Got Shell 93 Octane and now barely idles 1973 Dart 340

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Setting has to be determined with testing.

If depressing the throttle is needed when the engine is warm or hot, then that may be an indication that the carb is partly choked, rich, or is leaking fuel.
1) Is the choke plate at the top (the top flap thing) fully opened (vertical) after it has run a few minutes from a cold start in warm weather? When you try a warm restart, pump the accelerator 1/4 and release, and then go look at the choke flap. Is it still open?
2) While idling and fully warmed up, look straight down in the carb throats with a flashlight and see if there is any fuel dripping.
3) Stop the engine and watch and see if any fuel drips down the throats. Open the throttle slowly 1 time all the way and hold it; some fuel will squirt in to the primary throats. Look down into the bottom below the throttle plates and see if there is fuel pooled in the bottom of the manifold.

BTW, this thread may be better restarted over in the Fuel and Air section.
 
I don't have a compressor to blow out the idle circuit. Any other way?

Choke is open warm. I will look down the carb throats. I went on 2 test drives and seems to drive well at speed with power, but just seems to be to rough a idle. I will double check for vacuum leaks.

The engine doesn't seem to shake itself like a cylinder cut out or a misfire just seems not as smooth at times.
 
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Disconnected the vacuum line to the brake booster and plugged the manifold fitting. I got my highest vacuum reading setting the A/F mixture screws at 15.5-16" of vacuum. Plugged the vacuum advance and advanced the timing until the the RPMs raised and lock down the distributor and set the idle speed to 850 rpms.

Then reconnected the brake booster and started the engine and it's running like crap with vacuum gauge bouncing from 12-15" of vacuum and a higher idle. I cover the choke with my hand and rpms go up but still running like crap. Plus the hissing is back and I can hear it directly coming from the brake booster check valve via my ear and the noise via touch.

Looks like the brake booster/check valve is bad causing another vacuum leak. The hissing started at the same time of this issue started and the brake pedal has been soft and low since I got the car.
 
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nm9stheham said:
You will need tools to keep this type of car in good shape. Your first needs to be a timing light if you don't have one.

Timing by ear can be a disaster. Read pages 3 and 4 of this thread: Problem with Mighty Demon 750
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I do have a timing light and look at initially with it and it was at the top of the marks about 10 degrees someone told me on the thread by the marks. Earlier in the thread I stated that the balancer timing mark initially was at the very top mark just past (below) the water pump housing. It was stated that this was not optiumum. So I advanced it just a little until the RPMs raised and then backed it up. Without anymore timing marks on the engine, how are you to know what to set it at? I have since put it back to 10 degrees until I have the brake booster done.

Per this thread: 340 timing need some advice on rufff timing

"It's not uncommon for 340's to want 20* of initial timing. You might want to toss the factory timing specs in the garbage, they aren't set up for best performance. You've also changed things some, that throws a wrench in things.

Basic idea with car at idle speed you want, turn the distributor giving more advance, if the engine picks up RPM, it wants the advance. reset idle to where you want and repeat. You'll reach a point where it won't speed up much at all, you found where the engine likes initial timing level. As long as it will start when warm, not kicking back on starter or straining you then need to work on the mechanical curve in the distributor."
 
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And the thread I referenced was done by someone who did it by ear. Lucky there were no broken pistons.

Keep in mind that they guys doing as you cite have a lot more experience, probably better known carb setups, and a 'feel' for this process. Do as you think best but just be aware that you can get carried away. I would gain confidence in the carb setup and not being lean anywhere before tackling timing; lean + too advanced is a great formula for detonation.

As far as timing marks beyond 10 BTDC:
1. Set the engine at TDC. Then move the damper mark CCW to 10 BTDC in the timing cover scale, and make a new mark on the damper right by the 0 degree timing cover mark. This is your new 10 BTDC mark.
2. Move that new damper mark CCW to line up with the 10 BTDC mark on the timing cover and make another mark on the damper beside the 0 degree on the timing cover scale. This is now your new 20 BTDC.
3. And so on for 30 and 40 degrees if you like.

Now you take your timing from the new damper marks and reference them to the 0 degree mark on the timing cover scale. You can also buy and apply a timing tape to put on the damper that will have fine timing marks on it ready made. Easy to read in fine increments.
 
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^^^^^^ LOL.... I've been marking my timing marks like that for years... WORKS !! :D
 
nm9stheham said:
And the thread I referenced was done by someone who did it by ear. Lucky there were no broken pistons.

Keep in mind that they guys doing as you cite have a lot more experience, probably better known carb setups, and a 'feel' for this process. Do as you think best but just be aware that you can get carried away. I would gain confidence in the carb setup and not being lean anywhere before tackling timing; lean + too advanced is a great formula for detonation.

