Multiple starting issues maybe my fault

[harmony]

The problem I'm having may have been caused by my lack of attention to reading the manual properly. So I guess that's a good place to start. I was replacing my broken heat riser spring , on my 48 Chrysler 6 cyl. 251ci. It was broken when I got the car and other than being a little hesitant in cold weather for the first 5 or 10 minutes, the engine worked just fine. I'm thinking I should have left well enough alone. Anyways so when I wound the spring I looked at the paragraph just below the picture starting out “ when reassembling,,,” I failed to notice that that paragraph was referring to the 8 cylinders. It mentioned it should be about 1 1/4 turns. The previous paragraph is for my C-38 where it mentions to wind the spring 3/4 turn.

So I fired up the car and after about 10 minutes of driving it started to miss a bit and it got worse and worse and then backfired through the carb I believe, but I wasn't sure. I managed to get home which was another 10 minutes with a couple more backfires. It took a lot of throttle to keep it running but once I parked it I let the throttle off and it died.

This all may be a coincidence but when I tried to start it again about 3 weeks later (bad winter weather and parked outside) it would turn over but wouldn't fire. After a bit of troubleshooting I discovered I didn't have any spark. It had a new set of points and condenser about 300 miles ago. I then pulled the coil wire and it was rusty at the distributor end. I discovered that coil wire had no continuity. So I replaced the coil wire. My coil had a low number for resistance on the primary side 1.1 ohms resistance, so I got the coil from my parts car and it was 1.4 which was within tolerance, so I swapped coils. I also replaced the condenser with a brand new one from NAPA. I now had spark.

It now fires up, but it shoots up to around 2000 rpm immediately for a few seconds and then quits. I had a spare carter B&B EV1 carb that I recently rebuilt at the same time that I rebuilt the one on the engine. I tried them both on the car back when I rebuilt them about 500 miles ago and they both worked fine so I put one in the trunk for an occasion just like this. I swapped carbs and I got the same result. I read on line that the coil, if faulty can cause the car to start but then quit. So I bought a new coil, even though the primary and secondary readings seemed fine. (seconary side 8.4 ohms resistance)

I checked the compression and the front 3 cylinders are about 112 and the back 3 cylinders are about 115.

When it fires up I can keep it running sort of, if I keep working the throttle but it backfires through the carb. However if I hold the choke completely closed it will keep running without any throttle although,at a very high rpm.

So to me it sounds like I have a vacuum leak, but the vacuum line from the distributor to the carb seems fine and since I was swapping carbs I was conscious of making sure it was tight at the carb

So I'm wondering if with the heat riser being kept closed as the car warmed up with that extra tension keeping that heat riser door completely closed, not allowing the exhaust out, and also backfiring, I'm wondering if I blew an intake manifold gasket? If so is there anyway of checking that other than pulling off the manifolds?

Does all this sound related? If so, why would I loose spark? Oh btw, the distributor is tight so I'm confident the timing hasn't changed.

Any thoughts and ideas are very appreciated.

[greg g]

The position of the flap that controls the direction of the exhaust path is fully clockwise when the engine is up to temp.  The fully counter clockwise position which puts the flap in the vertical position is the one that directs exhaust gases up into the intake manifold exchange before exiting.  Wire it to stay in the fully clockwise position and see if things return to the pre tinkered with "normal"

 

The fast idle cam and linkage works in conjunction with the choke linkage.  It shouldn't have gotten involved when you were installing the spring, but stranger things have happened.

 

An overly heated intake charge can cause a lean burn condition which matches your loss of power and back firing.

Edited March 3, 2021 by greg g

[desoto1939]

When the weather is real cold and you canget the engine to turnover and the engine to run check the base of the carb. See is you are getting a white ice forming on the base of the carb whne it bolts to the manifold.  The heat riser is used to heat up the base of the carb on cold winter days and night and to prevent the ice from forming on the base of the carb.  This happened to my 39 desoto so that durin ghte winter months when driving the car and then coming to a red light the car would stall and quit becasue of the ice formation. So if the Heat riser is not working then you would have to pull out the throttle or choke to make the engine run faster and then when moving again relese the choke.

 

If you have a leak at the manifold start the engine get it warm then take a can of WD40 with the little extention plastic pice and go along the gasket area where is bolts to the engine block. Spray some as you go along the entire length. if the engine runs smoother then you will notice it when you find the broken gasket also test where the two halfs are bolted together same process.

