have no idea on how the set a proper air mixture. - Eric Idle

The idle screw simply moves the slider up and down. If you don't see the slider move when you turn the screw then something is incorrect. Usually this is caused by the throttle cable being adjusted such that the slider cannot reach the bottom. A simple test is to ensure there is slack in the cable, and check how far down the slider goes. Then adjust the screw. If you don't see slide movement then it's likely not the cable introducing the issue.

As for setting the idle. This is something that is done after setting the air mixture. If you cannot get the bike to idle at all then the pilot jet needs to be changed. Once there is a pilot jet that will idle, then adjust the air mixture. If you can't get it set properly, then the jet needs to be changed. To set the air mixture it is important to set the idle higher than you would normally run it. If you don't do this the engine could stall out during the mixture setting process. Setting the idle higher at this point is okay, because it is adjusted after setting the air mixture. I would start with the pilot jet that came with the carb. Polini is very good about shipping their carbs with jets that are in the ball park.

There is also the possibility of an air leak in the system. I just linked a video in the air leak testing thread.

Previously I asked if the documentation listed the proper ring gap. I was unable to find any docs on the Metrakit, but something in the range of .005"-.008" should be pretty close. Currently we don't have a ring gap tutorial, but Wisco has a nice page on ring gap. Changing the ring gap is a little difficult, because it is important that the ends remain square, and not have chips, or spurs. I've used sand paper in the past, and small files. There are special tools for doing it, but I don't have those, although it would be nice to have them.

[kaldis12]

I have some of them its too cheap here

[Berkeley]

HI guys have a look, Photos and Video attached thanks

Removed the head and checked the cylinder for scoring.. only some 'catching'?? but no marks or indents.. all smooth.. Ill leave the pics in high res so you can take a closer look.
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Cylinder Cleaned up with rag.
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https://youtu.be/0i4wr92qYZQ

Here is the link to the video electric starting and bump starting:

[kaldis12]

Duude, if this is a new cylinder it shouldnt look like this. Mine ran over like 800km and didnt even see anything bad like this on it.
And just pull that clutch in when you let the throttle go. Always pull the clutch. That engine braking in the video killed me.

[Berkeley]

... but i fitted a quick shift to it!!! hummm

[kaldis12]

Did you mean mechanical quick shifter or you you just quick shifting. In my experience none if them is good. But when you let the throttle go you didnt really pull the clutch in and you start slowing down(losing rpm) and didnt pulled the clutch in. Thats not really good. But back to the thread. That cylinder shouldnt look like that. How much did it ran?

[Berkeley]

Hi Kal it was a joke.

Ok the state of the cylinder and piston this was from riding it 84km in total since I installed it the other week. This was also messing around with bigger jets sizes etc etc. so all the mods that I have tried.
With the clutch when I got the bike going the other week if i pulled the clutch in then it would likely stall. so this is how I prevented it. but anyhow I normally dont hold the clutch in when i slow down.. only to change gear.

[jkv357]

I agree - that doesn't look right.

Cylinder wall should still be nice and shiny with a clear crosshatch still visible, not black and oily. Makes me think the ring is not sealing.

Maybe there's not adequate ring gap.

Seems like the revs just dropped off too quickly as well. Is it smoking a lot?