1980 L20b 720 Extra cab runs rough after new head gasket

[Captain Crazy]

I got the new Head Gasket on, Drove about 10 miles, ran really good, Now it idles fine , but when I accelerate it bogs down to where I pull over to the side of the road. Then I tac it up to about 4000 rpm and let out the clutch slowly while keeping her tac'ed up to get her home. Once home, seems to somewhat fix itself. I changed 8' of 1/4 vacuum line. It runs a little better, but, it still bogs down here and there, off and on. :confused:

[Captain Crazy]

I changed the EGR valve gasket today, Tinkered with it running off and on for an hour. Checked timing,12 BTDC, checked plug cap, it drove fine to the post office, about a 2 mile ride. I was there 15 mins. When I left I could barely get it home. It would idle fine, but when I would try and move it with the power down it would lag like hell like it was lacking gas, only could get it going 5 miles a hr. :confused: I seen a tow truck driver and asked him for advice, he said the head might be acting up after it warms up. It ran fine when i took it apart to changed the head gasket due to water loss.

ANY HELP ON THIS WOULD BE AWESOME.

[poopypants720]

Should have had the head looked at and likely resurfaced with it was off, maybe even the deck of the block too...

 

Did you replace the intake manifold gasket while you were at it to?

 

Likely you are having carb issues or vacuum leaks after resembling everything as well. Easy way to check... Can of carb cleaner sprayed intermittently along vacuum lines, sides of carb and intake manifold and even next to the distributor (on advance line) and listen to hear if it accelerates from sucking in c cleaner easily through a leak... Also...12 degrees is too far advanced... I'd go between 5 and 10 and allow the vacuum and mechanical advances do their job increasing timing through the rpm range.

[Captain Crazy]

I'll try that with the timing, my book says 12 btdc.

Thanks

[ggzilla]

12 degrees won't cause it to run rough, not even 20 (though it will be down in power)

 

Sounds to me like bad fuel, some dirt in the fuel bowl (sometimes runs good, sometimes not, but idles good).

[datzenmike]

12 degrees for the L20B in the '80.... 3-5 degrees for the Z series motors.

 

Your problem sounds like the carb. It likely had sediment in it that got stirred up. Intermittant jet blockage.

[poopypants720]

Aha.... Helps to read the title better. I'm so used to dealing with 720's having z motors I forget the first one was an L

[Captain Crazy]

I was thinking the carb also, When I did the head gasket, I took the head ex/intake and carb all off in one unit. I was turning the head back and fourth on the bench and that probrbly stired it up. I put that rebuilt carb on 15 years ago back in 1997. If that's the case going on with it, what do i do now?

 

Thanks guys for your help :thumbup: Knucklebump :thumbup: ..LOL

- - - - -

I didn't change the intake or exhaust gasket.

 

I took wood shop in High school, when I should have taken Auto :w00t: I was an electrician for 10 years. I don't mind working on stuff and turning the tools, But, I not a totel wiz at it at times either.

[ggzilla]

Sediment in the carb is easy to fix.

 

If you carb has exterior jets, just remove the bottom plugs and let it run out. Or, remove the top and let the bad fuel run out. Rinse is out with starting fluid or carburetor cleaner.

[Captain Crazy]

Thanks for the info ggzilla, and poppypants720, I'll look at my Datsun book to see about what your talking about. The location of the jets. I could have a clue to that, I'm a idiot when it comes to carb talk. :confused:

[Captain Crazy]

I have the Chilton book part #6816, 1970-89, page 292. you referring to the primary main jets # 17 and, secondary main jets #18 in book? I take those out?

[banzai510(hainz)]

make sure when you timmed it that the timmimplst at the dizzy is soemwhat in the middle of the slot. Not crank all the way over till you cant go anymore to get this 10-12degs. Then you might have put the dist off a tooth when puttin the oil pump in.

 

 

I thinking if you took carb off as a unit then its only the intake manifold that maybe is leaky but if it idles good then its sealed up perfect I guess a main jet or seconday jet could be plugged. But ck the electrical timming first.

[Captain Crazy]

I didn't have to remove the dist.

[banzai510(hainz)]

Carb then

I do a mexican tune up. Rev motor up to 7K and stick a rag over the carb. Hopefully it sucks the dirt out of the jets instead of sucking the dirt from the rag you just found on the ground.

[poopypants720]

Lol really? I'd rather just tear down the carb.... Its always good to get detained with your carb and how it works intimately anyways

[banzai510(hainz)]

Webers EZ

Stock carbs Im not good at.But it was OK before.

[Captain Crazy]

those bottom jets look like I need to pull the carb to get to them.?

 

Is the rag trick for reals. :poke:

[datzenmike]

I've removed the plugs and the jets up inside twice but very difficult. Have to shorten a 12mm wrench and grind a screwdriver down so it will fit up there. Much easier to do with the carb off... but that's a bitch sometimes too.

 

Use a can or WD-40 to blow out all the passages you can find. Check the tiny jets for flakes or crap. The holes are very small and easily plugged. Don't mix the primary and secondary jets... the primary is the smaller, around 100 the secondary around 150. ish.

[ggzilla]

Don't do the rag trick. If there is sediment, it will just happen again in a matter of days.

 

You don't need to remove the jets, just the jet covers which are locate on the bottom of the carb. Don't even need to remove the carb. There is little that can go wrong, just start with a cold engine because gas will run out.

 

#78, #81 in this diagram

[Captain Crazy]

You see in the picture above, The bolt #39, the I need to take the bolts off that are just under that number 39 right? I think it's the # 78 and 81? to clean what your saying right? and then 80 and 83 screws out?

 

A hour ago I took out the #46 in picture and cleaned it out and put it back, Again, It would just idle fine, but would not go down the word worth a damn. every time I would hit the gas it would bog down.

 

I'll tear into it tomorrow. Let me know on my question above. :thumbup:

[ggzilla]

46 is the fuel needle & Seat. Probably won't help any.

 

Get the old fuel away from the jets. #78 and #81 will do that. Taking the glass off won't do it., that only gets the old fuel out of the bowl, but not out of the jet pockets. The sediment will settle in the lowest spot.

[Captain Crazy]

Thanks for you info/help ggzilla,

After I take out 78-81 do the jets fall out? or do I unscrew them 80-83 to get them out. also, should I remove the glass cover and clean it out inside with carb cleaner.?

 

I had a 200x honda 3 wheel atc that I had to do this to a few years back as I recall now. The thing would only run with the choke on and someone told me to clean the jets, then it ran fine.

[ggzilla]

You can do whatever you want, be as thorough as you want.

 

What I would do is, remove the jet cover, lets the fuel out, replace the jet covers and be done. 5 minute job. Good chance of fixing it. But maybe it won't. Depends on if that is really your problem.

[poor-mans-720]

be more thorough... might as well, you are already in there... And you have a better chance of fixing the problem. buy a can of carb cleaner, and clean them good. If you do that, and it doesnt work. Then you know for sure that it wasn't the issue. Hate to do it half arse, then try a bunch a different other things, just to come back and do it again, more thorough, and find that it was the problem.

[datzenmike]

Remove 81 and 78 and reach up inside with a modified screwdriver and unscrew 83 and 80 which are the two jets. Likely the 80 is partially plugged. You might want to remove the front cover to the float chamber and rinse it out. Be very careful that part #44 doesn't fall outand get lost, it's very small. Use a can of WD-40 to blow out the small orifices.

 

I find that if you find a small enough screwdriver to fit ,it does not properly grip the slot in the jet and can easily slip off and chew it up. Get a larger one and grind the shoulders down so it will fit up inside the hole.