Having a annoying hard to find problem

[zah_chronicler]

.  I have a 1974 L18 620 with stock hitachi carb. 

 

My troubles began over a year ago now.  I had gotten this truck running from nothing to running like a dream.  I was using it daily with only some minor fiddling necessary to keep it happy.  One day while getting off the interstate it basically stopped wanting to accelerate at all.  I was able to limp it along in idle letting the clutch out slowly.  I have not since been able to get it to run smoothly.  I have been worried that an internal engine part broke but can't seem to diagnose what.  The best i can tell is that the engine is running incredibly rich.  All the spark plugs were fouled out with thick black soot.  I had already done work on the internals of the engine and rebuilt the carb when I first got it.  Everything worked fine for over a year so i don't think any of that work was a direct cause of this.  I have since tried to thoroughly check and clean systems of the engine.  It now will idle but not smoothly accelerate.  There is a white smoke in the exhaust that smells sometimes like gas.  when I do accelerate I can get the engine to rev as high as I want but get a lot of black smoke.  Not getting back firing.  plugs are getting black and wet now, seems to be gas and maybe some oil.  Now that it will idle I am also noticing a gassy smell to the oil. 

 

I have taken the carb off cleaned it thoroughly,

I have checked the entire electrical ignition system,(previously put the pertronix induction system on instead of the original points) found a resistor was only allowing about 9 volts into the main ignition coil, got that taken care of and now have 12v.   The cleaning and new part has helped but still getting really bad combustion. 

I am wondering if it may be the carb still or if I should look at other parts.

 

A compression test showed equal pressure on all cylinders but I don't know that the actual pressure should be.

 

I want my datsun to rise from the ashes again.

[Skib]

black smoke is fuel

white smoke is coolant

blue smoke is oil

[datzenmike]

When the engine has warmed up, pull the top off the air filter an look down into the carb. On the side closest the valve cover there is a choke plate. It should be fully open. Let me know what you see or post a picture.

[banzai510(hainz)]

Pertronix and points you want the resisitor in series to the coil. Keep the point from getting to much current and burning up the Pertronix. This is stock and also on the Pertronix instructions

 

blk wht wire to the ballast then to the + side coil.

there will be another wire that is the start wire that goes to the + side coil.

It might be 2 wires going in to 1 lug at the plus side coil.

 

Oh ps u want a point coil. NO SUPER COILS or MSD balsters

[racerx]

If he has petronix he should not have points..

[ggzilla]

I'm surprised no one has talked about the obvious -

 

> i can tell is that the engine is running incredibly rich

 

What is the fuel level when idling, as seen through the carburetor sight glass? Float Level is the foundation of carburetor adjustment. No other adjustment will be correct if the ful level is incorrect.

[Siempreloco]

Leak-down test it and get back to us to rule out a lot of internal engine issues.

[ggzilla]

Leak down test won't help with running extremely rich and even compression -- as long as the compression was above 120.

 

Fuel Level can be checked without tools just by looking.

[ssnapz]

compression test will be wrong with washes cylinders, i agree check the choke. see if you suck something into your carb or air cleaner. i got the insulation from my hood in my carb once, same problem

[datzenmike]

Leak down test won't help with running extremely rich and even compression -- as long as the compression was above 120.

 

Fuel Level can be checked without tools just by looking.

 

so can the choke setting. I agree running very rich.

[zah_chronicler]

i know for certain that the choke is working fine.  Electronic automatic choke opens as it gets going and stays open once hot.  The fuel level in the sight glass stays right at the etched mark

 

 

What is the leak down test Siempreloco mentioned

 

 

Also do i or do I not need a replacement resistor to go into the pertronix setup.  Still using stock coil

[Siempreloco]

Explain your "pertronix setup" a little more in depth to us, you are using a stock coil, stock to what, the vehicle or the setup? From my understanding you are using a stock to the vehicle coil with a electronic ignition module?  I have a pertronix flamethrower II coil on my truck. I have a dual points distributor. A ballast resistor is required in my scenario, and most likely yours, as Ggzilla has already said. You should have a "starting power" line that is a direct 12v line to the coil, and you should have another wire going through the ballast resistor to provide about 9v. When you turn your key to "start" the 12v current is sent to the coil to give it the proper starting boost it requires, after you release the key to the "on" position, it will then run on 9v as you drive and do everything else. If a ballast resistor is not used you will burn up the coil and the vehicle will run like shit. This is likely at least a PART of your issue, although as everyone has said, running pig rich seems to be a likely situation. Are you using a stock hitachi carb or a weber, holley, etc? Any misfiring when the engine is being revved up? Does it idle smoothly? 