As far as timing marks beyond 10 BTDC:
1. Set the engine at TDC. Then move the damper mark CW to 10 BTDC in the timing cover scale, and make a new mark on the damper right by the 0 degree timing cover mark. This is your new 10 BTDC mark.
2. Move that new damper mark CW to line up with the 10 BTDC mark on the timing cover and make another mark on the damper beside the 0 degree on the timing cover scale. This is now your new 20 BTDC.
3. And so on for 30 and 40 degrees if you like.

Now you take your timing from the new damper marks and reference them to the 0 degree mark on the timing cover scale. You can also buy and apply a timing tape to put on the damper that will have fine timing marks on it ready made. Easy to read in fine increments.
Click to expand...

Thank you for the advice and the tips which have been very helpful. I much appreciate it! I always side on the conservative side with caution. I will get the booster fix first and then get the carb and timing set,

What do most people set the initial timing for their mild 340s at?
 
OBTW, I made a mistake: turn the crank CCW to make the 10-20-30 BTDC marks, not CW. Sorry. I'll correct the prior post. I woke up in the wee hours realizing I'd told you wrong; it was 3:40 AM oddly enough LOL

Keep in mind that total timing has to be kept in mind. If you have a stock distributor with 20-22 degrees mechanical advance, then if you ended up with 20 degrees initial timing then the total would be 40-42. OK for light cruising, or a low compression truck engine (maybe!), but well past the recommended maximum of the mid 30's for an engine that gets beat upon and with some reasonably high compression. So, since you don't know your distributors mechanical advance curve, then the low 10's for initial timing is where I would stay. We are at 15 initial with a 10:1 CR 340, but we also have AL heads and quench, which help to combat detonation. 'It' (the engines idle) would like more, but we knew we were pushing the limits of advisable total timing, without modifying the mechanical advance. Your engine has unknown internals; just IMHO, better safe than sorry.
 
No worries. Thank you again and everyone for all their help. It's been about 25 years since I work on one of these. I set the timing back to about 12 degrees just a hare above the 10 BTDC mark, which where it was originally.

I am dropping it off at the shop that rebuilt the front end for the brake booster tomorrow morning and I am going to have the master cylinder done as well. The brakes have been low, soft/spongy since I got the car. They did look at that initially, but I noticed that just tapping the accelerator with the brakes fully engaged it will not hold the car.
Once the booster is replaced, then fine tune the carb and it should be good. With the booster disconnected/manifold plugged it runs steady 16-17" vacuum idling well. Shut it off and connect the brake booster line then vacuum gauge is reading 12-15" with a floating, irregular needle. I cover the choke plate with a shop rag and idle speed increases. I tried this with the brake booster connected and the idle speed does not.
 
So now you are up to 17 inches at 850 and 12 degrees initial.
I'd call that a stock cam.Or real close to it.
In which case, I would set the power-timing to 34/36, and let the initial fall where it may.
If you mark your balancer, with the hillbilly timing tape method, be advised that, after 3 copies, the 40* mark can be off by several degrees. The marks will be exactly as accurate as you make them.Stock 340s like a lot of power-timing.If your 36* mark is closer to 38 or 40, well, don't be surprised if things get expensive.
Timing tapes are like 7 bucks.....
 
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AJ/FormS said:
So now you are up to 17 inches at 850 and 12 degrees initial.
I'd call that a stock cam.Or real close to it.
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If I advance the distributor about a 1/4" more I get a higher idle and it runs better, but I don't see the stock damper mark anymore with my light until I add the custom damper marks. It could very well be a stock cam and have no doubt it is not. The Carter AFB is 625 cfm and I believe its stock compression, stock intake and exhaust manifolds.
 
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340s are supposed to idle rough. That's why we found them attractive back in the day; Factory race motors.
But I get the sense that your 340 is rougher than most.
Here's the deal; A stock 340 came with 5 Measely degrees, and stick cars idled just fine at 650 rpm with those 625AFBs.(I don't recall A/Ts, cuz I never had one). Power-timing was 36*.
So if your T-port sync is right, your Carter should also idle just fine at 650/700.
With the correct T-Port sync ; if yours does not, then it may have a mechanical issue.
So Having proved the T-port sync correct,and it is still rough, then you will have to do a compression test.And maybe a LD test, and maybe you will have to check the cam lobes or the cam-timing.
But before I would do that, I would pull the plugs for inspection. And I would check out the wires. These are easy to prove OK or not, and cheap to replace, if bad.By this time I'm assuming that the vacuum leaks are gone. I'm also assuming that your funky new carb-adapter has not introduced it's own odd running characteristics.I'm also gonna assume those EGR tubes in the bottom of your intake have been mechanically plugged, and that the AFB idle circuits are working. So that's a lot of assuming going on.But after all, we are on page 5 already.
But if the T-port sync has never been set, then you can spend hundreds of dollars and still have a crappy-running engine.Since I have not yet seen a report that yours is ok, Im assuming you havent checked it; and we are half way through page 5.And I'd rather not hear anymore about where your timing might be. You need to know where it is--exactly where it is ..This is most important as the rpm climbs,and as the loading increases.
 
