Idle Speed Adjustment

CatGuy · Post by **CatGuy** » Tue Apr 26, 2022 9:24 am

On my '26 how do I adjust the idle speed at the carburetor. I know how to adjust the fuel mixture, but I think that it is idling too fast. Also.....does a fast engine idle effect the smoothness of up-shifting? Is there a way to check the RPM?

Post by **Humblej** » Tue Apr 26, 2022 9:26 am

NH carb has a screw on the throttle arm to adjust idle. Fast idle will not affect shifting since you will not be driving your car at idle, you will be well above idle going from low to high gear or high to low gear.

Post by **TXGOAT2** » Tue Apr 26, 2022 9:29 am

A T engine in good condition can idle at 500 rpm or less. A high idle speed can affect shifting and will negatively affect braking ability.

rickd · Post by **rickd** » Tue Apr 26, 2022 9:34 am

Might make the upshift a little abrupt; you need to hear when the engine is ready to go into high. As far setting rpm, retard your timing all the way and adjust the idle screw on the throttle arm to an idle speed that keeps your car running and sounds right to you. Thats how I do it.

Post by **JohnM** » Tue Apr 26, 2022 10:25 am

A properly tuned T can be idled down so slow you can just about count each cylinder firing. It is recommend to set the idle as low as possible to get maximum engine braking while going down hills thus saving your brakes. Look at where the throttle rod connects to the carburetor for the idle adjustment screw.

CatGuy · Post by **CatGuy** » Mon May 02, 2022 8:53 am

I tried adjusting it and the screw was already backed out far enough that it wasn't touching the little cam on the carb. It has been suggested that the engine has a vacuum leak. Thoughts? Would that just be the manifold gasket?

Post by **JTT3** » Mon May 02, 2022 9:02 am

Perhaps the throttle rod is the wrong one and just too short.If you crank the engine and while it’s running take the rod out of the throttle arm on the carb and see if you can throttle it down using your hand to move the carb throttle arm. If so you need a longer arm. If not, are you sure you don’t have the needle adjusted to lean?

CatGuy · Post by **CatGuy** » Mon May 02, 2022 9:19 am

JTT3 wrote: ↑
Mon May 02, 2022 9:02 am
Perhaps the throttle rod is the wrong one and just too short.If you crank the engine and while it’s running take the rod out of the throttle arm on the carb and see if you can throttle it down using your hand to move the carb throttle arm. If so you need a longer arm. If not, are you sure you don’t have the needle adjusted to lean?

This car is a '26 and would it have had the Vaporizer Carb? It doesn't now. Could that be different linkage? I did play some with the GAV, but it didn't make a difference. This car also is missing under load in both gears.

Post by **TXGOAT2** » Mon May 02, 2022 9:21 am

Besides the possibility of a linkage adjustment issue or a vacuum leak, if your linkage is not holding the throttle partway open you may have a throttle plate that is loose on the shaft, or a badly worn throttle shaft. A vacuum leak can occur at any joint in the intake system. It's unlikely, but if you have extremely worn valve guides, that could contribute to a fast idle. The vaporizer linkage is very different from the regular carburetor linkage.

Post by **TXGOAT2** » Mon May 02, 2022 9:25 am

A miss that occurs under load is usually related to an ignition problem, typically a dirty, badly worn, or improperly adjusted spark plug. Plug wires that touch other wires can also cause a miss. A miss could also be related to a vacuum leak.

Scott_Conger · Post by **Scott_Conger** » Mon May 02, 2022 10:37 am

Take a picture of EXACTLY what you have and post it. That will eliminate 1/2 of the guesses and start to get you some real answers that align with your problem

That said, with almost zero exceptions, old carbs have worn throttle shafts and the castings where the throttle shaft goes is worn oversize as well. In this condition, you are running lean at idle, which requires enrichment and then will be over-rich at speed. Additionally, once you get the throttle set to where it is sitting on the idle screw, you may find that every time you "close" the throttle, it idles at a different speed...classic symptom of excess air entering past the throttle shaft.

Post by **JohnM** » Mon May 02, 2022 10:47 am

Push the lever with your thumb until the screw touches, it should idle down. You may have some slop in the throttle linkage preventing it from closing down completely. You can remedy that by slightly bending the rod to lengthen/shorten it.

Take a wrench and make sure the manifold and carburetor bolts are snug and you have good coils, points, plugs and clean timer. The model T is not complicated, keep tinkering. Experience is the best teacher.

