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View Full Version : A few 351w/ holley 4160 questions


Wouter
05-21-2007, 03:36 PM
Have been struggling with my holley 4160 carb for the past month and have a few questions: After changing valve covers and adding a pcv valve and breather I proceeded to hook this pcv valve to the vacuum port of the carburetor and noticed that the engine would run a bit rough at low rpm's. Tried to fix this by tuning the idle screw and air/fuel mixture screws but the engine continued run unevenly. Couldn't get it exactly right. Since it seemed to be a vacuum problem I decided to seal off both the vacuum port of the carb and the pcv valve. Measured the vacuum with a vacuum gauge. 15 to 16 in / HG at idle (650 rpm). Is this a reasonable vacuum for a 1990 351w. Also, since I sealed off the pcv valve, I have a bit of smoke coming out of the breather cap. Is this normal? Do I need a breather cap? Also noticed that the electric choke is connected to the + side of the coil. Normally a coil doesn't deliver continuous 12 V. Shouldn't the choke be connected to a different power source? Doesn't this drain electricity from the spark plugs? (I have recently converted to EI) Also, what is the normal dwell? 30? Sorry for the list of questions...

TMCNo1
05-21-2007, 03:46 PM
Have been struggling with my holley 4160 carb for the past month and have a few questions: After changing valve covers and adding a pcv valve and breather I proceeded to hook this pcv valve to the vacuum port of the carburetor and noticed that the engine would run a bit rough at low rpm's. Tried to fix this by tuning the idle screw and air/fuel mixture screws but the engine continued run unevenly. Couldn't get it exactly right. Since it seemed to be a vacuum problem I decided to seal off both the vacuum port of the carb and the pcv valve. Measured the vacuum with a vacuum gauge. 15 to 16 in / HG at idle (650 rpm). Is this a reasonable vacuum for a 1990 351w. Also, since I sealed off the pcv valve, I have a bit of smoke coming out of the breather cap. Is this normal? Do I need a breather cap? Also noticed that the electric choke is connected to the + side of the coil. Normally a coil doesn't deliver continuous 12 V. Shouldn't the choke be connected to a different power source? Doesn't this drain electricity from the spark plugs? (I have recently converted to EI) Also, what is the normal dwell? 30? Sorry for the list of questions...


30 degrees dwell is right and I would consider checking and even replacing the gasket under the carb. If it's leaking, because the carb is not bolted down tight or has a crack, it can draw air under the carb and create your rough idle problem. Just a thought!

Storm861triple
05-21-2007, 04:14 PM
To the OP, there are a couple things that don't seem right w/your set up.
1. Vacuum is not unacceptable, but seems on the low side, especially if you are at or near sea level. I'd expect to see closer to 19-20" of vacuum.
2. Smoke coming from the breather. That's from blowby past your piston rings. Although the PCV system is there specifically to ingest those fumes, it shouldn't be leaking to the point that you're blowing smoke out the breather at idle. How many hours on this engine?
3. TMCno1 is on the right track about a vacuum leak. The symptoms you described are the inline w/that problem. W/the engine running, spray brake cleaner, WD-40 or some other combustable around the manifold. If it changes the way the engien is idling, you have a vauum leak. Pin point the location that makes the biggest difference, and that is your leak.
4. The motor had NO PCV system before your valve cover change?

The choke is hooked up correctly...or at least in a way that will work fine. That "+ side of the coil" is power from your key. Drawing power from there won't "take power away from the spark plugs" unless the wire is too small to flow the curent for both, and it's not too small.

Wouter
05-21-2007, 04:44 PM
Thanx for the answers:
1. altitude 55m (close to sea level)
2. 770 hours on engine (should specify that smoke out of breather only happens since I sealed off the pcv valve but that, other than that, the engine runs very well since (smooth idle 650 rpm, good acceleration, 4200 rpm at full throttle)
3. will try the WD40 on manifold test. Where should i spray?
4. Motor had two different valve covers when I bought it: one original MC valve cover with PCV valve (but left open, not connected to anything), one OMC with fixed oil cap (also left open and not connected with anything)

Should also mention that the idle has steadied completely since disconnecting the carb vaccum from pcv valve. Could it be a bad valve cover seal?

Wouter
05-21-2007, 04:48 PM
Also, sorry to contradict but from holley marine carb installtion guide:

"For choke hookup, attach the bayonet end of the long electrical lead supplied to the positive terminal on the choke cap. The other end must be connected to an ignition-activated 12-volt source. The distributor side of the ignition coil is NOT a 12-volt source. It is a 7-9-volt source after cranking. The shorter wire and terminal assembly provided is for the choke ground. Connect the bayonet end of the wire and terminal assembly to the negative side of the choke cap. Connect the round terminal end to a good ground. The choke housing screws or the secondary diaphragm housing screws can be used for this. WARNING: Connecting the choke cap to the ignition or ignition coil could result in unacceptable choke operation, poor fuel economy, and possible engine misfiring, since the voltage delivered to the spark plugs will be severely reduced by the drain imposed by the choke cap. Suitable ignition-activated 12-volt sources are most electrical relays, as well as the leads to the accessories, such as windshield wipers. DO NOT connect this wire to the original equipment (O.E.) electric choke source. This may not be a 12V source."

Storm861triple
05-21-2007, 05:17 PM
Also, sorry to contradict but from holley marine carb installtion guide:

"The distributor side of the ignition coil is NOT a 12-volt source. It is a 7-9-volt source after cranking.

It is a 12v source after a conversion to EI if you did the conversion correctly. Easy enough to check; Key on, engine off, measure voltage at the + side of the coil. Or just move the choke to key'd power and not worry about it.

Spray the WD around the base of the carb, and anywhere else a vacuum leak potential exists; vacuum ports, vacuum plugs, manifold-to-head flange.

Wouter
05-21-2007, 05:30 PM
Thanx. That's what I wanted to hear

Wouter
05-22-2007, 05:09 PM
Storm861triple thanx for all the help. Located the vaccum leak (or one of them): very stupid but not where I would look: torn pcv grommet. Thankfully I recovered the whole thing before it made its way into the valve covers...

Storm861triple
05-22-2007, 07:21 PM
Cool! The flamable chit-in-a-can works every time! :)