Bryan's 1989 FJ1200 rebirth in Poplar Grove, IL

[Waiex191]

The emulsion tube (aka jet nozzle, needle jet) is held in place by the main jet. The tube slides out thru the top (the bore of the vacuum slides)

Thanks - that sounds easy!  I should check that on my GN as well.

[Waiex191]

Our local EAA chapter has a lathe.  I turned down a piece of steel rod to about .01" smaller diameter than the emulsion tube.


Unfortunately I don't have access to the Bridgeport so I cut a slot with my 4.5" grinder. Crude but effective.


I've popped out all 4.  It was easy.  Thanks Pat!

[Pat Conlon]

Glad it worked out. Be careful not to bugger the nub that fits the slot on the tube

Onward and upward...

[Waiex191]

Thanks Pat.  The slot cleared the nub nicely, so none of them were buggered.  I'll make another tool when it is time to put them back in.  I assume you want to send them home with something other than the main jet pulling them in?  Is there a shoulder that the tube hits on the way back in?

[JPaganel]

Thanks Pat.  The slot cleared the nub nicely, so none of them were buggered.  I'll make another tool when it is time to put them back in.  I assume you want to send them home with something other than the main jet pulling them in?  Is there a shoulder that the tube hits on the way back in?

When you put them in, you should be able to push it in with your finger. They aren't pounded in, or anything. They can be difficult to get out because of dirt and varnish, but they should not be difficult to get in, unless something is wrong.

[Pat Conlon]

Thanks Pat.  The slot cleared the nub nicely, so none of them were buggered.  I'll make another tool when it is time to put them back in.  I assume you want to send them home with something other than the main jet pulling them in?  Is there a shoulder that the tube hits on the way back in?

When you put them in, you should be able to push it in with your finger. They aren't pounded in, or anything. They can be difficult to get out because of dirt and varnish, but they should not be difficult to get in, unless something is wrong.

Yep ^^^

[Waiex191]

Thanks guys!  I got the emulsion tubes cleaned off and all the holes opened up.  The pilot jets were a challenge to get clear. Very small hole in those things. I tried soaking and blasting them. Managed not to launch any while using the air compressor - ever do that? I finally found some safety cable that was small enough to run through the hole. I had to snip the end and unwind the strands, and get a single strand. The .020 safety wire I had was too big.
I got the float seats also cleaned up nicely.  Took a small piece of scotch brite, rolled it up, put it in the seat, and spun it with a small screwdriver.  I now know what parts I need.  I'll be ordering from RPM today. 

[Waiex191]

Hey all,
I'm back looking for a little advice.  
Item 1: while cleaning out some carbon around the butterfly valve, I noticed that two of the needle valves stick into the bore a little, and two do not.  Is that normal?


I've never had them out, and in fact still have the caps on.  Should I mess with them at all?


There is the brass tube that sticks out of the carb bottom and seems to go up to the enrichening circuit.  On the bottom it sticks into a hole in the bowl.  It seems there is a tiny orifice there, a cavity underneath it, which is connected to the interior of the bowl.  I'm assuming the fuel slowly bleeds past the orifice to put a slug of fuel around that brass tube, for initial startup.  What is a good way to clear this?  I couldn't get my safety wire through it.  Nor could I blow it out with various solvents or compressed air.  The tube, the hole it goes into, and the passage to the bowl are all in line in this picture - from bottom to top.


I am thinking if there is no other good option, I could drill up from the bottom inline with the brass orifice plug, clean out the cavity, and then put a #4 screw or something small there.  I also wonder if that same problem exists in my GN400 Mikuni carb - I can't seem to get it to kick start when cold, I have to bump it.

[JPaganel]

Item 1: while cleaning out some carbon around the butterfly valve, I noticed that two of the needle valves stick into the bore a little, and two do not.  Is that normal?

Those aren't needle valves. They are idle air screws.  Yes, I'm being pedantic, but if you search for info, you won't find what you are looking for.

Yes, they aren't necessarily set the same.  If you want to clean out those passages, get ready for the tiniest o-ring you ever saw. If you have a carb kit, they are likely included. If you do not, I would not pull them unless I had replacement o-rings on hand. Also, those screws can be stuck, and if you strip them, will be problematic.

There is the brass tube that sticks out of the carb bottom and seems to go up to the enrichening circuit.  On the bottom it sticks into a hole in the bowl.  It seems there is a tiny orifice there, a cavity underneath it, which is connected to the interior of the bowl.  I'm assuming the fuel slowly bleeds past the orifice to put a slug of fuel around that brass tube, for initial startup.  What is a good way to clear this?  I couldn't get my safety wire through it.  Nor could I blow it out with various solvents or compressed air.

