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Discussion Starter · #1 ·
This is a bit more technical than simply rebuilding a carburetor - this is for the guys (and gals and TBD's) who want to become better at repairing a simple carburetor.

In the pics below I have done my best to document a specific problem with slide needles and jets.

Note, this needle is out of a Keihin FCR racing carb.

In this pic, you see damage to the anodize coating of the slide needle. This spot is where the anodize has flaked off.
This is right at the point just above idle where the fast idle warm-up occurs. Note the needle is not adjustable. This caused an over rich condition which was fouling the plugs during pre-race warm-up.
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In this pic you see a second spot where the anodize is worn through, this caused an over rich spot at cruising speed. Keep in mind the anodize coating is only about one thoudanth of an inch thick.
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In this pic you see where the needle is at idle and full throttle. There is visible wear between these two extremes.
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In this pic, you see the results of careless or improper handling or failure to use the proper tool to extract the needle during cleaning or tuning episodes. It may be the result of using needle nose pliers to lift the needle instead of using the factory provided needle extraction tool.
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What you don't get to see is the wear inside the needle jet. While the needle is in somewhat constant movement either shaking front to rear with pulse of air passing through the venturi or moving up and down with changes in throttle position. The constant movement wears the needle jet more severely than the needle as the needle is anodized and the jet typically uncoated bronze.

.001" wear on the needle and .002" wear on the jet = mixture that is completely outside the desired ratio. Poor engine performance, a loss of fuel economy and accelerated engine wear are the downsides. Easier starting and faster warm-up are the up side of this problem, but the upside does not offset the downside. You get faster acceleration with the correct mixture and possibly a win from not having to top off the fuel during an unplanned stop.

Questions?
 

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Wow..you have good eyes! Just hope you don't need to work on a Ford VV!! I was lucky to avoid those in my auto career.
 

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97 Polaris 500 sportsman 4x4 Indepedent shaft drive, 2000 Honda 450S foreman
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Let me ask, this could cause bogging as well? I see alot of posts people are complaining of bogging at heavy throttle. I know it’s fuel, air, spark, but exhaust is sometimes forgotten and all as one calculated.
Air passes into the engine via intake and is mixed with the fuel spray /mixture if not properly tuned either rich or lean conditions exist. What u show above is a specific item for a specific job at a specific tolerance, if those imperfections are past the anodized coating and into actual material fuel/air is able to do as it pleases causing erratic behavior of just about every kind depending on weather, temp, pressure, humidity and elevation right? I read alot of your messages, always on point and eager to teach after making sure that the students paying attention 😂 nice write up, i run nitromethane burning 1/5-1/6-1/8 scale rc models for almost 25 years now off and on used to race and had traxxas, Kyosho and losi as sponsors, they use a abc construction and either a 2-3needle carb, 1-high speed, 2-lo speed, u sometimes see 3-a mid/medium (don’t Ever touch or adjust)tjT is for mid range mix , plus a idol gap screw. They are extremely sensitive to weather change, they are 1 in the same as John force and his 18,000hp 350mph sub 4sec funny cars, same fuel. ..sameparameters, lower nitro content.
these engines arecapable of upwards of 33,000 rpm use a aluminum crankcase, brass sleeve and chrome piston, (ABC) unless u somehow separate a crankcase u can rebuild repeatedly until ur heart content, this translated to me doing all my own engine work on every thing thathas a combustion engine on it wifes car mytrucks amd everything else, quads, lawn equipment etc….I appreciate the time you took to remove that and do a write up for anyone, you will have helped at least 20 people without them even realizing it ….lol im 1 of em
 

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Discussion Starter · #5 · (Edited)
Let me ask, this could cause bogging as well?
Generally no - bogging is almost exclusively a lack of fuel, but too much fuel may cause a condition similar to a bog, but it is either a momentary drop in the acceleration curve or it gets progressively over rich to the point the engine dies as the RPMs increase. Now while a clogged exhaust will cause a bog, it is generally above a certain RPM and the back pressure simply limits the engine speed. An exhaust restriction rarely causes a change in fuel economy and the engines speed simply flattens to a 'no more than' RPM. Below that RPM the engine operates normally.

In the case of a true bog, the carb progressively leans out and the engine may either die from fuel starvation or simply not accelerate above a certain RPM (mimicking a restricted exhaust), but many times accompanied by spark knock prior to dying or constant RPM if the engine continues to run - whether it dies or continues to run depends on what RPM the engine is running at when the bog begins. If the bog is just above idle, it usually results in instant death of combustion. If the bog occurs above say 1/2 throttle, the engine may continue to run, but not above a certain RPM and spark knock may be detected.