CatGuy · Post by **CatGuy** » Tue May 03, 2022 8:14 am

Here are a couple pictures of the set-up I have. Does it look correct? This is for my '26.

Post by **Humblej** » Tue May 03, 2022 8:32 am

Scott,
Looks like you may need to bend the rod to make it a little longer so the screw will engage the stop.

CatGuy · Post by **CatGuy** » Tue May 03, 2022 8:36 am

Humblej wrote: ↑
Tue May 03, 2022 8:32 am
Scott,
Looks like you may need to bend the rod to make it a little longer so the screw will engage the stop.

I thought that I needed to turn the screw 'out' to slow the idle and 'in' to increase it? Currently it's all the way 'out'. I can turn it 'in' to increase the speed.

Norman Kling · Post by **Norman Kling** » Tue May 03, 2022 9:03 am

If you take out the cotter pin at the carburetor and it will move farther toward slow speed and idle slower, the problem is in the length of the rod. However, if it the throttle will still not move anymore closed and does not slow the idle, then the problem is a vacuum leak either in the manifold gaskets or in the carburetor itself.
Norm

Post by **Moxie26** » Tue May 03, 2022 9:24 am

Looks like the valve cover has to be removed, turned 180 degrees and reinstalled . Get yourself another throttle rod.

Post by **JTT3** » Tue May 03, 2022 9:27 am

Perhaps my suggestion was unclear, I’ll try again. If you remove the throttle rod off of the carb and use your hand to move the carburetor’s throttle arm can you move it towards you, further toward you than when the rod is in the carburetor’s throttle arm? If so the above advice concerning length of the throttle rod may help. By doing this with the engine running you will be able to confirm if there is a change in engine speed. Without physically removing the carb you can’t tell if the throttle shaft & flap are tight and moving in sync with the arm. Sometimes the arm & shaft are loose because the peening of the brass shaft where the arm is attach has given way. This is an easy fix though. If you do take the carb off, can you move the arm to close the flap completely? Place a mark where the throttle arm is when fully closed. I use a sharpie so I can tell where fully closed is when attached to the intake. That will help you visually when determining how much more length you may need when adjusting the rod length. I did notice the hole where the rod goes in the arm looks really good. It doesn’t appear there is much wear at all.

CatGuy · Post by **CatGuy** » Tue May 03, 2022 9:40 am

JTT3 wrote: ↑
Tue May 03, 2022 9:27 am
Perhaps my suggestion was unclear, I’ll try again. If you remove the throttle rod off of the carb and use your hand to move the carburetor’s throttle arm can you move it towards you, further toward you than when the rod is in the carburetor’s throttle arm? If so the above advice concerning length of the throttle rod may help. By doing this with the engine running you will be able to confirm if there is a change in engine speed. Without physically removing the carb you can’t tell if the throttle shaft & flap are tight and moving in sync with the arm. Sometimes the arm & shaft are loose because the peening of the brass shaft where the arm is attach has given way. This is an easy fix though. If you do take the carb off, can you move the arm to close the flap completely? Place a mark where the throttle arm is when fully closed. I use a sharpie so I can tell where fully closed is when attached to the intake. That will help you visually when determining how much more length you may need when adjusting the rod length. I did notice the hole where the rod goes in the arm looks really good. It doesn’t appear there is much wear at all.

Sorry, I must have gotten in a hurry and not read it.

Post by **Moxie26** » Tue May 03, 2022 10:13 am

The bend in the rod at the throttle in essence shortened the length of the rod therefore prohibited the closing of the throttle to reduce idle speed. I have a picture and I'm trying to post with no success. Any tips would be appreciated.

Norman Kling · Post by **Norman Kling** » Tue May 03, 2022 10:28 am

After reading Moxie's post, I agree with him that the valve cover should be rotated 180 degrees. The hole should be opposite the arm on the carburetor. I also think the throttle rod is backward. The bend should be on the side toward the steering column.
Norm

: engine cut2.jpg (16.16 KiB) Viewed 7758 times

: engine2 copy.jpg (13.21 KiB) Viewed 7758 times

Scott_Conger · Post by **Scott_Conger** » Tue May 03, 2022 10:40 am

Remarkable how a couple of photos can change a guessing game into real advice.

Post by **Moxie26** » Tue May 03, 2022 10:52 am

Was able to attach carburetor photo, but I got posted with my previous post above.

