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Discussion Starter #1 (Edited by Moderator)
There are basically two types of common carburetors used on ATVs. CV and standard. Both have slides.

CV = Constant Velocity. The throttle cable controls a butterfly valve on the engine side of the carb. The slide is operated by vacuum and uses a rubber diaphragm and spring combination to regulate how fast and how far it moves. The slide also has the Jet Needle.

Standard, often called Round Slide, but not all have round slides, the throttle cable directly controls the slide. The Jet Needle is also attached to the slide.

When 4 strokes flood, it can be very difficult to un-flood and even more difficult when using a CV carb.

The choke on all of these carbs is actually an enricher. It opens up another hole down into the float bowl that pulls more fuel into the engine.

Flooding is fairly common with ATVs, specially newly rebuilt or carb-cleaned ones.

If the ATV does not fire, pull the spark plug and look at it. If it is noticeably wet, you're flooded.

In CV type carbs, the float level is critical because of two factors. Set to high and the pilot circuit will get to much fuel and possibly the main jet will bubble more fuel up at idle. To low and the main jet will starve for fuel at higher speeds. There is a reason the tolerance is 1mm in all of these carbs.

Float level in non-CV carbs is also critical, but the tolerance is usually 1.5 to 2.5mm. Error on the side of to high and you typically won't have any issues.


Why is flooding so common in new rebuilds? When the engine doesn't start in the first couple pulls, the first thing people try is full choke, which floods it.
 

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Awesome

GREAT...great...write-up TheBearAK!!

Hopefully this helps those that have a flooded carb issue.


biz
:wink::wink:
 

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Agreed. Think this thread belongs as a sticky.
 

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Excellent and thanks Bear. How many beers would you like to rebuild my CV carb?
 

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Discussion Starter #5
hehe, well, I'm not an expert on them. I just ripped into it and figured all this stuff out. The fine art of actually tuning a carb still eludes me.
 

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When electronic fuel injection first came out I thought it was BS idea. Then I got something FI...not looking back.
 

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Having problems with my Suzuki quad runner 250. Cleaned the carb because it would start and cut off when I gave it gas. After reinstall it runs worse. It takes awhile too start and once it does I give it full throttle and it hardly stays running and spits and sputters plus exhaust smoke. Not sure if I have the lines hooked up correctly. Any help would be appreciated.
 

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Rebuilt Mikuni VM 26SS - Idle Screw doesn't affect idle.

Hello,

Just rebuilt Mikuni VM 26SS - (1987 LT230e Quadrunner) When running now somehow the Idle Adjustment Screw doesn't affect the idle. I just got the quad running again this morning and it starts/runs great until I let off the throttle. I'm turning the screw and nothing is happening to the idle speed. Does anyone have experience with this? What component did I eff-up on the carb rebuild? Thanks.

-C
 

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Discussion Starter #11
On mine, I discovered that there was originally a rubber tip on the end of the idle screw. Without the tip, it loses about 3mm of reach. I found a little nylon tip for mine in my junk box.
 

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On mine, I discovered that there was originally a rubber tip on the end of the idle screw. Without the tip, it loses about 3mm of reach. I found a little nylon tip for mine in my junk box.
Ah ha, thanks for the 'tip' —*Mine was a Moose rebuild kit and the guy essentially handed me the carb parts loose in a bucket, I'll take a look!
 

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I've got a flooding issue that I haven't been able to solve yet. I'm a new member and I've been searching threads to resolve my problem- but I haven't seen anything quite like what I've got. I have a 1985 ALT 185 3-wheeler. I have a new carb on it, new fuel pump, and the original petcock which appears to be just fine. Note: this is NOT a vacuum operated petcock, it's a standard petcock with ON OFF RES. The only vacuum line goes from a port on the intake boot to the center port on the fuel pump. Everything appears to be plumbed correctly based on what I have seen in the service manual and on some images online.

That said- I can crank it on the first pull and it runs just fine. Takes fuel great, you can drive it around and it does great- but then it starts stumbling and fuel pours out of the overflow tube! If i let it sit for a bit, the excess fuel runs out and then I can restart it- but once I ride it, it goes back to doing the same thing. All I can gather is that riding it actually creates too much fuel pressure- thus overcoming the force of the float on the needle in the carb. Has anyone ever run into this issue? I'm at a loss. I've tried two carburetors (one is the original, rebuilt) and a new one that I purchased on Amazon. Both have the same results. Is there any sort of fuel regulator associated with these systems? Is there any sort of regulator for the vacuum input to the fuel pump?

Also- I have checked the float height on both carbs. They appear to be within the specification listed in the manual.

Any help would be greatly appreciated!
 

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Discussion Starter #16
The only way it flows out the overflow tube is if the needle/seat is not closing when full.

Is that the old brass floats? Maybe it has a micro-hole in it and it takes a while for it to sink?


Not sure how it would build up pressure unless the vent lines were plugged, but even then it would just starve for fuel.
 
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