ztheusa

This 1967 427/390/converted to 400 just got out of the shop. I rebuilt the engine, transmissiom, driveline, front end, radiator, on infinititum.

The engine was reassembled with 9.25 CR pistons and some head work was done. The 400 manifold must be made out of gold, because that's what it cost. The carburators are all new Holly.

Everything is very tight and I need to get some miles on the car to loosen it up a little. I've had this car forever and driven it 150,000 miles. So, an overhaul was due. It is SO tight now. HOWEVER!

It has a hesitation, stumble, terrible drivability, off the line. Between 700 and 1400 RPM it just bogs down. It runs much better cold when it is getting choke so I believe it need more GAS.

What should I do?


Karl

ztheusa

BTW, doesn't it look nice without the front plate. I live in Washington where a front plate is required EXCEPT for "classic" cars over 25 years old.

The car is registered only ONCE, money will never come due again, gets a special plate for the REAR only. Best thing I've ever seen the WASHDOL do!

ztheusa

One other thing, the engine shop was able to overhaul the ORIGINAL engine and not deck off the "ALL" important NUMBERS!



Sorry for taking up so much bandwidth! But it is SO fun to have this midyear back. I HATE the term C2. What moron thought THAT up?

Seaside63

I'm with you on that. As far as I'm concerned there are 3 types of Corvettes.... Straight-Axles, Mid-Years, and Junk.

Oooppppssss...... running for the door.

67L36Driver

Check all the usual suspects.
Timing advance; not just at idle (vac can disconnected) but see to it that you get 36-38 degrees total.
Points; condition with stable dwell (28-32 deg). Check for excessive dist shaft wobble.
Plugs; fouling? heat range.
Vacume advance can; working or not, pin starts to move at 6-7 inches of hg and bottoms out at 14-15 inches of hg.
Centrifugal advance; stuck? weights binding on pivot pins?
Coil; intermitent short/open as engine temp goes up.
Secondary carbs; closing tight, not sucking air.

All specs are in the '67 CSM.

JohnZ

Connect the vacuum advance to the choke vacuum break hose with a tee so it sees full manifold vacuum; the stock configuration is "ported" vacuum. Big difference.

ztheusa

Thanks for the tips 67L36Driver. I'll have my mechanic check this.

And JohnZ, thanks as well.

JohnZ, can you elaborate a little on just where the takeoff point for the stronger vacuum is? My choke is thermal, I think. And I don't have power brakes.

Thanks,
Karl

ZRGator

[Sorry for taking up so much bandwidth! But it is SO fun to have this midyear back. I HATE the term C2. What moron thought THAT up?[/QUOTE]

I just had my 427/400 in the shop and the carbs were rebuilt. The problem of the "bog" my guy attributed to the jets. The stock jets were replaced with slightly larger pieces. The car runs like a raped ape now.

BTW, I agree with you on the C2 term . My car is a midyear and I'll always call it that. Good luck with the bog, I'm sure you'll get it fixed.

JohnZ

The pic below shows the stock configuration, with the distributor vacuum line connection at the base of the center carburetor - that's a "ported" connection (no vacuum at idle). Plug that nipple and insert a tee in the short hose that comes off the front of the gold-colored choke pull-off diaphragm at the center of the photo, and run the distributor vacuum line to that tee - that will give you full manifold vacuum to the distributor at idle.

ztheusa

John, Great photo. Thanks.

I took this to Del, my mechanic. He is very good and completely understands.

However, he wants me to put 500 miles on the car and try to get it running with standard GM specs. Then, if that won't work out he's willing to relocate the vacuum and re-jet the carb.

Sounds reasonable to me, except the part to run around with the hesitation for 500 miles!

Best

ztheusa

OK John.

It's funny. There already was a "T" off that choke line that was capped off. So I just hooked up the distributer with a short length of hose and capped off the old source.

I does run with less hesitation, but it also idles faster and now runs on when i turn off the engine. It might just be running with less hesitation because of the 1200 RPM idle---I don't know.

Sure is fun driving it around again. Especially since it is no longer my only car!

Best,
Karl

Seaside63

Question: How do you get a 6 passenger Corvette ?

Answer: BUY 3 OF THEM !!!!

Nice stable ya' got there Karl

ztheusa

Seaside,

The secret:

Only buy------Never sell!!!


Karl

JohnZ

That's perfectly normal, and to be expected - you now have full vacuum advance at idle, which increases the idle speed; just set the idle back down where you want it with the idle speed screw on the driver's side of the linkage (which will stop the run-on), and adjust the two idle mixture screws on the float bowl for highest steady vacuum with a vacuum gauge.

ztheusa

OK, JohnZ!

Couple of stupid questions.
1. What kind of vacuum gauge should I buy at Sears?

2. To which vaccum port should I attach it while adjusting the idle mixture?

Thanks again for your help.

Karl

67-427ci

JohnZ: I read you reommendation and made this change to my '67 last night (454/425hpHO GM Crate Engine with 427/435 3x2 Carbs) and the idle is much better. I did not get a chance to drive it since I am replacing the trailing arm assy's this weekend. From the way it sounds in the garage I think I will like it.
Roy

JohnZ

Photo below of a typical vacuum gauge - they're all pretty much the same. You can use the port just below the rear passenger side carb attaching stud (where the PCV hose attaches) for the gauge.

ztheusa

Like someone else said, you seem to always come up with a GREAT photo.
Thanks,
Karl