Holley 650

Mike, this can be many things. Since it's come gradually, could it be a vacuum leak developing?

Allow me to recommend my own site that deals with adjusting Holleys step by step. If you do all the step, I'm sure it'll be solved...

TuningMadeEasy

Thanks for the link. I know about that one.

The carb was sent back to Holley and they covered the problem under warranty. Their service and support is absolutely amazing!!! What I’m trying to figure out is how I managed to mess it up and apparently I did! Also, why it worked fine for a couple of months and then started having problems. It did start about the time that our hottest weather cooled some. Put my 600 back on and it runs perfectly. Here is what Holly said.

“The air fuel was just out of adjustment this is mainly your throttle plate opening on your transfer slots front to rear where either closed to much or open to much on the primary and secondary's, you have a max of .020 you can expose on the primaries with the plates closed and .015 on the secondary's.”

“As we received the carb it was basically just out of adjustment the Air was 27% lean and the fuel was 30% rich, fast idle was adjusted low the carb was set back to the factory specs and flowed and passed as a good carb.”

“Do you have an aftermarket cam installed? A lot of times this is where these adjustments become a issue and you have to balance the air out between the primary and secondary in order to get a smooth idle with the cam without exposing to much of the transfer slots.”

Mike

One trick to avoid having to open the primary throttles up so much that they go above the transfer slot on a wild cam engine, is to drill a 2mm hole in each primary throttle plate. I must say though that it's rare that it's necessary if the carb and ignition is properly adjusted. The cam has to be very wild. And as Holley says, if you can get the extra air needed to get a good idle via the secondaries, that's a better method (and reversable).

Insufficient initial ignition advance ...

Initial advance should be set in the range of 18 degrees BTDC, or as much as your motor will tolerate and still start when its hot, with the vacuum advance connected to "ported" vacuum.

Ideally you want to twist the distributor to achieve the highest possible intake manifold vacuum at idle. But of course, too much initial advance may make the motor too hard for the starter to crank when the motor is hot. Its possible to run a Cobra Jet at 20 degrees BTDC.

The problem would progressively worsen if some of the various slots or holes exposed below the throttle plate were slowly being plugged with carbon.

-G

The carb is only four months old. Holley was so helpful and it was outstanding that they would help me out with a carb that was a few weeks out of warranty.

Looking back on my maintenance log I did advance the timing a month or so after I installed the carb. I have more advance timing available but I wanted to use some caution. I’m running about 15 degrees initial and 35 total so I have a few more degrees available.

When I changed the timing I had to close down the throttle stop, so the throttle plates must have been way, way past the transfer slots before that. I’m still mystified how I managed to get the carb adjustments so far out of wack and not know it. The 600 is working perfectly but I’m going to put the 650 back on and see how it works.

I’ve been turning wrenches on cars since my first car at age 15, and it never ceases to amaze me how there is always more to learn.

Oh, and 15 was more than a few years ago!


Mike

Received the 650 back from Holley last week and installed it today. After installing and warming up the engine I found that the idle speed was a little too fast and the mixture just a tad too lean. Adjusted the idle speed and the mixture. Runs great! No hesitation! Dang, can’t believe I messed it up!!!

Holley has been absolutely fabulous in dealing with my carb.


Mike

Spoke too soon!! On my first cold start I found it had the same problem until the engine was warmed up and driven a few miles. Messed with the choke and had no success. So back to the 600 and I’m putting the 650 in cold storage.

Mike