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<  General Scootering  ~  Need jetting advice for stock PX200 engine w/ new Sito Plus
bitbear
PostPosted: Wed May 10, 2006 1:03 pm  Reply with quote
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I dropped one of Scooterworks' PX 200 engines in my Stella. Now I've changed out the stock 200 muffler with a Sito Plus. I went up from the stock 116 main jet in the SI 24/24 carb to a 118. It runs well after warming up for a couple of minutes, idles very nicely, but it 4-strokes/stutters very noticibly at low speed during warmup.

The plug looks good but I'm guessing it's a tad rich. The air mixture screw is down to about 1/2 turn out from the seated position. I'd love some advice from anyone with a similar setup...

1) Should I leave well enough alone and wait out warmups?
2) Should I try leaning up the air mixture screw even more?
3) Should I go back down to the 116 main jet?
4) Other ideas?

It seems to me the stock PX 200 engine with a Sito Plus must be a fairly common combination -- can anyone advise?

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Tom Lindsay
PostPosted: Wed May 10, 2006 1:33 pm  Reply with quote
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Well, let me start by saying I haven't worked on a 200 engine, ever. So take it with a grain of salt. But on stellas, people usually go up 4-6 points on the main jet when they put on a Sito+. Of course, that's from the catalyzed and very restrictive stock stella exhaust, so maybe the same isn't true coming from a non-catalyzed P200 exhaust. But I'd be leery of running it at the exact same jetting as the stock exhaust. Be sure to do lots of plug chops on a fully warmed-up engine to determine what's really going on. And ultimately, the warm-up period is warm-up, so you shouldn't expect the engine to be as quick and responsive then as when it's warmed up.

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Derrick
PostPosted: Wed May 10, 2006 2:16 pm  Reply with quote
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I'll chime in on plug chopping.

I find it is very hard to get a good reading with todays modern blended fuels. It leaves very little deposits and the plug stays very clean. I used to be able to get great readings back in the early 80's but not any more. This is just my experience. I think plug chopping was a great way to get a mixture reading but not anymore IMO. I have to really just feel and hear the engine to jet properly.

IMO there is just one way to jet a modified bike at home without a dyno or CO meter. START TOO BIG WITH THE MAIN JET. You have to buy a BUNCH of jets. This costs some money but it is cheaper then a new top end! Two stroke engines should "four stroke" on a main jet that is too big. Then take one step at a time down until it just cleans up. It must four stroke and then just clean up with a smaller jet so you have a reference point. If you just guess and use what someone else used you are asking for trouble. There are no short cuts to tuning.

The right main jet is just the begining of properly tuning a carb. Then there is the idle jet, mixer tube and air corrector (for Si style carbs - which suck by the way!). All of these things have to work together to create a SMOOTH and powerful engine. Otherwise your scooter will be SLOWER!

Most people have no clue and should not mess with their engine period! Most scooters get destroyed by thier owners - one way or another!
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Matty
PostPosted: Wed May 10, 2006 5:20 pm  Reply with quote
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Derrick rulez.

118 good for now, once you get a few hundred miles on it and it's all nice and broken in then maybe play around with it. I ran both a 116 and 118 and didn't really notice a difference with a sito plus, but every scoot is different so results will vary.

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Jeff
PostPosted: Wed May 10, 2006 7:23 pm  Reply with quote
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I will agree with Derrick that plug chops are very deceptive. I was doing them all the time when I kitted my stella last year and I still siezed it like a mofo. I was running a slightly cooler than stock plug to be safe and that threw everything off.

It is also VERY easy to cross thread the air mixture screw and if that isn't seated properly that can mess up plug chops too.

If you need extra jets ask around. The dealers rarely have the one you want but I would bet that there are plenty floating around town that people would part with.

I have at least half a dozen that I eventually went through before I was happy.
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bitbear
PostPosted: Thu May 11, 2006 10:41 am  Reply with quote
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Thanks, all.

After gathering research and a number of views, I'm gathering that the 118 main is probably correct so, next I'll carefully dial in the air mixture setting.

Derrick, I'm aware that stock SI's are just a starting point. What can you and others tell me about the advantages of other carbs? What are the benefits, how much do they cost, and do any of you have particular recommendations -- remembering that I'm running a 200 engine.

Thanks for your advice!

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Matty
PostPosted: Thu May 11, 2006 11:17 am  Reply with quote
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bitbear wrote:
I'm aware that stock SI's are just a starting point. What can you and others tell me about the advantages of other carbs? What are the benefits, how much do they cost, and do any of you have particular recommendations


What are you looking for? Are you going to kit the engine? Really keeping it stock is best. There are other carbs like a Mikuni but you'll lose the oil injection, have to get a manifold, new cables for throttle and choke, and a new air filter.

There is the Vortex carb which is a modified si carb that some people like, I didn't though. There is now a si 26/26g too which looks cool. But the difference of a 24 vs 26 on a stock 200 I bet would be minimal.

All depends on how much money you want to throw away and how many headaches you want. You can't go wrong with a stock set up.

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bitbear
PostPosted: Thu May 11, 2006 11:44 am  Reply with quote
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Thanks, Matty. I'd like to acheive any readily available performance enhancements -- but I do not want to spend my life tweaking. I'd like as much performance as I can get while sticking as close to stock as possible. That's pretty much why I went with a Sito Plus exhaust, for example. As a noobie though (I re-built a Vespa engine back in the early 60s when I was a kid -- but that was close to the dawn of time), I'm interested in learning what I can about all options and upgrades -- and I know very little about the so-called new performance carbs. One message I read suggested that one of the new carbs was much easier to to tune. Then, Derrick's comment that SIs "suck" led me to ask -- and learn -- more.

Thanks!

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Matty
PostPosted: Thu May 11, 2006 3:14 pm  Reply with quote
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bitbear wrote:
Then, Derrick's comment that SIs "suck" led me to ask -- and learn -- more.Thanks!


Welll Derrick thinks everything made after 1966 sucks! Yes a Mikuni carb is a better carb but is it worth the trouble on a stock bike? that's for you to decide.

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Derrick
PostPosted: Thu May 11, 2006 3:31 pm  Reply with quote
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Hey Mikuni carbs are new and they are the best. See I like some new things.
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