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2002 scrambler 500 2x4 Carb rebuild

3K views 13 replies 5 participants last post by  lateburd 
#1 ·
Hi - My son and I were riding today and the 2002 Scrambler 500 he has started idleing poor and stalling - Never had an issue before - I assume its time for a Carb rebuild as It has never been doen and I found the adjustment knob frozen , wont turn either way. How bad is a rebuild on this model ? I can fix most anything but Carbs have never been my thing !
 
#2 ·
Before jumping into the carb, I would check for water in the fuel, dirty air filter, spark plug problem and valve clearance.

I ran my CRF250 on the factory spark plug for 8 years - suddenly one day it started stalling and was hard to start after stalling - I had never had a problem and the valves had just been adjusted, so I presumed fuel - I drained the carb and looked for water - didn't find any and thought if there had been water it was gone now - I opened the petcock to expel any water that might be in the tank - I waited till the carb was completely empty, closed the drain, turned the gas on, waited for the carb to fill, the engine started easily and ran normally, so off I went - the first turn I came to, I closed the throttle to slow and the engine stalled - I made a bee line back to my truck and decided to change the $45 spark plug - I removed the seat, radiator shrouds and fuel tank to get access to the plug - installed the new one that I had always carried with me and tried again - lo and behold, the engine no longer stalled and was easy to start when killed either on purpose or not.

If it was fine and started acting up suddenly - it's probably not the carb
 
#3 ·
To each his own but a replacement carb on Amazon is only a few dollars more than a rebuild kit and much less frustrating. imho
 
#4 ·
Latebird the Plug is like 2 months old at best and the fuel was filled from a national station that morning right from the nozzle to the ATV not even into a fuel can and we filled mine as well mine is running fine so I dont think its the fuel, Air and fuel filter replaced with the spark plug - thats why I am leaning towards the carb - and with the adjustment knob frozen I cant even try to adjust it - Thoughts ?
 
#8 ·
My experience with spark plugs means I always start there first - I have seen new plugs right out of the box that would fire fine outside the engine, but not in the combustion chamber - I chased that gremlin for the better part of a full day before I figured it out.

I could not get the engine to fire and the plug was a brand new Champion - I was swapping parts off a running machine onto the non-running one - got down to everything had been changed except the spark plug so I took the plug out of the running one and put it in the non-running one - it fired right up - I put the parts off the non-running machine onto the previously running one and it would not start - took the plug out of the now running one and it fired right up - to this day, I will not use a Champion plug unless there is no other choice - I would use a Chinese Torch plug ahead of a Champion and I routinely replace Torch plugs with NGK.
 
#6 ·
I can't speak for all, but I believe the general consensus is that it is best to rebuild what is on the vehicle before the headache of tuning the 'will fit' replacement that Ebay, Amazon, Alibaba or any other internet seller offers. Would you prefer to rebuild the Golden Gate bridge or replace it with a 'will fit' replacement from Amazon at a fraction of the cost of what is already there?
 
#9 ·
Not nearly as many parts as a Quadrajet carb off an old GM V8 - most can be rebuilt without buying parts (usually just require a cleaning) - I'm not a fan of 'kits', but if a kit is $15 and a float bowl gasket is $20, Ill buy the kit just for the gasket and replace the other parts with the kit parts if they are the right ones for the carb being rebuilt - the key is cleaning - I prefer a commercial carb cleaning solvent (Berryman's Professional @ about $30 a gallon, but I buy it in a 5 gal bucket with a dip basket for about $80 - I also have a heated sonic cleaner with $60 a gal cleaning agent.

The Berryman's product I use 0901 in 1 gal and 0905 in 5 gal) has to be ordered - O'Rilley Auto Parts does not stock it - O'Rilleys stocks 0996 Chem-Dip (96 oz bucket) which is pretty good and B-12 spray cleaner (which is pretty good for cleaning the surface dirt off a carb) - Berryman's may be available from other auto parts suppliers also.

