Carb Overhaul - what is "needle-valve screw" and float adjustment

[Tieftoener]

Hello,

 

I disassembled and cleaned out the carbs last weekend per the service manual. To make sure I didn't miss something, I've been going through the forum threads and articles.

 

"mbrood" did a Carb Overhaul write-up in Tech section. In the 3rd to last paragraph he talks about the "The factory-set needle-valve screw..." The problem is, I have no idea what he's talking about. I'm concerned that I screwed in something too tight and ruined the needle valve now. Everything I unscrewed was TIGHT, so I put them back normal tight. I understand the needle valve and float relationship. He talks about a spring loaded screw for adjusting fuel flow. I don't understand what screw he's talking about. Can you guys help? Any references in the manual pages/pictures/ID numbers would really help.

 

Regarding float level, it never dawned on me to check or adjust for this change. I understand the principle of putting fuel in the carb and letting the float rise up to shut off flow. I don't understand (1) why fuel level is so critical in the bowl (I thought it just had to have enough fuel in there to be able to maintain flow... assuming more was better) and (2) how to know where the float is at shutoff point when the bowl cover has to be on in order to fill the bowl. How do you get the float to remain stationary so you can check it's position?

 

I read Squidley's recent thread on float level, and understand what he's measuring, but what has to happen at that level - start compressing the float needle valve spring? Or just making contact with the float needle valve?

 

I'm (obviously) very new to carb work and appreciate your time and input. I'm anxious to learn though

 

Many thanks in advance!

[steamer]

I believe the factory set needle valves your refer to have a brass cover over them, so you probable did mess with them. You would have to pry the covers off with a pair of pliers. Others here know more about this then I.

[steamer]

I should poof read what I wright. I ment you probably didn't mess with them.

[bkuhr]

I should poof read what I wright. I ment you probably didn't mess with them.

But you should have-for a proper cleaning

[steamer]

But you should have-for a proper cleaning

 

Good point.

[Tieftoener]

I believe the factory set needle valves your refer to have a brass cover over them, so you probable did mess with them. You would have to pry the covers off with a pair of pliers. Others here know more about this then I.

 

Brass cover? Where? Inside the bowl?

 

But you should have-for a proper cleaning

 

I don't see anything (unless there's another name they're using) in the service manual about this.

 

Can you guys point me to a section in the manual that I'm overlooking? Can we start from the exploded view on page 4-1 of the service manual?

 

"Needle Valve Screw"

- Is this the cap/screw that meets up with the "Float Needle Valve" at the fuel feed input to the bowl?

- The "Needle Jet Screw" identified here was screwed down tight onto the jet block when I opened these up for cleaning. I can't imagine this should be "loose" (not tight) since there is no spring to prevent the screw from backing all the way out (providing a locking mechanism).

 

Thanks for your input!

[oppelousas]

I'm pretty sure they are referring to the idle jet/air mixture screws under the brass plugs just below the diaphram cover screws on the outside. Not "IN" the carb. Excuse me if I am wrong. I am no mechanic. Good luck.

 

 

Brass cover? Where? Inside the bowl?

 

 

 

I don't see anything (unless there's another name they're using) in the service manual about this.

 

Can you guys point me to a section in the manual that I'm overlooking? Can we start from the exploded view on page 4-1 of the service manual?

 

"Needle Valve Screw"

- Is this the cap/screw that meets up with the "Float Needle Valve" at the fuel feed input to the bowl?

- The "Needle Jet Screw" identified here was screwed down tight onto the jet block when I opened these up for cleaning. I can't imagine this should be "loose" (not tight) since there is no spring to prevent the screw from backing all the way out (providing a locking mechanism).

 

Thanks for your input!

[Tieftoener]

I'm pretty sure they are referring to the idle jet/air mixture screws under the brass plugs just below the diaphram cover screws on the outside. Not "IN" the carb. Excuse me if I am wrong. I am no mechanic. Good luck.

 

OK... thanks! I actually just got a call from one of the members (whose name I've already forgotten) who explained the same thing to me over the phone. I'll take a look when I get home tonight and see if I can locate them.

 

Again, thanks to all for your input! I can't tell you how awesome it is to have such a great community of people I can go to that are so willing to help!

[bkuhr]

I'm pretty sure they are referring to the idle jet/air mixture screws under the brass plugs just below the diaphram cover screws on the outside. Not "IN" the carb. Excuse me if I am wrong. I am no mechanic. Good luck.

Brass plugs need hole drilled in them, then they are pulled out of the carbs and discarded. Spring loaded idle needle is under these plugs. Count and record turns until needle is bottomed(not hard or you will damage needle)(for each carb), then remove needle for cleaning. Starting point for reinstalling needles will be what was recorded earlier, probably 2-3 turns from bottom.

