340 slight dieseling when hot and hard start

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carrmann

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Took my duster on a very long road trip from NH to FL (about 1600 miles). Along the trip it slowly started running a little worse. Now when its warm, it doesnt want to shut off immediately(it kind of sputters for a second). It never used to do this. It is also hard to start now after being run for a while (unless I let it cool down). I popped the air cleaner off immediately after it dieseling for a second one time, and noticed vapor/steam coming out of the carb, making me think its leaking fuel past after shut down?? edit: cranks forever before firing, like a flooded condition.

Edelbrock 600 carb(1406), stock manifold with adapterplate, stock exhaust, rebuilt motor with a small cam (unknown specs). Could the 2 issues be inter related, and if so... what would you suggest to fix it?

could it be the carb needs a rebuild?? or adjustment of float bowls?



thanks
 
Sounds like the carb is getting too hot and boiling the fuel.
 
Where is the timing and what do you have for a timing curve?

How hot does the engine run and "don't tell me" the middle of the factory gauge

Vapor lock is always a problem with this "new world order" fuel. Best thing I did for the 67 before I went with EFI was to

Install a rear mount electric pump

pay attention to tube routing

Install a vapor return system using Wix 33040 / 33041 fuel filter

add a carb base insulator

You might consider blocking the exhaust crossover

and CHECK that the exhaust butterfly if you still have one is opening
 
67Dart273 said:
Where is the timing and what do you have for a timing curve?

How hot does the engine run and "don't tell me" the middle of the factory gauge

Vapor lock is always a problem with this "new world order" fuel. Best thing I did for the 67 before I went with EFI was to

Install a rear mount electric pump

pay attention to tube routing

Install a vapor return system using Wix 33040 / 33041 fuel filter

add a carb base insulator

You might consider blocking the exhaust crossover

and CHECK that the exhaust butterfly if you still have one is opening
Click to expand...

All GRATE ideas!!!

Here is a couple more.
Get a quart of water, (atf fluid if your in a area were you can get away with it. aka makes a LOT of Smoke) start eng,remove air cleaner, rev eng to around 3000 rpm. Now, vary slowly, dribble the liquid of your choice into the carbs primary barrels. do not let the eng slow down as you do this.

If its running on, become of carbon build up on the piston. It won't after your done!;)
 
Hard starting, which way?

Won't barely turn over on the starter or cranks forever and won't fire? Those are two "hard" starting problems that are not the same.
 
seafoam, suck half in from brake booster line or other induction method, let sit over lunch and then start it at a high idle and dribble the rest in through the carb. Same deal Cudafever suggested, billows smoke like a sky-writer but will clean intake and chambers like a white tornado. My 340 would be cranky starting when it was hot too, it would crank fast and I would keep pumping the pedal until it finally kicked over, classic vapor lock/fuel boil out symptom. I installed a carter electric pump behind the mech pump and it fixed that. helped during colds starts too, hit the electric pump to fill the bowls and it lights right off.
 
crackedback said:
Hard starting, which way?

Won't barely turn over on the starter or cranks forever and won't fire? Those are two "hard" starting problems that are not the same.
Click to expand...

What he said. If it is kicking back on the starter, probably a timing issue. If you have to crank forever before it fires,more than likely a flooding issue.
 
sorry.. duh lol. it will crank forever before firing. I have a good batt and a mini starter also. cant idle any lower (about 500 rpm in gear, 6-700 in neutral).

I was planning on seafoaming it (full treatment). I thought about the fuel being boring as well...

good idea 95teetee lol.

no idea on temp. stock gauge only. BELOW the middle of the factory gauge... lol.

no idea on the timing now, no way to check it at the moment (dont have my tools, may buy one). what should I set it at?? has all stock ignition.... no idea on the curve, does have vacuum advance.

Should I put insulation of some sort over the fuel line? it runs right on top of the block/manifold.
 
My guess, not enough initial timing.

Low initial timing = more throttle blade opening = dieseling issues
 
What kind of carb? Friend had a 69 GTS 4 speed with the 383 in it. Car ran great until one day it started dieseling, and hard to start. He ended up replacing a piece on the carb itself. I think it was the diaphragm or something like that? He didn't do any thing else but that. Cleared it right up.
 
edelbrock 600cfm 1406 i believe. will take a look at it tomorrow (its in a friends garage until I find a house).
 
crackedback said:
My guess, not enough initial timing.

Low initial timing = more throttle blade opening = dieseling issues
Click to expand...


x2. You can't check now, but you should have checked before you left...lol ;)
Loosen the distributor and turn it about 5° clockwise. The reset the idle speed. If it gets better, leave it - best not to upset the apple cart in the middle of a long trip. Then when you get home plan to tune it for real.
 
My guess is its running a bit hotter in the south. There isn't a lot you can do before heading home except wash the bugs out of the radiator and buy ethanol free fuel, and lower curb idle a tad. If the problems persist at home, adding a spacer under the carb will help.
OOPs maybe you're staying in Florida.
 
yea... the car is staying in FL. never had the issue in NH whatsoever. it developed as the trip went.

Im buying a timing light this week and will mess with it (looking for a house too, so not sure when I will get to it).

it has a small adapter/spacer between the intake/carb.
 
eddy carb is known for boiling fuel. Best to block off exhaust crossover and run a thermoquad.
 
ehaust crossover.. ie h/x pipe?

IMAG0118_zpsaf9b9d36.jpg
 
crossover is a cast passageway that runs underneath the carb between the heads. you can block it off with a metal plate under the intake gasket.
 
IF boiling fuel is what the problem is, there is zero need to block the crossover. It's there for a couple of reasons. Quick cold weather warm up and better fuel atomization. So if it's a street car, you probably want it left open. All you need is the THICK (1/4" or more) carburetor insulating gasket under the carburetor that everyone forgets about and even a carburetor heat shield. I recommend both.

You need to properly diagnose it first though, because you have the car, not us, so anything posted here is just a guess. Otherwise, you'll continue to chase your tail.
 
I'll be working on it in the next day or 2. going to check the timing, probably put some heat wrap on the fuel line, going to play with the carb some (change idle etc), seafoam treatment.
 
Cudafever said:
All GRATE ideas!!!

Here is a couple more.
Get a quart of water, (atf fluid if your in a area were you can get away with it. aka makes a LOT of Smoke) start eng,remove air cleaner, rev eng to around 3000 rpm. Now, vary slowly, dribble the liquid of your choice into the carbs primary barrels. do not let the eng slow down as you do this.

If its running on, become of carbon build up on the piston. It won't after your done!;)
Click to expand...


Spray gumout does a lot better job , than that 1960's fix
 
No properly driven musclecar ever carbons up LOL It might have rods sticking out the bottom end, it might have pushrods bent, but it won't have any carbon!!!!
 
RustyRatRod said:
IF boiling fuel is what the problem is, there is zero need to block the crossover. It's there for a couple of reasons. Quick cold weather warm up and better fuel atomization. So if it's a street car, you probably want it left open. All you need is the THICK (1/4" or more) carburetor insulating gasket under the carburetor that everyone forgets about and even a carburetor heat shield. I recommend both.

You need to properly diagnose it first though, because you have the car, not us, so anything posted here is just a guess. Otherwise, you'll continue to chase your tail.
Click to expand...

Agreed :coffee2:

...and buy ethanol free fuel...
Click to expand...

Is that possible apart from getting it at the track? I haven't seen ethanol free fuel at the pump for a few years now...
 
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