 

Also there isa gasket that goes under the base of the carb if you do not have a govenor onthe car check that this gasket has 4 slots and one of the slots will match up to a hole in the base of the carb and manifold.  This is needed to have this carb.

 

Rich Hartung

desoto1939@aol.com

[keithb7]

If you are interested, here is a pic of the underside of where your carb mounts. Bottom view of the intake manifold. The exhaust gas is deflected up into this cavity area to quickly heat up the carb base. Helping gas vapors stay in suspension. 
 

 

[harmony]

1 hour ago, greg g said:

The position of the flap that controls the direction of the exhaust path is fully clockwise when the engine is up to temp.  The fully counter clockwise position which puts the flap in the vertical position is the one that directs exhaust gases up into the intake manifold exchange before exiting.  Wire it to stay in the fully clockwise position and see if things return to the pre tinkered with "normal"

 

The fast idle cam and linkage works in conjunction with the choke linkage.  It shouldn't have gotten involved when you were installing the spring, but stranger things have happened.

 

An overly heated intake charge can cause a lean burn condition which matches your loss of power and back firing.

What do you mean by an overly heated intake charge Greg?

[harmony]

1 hour ago, desoto1939 said:

When the weather is real cold and you canget the engine to turnover and the engine to run check the base of the carb. See is you are getting a white ice forming on the base of the carb whne it bolts to the manifold.  The heat riser is used to heat up the base of the carb on cold winter days and night and to prevent the ice from forming on the base of the carb.  This happened to my 39 desoto so that durin ghte winter months when driving the car and then coming to a red light the car would stall and quit becasue of the ice formation. So if the Heat riser is not working then you would have to pull out the throttle or choke to make the engine run faster and then when moving again relese the choke.

 

If you have a leak at the manifold start the engine get it warm then take a can of WD40 with the little extention plastic pice and go along the gasket area where is bolts to the engine block. Spray some as you go along the entire length. if the engine runs smoother then you will notice it when you find the broken gasket also test where the two halfs are bolted together same process.

 

Also there isa gasket that goes under the base of the carb if you do not have a govenor onthe car check that this gasket has 4 slots and one of the slots will match up to a hole in the base of the carb and manifold.  This is needed to have this carb.

 

Rich Hartung

desoto1939@aol.com

The thing is I can't keep it running to try the WD40 Rick unless I want it roaring like it's staging at a drag strip!

[greg g]

If the flap doesn't move to the fully clockwise position when the engine is hot it will continue to heat the intake manifold when the heat is no longer needed for proper running. This could cause the mixture to lean out from higher than needed intake temperatures.

 

My heat riser is gutted and has a block off plate between the manifolds.  I have driven in temps from the low 40s to the mid teens with no I'll effects other than requiring the choke a bit longer during warm up.

[harmony]

8 minutes ago, greg g said:

If the flap doesn't move to the fully clockwise position when the engine is hot it will continue to heat the intake manifold when the heat is no longer needed for proper running. This could cause the mixture to lean out from higher than needed intake temperatures.

 

My heat riser is gutted and has a block off plate between the manifolds.  I have driven in temps from the low 40s to the mid teens with no I'll effects other than requiring the choke a bit longer during warm up.

But wouldn't everything go back to normal once the engine cools and the flapper returns to the fully clockwise position?  In my case I removed that new spring, at least until I solve this issue so the flapper is non functional and rests in that fully clockwise position.

[kencombs]

The symptoms sound like a lack of fuel to me.  Pump, filter, clogged line etc.

 

The exhaust heat riser would not have the effect you describe when starting, it  would only cause problems when fully warmed up.

 

And, always double check points and condenser.  Most carb problems are ignition caused.  Old (older than me!) mechanic told me that years ago.  Turned out to be true.

[harmony]

I forgot to mention that I have a glass fuel filter just before the carb.  It's getting good fuel flow.  Also when I checked the compression I pulled the fuel line off the carb and let it flow into a glass bottle.  It was a good strong consistant flow of gas. In one of my earlier posts awhile back I mentioned that I had fuel pump issues and I got a brand new fuel pump that has about maybe 500 miles on it.

