L20B hates cold weather

[metalmonkey47]

L20B W/ U67

Matchbox dizzy

Weber 32/36 Electric Choke

13* Static timing

160 average compression

 

 

This is not a new development, but I notice it a little more then usual. Anytime the ambient temp outside is below about 50 degrees, it hates running. It's fine once it warms up to operating temperature, but until it gets there it tends to want to stumble and choke when accelerating. I have to slip the clutch excessively when it's cold to keep the clutch engagement from stalling the engine. When warmed up, it's perfect and doesn't complain when i step on the gas. Just takes off like it should. 

 

It idles fine and I've gotten the choke adjusted perfectly. Everything on the ignition system is either brand new, or less then 5K miles on wear. Last week i pulled the rotor and dizzy to clean the contacts and saw no change. Plugs are recent NGK Platinum, @ .45 gap.

 

I really want to say that it has to do with jetting, but I haven't yet bothered with jetting the carb and I feel like it's running a little rich. No idea what it came off of before but I want to say that the main jet and secondary jet were BOTH 140 when I looked last. (Not 100%)

 

 

I feel like I'm leaving something out.. hmmmm

[datzenmike]

Choke not set correctly for the temperature or if set, may not have the fast idle correct. A cold engine wants a rich mixture.

 

I can get in my L18 automatic on a frosty morning, pump the gas to set the choke, two cranks, start it, slip into drive and it drives away.  Smooth as can be.

 

 

On a cold morning pull the air filter off and pump the gas. Look at the choke plate. It should snap fully closed.

[H5WAGON]

Maybe mine is running rich, but I don't have my choke hooked up....starts no problem. Just have to feather gas/clutch until warm.

[metalmonkey47]

Yes mike, mines set. I spent the last few days dialing it in when cold to find the sweet spot. My high idle is around 1600ish. (No tach, so just guessing by ear) Idle is set at 900. <That is confirmed.

Correct me if I'm wrong mike, but if my carb was jetted too rich, with the choke closed (less air=richer) it would potentially run poorly until the choke opens, right? I just figure, it sounds like a fuel issue. I know very little about jetting. It just smells rich when driving, but no smell when idling. 

 

I try to get away with just jumping in it and driving away, but it hates that. Even when warmed up, if it's around the 30's-50's outisde, it wants to stumble sometimes when I give it a little gas after coasting down a hill. 

[Dat Lurka]

My truck runs like poop till the engine is warm. It's just now getting cold here too.  

[Laecaon]

Im gonna say its all in the carb.

 

My motor wasnt too fond of the cold either with the weber. Manual choke. Had to choke it a lot to reach 1100 when cold. If let to idle until warm, it would peak around 1800rpm, and then drop back down to 1100 once warm with choke.

 

All sorts of hesitation and crap when cold. But I just used choke, which I hate. Difference of choke and not on my car was, slipping the clutch to get out of my driveway without, and with I could do a burnout in reverse. Without didnt really run unless I was on the throttle.

 

I am now running 38mm SUs, no choke hooked up. Takes a second to start, but has no issue idling at 400. Instant pick up and go, as in no hesitation ever! Its quite wonderful. I didnt change my timing (actually, I dont have vac advance right now... clearance issues)

 

So Doing a carb swap fixed all my issues? Must have been fuel related...

[moparvwfreak]

my truck runs like ass when its cold. stumbles and sputters till its warm. but my manual choke sucks. someone was stupid and got rid of the electric choke on it. now when i had my proper manual choke carb, it worked great. but this one just sucks. i just live with it till i get it warm and drive it like i stole it.

[RedBanner]

webbers with chokes? scoff! you just use the accelorator  pump......

[ggzilla]

Weber should run better cold than warm if the choke is correctly set.

 

I've gotten the choke adjusted perfectly

* Choke butterfly: FULLY closes when cold

* Fast idle: 1800-2400 for an L20B

* Choke vacuum break: opens the choke just about 1/16" inch as soon as engine starts. If it opens too far it won't run good until it warms up a bit.

[metalmonkey47]

Weber should run better cold than warm if the choke is correctly set.

 

 

* Choke butterfly: FULLY closes when cold

* Fast idle: 1800-2400 for an L20B

* Choke vacuum break: opens the choke just about 1/16" inch as soon as engine starts. If it opens too far it won't run good until it warms up a bit.

 

I'm gonna have to check my fast idle. The choke operation is for sure 100% as described above. 

 

I'm gonna go off a limb here and guess that it's gotta be carb jetting, because I still have the stumble when it's cold, and up to temp once choke is out of the question.

 

 

 

I'm gonna go pull the carb apart in a few min and mark the jet sizes and see what I have.

[bonvo]

it very well could be the jetting i dont think if this will effect your issue but those plugs seem to be gapped rather far my fsm for my 610 says .35 that is for points so i bumped mine up to about .40  and it had issues 

[screamer510]

How about point gap and timing for a single point L16 SSS dizzy with "hot" Jacobs electronic ignition?

I could say I'm having the same problem, same setup but with SUs.

[ggzilla]

Use the Jacobs recommendation for gap

 

You cant go wrong with 0.035" gap which works with stock or high energy systems.

[Laecaon]

My friends L16 with matchbox does not like .045 gap, runs better at .040.

 

I have the sentra dizzy and a Blaster 2 coil, just find with a .045 gap.

[ggzilla]

Yes, it does depend on the engine and the spark plugs. 0.045 gap is not too much for a matchbox -- they can fire up to 0.051 inch gaps (as in the B310 FU models with the 4-electrode NGKs). Although .043 is recommended for most engines.

 

Matchbox works perfectly fine with .035 gap. Wider gaps can help with mixture variance and especially with the lean mixtures datsun used starting in very late 70s.

