Mopar M1 Intake Manifold Question

[slepr1]

In a recent post I read someone saying their are common issues with the M1 intake at off idle. I've been having issues with my 440 with the M1 intake. Just off idle, as I accelerate, I get a hesitation. It doesn't go away when engine is warmed up. I'm running a Holley 850DP and we tried dyno tuning it, rejetting, power valve change, even removed the power valve and bumped up the jets (to eliminate low vacuum consideration). The hesitation won't go away. I have a new Edelbrock Performer RPM I can swap and will if that's what it takes.
Is the M1 the problem?

440, stock heads with springs and valves to match 509 cam, M1, 850DP, 3000 stall, 4.30 gears, heavy car (4100lbs).

 

[Cranky]

What is your initial timing set at and total and at what rpm?

 

[mentor70]

which holley 850 do you have? if you dont have adjustable kill bleeds, that may be an issue.

mopar .509 is a filthy pos on the low end, how much timing are you running?

the M1 as some quirks, read this article that Hughes engines did a few years ago on them.

http://www.hughesengines.com/TechArticles/4portedintakemanifoldsupdated08272007.php

 

[slepr1]

What is your initial timing set at and total and at what rpm?

I'm not sure. The dyno guy checked the timing and adjustments were made. I forgot to ask. I should have.

- - - Updated - - -

which holley 850 do you have? if you dont have adjustable kill bleeds, that may be an issue.

mopar .509 is a filthy pos on the low end, how much timing are you running?

the M1 as some quirks, read this article that Hughes engines did a few years ago on them.

http://www.hughesengines.com/TechArticles/4portedintakemanifoldsupdated08272007.php

I have the 4150 series. I never heard of adjustable kill bleeds so most likely don't have them.

 

[furryfrog]

I'm not sure. The dyno guy checked the timing and adjustments were made. I forgot to ask. I should have.

- - - Updated - - -




I have the 4150 series. I never heard of adjustable kill bleeds so most likely don't have them.

Mentor70 probably intended to say adjustabe air bleeds, by removing them and changing them out with different ones.

- - - Updated - - -

here is a pic

- - - Updated - - -

I don't know anything about the m1 intake or its characteristics, but I have been educating myself about the 4150, since I have a blow thru version on my car. First thing I would do is pull the carb off and make sure the throttle plates are sitting properly with regard to your idle transfer slots. The m1 intake is a single plane, and with your hotter type cam, your throttle plates are most likely open quite a bit so your engine idles, that could cause your off idle problems.

Some 4150 have an adjustment screw where the air cleaner stud goes to adjust the idle, so the throttle plates can stay where they need to be with regard to the transfer slots. Some guys drill holes in there throttle plates on the primary side, to keep the transfer slot adjustment.

- - - Updated - - -

Here, this may help

http://www.hotrod.com/how-to/engine/ccrp-0807-holley-carburetors-basics-guide/

 

[69 GTX]

check the timing first!

 

[super-bee_ski]

Good read mentor70

 

[slepr1]

Mentor70 probably intended to say adjustabe air bleeds, by removing them and changing them out with different ones.

- - - Updated - - -

here is a picView attachment 286707

- - - Updated - - -

I don't know anything about the m1 intake or its characteristics, but I have been educating myself about the 4150, since I have a blow thru version on my car. First thing I would do is pull the carb off and make sure the throttle plates are sitting properly with regard to your idle transfer slots. The m1 intake is a single plane, and with your hotter type cam, your throttle plates are most likely open quite a bit so your engine idles, that could cause your off idle problems.

Some 4150 have an adjustment screw where the air cleaner stud goes to adjust the idle, so the throttle plates can stay where they need to be with regard to the transfer slots. Some guys drill holes in there throttle plates on the primary side, to keep the transfer slot adjustment.

- - - Updated - - -

Here, this may help

http://www.hotrod.com/how-to/engine/ccrp-0807-holley-carburetors-basics-guide/

Wow that link came with allot of info. Thanks. I have the classic 4150. I'll have to do some homework before diving into this. I'm not that familiar with working on carbs. I've been lucky enough to not have any issues with Holleys, just this 850.

 

[383man]

I run the older Holley 850 that does not have the jets in the air bleeds and this 850 runs great on my car. I do use the Indy dual plane but I used the Holley SD single plane on my old combo with this carb and it worked great. I have only had to do a small amount of tunning to get it to work great on my car.
But I do agree that you always get the timing set right first before blaming the carb. Carb adjustments should always be last after the other settings are done. Ron

 

[slepr1]

The timing was set properly. This hesitation issue has been going on forever now. Multiple mechanics tried solving the issue and all of them started with the timing. I had the carb rebuilt but still had the hesitation.

 

[IQ52]

All of them started with the timing and everyone of them may have set the timing wrong.

First time I ran on a dyno the engine would hesitate and sometime even backfire through the carburetor. The dyno operator said, "Whoa, you better retard that timing, it's way to advanced. Knowing better, I advanced the timing another 10 degrees and all the hesitation went away. This dyno operator had more than 20 years experience but had never had the single plane, carburetor and camshaft combination that was on our engine. Your cam (dog that it is at lower rpm's) should have 20-24 degrees initial and 36-38 degrees total.

Previously four different people have inquired about the timing and I'm the fifth. What is your timing set at?

 

[reeltime]

After your timing check both accelerator pumps. You want the front one to move the instant that the gas peddle is pressed. The rear pump arm must be timed to move at the same time as the secondaries start to open.There are also plastic cams which Taylor how much and how fast it squirts the fuel in as the carb opens (accelerates)I would then adjust the four mixture screws. Using a vacuum gauge works best.Make sure your idle speed is enough to keep engine running.If it still acts the same I would change some jets then possible air bleeds.