Another problem

[Subfixer]

Seems everytime I fix one thing, I get another problem.

Here's today's mystery.. A beautiful day, low 70's. I replaced the fan clutch yesterday, and let the car idle for an hour in the driveway so I could watch the temperature. Stayed right at 180* the whole time. Verified with an IR gun. Took a one hour leasurely ride on the back roads to see how everything would perform on the road.

When I first started out, the car idled fine at 800 rpm. About 20 minutes into the cruise, the idle started to drop. At steady throttle in 4th gear between 1000 and 1500 rpm the car was starting to "buck" a bit. As I kept cruising, it got steadily worse.

I thought it was loading up, so I did a couple of blasts to 6500 rpm with no breaking up or any other problem, so it seems the ignition system is working correctly. By the time I got home, the car was barely idling at 550 rpm. It seemed to be running really rich. Engine temp never got above 185*, so I know it's not a coolant overheating issue.

Checked the timing, 10* BTDC, Dwell 30. No fuel leakage observed, but that may not mean anything.

Both float levels appeared to be correct when I pulled the sight plugs, but I knocked both front and rear float levels down about 1/2 turn each, but haven't made another run yet. Hoping that will fix it.

Car is a '64 vert, running a "correct as GM built it" '64 327/365 setup with LT-1 cam. M20, 3.36 rear. "New" restored 2818 carb installed last month.

Any other ideas out there? Thanks.

 

[Ken Anderson]

You've got problems with your "new" carb. I would suspect the idle circuit is clogged. Any backfires since the install. If so, the PV probably blew. Ask the rebuilder if he installed a backfire kit. Your "bucking" could also be a bad VA or stuck flyweights in the distributor.

 

[Subfixer]

No backfires since the initial startup last month. Idle circuit appears to be working properly. I followed Lar's tech article to the letter. Great off idle transition, idle circuit is fully adjustable. Don't think I killed the PV as the car runs great for the first 30 minutes or so after warm up. I drive it daily to work, but that trip is only 6 miles. Only have this problem on longer runs.

 

[IH2LOSE]

With out thinking about how the heat would cause this problems to show up.

What did you do with your distibutor,have you checked the vacum advance can linkage,could it be binding. or the cintrificul advance?

 

[Subfixer]

First place I went was the distributor. Vacuum advance still works, centrifical doesn't come in until around 1000 rpm. Car normally idles at 800.

Took another ride today and it did it again. I'll check the float levels again, but I'm strating to think that's not it either. Definately not running lean. Very rich by the time I got home. Barely idling at around 550.

 

[IH2LOSE]

I know this may sound silly but what posistion is the choke in when she starts running funny.I am not sure what carb you have but I purchased a rebuilt carb from a Caddy vendor for my 67 Deville As I am studying the the carbs to make sure they are the same.I noticed that the choke did not look proper.I put it on anyways thinking my original was funny,Needless to say the car would not choke on start up.After it warmed up it did choke.The fellow some how had the linkage wrong,and it did the same exact as what your describing

Have you checked to see if the choke is coming on.

 

[Sting Ray]

'Fixer,

If you shut the car down, and let it sit for a couple of mins does it start right up again? Might be vapor lock if you steel fuel line is getting to hot, just a thought.

Tom M

 

[Subfixer]

Choke is full open..

I did have a hot start problem ealier this month but I fixed that one. Turned out to be an ignition problem. Car starts right up all the time, but when hot, it is rich when starting. Definately not vapor lock. Vapor lock would create a lean condition and I have the opposite.

 

[Mikey1]

Check for any ignition cable to be penned in with any piece of the ignition shielding...especially the lower ones.

 

[Subfixer]

Thanks Mike. The car does not develope a miss, just idles down too much when hot.

Of course this leads to a bunch of other stuff not working. Like a cascade effect. Once the idle drops down to about 600 rpm or less, due to the solid lifter LT-1 cam, there's not enough vacuum at that speed to keep the vacuum advance fully deployed, (VC1810 - 8" vacuum for full advance) which in turn lowers the idle more, etc... By the time the engine is idling at around 500-550 rpm, the power valve is probably starting to open as well (6.5" PV) giving me a real rich condition.

As you can see, once all this stuff starts to screw up, it's really hard to tell what the real cause is because everything is wrong.

 

[IH2LOSE]

Thanks Mike. The car does not develope a miss, just idles down too much when hot.

Of course this leads to a bunch of other stuff not working. Like a cascade effect. Once the idle drops down to about 600 rpm or less, due to the solid lifter LT-1 cam, there's not enough vacuum at that speed to keep the vacuum advance fully deployed, (VC1810 - 8" vacuum for full advance) which in turn lowers the idle more, etc... By the time the engine is idling at around 500-550 rpm, the power valve is probably starting to open as well (6.5" PV) giving me a real rich condition.

As you can see, once all this stuff starts to screw up, it's really hard to tell what the real cause is because everything is wrong.

Did you figure out what the problem is yet?