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Post by scootnewb on May 8, 2018 20:30:31 GMT -5
Hi All,
After installing the parts in my signature I can't seen to get the carb tuning down. It exhibits both rich and lean symptoms. I checked for air-leaks and replaced a suspect GOOFIT manifold that wasn't making a good seal with the spacer.
Is it possible the jets I'm using as a base line are way off? I am using a 35 pilot and 92 main.
I'm thinking maybe the main jet is too small. The largest I have is 98 but I ordered a kit from partsforscooters.com
I have watched all the videos but even when it was stock, I was unable to tune it correctly.
I plan on putting back the stock air box because I've heard the Uni-filters are hard to tune with, I just have to remember where I put it.
I've watched loads of videos and read up a bunch too on carb tuning but I just can't seem to do it.
I am looking into getting something to monitor the engine temps too and an RPM gauge.
Any advice would be awesome!
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Post by ThaiGyro on May 8, 2018 22:35:08 GMT -5
Don't sweat it much...tuning is a tough thing to learn initially. You heard correctly, that Uni...really all foam filters and many oiled paper pod filters require much more fuel, so bigger and bigger jet sizes. The airbox in my experience is better for both tuning...and, if your live and play in the rain like we do, it is super nice to not suck water into your engine.
I won't attempt to guess pilot or main jetting. My four stroke is a 125cc. It would help others for you to post your intended driving conditions, where you live. Seasonal temperature range, humid or dry...sea level or mountain elevations.
Good luck!
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Post by scootnewb on May 8, 2018 23:32:10 GMT -5
I'll be riding it in the N.E. at sea level and yes in the rain.
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Post by scootnewb on May 9, 2018 1:05:56 GMT -5
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Post by tocoo on May 9, 2018 1:33:44 GMT -5
With the stock 139QMB of my scooter, and with my unsealed carburetor [black lid, diameter of 16mm for the plunger] the stock jets were 30 idle, 76 main. THen I used 30 idle and 80 main which was very nice.
With the stock sealed carburetor of my scooter, [metal lid and diameter of the plunger = 20mm], the stock idle jet was 30 and the stock main jet was 78. I use 82 for main jet and 33 for idle [only because the mixture is more than 3 turns unscrewed, with the idle jet of 30].
People who install BBKs have higher jets than me, like 35 for idle and 88 for main.
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Post by scootnewb on May 9, 2018 16:06:49 GMT -5
EDIT
So last night, before making this post. I adjusted the idle so it was better but never test drove it after that.
Now it shows signs of running lean. Back fires when getting going and cuts out throughout the throttle ranges.
I guess I will try 95 main jet but going any bigger on the pilot jet seems crazy. In fact i am thinking of going down to 33 on the pilot. Maybe I have an over sized pilot and and undersized main? Ugh, now it is raining out.
I guess I'll have to wait until tomorrow to really do anything. If anyone has a 50mm BBK with performance exhaust, and hi flow filter or modded air box - if you could please share you jet sizes that would be awesome.
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Post by scooterted on May 9, 2018 18:14:57 GMT -5
Youve been working alot lately on your scooter. Dont get frustrated!
Have you cleaned out the passages with carb cleaner?
Have you used carb cleaner to look for air leaks (that would be hard without the stock airbox)?
And have you installed the stock airbox yet?
How many turns out is your idle mixture screw?
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Post by scootnewb on May 9, 2018 18:26:53 GMT -5
I am not sure how many turns out the screw is at this point. I just put it away cause it started raining.
If there are air leaks, they must be between the manifold/spacer and head. There is only one vacuum line that goes from the manifold to the petcock with clamps and a fresh line. The other inlet on the manifold has a vacuum cap on it with a zip tie around it. Prior to that I had an after market manifold with only one inlet going to the petcock. I since removed that manifold because it seemed like there was a wonky seal between it and the spacer.
I have tried spraying carb cleaner around the hoses and manifold and it made no difference when idle. I think it is tight. However, I made another post asking about using some gasket sealant just to make sure.
The carb is brand new and so are the jets and I sprayed out the passages with Gunk carb cleaner.
Not yet. I found it a few minutes before making this reply.
I am sort of frustrated but more worried about causing damage from running it too lean. I thought about bringing it to the shop. I don't mind conceding that I may not have the skills / time to tune it but I do not trust shops in general. LOL.
EDIT:
But yeah, I got my other carb in here and I am putting in a 33 pilot and 95 main. I am going to pop it on tomorrow.
