carb woes

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chorty55

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By no means am i a carb expert, but I do know if you can see daylight through the carb body following the throttle linkage side to side, it's safe to say there's no adjustments to ever make gain on something as worn out as i was seeing.

Bought a new 2 barrel chinese carb from amazon. Probably a bad idea.

After engine is good and warm, and thermostat opens, it idles decent. although on the passenger side seems like it's running rich. Turning in the idle jet on that side until it mis-fires doesn't change anything. I can't get it to either stop being rich or cutting out from setting the needle too far closed. Both adjustments are equal. For a blind start, i turned them all the way in, and backed them out equally 1.5 turns.

Oddly if i place my hand over the carb throat, choking off easily half in air intake, it runs even better. The hotter the engine gets, the less spittering/sputtering it does with throttle tip in.

I drained the tank and fuel lines, brand new filters, and am using fresh rec fuel, no ethanol. I adjusted the accelerator pump to the less aggressive linkage hole, but if you snap the throttle open, it falls right on it's face on half the plugs.

Tomorrow i plan to buy a pertronix 40511 and fresh spark plugs.
 
remytherat said:
This suggests it's lean.

Why do you suspect it's running rich?

I think you probably have a vacuum leak somewhere.
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dark black exhaust and my eyes burrrn standing around it.

i'll try the idle screws the other direction after fresh plugs and spark can. I also found my vacuum gauge to double check a few things in the daylight.

If i gently tip into it, and work it up to 3000-4000RPM, all it does is backfire and smell like raw gas as it comes down back to idle.

I'm considering tearing apart the float bowl cover and checking what's all going on in there. Not sure if shipping could of jumped something out of whack and needles aren't floating/setting/moving freely.
 
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chorty55 said:
dark black exhaust and my eyes burrrn standing around it.
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Might be the AFR, but it might also be the timing.
If the timing is too early or too late there will be lots of partially burned fuel coming through the exhaust.

That said, just as background, its worth looking at how AFR typically relates to the burn products.
HC represents left over hydrocarbons, that is fuel.
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I agree with Remy that your test proves that at that rpm and timing, the engine prefers a richer mixture.
Further, since the transmission was in neutral (or park), the load was minimal. When the car is in gear the engine will want a slightly richer mix than when its in neutral.

At idle during warm up, the engine will need a mixture anywhere from 9:1 to maybe 12:1.
Once the engine is fully warmed up, the engine will idle strongest with somewhat mixtures still somewhat richer than stoich, typically something in the 13:1 range.

Now IIRC from another thread, your car is a '71 so it came with an emissions package. Idle mixture was targetted to be leaner, something like 14.0 to 14.1:1and used higher idle speed. Even though this increased NOx, the leaner mixes reduced HC and CO at idle and coast down. Now here's the 'bad' part. Instead of increasing base timing advance to match the leaner conditions, it was usually reduced. Initiating the burn later puts more heat into the cylinder walls and the exhaust gas. Hotter conditions and hotter exhaust help burn up left over HC components. This means less HC out the tailpipe.

So why might you need to know this? Because if distributor is truly the original one for your engine, then use the factory spec for your year for the timing(plus minus 2 degrees) and tune up rpm. It also should tolerate a slightly leaner idle mix than a pre-emissions engine. However if you're starting from scratch then you will probably find a little more power at even lower rpm with a pre-emissions timing and idle mix.
 
Engine is a 69., at least the timing cover is 69, and looks orginal. Not a vehicle application anymore.

The pcv I'm going to replace in question and reassurance, and 2 other vacuum lines, one goes to advance, other goes to choke pull. Choke pull immediately does its thing as soon as I start turning the starter. Advance diaphragm has no leaks, checked with a vacuum pump. There's no other vacuum lines. No brake booster, etc. Everything else plugged on intake.

Crank is advanced 4*, cam is 2*, according to gun when set at zero, it runs best around 12-14* btdc.

Neutral is a relative term. The crank is turning 3 hydraulic pumps and a probably larger then normal torque converter. So my park and neutral situation is a bit different regarding "engine load while in park".

I'm occupied today so won't be able to try anything, but the list of ideas is growing.
 
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Only suggestions I have is get a tach. Knowing the rpm is critical for timing and can be useful for fuel mix adjustment too.
And if the old carb works, then do a test to see if the wear around the throttle shaft is relevant. Like put some heavy grease around it to see if the engine picks up speed. Throttle shaft bushings can be installed if the old carb works except for the slop.
 
Mattax said:
Only suggestions I have is get a tach. Knowing the rpm is critical for timing and can be useful for fuel mix adjustment too.
And if the old carb works, then do a test to see if the wear around the throttle shaft is relevant. Like put some heavy grease around it to see if the engine picks up speed. Throttle shaft bushings can be installed if the old carb works except for the slop.
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old carb is trashed. leaks gas everywhere it shouldn't, and when you hold it up to the sun it leaks daylight from one side of the body to the other through the linkage. Not to mention it's had ethanol fuel in it for 15+ years. The stuff out of the tank look like mild coffee. I had to double check if i opened an oil line when i drained it, i was worried i opened a steel line for the hydraulic steering circuit by accident.

I couldn't get it all to drain out of the fuel tank because of the way it draws from the bottom of tank, so i made a long tube and vacuumed out all the fuel i possibly could, which worked better then i thought, although a bit sketchy pumping gas fumes through a shop vac with sparky brushes, 8 feet up in the air like a monkey in a tree with iron to fall down onto below if something blows up in my face.

Then i dropped 2 bottles of HEET fuel treatment, vacuumed that up, and added fresh fuel with another bottle of treatment, then ran the fuel line out to the carb until it was clean, and finally hooked everthing up to clean filters and empty new carb.

