Wierd Sputter and backfire.

[75LB620PU]

Hi there.

Been having some issues of when i shut the truck down.

It sputters and backfires and spins backwards sometimes.

its completely stumping me as to how that happens. 

Any info or advice to negate this affect would be much appreciated.

my rig is a 75 long bed 620.

l20b with w53 head.

Weber dgv5a carb

3 speed auto transmission

 

Thanks Guys

[Guest Rick-rat]

Check your timing, mine does that sometimes  but it has a stick so I just let the clutch out in gear when I shut it off

[datzenmike]

Weber? bet it doesn't have an idle cut solenoid on it. Well nothing you can do about that.

 

Is the idle speed too high?

 

The easy fix is to leave in drive when you turn the ignition off, then place in park. The load will cause it to stall faster.

[ggzilla]

Backfire is not normal, but the rest is normal dieseling.

 

Try setting the timing to stock. 10 degrees or whatever the underhood sticker says. Not the maximum for safe running, but stock to minimize side effect like this.

[75LB620PU]

Timing is set to 12°. The carb is a weber dgv5a, no cut off solenoid :/

When in park and no choke idle is reasonable. If I put it in gear and try and accelerate without the choke on. It instantly putters out and dies. If I pull the choke 1/4 closed. It runs really well in gear but idles at almost 3k in park. I've reset the idle a couple times. As directed by redline/weber. I try openeing the choke all the way before I shut it off. But it still idles a lot higher than before I closed the choke. Maybe a linkage is getting stuck somewhere?

[ggzilla]

Yes, when you pull the choke out, it is supposed to activate the fast idle cam. So that explains why it idles high with choke on.

[75LB620PU]

I'm gonna try and set it again in the morning. Without choke after completely warmed up and in gear. Hope it helps. If not. I'll just start shutting betty down in gear haha. Btw my trucks name is betty white. Old bitch with a temper and an attitude lol. Thanks for the help guys. Will update if anything changes or figure something out

[ggzilla]

This is the problem I would focus on. All the other symptoms may be side effects of your "adjustments" to get around this problem.

 

If I put it in gear and try and accelerate without the choke on. It instantly putters out and dies.

If the engine is fully warm it should drive well with choke off. The fact that it runs better with choke on indicates a severely lean carb problem. To some extent the idle mixture can be adjusted rich to compensate, but doesn't fix the off-idle mixture.

 

Lean carb could be a bad carb, or there could be vacuum leaks. Are you running a two-piece Weber adapter? If do I'd start there. Remove the top piece and tighten the bolts. Don't over tighten.

[banzai510(hainz)]

your accel pump squirting good on the carb?

 

when its timmed is you dizzy more in the middle of the adjustmant or is it cranked all to one side.?

 

Since you have a auto I heard you have to adjust differently

Olddatsuns.com has this in the tech section

[dr.feltersnatch]

what ignition are you running? if points when is the last time you adjusted or changed them? also i would check very closely for vacuum leaks.

[75LB620PU]

Im very skeptical of the jetting if the carb. Everywhere I've looked the combo doesn't seem right. And the aux venturies loose and rattle in the body of the carb.

Jetting is

 

Primary secondary

Main. 137 135

Air correct 165 160

Venturies 27 26

Aux. Vents 3.5 3.5

Idle jets ? ? (Could not find ant marking on the idle jets.

Acc. Pump 50

 

As far as the accel pump. It is pumping a good supply of fuel into the butterfly.

 

Dizzy is in the middle of the adjustment plate. I adjust points every other week to stay on top of them.

 

I have tuned the carb both ways for a stick and an auto. No change.

 

As far as vacuum leeks. The person I bought the truck from. Had started an emissions delete. But didn't finish. I am in the process of fabbing a plate to bolt on the end of the intake where the egr is currently bolted up still.

 

I've plugged all open vacuum lines with tubing, bolts and hose clamps.

 

It does have the 2 piece weber adaptor. And it's a hunk of junk. It's rtved together on the bottom one. So as soon as I can afford/find another. I'll be replacing it.

[banzai510(hainz)]

if you can IDLE THEN THE ADAPTER PLATE IS MOST LIKELY SEALED OK. and have no leaks.

 

Is the vacuum adv ing to the carb?

 

 

take a photo of the coil area .

READ CAREFULLY below:

Your 75 should be point ignition. if still so you should have a ballast resisitor and a point 1975 coil. If you have points and no ballast maybe your buring up your points and it arching.

But it this runs good at speed then its highly UNLIKELY its the proplem,

[ggzilla]

Points only need adjustment ever 3000 miles. Its in the owners manual - and most guys go for a year without touching them.

[ggzilla]

> the aux venturies loose and rattle in the body of the car

 

FIX or replace that carb. Of course it doesn't run right.

[75LB620PU]

They've always done this even when it ran good. But I'm gonna try and shim them until I can afford new ones

[75LB620PU]

Readjusted the idle and mixture today. Without the choke on I put it in gear and dies as soon as I try to accelerate. My buddy has a weber 32/36 with electric choke. He might not be using it so I'm gonna try and out that on and see if it does any better

[75LB620PU]

Okay.

New distributor electronic ignition

 

conversion kit.

 

Reset the timing to 14°.

 

Readjusted the carburetor.

 

I still can't drive without the choke on.

 

When I try and accelerate it cuts out as if it doesn't have enough fuel.

 

I put the mixture screw at 6 turns out and it will somewhat run and drive with out the choke.

 

But that is really too far out.

 

Any suggestions?

[ggzilla]

You were planning on replacing the carb adapter. I would do that now.

[75LB620PU]

I'm also Thinking of swapping the carb as well. My buddy bought a 620 and he has a spare 32/36 weber. Just have to rebuild it and hope it does better

[ggzilla]

Why bother to rebuild a carb if the problem is a loose adapter?

[75LB620PU]

I took the adaptor off and redid the gasket and used a gasket sealer I jb welded the studs in place because they were loose. I think the carb I have on is jetted poorly.

[banzai510(hainz)]

If your positive the distributor is good then swap the carb.

I highly doughtt the jetting is that bad off . maybe worn out or just junk.

[spoonman]

Hahahaha, this is my truck now!!!!! Lol.

[datzenmike]

How's that working for you?

[75LB620PU]

Haha spoon. I'm getting blown up all over about the truck and the progress. Congrats on how far you've taken her!