And you are right, I was point on for carbureted fuel controlled induction systems. I concentrated on one specific fuel circuit of the carburetor. You broadened the subject into areas and applications outside the parameters of the topic.

This was specifically a lesson in what to look for when attempting to correct a specific problem and an example of how a simple carburetor is not simple. It is a precision fuel metering device.
 

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97 Polaris 500 sportsman 4x4 Indepedent shaft drive, 2000 Honda 450S foreman
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Generally no - bogging is almost exclusively a lack of fuel, but too much fuel may cause a condition similar to a bog, but it is either momentary drop in the acceleration curve or it gets progressively over rich to the point the engine dies as the RPMs increase. And while a clogged exhaust will cause a bog, it is generally above a certain RPM and the back pressure simply limits the engine speed. An exhaust restriction rarely causes a change in fuel economy and the engines speed simply flattens to a 'no more than' RPM. Below that RPM the engine operates normally.

In the case of a true bog, the carb progressively leans out and the engine may either die from fuel starvation or simply not accelerate above a certain RPM (mimicking a restricted exhaust), but many times accompanied by spark knock prior to dying or constant RPM if the engine continues to run - whether it dies or continues to run depends on what RPM the engine is running at when the bog begins. If the bog is just above idle, it usually results in instant death of combustion. If the bog occurs above say 1/2 throttle, the engine may continue to run, but not above a certain RPM and spark knock may be detected.

And you are right, I was point on for carbureted fuel controlled induction systems. I concentrated on one specific fuel circuit of the carburetor. You broadened the subject into areas and applications outside the parameters of the topic.
No disrespect, lol I get carried away sometimes , i respect
Your knowledge in fact ibe been using
It to rebuild mt
97 500 sportsman, very helpful so far,
Apologies for
Goin on a tangemt there.
I gotta get
Me 1 kf thise damn manuals. Can i ask a question off topic?..u r a certified shop mech and have been a walking thesaurus on these machines, is there a way to make/do tjeu make aftermarket brackets or motor mounts for these models? I can’t get this engine to stay
Still, it still twists to left, i have changed the rear lower mounts, i see there are also 4 holes in engine casing for the mounts, the 2 lowest are used, the front and top right wre already recently changed. The bracket to the top right has a stripped hole kn top of engine case looking to tap it n chase threads and km making different isolators for carb bracket. I don’t want to run er til i have everything done 100% I don’t want to run it half
Ass. I appreciate your knowledge man and respect your
Answers thanks
 

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RE: bogging only

I had 05 500, it ran 100% perfect when I got it.
I did all the maintenance work, put the bike back together and it wouldnt rev.
I replaced spark, fuel, harness, air filter chasing the issue only to find that someone in the shop found and put on a pre-filter sock on the intake pipe (not the filter) and sure enough it was causing a bog down at high rev.

Moral of the story is that carbs are balanced, in racing the chop at idle because they are tuned for high end HP. In atvs they need balance to start and run hot.
 

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Discussion Starter · #8 ·
I did not interpret anything as disrespect - I thought I might just clarify what may have been confusing and then I revised what I composed, but was interrupted and didn't finish the revision for nearly an hour.

I'm trying to point out the finer points of problem solving.
 

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97 Polaris 500 sportsman 4x4 Indepedent shaft drive, 2000 Honda 450S foreman
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🤐 i am yet a pupil , I have no disagreement with anything said…apologies
 

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97 Polaris 500 sportsman 4x4 Indepedent shaft drive, 2000 Honda 450S foreman
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Im not even gonna look anymore about these stupid motor mounts, i believe po over tightened the front lower. The top right bracket that bolts to top of engine and side rail had a stripped hole in engine case, im gonna try to rethread it up a size and pray, what is happening is when heavy throttle is applied the engine is turning to left causing the clutches to get closer and make more slack in belt, I have brand new belt and im not putting it on until I resolve this issue . I don’t have a manual i definitely need to invest in 1, but the correct method of installing belt is to rotate the secondary inner sheave until it will open the clutch and allow belt to drop into the 2 sheaves correct? How far should it drop and could it have anything to do at all with the clutches themselves not operating in higher rpms as should? Im going to get that other bolt in the upper mount bracket and see what it’s doing, its sad the engine has balls for days, more than my 450S foreman amd thats my baby she will lift the fronts like this is normal behavior I really want to get this right …it will move under own power i was riding in alley behind my house last night after it sat for over a year with po. Sat another 3 months after I got it home and fires right up. Would be ashame if I can’t get this engine vibration taken care of, is there any aftermarket mounts/brackets or possibly a way to fabricate 1??? I think I would rather go that route and be sure it’s secure everywhere
 
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