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Excuse my ignorance here, but I have heard the term transfer port sync before. I worked on some Mopars in my high school years in 1980s and read it in your signature. I don't understand the first part, but I am seeing my old school mechanic tomorrow and see if he is clear on it. He is about 10 yrs. older than me.
Specifically this part:
"Transfer-Port sync; 1)With the speed-screw,set the t-port exposure under the T-plates,to about square to a little taller than wide. 2)Adjust the idle speed with bypass-air,and idle-timing."

I still talk to my HS auto shop teacher and will ask if he has heard the term and can explain in detail. He used to race a Coroner 426 max wedge in the 60s. Vacuum leak and plug inspection will be done first priority. I want to keep the engine mostly intake to 1973 as possible. Emissions stuff and all. The is a driving piece of Mopar history which is all my son and I want to do. Just a cruiser. Next update will be when it's fixed.

Thanks!
Eric
 
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Reply per my HS Autos teacher when asking about transfer port sync:

I found it interesting to pick his brain on the old school stuff and he was always my favorite teacher. He is probably in his late 60s now.

"Eric, you are making me dig deep into the memory bank. Things were word of mouth ‘in the day’ and magazine how to articles regarding performance were lots of engine builds, header selection, cam tests and how to tips on Holly carbs. I heard some info about it, probably ½ was wrong. Never played with that method myself. With high octane fuel readily available and cheap and no tail pipe emissions to worry about there were lots of problems solved by advancing the timing and richening the jets. A problem at the time, before reduction gear starters, was being able to crank the engine over with lots of initial advance. I remember rigging one engine with a switch on the primary side of the ignition so that the starter could get some engine speed going before the ignition was energized. Detonation also took its share of pistons. Sometimes things were pretty rude and crude."
 
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Got a call from my guy that was looking at engine and master cylinder/brake booster. The master cylinder was leaking and the brake booster is bad, but that is the least of my concerns.

He determined after running a scope that cylinders 5 and 6 were misfiring and confirmed by pulling spark plug wires on both cylinders with RPMS not dropping. He pulled spark plug on cylinder #5 and the side electrode was smashed to the center electrode like some had dropped it before installing it. He used a borescope and the top of piston #5 looks good.

A leakage test was done and 40% leakage on cylinders #5 and #6 was determined with hissing and vacating via the valve cover breather. He is telling me that the piston rings are bad, but no way to tell with dissembling. That is could have gotten real hot/overheated at some point, but this do not occur in my possession. It has been driven on the gentle side with me cause I know it's a 43 year car and has never been north of 50 mph.

I bought the car last Nov. and briefly drove it 10 miles before storage and snow in the Chicago area. It sat until this April and might have 250-300 miles on it before this. When I test drove the car it seemed to run OK at best, but when I had the front end work done, which I knew the ball joints and steering gear was bad at the sale time and the low brake pedal. The engine never appeared to have an ignition miss until that longer drive about 20 miles with getting gas. I was able to email the previous owner through the place that I bought the car outside St. Louis. Mind you I was told at pre-sale that the engine was supposedly rebuilt close to 20 years ago and has about 3,000 miles on the rebuild. The odometer has 95,000 on it but the 9 is not crisp and clean like the other digits, but it is a 43 year-old car.

Just by the look of the carb/intake gaskets, the mickey mouse of the heat control valve vacuum lines and the exhaust and and intake manifold gaskets not looking like 3,000 miles, but closer to 90,000 miles. I believe probably from the beginning the engine was running on 6 cylinders and always seem to sputter some water out the tail pipes until it got hot, which seemed to take a long time to warmup. When I started the car in April while diagnosing the brakes and lack of power assist, the engine had 12-14" vacuum at best. It was rough running and seemed to lack power, but it does have larger P235 tires on the rear. I had test driven a 1971 Duster with a 360 that had a lot more power, but I thought it was just cause it was a later 340/240 HP.

My mechanic is not into rebuilding engines nor has a machine shop that does, but he said it can get real expensive to do that. He recommends for now to get mild 360 performance engine built with 350-375 HP and pull the 340. The engine currently in the car is not original but the car is an H code. I will hold on the 340 and possibly pull it apart myself to see what happen.

