leaking seat?

[BLES]

Working on A Robin/Subaru EX21 that has a leaking seat (the non-replaceable type). A new needle didn't help, nor did burnishing the seat a bit. Any tricks other than replacing an expensive carburetor? Thanks.
BLES

[bgsengine]

Well I would say main thing is to verify where it is leaking - are you sure the needle/seat are the actual leak and not a crack or other seepage from elsewhere? have you tried checking the float itself for free movement, check the bowl to see if the float might be hanging up somewhere? Are you sure you got the correct needle? (for the exact engine spec, not a generic aftermarket one)

Get an otoscope and make a visual inspection of seat and needle tip (they are cheap at amazon and other places - just about anything with a light and magnification would do)

try a pressure test - perhaps see if it will hold pressure while holding float closed, etc..

Other than that, new carb time.

[BLES]

Well I would say main thing is to verify where it is leaking - are you sure the needle/seat are the actual leak and not a crack or other seepage from elsewhere?
Yup. Checked with pressure tester and bubbles out of needle bore.

have you tried checking the float itself for free movement, check the bowl to see if the float might be hanging up somewhere? Are you sure you got the correct needle? (for the exact engine spec, not a generic aftermarket one)
Yup. From Subaru in factory packaging. Needle was over $20 Cdn. $34 Cdn. retail!

Get an otoscope and make a visual inspection of seat and needle tip (they are cheap at amazon and other places - just about anything with a light and magnification would do)

try a pressure test - perhaps see if it will hold pressure while holding float closed, etc..
Yes, will seal with pressure on float but not with just upward fuel pressure on float.

Other than that, new carb time.

Hmmm. Not the trick I was hoping for!
Thanks.
BLES

[KE4AVB]

Manufacture got us over a barrel on this one. Double check the hole that tip of the needle goes into at bottom of the seat to make it is clean and smooth. UIt also needs perfectly round. Note any enlargement of this hole will cause the float level to change.

Having to buy a replacement part assembly because the manufacture doesn't offer the individual parts is getting fairly common. I have replaced Kohler carburetors just because a worn out throttle shaft. Until recently the replaceable needle seat in the Walbro used on the Kohler Courage and Command engines wasn't even available and still only available through Kohler in a repair kit.

[Arkie]

If using air pressure like from a hand held Pressure/Vacuum pump (mityvac) how about how much pressure would you expect a float needle/seat to hold back before leaking if the carb was held inverted and just the weight of the float. (like 2psi on a gravity flow and maybe 5-6 on a fuel pump type system or what?)

Instead of holding the carb inverted and just the weight of the float when pressure testing would it be a better test if the carb was sitting in it's normal position and gas in the fuel line and float bowl and then add pressure to the fuel hose for test?

[bgsengine]

If using air pressure like from a hand held Pressure/Vacuum pump (mityvac) how about how much pressure would you expect a float needle/seat to hold back before leaking if the carb was held inverted and just the weight of the float. (like 2psi on a gravity flow and maybe 5-6 on a fuel pump type system or what?)

Instead of holding the carb inverted and just the weight of the float when pressure testing would it be a better test if the carb was sitting in it's normal position and gas in the fuel line and float bowl and then add pressure to the fuel hose for test?

Yeah if you want to look for seepage - but weight of float should be enough to hold pressure to 3-5 PSI up to 8 PSI - once the fuel is supporting the float, it is the equivalent float weight that is pressing on the needle valve - if it can hold air for 1 minute it can hold fuel Most carbs I have tested will "pop off" the float weight at around 8 - 10 PSI (wet test) for me, my minimum is 5 PSI even for gravity feed systems (Fuel will seep where air will not) and then I'll pressurize to 10 PSI to see if it pops off and re-seats (or at 10 PSI , flick the float to pop off some pressure and verify it re-seats and holds air)

There's no standard rule for them unlike with 2-stroke cube carbs, because different carbs can have vastly different float weights.

I've had little success with trying to "burnish" a float seat myself so it usually gets a new carb - if the customer is paying the repair bill, I don't want it coming back in 3-4 weeks with a blown engine that *I* have to pay for because the crankcase flooded and had a lubrication failure.

[KE4AVB]

What anyone got to realize is that the needle and seat are very precisely made and machined. As carburetor operates fuel will (believe it or not) will wear these surfaces) along with normal wear of sliding in and out of the needle into the seat. The viton tips or rubber seats can take care of some of the variances in the seal surfaces but is a limit on how much they can do.

When burnishing a fuel valve seat it only cleans the seat and does not fix out of round condition, un-square condition or deep scratches. The burnishing is basically the same as using a flex hone on a bad cylinder. If it is out of round or worn one sided then it will only make it worse. Worst is any abrasive introduced can leave micro scratches that fuel can seep pass. These surfaces need to polished to mirror like surface.

Personally I even had to replace a few carburetors that had replaceable seats as I could not get them to seal around the outer mating surface.

As BGS said it better to bite the bullet and replace the carburetor then end up replacing the whole engine because a fuel leak that didn't get fully fixed.

This is just my opinion but I prefer the error on the cautious side when it comes things that can make things worse.

[bobodu]

I thought this was about Hillary's Depends...

[bgsengine]

I thought this was about Hillary's Depends...

Same difference?

[Arkie]

I thought this was about Hillary's Depends...

It DEPENDS! (let's get it POLITICALLY correct)