Desperately need help with 340 issue

[JG1966]

Let me start by saying I'm likely in the bottom 20 percent when it comes to Mopar troubleshooting among everyone on this board, so bear with me if i sound simplistic/stupid, but I really hope one of you guys can help me.
I can't get 340 to stay idling and now carb -- which I jist rebuilt -- is spitting fire. Here's the whole story. I installed an Edelbrock airgap on my 340. I've owned car for 6 months. Car ran fine before but it had a single plane Wieand and wanted more low RPM torque, but car ran fine. When I removed distributor, I noted rotor and vacuum canister positioning with photos. When I had carb off ( for the first time since I bought the car), I pulled out metering rods and jets to see if they had been upgraded/changed. Both were factory (secondary jets were stuck and I didn't want to strip them.) Did nothing else to carb. I also adjusted my mechanical advance limiter plate in distributor, for what it's worth.
Put everything back together. Gave a few pumps of gas and she fired right up. Running a little rough but I attributed that to putting in distributor a teeny bit off. Ran for 5 minutes or so looking for leaks at intake, valve covers, etc. No obvious leaks. All good.
This is where issues started.
I turned off car to hook up timing light. Then car wouldn't fire. I know timing was fairly close. After a while of trying, I figured maybe motor was flooded (and my battery was dying). Waited a couple hours, recharged battery, jammed pedal to floor and turned over, car fired and ran but only barely and stalled as soon as I let off gas. SO car ran fine when I started with bone-dry carb but was quickly flooded the first time I turned it off and tried to restart.
I bought rebuild kit for carb (750 Edelbrock electric choke 1411). Adjusted floats (they were way off). Cleaned everything. Reinstalled and still needed to feather gas to get to idle and had crackling backfire out exhaust. I had my buddy keep car running at about 1200 rpm and looked at timing. It was about 24 advanced. I moved to 16. Car still ran rough (I figured I must have messed up a metering rod or gotten dirt in a jet or something). Later today, I went out to try it again. This time I couldn't even get car to start and run -- admittedly poorly -- like earlier in the day even with gas pedal floored, and it shot fire out of carb twice. What is the most likely problem? I am 95 percent sure my timing is pretty close to 16* or so initial. It's certainly not way off. Is my carb toast? It was fine before I took it off. Will bent metering rod/bad jet, etc cause instant flooding and/or backfiring from exhaust and carb? I can't believe it is in any way related to manifold. I have two new metering rods coming in mail and pray that fixes it, but I'm not feeling too hopeful. I don't want to have to go buy a new carb if I can avoid it and if there's a culprit I'm missing. Any help/suggestions would be great. Thanks.

 

[cudajunction]

JAWESUS good luck

 

[DLevel]

I think in most cases you will find that a popping back thru the carb or out the exhaust is due to a timing or valve issue. Because the engine ran good before you took the distributor out I would look at that first. Had you ever had a timing light on this engine before as you've only oweed the car for a little while. Reason I ask is wouldn't be first time I've found the timing marks are not correct on an engine due to balancer or covers being replaced.

 

[JG1966]

I think in most cases you will find that a popping back thru the carb or out the exhaust is due to a timing or valve issue. Because the engine ran good before you took the distributor out I would look at that first. Had you ever had a timing light on this engine before as you've only oweed the car for a little while. Reason I ask is wouldn't be first time I've found the timing marks are not correct on an engine due to balancer or covers being replaced.

Thanks DLevel. I would immediately suspect the timing was 180 off or the timing marks were wrong, but it started and ran fine when I put in distributor two days ago after changing manifold. I haven't touched distributor since then other than slightly adjusting it trying to get it to start. I have use a timing light on it many times and the timing marks are fine. I'm going to double check that rotor points to no. 1 wire at TDC and firing order but I haven't messed with distributor since it initially ran well two days ago.

 

[4mulas]

Maybe you adjusted the float incorrectly and it's not getting fuel at all unless you pump the heck out of it, severe lean can cause back fire too?

You have several variables here. When I tend to do work like that I do one thing at a time, i.e.: would not have messed with a good running carb or distributor until after I have the intake in and running with no leaks. then do your distributor tune up, then carb tune up all seperate
from each other. Makes issues easier to diagnose.
Maybe borrow a known good running carb and just bolt it on. If it's still bad you know it's a distributor/timing issue

 

[Bb70charger500]

I was thinking 180 out also but since it ran fine for a bit I'd say that's not it well then you have a carb issue for sure but I still want to say your distributor is still not right since your back fireing. What's a stock 340 supposed to be ran at isn't it around 2-6° advance ? I'm not really good with the tech part I do it by ear so kinda hard for me . But someone will chime in I'm sure as for the carb pull it back apart and just double check everything to see that nothing is out of place and see what your float hight is at . Also make sure you didn't loose any of those tiny *** balls that are in there

 

[The Shoe]

Can you explain what you did when you "adjusted my mechanical advance limitor plate"?

 

[JG1966]

Can you explain what you did when you "adjusted my mechanical advance limitor plate"?

