pl2000n

The L36 has been newly, and completely, rebuilt. It's basically stock except cam and headers. The ignition is stock as well as the Q-jet. The intake manifold was a Weiand dual plane when I first fired it up after the rebuild. It ran great, but I had to replace the Weiand with the stock manifold due to hood clearance. Note, the stock manifold was on a running 454 just prior to installation so I know the manifold is good. I cannot get the engine to run now! The manifold is literally all that has been changed. The engine will sputter a bit but that's it. I've triple checked that the distributor was installed correctly. Yes, #1 sparks on the compression stroke. I've varied the timing all over from about 8 deg BTDC and 2 deg ATDC. I've racked my brain along with a couple buddies who are engine savey. My brain is out of options. One thing to note, on the driver's side cylinder bank (I didn't check the passenger side since it's such a PITA to pull plugs), #1 and #5 plugs are dry while #3 and #7 are soaking wet. Why would this be? Upon observation, #1 and #5 intake runners are elevated while #3 and #7 are lower, closer to the block. I've tried to get it to run on starting fluid and gas. Timing light shows a good spark. I'm getting 12.5VDC at the coil.

Any ideas? Thanks!

TimAT

Pull all of the plugs, dry them out. Spin the engine whole the plugs are out to dry the cylinders. Put all the plugs back in except #1. Put your finger in the hole and bump the starter to get it up on TDC-- look for the timing marks. Check the position of the rotor to #1 cap tower. If it's spitting as you say, it's flooded pretty and and the timing is not in a happy spot.

pl2000n

Will do TimAT, thanks. Do you (or anyone) think it's plausible that #3 and #7 would be wet while #1 and #5 are dry? That might be an unrelated observation.

Neil B

Since you removed the distributor during the manifold swap, there's a 99% chance the issue is with ignition timing. Go back a re-verify distributor install, firing order, and timing. Also check that you are getting fuel through the accelerator pump. Kinda funny, but I have run mine out of fuel during engine upgrades and it caused me to chase my tail a bit.

pl2000n

Thanks Neil, I'll do that. The timing light fire 4 deg BTDC, so it appears to be correct. Does any know what the voltage should be at the coil while cranking?

MelWff

it should be full battery voltage
are you sure during the intake swap you didnt do something to the carburetor float/floats to cause them to stick open?
while cranking look down the throat of the carburetor with the choke held open and see if you have gas dripping into the throats.

427Hotrod

Install some new plugs and pull the timing up....WAY UP to get it fired. Like turn it about an inch (vacuum canister toward left fender).

You don't want to keep cranking on a new cam and lifters and take a chance on damaging things.

JIM

drwet

I would bet the family ranch its an ignition problem, and most likely timing. Any amount of gas in the intake manifold will be enough to get it to fire. You could throw a couple of tablespoons of gas down the carb and it will fire and run for a few seconds if the ignition is there. I just don't think it is. I would start at the beginning again. Make sure the #1 plug is firing at 4 deg advanced ( 12 would be better) on the COMPRESSION stroke and that you're not 360 degrees out.

'75

Even though the timing light indicates you are 4 deg before tdc, you could still have the distributor 180 deg out of time. Recheck and verify you are on the compression stroke fro #1 and the rotor is pointing to #1 in the cap.

TimAT

That motor will be pretty happy with a minimum of 10* initial timing. Like 427Hotrod said, crank it WAY up.

Jeffs82c3

Are you running points in your distributor? If you are,make sure for proper gap.. Have you checked the color of your spark? Should be blue, if it's red or orange,bad coil... Good luck

68notray

It's going to be something silly. Even 180 out of time it'll at least fire back through the carb. Check to see if the coil is hooked up backwards. Another small thing on a Qjet carb and factory intake - make sure you have the spacer plate and the 2 gaskets or the heat riser pasa ge way is open and exposed. MANY guys make the mistake of slapping the single base gasket on there and wonder why it is crazy lean

Jebbysan

Blow the thumb on #1 as stated......look at your balancer. Is it close to or on #1? Now check rotor position.....is it close to or on #1?
Many problems like this are from a spun balancer or incorrect timng tab position.
It is simple to check...and afterward you can rule it out.

Good Luck,

Jebby

Jeff_Keryk

Pull #1 plug; have friend click ignition with thumb over plug hole.
When you feel pressure, rotate balancer to 6* or more BTDC.
Check rotor is pointing towards #1 on distributor.
If not, restab distributor.
Install #1 plug; hook up timing light; turn on key.
SLOWLY rotate distributor; when light flashes snug up hold down bolt.
Prime carb and fire that bad boy.

Sigforty

Did your intake gaskets shift when you installed the manifold? Did you test fit the manifold any? If everything previous posters are saying to check is all good, I would look at a vacuum leak due to gaskets not sealing the intake manifold to the head.

pl2000n

Thanks for the feedback, everyone. It's all very helpful, if for anything, to force me to make sure I've dotted my I's and crossed my T's. I've quadruple checked all timing aspects and wiring, and also valve adjustment/lash. All is as should be. The coil functions (measured at the + terminal) exactly per the Chevy OEM manual: above 9VDC while cranking (9.7VDC), 5-7VDC during "running" condition with points closed (6.1 VDC), and (of course) full battery voltage when energized with points open. When my "other life" workload permits, I'll bump the timing to 8-12 deg BTDC (excellent suggestion) and give it another whirl. What intrigues me the most in this thread is 68notray's input: make sure the damn carburetor gaskets are installed correctly! I'll check mine. But this did lead me down an academic path related to the heat riser, and the "Hot Slot" style intake manifolds (Lars - https://www.corvetteforum.com/forums...d-problem.html). Now I understand the purpose and how it works! The heat risers are out or mine (have installed headers) but now I understand how exhaust gases could enter the intake stream and mess up the A/F mixture. I'll check that out.

What I'm still puzzling over however, is how can plugs #1 and #5 be dry while #3 and #7 are soaked? Is it because #3 and #7 are more-or-less "gravity" fed (low elevation intake runners allow gravity flow from manifold into intake ports) while #1 and #5 (elevated intake runners) need the engine to start in order to create velocity? The manifold is a stock oval port GM casting #3947801 and heads oval casting #3931063. Correct gaskets are in place with proper sealant.

Sorry for the "book" but this stuff is interesting

calwldlife

aren't 1 5 fed from a different side of the carb than 3 and 7?

regardless, pouring some gas down the carb should get some kind of running.

how old is the carb? could the rods and seats been dislodged on one side
when you changed it from the other mani?
truly weird.

pl2000n

So I pulled the Q-jet and the gaskets are as they should be. The "hot slot" or "smiley" cavity in the manifold was plugged by an earlier owner so no chance of exhaust gases messing with the A/F ratio. What was interesting however is that the driver's side manifold plane had about 3/8" of fuel! Quite the puddle. The passenger side was bone dry. Not sure why the disparity but obviously my aggressive pouring of raw fuel down the horn was all for not. I also pulled the air horn off of the Q-jet to verify proper float and metering rod operation (per calwldlife's idea) and all is well. Anyway, I'll let the manifold dry out, advance the time, and give 'er a whirl.

calwldlife

check the plugs in the bottom
of the qjet.
for one side to be that flooded
other dry is some screwy stuff.

i guess i would crank with carb off and put hand over each
plane of mani to see if i could sense a difference in suction?

pl2000n

Good idea, I'll check the plugs. I had the same thought to crank the engine while the Q-jet is off (and coil disconnected!), but I good idea to get a sense of suction. As for the lower plane, driver side having the puddle, I (or my buddy) could have favored that side heavily when pouring the raw fuel in.

Thanks!