Backfire through carb 1904

sixbangr

New member
59 F100 223, Holley 1904, new 240 duel advance points dizzy. Just put the dizzy on a couple days ago. I changed the carb base to one without the valve in it and today I plugged the venturi hole . It actually ran better before I plugged the hole, it wasn't great but now it is worse. Timing is set at 5*, new timing chain, compression is 135-150, new plugs ect. After I did the dizzy I drove it around my yard and just about couldn't get it up my steep drive way. Really thought going port vac was the answer. Tried manifold vac yesterday and the timing jumped to about 50*, backed it way back and it would not run right at all.
 

hodaka100

Active member
only change one thing at a time and get more data on the timing. I assume you have an advance timing light... harbor freight has a cheap one.
 

bubba22349

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You will need to work on the centrivical advance curve some and then limit the vacuum advance to. Do you accually have any ported vacuum at the carb base?
 

sixbangr

New member
You will need to work on the centrivical advance curve some and then limit the vacuum advance to. Do you accually have any ported vacuum at the carb base?
my understanding was that these carbs had both venturi and ported vacuum, and by blocking the venturi it was supposed to give about 15* of ported. Found the info on this site. When I get back Friday or Saturday, I will try and figure it out.
 

bubba22349

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That is correct that on a stock Load O Matic (LOM) distributor it needs to use a matching carb with vacuum passages and a SCV to supply a mixture of both Manifold Vacuum and Venturi Vacuum to operate the LOM Distribitors advance system. Below is the stock distributors advance specs for reference and tuning. So yes to end up with a ported vacuum sorce to work with the new 240 / 300 six distributor the upper Venturi Vacuum source passage is plugged off along with part of the SCV conecting port that conectted it to the upper Venturi port leading to the out side Vacuum line. When the mod's are done you will only have a vacuum sorce from just below the Carb's throdle blade going to the out side port for the Distribitor line down to the Vacuum Advance canister. With a low idle RPM there is little or no vacuum at this port. You mentioned in you above post that you also changed the carb base, without seeing what parts and their vacuum passages that you are using I am not able to determine if your mod's will work correctly for a ported vacuum sorce. That said it should still run decent even with that vacuum advance line disconnect just using the Distribitors centrivical advance system. You need to check out your timing cruve and total timing first using some extra timing marks (or some timing tape) on the Dampner to see if that's right before adding the vacuum advance system into the mix, that's a separate operation under load with a vacuum gauge tuned at steady state cruse speeds on the hyway. Looks like your compression is good. Have you set your valve lash yet?

For referance below are all the basic tune up settings for a 1959 Ford 223 Six and the order of doing a tune up that I have used for decades for the quickest route to a great tune up. I used 8 to 10 degrees of base timing in my area, that 50 degrees of advance with the distributor hook up to manifold vacuum is going to be too much f the engine is otherwise stock build and if you back down your base timing way down to cominsate for it your just killing the engines bottom end pulling torque. It will be much better to limit the vacuum adavance amount instead there are easy ways to limit the vacuum cans amount of pull with a simple stop and some of the better vacuum advance canister units are ajustable through the vacuum port opening. Good luck
:nod:


These are the Basic tune up specs for a stock 1959 Ford 223 Six

1. Plugs are gapped at .035
2. Basic Point gap setting is .025 to get it running for optimal performance and economy set points to 36 degrees dwell reading
3. Base timing is set to 4 degrees BTDC.
4. With the Engine warmed up good the intake and exhaust valve lash is set to .015 H
5. Mixture setting is set at lean best idle i.e. Engine warmed up good then Tuned to Highest RPM next the mixture screw is then turned in 1/4 turn.
5. Curb Idle RPM is set to 450 RPM with engine warmed up good for a manual trans with the air cleaner also installed, (setting is 450 for an auto trans with it in drive with emergency brake set.

Cold Cranking Compression Test should be a minimum of 120 PSI.

Fuel pump test 3.5 to 4.5 PSI pressure.

