426 Street Hemi Idle Problems

[lyndondb]

OK, I am in need of advice. Where do I begin: My 1968 426 Hemi starts runs and shuts down great --- but will not idle for more than about 10 to 30 seconds.
Carburetor have been recently replaced. ?????

 

[pnora]

Flooding or lean? What is your fuel pressure?

 

[tonysrt]

Is the replacement carb new or used? Look in carb after the stall and move throttle to see if fuel is being pumped in when throttle is moved.

 

[HALIFAXHOPS]

OK whats shutting it down no spark or no fuel? Have to start there.

 

[Dragon Slayer]

What carbs? What choke system? You do need to isolate some issue if we are going to settle on the carb being the issue. It starts and if you immediately drive off it runs great? So fuel not issue. If you start and it stalls, does it start right again just not idling? So again it is not running out of fuel. If you start and idle up to a certain RPM 2k or 2.5K does it run fine. Is this a cold versus hot issue with choke? What RPM are you trying to idle at?

 

[RJRENTON]

OK, I am in need of advice. Where do I begin: My 1968 426 Hemi starts runs and shuts down great --- but will not idle for more than about 10 to 30 seconds.
Carburetor have been recently replaced. ?????

It would be helpful to know the carburetor numbers stamped on the left front mounting flange, for both the rear (primary carb) and the front carb (secondary carb). Are the carbs origional to the engine? Have they been "customized" by others? IMO....since the rear carb does a large percentage of the metering (80% +/-) it appears that would be a good place to start.....and ALL idle fuel begins with the primary booster venturii assemblies.....perhaps some of the metering passages is clogged or restricted.....just a thought.....
BOB RENTON

 

[AR67GTX]

Or is this a crate Hemi with a single 4bbl?

 

[Geoff 2]

When the engine shuts down, look in the carb bores & see if you can see fuel dripping. If so, carb flooding.

 

[lyndondb]

What carbs? What choke system? You do need to isolate some issue if we are going to settle on the carb being the issue. It starts and if you immediately drive off it runs great? So fuel not issue. If you start and it stalls, does it start right again just not idling? So again it is not running out of fuel. If you start and idle up to a certain RPM 2k or 2.5K does it run fine. Is this a cold versus hot issue with choke? What RPM are you trying to idle at?

4619 4620s stock newly rebuilt with new gas tank lines and fuel pump. Fuel vapor seperator present.
Only running ethanol fuel. thanks for the help.

 

[lyndondb]

Flooding or lean? What is your fuel pressure?

Stock fuel pump so I don't know the fuel pressure. I am going to check to see if it is flooding when it quits today. Thanks for all your help.

 

[lyndondb]

Is the replacement carb new or used? Look in carb after the stall and move throttle to see if fuel is being pumped in when throttle is moved.

Carbs are both used but rebuilt. I will check this today. Thanks a lot for your guidance.

 

[lyndondb]

Is the replacement carb new or used? Look in carb after the stall and move throttle to see if fuel is being pumped in when throttle is moved.

Car will start right up after it dies without touching accelerator.

 

[Dragon Slayer]

I would retorque intake manifold, make sure no vacuum leak. What choke are you using and does it pull open the choke valve slightly after start up.
You may need to adjust the idle mixtures, and set the idle rpm. Did they remove the small lock screw on the side of idle mixture? Are the front carb idle mixture screws accessible? The service manual can help. 68-69 carbs have the emission locked idle mixtures. They are hour glass shaped and unless you back off the lock screw (allen head set screw) they only turn in and out so far. Do not force them. Front carbs need lead removed to assess the slotted idle mixture screws.

Sounds like ignition and fuel are not the issue since it immediately restarts.

You should also add rpm with the front carb to ensure not lean at idle. Let it contribute 50-100 rpm and back off on the rear idle to get your target idle rpm.

 

[mrhemi]

What Dragon Slayer says! There is a detailed procedure in the 1969 FSM (possibly other years as well) on how to balance the two carbs to obtain proper idle / off idle performance. It is quite often not realized that a stock Hemi idles on the front carb as well.

 

[67 WS23]

When the engine shuts down, look in the carb bores & see if you can see fuel dripping. If so, carb flooding.

I just put my rebuilt carb on my 67 R/T. I ran the car a few minutes at a time by filling the bowls with a small squeeze bottle, no problem. Then I plumbed in the new Carter fuel pump and I have massive flooding. The car will run for about 5 seconds, then I can see fuel all over the top of the manifold. I removed the carb and lowered the float levels, still no good. After a little research, guys have had similar problems with the chineseum Carter pumps. Too much pressure for the needle valves to handle. So I ordered a Malpassi in-line regulator to lower the pressure to about 5 psi. The regulator should come next week. I will update with the results.

 

[Geoff 2]

It depends on which Carter pump you got.....The #4601 puts out 16 psi & is designed to be used with a reg.
The #4600 & #4594 are internally regulated. Have never heard of these causing flooding when used correctly.

 

[67 WS23]

It depends on which Carter pump you got.....The #4601 puts out 16 psi & is designed to be used with a reg.
The #4600 & #4594 are internally regulated. Have never heard of these causing flooding when used correctly.

It's the 3672 per rock auto. The regulator should take care of it. If I don't like the way it looks I'll spring for the Edelbrock pump. I just don't trust the original pump. The car hasn't run for 18 years so it could be pretty bad...

 

[Fran Blacker]

Check oil for the smell of gas!! If your dipstick reads over full, might want to drain the oil and change filter.

 

[67 WS23]

I just put my rebuilt carb on my 67 R/T. I ran the car a few minutes at a time by filling the bowls with a small squeeze bottle, no problem. Then I plumbed in the new Carter fuel pump and I have massive flooding. The car will run for about 5 seconds, then I can see fuel all over the top of the manifold. I removed the carb and lowered the float levels, still no good. After a little research, guys have had similar problems with the chineseum Carter pumps. Too much pressure for the needle valves to handle. So I ordered a Malpassi in-line regulator to lower the pressure to about 5 psi. The regulator should come next week. I will update with the results.

Update: The regulator works perfectly to tame the fuel pressure from the chineseum Carter pump on my 440. Dialed it to 4.5 psi and no more flooding my recently rebuilt Carter 4327S. Can stab the throttle with good response. The car can now run more than just a few seconds. This is the first time running the engine since 2006, running it on ethanol free 93 octane. Engine idles as smooth as I recall in the late 1990s when it was last registered. Will get it back on the street real soon.

 

[Geoff 2]

4.5 psi is a bit low, will give low fuel level; about 6 is better.