[harmony]

When I replaced the condenser I also checked the point gap and it was still at 20.  Since they have very few miles on them they still look new but I ran a points file over them and sprayed them with brake clean to be sure.  The lobe follower on them is still in good shape. They have a strong and consistant spark. 

[keithb7]

I’m doubting the exhaust flapper valve has much to do with the rpm complaints. However we are blind here, can’t see whats going on. 
 

My exhaust flapper valve is wired shut on one of my cars. It doesn’t seem to cause me any issues. I don’t drive it in winter months though. 
 

You’ve certainly got an interesting combination of symptoms going on. Maybe more than 1 thing is acting up. I’m thinking fuel related somehow. Yet carb swapping never fixed it. Back firing thru the carb? High idle. Wont run. Hmm. Wish I was there to help troubleshoot. 

 

[harmony]

9 minutes ago, keithb7 said:

I’m doubting the exhaust flapper valve has much to do with the rpm complaints. However we are blind here, can’t see whats going on. 
 

My exhaust flapper valve is wired shut on one of my cars. It doesn’t seem to cause me any issues. I don’t drive it in winter months though. 
 

You’ve certainly got an interesting combination of symptoms going on. Maybe more than 1 thing is acting up. I’m thinking fuel related somehow. Yet carb swapping never fixed it. Back firing thru the carb? High idle. Wont run. Hmm. Wish I was there to help troubleshoot. 

 

Yes you're right Keith.  None of it sounds related.  But everything went south 10 minutes of run time after I installed that heat riser spring with too much tension.  None of it makes sense.  It ran almost perfect starting flawlessly every time for as long as I've had it except for that fuel pump issue.  I can't understand why that coil wire rusted up and stopped sending spark??? I mean the rust was heavy around the end of the coil wire.  It took a lot of sandpaper wrapped around a phillips screwdriver to get the rust out of the distributer cap end.  Turned it upside down and the rust would have probably filled half a sewing thimble.   

I pulled the top off the carb before I swapped it and not a speck of dirt in it and the float bowl was set to the proper level and all the circuits inside seemed to be free and operating just fine.  ??????  

It sounds like a vacuum issue to me.  It's getting too much air and demanding more fuel to compensate so it's runing at high rpm right away.  That's just a theory since it will stay running at a high rpm if I keep the choke completely closed.  Btw, I can do all this because I have one of those trigger gismos that you clip on to the starter so I can stay under the hood.

[Doug&Deb]

Did you reinstall the heat riser spring to the correct tension? I made the same mistake years ago on my D-24. It would run for about 10 minutes until the fuel would boil in the carb causing vapor lock. Reinstalling the spring solved the problem.

[greg g]

Keep in mind the spring is bi metallic. It not the tension of the spring at work here it is tightening when heated and contracting when cool that is, the spring tension is basically to keep the flapper from flipping around with the flow of exhaust gasses.  It wants to be a directional vane not a flag. So the cold at rest position is for the flap to be vertical forcing the flow up into the cavity in the pic Kieth pasted.  If the spring weren't there the flap would go horizontal when you step on the gas and volume and flow speed increase pushing  the exhaust out rather than up first.

 

Have you checked to see if your choke is fully open when the engine is up to temp??  I am assuming it an auto choke being it's a Chrysler.

[Plymouthy Adams]

Correct me if I am wrong but was not this article by our own former member Graybeard?    A recommended read.

 

Exhaust Heat Risers Debunked – Myth and Fact (dodgepilothouseclub.org)

 

[harmony]

46 minutes ago, Plymouthy Adams said:

Correct me if I am wrong but was not this article by our own former member Graybeard?    A recommended read.

 

Exhaust Heat Risers Debunked – Myth and Fact (dodgepilothouseclub.org)

 

Thanks for that.  Too bad I didn't come across that article before I decided to replace it.  

[Plymouthy Adams]

I can only say that there are many a white paper on many subjects posted on the internet that are quick to access, good information and only a few words typed to find verse some of the time involved back and forth messaging on the forum.  I will not ever knock the forum for information except to say the answers are not always timely whereas a search and read on the internet is only limited by your wanting to get proactive in the learning process.  The forum can often glean the smaller particulars based on model but the principals of x systems are always just a few words away doing a search.

[kencombs]

I have owned a couple of vehicles with the carb icing issue described in the article.  In both cases the symptoms were alike.  It only reared its head under ,certain conditions.

