Chevy Nova Forum banner

1 - 20 of 29 Posts

·
Registered
Joined
·
692 Posts
Discussion Starter #1
When I drive my 63, whether its warm or cold outside, and I turn the car off. 10 minutes later it's like the car has been sitting for months. Carburetor seems to be dry. Have to turn it over a bit and pump the pedal several times to get it to start. It's always been like this. I put a 1" phenolic spacer under the carburetor and it helped a little but still annoying. Couple days ago when I turned it off it dieseled first time ever. Temp seems fine. Usually 180-190 depending on the outside air temperature. Is the gas is boiling out of the carb for some reason?
 

·
Registered
Joined
·
39 Posts
I have the same issue...the motor gets a lot hotter when it sits after running and shut off...I'm hoping to get a much better radiator to keep the temp down at 140 at idle...just to stop the fuel boil ...trying to get it to run longer than a 1/4 mile...just trying to deal with traffic with a cantankerous cam is tough enough...maybe I will make a vid on my phone tomorrow to show you what I mean...depends on weather
 

·
Registered
Joined
·
1,102 Posts
The ethanol in the fuel evaporates much more quickly than gasoline. With the addition of ethanol in the fuel, we are seeing vapor lock issues on motors with carbs. (Fuel injection runs at a much higher pressure which raises the boiling point of the ethanol so you don't have that issue). Other than running an electric fuel pump with a return line back to the tank to keep the fuel cool, there is not a whole lot that you can do.
 

·
Registered
Joined
·
692 Posts
Discussion Starter #7
Should have put this information in the initial post. 63 convertible.
327 right at 300 hp 18 deg initial timing with 34 deg total.
Standard distributor with Pertronix upgrade.
Ramhorn exhaust connected to Pypes exhaust.
TH350 transmission with oil lines running to radiator.
mechanical fuel pump
Cam is same specs as L79
Winters l79 intake
Holley 650 double pumper with manual choke. Fuel line routed along rocker arm. .Enters engine bay in front fender well. As far away from exhaust as possible. 1" spacer between carb and manifold.
4 core radiator with clutch fan and 180 degree thermostat. High volume water pump. Same pulleys as L79. Fan shroud.
Few thousand miles since rebuild.
On an 80 degree day engine temperature taken at thermostat housing is 190. After engine is turned off temperature at same location is 205.
Cold blooded starting in winter but just fine when it's above 60 degrees outside. Runs great and doesn't overheat. I have 2 other cars with small blocks. Another 327 and a 350. All stock. When I drive those cars under the same circumstances and turn them off when I start them I barely turn the key and they fire right up. Don't touch the gas at all.
 

·
Registered
Joined
·
1,180 Posts
I am assuming that while you are driving your car, everything is functioning normally and the engine has no issues with cruising or acceleration.

Drive your car as you would normally to experience the issue in post #1.
Shut the engine off and wait 10 minutes.
With the engine off, remove the air cleaner and move the throttle lever while looking down into the throttle bores of the carb. Did you see gas come out of the primary squirters?
  • If not, check carb's primary accelerator pump for correct adjustment... or possible leaks at accelerator pump diaphragm and/or fuel bowl & metering block gaskets.
  • If accelerator pump and all gaskets are in good working order and still no gas from squirters with movement of throttle lever, "fuel boil/evaporation" is probably causing your hard starting issues.
If you are seeing gas from squirters with movement of throttle lever, move to the steps below.

With the engine still off, remove the sight plugs from the side of the fuel bowls (be sure not to loose the little washers on the sight plugs)... did any gas come out of the sight plug holes?
  • If so, your float level(s) may be set too high, possibly flooding the carb as you attempt to start. Adjust float level.
  • If not, go to the next step below.
Push the front bumper up and down while watching the sight plug ports.... does gas trickle out of the sight plug ports?
- If so, your float adjustment is probably ok and I think something else beside "fuel boil/evaporation" is probably causing your hard starting issues.

If not, start your engine with the sight plugs still removed and repeat the steps above.
  • If gas does trickle out of the sight plug ports with the engine running, your may be experiencing some fuel evaporation in the fuel bowls due to the carb getting too hot. Recommend installing a heat shield under the carb.
  • If gas does not trickle out of the ports with the engine running (and bouncing the front bumper), your float level(s) are probably set too low. Adjust float levels to correct setting. Reinstall sight plugs.
Test drive car again.
 