Post by **JTT3** » Tue May 03, 2022 11:01 am

Scott, LOL. I assume, based on the picture where the rod is attached to the steering column, the person that put the rod on didn’t realize you can tap the stabilizer support around the spark, column & throttle up to put the throttle rod in the right orientation. It appears that the support was to close to put the rod in correctly so they turned it 180 out. Some really good observations by all. Amazing, maybe pictures do speak a thousand words. This really is what the forum was designed to do, helping others succeed!

CatGuy · Post by **CatGuy** » Tue May 03, 2022 11:20 am

Norman Kling wrote: ↑
Tue May 03, 2022 10:28 am
After reading Moxie's post, I agree with him that the valve cover should be rotated 180 degrees. The hole should be opposite the arm on the carburetor. I also think the throttle rod is backward. The bend should be on the side toward the steering column.
Normengine cut2.jpgengine2 copy.jpg

I can't get the pictures to be any bigger. This is an interesting twist. I wonder how long the last guy had it that way? Now, I know that the car is only 20hp, but to me it seemed like it couldn't get past 28mph.....on the flat. Could be then it's not getting the range it needs? I'd like to see some more pictures of the way the linkage and valve cover should be. I've got some homework....

Scott_Conger · Post by **Scott_Conger** » Tue May 03, 2022 11:25 am

Well, the valve cover can go on only two ways, and the same is true for the rod. If it appears that they're both presently wrong, I'm thinking this is an easy bit of homework...no?

Post by **TXGOAT2** » Tue May 03, 2022 11:29 am

A 1926 T open car in good condition ought to be able to run 40 MPH on a level road with no headwind. A closed car might be a little slower, but ought to do 35 or so. Some cars will do better. Headwinds will tax a T's top speed severely. Model Ts perform best at speeds from about 22 MPH up to 35-37 MPH.

CatGuy · Post by **CatGuy** » Tue May 03, 2022 11:32 am

Scott_Conger wrote: ↑
Tue May 03, 2022 11:25 am
Well, the valve cover can go on only two ways, and the same is true for the rod. If it appears that they're both presently wrong, I'm thinking this is an easy bit of homework...no?

I would think it would be easy. I've had the manifold off on my '28 A so this shouldn't be too hard.

Scott_Conger · Post by **Scott_Conger** » Tue May 03, 2022 11:38 am

It has been a long time since I've worked on later cars with 1 piece valve covers, but recall that it can be fished out just fine with manifolds left in place. I sure wouldn't pull a thing off until the two cover fasteners were removed and for sure found that it was an impossible task to remove otherwise.

Unless you've already done it successfully several times, you may find that getting the manifolds back on without leaks can be a bigger bag of snakes than you'd ever imagine. Try not to go there right now...try to fix one problem at a time without introducing others...

CatGuy · Post by **CatGuy** » Tue May 03, 2022 11:54 am

Scott_Conger wrote: ↑
Tue May 03, 2022 11:38 am
It has been a long time since I've worked on later cars with 1 piece valve covers, but recall that it can be fished out just fine with manifolds left in place. I sure wouldn't pull a thing off until the two cover fasteners were removed and for sure found that it was an impossible task to remove otherwise.

Unless you've already done it successfully several times, you may find that getting the manifolds back on without leaks can be a bigger bag of snakes than you'd ever imagine. Try not to go there right now...try to fix one problem at a time without introducing others...

Sounds good to me! I wasn't sure if I had to take the manifold off to do that or not.

CatGuy · Post by **CatGuy** » Tue May 03, 2022 12:06 pm

Is that possibly the wrong carburetor for a '26?

Post by **Chuck Regan** » Tue May 03, 2022 12:19 pm

Scott - picture of my ‘26.

Post by **Jerry VanOoteghem** » Tue May 03, 2022 1:10 pm

CatGuy wrote: ↑
Tue May 03, 2022 12:06 pm
Is that possibly the wrong carburetor for a '26?

No.

Post by **Jerry VanOoteghem** » Tue May 03, 2022 1:19 pm

CatGuy wrote: ↑
Tue May 03, 2022 11:20 am
I'd like to see some more pictures of the way the linkage and valve cover should be. I've got some homework....

- Remove the throttle rod.
- Remove the 2 bolts holding the tappet cover on.
- Remove the tappet cover. It may be tricky to fish it out. Removing the generator may help.
- Remove the old gasket and clean both the cover and the block where the gasket sat.
- Replace the cover, flipping it around end-for-end from its previous orientation. Use a new gasket and/or appropriate sealant. The hole where the throttle rod passes through should now sit below the centerline of the 2 mounting bolts.
- Intstall the 2 bolts. Get them snug but not "tight", as this will distort and warp the cover.
- Install a NEW throttle rod and cotter pins at each end.