I have an FBO advance limiter plate and I moved it from the 18 slot to the 16 slot because the 18 slot was still giving me about 24* mechanical advance. I wanted about 16 initial 18-20 mechanical so I tried the 16 slot to see what it gave me.

. http://www.manciniracing.com/fbomodilipl.html

 

[JG1966]

I was thinking 180 out also but since it ran fine for a bit I'd say that's not it well then you have a carb issue for sure but I still want to say your distributor is still not right since your back fireing. What's a stock 340 supposed to be ran at isn't it around 2-6° advance ? I'm not really good with the tech part I do it by ear so kinda hard for me . But someone will chime in I'm sure as for the carb pull it back apart and just double check everything to see that nothing is out of place and see what your float hight is at . Also make sure you didn't loose any of those tiny *** balls that are in there

It's not stock and ran very nice with about 16 initial timing (it also ran well at 6). I definitely didn't drop the tiny ball in there. I think it's a messed up jet or rod - or some issue with the carb -- but dont know why that would cause backfire. I guess it's possible my distributor "jumped" out of the gear when I loosened it to change timing but seems unlikely. I didn't loosen it that much.

 

[Bb70charger500]

Ah you got problems man! It takes alot of wiggle room for your distributor to jump I'd say play with the internals of the carb for a bit make sure nothing is out of place why your in there !

 

[condor74]

Back to basics. Verify you did not get a plug wire crossed.
On the carburetor, can you see gas flowing into the throat when the vehicle is off after attempting to start? If no then pump the accelerator and see if gas squirts into the throat. If it does you should be able to get it to come to life. If it isn't then you are most likely not getting gas into the carb

 

[JG1966]

Maybe you adjusted the float incorrectly and it's not getting fuel at all unless you pump the heck out of it, severe lean can cause back fire too?

You have several variables here. When I tend to do work like that I do one thing at a time, i.e.: would not have messed with a good running carb or distributor until after I have the intake in and running with no leaks. then do your distributor tune up, then carb tune up all seperate
from each other. Makes issues easier to diagnose.
Maybe borrow a known good running carb and just bolt it on. If it's still bad you know it's a distributor/timing issue

Thanks 4Mulas. You are absolutely right. I definitely should have stuck to one change at a time. Live and learn. I'm going to make sure timing, distributor are good and, if they are, then try a proven carb.

 

[JG1966]

Back to basics. Verify you did not get a plug wire crossed.
On the carburetor, can you see gas flowing into the throat when the vehicle is off after attempting to start? If no then pump the accelerator and see if gas squirts into the throat. If it does you should be able to get it to come to life. If it isn't then you are most likely not getting gas into the carb

Thanks Condor. I will check wires and TDC timing to ensure I'm not 180 off.
I am getting gas. I could see vapors when i pressed gas pedal and I could smell it heavy in my exhaust. I think I'm getting way too much gas. But why would that cause a backfire if my timing is close to right?

 

[condor74]

Thanks Condor. I will check wires and TDC timing to ensure I'm not 180 off.
I am getting gas. I could see vapors when i pressed gas pedal and I could smell it heavy in my exhaust. I think I'm getting way too much gas. But why would that cause a backfire if my timing is close to right?

I don't think it is because of your timing being off or 180 out by what you describe. It sounds like you crossed a couple plug wires when you had it apart. make sure the firing order is 1 8 4 3 6 5 7 2. a lot of times 5 and 7 are easy to cross.

 

[JG1966]

I don't think it is because of your timing being off or 180 out by what you describe. It sounds like you crossed a couple plug wires when you had it apart. make sure the firing order is 1 8 4 3 6 5 7 2. a lot of times 5 and 7 are easy to cross.

Exactly Condor, but it ran fine when I first started it and I haven't touched spark plug wires -- other than removing spark plugs one at a time to clean off gas. I guess something could have gotten crossed then but I really don't think so. I will double check anyway.

 

[brian6pac]

You didn't loose the check weight under the squirter nozzle did you?
Check and see if you have a good squirt when you open the throttle.

 

[JG1966]

Ok. Here's the deal. Firing order and plugs wires are right. I took out No. 1 spark plug, turned engine by hand and had a friend plug hole until pressure blew out his finger. Piston was at top, both pushrods are loose enough to spin and timing mark was at 0. My rotor is pointing at No. 1 cylinder. I'm definitely not 180 off and timing is certainty not off enough to cause a backfire.

 

[JG1966]

You didn't loose the check weight under the squirter nozzle did you?
Check and see if you have a good squirt when you open the throttle.

No. I used weight. It had a spring in there originally. I used the weight from rebuild kit. I definitely am squirting.

 

[Fran Blacker]

Your exhaust pushrod wouldn't spin if it was on exhaust stroke. The exhaust would be open. Distributor 180 deg's out, my bet?

 

[JG1966]

Your exhaust pushrod wouldn't spin if it was on exhaust stroke. The exhaust would be open. Distributor 180 deg's out, my bet?

Thanks, but I edited previous post after getting friend to help. I was on exhaust stroke before not compression. I'm not 180 off.