Rough Running after new carb

[winebros1]

25 Touring with new carb. It will only run at higher RPM's. It will not idle. I have the Texas T distributor as well. Plugs are gapped. It does not miss. It just won't idle. The intake is nearly ice cold as well. Any suggestions?

[Norman Kling]

Have you tried the hot air pipe on the carburetor? In high humidity, even in hot weather you can get icing inside the manifold and carburetor. Since you are running on a distributor, the speed shouldn't affect the idle unless the timing is wrong. But with magneto, you get a higher voltage at higher speeds which could make a difference. On one of my T's it misfires at idle when I first start up but runs fine at higher speeds. As soon as the engine warms up it smooths out. Is your idle poor even after it warms up" Maybe float level is set wrong causing it to be too rich at idle.
Norm

[Scott_Conger]

what kind of carb was the old carb?
why was it changed?
is the new carb a new carb or a carb which was rebuilt?
what kind of carb is the new carb?

Norm is right regarding carb stove, but your question lacks basic background information which could point to what is really going on beyond just the stove

[speedytinc]

Where did the new carb come from? Have you tried adjusting the mixture needle while running?
Have you gone back to the initial setting? That's 1 1/4 open on the mixture needle & should be a rich setting.
Does the new carb leak when let alone?

[winebros1]

So it is a brand new Holley NH from Mac's. Seems nice and tight with new =everything. It does not leak just sitting there. My older one did run fine a few years ago before I tore into everything again. Background: Engine done in 2014 with new everything but never really run or driven. I was in professional school so I dint have time other than to get it running each summer. Always did fine on the old Kingston. Now cleaned everything up again and finishing restoration. I took off the intake and the exhaust to replace the freeze plugs. Replaced with new gaskets and ran old carb. Would not run long so I checked all ports and holes and float level and needle. All adjusted a little but to no avail. Also noticed with the old it was really sucking in the gas in order to fire and run a little. So much so that it was leaking out the exhaust pipe. Intake was ice cold. With the new carb it runs at higher RPM's but is relatively smooth. It just won't idle. The intake does not seem as cold. I hope all this helps.

[Norman Kling]

Another possibility would be a vacuum leak at the intake manifold. You said you replaced the gaskets. What type gaskets are you using? How straight is your exhaust manifold? You need a straight exhaust manifold to get all the ports lined up with the block. You should use glands in all ports. If the back of the manifold hangs down so far the gland will not fit, you need to either straighten the manifold (look up posts on how to do this). Usually the intake will line up fine. You also need the glands. The best gasket to use is the copper rings which crush into place like the head gasket. When everything is lined up properly and tightened properly, and after warming up the car it is tightened again. If the intake manifold does not seal to the block, you will suck up a little air at that location. It affects either the two front cylinders, or the two back cylinders, whichever port is leaking. This misfiring is noticed most at idle, because only a little air is getting in and the higher speeds this small amount is does not lean the mixture enough to be noticeable. Even if you are using the 3 hole gaskets, you still need the glands to keep everything in alignment.
Norm

[winebros1]

Both manifolds are straight. New exhaust manifold and resurfaced intake. I am using the copper gasket with the spring like ring pieces that help line up. But I'v been wondering about a leak. How would I test for that?

[TXGOAT2]

You may not have a carburetor/intake issue. Are you certain what came out the tailpipe was gasoline, and not gasoline-scented water or coolant? You may have a head gasket leak. It would be very unusual for liquid gasoline to be present at the tailpipe.

[winebros1]

I thought that too. But it is not doing the same thing with this new carb. And with the old carb it did it because I had to keep at nearly full choke just to keep it running even for a bit

[Scott_Conger]

Filtering out all other red-herring facts - The Bottom Line: everything ran fine until the intake manifold was removed and replaced to replace freeze plugs.

It's not an uncommon problem which can bedevil even the most experienced "T" mechanic, and fits all of your described ailments with either carb.

[winebros1]

Okay that makes sense. How can I test that? Like smoke a cigar and blow the smoke towards the intake to see it get sucked in? And thanks everyone for questions and answers. I really appreciate it. I'm really wanting to pick up the hobby again. Just bought a 15 roadster as well to do

[speedytinc]

Okay that makes sense. How can I test that? Like smoke a cigar and blow the smoke towards the intake to see it get sucked in? And thanks everyone for questions and answers. I really appreciate it. I'm really wanting to pick up the hobby again. Just bought a 15 roadster as well to do

Spray brake cleaner. Motor speed will change when you find the spot. Caution: dont let the vapors/spray get into the carb air intake, that can cause unnecessary confusion. Although you will want to spray the carb flange also.

[Steve Jelf]

Especially if the area around the ports is pitted, but even if it isn't, I add a little hi-temp RTV to those copper gaskets to raise the odds of getting a good seal.

[winebros1]

Thanks all for the help. Indeed the front side of the intake was not aligned and sealing properly. It was adjusted this am and solved that issue.

[RajoRacer]

I prefer to mount my intake manifold first using the half clamp or turned full clamp as one can actually verify that it seated correctly then mount the exhaust while looking down at all 4 ports to verify it seated properly.

[speedytinc]

Apparently, the fail was from not using the ring & gland type gaskets.

[Scott_Conger]

I'm glad you solved the problem...good for you

[Jerry VanOoteghem]

Apparently, the fail was from not using the ring & gland type gaskets.

"...I am using the copper gasket with the spring like ring pieces that help line up."

Apparently not...

[RajoRacer]

A few years back, there were some too long steel glands floating around thus resulting in the manifold not fully compressing the copper ring ! Easy enough to check the depth of both block & manifold then do the math.

[Scott_Conger]

Aircraft snips are your friend

[speedytinc]

A few years back, there were some too long steel glands floating around thus resulting in the manifold not fully compressing the copper ring ! Easy enough to check the depth of both block & manifold then do the math.

Also , if the block has been machined in the manifold side, the ports are rarely rebored to correct the depth loss.
The ring height should be checked before assembly when using rings. That covers both possibilities. No assumptions.

If you didnt pre-check, You can post check. Look down between the manifold ports & the block. The rings should be uniformly flattened to between 1/16 & 1/32".

[speedytinc]

Apparently, the fail was from not using the ring & gland type gaskets.

"...I am using the copper gasket with the spring like ring pieces that help line up."

Apparently not...

There I went assuming.