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Cold starting issues after engine rebuild


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Info :

Have brand new rebuild on 351c 4v, I tweaked cam to more aggressive ...around Boss 351 specs. , added new 2.25" exhaust( no cross pipes) New Quick Fuel 650 carb.

 

Issues on cold start here in South Florida, not really cold: cranks right up everyday, but stumbles and spits and conks out usually unless I really give her gas. Generally starts up and grumbles on second start... But she really needs to wam up about 5 minutes before I take off!

 

Is this normal for my set up?

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Not having all the facts, so I'll start with the carburetor.. Is the choke plate fully closed when the engine is cold? Does the choke pull-off open the plate too soon, which creates an immediate lean mixture. That is where I would start.. There are markings on the choke cover and from what I can recall, (correct me if needed) the index should be on the 3rd mark of the choke cover.. It's the starting point for the choke setting. Move it richer or leaner as needed.

 

Secondly, the high idle may not be set high enough during initial start up to keep the engine running.. Especially with a performance cam installed. You'll need to review the cam spec sheet that came with the cam, or just start experimenting with the cold idle until you can keep it running as it warms up and the choke opens..

 

It's a tricky situation, but with time and patience you'll get it to where it will start and run on it's own.

The person who says it cannot be done should not interrupt the person doing it. 

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I'll second the choke adjustments and fast idle set up as the most likely place to start.

http://www.7173mustangs.com/gallery/1_01_07_15_8_53_18.png

 

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!

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.

In addition to setting the choke t the optimal setting, you need to tune the engine . This includes checking jetting, test when the secondaries open if its a vacuum secondary carb, and testing timing to see if it is optimal for your setup.

 

Below is one of the things I would do.

 

SETTING TIMING CURVE

 

Before you start driving it normally, I would set the timing curve so it is optimum for your particular setup . Below is just one way to do that.

 

1. Disconnect and plug the vacuum hoses to the dist if you have any and leave them plugged permanently or until further notice.

 

2. Start your timing at 8 degrees BTDC.

 

3. With the engine warm and idling, advance the timing 4 degrees . Listen for an increase in rpm and irregular/rough running.

 

4. If the rpm increases and it still runs smoothly, reset the idle speed then increase the timing 2 more degrees and check for the same things.

 

5. Retard timing back to 8 degrees btdc.

 

6. Reset the idle speed.

 

7. Increase the rpm to around 2000 then advance the timing 4 degrees . Listen for an increase in rpm and irregular/rough running.

 

8. If the rpm increases and it still runs smoothly, reset the engine speed to 2000 rpm then increase the timing 2 more degrees and check for the same things.

 

POST RESULTS

 

 

TEST DRIVING

 

After setting the timing curve you can do the following test to see if you have too much advance.

 

Get the engine up to operating temp.

 

Drive at around 20 mph in second gear for a few seconds then floor the gas pedal as fast as you can until you reach around 30 mph and listen for even the faintest pinging sound coming from the engine . If it pings, you have too much timing for the octane gas you are using . You can either reduce the timing some or use a higher octane . The highest timing level you can run without it pinging and/or running erratic will SAFELY provide the most power.

 

It may ping in hot weather even if it does not in cold weather . If you find this to be the case, the easiest thing to do is reduce the timing until it stops or try higher octane gas . If it still pings with the highest octane gas, you can reduce the timing then.


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CARBURETOR GAS LEVEL

 

Set gas level so it is just below the inspection screw holes or just 1/4 of the way up on the clear sight glass with the engine idling or just after you turn it off.

 

If your carb has screws in the inspection holes, put several paper towels next to the carb before you remove the screws because it may drain a bit of gas out.


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IDLE FUEL MIX SCREWS

 

1. With the engine off, turn both screws in until they just barely stop turning and count the turns as you turn them in.

 

2. Turn them both out equal amounts to where they previously were . If they were turned out different amounts, simply split the difference so they are both turned out the same amount.

 

3. With the engine warm, turn both screws 1/8th turn at a time until the highest idle is achieved then turn them both in 1/16th turn . You may have to try turning them in both directions to find which way provides the highest idle.

 

Step 3 should be repeated after all other changes are made.

 

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