overheating after fitting 70cc kit (am6)

[rono]

First post so hi all.

Now onto my problem(s)
I recently bought a 02 plate rs50, it wasnt running when I bought it but it was cheap enough to take a chance on.
I got it home and fired it up(took a while!)
It was smoking it's tits of so I presumed it was a headgasket and left it to idle for a few minutes, I topped up the coolant but that went all over the floor instead, I instantly turned the bike of and took the fairing of to check the problem assuming it would be a broken hose but nope.
Turns out the head was cracked, so I quickly scoured ebay for a new cylinder kit and ended up buying a 70cc kit, its only a cheap one but I bought the bike to sell on so no worries there.

New kit was fitted and although it took a while to fire up it did and idles fine with no scraping noises etc, however...
The bike is now overheating fairly quickly, I'm well out of the loop with bikes so this is where you boys come in.
It came with an open filter so I've bought a second hand airbox to go on and I've also got a 98 main jet to fit so once its run in it should have a fairly decent base setting but I need to be able to solve the overheating issue before I list it for sale.

Any ideas on where to start?

Bit of info to help you diagnose the problem....
2002 rs50 with an indicated 23k on the clock.
70cc kit fitted, rings are located fine and piston is not scraping.
Standard carb with open filter(i do have an airbox and 98jet to fit)
Aftermarket exhaust, its got an arrow backbox but the front pipe is battered with plates welded over so no idea on actual make(no washer)
Cant ride it due to not being licensed but I have rode it briefly and it dosnt stutter etc at all(not gone over 4kish yet tho)
Plenty of 2stroke oil and coolant is topped up but I havnt bled either yet(obvious first port of call but havnt had time yet)
Any help is much appreciated, btw im fine with spanners and can tackle any job its just knowing what to look for, I've been riding dirt bikes for well over 10 years and used to have a tzr125 as my road bike so I'm not new to them I just havn't messed with one in a good few years!

[camb00]

Jets too small dont ride it, state your full setup with carb size

[rono]

It's running the standard carb so whatever size that is and I'm pretty sure its the standard jet, like i said I've qot a 98 main jet, I was recommended the 98 jet to use as a starting point for running in by a well known and very respected scooter/moped dealer/tuner in my area but that's based on running the standard airbox and tuning later on.

[RS_Patrick]

Wich kit did you buy?
What Carb is under there exactly?

98 mainjet is way to big if your going to fit the Stock airbox, at least by 10 sizes or more depending on what carb is under there.

And it sounds like you got a airlock in the system, or maybe the waterpump is broken, wich is likely since you mentioned you had a cracked head before.

If it is overheating like camb00 said from a to small mainjet you got a reall problem because the piston gets only cooled by the fresh mixture comming into the crankcase, theres basicly not heat transfer from the piston trough the rings into the cilinder, so if you dont get enough mixture in there the piston heats up and expands till it seizes it self up in the barrel, only wen its in the process of "seizing/scraping the barrel" you see the cooling fluid temprature rise as the heat from the scraping piston transfers into the cilinder.

I think your waterpump is not working as everything points to that with the cracked cilinderhead you had before, or the system has not been bleeded properly, otherwise you also have trouble starting it and it probably wouldnt run under 4k wel at all.

[rono]

The carb is a Delorto and the code is ph86
I dont know the jet size as I've not had a look yet.
I was thinking its either an airlock in the coolant system or possibly the 2stroke pump, again I've not had time to bleed them yet.
The bike runs sweet as a nut, although it does take a little while to fire up, presumably because its a new barrel/piston and is still a little tight.
The old barrel/piston was near enough perfect it was just the head that was cracked, I couldn't say if the pump or thermostat is broke as I only get it out of the garage as and when I get a chance and that's usually only for 15 mins.

This is the kit I bought...
http://www.ebay.co.uk/itm/1906302149...84.m1439.l2649

[rono]

i tried to leave a post earlier but it said mods need to approve?

the carb is a Delorto ph86, no idea what size jet is currently in it as ive not taken it apart yet.
the kit was just some cheap ebay kit, the bike runs fine, no odd sounds etc its just overheating wich i think is either an airlock in the coolant system or the 2stroke pump needs bleeding through, although it is possible the jet is far to small now, ill try the 98 with the open filter and see if that helps.

[RS_Patrick]

Thats a DelLorto PHBG than (not PH86) wich is an after market carb.

You really should check the Waterpump mate, because the cilinderhead did not crack out of its own, they probably never replaced the waterpump and one of the previus owners might have had water in there for a while instead of cooling fliud in wich case it would be a miracle if it did 23k

Its probably not because of a lack of oil that it overheats, it just seizes if its not getting enough oil with out (much) warning.

But in any case its a good idea to go by everything related to carburation and intake to make sure there are no other problems.

Watterpump revision kits for your bike are really easy to get and luckly really cheap incase it is the pump, so dont bother with trying to fix it or just replacing a bearing or seal from it, your much better of getting a revision set for the pump.

[rono]

cheers for the advice, really appreciate it.
is there any way i can check the operation of the water pump?
for instance could i take of the return hose to the radiator, let the bike idle and see if the water flows through?

as for the carb, do they make them in different sizes? a quick google search says they come in various sizes, any way to check what size mine is?

[rono]

quick update...
I got the bike out for a quick tinker and first thing i done was bleed the 2stroke pump and thats fine and seems to be operating fine.
next i removed the casing for the water pump, i was greeted by what looked like a huge clump of sand, so i cleaned all of that out and flushed through the engine and rad with fresh water, lots of mucky water came out but its nice and clean now.
with the casing still of i turned the bike over but the impeller isnt turning so that's obviously at fault.

Those revision kits you mentioned, are they easy enough to fit?
I'm fine with any mechanical jobs but if its a pain in the a$$ job i would rather know before I start

[nicketynoo]

They are easy to fit but you have to remove the engine casing. Sounds to me though that the plastic gear inside has come adrift from the impellor shaft. there's a small pin that locks it onto the impellor shaft, but you wont know whats gone wrong till you open it up. Worth getting the kit anyway. Don't forget you'll have to drain the oil.

[RS_Patrick]

You just need to remove the clutch cover, usualy the plastic gear goes out because theres to much play on the impellor shaft, so like nicketynoo said, best to get one of those revision kits and replace the whole thing, especaily if there was so much gunk and stuff in there you can bet its all gone anyway.

Make sure you get good engine oil, Fully Syntetic 10W-40 4T Motorcycle oil for use with Wet Clutch, thats much better than the Gear oil Aprilia recomends.

For new fluid get something thats ready to use, not stuff you need to mix your self, you can test and flush it with water, but you want to get cooling fluid in there ASAP for the pump and to prevent corrosion