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Post by rani on Jul 28, 2008 19:17:49 GMT -5
Hi everyone. I have a real quick question on re-jetting the carb on my Jonway 50cc. I'm still learning all this stuff, so forgive me if I get some of the terminology wrong. I currently have an 85 jet in my scoot. I bought it from Scootertronics. Their website says that to upgrade the scoots, they put a 95 jet in the carb and put on a free-flow air filter. The site is a little confusing about whether anything needs to be done to the exhaust if we do this. I sent an e-mail to Scootertronics but haven't gottena response yet. I'm just concerned that this may be too big of a jet for my little scoot. I don't want to take a chance on doing something that will screw up the scoot. DH thinks it will be o.k., but I want to check with you all before we ordered the parts. I also read something about cutting one of the wires (CDI?) to help de-restrict the scoot. How do I know if I have one of these and how do I tell which wire it is? I think we have six total wires. As far as restrictions in the exhaust, DH looked and said there are no restrictors there. Any help you can provide would be appreciated! I just want to get another 5 - 10 mph out of this scoot! I have to be on a main road for a short part of my commute and I'm really nervous that I can't keep up with traffic. It's either get this one pumped up or sell it and buy a bigger bike. I'd rather hang onto this one. I've become quite attached to the little guy! Thanks in advance.
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Post by lbo on Jul 28, 2008 21:08:04 GMT -5
The only way to be certain you are running the correct size main jet is by doing plug chops. You need to run the engine wide open for a mile or so. Kill the engine at WOT and come to a quick stop while still holding the throttle open, pull the plug and take a reading. There are places online to reference plug readings.
As far as your CDI, I have no idea.... I wouldn't go cutting wires until you are 100% certain.
Not sure if you have a 2 stroke or 4, but a performance exhaust will give you more bang for your buck especially on a 2 stroke..... the exhaust is often times a common point of restriction too.
Good luck.
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Post by stiks on Jul 29, 2008 5:04:42 GMT -5
right jet like above said read the plug. dark brown (pretty dark from my experiance) means to rich (needs more air or less gas), light tan color right about where you want it, ashy white means to lean (more gas or less air). CDI best to buy an unrestricted one.. usually they are Rev-Limited and with having 6 wires i think you may have one of them. a couple places carry them. i may chop and weld on my scoot but cutting wires to a main engine part seems a bad idea to me. with 6 wire cdi im thinking you have a 4 stroke. i have seen a few types of resriction baffles in exhaust pipes.. if it is real quiet it is probably restricted. and a good aftermarket pipe (like an MRP racing exhaust) can defiantely help your scoot breath out to help that larger jet and free flow filter work to there fullest.. oh and welcme to the pound and to the world of scooter tuning
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Post by rani on Jul 29, 2008 18:20:41 GMT -5
Thanks, guys. I have a couple of more questions, though. Again, excuse my ignorance. I'm really a newbie to all things mechanical, but I feel like I'm learning fast. The only way to be certain you are running the correct size main jet is by doing plug chops. You need to run the engine wide open for a mile or so. Kill the engine at WOT and come to a quick stop while still holding the throttle open, pull the plug and take a reading. There are places online to reference plug readings. We can definately do that, but I guess my question is what do you mean by "correct size main jet"? I know I have an 85 now. If I wanted to change it out to a 95, wouldn't it just be a matter of adjusting the air/fuel mix going into the carb to make the 95 the "correct size jet"? Or will it really hurt the scoot to put a wrong size jet in the carb? We're aware that adjustments will need to be made to the mix with a new jet and air filter, but will it hurt my scooter to even try it? It is a 4-stroke by the way. If we decide to go the exhaust route, any suggestions on a kit? How much would this cost? From what I've seen, it can be rather pricey. Would be better off changing out the roller weights? Or would I be better off just getting a more powerful bike? Thanks again!
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Post by lbo on Jul 29, 2008 19:52:29 GMT -5
I think you are confusing the A/F adjustment with the main jet within the carb....... you can't increase the amount of fuel the engine gets by a screw adjustment. The A/F screw controls the air/fuel mixture at idle.... the pilot jet is responsible for the fuel delivery at idle and low RPM's. The main jet sizing refers to the actual "hole" size if you will of the jet responsible for fuel delivery at WOT. The only thing that will truely hurt your scoot is getting to much air, not enough fuel, at high RPM's as this lean condition can burn your engine up. Adding a high flow intake requires more fuel to compensate the additional air flow, something only a larger main jet can provide. Hope it makes sense, maybe this picture can help a little; On a side note, roller weights are an easy and often overlooked tuning aid. Ideally you want your engine's RPM's in the peak powerband. The correct roller weights will help keeping the engine in this powerband throughout your accleleration all the way to top end. Changing exhaust/intake/other engine mods will result in having to re-tune your CVT transmission to accomodate these changes perfomed with the engine.
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Post by rani on Jul 29, 2008 20:18:10 GMT -5
I think you are confusing the A/F adjustment with the main jet within the carb....... you can't increase the amount of fuel the engine gets by a screw adjustment. The A/F screw controls the air/fuel mixture at idle.... the pilot jet is responsible for the fuel delivery at idle and low RPM's. The main jet sizing refers to the actual "hole" size if you will of the jet responsible for fuel delivery at WOT. The only thing that will truely hurt your scoot is getting to much air, not enough fuel, at high RPM's as this lean condition can burn your engine up. Adding a high flow intake requires more fuel to compensate the additional air flow, something only a larger main jet can provide. Hope it makes sense, maybe this picture can help a little; On a side note, roller weights are an easy and often overlooked tuning aid. Ideally you want your engine's RPM's in the peak powerband. The correct roller weights will help keeping the engine in this powerband throughout your accleleration all the way to top end. Changing exhaust/intake/other engine mods will result in having to re-tune your CVT transmission to accomodate these changes perfomed with the engine. Thanks! I know the size refers to the size of the hole in the jet. We had it out this weekend, so I know exactly what it looks like. I also found out the hard way that you have to adjust the A/F mixture with a screw on the bottom of the carb. (It was very hard to start after we put it back together. Adjusting the A/F mix fixed that problem.) So it sounds like I'll be good if I change out the air filter along with a larger jet to make up for the increased air flow, right? Can I safely do this without touching the exhaust system? I think we may also try the roller weights. If you had a choice, which would you do first? The weights or the carb adjustment? Like I said, I only really want another 5-10 mph and I'm looking for the fastest, easiest, cheapest way to do it.
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