Edelbrock 1406

[deerkiller]

Truck info -   1978 Chevy K5 with 350 & 350turbo. Summit RV cam 1102. Edelbrock 1406 carb.

New fuel pump, timing chain, cap,rotor,wires,plugs vacuum advance and mechanical advance ( Mr gasket 929G with lightest springs)

Timing is set - initial 17 and total 36. (Going to turn it down a hair , has a very light ping) 

Carb had this issue prior to the cam install (about a week or 2 ago)



Took a good look at my carb today to try to figure out off the line bogging (only when  motors cold really) and real quick revs bog too (most noticeable when done by hand under the hood)

Check the float levels, were a little off so I adjusted accordingly.

Under the air horn looked clean. Metering rods weren't gummed.
Checked to see what step springs were in it, they are the silver (8" vac.) springs. I pull 20 vac. at idle and about 17 stopped in drive.

Accelerator pump works fine

Fuel pressure is questionable but I don't have any symptoms of to much fuel. Gauge bounces but when revved shows about 5-5.5psi.   (Not a liquid filled gauge)

Only thing left I can think of are the jets/rods.

Guy I bought it from claimed to have rebuilt it, looks pretty clean on the inside, and the gaskets look new too)

[rich weyand]

The 8# springs are fine with that much vacuum.  5# is standard, but with that much vacuum you will get into the power circuit late and bog in the transitions, so that's fine.

Could be not enough accelerator pump.  One thing to try is to move the accelerator pump actuator arm to the inner (closer to the carb) hole in the lever.  That will give you a richer mixture on transition.  There's three holes: which one is the arm in now?  Was the accelerator pump rebuilt when he worked up the carb?

How did you set the idle mixture screws?  Running too lean on idle will give a rough off-idle transition.

And here's the killer: Where do you have your vacuum advance connected?  On the driver's side port (ported vacuum) or on the (slightly lower) passenger's side port (manifold vacuum)?  Connecting to the ported vacuum is emissions nonsense; you want to be connected to manifold vacuum so that the vacuum advance is pulled in at idle.  Connecting it to ported vacuum will give you the hesitation you are seeing.

[rich weyand]

Sorry: got them backwards from memory, but I just checked the manual.  "Timed" or ported vacuum is passenger's side; the one you want to use, manifold vacuum, is driver's side.  It's the lower one in any case that you want.

[deerkiller]

I've tried moving accelerator pump holes, it's on the middle now.

Thought about replacing it but you can see/hear it squirting

Also have the dizzy on the driver side port ( manifold vacuum)

Choke seems to operate normally too, haven't played with richning our leaning it out though.

Seems to run rich if anything, plugs are a little dark, not "bad" though. Can smell the richness at idle though and after you shut it off

The idle mixture screws I set with rpm according to the manuel, have done it with vacuum before

[deerkiller]

Maybe bog wasn't the correct term

I'll go to go from a stop and it'll pull forward, choke/cough, then go



And when revving it quickly I can hear it suck air but no rpm increase right away - I'll post a video of this in the morning

[rich weyand]

What intake manifold?

[454Man]

Im for it being rich... hints the cough in bog. Plugs say it all

[rich weyand]

Yeah, rich on the idle mixture could do it, if it's way rich.  You might try the turning the idle mixture screws 1/4 turn CW, then try another 1/4 turn CW, and see if the problem goes away or gets better with either of these.

[deerkiller]

Makes sense, I thought the farther they were in (clock wise) would be richer. I had them almost all the way out.

Never even thought to check those, thought they were *just* idle

I screwed them in until it started running crappy, turned it back until it was borderline smoothness then went another 1/4 turn. Seems to rev better now, haven't taken it for a drive yet though.

Intake manifold is stock

[rich weyand]

No, they're like faucets for the idle gasoline.  Righty-tighty, lefty-loosey.  You had the poor thing about as rich as it could go.

OK, manifold isn't the issue.  An air-gap manifold without carb heat can exhibit similar performance issues.
 

[deerkiller]

Glad it's solved , had been a headache since day one. Thanks guys for the help!

[rich weyand]

Here's my method to set those idle jets if you don't have an A/F ratio meter or vacuum gauge.  With the engine off, screw them all the way in to the stop.  Back them out 1-1/2 turns.  Start the engine.  Adjust the idle to 700 rpm with a timing light that has a tach function.  Now back them both out 1/4 turn.  Speed up, or slow down?  If speed up, back them both out another 1/4 turn.  Continue until backing them out 1/4 turn slows the engine down.  Then turn them both back in 1/2 turn.  Readjust the idle speed.

[dalefan613]

good info

[Elpresidente]

Always check for vacuum leaks and the fuel filter first. All around the carb, all vac lines including the brake booster (had an issue with that recently).
Once my truck did that, only when cold. It was because I had a leak from the carb being a bit loose. It went away when the engine heated up because everything expanded enough to seal off the leak.