Mystery of the Manifold

ratface

Member
Tractor is a 1949 front mount. A brief history is that this was a great running tractor before I changed a leaking exhaust manifold around number 4. Since then I have had loss of power and could not do anything without getting a black soot all over my plugs. It is so bad you can see it coming out of the exhaust connection. Tried to no avail to adjust the carburetor. Memebers here thought maybe it was damaged by not laying it upright during the manifold change. Had the carb rebuilt by Royce with identical results. I can get 400-500 rpm at low idle and 2200 at high. Followed Dell?s carb adjustment instructions. I have spent hours in the field moving the needles 1/16 at a time and I can get marginal improvement by enriching idle screw which is not helping my sooting issue. Tractor starts and runs great with no load. Any load and it has trouble, even reverse taxes it. It has also developed a knocking sound which seems more centralized on the carb side and closer to the oil pan although the oil pressure remains the same. Removed belt to eliminate water pump and it had no effect. Pump is ok. Tried a different distributor on the tractor trying to eliminate an electrical issue. The plugs are gapped correctly, the spark is strong, wires are on right. All new parts in distributor, points gapped at .015. Followed Bruce?s diagnostic procedure with the test light and it all checks out. Points open and close properly, used a jig to set static timing. If it?s not a carb or electrical issue where would you suggest I go next? Or am I missing something in the carb or distributor? All thoughts encouraged!
 
Have you checked for a vacuum leak? Get a hand propane torch and carefully spray it (unlit of course) around the intake manifold at the carb to manifold interface & the manifold to block gasket of the tractor while it is running. Or, you can use carb cleaner or WD40. If it speeds up, you found the leak. Sometimes (rarely) manifolds crack or get rust holes.

Does your manifold have a port for a vacuum gauge?
75 Tips
 
"black soot", to me says dry vs wet. That is result of too rich. Thus you still have a carb problem.
 
Try your old manifold to see if problem goes away.

Is your exhaust pipe/muffler plugged causing exhaust to come out of connection at manifold?
 
I am collecting all these thoughts and will try them on my next visit to the haunted red belly monster machine, unfortunately it is at a small rural place in Northern IL which I only get to several times a month. Will investigate all responses. It is an aftermarket manifold which seems heavier and beefier than the original and they just cast over that port fitting which was in the original. I know what a vacuum leak is but don't know why it affects a carburetor. Anyone have any possible guesses as why any of these conditions would suddenly cause a slight knocking noise? This tractor is, "Jamaican me crazy".
 
" I know what a vacuum leak is but don't know why it affects a carburetor. "

What happens when you adjust a carb?

You are changing the air/fuel mixture ratio. Just that little needle moving in or out 1/64" or less makes a difference.

What do you think a leak in the manifold will do to that mixture adjustment?

I'm think carb or vacuum leak because w/ a rebuilt carb & distributor, it should idle under 400 rpms. Easy. All of mine do.

Start w/ adjusting thae carb. Again.

But do it like this:

Make sure the tractor is at operating temp; that usually takes 10 ? 15 minutes at idle depending on ambient temp.

Both Ford and Marvel/Schebler (assuming you have a M/S carb ) say to set both the side-pointing idlemix and the down-pointing mainjet to 1-turn as a starting point. I set the down-pointing mainjet to 1-1/2 turns and don't fool w/ it until the final step.

Then adjust the side-pointing idlemix for fastest idle; not the smoothest idle.

Next, adjust the behind the carb idle-speed set-screw for very slow 400-rpms idle. Do that idlemix adjust for maximum idle at least 3-times. Make sure that you turn the screws slowly, like 1/8 of a turn at a time & wait a second or two for the engine to catch up. Take your time!

Do it like this:

1. Adjust idle mix jet until RPM increases

2. Adjust idle-mix set screw until the engine nearly stops (as slow as you can get it unless you have a tach that tells you 400 rpm)

Repeat steps 1 - 3 three times.

Remember the side-pointing idlemix is out for lean, in for rich.

If you do not have any problems inside the carb, it is easy to get the idle down to 350 - 400 rpms.

Your last step is to go back to the main jet. Remember, in for lean, out for rich. If you end up turning it OUT more than ? turn for max power (remember, you already had it 1 ? turns out) then stop right there because you have a dirty carb or a fuel problem.

