Problems after carb rebuild

[Jim Arm]

I have had my 8N for about half its life and it has served me well, but not a lot recently.
When it had trouble starting (and then not at all) I sent for the comprehensive rebuild kit sold here.
The rebuild (petty sure its first one) went smoothly and it started and ran really well afterward.
Then it began to leak, with fuel up to and through the gasket and then wetting the intake throat.
After trying everything we can think of, with perhaps ten or fifteen strip downs, nothing has solved the problem with testing on the bench and on the engine.
A few things that seem possible are: 1) The inside of the new float jet has tapered sides instead of the stock straight ones, allowing the float needle to fall out when the float is fully down. This needs the clip to hold it in and the clip itself may stop the needle from closing. 2) The drain plug ( and the plug with valve in the kit) do not plug. They seem to be pipe threads that do not match the hole treads. After losing four or five, bowls full, I found the 78 year old plug seats all the way an seems to work.
Sorry. Long winded and luckily not urgent. Any ideas welcome.

 

[R Geiger]

is the float full of fuel?

 

[pauls9ntractor]

I have had my 8N for about half its life and it has served me well, but not a lot recently.
When it had trouble starting (and then not at all) I sent for the comprehensive rebuild kit sold here.
The rebuild (petty sure its first one) went smoothly and it started and ran really well afterward.
Then it began to leak, with fuel up to and through the gasket and then wetting the intake throat.
After trying everything we can think of, with perhaps ten or fifteen strip downs, nothing has solved the problem with testing on the bench and on the engine.
A few things that seem possible are: 1) The inside of the new float jet has tapered sides instead of the stock straight ones, allowing the float needle to fall out when the float is fully down. This needs the clip to hold it in and the clip itself may stop the needle from closing. 2) The drain plug ( and the plug with valve in the kit) do not plug. They seem to be pipe threads that do not match the hole treads. After losing four or five, bowls full, I found the 78 year old plug seats all the way an seems to work.
Sorry. Long winded and luckily not urgent. Any ideas welcome.

Change back to the original float. Too many of these kits have a float with gobs of solder weighing them down.

 

[Jim Arm]

Change back to the original float. Too many of these kits have a float with gobs of solder weighing them down.

Using original, It is in good condition. Thanks.

 

[used red MN]

1) The inside of the new float jet has tapered sides instead of the stock straight ones, allowing the float needle to fall out when the float is fully down.

I would have to see this to believe it. Unless you mean the very top edge has more of a chamfer or tapered edge on it. On the float behind the hinge pin towards the edge of the carb bowl is a flat tang. That is to be bent to set the amount the float can drop so the float needle can’t come out.
I am going to link another thread I made a reply to recently. Previous thread on Ford MS carbs
Look at the last paragraph in my reply 18. About a possible fix for a habitual leaky float needle. Also the MS manual linked in that thread will be very helpful for you.
You can also monitor the fuel level in a carb with a hose barb that will fit in the bowl drain and a clear piece of gas resistant tubing. This thread explains this better.
Thread on monitoring carb fuel level

 

[soaked]

Hi Jim,
Did you run a 3/8 - 27NS tap down the threads for the float seat?
Sometimes the old cast iron threads grab the seat tight, but before the crush washer can seal. Gas leaks out past the threads and loose crush washer and is difficult to find.
If plumb a short bit of fuel line, to the upside down top half, and place paper towel or TP under, gas from the fuel line will either leak out, or not. Wet paper is easy to see...
Pic is rotated on its side to save scrolling...

 

[HarryVanderpool]

I would grind the end of the tap, flat. Thus making an "end tap".

 

[Jim Arm]

Hi Jim,
Did you run a 3/8 - 27NS tap down the threads for the float seat?
Sometimes the old cast iron threads grab the seat tight, but before the crush washer can seal. Gas leaks out past the threads and loose crush washer and is difficult to find.
If plumb a short bit of fuel line, to the upside down top half, and place paper towel or TP under, gas from the fuel line will either leak out, or not. Wet paper is easy to see...
Pic is rotated on its side to save scrolling...
View attachment 146995

Thanks soaked,
I would have used the tap route if I had one, but I realized the washer was loose after my first attempt and gradually got it tightened down enough to stop a leak. That left several more days of trying to find where the new stuff was leaking. I made a jig where I could work on the carb right side up at eye level, using various strength rubber bands to control the float.
The new drain plug may have worked with tapping the hole, but I went back to using the old plug with an o ring. I am still not sure if the new plug might not be pipe threaded, but I never got it to seal.
I have a graduated feed tube going into the fuel inlet. I thought the drain plug would stop the leaking, but I still can't get a 12 hour period where the needle system seems to hold.
Any other thoughts would be welcome. I am an old man working on an great old machine and I have plenty of time to get it right.

 

[soaked]

Hi Harry, I've been meaning to grind it down also, but there is room to run it down far enough to chase the threads as is

Hi Jim,
I get the black Vito tip material on my fingers if using carb cleaner. Wonder if soak in gas that would help the needle seal.
Have read about "coining" the tip. Never tried it. Apparently one hits the needle into the seat with a firm smack....

Your Marvel Schebler carb came with 1/8 pipe on the drain plug.
One of my older aluminum clones has BSPT thread-- and no crush washer.
Had a newer clone with crush washer, thinking it was British Special straight thread, but not positive.

