Carb Help needed please!

[Fred K-OR]

As some of you may know, I am the one that knows little about the finer workings of the old Model A. So I always have lots of questions.

Being bored in these winter months, I decided to try my hand and rebuilding an extra carb. Well I got all the main pieces I needed, upper and lower bodies and ordered new parts from one of the vendors and got everything put together. Put it in the old coupe, was surprised it started, but the old rig just did not run well at all.

The problems: 1) it is running to rich. Ruff running with black smoke out the tail pipe. Turn the GAV all the way in but does not make any difference. But I did find that I needed to put in the little fitting in the GAV hole. Put this fitting in, started it with the GAV all the way in and still the same problem
2) second problem is that when I take it out for a drive, when I press on the gas, the carb backfires and it almost quits. This does not make sense based on problem #1 above.

So what am I doing wrong? Do I have something plugged up somewhere? If so where" Do the upper and lower bodies I pickup up have a problem in them somewhere? I did use all new parts for all the things that can be changed in the carb. I was thinking that I should swap out the upper and lower bodies with a known good one. This may be my next step. Bought the new parts from one of the best suppliers in the industry. Please help this old bored guy.

[160B]

Start here at Model-A.Org website. Everything you need at one website, but there is a lot to digest.

http://model-a.org/

here is a table for trouble shooting

http://model-a.org/troubleshooting.pdf

[jm29henry]

Great to ask questions,!!! We all need to learn.Did you set the float.? What are your jet sizes? Are all passages clean? Do you have the jet in side the GAV ?do you have any books for specs?

[30aadoodlebug]

Hows the float level? I had a similar problem with a zenith i rebuilt, and the float was set too high.

[AL in NY]

I don't know how thorough you where in rebuilding the carburetor, but all brass plugs should be removed and the passageway cleaned, especially under the GAV needle. In most vendor carburetor kits, the jets are not the correct size. Before using they should be flow tested. Fuel float should be checked for leaks and set to the correct height.

[160B]

Sponsored Links (Register now to hide all advertisements)

Also at Model-A.Org website.

To aid in troubleshooting, common symptoms are noted and their most common causes are identified.

http://model-a.org/symptoms.html

[Fred K-OR]

Originally Posted by jm29henry

Great to ask questions,!!! We all need to learn.Did you set the float.? What are your jet sizes? Are all passages clean? Do you have the jet in side the GAV ?do you have any books for specs?

I did set or checked the float.
The jets were all new purchased from Brattons. So I assumed they were the correct sizes.(maybe this assumption is my problem). I tried to blow all passages out with air. I did put the jet inside the GAV.
So tried to do the things that I heard were the things to do. But somewhere I have not found the problem(s).

[Fred K-OR]

Originally Posted by AL in NY

I don't know how thorough you where in rebuilding the carburetor, but all brass plugs should be removed and the passageway cleaned, especially under the GAV needle. In most vendor carburetor kits, the jets are not the correct size. Before using they should be flow tested. Fuel float should be checked for leaks and set to the correct height.

I have not removed the brass plugs which in this case, maybe I should do being I purchased the upper and lower bodies and do not know what shape they are in. I did check and set the float valve for adjustment and float for leaks. But looks like I need to get into it more!

[Fred K-OR]

Originally Posted by 160B

Also at Model-A.Org website.

To aid in troubleshooting, common symptoms are noted and their most common causes are identified.

http://model-a.org/symptoms.html

Good stuff 160B. I forgot about Bert's web site which has much info that I need to study.

[Gary WA]

Jet Sizing-all old washers removed from jets including gav.No washer on idle jet!

[160B]

Originally Posted by Fred K-OR

I did set or checked the float.
The jets were all new purchased from Brattons. So I assumed they were the correct sizes.(maybe this assumption is my problem). I tried to blow all passages out with air. I did put the jet inside the GAV.
So tried to do the things that I heard were the things to do. But somewhere I have not found the problem(s).

New jets are not correctly sized and to be successful in the rebuild jets must be flow tested and appropriately resized to provide correct flow. Also if passages are not verified clear you will not be successful in your rebuild.

[Fred K-OR]

Originally Posted by Gary WA

Jet Sizing-all old washers removed from jets including gav.No washer on idle jet!

\


Gary, looks like you have done a few carbs. I am still learning and have a lot to learn.

I think the first thing I need to do is make sure all the crud is out of the lower part of the carb. I saw a lot of rust in this part and thus I am thinking that some of the passages are plugged up.