The stock Load O Matic Distributor timing advance cruve should map at these amounts.
500 RPM has 3 1/2 to 4 1/2 degrees advance at .50 inches of vacuum
1000 RPM has 8 1/4 to 9 1/4 degrees advance at 1.8 inches of vacuum
1500 RPM has 11 3/4 to 13 degrees advance at 3.8 inches of vacuum
2000 RPM has 14 1/2 to 15 3/4 degrees advance at 6.0 inches of vacuum

It's also important to have clean tight wiring and ground conections plus a battery that's at its full charge. The voltage you read at the battery post should be the same while cranking at the coil's + posative post.
 

sixbangr

New member
That is correct that on a stock Load O Matic (LOM) distributor it needs to use a matching carb with vacuum passages and a SCV to supply a mixture of both Manifold Vacuum and Venturi Vacuum to operate the LOM Distribitors advance system. Below is the stock distributors advance specs for reference and tuning. So yes to end up with a ported vacuum sorce to work with the new 240 / 300 six distributor the upper Venturi Vacuum source passage is plugged off along with part of the SCV conecting port that conectted it to the upper Venturi port leading to the out side Vacuum line. When the mod's are done you will only have a vacuum sorce from just below the Carb's throdle blade going to the out side port for the Distribitor line down to the Vacuum Advance canister. With a low idle RPM there is little or no vacuum at this port. You mentioned in you above post that you also changed the carb base, without seeing what parts and their vacuum passages that you are using I am not able to determine if your mod's will work correctly for a ported vacuum sorce. That said it should still run decent even with that vacuum advance line disconnect just using the Distribitors centrivical advance system. You need to check out your timing cruve and total timing first using some extra timing marks (or some timing tape) on the Dampner to see if that's right before adding the vacuum advance system into the mix, that's a separate operation under load with a vacuum gauge tuned at steady state cruse speeds on the hyway. Looks like your compression is good. Have you set your valve lash yet?

For referance below are all the basic tune up settings for a 1959 Ford 223 Six and the order of doing a tune up that I have used for decades for the quickest route to a great tune up. I used 8 to 10 degrees of base timing in my area, that 50 degrees of advance with the distributor hook up to manifold vacuum is going to be too much f the engine is otherwise stock build and if you back down your base timing way down to cominsate for it your just killing the engines bottom end pulling torque. It will be much better to limit the vacuum adavance amount instead there are easy ways to limit the vacuum cans amount of pull with a simple stop and some of the better vacuum advance canister units are ajustable through the vacuum port opening. Good luck
:nod:


These are the Basic tune up specs for a stock 1959 Ford 223 Six

1. Plugs are gapped at .035
2. Basic Point gap setting is .025 to get it running for optimal performance and economy set points to 36 degrees dwell reading
3. Base timing is set to 4 degrees BTDC.
4. With the Engine warmed up good the intake and exhaust valve lash is set to .015 H
5. Mixture setting is set at lean best idle i.e. Engine warmed up good then Tuned to Highest RPM next the mixture screw is then turned in 1/4 turn.
5. Curb Idle RPM is set to 450 RPM with engine warmed up good for a manual trans with the air cleaner also installed, (setting is 450 for an auto trans with it in drive with emergency brake set.

Cold Cranking Compression Test should be a minimum of 120 PSI.

Fuel pump test 3.5 to 4.5 PSI pressure.

The Load O Matic Distributor timing advance cruve should map at these amounts.
500 RPM 3 1/2 to 4 1/2 at inches vacuum of .50
1000 RPM 8 1/4 to 9 1/4 at inches vacuum of 1.8
1500 RPM 11 3/4 to 13 at inches vacuum of 3.8
2000 RPM 14 1/2 to 15 3/4 at inches vacuum of 6.0

It's also important to have clean tight wiring and ground conections plus a battery that's at its full charge.
Did some more research on the carb I have. Turns out it is a model 1960 from a 56-57 F100. Any way I took the stop out of the venturi hole and it stopped backfiring. Still didn't run great but was way better. Took your advice and pulled the vac line and plugged it. Had to richen the mixture a turn more out at least to get rid of the dead spot. Backed it out to the end of my drive and made it up the hill. Not perfect but better than it has been. There is a member named "peeeot" who has this same carb and dizzy who mentioned plugging that venturi hole and his is working like it should. No idea why it won't on mine. Tomorrow or Monday I will work on it some more. Maybe a dizzy recurve will help too.
 
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