·
Moderator
Joined
·
6,267 Posts
I am assuming that while you are driving your car, everything is functioning normally and the engine has no issues with cruising or acceleration.

Drive your car as you would normally to experience the issue in post #1.
Shut the engine off and wait 10 minutes.
With the engine off, remove the air cleaner and move the throttle lever while looking down into the throttle bores of the carb. Did you see gas come out of the primary squirters?
  • If not, check carb's primary accelerator pump for correct adjustment... or possible leaks at accelerator pump diaphragm and/or fuel bowl & metering block gaskets.
  • If accelerator pump and all gaskets are in good working order and still no gas from squirters with movement of throttle lever, "fuel boil/evaporation" is probably causing your hard starting issues.
If you are seeing gas from squirters with movement of throttle lever, move to the steps below.

With the engine still off, remove the sight plugs from the side of the fuel bowls (be sure not to loose the little washers on the sight plugs)... did any gas come out of the sight plug holes?
  • If so, your float level(s) may be set too high, possibly flooding the carb as you attempt to start. Adjust float level.
  • If not, go to the next step below.
Push the front bumper up and down while watching the sight plug ports.... does gas trickle out of the sight plug ports?
- If so, your float adjustment is probably ok and I think something else beside "fuel boil/evaporation" is probably causing your hard starting issues.

If not, start your engine with the sight plugs still removed and repeat the steps above.
  • If gas does trickle out of the sight plug ports with the engine running, your may be experiencing some fuel evaporation in the fuel bowls due to the carb getting too hot. Recommend installing a heat shield under the carb.
  • If gas does not trickle out of the ports with the engine running (and bouncing the front bumper), your float level(s) are probably set too low. Adjust float levels to correct setting. Reinstall sight plugs.
Test drive car again.
Good write up.

If you note that fuel is evaporating, check the carb temperature with a infrared gun. As well do you have the choke off blanks(I think that is close to what they are called) on the intake gasket. That will reduce some of the manifold temperature.
 

·
Registered
Joined
·
692 Posts
Discussion Starter #10
When driving the car runs great. No issues with acceleration at all. Mash the pedal and it goes. I'll try to drive it today and follow your instructions. Supposed to rain. If it doesn't I'll take it for a spin. What is a "heat shield under the carburetor"? Is that the pan on the bottom of the intake manifold you're referring to.
 

·
Registered
Joined
·
1,180 Posts
What is a "heat shield under the carburetor"?
The "heat shield" I am referring to is a thin aluminum plate that is installed between the base of the carb (or carb spacer) and the intake manifold. See image below - red arrow.
It helps to reduce the radiant heat from the intake manifold from heating/boiling the gas in the fuel bowls.
404677

See reviews from link below.
 

·
Registered
Joined
·
692 Posts
Discussion Starter #13
OK. It turned out to be a beautiful day in the north west. Went for a nice long drive. When I pulled into the drive way the thermostat housing temp was 192. Top of intake manifold just under the carb spacer is 210-215. Parked it and let it sit for 14 minutes. Looked down in the carb and worked the throttle and fuel does squirt out immediately. Pumped it 4 times just to make sure. Fuel each time. Started better but doesn't just fire right up like I think it should. I wouldn't think I would have to pump that much fuel in it to get it to start. Especially when its warm.Plus the dieseling when I shut it off is new. Just started doing that the last time I drove it and again today.
 

·
Registered
Joined
·
39 Posts
Plus the dieseling when I shut it off is new. Just started doing that the last time I drove it and again today.

that could be a too high idle speed...my idle speed is 1100 rpm...it acts better at 1400 rpm at idle...but will diesel when I shut it off
 

·
Registered
Joined
·
1,180 Posts
Went for a nice long drive. Parked it and let it sit for 14 minutes. Looked down in the carb and worked the throttle and fuel does squirt out immediately. Pumped it 4 times just to make sure. Fuel each time.
Ok... so the gas in the fuel bowls is not evaporating.
  • Did you get a chance to remove the fuel bowl sight plugs to check on the float levels?
Did you ever remove the carb to check how much of the Transfer Slots (located under the carbs primary throttle blades) are exposed?... Square or rectangular shaped transfer slot exposure?
NOTE: Additional information regarding Transfer Slot exposure shown in the link below.