If that doesn't work, check for a vacuum leak.
75 Tips
 
The carb is a MS TSX 241B rebuilt by Royce and as you know he puts them on his tractor before shipping. I literally took it out of the packaging and installed. It's only run on the tractor one day. I use a hand held laser tach with a reflective strip on the fan housing. I had it at 400 low rpms and 2200 high rpms per the laser device, adjusting in similar fashion per your directions which are also similar to Dell's carb adjustment guide which I printed years ago and used. If carb is indeed set at these settings how much better can I get it? Is it that sensitive that I might be off 1/64 causing all my issues? Thank you for the sensible explanation on vacuum leaks, seems intuitive after hearing it explained that way.
 
At speed, turn the main adjust needle all the way in and see if that will kill the engine. If not, then it is sucking fuel from some place that it is not supposed to be.
 
I agree with JMOR. Put the old manifold back on and see how it runs. IF you used an after market manifold that may be your problem. Someone a few years ago had a similar tale and there was a defect in the manifold.
 
"At speed, turn the main adjust needle all the way in and see if that will kill the engine."

It dang well better! :)
When it left here the idle was set at 400 RPM by the proofmeter.
Top RPM was 2200 by the PM.
Idle air adjust screw was set at 1/2 turn, main at 1 3/4.
No black smoke or soot at all.

One thing to note, the carb worked the same before and after
the rebuild on his tractor but not on mine. I tested it prior
because of his unique circumstances. So essentially two
different carbs there.
As I understand it, ratface also tried a spare carb that didn't work.
Correct me if I'm wrong on that one R.

I'm not being defensive, I'm trying to get all the information
out here so we can help him get his tractor running again.
Once we figure out the problem, the carb will need to be
adjusted again so the instructions are relevant to the cause.

Is this the type of manifold you have now?

38399.jpg


38400.jpg
 
Please information and ideas is what I'm seeking. Royce I did try a 1 year old rebuilt Tsx 33 that if you remember the needle was sticking open. I did tap it back into place and had identical results with that carb. So to clarify and reiterate there have been two separate distributors and two separate carbs on tractor and none have made a difference. Tractor runs terrible because plugs get coated in soot. That picture of the manifold is indeed similar to the one I installed. I have attached the only picture I have of mine which is from underneath the tractor. It is beginning to appear that the issue is mixture related with something effecting mixture other than the carb settings themselves.
a232888.jpg
 
Will it run okay with rubber hose from the air cleaner disconnected at the carburetor? Someone stick a rag into the air intake of the air cleaner? Air cleaner plugged?
 
"Please information and ideas is what I'm seeking."

Yep, and that's what all these fine fellows are here to provide.
The more information we can provide them the better they can
assist with the current problem. It isn't easy to do long distance!

It doesn't need to be running full throttle.
Turning the main needle all the way in should kill the engine.
No need to reef it down, it should shut the fuel off with a light seat.
 
Roger here is a picture of the mesh filter before I cleaned them. Then I crawled underneath with a flashlight to inspect the breather housing and it was really clean, you could see the red paint. Which leads me to this question, do you fill the outside or inside of the oil cup, and what are those holes for, to flow into the middle of the cup or to the outside or just to level it all out?
a232894.jpg
 
Ratface ,Have you tried running it with the air cleaner disconnected from the carb? Is the choke butterfly open all the way?
 
(quoted from post at 20:55:12 07/25/16) Ratface ,Have you tried running it with the air cleaner disconnected from the carb? Is the choke butterfly open all the way?
Hmmm, remember that guy that had the choke that worked backwards?
I can't remember who it was but when I rebuilt his carb I had
to put the choke in backwards for it to work with his linkage.
 
Yep, there is more to this story than has been revealed yet. Like Paul Harvey, I'm waiting for "the rest of the story".
 
(quoted from post at 16:35:01 07/25/16) "At speed, turn the main adjust needle all the way in and see if that will kill the engine."

It dang well better! :)
When it left here the idle was set at 400 RPM by the proofmeter.
Top RPM was 2200 by the PM.
Idle air adjust screw was set at 1/2 turn, main at 1 3/4.
No black smoke or soot at all.

One thing to note, the carb worked the same before and after
the rebuild on his tractor but not on mine. I tested it prior
because of his unique circumstances. So essentially two
different carbs there.
As I understand it, ratface also tried a spare carb that didn't work.
Correct me if I'm wrong on that one R.

I'm not being defensive, I'm trying to get all the information
out here so we can help him get his tractor running again.
Once we figure out the problem, the carb will need to be
adjusted again so the instructions are relevant to the cause.

