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Old 04-27-2020, 06:23 PM   #1
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Default Getting my 31 to run right.

So, I got out my 31 and got it running but, just like before I just can't seem to get it to run well. Pretty sure it's a fuel issue as I can get fit to run OK if I hold the choke out at just the right "sweet spot" but it needs to be held open even when warmed up and driving so obviously it isn't getting enough fuel (or too much air). Everything in the distributor is new and timing is dead on, everything inside the carb is new as well as the intake and exhaust manifolds. I have not done anything with the valves. However, I am noticing what appears to be anti freeze on the outside of the block as if its coming out from the head gasket. Not much but the block is not clean like it should be. Head gasket pooched maybe??. thoughts. BTW, I did do a compression check 2 years ago and IIRC they were all within a couple pounds of each other in the mid-high 50's
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Old 04-27-2020, 06:36 PM   #2
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Default Re: Getting my 31 to run right.

Could be the manifold gasket leaking or some other vacuum type of leak. Of course it could be dirt in the fuel, what kind of filter do you use? Sounds like it is something fuel related since your distributor is rebuilt. It will be a process of elimination, I have sprayed something like carb cleaner on the gasket area of the manifold while running to see if it shows a leak is sucking air into the motor. If you have a spare carburetor, swapping that would tell if that is the problem.
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Old 04-27-2020, 06:47 PM   #3
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Default Re: Getting my 31 to run right.

2X manifold gaskets.....have they been retightened recently ?
'A's" run pretty thick, soft gaskets which continue to 'shrink' with each motor warm up.


Use a paper towel to check your hose to radiator connections for that anti-freeze leak.


'Dialing in' takes time but eventually rewarding.
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Old 04-27-2020, 07:12 PM   #4
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Default Re: Getting my 31 to run right.

Intake air. Leak. Retorque your head often
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Old 04-27-2020, 08:21 PM   #5
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Default Re: Getting my 31 to run right.

So, I checked the intake torque and tightened them down about a 1/2 turn or so, then checked the other bolts and found that the two bolts that hold the intake to the exhaust manifold were not even finger tight (DOH!) so I thought EUREKA!. Torqued them down as well as checked the carb flange bolts. Checked the head bolts and found most required 1/2 to 3/4 turn for a 60 Ft/lb torque. Figured Im getting somewhere. Checked the GAV and found that, while I THOUGHT I was adjusting it, I was just turning the knob, not the rod so I torqued the know good an=d tight so I can turn the GAV rod. Took it for a drive. Better but still needs the choke pulled a bit to get it to run well. Without the choke, it misses a bit and backfires. Pull the choke a bit and it takes off and seems to run not too bad. Idles much better now. Running the GAV out one full turn. Any more doesn't help and any less runs worse.
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Old 04-27-2020, 08:46 PM   #6
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Default Re: Getting my 31 to run right.

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You didn't mention what kind of carburetor …………. Cast Iron Zenith? Pot Metal Tillotson? Other? If it is a Tillotson, there's a good chance the flange where it bolts to the intake manifold is warped and causing a vacuum leak. If it's a Zenith, possible clogged passage somewhere because, when warmed up, you should not have to have the choke rod opened a full turn. So, if the problem is in the fuel system, it's either a vacuum leak or lack of gas flow in the carb.
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Old 04-27-2020, 09:07 PM   #7
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Default Re: Getting my 31 to run right.

Cast Iron Zenith. I agree with what you are saying just not sure where to look. Had the carb apart and everything in it is new and it looks new inside. I don't recall for sure but I think I may have blasted carb cleaner through every orifice when I had it apart 2 years ago.
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Old 04-27-2020, 09:15 PM   #8
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Default Re: Getting my 31 to run right.

Good that you got the head torqued back down. That hopefully will help with the head gasket seepage.
The two bolts holding the intake manifold to the exhaust manifold won't make any difference on how it runs. I leave those loose until I get the four nuts on the manifolds snugged up. If the four manifold nuts were a bit loose for a while it is possible that you had exhaust gasses getting by the gasket and eroded it causing a leak that can't be fixed by tightening it back down. Spray some starting fluid all the way around the manifold gaskets and carburetor mounting gasket while running the engine to see if the engine speed changes.
When you rebuilt the carburetor did you happen to forget to install the venturi?
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Old 04-27-2020, 09:21 PM   #9
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Default Re: Getting my 31 to run right.

I would be surprised if the gaskets were compromised. They had a total of about 10 miles on them since install and they weren't all that loose. I did spray brake clean around all of the intake surfaces and did not get any RPM change. Im going to town tomorrow and can get some ether and try that. The carb was rebuilt when I got the car. IO just took it apart to check it all out because it wouldn't run right. As far as the venture goes, I can't really say.
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Old 04-28-2020, 07:28 AM   #10
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Default Re: Getting my 31 to run right.

Do you have another known good carb you can swap in, or can borrow one from some one? Was this carb tested and running well 2 years ago? Was it stored drained of gas, if not may have varnished up in jets/passages. If carb perhaps try cleaning again and installing Renners flow tested jets.
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Old 04-28-2020, 07:36 AM   #11
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Default Re: Getting my 31 to run right.

https://www.fordbarn.com/forum/showthread.php?t=266328 and https://www.fordbarn.com/forum/showthread.php?t=271572

Here's a thread I started when I rebuilt mine, I learned a lot and these guys helped me through it. Check the links given as they are very informative. I still don't understand the carburetor entirely but I have a much better understanding than before. Thanks again to the guys who helped.
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Old 04-28-2020, 07:47 AM   #12
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Default Re: Getting my 31 to run right.

