L20B hates cold weather

[metalmonkey47]

I do also remember both my primary and secondary main jets were identical, which doesn't seem right to me. Wouldn't the secondary be larger? 

[datzenmike]

For the '78 L20B truck 103 Primary and 160 secondary.  A few either way will still work. California are 101 and 158 to run leaner.

[ggzilla]

>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.

 

That could be an ignition problem.

 

 

> 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.

 

It won't run well when cold since it has no heat riser nor any heated air intake. About the only thing you can do is richen up the choke overmuch (but make sure it still opens 100% when warm).

[LenRobertson]

I do also remember both my primary and secondary main jets were identical, which doesn't seem right to me. Wouldn't the secondary be larger? 

Could you be thinking of the Main Air Bleeds, one for each barrel, side by side when the top of the carb is taken off? Mine are stamped 60 and 60, and didn't seem correct that both barrels would be the same. However, the Volume 2 Issue 1 Dime Quarterly, page 13 has a very useful chart giving jet sizes for 1969-79 carbs. It shows several of the carbs using the same size Main Air  Bleed for both barrels, while some carbs use a larger number Main Air for the primary (like 70 primary, 60 secondary).

 

http://dimequarterly.blogspot.com/p/back-issues-ordering.html

 

The Primary Main Jets located down under the float bowl all are a larger size for the secondary. For example, my carb has a 104 Primary Main Jet and a 160 Secondary Main Jet. Looking at the chart in DQ, it appears I have a '78 or '79 non-California carb. The chart is useful to get some idea which model/year carb you have, assuming it hasn't been re-jetted. I don't think it is as common for jets to be changed in a stock carb as in a Weber, but you never know for sure.

 

Len

[metalmonkey47]

I REALLY need to get into my float bowl. I THINK the air bleed jets were both 60's, and the main jets I was looking at were the ones in the bottom of the float bowl.

 

Mike, those are stock numbers? If so my truck is running lean at WOT, and rich at partial throttle? 

 

I have ZERO vacuum leaks checked with brake parts cleaner.

 

 

 

 

I've noticed that no matter what the temp is, if I coast for a few seconds and get back on the throttle my truck will stumble pretty bad before I have any power. I have lots of mis-fires for a second or two and everythings fine.

 

 

 

I dunno, it's just all a little strange. I also have some funky steering issues... but that's for another day. I can figure that out I'm sure. 

 

 

 

 

I'm gonna go get all the jet numbers tomorrow and post them. I really think I might be having an issue there, even if it's not what's causing this. 

 

 

 

 

 

 

 

 

 

 

 

GGzilla, can you elaborate on the ignition problem? I've been over every inch of my ignition and haven't found any bad spots. My cap/rotor were freshly cleaned, plugs are new, wires are new, matchbox dizzy is good with a good vac advance and proper timing, etc. Only thing I haven't done is get the primary/secondary resistance for my IGN coil and tested it. 

[ggzilla]

Air bleeds are the same on primary and secondary

 

Yes, measure the primary and secondary resistance of the coil. It only takes a few minutes to compare the measurements to the FSM.

[metalmonkey47]

Thanks Lacaeon! Just got a copy of the Weber tuning guide and I'm reading through it. 

 

 

BRB later with more thoughts... 

[LenRobertson]

I was just rereading this thread and finally caught that you are running a Weber, not a Hitachi. I've been working on my Hitachi so much lately I've got that carb on the brain. So my reply was not accurate for a Weber, except the same DQ article I referred to (Vol 1, Issue 3) also includes both Hitachi and Weber tuning info. It is a 2 part article and the issue with the second part has a separate Weber story (Vol 2, Issue 1). Maybe you've already found it. If not, it is worth looking at.

 

Len

[metalmonkey47]

Len, any help is good. The carbs are not too different and the concept is the same.

 

I've got the tuning guide and I need to read through it..

 

 

 

 

Jet sizes:

 

Main:

Primary = 140

Secondary = 140

 

Air Jets:

Primary = 170

Seondary = 160

 

Emulsion tube had no markings on it. 

Power valve is good. 

 

Accelerator pump is good.

 

 

 

Dime Quarterly tuning chart lists CORRECT jets as....

 

Main:

Primary: 115-120

Secondary: 170

 

Air Correction Jet:

Primary: 65

Secondary: 65-70

 

Now, Datsun 1200 lists the air jets as a 170-160, but Dime Quarterly specifies differently. Can someone elaborate? What am I reading wrong? 

[ggzilla]

It depends on which Weber your have. Jets are proportional to the venturi sizes first and foremost.

[Dat Lurka]

I fixed my fuel delivery issues and I got a working choke now. I can start it up first try with full choke and half throttle. Makes my job much easier.

[Siempreloco]

Id take a look at that coil you're using.. maybe just try to go back to a good canister coil ....but that's just my opinion.

[LenRobertson]

I'll likely add to your confusion. It has been a long day of not doing very much. Wears me out.  I'm not sure which DQ chart you are looking at. In Volume 1 Issue 3, page 9 the chart there for a Weber 32/36 DGV gives Main fuel 1.40/ Main air 1.60. Secondary fuel 1.35/ Secondary air 1.70

This page at Datsun1200 http://datsun1200.com/modules/mediawiki/index.php?title=Weber_DGV_Tuning about 2/3 down the page under "L-series engine" gives a similar set of figures, and says it is "...for a stock 510 with L16 engine".

 

But I realize I'm too tired to compare your set of sizes with these from DQ and Datsun 1200. Maybe in the morning it will make more sense. It doesn't look like the jets you have are very far off the recommended sizes, although maybe the air jets are switched?

 

Len

[metalmonkey47]

So I'm actually pretty confused now. I miss-read dime quarterly. The above values were for the DCH carb, not the Weber. The following are for the Weber.