Is this the type of manifold you have now?

38399.jpg


38400.jpg

I installed the YT manifold a week or three back and have had no issues, re-torqued it last weekend after running it a few hours
the week before, did some light work since and all still is well...
 
(quoted from post at 23:47:40 07/25/16)
I installed the YT manifold a week or three back and have had no issues, re-torqued it last weekend after running it a few hours
the week before, did some light work since and all still is well...
I haven't installed one of the manifolds from YT Cliff, so I can't speak to those.
The one in my picture cannot be mounted on the original studs as
it doesn't have a flat surface to mount to the block.
It either has to be mounted with bolts or have extra long replacement
studs installed to reach out far enough to stick through it.
 
(quoted from post at 20:59:01 07/25/16)
(quoted from post at 23:47:40 07/25/16)
I installed the YT manifold a week or three back and have had no issues, re-torqued it last weekend after running it a few hours
the week before, did some light work since and all still is well...
I haven't installed one of the manifolds from YT Cliff, so I can't speak to those.
The one in my picture cannot be mounted on the original studs as
it doesn't have a flat surface to mount to the block.
It either has to be mounted with bolts or have extra long replacement
studs installed to reach out far enough to stick through it.

Oh, OK now upon further lookin at the pics I see that the bolt bosses are longer and making the stock studs unusable
at first glance it looked the same, guess I picked the right vendor.... 8)
 
may or may not be your issue, but i had a issue with a aftermarket manifold,the casting was too thick, and the lower part of the manifold actually overlapped onto the covers for the lifters, so it wasnt sealed against the block like it should be. i removed it, put the stock gaskets on the manifold and used a permanant marker to mark the metal that needed to be removed. i used a angle grinder to remove the metal taht wasnt needed, did it at a angle and used fine sandpaper on the face of the manifold mating surface once i was done. my vacuum leak was quite a bit worse though, tractor would barely start. even if your not having the issue i was with the casting overlapping the lifter covers, i would at least check the mounting surface for "trueness", a flat block of wood with about 220 grit sandpaper. and it wouldnt hurt to do a compressiuon check, i didnt see that mentioned, wouldnt hurt to check that off the list of potential "bugs".
 
I see a vacuum leak causing a lean condition, not a "black dry soot" rich condition. Still waiting for "the rest of the story".
 
Hold a rag over the end of the exhaust until the motor almost chokes out then pull the rag off , then you will see a big puff of black smoke .

It is not uncommon for a mass produced cheap manifold to have casting debris in the number 1 or 4 exhaust port . I remember Hobo getting a blocked manifold once .

Before I pulled the manifold , I would check air flow though the intake and exhaust of each cylinder by using compressed air in the spark plug hole .
 
The holes are to level the oil. Fill to the marked line on the outside/inside. Do not overfill.

Did you try running without air cleaner hooked up?
 
Gentlemen; Black smoke has to be excess fuel or restricted air. I noticed below it would appear he may have "rebuilt" the air cleaner at this same time. He has a picture of the media (steel wool or ?). Did he overpack the aircleaner causing a restriction, i.e. choke condition?

I asked him to remove the rubber hose connedting the air cleaner to the carb but do not see any response to doing that, to eliminate problems with the air cleaner side of things.

I don't see how manifold problems could cause an over rich condition, maybe lean, as it is "after the carb"??

There has to be more to the story than what we are being told.
 
Roger this is a long thread so to reiterate I'm not near the tractor and may not get back to it for several weeks but am chomping at the bit to try some of these remedies. I appreciate your patience and will post back when this is finally resolved. The mesh you see in the picture has been running in this tractor for 15 yeas and I did not rebuild the air cleaner, just removed the mesh to verify there was no obstruction.
 
Ken I assume this test would identify a possible obstruction in the aftermarket manifold? Could you detail to me more precisely how I would perform it. Would I need any special fittings or just an air tip on my compressor?
 
I would blow off the top of the head and remove the spark plugs . With the tractor out of gear use the fan to rotate the motor until you see the number 1 exhaust valve open . A rubber tip blow gun or maybe a rag to help seal and blow air into the cylinder . I would do this on all 4 cylinders and see if I could hear one that sounded different . May not confirm anything or it may give you a place to look . Caution , if a piston is not all the way down and you blow air in the cylinder it most likely will make the fan turn , watch your fingers .
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top