Yes, that's the idle circuit. Yes, you need that clean, or you will have hard starts.

Because this hole is two holes meeting, you can't really shove a wire all the way through. And the wire does need to be tiny. I think I used a bristle out of a wire brush, or a strand out of a wire.  Otherwise, soak, and soak, and soak. Maybe boil, then soak.

I am thinking if there is no other good option, I could drill up from the bottom inline with the brass orifice plug, clean out the cavity, and then put a #4 screw or something small there. 

Never heard of anybody trying that. Wouldn't do it myself, unless I had spare bowls on hand.

I also wonder if that same problem exists in my GN400 Mikuni carb - I can't seem to get it to kick start when cold, I have to bump it.

Very possible. Tiny holes clog easy.

[Pat Conlon]

Pull those plugs out, carefully.
You have to get to the air/fuel idle mixture screws under the plugs for removal and proper cleaning.

The choke circuit fuel pickup at the bottom of the bowl is commonly plugged. That's where all the sediment and varnish settles.  Soak, piano wire, compressed air or ultrasound are your options. Don't drill.
*Be careful* if you spray your carb cleaner down that passage the spray will come out the bottom port on the bowl and...HIT YOU RIGHT IN YOUR FUCKING EYE... (don't ask)

The tips of idle/fuel mixture screws poke down into the carb throat....as you see....some do, some don't.
That's the rub.
Unfortunately the threads cut in the carb body on these mixture screws are not precise. They can differentiate 1/8 to 1/4 turn between the 4 carbs.
IOW if you screw in these idle mixture screws "until lightly seated" then back these screws out 3 turns, you would think your idle mixture screws would all be the same....but you would be wrong. One carb may be slightly rich, one carb may be slightly lean. Yamaha factory techs never had to worry about these screw threads being imprecise because they set the idle mixture with a 4 channel gas analyzer. (That's what the ports are for on the bottom of your header tubes) Setting an even mixture between the carbs was easy, just watch the gauges.

Back to setting your idle mixtures by hand.....Randy at RPM told me about the "Thumb Nail" method of idle mixture adjustment.
The key to getting equal air/fuel idle mixtures between all 4 carbs is to: Start the adjustment with all 4 needles in the exact same position.
You do this with your thumb nail.
When your carbs are off, screw IN the idle mixture screws until the tip pokes into the throat. Now take your thumb nail and feel the protruding tip, now with your other hand turn out the mixture screw until the point where your thumb nail slides off the tip of the mixture screw. *stop*
Do all 4 carbs like this....Now all 4 carbs will have the air/fuel mixture screw at the exact same starting position.

I have found about 1.0 to 1.5 turns OUT from this position is a good starting point for final tune.

To demonstrate my point about the uneven threads, after setting all 4 screws with your thumbnail, they are all even....now turn IN the screws and count the number of turns in until they are "lightly seated".
I'll bet you a jelly donut you will get slightly different counts between the carbs.

You can write down these differences in your log book, and/or mark them with a felt pen on the caps of the carbs.
From the thumbnail test point all carbs are even:
If one carb's mixture screw goes IN one full turn until lightly seated that carb is marked 0
If one carb's mixture screw goes IN only 3/4 turn....that carb is marked -1/4
If one carb's mixture screw goes IN 1 1/4 turns until lightly seated.....that carb is marked +1/4
This is just for future reference, down the road, in case you get the number of turns mixed up and have to go back to the starting point with all the needles at the "lightly seated" position, you have the needle position differences recorded.


While the carbs are off, use your thumbnail and set those air/fuel idle mixture screws exactly the same between all 4 carbs...as a starting point for fine idle mixture tuning.

Thank you Randy.

Pat

[Old Rider]

The choke circuit fuel pickup at the bottom of the bowl is commonly plugged. That's where all the sediment and varnish settles.  Soak, piano wire, compressed air or ultrasound are your options. Don't drill.
*Be careful* if you spray your carb cleaner down that passage the spray will come out the bottom port on the bowl and...HIT YOU RIGHT IN YOUR FUCKING EYE... (don't ask)

The tips of idle/fuel mixture screws poke down into the carb throat....as you see....some do, some don't.
That's the rub.
Unfortunately the threads cut in the carb body on these mixture screws are not precise. They can differentiate 1/8 to 1/4 turn between the 4 carbs.
IOW if you screw in these idle mixture screws "until lightly seated" then back these screws out 3 turns, you would think your idle mixture screws would all be the same....but you would be wrong. One carb may be slightly rich, one carb may be slightly lean. Yamaha factory techs never had to worry about these screw threads being imprecise because they set the idle mixture with a 4 channel gas analyzer. (That's what the ports are for on the bottom of your header tubes) Setting an even mixture between the carbs was easy, just watch the gauges.