So the slate is clean besides some timing and adjustment screws

my gun doesn't do RPM, but i might have dibs to borrow one this weekend.
 
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chorty55 said:
Bought a new 2 barrel chinese carb from amazon. Probably a bad idea.
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Don't get rid of your original carb just yet. You might still need it. At the very least to use as a reference. Is it a bbd? We have had a few of the Amazon rochester 2bbls come through the shop. Jet is using them now as a core for their race carbs. So far they have all been terrible. Hopefully you have something you can work with. Good luck with your project!
 
92b said:
Don't get rid of your original carb just yet. You might still need it. At the very least to use as a reference. Is it a bbd? We have had a few of the Amazon rochester 2bbls come through the shop. Jet is using them now as a core for their race carbs. So far they have all been terrible. Hopefully you have something you can work with. Good luck with your project
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https://www.amazon.com/gp/aw/d/B07GJCBPMJ/?tag=fabo03-20

thsts the one I'm dealing with and struggling to find ground zero.


this one I bought back in 2020 for the other 318 in the allis Chalmers, and it worked beautiful right out of the box. Nice tip in, choke works as intended, mellow hit on all 8 idle.

https://www.amazon.com/Twilight-Garage-Carburetor-MB-172-HCY-1967-1980/dp/B07K7FNM62?tag=fabo03-20
 
chorty55 said:
https://www.amazon.com/gp/aw/d/B07GJCBPMJ/?tag=fabo03-20

thsts the one I'm dealing with and struggling to find ground zero.


this one I bought back in 2020 for the other 318 in the allis Chalmers, and it worked beautiful right out of the box. Nice tip in, choke works as intended, mellow hit on all 8 idle.

https://www.amazon.com/Twilight-Garage-Carburetor-MB-172-HCY-1967-1980/dp/B07K7FNM62?tag=fabo03-20
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That always surprises me when I see the price. If you still have the other carb that works well maybe you could try a swap as a diagnostic test.
 
Its worn out man. The moment it draws fuel it leaks everywhere. Everywhere. Out the throttle sides, out the bottom, out the plunger, makes puddles on the intake as soon as the fuel pump starts pumping. I promise it hasn't been apart since the Assembly line back in 1969, sat with ethanol fuel in it for 15 years, and the aluminum housing is so worn the linkage has egg shaped the bore, has grooves cut in the steel shaft, and day light passes through it side to side. Its garbage. Its had 40 years of throttle teasing around the property. The only time it mostly stops leaking is once the engine is running and drawing the fuel back in from vacuum past all the gapes and chaos on the housing.

I haven't tossed it yet, at the same time this carb so far, as shitty as it tips in, idles 200% better then the other one I just described. No surprise either.
 
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chorty55 said:
The moment it draws fuel it leaks everywhere.
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Carbs don't draw fuel.
Fuel enters the bowl the same way water enters a toilet tank.
upload_2020-1-27_16-11-39-png.1715460157


Any fuel coming from anywhere else, or in your case from everywhere else, tells us exactly what is going.
Would be good to read on how a carb works. Makes diagnostics a lot easier.
Chrysler Tech did a decent job on the fundementals in 1966 and 1970.

Browse MTSC by Model Year – 1966 – MyMopar

mymopar.com mymopar.com
 
The moment it gets fuel it leaks everywhere

Draws fuel, gets fuel, it leaks fuel. Every where. There's no.bushing or orings to save oblonged or egg shaped aluminum bore.

A man shouldn't be able to see the sun through the carburetor housing. The carb was drawing more air from everywhere else besides through the air filter.

Its garbage. Whether I understand it drawing fuel or being delivered fuel.
 
chorty55 said:
Its worn out man. The moment it draws fuel it leaks everywhere. Everywhere. Out the throttle sides, out the bottom, out the plunger, makes puddles on the intake as soon as the fuel pump starts pumping. I promise it hasn't been apart since the Assembly line back in 1969, sat with ethanol fuel in it for 15 years, and the aluminum housing is so worn the linkage has egg shaped the bore, has grooves cut in the steel shaft, and day light passes through it side to side. Its garbage. Its had 40 years of throttle teasing around the property. The only time it mostly stops leaking is once the engine is running and drawing the fuel back in from vacuum past all the gapes and chaos on the housing.

I haven't tossed it yet, at the same time this carb so far, as shitty as it tips in, idles 200% better then the other one I just described. No surprise either.
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Sorry I wasn't clear. I mean to use the carb from the allis for diagnostics. These bbd carbs have different calibrations for different year, model and application. The replacement carb fits 1967-1980. It's a compromise and even if it's working properly the calibration may not be right for your engine. Which is why I wouldn't get rid of the old carb yet as it may offer some clues if you need them at some point in trying to figure this out.

First I would try the allis carb and if it works bite the bullet and get another from the same supplier. If it still doesn't run good then I would look into the motor and make sure something else isn't causing the problem.
 
I really thought about doing that, but I might need that machine later this year. Using both and a truck between helps move alot of material at once.
 
chorty55 said:
I really thought about doing that, but I might need that machine later this year. Using both and a truck between helps move alot of material at once.
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It's just temporary to see if the motor or the carb is the problem. Or worse case scenario both.
 
Have you checked the float level on the new carb? That would be the first thing to check. It is a looooong way to the US from China, carb could have got knocked around.
 
chorty55 said:
I'm considering tearing apart the float bowl cover and checking what's all going on in there. Not sure if shipping could of jumped something out of whack and needles aren't floating/setting/moving freely.
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Bewy said:
Have you checked the float level on the new carb? That would be the first thing to check. It is a looooong way to the US from China, carb could have got knocked around.
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