[midgetracer]

Renners Corner sells the flow tested jets. They also have all necessary parts at a reasonable price. I would not drill out the brass plugs. Many carbs have been ruined doing that. I use a fine stainless wire to run through the passages and usually get all the rust and crud out. Good luck

[RonC]

Originally Posted by AL in NY

I don't know how thorough you where in rebuilding the carburetor, but all brass plugs should be removed and the passageway cleaned, especially under the GAV needle. In most vendor carburetor kits, the jets are not the correct size. Before using they should be flow tested. Fuel float should be checked for leaks and set to the correct height.

I wouldn't drill out and replace plugs. You run the risk of cracking the casting when forcing in new plugs. Not necessary. Glass bead the passages and run paper clips through the passages to check

[Jacksonlll]

I hope you did not leave out the venturi!!!!!! It has been done.

[zzlegend]

Fred, if that bottom piece was very rusty, you might want to soak it for a day or two in some evapo-rust. It works great for removing rust. As stated earlier, get a piece of fine wire and run it thru all the orifices. That's what I always do when I rebuild them. I would not do any drilling on any of it unless absolutely necessary. Patience, patience. You will get it. Just my 2 1/2 cents. Good luck with it.

[Terry, NJ]

The problem is that a little too much gas is getting through as opposed to too little. Go through all of the fuel regulation parts of the carburetor, Float, float valve, jet sizes ETC. There are no mysteries in mechanics, only questions whose answers are not immediately obvious!
Terry

[Big hammer]

Hidden passage's need to be open, I believe Tom Eddy has talked written about this! Using a paper clip and bending to get through the passages. Following the step by step and you will successful in your rebuild :-)

[Fred K-OR]

Originally Posted by Jacksonlll

I hope you did not leave out the venturi!!!!!! It has been done.

Don't laugh you all! I did do that on another carb

[Fred K-OR]

Thanks guys. You gave me a lot to work on the. Great challenge to work on in the cold garage.

[wingski]

Make sure all the gas is out of the carb and bring it into the house where it's warm. Cold hands and carburetor work don't go together.

Mike

[johnbuckley]

Simple things first.... 1) Is it leaking gas at all?.. when idling ?... when running? or not at all. Is it rich at idle or when running? 2) You Say it's running rich therefore it's most unlikely to be a blocked passageway (other than the air passage at the idle air mix screw which hardly ever gets blocked)..... YET... as you say when you floor it it backfires which certainly could indicate a weak mix
.. so we have ... if running rich .....
A) You didn't by any chance get the GAV seat and the comp jet mixed up and put them in the wrong places?? ( yes...we've all done it !)
B) lack of or poor seal at comp jet gasket can cause rich running withour any visible sign of leakage
C) Assuming solution is not A) or B) then I would suspect either main or comp jet are too large.
if running weak ... suspect crud in passage way or in a jet, or crud preventing good fuel flow from tank.
RonC said "I wouldn't drill out and replace plugs. You run the risk of cracking the casting when forcing in new plugs. Not necessary. Glass bead the passages and run paper clips through the passages to check".... I totally agree with him.

[Tom Endy]

attached article may be of help.

Tom Endy

[Fred K-OR]

Originally Posted by wingski

Make sure all the gas is out of the carb and bring it into the house where it's warm. Cold hands and carburetor work don't go together.

Mike

Good point Mike.

[Terry, NJ]

Thanks for posting this!
Terry

Originally Posted by Tom Endy

attached article may be of help.

Tom Endy

[Purdy Swoft]

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Use a good quality carb cleaner in a spray can with a tube in all of the passages with the jets removed . Replace the original jets and give it another try .

[sofield]

I would agree with RonC. Don't fool with the brass plugs. There is a good chance that you will screw up and destroy the carb halfs. Do a complete disassembly and use a common paper clip. you will have to bend the clip in different shapes to get through the 5 passage ways. Use a needle nose pliers to help to push the clip through.(Be patient) then use compressed air to blow them out. Then have the two half's bead blasted and make sure to get into each 4 passage ways. Then redo the the compressed air to the passage ways. Have the 4 jets flow tested. Here are good flow test # Main Jet 158 ML, Cap Jet I73 ML, Comp Jet 143 ML, Idle jet 54 ML. Place a gasket under all except the idle jet. Turn the throttle screw 1 1/2 turns open and the air adjustment also the same and AVR nob (Choke rod) 1/4 turn counterclockwise. two main things to remember clean passage ways and jet flow rates This should get you up and running. Sofield

[Fred K-OR]

Originally Posted by Tom Endy

attached article may be of help.

Tom Endy

Thanks Tom for your excellent article. I have copies of it but f0rgot where I put it. So great that you posted it again. Thanks.