 

Try it at .035 to rule out a gapping problem.

[screamer510]

THANKS, good info here.

Dan

[DanielC]

I do not know of the L-20-B uses a water bypass to heat the manifold or not, or if it uses exhaust gas to heat the manifold, but either way, in cold weather you need it.  Not so much in the Summer.

Same thing with drawing heated air off the outside of the exhaust manifold.

It might help to block off part of the radiator witha sheet of cardboard, to keep under hood temperatures higher.

 

Yes, I know you lose power heating up the air in the manifold, and before it gets to the carburetor, but in winter, the engine is much happier if you do that.   It helps vaporize the gasoline going into the engine.

 

Just an opinion, if your engine runs good when cold, you are probably running a little too rich, because some gasoline in the luquid form is reaching the cylinders, and possibly washing oil off the cylinder walls, and even getting into the crankcase, and diluting your oil.

 

I know you will hear recommendations to not warm up an engine.  These recommendations come from the EPA, who would rather your old car wear out, so you buy a new one.   Car manufactures would also like to sell you a new car.  Let the engine warm up for a little bit, longer if colder.  Drive it easy when you first stare moving.  Do not thrash a cold engine.

[banzai510(hainz)]

I persoanlly dont think its the carb jetting. Cause if was running good before the jetting hasent changed. Only the tempature,

This is one reason I prefer the manual choke. Elecric is good if it works right. And needs adjustment if moved.  Once I moved a electric I could never get it right. it either stayed on too long or not long enough.

 

no heater line in a cold area carb mayb ice up esp on a very cold rainey. But your in Atlanta and cant seeing the temp being all that cold yet.

[metalmonkey47]

So I finally got around to plug gam. I just bought a new set of plugs (as cheap as they are) and ran the .40 gap since that's what the stock matchbox L20B plug gap is factory and it runs the same.I found a small vacuum leak but sealing it didn't make any difference at all.

 

I haven't had a chance to get the jets out yet to check sizes, so I'll probably be busy doing that Saturday. 

 

I'm gonna put a piece of cardboard in front of the radiator tomorrow, since that helped last winter.

 

 

I've been thinking a lot about it lately, and I feel like I'm losing power somewhere. I drove a 109HP Versa that felt like a GTR compared to my truck. My truck has always been a little 'funny' in the way it runs, it's just worse when cold. When it's up to temp it's okay for the most part. But when outside air temps are really low it tends to stumble a lot even when it's up to 190 degrees, 

[ggzilla]

Yes, new plugs are unlikely to fix anything like that. Just the gap if wrong can be re-gapped.

 

 

Is your hot air-intake hose missing?

 

Is the heat riser flap stuck?

 

Time to check for vacuum leaks. Especially check for leaks in the air cleaner housing hot air intake diaphragm.

[metalmonkey47]

I'm have a Weber without a heat riser, and an emissions-free L18 intake manifold.

 

I also have a high-rise steel carb adapter that I need to check. I've look with brake parts cleaner for vacuum leaks before, but something tells me I might have a slight leak around the base. 

[datzenmike]

You have a '76 so will have the intake heated by the exhaust but the little heat riser valve could be stuck closed. Its up under the intake behind the carb. It's just below the horizontal EGR pipe on the exhaust and has a coil spring around it. The spring opens it when cold and relaxes when warmed and lets it close. It has to be loose and free to move. If the spring is broken wire it open so the manifold is eated for the winter.

 

You should have a heated air supply to the carb also to prevent carb icing in cold damp weather. Freezing rain, do you ever get it where you are? I wrapped a cut open Maxwelhouse coffee can around the exhaust with stove pipe wire with a short length of aluminum dryer hose to the carb. It works!

[Farmer Joe]

does it have the water in the intake? 

 

see if the carb is getting frosty where it meets the intake or adapter. 

 

webers freeze up in the cold. i had bad problems with mine freezing when i had the header still. my old isuzu's did the same too. 

[ggzilla]

Fix the heated air issues.

 

Mike's method works with headers, and is needed in humidity under 37 degrees or so to prevent carb icing.

 

Secondly, for good running cold starts, make sure the Heat Riser turns freely and does not flop around

 

 

Check for vacuum leaks.

 

Don't start with the carb flange, it's far more common to leak at other places including:

* broken hose ends

* Vacuum Advance

* Air Cleaner heat-flap motor (diaphragm)

* EGR Valve (newer engines)

* PCV valve sticking - causes part-throttle problems

 

Carburetor leaks

* choke vacuum break (or Weber choke pull-off)

* Loose throttle shaft

* Loose base nuts. Do not overtighteen

* Loose adapter plate (Weber)

* Cracked adapter plate (Weber) - caused by overtightening

* Carburetor Dashpot (some engines)

* Throttle opener (some engines)

* Dashpot (some engines)

[metalmonkey47]

Sorry about the delay guys, the weather's dropped to about 30-40 daily now, so I wanted to drive it and see how it ran before coming back here.

I have a non-emissions L16-L18 manifold. (Not sure which) and it's also not water cooled. I have a stock U67 manifold somewhere, but don't plan on putting it on. I also don't have a heat riser since I have a header/weber. 

 

I've noticed that when I rev it out (about 6K) and shit into the next gear, it stumbles pretty bad before taking off again in the next gear. I feel like i'm missing power in my top end too. 

 

 

My carb adapter is a high rise steel adapter. I need to pull it off and make new gaskets with some cork/rubber material. 

 

Another thing I've noticed is that when it's cold, my truck idles LOW (even after bumping the high idle up) until I've had it running for a minuet to warm up. I haven't had a chance to check the choke linkages, so I need to get a rush on that.