327 right at 300 hp 18 deg initial timing with 34 deg total.
Standard distributor with Pertronix upgrade.
IIRC, Pertronix sells different upgrade kits for Chevy distributors (Ignitor, Ignitor II, Ignitor III)... and each different Ignitor system specs a specific coil primary resistance.
  • Do you know what Pertronix Ignitor system... and what coil you are currently are using?
  • Are you powering the coil + / distributor with full battery voltage (12+ volts)?
Do you know what specific spark plugs you are using?... and what the spark plug gaps have been set to?
- It would also be helpful if you remove a couple spark plugs and let us know what the insulator tips look like (posting a couple photos of the spark plug tips would beneficial).
What type of spark plug wires are you using?... Spiral core?... Solid Core?... Resistance?

How do you currently have the distributor's vacuum advance hooked up?.... "Full Time" manifold vacuum?... or "Ported/Timed" vacuum?
  • There are benefits to connecting vacuum advance canister to a "Full Time" vacuum source, but only when a vacuum advance stop plate is also used.
Note: Maybe Old Man (SNS Member) will chime in with additional info.
 

·
Registered
Joined
·
387 Posts
Run-on is typically due to the throttle being open too far as described by Rifraf and Nova 71-436 above. This can also cause your hard start by pulling too much fuel from those open transfer slots when you first hit the starter causing a rich condition.You may have to advance your timing a bit (idle speed will increase) then turn the idle screw to lower the idle speed. If you go 2 degrees, you'll be at 20 deg initial and 36 all in, which should work, but listen carefully for detonation. If you are running vacuum advance, and notice a part throttle or cruise miss, you may need to dial back the timing or adjust the amount of vacuum advance. Carefully check for vacuum leaks as well.
 

·
Registered
Joined
·
692 Posts
Discussion Starter #17
Well, heres what I know. Pertronix is Flame Thrower II with correct coil. Plugs are AC R45 gapped at .036. Plug wires are AC Delco premium 7MM. Not sure what the core is. Fuel is at the bottom of the sight hole. Bumping the car makes it spill over. Vacuum to the distributer picture is attached as well as a couple spark plugs. I have not looked at the transfer slots. This carb was on the engine when it was Dyno tuned. Only thing I have done since was add the 1" phenolic spacer and adjusted the curb idle. The idle I did recently and could account for the recent dieseling.

p.jpg q.jpg r.jpg s.jpg
 

·
Registered
Joined
·
1,180 Posts
Based on the information (and photos) shown in the above post, nothing really jumps out as being wrong... although I would be curious how much of the transfer slot is showing under your carb's primary throttle blades.

Your distributor's vacuum advance is connected to a "Timed/Ported" vacuum source. Nothing wrong with that... but you could consider switching your vacuum advance to a "Full Time" vacuum source, but may involve making some changes the both the mechanical and vacuum advance curves in your distributor. One of the common ways to fine tune the distributor's vacuum advance is to install an adjustable vacuum advance canister and also adding a vacuum advance limiter plate (to limit the total amount of vacuum advance at the crank to around 10°- 12°) and adjusting your mechanical advance curve accordingly.
Below is a kit that includes the items needed to accomplish the above.

There was a gentleman on this forum (Old Man) that would email detailed directions for fine tuning the mechanical and vacuum advance for a Chevy distributor by sending and email request to [email protected]

Below are a couple links to articles that help explain the benefits of full time vacuum advance vs ported vacuum advance (when set-up correctly).

 

·
Registered
Joined
·
692 Posts
Discussion Starter #19
Thanks a lot for all of the input. I was hoping it was something simple. Like I said earlier the car starts easily when cold and runs great. It is just annoying trying to restart it when it's warmed up.
 

·
Registered
Joined
·
51 Posts
A few things come to mind.
1. Is your coil internally resisted or externally resisted?
If you are Using resistance wire ignition with an internally resisted coil, it might have problems starting since temperature changes the resistance of the wire.
2. Your ignition switch is supposed to
“ un resistor” Your ignition to counteract low voltage due to starter drain on the battery. Is it doing it?
So if your ignition switch doesn’t give your coil full voltage on start, during the start sequence, coil voltage could be 6 Or 7 volts.
3. Try adding another ground wire to the body from the Frame, and check the one from the battery to the engine.
 
1 - 20 of 29 Posts
Top