vapor lock fresh L20B with a weber, return line? or fuel pump?

[TheBirdistheWord]

l20b stock 86mm pistons

A87 peanut head

fel pro head gasket

weber 32/36 

 

All of the accessories and manifolds were transferred from a very tired, but running L20B with a W58 head.  I was able to break the motor in almost entirely (400 miles) before the problem started, and everything has been performing reliably like this up until a week ago.  Now, once I hit operating temp the carb will start coughing and cutting out randomly mostly at lower rpms to idle.  If I try to just punch it to push through it, it will fall flat on its face and then shut off.  Usually waiting ten minutes and leaning out the air fuel screw will get it started and get me just about that far.... ill hop back in and slowly take off and it will fall on its face and then die.  Ive also recently discovered that venting the gas tank by removing the cap speeds up time it takes to start it again, subsequently I figured out you shouldn't leave the gas cap off.....

 

I have tried different combinations of minor adjustments/corrections to verify that the A/F is at least "ballpark," plugs are a golden brown which also suggest it isnt a problem with the A/F or spark.  Idle set at 800 with oil pressure 22psi at operating temp, and timing set at 12 degrees BTDC.  Measured the float valve a few different times because I didnt know what I was doing at first, it is set at 41mm.  Most things I read, and most people I have spoken to say a weber shouldn't need a regulator if everything is operating properly, I installed one anyway.  It didnt help... 

 

So, I consulted with one of the guys at datsonville and he suggested the fuel pump and adding a return line some how, and as I have been typing, the pump seems to make the most sense considering I just put it through hell with a break in addition to 10k on a tired engine.  Should I also be looking for the stock return line that later model datsuns were fitted with?  I guess a better question is should I expect the same problem down the road if I dont install a return line?

 

 

edit: who makes OEM equivalent pumps? unfortunately I tossed a perfectly good L16 pump thinking it inferior to the shiny aftermarket one...

 

any other input? what am I missing?

[laotsu]

Flatcat has one up for dibs on the pay it forward to thread

[cruznude]

I don't know what to tell you.  I have had the same motor and have had the same problem w/o the weber and what I resorted to to get some 5/8 pipe insulation and put it over all the fuel line from the tank up to the engine compartment.  After doing so, I didn't seem to have this problem again.  I am also putting on the weber 32/36 and now I'm concerned about vapor locking again.  I have eliminated all the smog shit and now I might steel braid the fuel line.  We'll see.  Go back into the engine threads and I posted a thread on the L20b vapor locking and theres all kind of good stuff to look at.  I'd bring it to you but don't know how to do that.

[datzenmike]

Not vapor lock. It's not near warm enough for that.

 

Not fuel pump as it runs well when cold with the choke on. With the chooke on the carb uses more fuel. If the pump can provide enough gas when the choke is on it can do so when warm....

Take top off carb and remove and clean the primary jet it seems to be part plugged. Perhaps the primary idle jet too. Use a can of carb cleaner with a straw to blow out the internal passages.

 

[banzai510(hainz)]

What Mike said

Vapor lock is rarely the case.

 

I run a sidedrafts on my 510 and only near really HOT days in stopped traffic I got to really worry.

No braided lines ect.

stock mechaical fuel pump delivers enough fuel.

 

 

Is the timming set at 12 degress but in the middel of the timming adjustment on the dist or is it cranked over all the way to one side to get to 12deg BTDC. then could be loose or misalighned dizzy

 

carb adapter cracked? loose intake? Loose carb

Carb squirts gas when cycled?

[datzenmike]

YES! a cracked adapter plate or loose mounting bolts could also be the problem. Grab carb and pull on it. Does it move?

[TheBirdistheWord]

Okay, timing is on the far end of the adjustment pedestal the lowest I can get timing set at is 8 BTDC, as long as I can adjust it to 12 degrees shouldn't I be fine?  I checked the mount bolts yesterday, they all took about another half turn which helped my idle but didnt mitigate the problem entirely.  I should also mention that I did find some debris partially blocking the primary idle jet, obviously removing this helped my idle as well.  Going to inspect the other jets after I get some food.  I didnt check them when I inspected float valve because it didnt appear I would be able to get to them with any screw driver I had, any suggestions? 

[banzai510(hainz)]

I notice if the oil/dizzy spindal is installed correctly the timming plate should be close to the middle at TDC .

there is a 8mm bolt you can loosen the timming plate itself but reaaly you need to know at TDC is your spindal in the 11/25 1128 position. then install the dizzy. where dizzy locks down then adjust your dizzy righ to that plug wire. adjust both timming plate and dizzy you you have middle of the plate. then lock it down. adjust a little advance to get running. then use a timming light. Then if you retard the dizzy you should be able to go to zero or even more. adv you should go beyond 20degs EZ

 

 

what I think could be happening is your going out of time as the motor speeds up. Plus the clooged jet part your idle issue.

[TheBirdistheWord]

Thanks! I watched those videos religiously before and during assembly of the engine.  My next question was going to be about the adjustment pedestal effecting the advance timing at higher RPMs.  I just cleaned the primary jets and light amount of debris came out, kept cleaning until no more debris was present.  Side note, I didnt remove the emulsion tubes, I hope that doesnt bite me later, I will adjust the timing pedestal next.

[TheBirdistheWord]

Adjusted the distributor/pedestal so I can time the engine properly, I am still detecting a slight miss at idle that turns into the same "fall on face " mode at partial throttle.  However, this time I was able to stomp on it and get her to push through it.  So, the last test drive it didnt die at all, I am going to remove and clean primaries and associated passages again just to be sure.

[banzai510(hainz)]

idles then goes to the main jet..If puching it its bypassing the main and going to the 2ndarys.

