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1984 350XT flooding out going downhill

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Anyone experience this. I have a 1984 350 XT - California model. It runs fine uphill and on the flats, but floods out going downhill. It back fires a lot and then dies. It starts right up after I let it sit for about 1 minute.

About 10,000 miles on engine

Replaced items

float valve and float valve seat, I adjusted float height to manual specs, nothing then I tried the method where the float is is set to be level with the bowl, worse.

rubber intake manifold boots

spark plug

Modified items

removed - carbon canister

No modifications to carburetor or engine.

Ongoing action

I have a mechanic working on it and he found a missing seal. He used silicon to replace the seal, but it still floods out going down a long hill (3-4 minutes long). I am sure that it didn't do this 6 years ago, but I have not been able to solve my problem since.

Mechanic check that valve clearance was accurate

Mechanic ideas

1. put carbon canister back on to see if this makes a difference

2. the gas tank is air tight and has a valve inside of the tank to let air in, possibly replace this valve - I am going to ride downhill with gas cap loose to see if letting tank breath helps

3. might be the faulty coil - although bike only runs bad when going downhill.

I like this bike but it is no longer a pleasure to ride.

Edited by superdoug3
added details on what I have done

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I'm working on this very same issue with my 90 with 14,000 miles on it.

I have a great mechanic on this now as I gave up. I'll post as to what he finds.

Mine is hard to start after it gets hot unless you hold the throttle wide open.

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I had a vast improvement today on my test ride

1. I put the carbon canister back on

2. I left the gas cap loose - the gas tank is not vented.

I can not ride like this because when I drop the bike the gas runs onto the ground, but I am much happier.

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umm , Why not get a vented gas cap ?

The CA version vents through the charcoal canister via a rolover valve built into the tank. A vented cap would be redundant and expensive.

When you remove the canister, you have to route the vent line that comes from the tank to somewhere else. Make sure ther arent any dips where liquid can set. You also have to cap off the nipple on the carb that the line from the canister went to. It would also be a good idea to replace the main jet with at least a non CA jet, or a 130 from the xt600.

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Obviously , his is not stock Ca model as he said "2. I left the gas cap loose - the gas tank is not vented." Something has to be different ...

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The CA version vents through the charcoal canister via a rolover valve built into the tank. A vented cap would be redundant and expensive.

When you remove the canister, you have to route the vent line that comes from the tank to somewhere else. Make sure ther arent any dips where liquid can set. You also have to cap off the nipple on the carb that the line from the canister went to. It would also be a good idea to replace the main jet with at least a non CA jet, or a 130 from the xt600.

thank you for the detailed tech specs. After reading your reply a 2nd time, I think you have solved my problem. "CA model vents through the rollover valve and carbon canister"

hence I need to replace the Rollover valve.

When I originally did the canisterectomy, I routed the hose from the tank into the carburetor where the canister originally went into. LOoks like I did it wrong.

I was thinking of leaving the canister on as this seems to have helped some.

Edited by superdoug3

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Obviously , his is not stock Ca model as he said "2. I left the gas cap loose - the gas tank is not vented." Something has to be different ...

This is my mistake. I am almost certain that this is a stock CA model. I assumed that the canister, airtight gas cap and roll over valve in the gas tank provided a closed system and thus no venting. JsnMid above explained that the rollover valve provides venting to this closed system. I will purchase a new rollover valve.

Edited by superdoug3

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You don't likely need a new rollover valve. If it works with the canister on, there is nothing wrong with the valve. Personally, I wouldn't remove it either. It's pretty nice to not have gas leak out of the vent when the bike is taking a dirt nap.

The Rollover valve does not provide the venting directly. It just keeps the canister from filling up with gas it a tipover. If you look at your canister, you will see there is another line on the bottom that goes no where. That is the vent to the vent to open air. It is not a closed system.

The line from the rollover valve needs to be vented to the open air. Just like a vented gas cap would be.

Then just cap off the little nipple on the carb where the line from the canister went into the carb.

pd350- he had the vent connected to the carb so it wasn't actually venting.

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Jsnmid:

Good news. With the information you supplied about how the canister works and how to do a proper canisterectomy, the problem is solved. The canister seems almost plugged, so I will remove it.

As far as a larger jet - is a larger jet needed because I will now be getting more air with the canister removed. Should I run the bike and check the spark plug for running lean

Edited by superdoug3

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"The tube on the bottom end of the canister looks like it could be blocked, so I will open it up, perhaps this is the solution."

Always try the easiest first . 👍

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great advice - I did try to unblock tube first and then I tried blowing through canister and it was quite hard to blow through, so then I decided to remove it. Bike is purring now. will check spark plug for mixture and decide on main jet size over the winter. only a few days before the snow flies.

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