Author Topic: Vapour lock? (Read 11913 times)

GLENN 70 · « **Reply #25 on:** February 03, 2014, 05:39:07 pm »

I know big blocks like timing and make hp up there and 39 is high these days ,if the engine likes it and no pinging and you always run 98 fuel, well maybe . But 36 would be safer unless you want every bit of hp you can get . That 1/2 inch heat spacer will help to keep the fuel cool .Ask some engine guys on here about the timing you should run .

McBrain · « **Reply #26 on:** February 04, 2014, 08:22:14 am »

Thanks Glenn

shaunp · « **Reply #27 on:** February 04, 2014, 09:24:20 am »

If you want to give it more timing down low, you need to buy a Mallory or MSD dissy you limit the overall advance quiet easily so you don't get into trouble up high in the revs where you can't hear it ping

McBrain · « **Reply #28 on:** February 04, 2014, 09:38:19 am »

Is it possible to adjust the mechanical advance to achieve the same?

GLENN 70 · « **Reply #29 on:** February 04, 2014, 10:15:40 am »

Depending on your dissy ,you can set it or get it set up .I think 39 deg is to high 34 or 36 is what be best and safe as you may not hear it ping up in the higher revs ,but your engine needs more timing down low because you have a performance cam , you can not just bring the timing up because it will raise it in the top as well ,thats where they set it up inside so its just right .Your engine may need 14 or 16 deg to run nice at idle in gear with the engine combo .So say they set it up at 16 deg static they will put 18 or 20 in the dissy ,total timing will be 34 or 36deg .Now that makes sense to you.

McBrain · « **Reply #30 on:** February 04, 2014, 12:04:32 pm »

I found these links which may be of interest:

http://www.bob2000.com/dist.htm
http://www.gofastforless.com/ignition/advance.htm

This one shows the slots at the centrifugal weights which limit the total amount of mechanical advance.
http://www.mustangmonthly.com/techarticles/mump_0904_how_to_rebuild__autolite_motorcraft_distributors/photo_29.html

lukep6470 · « **Reply #31 on:** February 04, 2014, 05:33:17 pm »

Where is your fuel line routed under the car? Does it go through the frame rail like the original or is it coming up the tunnel?

I've installed EFI with data logging and I am seeing engine bay temperatures of 65+ when turned off for a couple of minutes after sitting in peak hour traffic for ages. I've seen it as high as 70 which will pretty much boil fuel. This is in a 67 with a standard bonnet (Not GT). I think a GT bonnet with the slots or a Shelby scoop bonnet would make a LOT of difference.

McBrain · « **Reply #32 on:** February 05, 2014, 03:36:51 pm »

Fuel line comes through the rail. It's the GT bonnet but I'm not convinced it would shed much heat, especially when stationary.

I have a digital thermometer I should put it on the fuel line and bowls and see what I get.

GLENN 70 · « **Reply #33 on:** February 05, 2014, 05:04:59 pm »

Your fuel line is going to get hot ,try to make sure its clear of sitting on the block from the fuel pump ,you can foam/rubber sleeve the fuel line it you really want .Get the 1/2 inch heat spacer it will work ,try and put your hand on the carby now after going for a run then try after you fit the spacer you will be shocked .

McBrain · « **Reply #34 on:** February 09, 2014, 07:23:11 pm »

Go some time with the car today.

So I took the distributor apart to look at the mechanical advance.

The cam plate was set on '13L' i.e 26 deg advance, which is too much. In addition to this someone had put a plastic bush around the tab that fits in the slot, effectively limiting the travel and adding another 2-4 degrees.

So I removed the bush and spun the plate to use the 10L slot.

Reset timing and I now have:

Initial static 12 deg
at 2000rmp 32 deg (with vac advance disconnected).

Nice, this is what I wanted.

Now the problem I have is setting the vac advance. Testing the timing in idle with the vac advance connected I was getting the timing advancing alot at 2000 rpm, like 60 deg (hard to tell).

I read that it was difficult to set the vac advance in neutral as their is no load on the engine so I decided the best way was by road test. It's pretty close but a bit of pinging under max load.

Now I can't change the mech advance and I don't want to retard the initial so how can I reduce the max amount of vac advance? The can has an adjustable spring with calibration washers but I think this just changes the rate of advance.

Is there supposed to be a limit stop on the vac advance arm?

The vac can is a +10deg by the way.

shaunp · « **Reply #35 on:** February 09, 2014, 07:33:14 pm »

Don't worry too much about the vac, there is no/little Vac advance under max load only cruise, as soon as the engine comes under load the Vacuum will drop as will it's effect on advance. The Vac advance should be on the ported vacuum on the carb not direct to the manifold vac. Some advance cans can be adjustment via an allen key through the hose port.

McBrain · « **Reply #36 on:** February 09, 2014, 08:39:07 pm »

Yes, it's on ported vacuum.

