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Discussion Starter · #1 ·
Hi.

I'm looking to replace my stock PD24J carb with a quality but inexpensive unit. The scooter is a Dong Fang brand "Razor 150" sold through Redfox Powersports. I see Amazon in the USA has them from 20 to about 50 dollars. I think a 20 dollar carb may be cheap quality wise but the one 50 dollar model I found (GoKart Exports brand) seems overpriced compared to the average price. I just don't know which brand to trust.

The bike is 6 months old. (my first motorcycle) I want to replace the carb because I don't have access to the fuel/air mixture screw like you see in this post (It's covered up with what looks to be a solid piece of metal):

https://www.reddit.com/r/scooters/comments/gg6j83
I know I can remove the plug but I'd rather not and just go with a better quality carb that may preform better.

You see no matter how I adjust the idle speed screw, the bike wants to kill easily and I suspect I'm not getting the power I should. I live right at 3 feet above sea level and I understand the fuel/air mixture is factory set for a much higher elevation. I read that someplace because they want to set them at an average that makes most people happy. I have no actual way to determine the exact sea level my fuel/air mixture was set for.. I assume perhaps it's set for the location of the factory where the bike was made.

Ya know that purring like a kitten sound you try to achieve, I can never get that. Of course it's possible as a newbie I'm still not adjusting things right and don't need to mess with the fuel/air screw at all.

Your thoughts? Thank you.
 

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I wouldn't worry about the quality any more then the rest of the Dong Fang scooter, but if in doubt and as you say they are cheap, why not order 2 and hopefully one of them will work good.
The carburetor in the photo is a CV (Constant Velocity) carburetor, they are designed to be less affected by elevation changes and temperature shifts.

Did you clean the emulsion tube real good? It is accessed from the bottom of the carburetor, looks like a brass tube with holes in the sides.
 

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Discussion Starter · #3 ·
I wouldn't worry about the quality any more then the rest of the Dong Fang scooter, but if in doubt and as you say they are cheap, why not order 2 and hopefully one of them will work good.
The carburetor in the photo is a CV (Constant Velocity) carburetor, they are designed to be less affected by elevation changes and temperature shifts.

Did you clean the emulsion tube real good? It is accessed from the bottom of the carburetor, looks like a brass tube with holes in the sides.
Thanks for the reply and good info. No I didn't clean anything because I don't see how anything could be clogged or dirty. I've only put 100 miles on using 8 mile round trips to the lake for fishing. The 8 and a half pound 27 inch red fish was worth it. I can't tell you if my carb is a Constant Velocity variety. I don't know that I could replace my carb with one or if I have to go back with the exact same style as stock. Do you think adjusting the fuel/air mixture would help once I can get to it either by taping the plug out or replacing the carb?
 

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It's silly to buy another carb while you still have one with the mixture screw plug undrilled to get to it.

The aftermarket carbs are not matched nearly to your engine as close as what comes on it. The original carb will always be best and closest in the calibration.

Some engines need that mixture screw adjusted as soon as the new engine carbon coats or maybe 30 minutes driving, the engine fuel demand is different with a clean piston top vs. a carboned up one. I had a new Honda 750 that did that in the first hour of running it, the engine began to idle off and the idle mixture screws had limiters to only turn part of a turn, ground off to turn as much as wanted and the engine instantly went back to a perfect idle. Because the mixture screws are set lean for emissions but carbon coating often calls for slightly richer.
 

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The screw setting that is plugged (tamper proof) in theory should not need to be touched if the bike was working good to begin with and nothing has changed to make it run different, so if it's a maintenance issue and not due to modifications to the engine then cleaning of the carburetor would be the first thing I would do, the good news is all the problems will be in the bottom half of the carburetor where the gasoline and possibly water and or dirt can be found. Other things to check would be air cleaner, if the bike see's a lot of dirt dust.
Constant Velocity carb is easy to spot by the big round chamber at the top of the carburetor that houses the vacuum dashpot. It typically has 2 air valves, one is a butterfly valve that you open with a cable and the second is one that is opened by the engines intake vacuum.

... and yes it would be silly to buy anything before even looking at what the problem might be (y) trying to adjust out a problem rarely solves the original problem
 

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'The screw setting that is plugged (tamper proof) IN THEORY should not need to be touched if the bike was working good to begin with and nothing has changed to make it run different...'

