Jared Zecchel

Hey everyone, in need of a little advice.

My engine was running fine (maybe a little too rich) until I swapped the spark plugs. All of a sudden the engine starts misfiring and running terribly even after i checked the gaps.

I watched the mechanic down the street tweak the carb a little and he seemed to set everything strait.

Maybe a week later it starts running crappy again. I took it back and he said that the engine was flooding and to rebuild/buy a new carb.

Now it wont idle unless the choke is fully on which makes me think that the engine isn't flooding but rather it has a vacuum leak.

I rebuilt the carb to be on the safe side but still nothing.
I tried the WD40/Carb cleaner spray trick but still nada.

I pumped a bit of smoke in there and there seemed to be a pinhole leak by the opening for the throttle rod but not enough that i would suspect it to make such a drastic difference in the car's performance.

Any idea's?

Gun Jam

Okay lets see....It was okay, it was running well(ish) and you parked it and changed plugs and now its crap.

If you are sure you told us everything and you used the proper plug...(is it the same lenght electrode and insulator as the original? Whats the number?) and you go to start it up and its terrible then 99% chance its not the carb.

Before messing with the carb and maybe making things worse start with basic:
Was okay --> plugs--->crap so things that are related to that:

1) wrong plug
2) accidentally bent an electrode when installing (no gap)
3) Put the wires on wrong maybe 7 is going to 8 and 4 is going to 3
4) wires not actually seating on plug cap (improperly installed)
5) Old plug wires cracked internally when you moved them and now are causing high resistance.

I would start there

let us know how it goes.

-Gun

Jared Zecchel

Thanks Gun,

I replaced the spark plugs with the exact ones that were in before and the wires are relatively new. I've checked all the wires and plugs with a multimeter and they all check out ok. They're all gapped properly and i put dielectric lube around the boots to keep it from arcing.

Everything checked out well on that end but it kept misfiring. I assume it could have been due to a weak coil as it was original. I swapped out the coil and points for a pertronix set (bypassing the resistor wire as required) and it still sucked.

All in all I think the ignition can be left out of the picture.

I should mention, I just replaced the factory vacuum hard line to the auto tranny with a hose so i could add a second vac port. With a Vac gauge the engine read a steady 20 inHg with the choke fully closed but started to falter once the choke got let off till the engine eventually died.

Could this possibly be pointing to fuel starvation rather than vacuum leak?

Gun Jam

Using carb cleaner like Barrymans B12 is a good way to hunt for vac leaks.

spray it lightly around the base of the carb with engine running. If you hear the engine bog that would be the source of the leak. Dont spray it really hard or the vapor and splash will be drawn down carb and give false positive. Throttle rods usually leak a small amount.

Also check along the intake to head seal and back of carb as well

if all that checks out then it could indeed have a plugged idle circuit on the carb. The choke causes the booster ventures to activate early and effectively bypasses the idle circuit

what carb is it?

-Gun

Jared Zecchel

Ok! Big news.
When I cleaned my carb previously i didn't put any wire through the jet. Apparently i missed some varnish or something.
Re cleaned/air blasted the jet and reassembled and it idles perfectly fine!!!

Two things however,
Not having a tachometer, I'm not entirely sure whats an acceptable idle.
I tuned it to the steadiest amount of vacuum and it seems to be stable around 20Hg's but it seems to be idling quite high..
Also when I put it in gear the vacuum drops to about 15Hg's.

Is this a normal amount of loss? I can't be sure but it also feels like maybe a slight hesitation on acceleration from stop. Maybe its cause I've been driving my moms mazda where the throttle response is amazing.

Thoughts?

Gun Jam

If you've got 20" at idle chances are its a bit high...but you want to check idle RPM with it in gear because loss of RPM from N to D is normal. RPM in D should be around 850...if it sounds high its high. If it sounds okay and you have 13 to 15" of vac thats probably an acceptable idle speed.

If you have hesitation on acceleration from stop that would indicate the idle circuit is too lean. you'll have to look to find the idle adjustment screws for your particular carb. Chances are you'll eliminate the hesitation on accel and reduce the amount of RPM loss from P to D when you get the idle screws set right. I would run both (or all 4) idle screw in until they stop count the number of turns it takes to lightly seat each screw....write down the screw number and turn count...Find the avg turn count and set all the screw to that many turns out. Then make each one 1/4 richer (anti clockwise rotation)

You may have to reset idle speed test and see if its better or worse.


-Gun

fastbackford351

It figures that it was something boogered up in your carb. When my lawn mower does the same thing, invariably when I disassemble it and run a wire or air through all the passages it purrs like a kitten.

barnett468

.
need to know engine size and build info and compression and carb.

the idle should be pretty low like 650 rpm

if it has a performance cam and a stock converter it can drop the rpm too much when you put it in gear

with a low idle, check the timing then remove an plug the distributor vacuum advance line and check timing again.

with the engine idling and vacuum hose plugged, advance the timing 4 degrees and see if the rpm increases.