The cleaning agent I use in my sonic cleaner is Master Fluid Solutions Master Stages Clean 2020
 
#10 ·
So, from what I gather reading this thread... It is very involved. Might be best for a dealer or independent ATV mechanic to tackle this. Good luck!!


biz
:wink
 
#12 · (Edited)
I have two of those cheap carbs on the shelf, one for a 330 trail boss and the other is for a 200 Phoenix. I guess you know my thoughts.
So why did you buy them?
To each his own, however I detest rebuilding carbs, with my eyesight and big fingers those little parts are my achilles heal.
I swapped the 325 carb with one from Amazon (fuel filter included, even the pilot screw came properly adjusted) 30 minutes later I was washing my hands and quad runs beautifully. Quick and easy for $40. but that's just my humble opinion
 
#13 ·
I have two of those cheap carbs on the shelf, one for a 330 trail boss and the other is for a 200 Phoenix. I guess you know my thoughts.
So why did you buy them?
To each his own, however I detest rebuilding carbs, with my eyesight and big fingers those little parts are my achilles heal.
I swapped the 325 carb with one from Amazon (fuel filter included, even the pilot screw came properly adjusted) 30 minutes later I was washing my hands and quad runs beautifully. Quick and easy for $40. but that's just my humble opinion
I guess what I was attempting to say was I bought them trying fix them on the cheap and easy. The phoenix I had to take to the dealer and they requested the original carb because it was serviceable. The 330 was similar, the fellow that was helping me out asked for the original and not the China product. They both were cleaned and the machines were good to go. So that is why I have two on the shelf.
 
#14 ·
Sometimes you get lucky, but the majority have had bad luck - including myself - I have boxes full of old and new carbs. Worst experience? A customer brought me an 04 Arctic Cat DVX400 with a brand new carb on it. His complaint; it would start and idle, but wouldn't take throttle. In my experience I determined it was not getting enough fuel as the throttle was opened. I removed the carb, opened it up to check the jet sizes - no size engraved on the jets - I looked at the outside of the carb - a HUANSONG HYQZC - on the other side WML0177 PD36J-C

When I started working on the vehicle, I did not know it was a Chinese 'will fit' unit, but when I went to remove it I thought it was curious that the throttle cable had a loop in it to enter the operator chamber on the air filter side. I was accustomed to seeing the cable enter at the 1:00 o'clock position, not the 8:00 o'clock position. My first obstacle was Mikuni jets did not have the same thread as the Chinese clone. So I started drilling out the main jet (I have an assortment of decimal drill bits in .001 increments). I improved the performance substantially, but determined that by the time I got it right it would cost more than a new carb. I asked the owner what happened to the original carb and he said he was trying to make the vehicle faster and was drilling out the jets. He explained he knew he bucked up when he broke a drill bit and found out the slide wouldn't move. In his effort to remove the slide, he tore the rubber diaphragm off the slide. He found one on Amazon for $45, bought it, put it on and found out it wouldn't run above idle, so he brought it to me.

Now the Mikuni carb for the Acrtic Cat DVX400, Kawasaki KFX400 (KSF400) and the Suzuki LT-Z400 is the exact same carb. In case you didn't know it, the quads were manufactured by Suzuki. Kawasaki owned Suzuki at the time sold Arctic Cat complete vehicles except for the plastic. They came complete with carb, air box, electrics and used the same Mikuni carb with the exact same calibration - plastic, wheels and tires were proprietary to the vendor. Parts from Kawasaki is cheaper than parts from Suzuki and Arctic Cat parts are exorbitantly high priced. The first time I ordered an Arctic Cat part it came in a package with the Suzuki part number pasted over with the Arctic Cat part number. The Suzuki part was about 1/5 lower priced than Arctic Cat.

I ended up ordering a Mikuni carb from Kaw $437, Suz $627 and AC $788 - installed it, adjusted it and it was done. I also had to have a new throttle cable because the owner messed it up trying to stretch and bend it to get it connected to the cheap carb.

I usually don't have many problems with Chinese carbs on Chinese machines, so TaoTao, Eton, Dinli, Yamaha Vino scooters, Suzuki LT50 & LT 80, Arctic Cat 90, Polaris 50's and 90's, Jonway, Coolster, Kawasaki KFX50 and numerous other brands and models, but 20 out of a hundred Chinese carbs are junk out of the box. Weigh the advantages and disadvantages and make your choice.

BTW, Chinese carbs are not good aluminum - they are mostly zinc - they are easily damaged by alcohol and most OEM manufacturers will not warranty them if they have had gas in them. They can also be damaged during cleaning and can be damaged while running if ethanol blended fuel is used.

Just my experience, but I keep the Chinese carbs on hand (2 of each). Damn scooters need them frequently and they are cheaper to replace than clean.
 
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