I'm confused now. I thought that the vac was giving some 'intelligent' advance when needed and when the engine isn't spinning fast enough to give a lot of mechanical advance?

So if I'm climbing a hill at, say, 40km/h and I put my foot down the vac advance will advance the timing (up to 10deg on my can) on top of whatever the mechanical might be. It's this situation that is most likely to cause pinging.

So ported vac is zero at idle because the throttle is closed, but as soon as the throttle opens vacuum will increase, but if the engine is under load the vac will be less, therefore less likely to ping.

GLENN 70 · « **Reply #37 on:** February 09, 2014, 08:45:15 pm »

Whats the timing at say 1000 rpm then at around 2500 rpm with the vac line not on .Where have you got the vac line hooked up to when you have it connected .12/14 deg and 34 deg total would be nice .

GLENN 70 · « **Reply #38 on:** February 09, 2014, 08:46:16 pm »

Sorry did not see your last post i was writing at the same time .

McBrain · « **Reply #39 on:** February 09, 2014, 09:16:09 pm »

Quote from: GLENN 70 on February 09, 2014, 08:45:15 pm

Whats the timing at say 1000 rpm then at around 2500 rpm with the vac line not on .Where have you got the vac line hooked up to when you have it connected .12/14 deg and 34 deg total would be nice .

Yep, that's what I have. 12/13 deg initial and 32 total with no vac line. Vac connected to ported on carbie.

GLENN 70 · « **Reply #40 on:** February 09, 2014, 09:31:24 pm »

I cant remember all the details ,auto or manual ,kick down connected and what fuel do you run in it .... 32 total could come up a bit but is ok .

shaunp · « **Reply #41 on:** February 09, 2014, 10:00:55 pm »

Quote from: McBrain on February 09, 2014, 08:39:07 pm

Yes, it's on ported vacuum.

I'm confused now. I thought that the vac was giving some 'intelligent' advance when needed and when the engine isn't spinning fast enough to give a lot of mechanical advance?

So if I'm climbing a hill at, say, 40km/h and I put my foot down the vac advance will advance the timing (up to 10deg on my can) on top of whatever the mechanical might be. It's this situation that is most likely to cause pinging.

So ported vac is zero at idle because the throttle is closed, but as soon as the throttle opens vacuum will increase, but if the engine is under load the vac will be less, therefore less likely to ping.

In theory vac advance is mostly for fuel economy when the engine vac is high ie light load and cruise speed, as soon as you nail it the vac will drop to nothing till the revs pick up and gas speed increases again. Engine with big cams and low vac don't normally run vac advance cause it has little effect on these and in a race /hipo type set up what's fuel eccon anyway.
Your issue, depending on the revs when it pings at will more likely be related to the actually advance curve if your static timing and overall is ok.

GLENN 70 · « **Reply #42 on:** February 09, 2014, 10:31:44 pm »

The timing maybe coming to soon ,it might be only 32 but how early is it coming in .It might pay to get the dissy set up from a work shop if you still have problems .It wont cost much if you just take it in .

shaunp · « **Reply #43 on:** February 09, 2014, 10:41:43 pm »

Or just buy a new MSD/Mallory etc, they come with extra advance springs so you can play, easy to limit all in as well.

GLENN 70 · « **Reply #44 on:** February 09, 2014, 10:43:08 pm »

Hey Shaun what dissy was it anyway .

shaunp · « **Reply #45 on:** February 09, 2014, 10:53:45 pm »

I think it maybe just the original one.

McBrain · « **Reply #46 on:** February 10, 2014, 08:01:03 am »

Yes, it's the original Autolight dissy C8WF.

It has the two standard springs, one stiff, one soft.

I'm going to install a pertronix, after that if it still bothers me I'll take it somewhere to get it curved. - Don't get me wrong, it goes great, I just want to get it setup just right.

By the way, I measured the temperature of the chrome inline fuel filter can which sits above the intake manifold just before the carbie. Max was 64deg C after a few minutes standing. Boiling point of petrol is 95C but 64C is still high - time to fit the spacer.

lukep6470 · « **Reply #47 on:** February 10, 2014, 11:23:22 am »

Does the Autolite Dizzy have the same vac advance adjustment as the aftermarket ones?

The aftermarket Vac advance units have an allen key adjustment inside the port you connect the hose to.

GLENN 70 · « **Reply #48 on:** February 10, 2014, 11:31:38 am »

I think so .

McBrain · « **Reply #49 on:** February 10, 2014, 02:07:10 pm »

Quote from: lukep6470 on February 10, 2014, 11:23:22 am

Does the Autolite Dizzy have the same vac advance adjustment as the aftermarket ones?

The aftermarket Vac advance units have an allen key adjustment inside the port you connect the hose to.

no, it's the one with washers on the spring that you add/remove.

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Author Topic: Vapour lock? (Read 11913 times)