I had a main jet barely plugged with e tiny tiny rock and would run Ok if I pulled the choke(if manual)

Clean it out then was OK. But you got to take the carb apart.

 

I have a stack of Weber DGVs and I usually just swap out a carb as they are EZ to get the bolts and just run them to see if the proplem changes.

I seen a 521 I was working on and it had poping issies and I said Fuck it swap the carb and it was just a best guess as he said he got it from another ratsun memeber. I said thats the proplem!!!!!!!!!!

 

 

If you got points ignition make sure it stcok type set up and condensor is good. But doesnt sould like that is the proplem. or loose distrshaft wear it wiggles. cause points to open up to early.

[TheBirdistheWord]

Ignition is electronic (matchbox) when I inspected the oil drive shaft(?) clearance it was out of spec, not by much. I just rolled with it knowing it can be hard to source quality used front covers. timing seems to be sorted out now, I am inclined to say that's a non issue since I got such a positive result from cleaning the carb.

[TheBirdistheWord]

inspected the adapter plate, no cracks. According to the diagram datzenmike posted, my idle jets were swapped, had a 60 in the main and a 50 in the secondary. Curious, the air correctors were swapped as well, 165 in the main and a 160 in the secondary. I swapped both and it idles alot better now, unfortunately is still wont stay running. Engine bogs immediately and heavily on anything other than feather light throttle and will die if moderate/heavy throttle is used if you get it through the bogging. Going to take off the top of the carb again to make sure I didnt misplace anything, im thinking I might have mis-read the air corrector and swapped them prematurely.

 

any other ideas?? kind of beating my head against a rock now...

 

Edit: the emulsion tubes I took out read f50 in the main and f-6 in the secondary. They sort of correlate to the diagram but the picture suggests the more restrictive of the two should be in the main which in my case would be the f-6, but that definitely doesnt correlate with the diagram...... now what am I missing?

[Stoffregen Motorsports]

The only way you're going to figure this one out is by making a checklist.

 

Have you blown air back throught the fuel line to the gas tank?

All hoses good and not collapsed in on themselves?

Filter not clogged?

Jets clear?

Base gasket not torn?

Accelerator pump working?

Fuel pump putting out enough flow?

All intake manifold bolts tight?

Vacuum leaks at intake/exhaust gasket?

How do the spark plugs look?

Etc...

 

This definitely sounds like a fuel delivery problem, so focus your efforts there and check all systems to 100% before proceeding to the next one.

 

And if you find the problem, let us know what it was.

[TheBirdistheWord]

 

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So, this was what the power valve looked like.  Got a basic rebuild kit that had one included, all bolts are tight, fuel lines clear, carb disassembled and cleaned  engine still wont idle, and it seems to still have a very dramatic bog on initial throttle if I am able to nurse it into running. Havent checked for vacuum leaks yet, I am apprehensive about drenching my freshly painted motor with carb cleaner or brakleen.  I am admittedly just thinking about this now, thats the only way I have seen it done,  how else can I check for leaks? still seems like a carb problem.... maybe linkage? I am fiddling with it now.

[TheBirdistheWord]

eliminated all vacuum leaks, there was a big one under the adapter plate that I over looked because the gasket "looked" okay. Motor will start every time no more stalling and runs decent, other than a miss from low up to mid rpms and I finally get consistent color reading across all plugs.  However, now when I have the mixture screw dialed to where it will start and idle, the plugs all look more white/grey vs golden tan/brown.... running lean, ok so I dial out the mixture screw to mitigate that and upon ANY adjustment to allow more fuel in the engine stalls, floods, and wont start unless I lean it out again.  I am assuming now that this is a jetting problem, im not sure which one needs attention according to my condition.

 

anyone have some insight one this?

[datsunaholic]

Mixture screw only affects idle mixture.  Once off idle, it has virtually no effect. Well, unless you back it off so far it's just dumping fuel in.  But it's uncontrolled at that point, might as well just take the fuel hose off and stuck it down the carb throat.

 

If you want to richen it during normal running, you need to put larger main jets in (and change the other air control jets and such to compensate).  Very rarely can you change one jet and leave everything else the same.  Once you change a jet, the whole carb needs to be tuned.  There are weber tuning guides out there, I don't have links offhand.

[TheBirdistheWord]

word, thanks for that, needed a general direction to look.  It was my understanding you could do minor adjustments in jet sizes without throwing everything off.  Wouldnt going from a 140 to 145 be considered minor? seems the carb is operating at 90 percent, can I not just bump up the main to get it on point?

[datsunaholic]

It's possible.  You can do the carb "tuning" by trial and error, but it makes for an expensive proposition having to buy all the jets.  Or it can be done on a flow bench, which is even more expensive.  Small adjustments MIGHT work changing a single jet, but might not.  If getting the nice brown color spark plugs is the goal, it'd work.  If you want to get rid of the off-idle bog, probably not.   But it certainly can't hurt- unless you throw away (or trade off) the old jets, you could go back to them if it doesn't work.  Well, unless you make it MORE lean, which is a bad thing.  Too rich=fouling, and time spent cleaning things.  Too lean = engine damage, and new pistons and/or heads.

[TheBirdistheWord]

A wide band is up next for tuning it. The collector is bent at the flange that mounts to the manifold and it audibly leaks, new gaskets didnt work.  So, I got a new flange and plan to have the exhaust shop make a new collector with an O2 bunge in it.  I seem to have worked it out with a set of new plugs, and minor idle screw and mixture adjustments.  Fouled the last set in about 100 miles tracking down the aforementioned vacuum leak.  I guess its been figured out, my carb needed servicing, I feel dumb that is all it was.  I hasnt stalled at all today, and fires up every time now!  I hope the wide band helps me out with the bog....

 

Thanks for all of the input!