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Discussion Starter #101
I haven't been here for a few years. I see the images in my OP are gone. They were linked from my gallery here. I'm not sure if the new website format killed the links or Tubby removed them in the edit he did in 2016. Asking if I should link them again?
 

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You can add the pics again Tim. The gallery was removed by the new administration staff. Too much spam and hard to maintain and keep up with. So you’ll have to find another method or use the Forum uploader to re-add them. As for Tubby, he’s been absent from the Forum for a little over two years. He was battling health issues back then so I don’t know what’s happened to him.


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I've only had my quadrunner for a month now, and haven't ridden it much--but I think the oil I changed out smelled a bit like gas, and the last time I moved it, it seemed like the oil level had gone up. So I have a little concern there.

It has been sitting for a few days but I pulled the vac line to the petcock, and it is dry. I already replaced the fuel pump so I don't think it's that... and it's just possible that oil fully drained down and/or I was parked on an incline so the level in the sight glass would be different.

Anyhow, my question is, on the petcock, if it is set to Pri(me), how could fuel get to the engine? The fuel pump is still in the way, and if the engine is off, there is no vacuum to operate the pump. I usually think of a pump that has no power source as being unable to pump. Can this pump pass fuel without vacuum?
 

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If left on Prime....the fuel will siphon into the crankcase through the carb....especially if the tank is over half full. The float needle will slowly leak fuel through it with the constant preasure. On prime it by passes the fuel vacuum cut off.
 

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You should only use prime as a diagnostic tool to troubleshoot carb issues or when priming the float bowl. You should only use On or the Res setting as both these settings utilize vacuum. As mentioned by TC, in Pri fuel flows regardless of if your atv is running or not. When your atv is off, fuel will contaminate your oil as mentioned by the following process.


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I don't understand--the fuel pump will pass fuel even when it doesn't receive a vacuum signal?

I took apart the old pump and saw some one way valves, but I didn't look to see if they used springs to keep them shut nor study it very much before I put it back together. I should take it apart again (it's in a recycling bin somewhere) and see if will pass fuel without vacuum--it sounds like it.

FWIW I leave mine either on reserve or on, not on full. Which says bad petcock if I am truly getting gas in the oil.
 

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The vacuum fuel petcocks have 3 settings, On/Pri/Res. There is no (Full) position. Both the On/Res positions utilize vacuum, whereas Pri (Prime) does not. Pri is gravity fed and flows regardless of if the engine is running or not. You should only utilize the On position as you are utilizing the upper pick up tube in the tank to draw fuel. In Res, you are utilizing the lower pick up tube which draws fuel near the bottom of the tank. Though since the Res pick up tube is situated near the bottom of the tank, you are susceptible in picking crud since it’s near the bottom. The pick up tubes have fine screens on them to filter out any sediment/crud. Though they are not 100% in stopping everything.


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My bad--meant to say, I don't leave it on Prime.

I guess it makes sense--if the engine is not running, you want fuel to go through the system and prime it. Thus the fuel pump must be able to pass fuel without a vacuum source, using just gravity.
 

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Okay here's what I have going on. I have pretty much the problems all you have experienced with the vacuum petcock. First I have a gas shut off valve right ahead of the carb because I was tired of gas getting into my crankcase to dilute the oil. I replaced the petcock with a new vacuum one just as it was. What happens is when I start the ATV it runs on the carb fuel bowl, runs that out and then starts this chug chug chug because of the wee bit of gas it's getting from the fuel line. I have a clear filter on the line and I can see how little is pumped in. It does not matter where the petcock lever is set, that is primary, reserve, etc.. So I found the best thing to do while it's chug chug chugging is to let it idle as less gas is used. It eventually fills the carb bowl some and it'll rev and then run out. It keeps repeating the process for about five minutes, then she runs like the day she was new. Next day does the same thing. It's as though she has to warm up but this is in warm weather too!! Here's what I have done. I replaced the petcock as mentioned. Next I put on a new vacuum fuel pump. Previously I was talking the old pump apart and cleaning it. I never found anything wrong with it. Okay replaced that and I pulled the carb and thoroughly cleaned it and adjusted the float level an put it back on. Still chugs till five minutes are up. Have left it this way for a couple of weeks. Today I put a new manual petcock on it. No more vacuum operated and YES I did block off the vacuum line at the carb. Same damn thing: chug chug, chug, chug, for about five minutes. Everyone told me put a manual petcock on it. Now I'm at a total lost and I don't think there is anyone in the whole U.S. that can fix this SOB. I hope none of the rest of you go through this.
 