[Tieftoener]

Brass plugs need hole drilled in them, then they are pulled out of the carbs and discarded. Spring loaded idle needle is under these plugs. Count and record turns until needle is bottomed(not hard or you will damage needle)(for each carb), then remove needle for cleaning. Starting point for reinstalling needles will be what was recorded earlier, probably 2-3 turns from bottom.

 

Can I get replacement brass plugs at the dealer (or other parts place)?

 

In looking at page 4-2 of the manual, is this identified as the "Pilot Screw"? I see a spring there.

 

Also, how do I get to the Purge Jets 1 & 2? Purge Jet 2 appears to have the inlet from the hole inside body behind the main diaphragm. Is the other one on the other side? Guess I'll have to take the diaphragms out again and see if I can spray some carb cleaner down those holes...

[Snaggletooth]

Ok, looking at the outside of the carb, at the diaphragm side, you see two arrows in the pic. The arrow on the left is pointing at the recess where the idle air adjustment screw is. This screw SHOULD NOT BE TIGHT. EVER! Standard setting is turn in lightly until it just seats gently then back it out 2 1/2 turns for a good start on being correct.

 

If you crank this screw in hard you can damage the housing body. There is no seat on the screw other than the body itself.

 

Now if your carbs have never been touched there might well be a pug in that holes. You can drill a same hole PARTLY into it and pull it out with a small screw. If you desire, PM Dinghy (Gary) and he did have new plug available a while back.

 

If these needles have not been removed ever you might have some build up in there causing idle issues when you put them back on.

 

The needles you pull out will have a spring, washer, and an o-ring in there also.

 

The arrow on the right side is the drain screw to the fuel bowl. When you open that the black rubber lines coming through the rack brackets will begin to flow if the carb is getting fuel properly.

 

Hope some of that helps.

 

Mike

[Tieftoener]

Ok, looking at the outside of the carb, at the diaphragm side, you see two arrows in the pic. The arrow on the left is pointing at the recess where the idle air adjustment screw is. This screw SHOULD NOT BE TIGHT. EVER! Standard setting is turn in lightly until it just seats gently then back it out 2 1/2 turns for a good start on being correct.

 

If you crank this screw in hard you can damage the housing body. There is no seat on the screw other than the body itself.

 

Now if your carbs have never been touched there might well be a pug in that holes. You can drill a same hole PARTLY into it and pull it out with a small screw. If you desire, PM Dinghy (Gary) and he did have new plug available a while back.

 

If these needles have not been removed ever you might have some build up in there causing idle issues when you put them back on.

 

The needles you pull out will have a spring, washer, and an o-ring in there also.

 

The arrow on the right side is the drain screw to the fuel bowl. When you open that the black rubber lines coming through the rack brackets will begin to flow if the carb is getting fuel properly.

 

Hope some of that helps.

 

Mike

 

Mike, that's fabulous - THANK YOU. I know what you're talking about now - mine are still "plugged." I'll open these up and clean them up.

 

Do I need to seal that end cap back up? Perhaps just use a rubber plug (similar to what's used in the jet body?

 

Thanks everyone!

[Snaggletooth]

Mike, that's fabulous - THANK YOU. I know what you're talking about now - mine are still "plugged." I'll open these up and clean them up.

 

Do I need to seal that end cap back up? Perhaps just use a rubber plug (similar to what's used in the jet body?

 

Thanks everyone!

 

I'd bet most the bikes out there have not been replugged. It's really not required. The plugs that Gary had look a bit it the plastic tips off a Bic pen. It's pretty much to keep that recess clean. A much as I tinker with my bike I didn't bother plugging them.

 

When you pull those plugs and remove the needles take the time to check the small o-rings on them. I use a real fine strand of copper wire to fish them out. If they are brittle or damaged there is no other seal there to keep from sucking air in.

 

Mike

[MiCarl]

The plugs were required by the EPA to keep you from adjusting them. There is really no need to replace them. When you drill the old ones use high speed and light pressure, you don't want to drop through and bugger the pilot screw. Then screw any kind of self tapping screw (I use a sheetrock screw) you have lying around into the hole and pull on it with pliers to get the plug out.

 

If you cleaned the carburetors with them in they're not cleaned properly. Time to redo them.

[Snaggletooth]

The plugs were required by the EPA to keep you from adjusting them.

 

Yep.... and that did a lot of good. :crackup:

[dingy]

Below is a link to the replacement plastic covers for the neeble jet holes.

 

I had a carb that a wasp built a nest in one of the open holes.

 

$8 shipping included for 4 of them.

 

http://www.venturerider.org/classifieds/showproduct.php?product=3754&title=1st-gen-carb-needle-jet-hole-covers&cat=33

 

Also attached is a picture showing the needle valve point sticking through the venturi when it is seated.

 

Gary

[Tieftoener]

Thanks again to everyone!

 

Checked them out last night. I'll pull them out and clean them this weekend. I feel soooo much better knowing that I didn't "screw something up" (pun intended) last weekend. I'll be sure to be gentle and look forward to getting this cleaned out for a smooth running machine...

