I took my car out for some more "break in miles" for the new motor and brakes etc.... it seems to run great and stops just fine but it does something kind of wierd...

When I first come to a stop the car idles around 1300-1400 RPM and then slowly drops down to 900 and then idles there just fine.... it takes a minute or two for this to happen after a complete stop......

The motor is a 355 with a Comp 284H. MSD distributor ( no vac advance) and a Holley DP.... like I said the car runs fine and idles well at 900 RPM.... I just thought it was kind of wierd for the idle to stay at 1400 RPM and then drop over a minute.....

Is this normal for a new motor ????

Check your throttle return spring.

If the throttle return spring doesn't do it, check to see if the choke is holding it open.

If that doesn't do it, check your power valve rating. The Holley DP comes with a 6.5" valve stock, if your engine vacuum is close to 6 or 7 inches it can cause the valve to open at weird times. With the car in gear take your lowest steady vac reading and subtract 2.5" to get the right power valve.

Just an idea.

At what rpm does your mechanical advance curve start? You may be catching the bottom end of the curve as you reduce the thottle. As the rpm dips slightly, the timing drops, which reduces the idle, which drops the timing even more, until you are down at the stop.

I'm with oneofakind67. I had similar issues, swapped in stiffer springs for the advance weights, problem gone.

I'm using the MSD Pro-Billet with the one light blue and one light silver springs and the black advance stop bushing.....

The guy that will be dyno tuning my car suggested I start with those........

He also built the carb for me too...... the carb is actually more like an HP series carb than the DP and is a mechanical secondary... he built it specifically for my combo, so I dont really know the details.....

The return spring is a double spring, its intact and pretty damn tight... it springs the throttle back very well....

As far as vaccum.... the cam is a 284H, so I'm sure it doesnt pull much vaccum at idle.... I dont have any vaccum accessories....

Another idea -

Look closely at how your air cleaner fits. I had a similar problem and found that the air cleaner base was interfering with the secondary accelerator pump and holding the secondarys slightly open, which caused a fast idle problem.

do you have power brakes? if so check your hoses and plunger seals .

No power brakes.... the air cleaner has plenty of room... the linkages moves feely and doesn hit anything.....

I have the same thing going on with my 1050 dominator. I haven`t found a solution yet, but I believe it is related to the fuel curve and idle circuit. I installed an air/ fuel ratio gauge and it reads slightly rich right when I stop with the idle running fast. After a short time the mixture slowly leans out and the idle speed drops. I haven`t had a whole lot of time to play with the carb yet though. Brent

could the float cause a problem ? level too high? :confused: