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See what happens with 18 degrees of timing at 2500 rpm.
Hemi high idle
- Thread starter gumper
- Start date
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TT5.9mag
Two atmospheres are better than one
That is a handy piece of information right there.
TT5.9mag
Two atmospheres are better than one
You did not mention the idle stop screw on the secondary side of the carburetor. When you pull the carb to solder up the holes in the throttle blades, make sure the secondary is closed tight, but not sticking.
DionR
Well-Known Member
I intended to use one, but for now the port is plugged to rule that out as a factor.
I bumped it down at 15 at one point. All it did was make the engine run rough.
Going to throw a piece of tape over the holes just to experiment next time I start it.
I covered the carb inlet while it was running to see what happens and the engine did die after a few seconds. It was entertaining to watch the vacuum suck the squirters down. I feel that if there was a vacuum leak it would have kept running longer but maybe I’m wrong. I have a video of the test which of course I have to figure out how to upload.
Awesome!
Ditto on soldering the drilled holes.
racerjoe
Well-Known Member
I think the holes in the carb plates are the source of your problem. it doesn't take much air for my 5.7 with a 90mm single throttle body to idle. The throttle blade is closed all the way and only the IAC lets air in for idle, which is a very small orifice. I guess maybe because the heads flow so well it doesn't need much? I don't know, but it sure seems like noticeably less throttle opening is needed to keep these hemis running at idle.
I soldered the holes closed and still no good. Both the primary and secondary idle screws are backed out as far as they can go. I’ve opened the idle screws about 5 turns. The lowest I can get the idle is 1800. I put air to the intake with the carb covered and sealed and sprayed everything with soapy water. Cannot find any leaks. The only things left is put RTV around the intake ports if the orings aren’t sealing, and change carbs.
As a bonus my shifter cable apparently has melted despite using a DEI fire sleeve and header wrap to keep the heat off it. This Hemi thing has been a nightmare for me.
As a bonus my shifter cable apparently has melted despite using a DEI fire sleeve and header wrap to keep the heat off it. This Hemi thing has been a nightmare for me.
TT5.9mag
Two atmospheres are better than one
Check your grounds. Maybe the electrical system is grounding through the cable.
TT5.9mag
Two atmospheres are better than one
What happened when you pulled timing?
Engine ran rough but stayed at the higher rpm.
I do think I found the issue. The MSD Hemi 6 box uses the 32 tooth reluctor wheel which I did put on the crank. It’s a 2009+ engine though, so it had the 58 tooth wheel plus the sensor for the 58. I didn’t change the sensor to the older 32 tooth style. Going to change that tonight since it’s pretty much identical on the outside and see what happens. That’d make sense that it thinks the engine is spinning twice as fast as it actually is.
TT5.9mag
Two atmospheres are better than one
Interesting, how would it “control” the engine? It has no ability to manipulate the throttle body, and you said your timing is at ~22 degrees?
It is set at 15-25 depending on the RPM. I’m not 100% sure this is it yet, but it is as good a theory as any right now.
It did already have the right sensor, so that’s not it. Put a smoke machine on it and there are zero vacuum leaks. At this point I’m entirely out of ideas.
No vacuum leaks.
Carb throttle blades are shut as far as possible.
I soldered the holes in the blades.
The timing is backed all the way down to 10.
I can put my hand over the carb and plug the air bleeds with no effect.
Idle bypass screws are out 6 turns each.
Float levels are fine.
I’m baffled.
No vacuum leaks.
Carb throttle blades are shut as far as possible.
I soldered the holes in the blades.
The timing is backed all the way down to 10.
I can put my hand over the carb and plug the air bleeds with no effect.
Idle bypass screws are out 6 turns each.
Float levels are fine.
I’m baffled.
What is this hose coming off your intake manifold?
Where is it routed too?
☆☆☆☆☆
Where is it routed too?
☆☆☆☆☆
Time to backtrack a bit and get back to basics.
Now your Holley Single Plane Hemi manifold has a flange to fit the Square Bore carburetors.
Take off the Fast Idling Holley 4150, and put on a good known working simple square bore carburetor 750 cfm or less.
A good running Edelbrock 1406 600 cfm (for test purposes).
Or an Edelbrock AVS 2 650 cfm.
Or any other 750 cfm (or less) known good square bore carburetor you have available.
Fire it up and regain the control of your engine.
Once you get it to simply fire up and idle properly, then you can build it back up to the CFM you desire with the final new carburetor of your choice.
2 steps backwards, one step forward.
☆☆☆☆☆
Now your Holley Single Plane Hemi manifold has a flange to fit the Square Bore carburetors.
Take off the Fast Idling Holley 4150, and put on a good known working simple square bore carburetor 750 cfm or less.
A good running Edelbrock 1406 600 cfm (for test purposes).
Or an Edelbrock AVS 2 650 cfm.
Or any other 750 cfm (or less) known good square bore carburetor you have available.
Fire it up and regain the control of your engine.
Once you get it to simply fire up and idle properly, then you can build it back up to the CFM you desire with the final new carburetor of your choice.
2 steps backwards, one step forward.
☆☆☆☆☆
"Process of Elimination"
You have to keep trying things, until you start getting things to move in the desired direction of your quest.
Keep ruling out: What is good, and What is not good.
If carb swaps don't make a change then you know you have a serious ignition system problem. As you stated the previous ignition system owner had the same problem you are having now.
You are talking mili-volts on that MSD Hemi 6 ignition, and things can go wrong.
Electricity follows the path of least resistance, weather it's the desired path or not.
.
You have to keep trying things, until you start getting things to move in the desired direction of your quest.
Keep ruling out: What is good, and What is not good.
If carb swaps don't make a change then you know you have a serious ignition system problem. As you stated the previous ignition system owner had the same problem you are having now.
You are talking mili-volts on that MSD Hemi 6 ignition, and things can go wrong.
Electricity follows the path of least resistance, weather it's the desired path or not.
.
Converting a Gen III Hemi to a carburetor requires specific ignition control modules (like those from MMX or EFI Source) to manage spark timing without the factory ECU. Ensure this system is functioning correctly, as a malfunction can cause erratic timing and backfiring.
As you have stated, sometimes backfires on startup.
.
As you have stated, sometimes backfires on startup.
.
It’s fixed. Long story short, #4 was MIA. I don’t know why a cylinder not firing would make the idle speed high, but it’s all working now. Now I have to go back and undo all the carb changes I did and start back at the baseline.
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