Back to setting your idle mixtures by hand.....Randy at RPM told me about the "Thumb Nail" method of idle mixture adjustment.
The key to getting equal air/fuel idle mixtures between all 4 carbs is to: Start the adjustment with all 4 needles in the exact same position.
You do this with your thumb nail.
When your carbs are off, screw IN the idle mixture screws until the tip pokes into the throat. Now take your thumb nail and feel the protruding tip, now with your other hand turn out the mixture screw until the point where your thumb nail slides off the tip of the mixture screw. *stop*
Do all 4 carbs like this....Now all 4 carbs will have the air/fuel mixture screw at the exact same starting position.

I have found about 1.0 to 1.5 turns OUT from this position is a good starting point for final tune.

To demonstrate my point about the uneven threads, after setting all 4 screws with your thumbnail, they are all even....now turn IN the screws and count the number of turns in until they are "lightly seated".
I'll bet you a jelly donut you will get slightly different counts between the carbs.

You can write down these differences in your log book, and/or mark them with a felt pen on the caps of the carbs.
From the thumbnail test point all carbs are even:
If one carb's mixture screw goes IN one full turn until lightly seated that carb is marked 0
If one carb's mixture screw goes IN only 3/4 turn....that carb is marked -1/4
If one carb's mixture screw goes IN 1 1/4 turns until lightly seated.....that carb is marked +1/4
This is just for future reference, down the road, in case you get the number of turns mixed up and have to go back to the starting point with all the needles at the "lightly seated" position, you have the needle position differences recorded.


While the carbs are off, use your thumbnail and set those air/fuel idle mixture screws exactly the same between all 4 carbs...as a starting point for fine idle mixture tuning.

Thank you Randy.

Pat

Thanks Pat for a very good and explaining post on the topic i have eperienced exactly what you are talking about on the mixturescrews has different depths of treading and will not be the same settings when finished tuning them.I use another method when setting them by looking down the plugholes and at the plugs
if it is soting on top of the pistons after some riding   then its to rich and if the engine starts popping then its too lean.This method has to be used on fresh
clean pistoncrowns and if it has sotted i use Q-tips thru the plughole to clean the little ring in center at top of the pistons and drive some more before i check it again.

[Waiex191]

Thanks all for some very helpful replies.  Since my last post I've also discovered the carb files section, and there is a wealth of good information there.

I've had no luck clearing the passage in the bowl for the choke circuit.  However, I've bought woodcreekpete's 1990 carbs he had for sale.  Missing diaphragms, but mine are good.  Between my plogged bowls, broken float supports, and ruined float, his carb parts should make me whole again.  I've also got an order into RPM for o-rings, screws, and a couple other things.

So having learned about this passage in the bowl, and also the emulsion tube, I did take my GN carb apart again.  The bowl passage was clear.  Here is the GN emulsion tube next to a cleaned off FJ tube:


Here it is after I cleaned it.


Still took me 4 good kicks to start, where I would expect one.  That could have been because the bowl was dry and fuel hadn't bled up into that chamber through the little orifice yet.  But, it ran like a new bike, if slightly slower than an FJ.

[JPaganel]

That is some serious crustification.

Good on ya fixing it.

[Waiex191]

My FJ project is getting closer to the front of the queue.  Had a few diversions as always. Got the GN running good, replaced some seals and swapped in the clutch from the parts bike. No more oil leaks and the clutch doesn't slip when cold anymore. Interestingly the disks were not worn that I could measure, but the springs were compressed below the spec value. Currently I'm fixing leaks in my hangar roof which is a lot of fun.  My parts have come from RPM and Pete's carbs are on the way from Canada. Here is a pic of the FJ patiently waiting. I took it from the scissor lift I borrowed.

I'm considering pulling off the heat shield to clean.  Any tips or pitfalls?

[fj1289]

I'd leave the shield attached to the brackets.  They are held on my rubber plugs that probably aren't real pliable any more - good chance you'll break them if you try to remove the shield from the brackets.