So said and caps mine. I'd have to ask why it is COMMON to have to set idle mixture and then come back later to final adjust it again on new motors within a very short period of time? I saw it so many times when working on emissions engines I couldn't count. The reality of carbon coating is well known to racers, not running across it screams not paying attention.

If the theory had basis in fact nobody would have to come back later to drill plugs out, defeat idle mix limiters, and such and I must have totally dreamed up the ragged idle my brand new bike went into after just one day. Luckily I was smarter than that theory to have it fixed in about ten minutes of grinding on float bowl limiter tabs to be able to change the OEM idle setting set by gas analyzer which was supposed to be right (in theory). Passing failed tailpipe inspection with slight miss? Readjust the idle mixture to rich side to stop the miss and then sneak back up on lean to a 50 rpm drop but just shy of the miss due to lean from OEM and then vehicle passes HC/CO instantly. I used to get a hundred dollar bill to do that and dropping the timing way back to lower NOx, we called it the 'inspection tuneup'.

One has to read the books and manuals but at the same time be smart enough to toss out what obviously does not work in your personal present reality. Matrix indeed.

Of course the carb could simply be dirty already, you can't look and tell, it being anecdotal.
 

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Have you ever bought a new engine and Not found loose material in the carburetor after a while? I took the bowl off a new zero turn tractor and there was a spare main jet rolling around in the bottom of the float bowl, made in India Briggs&Stratton engine it said on it, everything else said John Deere, it ain't no Deere I can tell you that, but it does run a little better now, oh and come to think of it the fuel pump was also defective and had to be replaced
 

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I rarely bought engines, rather built them myself for whatever the need. No problems to speak of, maybe once in a hundred if that many. I simply check too much stuff and never put a carb on anything without going through it first even new. Usually because I change them up somewhat from new.

Irrelevent anyway if I fix bad running by simply adjusting carb. Not saying it is correct but most carbs can stand a bit of trash in them anyway with no bad effect. Why the metering fuel entrances are commonly above the bottom of the bowl.
 

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Discussion Starter · #10 ·
Great conversation gents. I'll try to attack the problem head on first before I buy a carb. I haven't a clue how many metal shaving are floating around in there. Next oil change is at 300 miles. The first gallon of fuel I ran was 91 octane ethanol which seems to run through pretty fast but I put that down to idle being too high. The idle wasn't factory set, it's part of the setup along with adjusting the throttle according to my manual. I was able to adjust it to the point just before the back tire started spinning and it helped a lot though I'm sure the bike never ran as intended. I replaced the oil, spark plug and gear oil before I ever started it. I'm a Haynes manual guy who fixed all my cars cus I couldn't afford the shop. Too bad Haynes don't make manuals for my scooter but I have 40 assorted Gy6/Chinese scooter manuals gathered from all over the net.

Next I ran non Ethanol fuel because I read they were better for scooters. The one place I have to buy it is not close and it's not cheap. I may try to remove the ethanol myself by mixing it with water, letting it settle then draining off the water ethanol mixture that settles at the bottom should I decide to continue using non ethanol fuel. Seen lots of videos on it, like the Project Farm channel. I know it's bad for carbs and since Ethanol is hydrophilic it can bond with the moisture in air in the gas tank and contribute to rust as well as put moisture in the carb I understand. I haven't gotten close to my 90 mpg this scooter is supposed to get. I chalk that up to everything not being set right as this is my first bike as well as not being broken in yet. That's my aim, I wanna get a good benchmark on the mpg and get it to it's best speed potential, that's "55 plus" depending on rider and road. I haven't gone past 40 as I'm breaking it in. I weigh about 115 and have no more than10 lbs of stuff under the seat. I'm not a drag on the bike. I want to hit that 55 mph with as close to the stated 90 mpg as I can get. I should get an RPM gauge the bike didn't come with one. .

The specs do say it has a speed limiter. I have not tried to find and remove any restrictions yet but I figured I'll look into those things after I have a baseline. Thank you both for your insight.
 

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Don't remove ethanol from the fuel unless you have a way to make the lost octane back up as the ethanol comprises a good part of the octane number, another reason why they use it.
 

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If you decide to remove the cap covering the fuel mixture screw by drilling it use a limiter of some sort on the drill so your drill does not contact the screw. All it takes is a touch to spin the screw in. Some of the screws are Very Close to the cap so you only want to drill far enough to get a metal screw in the cap for removal. Also it would be good to know the original setting of the mixture screw.

S F
 
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