[Tieftoener]

Below is a link to the replacement plastic covers for the neeble jet holes.

 

I had a carb that a wasp built a nest in one of the open holes.

 

$8 shipping included for 4 of them.

 

http://www.venturerider.org/classifieds/showproduct.php?product=3754&title=1st-gen-carb-needle-jet-hole-covers&cat=33

 

Also attached is a picture showing the needle valve point sticking through the venturi when it is seated.

 

Gary

 

Awesome, thanks Gary. I'll keep an eye out for that hole...

[dynodon]

Tief...,

 

You asked about carb float stuff. I have not had the carbs on my VR apart, but a car carb float should work pretty much like a bike float.

 

The float has a tab that contacts the needle valve that shuts off fuel flow INTO the bowl when the fuel gets to the correct level. If the float is set too high, it could overflow and flood the engine or worse. If set too low, the fuel won't be pulled out of the bowl properly, and you could run lean.

 

To set the floats on every carb I have seen (again, maybe the Yamaha floats are different, so someone correct me if I am wrong) you turn the unit with the float and needle valve attached upside down so the float is pushing only with its own weight on the needle valve. The tab that touches the float is the part you usually bend to get the float level right. most car kits include a measuring device the measures the right height from the surface of the carb body to a given point (usually the pinched seam) on the float.

 

While there make sure the float does not have any fuel in it, they can develop leaks if hollow, or they could soak up fuel if old enough and not hollow. Most are brass, some are plastic.

 

I hope this helps, and If the Venture carbs are a lot different, I hope I didn't screw you up!

[Tieftoener]

Tief...,

 

You asked about carb float stuff. I have not had the carbs on my VR apart, but a car carb float should work pretty much like a bike float.

 

The float has a tab that contacts the needle valve that shuts off fuel flow INTO the bowl when the fuel gets to the correct level. If the float is set too high, it could overflow and flood the engine or worse. If set too low, the fuel won't be pulled out of the bowl properly, and you could run lean.

 

To set the floats on every carb I have seen (again, maybe the Yamaha floats are different, so someone correct me if I am wrong) you turn the unit with the float and needle valve attached upside down so the float is pushing only with its own weight on the needle valve. The tab that touches the float is the part you usually bend to get the float level right. most car kits include a measuring device the measures the right height from the surface of the carb body to a given point (usually the pinched seam) on the float.

 

While there make sure the float does not have any fuel in it, they can develop leaks if hollow, or they could soak up fuel if old enough and not hollow. Most are brass, some are plastic.

 

I hope this helps, and If the Venture carbs are a lot different, I hope I didn't screw you up!

 

Hi Don,

 

Thanks. I believe I understand these basic principles and the "extremes" of way too much fuel causing overflowing and way too little fuel causing a lean condition.

 

What I have a hard time understanding is why its so critical that the float be within a mm or two of spec'd height for shutting off the needle valve. With bikes and boats, there's a whole lot of sloshing around with the roll/pitch changes while riding, which would certainly affect the fuel level in the bowls a whole lot more than a mm or two adjustment for the "optimal spec'd shutoff point."

 

Am I off my rocker?

 

Thanks for helping set me straight...

[MiCarl]

The (relatively small) pressure drop in the carburetor throat allows air pressure to push fuel through the jets and into the air stream. Because the pressure differentials involved are small it doesn't take much change in the fuel level to significantly impact the amount of fuel pushed into the intake.

 

Before the 80s the manufacturers specified a float height, much like dynodon described.

 

By the mid 80s though the EPA had cracked down enough on emissions that the manufacturers had to run them on the very edge of too lean. The float height method is too crude to get the level to a point that runs well without violating emissions. From that point on the spec is for an actual fuel level measurement rather than a physical float height. Your service manual will describe how to measure it.

 

The plugs over your pilot screws is for the same reason: the engine is set up lean enough they shouldn't be turned in, and turning them out will violate emissions standards.

[jasonm.]

it's very confusing when the WRONG verbage is used. The only needle in these carbs are the large needle in the slide assy. Something that does not need attaention when cleaning the carbs. The issue does sound simply to be the LOW speed screw adjustment. FYI- there are small o-rings on these screws. And they will not seal up once you adjust these...due to age. It's best to replace these tiny orings, then adjust. Dirt bike shops have them. But from yamaha you must but the whole screw assembly...not cheap. the parts are screw, spring, washer and o-ring in this order then installed on the screw. Use a dab or grease when putting the parts on the screw. Otherwise they will fall and you will hate yourself:fingers-crossed-emo As for plugs..I used the old "jet plugs". These are the ones inside the carb on the jet block. They are rubber and seal great. New ones are over $5 ea. That's why I used the old ones which were still in fair shape.

Edited February 3, 2012 by jasonm.

[Tieftoener]

Thanks Jason. And thanks for the grease tip to hold the parts together during reassembly - Good call! I'm trying to find replacement O-rings. Hopefully, I can get the carbs back on this weekend.