Tell us more about how you rebuilt the carb. I had a friend rebuild a Zenith for me and he just replaced parts. Problem is modern jets are likely not sized right. You need to flow test the carb and possibly re-size the jets. Frankly, spending a couple hundred bucks or so on a fully rebuilt and tested Zenith from Bert's is money well spent.
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Old 04-28-2020, 07:58 AM   #13
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Default Re: Getting my 31 to run right.

Quote:
Originally Posted by Greg Jones View Post
Tell us more about how you rebuilt the carb. I had a friend rebuild a Zenith for me and he just replaced parts. Problem is modern jets are likely not sized right. You need to flow test the carb and possibly re-size the jets. Frankly, spending a couple hundred bucks or so on a fully rebuilt and tested Zenith from Bert's is money well spent.
Some venders flow test their jets to insure they are correct when shipped. Renners Corner is the vendor is often mentioned. I believe Berts is another vendor, I know Berts flow test their jets when rebuilding carbs.
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Old 04-28-2020, 08:43 AM   #14
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Default Re: Getting my 31 to run right.

Might be a good idea to check engine compression and vacuum and rule them out.
carry on
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Old 04-28-2020, 07:30 PM   #15
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Default Re: Getting my 31 to run right.

So, I got back from town and, after reading the posts about jet size, I thought I would tear the carb apart again and look things over. For the record, I didn't rebuild the carb, the previous owner did. He owned the car for 10 years and never drove it out of the yard. I have another carb here for parts so I thought I would compare jets. As near as I can tell by wire micing the jets (sort of) they appear to be the same-ish. The old jet was marked "19", the new jet no markings. I took a welding tip cleaning set and ran one through the old jet a few time to clean it up and decided to try it in place of the new one. I also blew brake clean through every orifice and took the GAV apart to check that out as well. Everything LOOKED pristine in there but looks can be deceiving. So, put it back together put it on and the engine fired immediately and sat running smooth with the GAV out one full turn an the idle air at 1 1/2 turns. Took it for a drive and it ran better than it ever has since I've owned it. Not perfect but pretty good. HOWEVER, in order to get it to run relatively strong, the GAV needs to be turned out about 2 full turns or more. That suggests to me that perhaps that jet is not flowing enough and the GAV has to make up the difference. While i have a ways to go it's looking encouraging. Another thing, it started to blow anti freeze out the cap and the motometre went up to the bottom of the "running temp" circle. Not sure what to make of that as this is the first time I've seen the motometre register anything and it's my understanding that they are not to be relied upon. Also, when it started to blow coolant I was about 4-5 miles down the road doing about 35-40 MPH wide open and when I saw the coolant realized that I had left the advance lever in full retard (DOH). Advanced the timing on the way back and got it up to almost 55mph. When I got back to the shop, it did not seem to be overheating but it also didn't look like any coolant came out the overflow. That tube may be plugged. Still having trouble getting a good exhaust seal from the manifold to the pipe also.
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Old 04-28-2020, 07:50 PM   #16
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Default Re: Getting my 31 to run right.

Your making good progress. Water coming out from the cap is not necessarily an indication of over heating but of a poor seal on the radiator cap and possibly over filling. If over heating the coolant should be pushed out of the overflow tube not the cap. Easy to check to see if the overflow tube is plugged.
Coolant can be pushed out of the radiator under load if a head gasket is leaking.
Best way to be absolutely sure what the temperature of the coolant is to get a dial meat thermometer and place it directly into the top of the radiator into the coolant. Maybe it is just me but having one in your Model A tool bag is a must.
Lots of folks use the laser thermometers to read temps. They are okay but useless if the battery runs out.
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Old 04-28-2020, 09:09 PM   #17
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Default Re: Getting my 31 to run right.

You can also check for air bubbles in the coolant with the motor running. Then additionally block the wheels, have someone with the brakes on load the motor in gear slipping the clutch, and check for bubbles. You will see water pump turbulence, but not bubbles which would indicate head gasket.


A better test is a Coolant Block Test - tests for exhaust gas in the radiator top tank. Can have done at a shop or do yourself


https://www.napaonline.com/en/p/BK_7...RoCZrAQAvD_BwE


Cheaper on eBay/amazon.


At idle the motor/carb runs off the Carb idle Mixture screw and the GAV, above idle the motor depending on conditions (RPMS/load) runs off the other passages/jets. Above 800 RPM GAV should not have much if any effect on motor running.





Replacement Jets are notorious for not flowing correctly - reason why flow tested replacement jets are recommended when replacing jets. Micing and cleaning is not a substitute for making sure the jet passages are sized properly for proper flow.


An additional way to measure coolant temp is to install a temp gauge via the Head coolant outlet neck.


Also check to make sure the throttle and choke plate shafts fit snuggly in their bushings, another cause of lean running requiring more GAV. Also a cause of poor idle.
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Old 04-28-2020, 09:35 PM   #18
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Default Re: Getting my 31 to run right.

How about checking to see if there is a leak coming from the line going to the windshield wiper if you are using a vacuum type wiper. Sometimes this is a common area for a leak that can lead to a rough running "A". Simple check would be to disconnect the line and block it off to observe any change.
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Old 04-30-2020, 10:08 AM   #19
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Default Re: Getting my 31 to run right.

I don't have a line for the wiper. Just have a plug in the manifold but I took the plug out and put teflon tape on it just the ensure that it wasn't leaking even though I was pretty certain it wasn't.
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Old 04-30-2020, 10:10 AM   #20
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Default Re: Getting my 31 to run right.

I ordered a booklet on tuning the zenith carb, flow testing the jets and such so will give that a go and see what happens.
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