4180C Carb Questions

[Cruizer67]

I have an 84 Gt with a 4180C carb list number 50151 I rebuilt is but think the power valve took another dump. In the meanwhile I have a spare 4160 carb that I put on and the car hasn't run this good in a while .. that being said I was wondering if I could interchange the float bowls between the carbs? If not is it safe to plug the two hoses that were originally meant to be plugged into the float bowls front and rear. I know California Smog is sometimes a pain in the butt.. was wondering if anyone in California has gotten away from the 4180 C carb and has passed smog. If so I may have a 4180 for sale

any and all input in welcome

thanks

[The Bandit]

I have an 85GT with a list# 50265 4180C carb which I believe they are same. I'm using a 8.5 single stage power valve with 4150 rear metering block holley part#34-6. This setup allows you to use jets on the front & rear metering blocks. I'm using 64 jet in the front & 72 in the rear. You might have to see what works best for your car. When you get ready to smog then put the originals in the front which is 62.2 & 68 in the rear or put your original metering block back on. Hope this helps.

I'm also looking for a base plate for the 4180C carb with the 4 idle mixture screws.

[JACook]

On a 4180C, a leaking accelerator pump transfer tube is often mistaken for a leaking power valve.
The power valves are hardly ever at fault, if you're using Holley parts, though sometimes they may
not be tight enough, causing a gasket leak.

The accelerator pump transfer tube o-rings are a very common leak point, primarily because of
left-over debris in the holes, and on the inside diameter of the tube where the o-rings seat. These
surfaces must be absolutely clean and smooth, or you'll have chronic leaks. Another common
problem is if the o-rings are installed dry, and/or the wrong ones are used, they can get pinched
when you install the tube and metering block. The latter is a problem even if they don't get pinched.

The rebuild kits come with two sizes of o-rings that are very similar in size. The accelerator pump
transfer tube takes the smaller of the two sizes. If the tube has any damage at all, it needs to be
replaced. Holley part #26-23, costs about $8, and comes with the proper o-rings already on it.

[xctasy]

Posted elseware

[xctasy]

post above ^

[xctasy]

See above

[BaconB8]

I've passed and failed using 4180c's and 4160 carbs.

The only way to know what 'may' happen is to tune using a wideband o2 sensor. The last time I failed I was using a 4160. The same setup that had passed two years prior. I also had brand new cats. Swapped over to the 4180c and adjusted the idle with a wideband, and it passed with EFI-like numbers. I had the wideband running while the car was testing. The smog guy saw the meter running, and knew I wasn't some hack with a standard screwdriver and a vacuum gauge winging it. The wideband meter is the only way to accurately predict what will happen. Tuning by ear is no longer a data point, but rather a waste of time.

Rebuild the 4180 or do a full 86 efi swap.

[mrriggs]

On a 4180C, a leaking accelerator pump transfer tube is often mistaken for a leaking power valve.
The power valves are hardly ever at fault, if you're using Holley parts, though sometimes they may
not be tight enough, causing a gasket leak.

The accelerator pump transfer tube o-rings are a very common leak point, primarily because of
left-over debris in the holes, and on the inside diameter of the tube where the o-rings seat. These
surfaces must be absolutely clean and smooth, or you'll have chronic leaks. Another common
problem is if the o-rings are installed dry, and/or the wrong ones are used, they can get pinched
when you install the tube and metering block. The latter is a problem even if they don't get pinched.

The rebuild kits come with two sizes of o-rings that are very similar in size. The accelerator pump
transfer tube takes the smaller of the two sizes. If the tube has any damage at all, it needs to be
replaced. Holley part #26-23, costs about $8, and comes with the proper o-rings already on it.

I've been struggling to get the transfer tube on my carb to stop leaking. I cleaned the bores, polished the tube, replaced the o-rings several times, tried two different tubes, and assembled it each time with RuGlide. Finally, I ordered some "Square" o-rings from McMaster-Carr and that seems to be the key.

https://www.mcmaster.com/#1170n16

[JACook]

Square-section O-rings are probably not a bad idea, but these carbs originally used the round-section style,
and up until oxygenated fuels came along, they worked fine. They still work fine with oxygenated fuels, as
long as the carbs don't dry out. But oxygenated fuel is why the old O-rings often look like they were square.
The fuel swells the O-rings to fill the grooves, but when the material dries out, it shrinks and will leak when
the carb is used again. After some time, it will swell again, but not as much as before, so after a few of these
cycles, it's done.

I've looked at many different materials, and the only reasonably priced material I've found that consistently
works long-term with oxygenated fuels is Viton GFLT (what the green Holley 'alky' accelerator pumps are
made from). Why Holley does not use GFLT for their accelerator pump transfer tube O-rings is beyond my
comprehension. And, unfortunately, places like Mc Master-Carr don't carry them either.

When you say you 'tried two different tubes', were either of them new from Holley, with the correct O-rings
already on them? I ask this because the most common problem with these O-rings apart from surface prep,
is using the wrong ones. This is because the correct O-rings don't look like they are (though it appears you've
already figured out they are -006).



I'm not saying you, specifically, but a lot of guys mistakenly think O-rings seal against the sides of the groove,
and try to fit the larger -007 O-rings that come in the carb kit, because it looks like they will fill the grooves
better. But that's not how O-rings work, and the larger O-rings will just distort and leak, even if you do manage
to get the metering block in place without nicking them.

From your description, it sounds to me like the transfer tube or bores still have some surface imperfections that
the square-section O-ring's wider contact patch is better able to deal with. Then again, I've never used Ru-Glyde,
and looking at what's in it, I can't say I would. Viton does not like potassium hydroxide. Normally I use a smear
of ATF or TransGel.