Engine Surging

[69volunteer 84]

I don't drive my car as much as I would like--it has been sitting in my storage unit for the last couple of months. I took it out Saturday evening and after first start up, in gear, the engine will surge up and down maybe 500 rpms. Pop it into neutral and it goes back to idling fine. This is only when I am siting in D or R with my foot on the brake or if I am slowly backing out of the drive way.

 

After warm up, the problem goes away.

 

Fuel issue? I have never been one to use Stabil or some other fuel storage additive but recently picked up some.

[Mach1 Driver 560]

here's some other ideas courtesy the internet:

PCV

Ignition system

A/C compressor cycling on/off due to low refrigerant

Plugged/restricted exhaust

Clogged fuel filter

Fuel system pressure issue

Air in cooling system  ??

Vacuum leak

 

 

[ray1970 88]

Most fuel additives don,t work very well if at all with the current fuel blend we have at the pumps..

But people keep buying it...It gives someone a job...

Surging would normally be from running lean be it an air leak(split hose or fallen off) or a lightly plugged jet and possibly dead fuel.

The current fuels can corrode an all ready small jet into something barely usable over time..

If you dont use the car much you my still have the gas in the tank from last year or the year before..

This is not good because it will lose much of it ability to start your motor and have it idle well..

Thats why racers only use fresh fuel....And give the old stuff to there friends..

 

At the very least I would turn the air screws all the way in than readjust them.

This my push some of the corrosion off the port and needle if there is any..

[Brian Conway 264]

My vote ?  Vacuum leak.  Brian

[ray1970 88]

Keeping in mind that it ran good before the car took a long nap..(but I don,t know that)

Carburetor or fuel or both would be at the top of my list..

After a motor warms up air leaks don,t tend to get a lot better at least the surging kind.

 

But have I been wrong before!!!Sometimes more than twice.

[69volunteer 84]

_{Thanks for feedback.....car runs fine once it is warmed up so how would a vac leak go away after the engine is warm. I try to only fill about 1/4 tank or 1/2 tank at most so that fuel doesn't sit long. Carburetor is almost brand new. I'll check the fuel filter but it is also new. The car doesn't sit for too long....last drove it in February or March....was driving it pretty regularly then without issue.}

 

_{Speaking of Stabil, I recently bought a Champion portable generator/inverter and they recommend using Stabil in their generator engine. I have not been a believer and try not to let gas sit for very long.}

[Rsmach1 71]

What carb do you have?

 

Edit also how much ethanol is in your local pump gas?

 

I'm leaning towards carb/fuel.

 

Here is an interesting tidbit http://www.drivenracingoil.com/news/dro/training-center/articles/protect-yourself-ethanol-is-killing-your-carburetor/

[69volunteer 84]

Edelbrock 500

 

10% ethanol here in TX.

 

I knew about the fill the fuel tank/cell to prevent moisture being absorbed into the fuel. I don't follow that on this car and maybe should. I can get ethanol free but need to drive to the other side of dallas to find it. Maybe its worth it.

[Rsmach1 71]

1st think I'd try is to run the tank low and get a fresh tank of fuel. Also check for vacuum leaks all around the carb and check fuel pressure(do you have a vacuum/pressure gauge?) When you say almost brand new, how long has the carb been on the car?

 

Edit also check your choke setting and operation.

[ray1970 88]

Dead fuel will not vaporizes very well if at all in a cold motor..

The 10-15% ethanol only makes matters worse so far as carburetor problems..

Getting non ethanol fuel is a short term fix for a long term problem if you dont use the car very much..

A full tank of fuel will last way longer than a near empty tank most of the time..

[Rsmach1 71]

+1 with Ray. I'd also get in the habit of starting the car and bringing it up to temp bi-weekly or at least monthly when being stored. Dried up carb gaskets/seals might also be causing issues.

[69volunteer 84]

Thanks guys for the input....I may invest in some 5 gallon tanks to fill periodically on my way out of town--I believe there is a non-ethanol station on the way to Houston that I pass. I'll check for vac leaks as well.