Norman Kling · Post by **Norman Kling** » Tue May 03, 2022 1:24 pm

That looks like a Holly NH with the swivel on the adjustment rod. Correct for a 26. You should be able to get the valve cover off. Might be a bit tight behind the generator, but it can be done without removing the manifold.
Norm

Post by **Moxie26** » Tue May 03, 2022 4:35 pm

Scott, I agree with the others... That is a correct carburetor for a 26 Model T Ford.

Scott_Conger · Post by **Scott_Conger** » Tue May 03, 2022 4:43 pm

Scott and Chuck have the correct carb, with all correct features for a '26

Jablonski, technically, does not. His has the (earlier) long throttle lever and (later) friction swivel for mixture control. It is a marriage. Probably a shotgun one at that. Mixing and matching of NH parts is a very common thing, and there is no reason to believe that the marriage will not last.

CatGuy · Post by **CatGuy** » Tue May 03, 2022 5:10 pm

I've ordered the correct rod and a new gasket to do this the right way. I like to keep things like Henry intended.....as much as possible.

Post by **Moxie26** » Tue May 03, 2022 6:27 pm

Scott... I do have an NH carburetor and yes it is an earlier type straight through bore that was only used for a few years before the later NH changed to the hump back bore. ...... The mixture need needle assembly, (needle and mixture adjuster ), is true to the '26-'27 NH. Conger failed to identify the aluminum intake manifold that was used on the early teens Model T engines, also lack of the intake hot air heater . Good luck fixing your T. Keep us informed of your progress !!!

Post by **Moxie26** » Wed May 04, 2022 10:01 am

Scott... Please post another picture of the driver side of your engine Thanks

Post by **JTT3** » Wed May 04, 2022 10:45 am

Robert a little thread drift, is that a high volume intake? With the straight through NH coupled with the intake do you really see an improvement in performance? Does the combination increase fuel consumption vs the humpback NH?
Thanks John

Post by **Moxie26** » Wed May 04, 2022 5:06 pm

John... You have a good eye. Yes that is a 1913 aluminum intake matched up with the straight through NH carb, and yes I do notice improved all around engine performance.

Post by **Moxie26** » Wed May 04, 2022 5:13 pm

Fuel consumption compared?... That's a good question... On trips I always do change the mixture to lean out a little bit better... More smiles to the miles. With practice, I only ran out of gas once, and I was right here in town.

Post by **Craig Leach** » Thu May 05, 2022 12:46 pm

Hi Scott,
Looks like you hit a gold mine of info on this one. To answer your last question they make laser tachometers that can be had online in the $20 to $40 range. You put a small piece of reflective tape that comes with it on the crank pulley and shine the laser on it to get a RPM reading. There are small engine tachometers that can be calibrated to your engine* by the number of sensor raps on a plug wire and programed for the type of engine. You will need to determine the accurate RPMs to calibrate. Then you can calculate your speed by the tire size & gear ratio if you want.
* I have not tried this on a stock Ford ignition, the number of times the coil sparks may effect calibration accuracy?
Craig.

Post by **Moxie26** » Tue May 10, 2022 10:53 am

Good morning CatGuy.... Have you had the opportunity yet with your new parts to fix your problem?

CatGuy · Post by **CatGuy** » Tue May 10, 2022 11:39 am

Moxie26 wrote: ↑
Tue May 10, 2022 10:53 am
Good morning CatGuy.... Have you had the opportunity yet with your new parts to fix your problem?

No. I ordered the parts from Lang's and they just shipped yesterday. I wonder if they were closed a few days?

CatGuy · Post by **CatGuy** » Tue May 31, 2022 8:19 am

To update you on this....Yesterday we took the valve cover off to switch it around and found it was already on properly. From what we could tell. The valve cover has an end that is rounded and one that is squared off. We figured it should match the engine block in that way so we put it back like it was. I'm a little disappointed to say the least. I was hoping that that would solve my high idle. I think it's idling too fast, but I've not been around any other T's recently to tell. I wish there was a way to hook up a tach to it. I have an old 70's multi-function meter / tester. On a positive note I was able to put new gland rings and copper rings (old style) manifold gaskets so that will be nice. Then the carburetor spider broke.....