Here is my response from the previous owner. Mind you I am not going to waste $1,000 to transport the car to from St. Louis:
Eric

That car was running great and driving great when it was sold . The miles are correct on the rebuilt engine ...I know because I personally bought this car in California in the very early 90's and then I bought it back from the guy I sold it to, only 20+ years after I sold it to him..... He had an engine built for it using most of the original "hard" parts except for the block as it was broke...

This was a great running car last fall while in the showroom and I can't imagine why it would have a problem now



However, with all that being said , this is the only solution I can provide 8 months after the purchase of a 43 year old classic car

which do not have warranties .... If you can get the car here I will personally have the engine diagnosed at our recommended engine shop which is very

close to our showroom here at F*** L*** and I will pay to confirm your diagnosis ...

If my shop confirms your diagnosis then I will handle payment for repairing the broken piston rings myself


I will not pay for a repair provided by any other vendor or repair shop at any other location, in any state

This repair offer is good for the engine only , as the brakes will have to be covered by you .....

Again, I would be paying for this out of my pocket because the car came from me thru F*** L*** to you

Best regards

Mark H****

Service Mgr
 
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Pretty nice offer for someone who has zero liability on a classic car 8 mos after the sale.
Wonder why.
I think if I were you I would just pull that 340 and stick a basic 360 in it until I got the 340 done.
At least you could drive it.
 
TrailBeast said:
Pretty nice offer for someone who has zero liability on a classic car 8 mos after the sale.
Wonder why.
I think if I were you I would just pull that 340 and stick a basic 360 in it until I got the 340 done.
At least you could drive it.
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When I bought the car, part of the negoigated deal was to have it trailered to the Chicago area at no additional cost. He knows that I don't have the means to transport the car 6 hrs one way and to pay for it myself would probably be $500 each way, plus my time off of work. I think he is calling bluff and would the bare min. just to get it to run.

I am looking at a 360 classic cruiser build by MRL Performance for now and then put the 340 on a stand in my garage, so that my son and I can work on it and see what went wrong.

It all sounds suspicious or questionable.
 
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Probably would indeed do the bare minimum. 3000 mile on a rebuild that long ago will be variable. If it was left sitting for several years and formed rust in cylinders, then it could possibly damage the rings/bores/pistons. Needs to come apart to really see what is what.

If 'twere me, I'd put some Marvel Mystery oil in the cylinders 5 and 6 and let it set a while and work it over by hand several times, and add a bit of MMOil each time, just on the off chance that the rings have gotten stuck in the grooves due to old crudded oil in the ring grooves. It may be a 'hail mary' with low odds to do any good, but you never know 'til you try. Stranger things have a happened inside engines. 'specially since cylinder 5 was obviously dead with the bad plug. And it would be worth seeing how it runs with #5 alive again.

Water out of the tailpipes while warming up is normal BTW. That is not any specific indication of problems.
 
nm9stheham said:
Probably would indeed do the bare minimum. 3000 mile on a rebuild that long ago will be variable. If it was left sitting for several years and formed rust in cylinders, then it could possibly damage the rings/bores/pistons. Needs to come apart to really see what is what.

If 'twere me, I'd put some Marvel Mystery oil in the cylinders 5 and 6 and let it set a while and work it over by hand several times, and add a bit of MMOil each time, just on the off chance that the rings have gotten stuck in the grooves due to old crudded oil in the ring grooves. It may be a 'hail mary' with low odds to do any good, but you never know 'til you try. Stranger things have a happened inside engines. 'specially since cylinder 5 was obviously dead with the bad plug. And it would be worth seeing how it runs with #5 alive again.

Water out of the tailpipes while warming up is normal BTW. That is not any specific indication of problems.
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I know my mechanic suggested letting some top end cleaner soak in cylinder #5 overnight to give that a try. This explains the exhaust tone changing cause it was dropping 2 cylinders. It kinda just sucks after this developing on it's own without knowing the whole history of the engine. This is just to make my current matters worse. This can be fixed. In the past week, I have found out that my father is terminally ill/end of life after years of dementia.
 
After a few days of debating and researching, I decided to go with the 360 LA engine Classic Cruiser build from MRLPerformance, since it is comparable to the stock 340 that was in there. I'm not too concern since it was not numbers matching anyway and will try to make it look like the 340 as much as possible.

I will move over the alternator, power steering and the stock 340 exhaust manifolds. I will have the front 727 transmission leak addressed and change out the u-joints as well, since they were making some clunks at times.

Is there anything that I need to be concerned with swapping the 340 for the 360 that will not be compatible?

I will then tear down the 340 as time allows when it is in my garage to try and find out what went bad. A stressful decision and felt like I was kicked in the groin, but it will work out in about 4-5 weeks.

Happy Father's day to all the Dad's out there. I paid a visit to my Dad today, please cherish all the moments that you can with your kids.
 
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