 

 

 

 

SUGGESTED JETTING VALUES

 

                     Primary                     Secondary

Fuel        125-130-135-140         85-90-95-100

Air               150-160-170              95-115-125

Idle                   60-70                        40-50

e-tube                 Fll                              F9

Pump                45-50                         N/A

 

Once you are happy with your primary

jetting, you may choose to work on the idle

 

Yesterday I switched my two air jets around, 160pri, 170sec, and it seems to run better at partial throttle before the secondary opens.  

 

According to the value's above, my primary jetting would be about right, and my secondary jetting would be wayyy too rich with wayyy too high of an air mixture.. I find it strange that the secondary jets would need to be smaller on the larger Weber, where as the suggested jetting for the Hitachi would be larger then the primary. 

 

 

 

Can someone explain why the jetting on the secondary would be smaller then the jetting on the primary? I need to order stuff for my secondary I guess. 

[LenRobertson]

I'm starting to wonder if the 85-90-95-100 line in the DQ chart may be a typo. It doesn't come close to any of the other recommendations I've been reading. The other DQ chart, Datsun1200 page, and a Google search for "Datsun L20b Weber jetting" (which is mostly Ratsun posts) seem to mostly recommend about 140 main fuel and secondary fuel only 5 more or less from that (like 140/145 or 140/135). I think there was one recommendation for 140/140 which is what you have. Maybe just run your 140/140 for awhile unless it obviously isn't running right. It also may be the air bleeds or emulsion tubes aren't exactly right for your 140/140 fuel jets, so if it isn't running quite right, the fuel jets may or may not be the problem. I suppose you saw the chart in the one DQ article on how to id your emulsion tubes.

 

Len

[racerx]

Do you think .45 is too much gap for spark plug.  I have pertronix, no points, NGKs (L18) and my spark plugs are set at .35.  This is based on .32 for stock and you can go higher with elect. dist. and hi-perf. coil set up. 

[DanielC]

Engines need gasoline VAPOR to run.  If you do not have a way of heating up the intake manifold in cold weather, AND a way of getting warmer air into the carburetor, you engine will run like crap.  This is because liquid gasoline just runs down the intake manifold, does not evaporate, or burn, and then washes oil off the cylinder walls, and finally gets pushed into the crankcase.

 

When the liquid gasoline comes out of the carb venturi, the liquid gasoline starts to turn into a vapor.  THAT COOLS THE AIR GOING THROUGH THE CARB EVEN MORE.  If it is already cool, and humid to begin with, it is very likely ice is forming inside the carburetor.  In severe cases you can see the ice, or frost on the outside of the carburetor.

[ggzilla]

> Do you think .45 is too much gap for spark plug. I have pertronix

 

YES. Pertronix Ignitor 1741 is not a high-energy setup. It can fire gaps up to .035 inch. It requires a points-type coil.

 

If you have Ignitor II that is advertised to do it.

[ggzilla]

What DanielC ^^ said.

 

Back to "L20B hates cold weather" ...

 

I wouldn't be looking at the carburetor jetting if it runs decent in warm weather.

 

I'd be building a sheet-metal hot box over the exhaust and fit a stocker air cleaner over the weber (ratsun-style) and feed the hot air intake of the air cleaner.

[LenRobertson]

A "cold weather" air cleaner seems easy to try:

 

http://community.ratsun.net/topic/10977-stock-air-cleaner-to-weber-mod/

 

Probably any year Datsun air cleaner will work for the mod. For that matter, probably another make would even work. As long as your hood will close. You can always go back to the Weber air cleaner in warm weather.

 

Len

[metalmonkey47]

Alright, going back to all that in a moment...

 

had some off time yesterday so I pulled my carb and found this:

 

 

Can anyone tell me what's wrong with this picture??? Fawking brand new vacuum line broke and I didn't notice it because of the steel braiding over it. (I tucked some of my lines, and they were melting on hot stuff.)

 

I looked over it before but didn't see it until now. I pulled the carb adapter off and made new gaskets for the carb/adapter with some cork/rubber material. Got it together, and noticed the difference instantly. The truck is 100x better then before. I still have an issue with my top end, which i still think is jet related. When I open the throttle up past the secondaries, I can actually feel a loss in power after about 4K RPM. I have great midrange and torque, but my top end still suffers.

 

 

 

As far as the heat riser, I've gotten an aftermarket K&N from a friend that I'm gonna try to modify to run hot air off of the header. The weather hasn't been cold enough to test it after fixing my vacuum leak though so i may not need it.

[ggzilla]

Yes, it means fake metal braiding is a bad idea. Looks nice but ...

 

Why did new vacuum hose crack like that? Most likely because it was cut too short and vibrations broke it. Always have a little play in the hose, unless the hose is clamped in places like stock hoses.

[metalmonkey47]

Yes, it means fake metal braiding is a bad idea. Looks nice but ...

 

Why did new vacuum hose crack like that? Most likely because it was cut too short and vibrations broke it. Always have a little play in the hose, unless the hose is clamped in places like stock hoses.

It wasn't fake, it's purpose was to keep the hot t-stat housing from melting the rubber.

 

I trimmed it so it had an inch of play, and secured it with some wire clamps to keep it from moving around. Seems like it was just very cheap vacuum line. It was dry rotted and all sorts of crappy right on that end.

[ggzilla]

Yes, get some better hose. Nissan genuine vacuum hoses can run at 220 degrees. They need no shielding from the thermostat housing.

[banzai510(hainz)]

your car runs that much differenctg w/o a vac hose?

re ck the timming.

 

I have tried running a vac hose and w/o a vac hose and soemtimes I cant tell the difference.