Post by **speedytinc** » Tue May 31, 2022 8:40 am

CatGuy wrote: ↑
Tue May 31, 2022 8:19 am
To update you on this....Yesterday we took the valve cover off to switch it around and found it was already on properly. From what we could tell. The valve cover has an end that is rounded and one that is squared off. We figured it should match the engine block in that way so we put it back like it was. I'm a little disappointed to say the least. I was hoping that that would solve my high idle. I think it's idling too fast, but I've not been around any other T's recently to tell. I wish there was a way to hook up a tach to it. I have an old 70's multi-function meter / tester. On a positive note I was able to put new gland rings and copper rings (old style) manifold gaskets so that will be nice. Then the carburetor spider broke.....

The plate should have a relieved area that coincides with the generator. It will be obvious. Hole still in the wrong location? Its possible that someone took a vaporizer valve cover(no hole) & drilled their own hole in the wrong spot. Look for pictures of other motors to get a clear idea where the linkage hole should be.

Post by **RajoRacer** » Tue May 31, 2022 11:26 am

I just ran into that issue - Vaporizer cover plate with a "willy-nilly" hole drilled through - owner took a correct sample cover from me and the machine shop opened it up - throttle problem solved !

CatGuy · Post by **CatGuy** » Tue May 31, 2022 11:32 am

RajoRacer wrote: ↑
Tue May 31, 2022 11:26 am
I just ran into that issue - Vaporizer cover plate with a "willy-nilly" hole drilled through - owner took a correct sample cover from me and the machine shop opened it up - throttle problem solved !

Was that causing your car to idle too high?

Post by **speedytinc** » Tue May 31, 2022 12:20 pm

CatGuy wrote: ↑
Tue May 31, 2022 11:32 am

RajoRacer wrote: ↑
Tue May 31, 2022 11:26 am
I just ran into that issue - Vaporizer cover plate with a "willy-nilly" hole drilled through - owner took a correct sample cover from me and the machine shop opened it up - throttle problem solved !
Was that causing your car to idle too high?

The throttle plate is not closed all the way or has a bad sloppy throttle shaft. The throttle lever has an idle stop screw to turn the idle down, but it must hit the stop on the carb.

Post by **RajoRacer** » Tue May 31, 2022 1:02 pm

The throttle rod was hanging up on the cover !

Scott_Conger · Post by **Scott_Conger** » Tue May 31, 2022 4:51 pm

I just measured the one car I own that has that cover...the hole for the throttle rod is about 1/2" rearward of the mechanical center of the cover when measuring from mounting bolt to mounting bolt...meaning, from the rear bolt measuring forward to the center of the hole, it is about 4 1/8" and measuring from the front bolt hole back to the center of the throttle hole, it is about 5 1/8"

the speculation that your cover is an improperly modified vaporizer engine cover is very astute

Post by **speedytinc** » Tue May 31, 2022 5:20 pm

The hole is also not in line with the mount holes. It is lower.
Without pulling a cover, i couldnt say exactly the dimension.
The picture shown in this thread appears to line the upper hole edge with the center line of the mount holes.

Scott_Conger · Post by **Scott_Conger** » Tue May 31, 2022 6:28 pm

John

thank you for pointing that out. My valve cover is not an oblong hole, but simply about a 5/8 round hole. Perhaps mine is also a modified vaporizer cover...it's the only car I have that is a single cover and never even considered that it might not be "right". Boy, the things you learn...

Post by **speedytinc** » Tue May 31, 2022 6:56 pm

Scott_Conger wrote: ↑
Tue May 31, 2022 6:28 pm
John

thank you for pointing that out. My valve cover is not an oblong hole, but simply about a 5/8 round hole. Perhaps mine is also a modified vaporizer cover...it's the only car I have that is a single cover and never even considered that it might not be "right". Boy, the things you learn...

I have seen & had both oblong & round holes in original appearing cover doors. Its another of those little Ford changes.
The oblong much more common. I have noticed the round hole covers have worn spots from throttle rods. Thus my conjecture the round hole was first, but changed to a larger oval hole. I would not assume yours is wrong. In fact, a careful inspection should show the hole was punched.

Scott_Conger · Post by **Scott_Conger** » Tue May 31, 2022 9:33 pm

thank you John

I had considered that it might be an early variant, but honestly, since this is the first I've really looked into it carefully, I wasn't sure exactly what I had. What you mention makes perfect sense. I had never had occasion to pay enough attention in 15 years to even notice it before. If I hadn't gone out to measure the location today, I would still be in the dark about it...like I said, the things you learn! Thank you again.