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f925
04-21-2013, 04:01 PM
So being a carb noob I need some help trying to tune my 351w w/ 4160 carbs.
My current scenario is starts with a closed choke just fine, but will not start with choke even 1/4 open unless it has a little throttle. As the choke opens to about 1/8-1/4 the motor dies. My base setting for idle adjustment is 1 1/2 turns out on both sides from lightly seated. My choke is set where when cold it is completely but lightly seated in a fully closed position.

Now, my noob theory is as the choke opens it starts to run more lean, so I would think I would start by opening idle screws up 1/8 turn or so and trying again. Am I on the right track?


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SkiDaddy
04-21-2013, 04:57 PM
Can you get it to run with the choke fully open? Can you get the engine warmed up? I don't think you tune the carb with respect to the choke plate position.

Ideally, you would get things warmed up, and connect a vacuum gauge to a vacuum port downstream of the carb (I use the PCV port on the spacer plate between carb and intake.) While keeping an eye on the vacuum gauge, slowly adjust one of the idle air screws until your vacuum is maximized (my recent carb tune was around 1.5 turns out from fully seated) then make the same adjustment on the other side. Then, adjust your idle speed with the idle adjustment screw to around 700-800, if it needs it....then adjust the idle air screws again, then adjust the idle again, if it needs it.

I'd say get the carb in the ballpark with this method and then worry about the choke. There might be something else going on if you are having a problem with choke opening causing the engine to die.

Disclaimer! I'm definately not a carb guru, but I have done a rebuilt and re-tune recently and she's purring like a kitten.....93 Prostar with 4160 carb also.

Good luck!

Cloaked
04-21-2013, 05:15 PM
Can you get it to run with the choke fully open? Can you get the engine warmed up? I don't think you tune the carb with respect to the choke plate position.

Ideally, you would get things warmed up, and connect a vacuum gauge to a vacuum port downstream of the carb (I use the PCV port on the spacer plate between carb and intake.) While keeping an eye on the vacuum gauge, slowly adjust one of the idle air screws until your vacuum is maximized (my recent carb tune was around 1.5 turns out from fully seated) then make the same adjustment on the other side. Then, adjust your idle speed with the idle adjustment screw to around 700-800, if it needs it....then adjust the idle air screws again, then adjust the idle again, if it needs it.

I'd say get the carb in the ballpark with this method and then worry about the choke. There might be something else going on if you are having a problem with choke opening causing the engine to die.

Disclaimer! I'm definately not a carb guru, but I have done a rebuilt and re-tune recently and she's purring like a kitten.....93 Prostar with 4160 carb also.

Good luck!+1

Also, you may consider that the choke is out of service. The coil inside of the choke body can go bad. Replacements are easy and inexpensive.

http://www.skidim.com/prodinfo.asp?number=RN0067-1

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j.mccreight@hotmail.com
04-21-2013, 05:40 PM
Another thing to look for is after engine has died or shut off look down the throat to see if gas is leaking down the venturi.

f925
04-21-2013, 05:42 PM
The choke functions perfectly. My problem is it will only idle for 30 seconds or so before it dies every time. The only thing i can relate when it cuts out to is the position of the choke plate. It will run at higher revs with the choke wide open, i just cant seem to get the idle right.


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j.mccreight@hotmail.com
04-21-2013, 05:56 PM
make sure the accelerator pump fulcrum is operating properly it could be trying to flood the engine while it's running,

here is a holley pdf you can download

f925
04-21-2013, 06:08 PM
I finally got a solid idle, it seems to need to warm up at an idle around 1000 rpm. After that i got her purring like a kitten at 800 rpm. Warm start seems to take 2 trys but she goes with a touch of throttle.


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f925
04-21-2013, 06:25 PM
Now my problems are in higher rpm ranges. 3500 rpm seems to be the cut off for smooth operation. At 3500 it stops accelerating, and looses rpm with more fuel. I will post a video to youtube and link it if someone wants to see my drop off, as far as i know I have very little control over the carb at those ranges. I am used to having a high rpm adjustment screw to tinker with. Also what should I consider to be a safe redline for this motor?


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f925
04-21-2013, 06:27 PM
My accelerator pump was way out of wack. I grabbed the instructions from the rebuild and got it back in line. Thanks for the advice though! 3500 still seems to be as far as she wants to go.


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j.mccreight@hotmail.com
04-21-2013, 06:51 PM
check secondary diaphragm, see if secondaries are moving, I once had a pinhole in mine that prevented above 3500 rpm operation

Cloaked
04-21-2013, 06:54 PM
Also what should I consider to be a safe redline for this motor?


Sent from my iPhone using Tapatalk4500 max for me... I try to stay 4000 - 4300. On a 1:1 your MPH are about the same. I mean, how fast (or high RPM) do you really need?

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f925
04-21-2013, 07:00 PM
I am not sure how high an RPM I need. I do know it is a velvet drive 1.52:1 trans. At this point that is obsolete as there is no transmission attached at the moment. I would however like to know that everything works well through out the rpm range. I will say that 4200 is my target then for smooth operation.


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Cloaked
04-21-2013, 07:05 PM
PDF for a Holley 4160 Rebuild.... and a few other pieces of info that you may or may not find useful....

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f925
04-21-2013, 08:04 PM
check secondary diaphragm, see if secondaries are moving, I once had a pinhole in mine that prevented above 3500 rpm operation

10-4. I just switched this one out, but on the recommendation I did check it. The diaphram seems to be fine. What I did notice is that I do not seem to get fuel on the secondary side. I have run out of time to trouble shoot any further tonight but I seem to be on the right track. Thanks guys, I am not sure I could have done this with out your help!


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f925
04-21-2013, 10:51 PM
http://www.youtube.com/watch?v=yuzy0_04FOg

Note in this video between 0:21 and 0:30 I did not change the throttle position. The motor rev. variation is not my doing. I do believe once again that my secondary is not pumping fuel. At least not from anywhere above the butterflys where I can see. I will have to get a vacuum gauge to tell you more. Any suggestions on what could cause this would be much appreciated. I did check the secondary diaphram and it seems to be in perfect condition. Even after pulling it apart I still have the same run characteristics at 3500 rpm.

j.mccreight@hotmail.com
04-21-2013, 11:27 PM
are you driving the boat or reving in the driveway, the motor needs to be under a load like actually driving to have the secondaries work...

f925
04-22-2013, 12:06 AM
are you driving the boat or reving in the driveway, the motor needs to be under a load like actually driving to have the secondaries work...

Well, yup, this could indeed be a problem. There is no load on this motor, nor will there be for a while. I suppose at this point there is not much more I can do to tune until I have it under load then. Thanks. I feel a bit silly not having known or thought about it, but indeed load will change the running characteristics of the motor overall. It always does. :uglyhammer:

You have been a huge help through out this process. Thank you for holding my hand through my motor/ carb troubles. I am sure in a few weeks when I get her wet I will be relying on more help!