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Post by motorhead on Jan 10, 2011 22:51:26 GMT -5
Hello everyone. I repair scooters in Orlando FL and I have a lot of success repairing and tuning 4 stroke scooters. But 2 strokes on the other hand are still a mystery to me. Can anyone tell me why minarellis (or 2 strokes in general) can only run correctly with the stock air box? Or better yet what have you done to your 2t scoot to run a racing air filter successfully? :help:
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Post by 90GTVert on Jan 10, 2011 23:16:38 GMT -5
:welcome:
The stock airbox makes it a lot easier to tune, but you can certainly use free flowing filters. The biggest problem with open airboxes is that the increase in noise and effort shows little gain, especially on scoots with the stock carb. I'm even using the stock airbox on a 21mm Dellorto fed 96cc minarelli stroker.
You will need to completely re-tune the carburetor when adding an open filter. Larger main jet, idle mixture adjustment or in some cases pilot jet swap, and perhaps changing needle clip position.
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Post by 190mech on Jan 11, 2011 6:29:33 GMT -5
Welcome! I prefer the stock airbox,even when I increased the cc's from 50 to103.Like Brent said the open element filter is noisey and if any makes little power increases.Pull the rubber snorkel out of the airbox as thats a major restriction.I even opened the hole to an oval about half again the size.When I installed a Mikuni VM22 there was no longer room for the box,so I mounted it on the CVT housing.Here is the thread; 49ccscoot.proboards.com/index.cgi?action=display&board=2perform&thread=497&page=1 |
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Post by motorhead on Jan 11, 2011 10:33:10 GMT -5
Wow, I can't believe you guys are running those setups with the stock box. I guess the science is done for us and there just isn't much improvement beyond a 2t airbox. I've repaired two minarellis where that all was wrong was that the airbox was missing screws to keep it completely closed. What really baffles me is that I bought a 99 sr50 LC. It came with 70cc kit, leo vince rr pipe and 20mm mikuni carb w/ 85jet. Here is the kicker. It has no air box/filter and no room whatsoever to fit one. But the previous owner ran it successfully to the point where the connecting rod melted against the stock crank. But When I swapped the crank and reinstalled the same setup it came with the bike wont run beyond idle. How could this bike have worked previously? I know good and well 2t's need airboxes. I have also attached a pic. Attachments:
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Post by 190mech on Jan 11, 2011 10:49:53 GMT -5
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Post by 2strokd on Jan 11, 2011 12:17:31 GMT -5
Whats to say the airbox was off when he blew it up?
Welcome to the forum!!
They will run with or without an airfiler, or box of any kind depending on the jetting?
Guys run at the track w/out anything on the carb.
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Post by lshigham on Jan 11, 2011 12:59:09 GMT -5
Mine will run fine without the stock airbox, showing 12.5 HP at the rear wheel. Obviously, jetting changes are needed.
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Post by motorhead on Jan 11, 2011 13:41:40 GMT -5
Thanks for the welcome by the way, I am glad to be here. Maybe soon I'll be of use to you all.
I am ordering a stock minarelli airbox that I will duct like 190mech's scoot. And we'll see what happens. In the meantime I'll try a 110 jet. by the way lshigham, what size jet you running?
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Post by lshigham on Jan 11, 2011 13:54:55 GMT -5
88, but I have a different engine, scoot and carb.
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Post by limitededition on Jan 12, 2011 10:53:48 GMT -5
 The stock airbox makes it a lot easier to tune, but you can certainly use free flowing filters. The biggest problem with open airboxes is that the increase in noise and effort shows little gain, especially on scoots with the stock carb. I'm even using the stock airbox on a 21mm Dellorto fed 96cc minarelli stroker. You will need to completely re-tune the carburetor when adding an open filter. Larger main jet, idle mixture adjustment or in some cases pilot jet swap, and perhaps changing needle clip position. i agreee with the admin you should do that i also had this problem and i increase a air and petrol mixture and it goes like mad but now i have problem with the carb its 24mm and i probebly should put smaller jets to it and a bigger air filter  |
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Post by motorhead on Jan 12, 2011 12:17:02 GMT -5
Also, could a broken choke keep a scooter from running beyond the idle throttle position? Because I always thought a choke was just for helping to start a bike and was useless once it got going???
Both minarellis I am working on (99 sr50 & vento r4) seem to have broken chokes. I've taken out the choke from the carb on the sr50 and the choke lever doesn't move the choke up or down. And on the vento r4 one of the two wires coming from the electronic choke is cut.
I am going now to order some new chokes and switch the chokes out but in the meantime I would like to know the answer to the question above.
cheers
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Post by 90GTVert on Jan 12, 2011 12:34:14 GMT -5
If your tune is close, an enricher that is always open shouldn't prevent you from revving above idle, but it woudl definitely affect the state of tune. Good call fixing both of those. The electronic enricher should be adding fuel with no power to it. The cable operated enricher could go either way, depending where it lets the barrel at the end sit. If it's stuck closed, as it would be set after warm-up, it shouldn't affect anything after it's warmed up for a bit.
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Post by motorhead on Jan 13, 2011 16:09:10 GMT -5
I took the engine off the bike last night and rechecked the compression and crank case sealing. It was all good. Then...
I ditched the leo vince rr pipe today and put on a stock minarelli exhaust and the bike runs like beast mode now. W/o air filter even! Its jerky and I have to pump the throttle before the engine catches and then it can accelerate. I think I am running rich and it's maybe since the choke is stuck open. I'm going now to rectify this.
As for the leo vince rr pipe. I have never gotten a performace exhaust to work on a 2 stroke. I tried a LV on a (morini) TGB laser last fall and it slowed the bike down 10mph.
What is with expansion chamber pipes? Why would it kill a bike like that?
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Post by motorhead on Jan 13, 2011 16:39:36 GMT -5
This is strange. I had to take off the stock exhaust because it was running on the rear wheel. So i put the vince back on and it runs now. The acceleration is so huge i have to tuck my body against the gauges to keep from flipping off. It still has the jerking and i have to pump the throttle still but this is trange that now it runs.
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Post by drawkward on Jan 13, 2011 18:07:30 GMT -5
I took the engine off the bike last night and rechecked the compression and crank case sealing. It was all good. Then... I ditched the leo vince rr pipe today and put on a stock minarelli exhaust and the bike runs like beast mode now. W/o air filter even! Its jerky and I have to pump the throttle before the engine catches and then it can accelerate. I think I am running rich and it's maybe since the choke is stuck open. I'm going now to rectify this. As for the leo vince rr pipe. I have never gotten a performace exhaust to work on a 2 stroke. I tried a LV on a (morini) TGB laser last fall and it slowed the bike down 10mph. What is with expansion chamber pipes? Why would it kill a bike like that? Are your pipes restricted? These companies must sell the performance pipes with restrictions to meet certain EPA requirements. They make it fairly easy for us to remove the restrictions though, most of the time. If you are having trouble getting the bike into high revs (where two stroke's generate their power) then adding a chamber to your exhaust won't help things. |
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