 

High humidity and temps in a certain range, above freezing but below 50 or so.   They would start and run fine for a few minutes.  Then would refuse to run above idle.  The cause was a huge ice mass forming on the venturi and blocking airflow.

 

Easy to spot once I figured out the suspected problem, just pop the top of the air cleaner and look.

 

But, in my case they were starving for air, not fuel and choke would just make it worse.

Edited March 3, 2021 by kencombs

[Silverdome]

Have you checked the static timing? I'm thinking the backfire might have caused timing chain/gear damage possibly. If you think it's a vacuum leak block of the top of the carb completely, if the problem remains then check all vacuum lines and ports then carb and intake gaskets.

[keithb7]

Things can happen unknown to us, causing bad symptoms that leave us scratching our heads.  Try and erase all you have done, and start over like you have no knowledge of the work you did. Start fresh and begin trouble shooting. The recent work you have done is likely influencing and limiting your troubleshooting to solve this.

 

Here is an example:

 

I had a decent running engine. I took out the spark plugs to gap and clean them. Put them back in. All plug wires were labeled upon disassembly and put back in proper order.  Car would not run right. Very hard starting. Misfiring bad. Would not idle. What the heck did I do? It was a simple task. I started tearing in and checking things. Ignition system, fuel, you name it. I was scratching my head like you are now. I was running out of things to check strictly related to the work I had just done. I was flustered. Finally I broke down and started over with a compression test. I found a couple of low psi cylinders, and 1 was completely dead. I took the head off and found a bent valve. WTH? Why? I dug around a bit with a flash light and a mirror and found the remains of a small hex screw.  1 piece was in the cylinder, another in the exhaust port. The screw sure looked like one that would mount a voltage regulator to the firewall. Which happened to have 1 of the 4 mounting screws missing. The car was new to me at the time. I had only owned it for about 3 weeks.  The previous owner had probably dropped a screw and never found it. Seems that it landed down in the well of the sparkplug  mounting hole in the cylinder head. Where it sat, until I lifted the plug out. Into the combustion chamber it dropped. Unknown to me, I had put the sparkplug back in and started the engine. A bent valve was the result.  I learned a couple of good lessons from my example:

 

1. Be diligent in using compressed air around the spark plug base to clean out any dirt or other foreign objects

2. Asking questions on the internet will get you tons of different answers, leading you down various paths. Getting the right answer from someone, is like winning the lottery.

    Kind folks offering assistance are blind to what you are seeing there at the car, throwing out ideas to check. Also their responses are influenced by their personal             experiences. 

3. Open your mind to any and all options when troubleshooting.  Don't zone in on the work you did. Old cars have about 1 million things that can go wrong and compound.

4. Study automotive theory. Read lots about it. Then lots more. A deep understanding of all automotive systems will improve your troubleshooting skills immensely. 

5. I leaned how to do a valve grind by hand. Lol. That was the biggest lesson.

 

My problem is likely not your situation at all. I used it as just an example how things can unfold with car maintenance sometimes.  To maybe guide you to remove the blinders you may have on, due to the work you just did. Good luck. Keep at it and report back. We can help guide you. 

 

Just because we all like photos....Here was my eureka moment when I pulled the head. Doah!

 

 

[Hamilton]

As someone mentioned, we're kind of flying blind here, but I suspect (coincidences happen, after all)  that you have more than a single issue to identify/address. 

 

I was trying to think of whether there was any way possible for an accelerator pump to act up so badly that it would inject fuel briefly at start up (causing the brief spike in RPMs you mentioned) but then not deliver it upon acceleration (causing the backfires).   However, given that you said both carburetors worked before, but neither does now, other than a possible leak at the mounting point, we might safely assume that component isn't an issue, which is why I think you're dealing with more than one.

 

The inability to idle without constantly working the throttle and the 2K idle when holding the choke closed both speak to your air/fuel mixture - the likely culprit, as mentioned in earlier responses, being a vacuum leak.  The good news is that the number of locations for a vacuum leak to occur is pretty limited on these old flatheads.  Still, you need to diligently and carefully check them all.  

 

You're probably also looking for an electrical and/or timing issue.  Worn or sticking distributor components can cause backfires, as can something as simple as a hairline crack in a distributor cap.  It's just a matter of testing and eliminating one potential culprit at a time.