[Fred K-OR]

Well I did make some progress today. At least I consider it progress in that when something seem to go right, it feels like progress for me, the guy that does not know what he is doing.

I put my "good" carb(the one I have had on the coupe and it has run great) back on the coupe today. Took the bottom half off the "good" carb and put the bottom half of the carb ("bad" carb) I am trying to get going on the top half of the good carb that was on the coupe. Started up the rig and bingo, the same problems are there that I have had with the bad carb when I put it on the rig. Many of you that know how to rebuild carbs probably knew that this would happen. But old me had to do it on a trial and error effort.

So to me this indicates that the bottom half of the bad carb is messed up somewhere. So now I need to start doing some of the many good ideas you all have suggested in the above comments. I had a can of carb cleaner sitting around so after taking all the jets out of the bottom half, I put it in the can of carb cleaner. Think I will let it soak there for a day or so and then try to clean out passageways with paper clips and then blow them out. Then check over my parts (jets, etc) to make sure they are OK. Then put things back together and give it a try.

Again thanks for all your help and if you don't mind I will let you all know how things work out.

[700rpm]

Fred, Dave Adair has the carb jet testing setup if you want to flow test your jets. (This might be in the club tool trailer, but Dave will know). Also, I got some of the rcommended Renner's jets and put them in my coupe, but I didn't notice any difference from what I had, which had not been flow tested, but were all original jets.

[Fred K-OR]

Originally Posted by 700rpm

Fred, Dave Adair has the carb jet testing setup if you want to flow test your jets. (This might be in the club tool trailer, but Dave will know). Also, I got some of the rcommended Renner's jets and put them in my coupe, but I didn't notice any difference from what I had, which had not been flow tested, but were all original jets.

Thanks Ray. If the stuff I am in the process of doing now, don't work, then I will have to look at your idea with David. I also have a number of jet sets that I can swap out and check out each one.

[Brian T]

Just a thought, in your original post you said you installed the jet below the GAV, I do not remember, but aren’t the compensator jet and the GAV jet the same thread size?, if so if the 2 are switched it would run to rich , again just a thought.

[[email protected]]

Originally Posted by RonC

I wouldn't drill out and replace plugs. You run the risk of cracking the casting when forcing in new plugs. Not necessary. Glass bead the passages and run paper clips through the passages to check

Good discussion on paper clip method discussed before:

https://www.fordbarn.com/forum/showt...ght=paper+clip

[Fred K-OR]

Originally Posted by Brian T

Just a thought, in your original post you said you installed the jet below the GAV, I do not remember, but aren’t the compensator jet and the GAV jet the same thread size?, if so if the 2 are switched it would run to rich , again just a thought.

Brian, yes I did check that out and yes I do use the jet below the GAV. From what I understand, the longer of the two jets goes in the GAV. I think I originally put the wrong (the shorter one) in the GAV and somewhere I saw where I should have used the longer one. Is this correct guys? The longer one goes in the GAV??

I am going out this A.M. to see how the soaking of the lower part in carb cleaner did. Then I will try some of the suggestions Tom Endy has in his write up using paper clips to clear the passages. Will hope for solution this time

[Benson]

Yes larger port one is GAV seat ...

The comp jet has much smaller port ... and usually shorter

[Fred K-OR]

Originally Posted by Benson

Yes larger port one is GAV seat ...

The comp jet has much smaller port ... and usually shorter

Thanks Benson. I got that correct this time and I did notice the larger port on the GAV.

[Fred K-OR]

Hey guys, I won! The old carb works!!!. I know it probably isn't as good as one that would have been rebuilt by someone that knew what they were doing, but it works quite well on my old driver 29 coupe.

To fill you in on the last things I did, based on a number of your ideas, that made it work well, I will try to list them off.

1) I soaked the bottom half of the carb in carb cleaner over night.
2) This A.M. I took it out of the cleaner and proceeded to do a number of thing you all had suggested.
3) After washing the cleaner out of the carb, I followed Tom Endy's procedure using paper clips to assure all channels were clean.
4) Then I used air to blow out all of the channels.
5) Then I rechecked what I had done with the fitting down in the GAV channel. I made sure I put in the longer of the two fittings I had.

Then I put everything together with same other parts and put it on the rig and started it up. It seemed to work great so I took it around the block. Still worked great on a little drive. But it did "back off" a bit through the carb when I let up on the gas after giving it a big shot of gas. So may still have a bit of something going on. So I need to get it out on a longer drive under all conditions, to see what it is going to do.

Well better end this chatter and just say thank you all for the ideas on what to do. I think I am getting close to having a fairly good carb. It has been an interesting educational experience for this old guy.