Considering a kymco bbk for sa50 some questions

[needmoreinfo]

http://pages.ebay.com/motors/link/?nav= ... 01&alt=web

Just wondering if anyone has experience with it. Cheaper than a polini corsa and 8 more cc. What kind size carb would I need. Are the Taiwan bbk any good. I see most people replace the bbk often due to failure anyway. Thoughts? - needmoreinfo

[tazland001]

Thats a good kit. Just make sure you break it correctly. 24mm carb would work good. If your new at this I would get a temp gauge.

Taz

[Wheelman-111]

Greetings:

Caveat Emptor. Let's take the "80cc" claim first. It's a 48mm piston/bore. That works out to 74.7cc with a stock stroke crank. Apparently folks in the South Asian countries have a little problem with Math, because all of their advertised displacements are overstated.

Next, look at the piston carefully. See the boost port window? Slag on the casting which nobody bothered to file and clean up. That's on the item they photographed for the listing! If they don't take enough care to tidy up the parts they're going to photograph, what do you think the quality of the parts in the box they send you will be?

If you do get that affordable kit, you can get it to work reliably if you be sure to evaluate the edges of all the port windows and file a tiny chamfer to prevent the knife edges from scraping all the oil off the piston skirts. But even doing that, I wouldn't expect Corsa-class or even Italian Iron-class performance. You do get value for the money with the Italian products.

[tazland001]

Really. If Taiwan kits suck so bad then why can people install them and get up to 8,000 miles on them without any port work? You guys all ran Taiwan bores at one time or another. G8 has a bike with a Taiwan bore in it. Wheel you have used Taiwan bores with good success. What about all the other members on here that used Taiwan bores with great success. I think you get the point. How about all the people in Japan, the Philippines , Hawaii, ect that race Taiwan bores with out issue.

Now we know the port work on the Italian bores is better but that does not =more life or performance in the long run. Now the corsa is a monster bore but the other 47mm cast bores from Italy are no faster or dependable than a Taiwan bore. This is a debate that has gone on the forums for a long time.

The main problem with cylinder failure is wrong jetting, not enough oil, or over heating. If you take any BBK and install it and wot it for say 10 miles it will burn up and soft seize. It does not matter what kit it is. Everyone knows this is true except newbs. Can you image being new at this again and installing a 47mm corsa and wotting it around with everything stock. It would burn up so fast. Or imagine putting a pipe and 47mm on and then taking it on a long country road drive for like 50 miles at wot. We know what would happen and it wouldn't be pretty.

G8 you seem like a nice guy but d*** bro your like an ambulance chaser. Thats right I said it.

Taz

[Wheelman-111]

Greetings:

I hold nothing against Taiwanese products except that they don't appear to exercise very good quality control. The critical bore size/piston diameter is a question of good luck. If you happen to get a kit where the two match well, that bore will run as long as anything Italian, I grant you. But if you don't it'll slap or seize if the piston is too small/big for the bore. We're talking a few thousandths of a mm here that makes all the difference. A company that doesn't bother to shave casting slag from its piston windows is unlikely to care enough to get that precise match. Plus every one I've owned had razor-sharp edges on the port windows, and a newbie may not know to chamfer them. On my first try I didn't and fried a 51mm kit almost on contact. A second kit didn't fare much better, lasting a month or so. Now I know there's a bigger difference between a 51 and a 50 than the number suggest - Proportionately thinner cylinder wall on the 51. But even carefully chamfered and installed, my 50mm piston ran fairly well but soft-seized once or twice. The piston was simply too big, and I should have honed to obtain the correct clearance. BTW the 50 wasn't any faster than the Polini Contesta 47mm I have now.

In a way, I do see the worthiness of taking a Taiwan kit and doing the little work it takes to clear the obvious hurdles. If you can get it to work and go fast, it's more Noble than the turn-key Italian products that require no such effort, and you got yourself a bargain.

[tazland001]

Your right wheel the 51mm Rumina was a lemon. That 51mm heated up to fast. If I remember correctly you had the 51mm on your stroker build but I can't remember what flash build that was. BTW I loved reading all of your build threads. On my first 2 50mm builds I soft seized them a few time to. I learned really fast how to avoid that.

You don't actually have to do port work. The most important thing on a 50mm is to break it in nice and slow.The ports dull fast. The 50mm walls are just a bit thinner than any 47mm and requires a longer break in for long life. After the longer break in you can start really punching the 50mm and it can handle a lot of abuse.

A ball hone work good if you want to semi-chamfer the ports.


Taz

[Dbroogs]

Needmoreinfo,

Main takeaways from above are as follows:

Proper Jetting

Proper Break-in

Do what you want man, those were some valid points discussed by very knowledgeable people.

[tazland001]

G9 your comparing a 47mm to a 50mm bore. Bore a corsa to 50mm and then tell me the results.

90 miles at wot. Say if he was doing 60mph at wot then he rode it an hour and half at wot. Then why do you recommend temp gauges if the kits don't overheat??? Are you telling me G9 that italian kits never soft seize or hard seize???

Another thing is that wheels flash(#?) build was with a stroker. The 51mm and 50mm was on a stroker kit. Those stroker kits add more heat to the set up. Some people have had good luck with that build and some people have not. I personally would not add a 50mm or 51mm to a stroker air cooled build. I have done my fair share of stroker builds on the yz85,rm85, and kx85's but they are liquid cooled engines.

G9 it does not always look like you after $$$ but a lot of times it does the way you angle things.

taz

[benji]

G8 you seem like a nice guy but d*** bro your like an ambulance chaser. Thats right I said it.

Taz[/quote]
Hahaha