 

On the subject of backfires: it shouldn't be too difficult to identify the source.  Obviously, the direction from which the sound came is a major clue.  If you're uncertain of that, think back in your mind's ear to how they sounded.  A carb backfire is more of a popping sound (sometime pretty loud, to be sure).  On the other hand, tailpipe backfires are typically more of the BANG! variety and can even sound like gunfire, an attribute I wouldn't associate with one emanating from a carburetor.

 

Good luck!  Let us know what you find.

[Kilgore47]

If your problem is a vacuum leak - One source could be the vacuum advance module.  The diaphragm can fail over time.  The one on my P15 failed.  I disconnected the vacuum advance tubing at the base of the carb and plugged it as a temporary fix to get the engine to run and idle.       

[harmony]

7 hours ago, keithb7 said:

Things can happen unknown to us, causing bad symptoms that leave us scratching our heads.  Try and erase all you have done, and start over like you have no knowledge of the work you did. Start fresh and begin trouble shooting. The recent work you have done is likely influencing and limiting your troubleshooting to solve this.

 

Here is an example:

 

I had a decent running engine. I took out the spark plugs to gap and clean them. Put them back in. All plug wires were labeled upon disassembly and put back in proper order.  Car would not run right. Very hard starting. Misfiring bad. Would not idle. What the heck did I do? It was a simple task. I started tearing in and checking things. Ignition system, fuel, you name it. I was scratching my head like you are now. I was running out of things to check strictly related to the work I had just done. I was flustered. Finally I broke down and started over with a compression test. I found a couple of low psi cylinders, and 1 was completely dead. I took the head off and found a bent valve. WTH? Why? I dug around a bit with a flash light and a mirror and found the remains of a small hex screw.  1 piece was in the cylinder, another in the exhaust port. The screw sure looked like one that would mount a voltage regulator to the firewall. Which happened to have 1 of the 4 mounting screws missing. The car was new to me at the time. I had only owned it for about 3 weeks.  The previous owner had probably dropped a screw and never found it. Seems that it landed down in the well of the sparkplug  mounting hole in the cylinder head. Where it sat, until I lifted the plug out. Into the combustion chamber it dropped. Unknown to me, I had put the sparkplug back in and started the engine. A bent valve was the result.  I learned a couple of good lessons from my example:

 

1. Be diligent in using compressed air around the spark plug base to clean out any dirt or other foreign objects

2. Asking questions on the internet will get you tons of different answers, leading you down various paths. Getting the right answer from someone, is like winning the lottery.

    Kind folks offering assistance are blind to what you are seeing there at the car, throwing out ideas to check. Also their responses are influenced by their personal             experiences. 

3. Open your mind to any and all options when troubleshooting.  Don't zone in on the work you did. Old cars have about 1 million things that can go wrong and compound.

4. Study automotive theory. Read lots about it. Then lots more. A deep understanding of all automotive systems will improve your troubleshooting skills immensely. 

5. I leaned how to do a valve grind by hand. Lol. That was the biggest lesson.

 

My problem is likely not your situation at all. I used it as just an example how things can unfold with car maintenance sometimes.  To maybe guide you to remove the blinders you may have on, due to the work you just did. Good luck. Keep at it and report back. We can help guide you. 

 

Just because we all like photos....Here was my eureka moment when I pulled the head. Doah!

 

 

Woow!  I'm always thinking about crud getting in the cylinder when pulling plugs because of that natural funnel in the head around the plug.  I even got a tiny brush out of my tool box, to get as much stuff out of that recess before I pulled the plugs.

 

[harmony]

Problem solved ?   Time for a wobbly pop or even two. 

So I got to thinking about pulling the intake manifold off to check for the gasket to be blown and someone suggested it might even be a cracked manifold.  So I decided to inspect the manifold with a super bright LED flashlight and a mirror.  That's when I noticed the 5/8" plug on the firewall side of the intake manifold was  missing. I got another plug, stuck it in and she purrs like a kitten.  Begging me to take her for a spin.  But the sun is setting and wouldn't you know it, but rain is setting in for a few days starting tomorrow. 

Soooooo, now I'm wondering could all that happened be related or was it all just a bunch of coincidences happening at exactly the same time???