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New Motor Woes

Stoopalini

Stoopalini

1/2 ton status
Joined
Oct 17, 2000
Posts
999
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Location
Austin, Texas
I just finished installing the new motor in the Blazer, and am having some issues I hope some of you can shed some light on.

The motor is as follows:
  • 4-bolt SBC 355 roller block with 6" rods and 6" style pistons
  • Comp Cams 08-500-08
  • Roller lifters, hardened pushrods, 1.5 roller rockers
  • 305 style heads opened up to 63cc with 1.94 and 1.5 valves
  • Guesstimated 9.5:1 compression
  • Edelbrock performer dual plane manifold
  • Brand new SMI Stage 2 Quadrajet
  • Hooker super comp shortie headers
The issue I am having is dieseling when shut down, but only once it's warmed up. If the motor is warm, and I turn it off, it will diesel for a bit, then shut down with a large spray of fuel coming out of the carb. This makes me think it's running very rich. I've tried adjusting the timing to 0* and 10*, and the same thing happens.

I've checked for vacuum leaks, and cannot find any. The only vacuum lines hooked to the carb are the vacuum advance, and the line which goes to the vacuum reservoir/HVAC controls. The only vacuum lines hooked to the manifold are the brake booster, tranni line, and PCV.

The idle is not that high, but since I don't have a tach, I'm not sure exactly what it is at. I put a vacuum gauge on the manifold, and it read 15 on the gauge. When I installed the motor, my brother gapped the plugs and put them in. I found out yesterday he gapped them at .038. I know factory recommended is .045. Should I run the factory gap with this motor, or should I run some other gap considering the build up? Could the .038 gap cause the dieseling problem and fuel spray upon shut down?

Any help/advice/opinions are greatly appreciated!

Thomas.
 
what kind of gas are u running? we have a truck here at work that diesels if you have cheap gas in it. tried playing with the timing but didnt help. if you've got 9.5 to 1 u should be using premium anyway tho.
 
What are you running for pistons, flat tops, dish etc? And what is the volume of the dome/relief?
 
Running 93 octane and using flat top pistons.
Not sure on the volume of the dome ... I know the heads were opened up to 63cc?

Thomas.
 
Not sure what RPM the idle is set at because I don't have a tach. I have the idle screw out completely, so the adjustment screw on the linkage is adjusted as low as it can be.

Thomas.
 
How are the marks on your ballancer? Is it possible that the marks are off and what you think is 0* is really 5-10? The fact that you have the idle adjustment screw and are still able to idle without loping or missing leads me to beleive you're still over advanced.

What about vacuum advance? Is it disconnected while you're timing it? If so, it's adding 8-12 degrees to your static timing at idle if it's hooked up to the manifold port on the carb.

With 91 octane, my truck pings under light load and diesels like a Cummins when I have my vacuum advance hooked up, but disconnected it runs fine.....

I would suggest pulling the vacuum advance, plugging the port on the carb, then setting the timing like that, and then give it a test drive.

-Mike
 
When I was putting the motor in, I took a spark plug, broke the ceramic off of it, and welded a small rod to the end. I then screwed this into the #1 hole and rotated the motor around clockwise until the piston hit the rod. I then marked the balancer and rotated the motor counterclockwise until the piston hit the rod and made a 2nd mark on the balancer. I then measured the middle of the two marks and adjusted my timing pointer to set this as 0*. I'm pretty sure the balancer markings are good, unless I performed the procedure improperly?

The vacuum advance is plugged into the ported vacuum located at the front, base, passenger's side of the carb.

I'll try disconnecting the vacuum advance and see what happens, thanks for that. Any idea if the vacuum gauge reading of 15 is normal for this motor at idle?

I went to Autozone today and tried to buy the Quadrajet adjustment tool, but they only had an OEM carb adjustment tool, and it didn't look right; so I didn't buy it.

Thanks for the input everyone,
Thomas.
 
After talking to a guy at Advanced, I thought maybe the distributor may be stabbed off a few teeth, because the #8 and #1 terminals on the cap were not parallel with the front of the truck.

I lined the motor up TDC and removed the distributor. I then re-stabbed it so the rotor is pointed at #1 with #1 and #8 parallel with the front of the truck. I then timed it to 10* and am having the same problem, except the motor feels much better now when cruising around. It still diesels when I shut down though :frown1:

With the motor at idle, should the idle change much if I disconnect the vacuum advance? I tried this and the idle did not change at all. Maybe my distributor needs replacing?

Thomas.
 
If it' is in fact on the ported port on the carb, it won't affect it at idle, which puts you back to square one.

I'm out of ideas...
 
Thanks for your input, guess I'll keep working at it. Next thing I am going to do is regap the plugs from .038 to .045 and see what happens.

Thomas.

PS) One more post to hit 1k :cool1:
 
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