 

[Jim Arm]

Close to two weeks later, this thing is still resisting us.
I have always used the technique of replacing (or changing the setting of) a problem part one thing at a time to pinpoint the culprit. This started out with a comprehensive carb rebuild and a dozen or more disassemblies and reassemblies have left persistent leaks at the needle valve. I think I have tied all of the suggestions here so far.
There are four ways to try the new jet new needle, old jet new needle etc. Then, of course you can use the new clip or no clip (the way it started) with each.
On a bench rig and using a light rubber band to simulate the float lift, I got 24 hours of no leak. AHA, one would think. Nope, putting the bottom back on the reservoir fills to overflowing every time.
I think I will order just the inlet and jet from YT unless anybody here has another idea.

 

[soaked]

Wonder if the nozzle crush washer is sealing. Is the new nozzle identical to the old one? I seem to remember a post where the new nozzle had longer threads at the bottom, allowing it to touch the main jet before the nozzle crush washer could seal tight.

 

[Powered By IH]

Close to two weeks later, this thing is still resisting us.
I have always used the technique of replacing (or changing the setting of) a problem part one thing at a time to pinpoint the culprit. This started out with a comprehensive carb rebuild and a dozen or more disassemblies and reassemblies have left persistent leaks at the needle valve. I think I have tied all of the suggestions here so far.
There are four ways to try the new jet new needle, old jet new needle etc. Then, of course you can use the new clip or no clip (the way it started) with each.
On a bench rig and using a light rubber band to simulate the float lift, I got 24 hours of no leak. AHA, one would think. Nope, putting the bottom back on the reservoir fills to overflowing every time.
I think I will order just the inlet and jet from YT unless anybody here has another idea.

Is there a valley on the float where the needle valve rides?

If so, the needle could be catching on those ridges. Sand it flat and possibly solder, and see if that makes a difference.

 

[Jim Arm]

Amazingly smooth for 78 years old. But I will check again. Thanks

 

[Jim Arm]

Wonder if the nozzle crush washer is sealing. Is the new nozzle identical to the old one? I seem to remember a post where the new nozzle had longer threads at the bottom, allowing it to touch the main jet before the nozzle crush washer could seal tight.

I will check again.

 

[used red MN]

Wonder if the nozzle crush washer is sealing. Is the new nozzle identical to the old one? I seem to remember a post where the new nozzle had longer threads at the bottom, allowing it to touch the main jet before the nozzle crush washer could seal tight.

I will check again.

Should be able to set the carb bowl by itself level on a bench and fill it with gas to a level above the hex on the main nozzle but not high enough to come out of the top end to see if the gasket leaks.

 

[soaked]

Found the post from TJ in KY, this was his pic.
New one is longer...

 

[Tall T]

A few things that seem possible are: 1) The inside of the new float jet has tapered sides instead of the stock straight ones, allowing the float needle to fall out when the float is fully down. This needs the clip to hold it in and the clip itself may stop the needle from closing. 2) The drain plug ( and the plug with valve in the kit) do not plug. They seem to be pipe threads that do not match the hole treads. After losing four or five, bowls full, I found the 78 year old plug seats all the way an seems to work.
Sorry. Long winded and luckily not urgent. Any ideas welcome.

There's a tang on the backside of the float arm center that governs the float drop.
If all is right with that then when the float are at their lowest position (bowl empty) , the needle CAN"T fall out
because the tang comes to bear against the outside of the needle barrel.

You said the clip "holds the needle in". ?? Not quite. . . It is the opposite of that.
When the floats drop they "pull" the needle down with them because of the clip, so the needle can't stay stuck in the seat.

I use the needle that takes the clip.
Perhaps you installed the clip incorrectly (upside down).
There's no way it should keep the floats from rising and shutting the valve.
You can see if that's working properly before you put the two halves together by turning it upside down and back upright.

Are you sure the needle seat is tight enough, using a wide bit to span it properly notch to notch for tightening.
If you don't have a wide enough bit, use a brake adjust tool and vise grips or some such.

 

[Jim Arm]

Found the post from TJ in KY, this was his pic.
New one is longer...
View attachment 147991

Main jet tube? Does have any effect on fuel level or needle valve closure?
What I have is a constant c.10ml fuel leak per 24 hours. This is not enough to cause performance problems but a PITA if I forget to turn off the gas when it is going to sit.
I was spoiled by 40 + years of not having that problem.
It starts and runs so well, I am tempted to just live with it and would if I needed before haying next month.

 

[soaked]

Hi Jim,
If the nozzle washer leaks fuel into the throat, the needle will stay open trying to fill the bowl to the 1/4" setting. (The lower part of the washer is .5 to .6 below the gasket surface.)

Of course it would have nothing to do with needle to seat fitment, or leaks found there.

I was reacting to these words from post #10

"On a bench rig and using a light rubber band to simulate the float lift, I got 24 hours of no leak. AHA, one would think. Nope, putting the bottom back on the reservoir fills to overflowing every time."

 

[used red MN]

Hi Jim,
If the nozzle washer leaks fuel into the throat, the needle will stay open trying to fill the bowl to the 1/4" setting. (The lower part of the washer is .5 to .6 below the gasket surface.)

Of course it would have nothing to do with needle to seat fitment, or leaks found there.

I was reacting to these words from post #10

"On a bench rig and using a light rubber band to simulate the float lift, I got 24 hours of no leak. AHA, one would think. Nope, putting the bottom back on the reservoir fills to overflowing every time."

If soaked description wasn’t clear enough heres this. I was going to take a screen shot but decided to just link the whole manual. Look at page 7, even though that is not a cutaway of a TSX the idea is the same. See how it shows the level of the fuel above the hex and the gasket under it on the power nozzle. Fuel leaking past that would leak into the carb venturi/air passage simulating a leaking float needle, which overfills the bowl and then fuel flows out of the end of the power nozzle.
Need proof or additional datum? I gave you info on how to monitor the fuel level in the carb bowl in the last part of my reply 5.
M-S carb book