I've already decided to get a 100% new turnkey engine with fuel injection. I just need to sell my Tundra first. At this point, just trying to decide whether or not I want to continue to tinker with the current engine or if I just want to be done with it. One thing I will do is pick up the book you suggested.

Thanks,

DC

 

Hey Mark,

Talked to the previous owner. He was real proud of this engine and is concerned about what has happened to it. He said he had a leak down test done which came up excellent for each cylinder. However, my compression tests, vacuum tests and the slight smoke I get when the engine is cold all point to worn rings. Question: Could my compression readings be correct and still have good leak down? He thinks the leak down test is more important than the compression test and wants me to get another one. I'm just wondering if it is worth the trouble at this point.

Thanks,

DC

 

If the PO says he is concerned then maybe another set of eyes would be worth the investment. See if you can find a shop to check it for you before you give up on it.

-Mark.

 

I'll probably do that. The PO is a good guy and he just wants to help me solve the problem.

Could my compression readings be correct and yet each cylinder still have good leak down results?

DC

 

Now that the new fuel pump was on, I tuned the carb yesterday. When I first fired it up, it was running very rough and wouldn't stay running unless I kept the rpms above 1500. It didn't take long to smell raw gas coming from the exhaust. Shut it down and found the primary float was stuck wide open. I could not get it to stay adjusted properly so I replaced it. The new float did stay adjusted and I was able to tune the carb. Used the tach and the vacuum gauge and set the mixture screws to where I got the highest reading on both. Then turned them about 1/8 of the turn to lean it out a bit. When I drove it, at first it had a stumble just off idle. But, after driving it around for a few miles that went away. It seemed to run much better and I even unexpectedly left a little rubber on the street at one stop. Thought my carb troubles were over. Wrong.

Fired it up today and for about 30 seconds it was running very rough again although it would idle by itself. It eventually "cleared its throat" and the fast idle kicked in and it ran okay. However, after the idle went back to normal, driving it around showed that I am back to where I started with the quality of the idle. Is that just the nature of the beast with double pumpers?

I am now thinking of replacing the carb. Any suggestions?

I haven't yet found a new vacuum advance so I need to do that first, then get the distributor right before trying one last time to tune this carb.

On Saturday, after replacing the primary float and then tuning the carb, the vacuum picked up a bit from 10" to 12". How much could an out of tune carb impact the vacuum at idle?

Thanks again for all the help.

DC

 

Instead of buying a new carburator at this point, I would suggest you get yours working the way it was designed to. You'll get a debate on the suitability of DP carbs for the street, but it's not debatable that they can and should work just fine. As I stated above in post #29, I had problems from the get-go with my 4150 Holley, but I got it straightened out and it runs just fine on the street. Not the greatest gas mileage, but it has no drivablilty problems whatsoever - it idles fine, and pulls strongly from idle on up. No hesitation, no flat spots, it drives like a modern fuel injected car does.

Don't just throw money at the problem, get your carb fixed and tuned correctly first, and then at a later time if you decide to swap carburetors for some reason, you can do that.

Cheers,
Pete

 

So far I have replaced both floats and it looks like the new floats along with a fuel pump of proper pressure have finally allowed me to maintain proper fuel level. The previous owner and I rebuilt the carb in his garage (new power valve, needle and seats, gaskets etc). I may have to take it apart and clean it good like you did. And once I get the vacuum advance fixed maybe it will help smooth out the idle.

I may have to get some professional help which may also be throwing money at the problem (and away given the compression readings). I'm really frustrated with this engine right now. Thanks for your help and insight.

DC

 

Finally found the time to get the Vette to a good mechanic after I finished what tweaking I could do.

I had already installed a new stock fuel pump and replaced both floats in the carb which cured the flooding issue.

Distributor was gunked up, curved wrong and was only providing 14 degrees of advance. I took it apart, cleaned it up, installed springs according to Lars - got the mechanical advance to provide 18+ degrees of advance and the timing to come all in just above 2500 rpms.

Vacuum turned out to be good. My brand new vacuum gauge was bad and reading low. Vacuum is now running better than 15" which mechanic said is about right for the way this engine is built.

Mechanic found the following:

Compression was so good no leak down test was needed. My brand new compression gauge had a couple of buggered threads and was very hard to install in the three cylinders with bad reads so I was not getting a good seal.

HEI distributor was only getting 10 volts. Apparently the lead to a points style distributor is a "resistance wire" and had to be replaced to get full voltage to the HEI unit. I now have a new proper "pink" wire. Verified distributor curve was good.

Main problem with cold start and rough idle was a bad electric choke.

Two bad plug wires. Replaced them all.

Carb was running rich and had to be rejetted. Plugs had to be replaced.

Vacuum advance was replaced with an adjustable unit.

I ended up having it dyno tuned. Picked up 56 rwhp from first pull until final tune. Expensive tune and troubleshoot but the engine runs fine now and is ready for me to pick a fuel injection system.

Thanks to all who helped.

DC