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Post by greginisn on May 9, 2018 20:02:31 GMT -5
Hi,
For what it's worth my Tao2 is a 2017 49cc and the carb came with #30 and #75 jets. So you have a baseline for stock your installed jets don't sound that far off if any but you certainly seem to have something messed up some place. I'm not so sure how carb cleaner will test for leaks but I would try some diesel starting spray (ether in a spray can) cuz that will surely show intake system leaks. I had to use it for years to get my lawnmower started so It will burn and if you do have a vacuum leak that stuff will help prove it for sure.
I was going to say to have another go at cleaning the internal passages of your carb but you have already a different (new?) carb for it so that probably rules out carb problems unless you ARE jetted too big. I'm thinking your main jet should end up somewhere between a #85 to #95 if I had to make a guess. Depending on your local altitude.
Good luck
Greg
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Post by scootnewb on May 9, 2018 20:04:41 GMT -5
Thanks man. I am at sea level. I have another carb in here and have put the pilot down to 33 and raised the main to 95. And I noticed something. The new Keihin I have on there now does not have this screw in that hole. What does that thing do?
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Post by 3strokeengine on May 9, 2018 20:24:29 GMT -5
Thanks man. I am at sea level. I have another carb in here and have put the pilot down to 33 and raised the main to 95. And I noticed something. The new Keihin I have on there now does not have this screw in that hole. What does that thing do? Thats a drain screw for the float bowl
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Post by scootnewb on May 9, 2018 20:27:06 GMT -5
EDIT. Oh i see ... Thanks
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Post by FrankenMech on May 9, 2018 20:56:00 GMT -5
Look at exploded pictures of your carb in the manual or on the manufacturer's website. Spray carb cleaner through all the passages to learn where they go. Check some of the theory of operation diagrams and get to know your carb.
Remember there is no such thing as vacuum sucking fuel out. It is air PRESSURE forcing fuel from an area of high pressure to an area of lesser pressure, usually through some sort of restriction like an orifice.
Pod filters require larger jets because there is more pressure in the carb intake than with a stock airbox. The stock airbox is an airflow restriction which becomes part of the carb 'system' when it is installed.
When I bought a new carb I purchased a 'performance' carb rather than a stock replacement type carb. The performance carb was jetted to work with a pod filter out of the box. I also vented my carb fuel bowl to the carb air intake like a normal automotive carb instead of to atmosphere. I used a oiled paper and screen (K&N) type pod filter and the carb worked correctly right out of the box. A small tweak of the idle mix and it ran perfect like it was designed to do, no tuning needed. The stock replacement carbs are designed to work with a stock type airbox and because of differences in the stock airbox between models will always require tuning. I use a tin can cover over the pod filter to exclude water spray. My crankcase vent runs to the side of the filter cover and a heated air intake draws air from the engine shroud.
I run in the rain or snow, down to about 25°F, good weather or bad, all year long. I have also been running carbs on vehicles for over 50 years. I also use a Vito Performance parts adjustable jet to add some extra fuel for cold weather, about 1/8 turn. I do not run an enricher on my carb so it is a little cold blooded on startup but by the time I get my gloves and helmet on I am ready to roll.
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Post by scootnewb on May 9, 2018 21:24:37 GMT -5
Thanks. Yes the Keihin I ordered is supposed to be a performance racing carb. So was the one it is replacing. I never had a stock carb on here. I had to replace the carb in order to drive it home from the seller and I just left it there.
The Keihin came with 33 pilot and 85 main.
I have no idea what the first replacement carb had in there other than the ebay seller said it had an 85 main. The screws are in that one so tight, if I keep trying to remove them, I will strip them.
I am going to go back to the stock jets with the Kei-hin and start from there.
I see I was confusing the float bowl drain hose with the float bowl drain screw.
What air filer do you have? It may be worth looking into that one because it rains here a lot.
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Post by scootnewb on May 10, 2018 8:44:58 GMT -5
I think I got it. I put the pilot jet back down to 33 and upped the main just 1 size to 93. I was able to get it idling correctly without radical adjustments on the idle fuel mixture screw and when I rode it and went from WOT to 'not' and it did not stall. There weren't any back fires.
I want to go up to 95 96 (I don't have a 95) and see if there is any improvement.
But I don't think it is a good idea to ride it any longer since the plastic bucket below the seat has gotten damaged from riding it without any other body plastic and it now rests on the valve cover.
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