 

A leak down test is a more intense compression test, basically, it lets you know how much blowby you get through your cylinder, it requires a leak down tester and an air compressor, screws in to a spark plug hole set to TDC, blows air into it and sees how much escapes. You'd like it to be about 20% or less.

 

Compared to some of these guys here i'm no guru but ive done my fair share of datsun troubleshooting as well and the biggest thing i've learned is TAKE PICTURES for us of everything and anything you can think of, and give us as much information as possible, someone will see this and know exactly what's wrong with the right info.

[banzai510(hainz)]

With a Pertronix your use the stock coil from your truck and the ballast resisitor. As pr the instructions.

 

points and Pertronix or a Hotspark or Unilite want the stock higher resisitance . input

 

 

no not use other coils if you dont know the inout resistsance.

 

with this truck I would ck the cam timming. if good then ck the dist timming with a light if good. You know the elelctrical system is Ok then ck the valve lash. spark plugs

 

 

if coil feels realy HOt then soemthing is wrong

[xtrememotorworks]

Had a few petronix go bad on me, some just died other slowly went. Would run real rich to due to bad spark, cut out, sometimes even shot fireballs out the tail pipe lol I would take a hard look at that if your confident the carb and compression is good.

[datsunaholic]

I had this happen once in that one of the main jets backed out and fell into the plug. It was basically a wide-open fuel drain into the manifold.  Checking that requires removing the carb though.  Well, you CAN get the jet plugs off with the carb installed if you are really good with contorting your fingers.

[zah_chronicler]

Thanks I will check some of this out.

 

I will remove the jumper bypassing the ballast resistor  I was getting the 9v out of it and thought that might of been the problem.  I haven't ran it much since doing that. Hope the coil is still good

[banzai510(hainz)]

xtrememotorworks

I have never had a Pertronix go bad.

Just read the instruction and use the stock spec coil and ballast resisitor as it sin the system and should be fine.

I only had the magnet ring go bad on one unit. the tape wore out.

what I do is when I put one in I supper glue the tape edge so it dont peel off. maybe even good to super glue the magnets in the slots incse tou pull the mag ring off the magnets stay on the dizzy shaft.

[xtrememotorworks]

xtrememotorworks

I have never had a Pertronix go bad.

Just read the instruction and use the stock spec coil and ballast resisitor as it sin the system and should be fine.

I only had the magnet ring go bad on one unit. the tape wore out.

what I do is when I put one in I supper glue the tape edge so it dont peel off. maybe even good to super glue the magnets in the slots incse tou pull the mag ring off the magnets stay on the dizzy shaft.

 

Will admit the few that went bad where not installed by me, but saying that, they did go bad and the vintage BMW race shop down the street keeps a hand full of spares in the the race trailer, they have had a few problems also.Seems like most are the ignitor, the II seem to hold up better, again I think its more to due with set up and people getting "creative" with wiring lol Last one I had I put over 20k on it with no problems. I do find most go bad due to being hook up incorrect. To me its worth buying one and trying, worse case you have a good spare in the clove box, you know if it does go bad it will be in the middle of nowhere!

[banzai510(hainz)]

ON 4 cylinder long as its close to 3 ohms when key ON that would be perfect.

Only on key START the ballast is bypassed where coil get to see more voltage. as the starter is loading down the system.

I have installed 3 on my datsun and a Jeep and a guy who has a corvett and all still working.

 

most is people swapping i low EI coils and bypassing thr resisitor. Its in the instructions.

 

if you want more spark go with a EI matchbox set up and coil.

 

Pertronix is really a point conversion than a true EI set up. Just no points to fuck with.