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  #1  
Old 06-23-2018, 11:43 PM
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Default Engine Timing/Carb Fine Tuning

Hello,

I have trying to adjust the timing and vacuum on my 62 HT with Holley 4100. I am struggling to find the correct settings and from what I'm reading I'm not alone. Some say use a timing light while others say tune by ear and other methods. Reading some success stories inspired me to tackle mine. For a brief time last month I had the engine running the best it ever had. But sadly, it has gone bad again and I cannot seem to duplicate it. All I had done different was lean out the carb and then put it back to where it was.(2 1/2 turns on the idle mixture screws trying to increase vacuum).

I had the rpm at 1dle (650) with 18hg of vacuum and the surging engine issue that had plagued me for years disappeared. The timing was around 10 BTDC and the smell of exhaust fumes that ran rich improved as well. When I pulled the plugs, they were all carbon fouled. I clean them all and reinstalled them. Can Anyone recommend any tips in fine tuning my engine/carb, (petronix 2/ igniter coil) that can help me fix a sick engine. Thanks.
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Old 06-24-2018, 09:14 AM
OUR5T8BIRD OUR5T8BIRD is offline
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Quote:
Originally Posted by flyinthermals View Post
Hello,

I have trying to adjust the timing and vacuum on my 62 HT with Holley 4100. I am struggling to find the correct settings and from what I'm reading I'm not alone. Some say use a timing light while others say tune by ear and other methods. Reading some success stories inspired me to tackle mine. For a brief time last month I had the engine running the best it ever had. But sadly, it has gone bad again and I cannot seem to duplicate it. All I had done different was lean out the carb and then put it back to where it was.(2 1/2 turns on the idle mixture screws trying to increase vacuum).

I had the rpm at 1dle (650) with 18hg of vacuum and the surging engine issue that had plagued me for years disappeared. The timing was around 10 BTDC and the smell of exhaust fumes that ran rich improved as well. When I pulled the plugs, they were all carbon fouled. I clean them all and reinstalled them. Can Anyone recommend any tips in fine tuning my engine/carb, (petronix 2/ igniter coil) that can help me fix a sick engine. Thanks.
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  #3  
Old 06-24-2018, 11:44 AM
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Do you mean Autolite 4100? 2 1/2 turns is way too excessive. You should adjust the idle mixture using a vacuum gauge. Turning it too far out isn't going to increase vacuum. It's only going to make it too rich.

John
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Old 06-24-2018, 05:13 PM
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Default carb tuning

Hello John, Sorry I meant Holley 4160. Both idle mixture screws were way off. One at 4 1/2 turns and the other at 3 1/4 turns. I wonder if they worked themselves loose. Can turn screws with finger nail. Maybe time for a rebuild.

I cannot duplicate 18hg of vacuum. Most I can do now is 15hg. I will re check all the hoses to make sure I did not miss a crack or hole somewhere. I guess I am looking for a systematic procedure so I don't get ahead of myself and bypass a step. I never got to setting total advance and could not find any markings in the distributor to calculate that. I hear a little pinging now at idle and have retarded the timing a little. Does not seem to be there while accelerating. There is a momentary flat spot (dead zone) when accelerating though. I will pull the plugs to see if the carbon is building up again. Odd thing though..... the timing light would not come on until I raised the rpm when setting initial timing. This is a new timing light with a tachometer. ????????
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Old 06-24-2018, 11:47 PM
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Give us a background on your engine. How many miles are on it? Is it stock?

How much slop is in your timing chain?
---measure this by putting your timing marks on ten degrees BTC, pull the distributor cap off then manually move your crankshaft back and forth with a long extension. From 'end to end' as you go back and forth, how many crank degrees do you get before the rotor starts turning. (This is where your hesitation is coming from.)

As your timing chain stretches, the cam/crank timing slowly retards the cam. Sometimes, your timing light marks will 'jump around' indicating chain slop.

Vacuum comes from the relationship between the pistons and valves. Loss in vacuum can come from leaky valves but more commonly from cam timing. - Dave
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Old 06-25-2018, 12:33 PM
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Hello Dave,

The previous owner had the engine rebuilt at around 25, 000miles. I have owned it since about 63,000 miles and it has 78,000 miles now. Its stock with pertonix 2 and flame thrower coil. Holley 4160 carb. I use only shell Vpower fuel.

I will look into the timing chain issue you suggested. I tried to tune it last night again using vacuum gauge. I was able to get the vacuum up to 18 1/2 hg by rotating the distributor but it seemed a long way from the timing marks. It did sound like it was running better though. I thought I heard some pinging so I retarded it the more I turned the distributor, the worse the engine sounded so I shut her down and decided to investigate more. I confirmed the timing marks were on by bringing up the piston #1 on compression stroke and watching when it reached TDC and confirmed the marks and balancer were right on "0".

I will check all vacuum hoses again, and piston # 1 plug was carbon fouled again even though I have adjusted the idle mixture screws and been running her lean for the last few days. I was thinking the carb could need a rebuild? I will have to step by step go through each scenario until I can figure it out.
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Old 06-25-2018, 12:42 PM
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Is your carburetor 600 cfm or 750 cfm. There are two different 4160 models. A 600 is what you should be using. A 750 will run too rich no matter how you adjust it.

John
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Old 06-25-2018, 04:37 PM
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When I set timing I unhook the vacuum advance hose and plug it.
I then start the motor and turn the distributor to advance the timing until I get the fastest smooth idle and highest vacuum reading then lock the distributor down and turn off the motor.
I then restart the motor and if it ‘fights’ the starter motor (i.e. the starter struggles to turn the motor over) I back off the timing a degree or two at a time until the starter isn’t struggling so much.
Then I re attach the vacuum hose.
I the start the motor a couple of times to see if all is well then road test the car, if it barely ‘pings’ under load on an uphill section of road in high gear I consider the job done, if I have what I consider excessive pinging I then back off the timing a degree at a time until I’m satisfied there is minimal pinging.

Caution: Your result may differ from mine, I know the condition of my distributor, carb etc.
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Old 06-25-2018, 05:13 PM
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Hello John,

For my model 80457-3 it shows it as 600cfm.


Hello Scumdog,

Do you look at the timing marks? Using the vacuum and disregarding the timing marks, it sounded good but the timing seemed way off from the harm balancer. I am almost sure it hasn't slipped. I will try that again. Another member suggested that as well and I tried last night but the slight pinging made me back off. I will try it again and take it for a test drive. I just don't want my lack of experience damage the engine. I'm not sure how fast pinging will progress and eat up the engine. Im missing some fine driving weather.
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Old 06-25-2018, 05:49 PM
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I wouldn't blindly trust your timing marks. If you haven't verified TDC then using scumdog's method should get you in the ballpark. I've found that 10 degrees BTDC or higher usually causes some pinging even using high octane gas. I try to shoot for 8-9 degrees. It takes a long time for pinging to do real damage. A few test drives isn't going to hurt. As for tuning your carburetor make sure the air cleaner is on and the engine is warmed up with the choke fully open. An RPM of 650 is ideal. Hook up your vacuum gauge. Turn one mixture screw clockwise until the engine begins to miss, then turn counter-clockwise until you reach the highest vacuum. Then turn clockwise very slowly until the vacuum begins to drop. Turn counter-clockwise about 1/8 turn. Recheck and adjust your RPM if needed. Repeat with the other mixture screw.

John
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