[455abody]

Hello there I just got my 455 back in my car and trying to work out the bugs. My question is where is the best port to plug the distributor vacumme advance hose to? I thought I had read the manifold port is best but not sure. Does anyone know the best manual out there for engine hose routing. Thanks Brian

[tc]

Depends on how the idle quality is and how the distributor is set up. I have 14 degrees initial ( no vacuum hooked up ). Then I plug the hose into the manifold, having the vacuum canister set for 10 degrees max, giving the engine 24 degrees at idle. The engine idles better at 24 than 14. Also have 20 degrees in the mechanical advance. So 34 degrees open throttle and 44 cruising down the highway.

[455abody]

I have a Mallory Unilite distributor after it warms up it is running decent. But it is hard starting when cold my carb has been redone by Sean Murphy. I think I need to play around with the timing and check some different vacumme options.

[Schurkey]

Originally Posted by 455abody

I have a Mallory Unilite distributor after it warms up it is running decent. But it is hard starting when cold my carb has been redone by Sean Murphy. I think I need to play around with the timing and check some different vacumme options.

Choke?

[tc]

Also, lower initial timing is easier to start the engine. Might need to check the carb out, as posted above. Check to see if there is accelerator pump gas when cold. Sometimes just learning the procedure, as in gas pedal pumps before starting, etc, takes time.

[455abody]

Yes I have the divorced choke and its hooked up.

[Greg Reid]

How is the choke set up? Vacuum pulloff hooked up and adjusted?

[Schurkey]

Originally Posted by Greg Reid

How is the choke set up? Vacuum pulloff hooked up and adjusted?

...and does the choke blade actually CLOSE?

What carb?

[Will]

Forget about vacuum advance until you have the engine well tuned and running right.

[steve25]

Vacuum advance will not help a cold motor in starting!
The choke being set up to be closed off all the way when first cranking the motor and added initial base timing above 10 degrees along with a starter, cable and battery set up to spin the motor fast enough are key parts, also a winter blend fuel depending on where you live.

[Cliff R]

Actually using manifold vacuum to the advance can make some engine harder to start warmed up. When you fine tune the idle speed and mixture screws using manifold vacuum advance the throttle plates in the carb are closed down more. I've ran into a few combinations here, usually with larger cams in them that refused to start if/when we were adding a lot of timing at idle via the vacuum advance on manifold vacuum.

Keep in mind that until the engine fires and starts making enough vacuum to apply the advance the timing is retarded considerably from where you fine tuned things fully warmed up and heat soaked.

I put up some good information on the topic of vacuum advance recently to help folks understand how it really works. Even many "guru's" and resident "experts" do not understand vacuum advance and continue to put up inaccurate information about it. Probably doesn't help that decades ago some very lengthy articles were written about it and they are still copy/pasted today. Although much of that information is helpful there are several flaws with it and it only serves to further confuse folks when they are trying to set timing and tune their engines.

What has thrown another monkey-wrench into the equation here is that cam companies have been pushing tight LSA so folks can have the "bling" factor when they idle thru the parking lot at your local cruise night or car show. Combine that with the proverbial brick wall of 9.5 to 1 compression for pump gas and many of these engines end up with too much overlap and not enough compression to offset the negatives involved there. The poor signal produced at idle from tight LSA and increased overlap require MORE timing and fuel to make the engine happy. Where an engine will a very well chosen camshaft for the CID and compression will make good vacuum and fine with 8-12 degrees (or less) initial timing at idle it's not uncommon these days to see folks having to use upwards of 18-24 degrees and a LOT of idle fuel available to get their new engine to be happy below about 900-1000rpm's.

Not really a big deal if you have good tuning skills and I'm not condemning tight LSA, just pointing out that it's easy to run into tuning issues if/when the engine isn't making good vacuum at low RPM's because of the cam choice made during the rebuild.......Cliff

[F ROCK]

"...But it is hard starting when cold..."

Just cold; or cold from sitting a few days?

The gas evaporates out of my Qjet if I let it sit for 2-3 days. Then it takes a lot of cranking for my mechanical pump to refill the carb.
If my car sits, I use an eyedroppers worth of gas in the carb for prime so I don't have to crank so much...

[steve25]

Today's 10% cut pump fuel also makes a non fuel injected motor 10% harder to light off, especially when temps fall below 40 degrees!

[Cliff R]

Why does it take "a lot of cranking" to get the carb to refill?

Why would you have to put any fuel into the carb to get it to fire off?

The accl pump does that for you and the fuel under the pump is trapped in a confined space and you still should get several shots of fuel to the engine even if the fuel level in the carb is low or empty.

In many of these cases where we see folks have difficult cold starts the accl pump seal is defective and weak or no pump shot, or it has to get wet again with fuel before it swells back up and starts working.

A good modern accl pump assembly with a flouroelostamer seal and garter spring to keep in in contact with the pump bore will not swell up, shrink, fail or not provide a positive pump shot during a cold start.

Another problem we see with poor or lack of good accl pump function is failing to gently seat the check ball during the rebuild to make sure it's not allowing fuel above it to drain back some.......Cliff

https://cliffshighperformance.com/Qu...-pump-assembly

[455abody]

I think I need to figure out how to adjust the choke. When the carb came in I hooked the small rod to the choke lever and that was it. It keeps the plate about 3/4 shut. I have a service manual I am going to see if it has any info on that. I am thinking it is choke issue and base timing issue. I am going play with this weekend, Brian

[Cliff R]

The divorced choke should lift the fast idle cam to the highest position and tightly close the choke flap when you move the throttle once on a cold start. At the same time the accl pump will put a shot of fuel into the intake.

If the choke flap isn't going completely closed the link is too long or the choke coil isn't working correctly. Could also be a linkage issue with the carb but the first statement assumes the carb is correctly assembled.......Cliff

[455abody]

Cliff would you recommend bending the choke rod so the throttle plate is closed at startup? Thank you for your info! always on the money

[steve25]

Yes, if the choke rod has Bend in it to absorb lenght then bend it out some to get the choke fully closed when you have stabbed the gas pedal once, as that's why the bend is there.

Then you will likely have a far more happy to Fire over motor when it's cold!

This will work fine as long as the choke will still open all the way when hot and not drift back to a somewhat closed position.

[Schurkey]

https://www.chevelles.com/techref/Ad...tic_Chokes.htm

[moontower69]

That's my experience. Ported is bs emissions creation of early 70s and will just increase your operating temps at the stoplight big time. Ported takes a good running engine and makes it run hotter and hurts throttle response.

Like Cliff said, once you get it tuned properly, manifold should be fine unless cam selection is way off (ie, too much duration for the compression ratio and combo of car and gearing)