Tuning help

877 Views 5 Replies 2 Participants Last post by 66gt350, Mar 13, 2001

Discussion Starter · Mar 12, 2001

I've been duing some tuning of a new engine and have a question for a few of the experts out there. I have a newly rebuilt 289-2V with a rebuilt distributor (single point, dual vac) and rebuilt (Cal Carbs?) carb.

I have a slight bog off idle (e.g. stop sign).

The carb instructions suggest the carb has been test run and tuned. It suggests that I advance my timing as far as possible to maximize my idle. It also says I can't go too far as the idle will get poor and it will ping under load.

I've found that's not 100% true. I've been able to get it to idle highest at 22deg adv (w/o vac and at 600rpm in drive). This got rid of the bog completely however, when I was this high the engine eventually died (overheated?).

Does high advance equal overheating?

What could the source of the bog be when I go back to 6-10 deg advance? Why does it run so well at 22 deg?

Details:
29 deg dwell (26-30 recommended)
timing with bog 6-10 deg ATDC
rpm 600 in drive with lights on
vac advance and mech advance seem to be working fine.

Randy

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bishir

· #2 · Mar 12, 2001

Your 22 degrees of advance sounds a whole lot better than your being 10 degrees retarded and getting the bog. It's not unusual to run over 30 degrees of Total advance. Yes, it can cause you engine to overheat, but I don't think that is the reason it died. Perhaps you need to back it down a little. What does you temperature gauge show? Being to retarded can cause you to overheat too.. good luck!

See my 69 convertible and the VMF parking lot at: http://www.geocities.com/Bishir1/FrontPage.html
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Discussion Starter · #3 · Mar 12, 2001

I agree that no bog is better (although pushing the car may get "old"). I don't understand why 22 deg's is better on a car that ought to be at a factory 6 deg (I'm pretty sure the timing chain is set right and it idles SMOOTH anywhere from 6 to 22 deg's).

The 22 degrees was w/o vac advance and at 600 rpm (i.e w/o mech advance) so I'm sure my total was >30.

The temp guage read above normal but still less than 1/2 way. There was no sign of boil-over, etc. The engine started missing, then died and wouldn't restart until after it had cooled (I assumed over-heat and/or vapor lock although I was getting a good shot of fuel when I looked in the carb). I run a stock 289 set-up (i.e. OEM radiator w/ no shroud) and I had the hood open (so poor airflow) with an ambient temp of about 70 deg's (Houston area).

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66gt350

· #4 · Mar 12, 2001

Unless you checked out exactly where TDC is on your balancer or it's a new harmonic balancer, you can't go on the exactness of the timing mark. Over time the balancer could spin, causing the marks to be way off.

Like the court jester (bishir) said -- having too much or not enough timing could cause your engine to overheat. I normally advance the timing as much as I can, until it starts to ping and then I back off a coupe of degrees. But, since you siad that you weren't getting boilover, I would believe that you were over heating. I would seriously consider getting a fan shroud, they are worth it. When I put one on, I noticed a significant drop in temperature.

Rob
Member: Slightly Modified
66 coupe 302
66 fastback 351W

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Discussion Starter · #5 · Mar 12, 2001

Thanks.
Yup, new harm balancer too. Unfortunately, I didn't measure it's exactness and, if I remember the procedure I'd need to pull the heads and use a dial indicator (probably not worth it at this point). Maybe a few degrees of timing here but could a new one be off 10 degrees or more? I don't know.

This is the first car I've owned w/o a fan shroud and I don't like it. I was trying to do the concourse-thing and since I don't have A/C I have the smaller 289 radiator (non horse-collar mount) and no shroud...do they even make one for the smaller radiator?

If I'm overheating now, albeit with an open hood and no forced air-flow, I can't wait for the Texas summer!!

Randy

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66gt350

· #6 · Mar 13, 2001

To check for TDC you don't need to pull the heads. There is another way....But what you'll need is a piston stop. Basically something to screw into the sparkplug hole to stop the piston, hence the name. LOL /forums/images/icons/smile.gif You just rotate the motor until it stop, make a mark on the balancer by the pointer. Then rotate the motor the other way, until it stops, make a mark. The center between the two marks will be TDC. Since you have a new balancer, I'd say that it's fairly close.

As far as overheating...Have you taken a peek inside your radiator? How clean is it? Could it need to be boiled and rodded out? How many blade fan do you have? Increasing the number of blades will increase the amount of air that it pulls.

Just a couple of more things for you to ponder.

Rob
Member: Slightly Modified
66 coupe 302
66 fastback 351W

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