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The next day I switched the two vacuum hoses and got the same results. A friend wanted to know if I hook a bottle of gas and a hose to carb and shut the ATV gas system off if it did the same thing. It does not. So it has something to do with the vacuum and the vacuum fuel pump. Like I said two fuel pumps do the same thing.
 

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Sounds like it might be a carb problem.... are you SURE the idle jet is clear?
 

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All fresh rebuilt. TC when first started for the day it's not getting gas as you can see it in the clear fuel filter. Carb is rebuilt and cleaned very well. Once she gets over her fit carb runs her smooth as can be. I checked to see if there was vacuum on the two ports (only using the one now after putting in a manual petcock) and there is plenty of suction there. I've also run the carb/ATV with a bottle of gas and hose hooked to the carb and runs fine even when first starting it up. So it's vacuum related and fuel pump related. Second fuel pump on her. Yes when I cleaned the carb I made sure to clean those vacuum ports. Never seen anything like this.
 

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Okay I have narrowed it down. I put a separate bottle of gas again on the carb and had the ATV's fuel line shut off. It does the same thing so now that isolates it to the carb. Something is sticking and it's either the float or needle valve. The needle in it now is a neoprene and the one before it (which did the same problem) was the solid brass type. I really don't think it's the needle sticking. It's also not a choke related problem. Today it's very warm and I only used to the choke to start it, which I didn't need to, but had it running without the choke fine until it started it's problem. We know the carb is isolated from the cylinder head by that rubber manifold so it's not a problem where the heat is finally warming up something. These aren't like car carburetors that need warmed up. So what could it be? Could it be something other then the carb?
 

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Tore the carb apart and something unusual happen. The needle valve brass seat that is pressed into the carb body and an O-ring holds it and seals it was pushed out! It's a loose fit so I put the old needle valve seat in with a new O-ring and it's nice and tight. Also on that other seat the filter screen wouldn't stay attached. Al lot of those rebuilt kits on Ebay are junk and that's where I got it. I'm having trouble getting the right float level set. Will go at it tomorrow again.
 

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They usually have a screw to hold them in.
 

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They usually have a screw to hold them in.
[/QUOTE]

My son tore it off the ATV while I was out. Have to go take the fuel bowl and see if there was a place for a screw. I need to reset the float level as it's too lean now. Very little changes on that needle tab make huge running changes!
 

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TCIII....thanks for mentioning that screw. It wasn't there, luckily the rebuild kit had a new one. Installed that and adjusted the float lever and apparently hit the right spot. It's running like new and it doesn't do that chug chug chug anymore at first start up. Whew! Lot of work, but it's right now.
 

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Glad you got it going...... Some people just give up on carbs,,,,,unless they are physically BROKEN,they can all be returned to factory new working condition....just takes time and patience .
 

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Anyone if the future having a problem like mine I think the first thing to do is hook a vented bottle of gas with a hose to your carb and see if it runs correctly. If it does then it's either the petcock or vacuum fuel pump. If it doesn't then work on the other two. Let me tell you that float level is a very sensitive and takes a little time to get it correct. I hope what has happened to me helps the rest of you.
 

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I have a 2007 Vinson and have replaced the petcock, cleaned jets, replaced jets and float needle and no matter what position the petcock is in, the Quad; starts, idles but within a few feet in 1st gear stutters and dies. I have also had it backfire. These steps were all under the assumption that insufficient fuel was getting thru the carburator. Now I am considering a whole new carburator purchase as I cannot find a Service dealer I trust. What have I missed? Oh, yeah how does one tell which carburator to order as there seems to be 4 different carbs with slightly different part numbers.
 
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