Carb rebuild?

[FauxRoux]

I bottomed mixture out, then turned her 5 full rotations out.....she now idles. I can even accelerate if I BARELY feather it...any harder and she still falls on her face (which was the original problem when all this began) ...but this makes me feel heaps better... :rofl:

 

Glad to see its my overly cautious nature with things im inexperienced with that seems to be the biggest issue so far.

[FauxRoux]

Idle sounds good.....but i pushed to 7 full rotations out on the idle mixture and no change at all....I can get acceleration with the lightest of feathering but anything more and she bogs and will die if pushed.

[datzenmike]

Well there is the idle mixture screw. It's a small hole below the throttle plate with a pointed screw for adjusting fuel flow. It is for setting the idle mixture only at idle, so if the idle speed is too high it will have little effect.

 

Next is the slow speed system. It shares the fuel supply with the idle mixture system and is a vertical slit in the primary throttle wall directly above the idle mixture hole. This opening is at the throttle plate and above it. As the throttle plate rises upwards it exposes more and more of this slit, and intake vacuum helps suck out more fuel to mix with the more air let in. This system makes smooth slow acceleration possible from an idle. It's purpose is to allow the engine to rev up and begin to draw larger and larger amounts of air in (with fuel) without 'falling on it's face' from being too lean.

 

Next the primary system comes into play as the accelerator opens further and further. The slow speed system now cannot supply enough gas and the engine is now drawing enough air for the venturi to form a vacuum and suck larger amounts of fuel in through a fixed jet in the fuel bowl.

 

Next is the secondary system. When even more acceleration and power is needed a second barrel is pulled open by a throttle position past 50% open and a vacuum signal from the primary venturi.

 

The accelerator pump system is used when the throttle is suddenly opened at low speed and the air flow is not sufficient to form a vacuum in the venturi. It bridges the gap between idle / slow speed and full opening of the primary. Normally the mixture would go very lean from too much air and not enough gas so the accelerator pump dumps a squirt of raw gas into the primary barrel. It has a system of two one way valves using a spring and a ball bearing. Neither seal very well so if the throttle is opened relatively slowly (and the engine has time to speed up) the squirt of gas is very weak because the fuel can leak past the ball bearing. If the throttle is opened very fast (and a larger amount of fuel needed) a larger squirt is supplied. This system saves a lot of gas as compared to say a 32/36 weber which has a diaphragm pump.

 

There is also a vacuum operated high speed enrichment (or power) valve. Vacuum passes through a hollow screw in the carb base and sucks a valve open allowing more fuel to be sucked into the primary. It's always best to be running slightly too rick when floored at high speed.

 

 

I would say your slow speed system is lacking if it cuts out just above idle.

 

 

Things to try to clear out the idle mixture and slow speed fuel supply is to remove the idle cut solenoid. Get a can of carb cleaner, one with the red straw to direct the spray, and force the spray into the hole. This will go down to the slit and hopefully dislodge or dissolve any obstruction and it will also go backwards to the slow speed air bleed. Try it. It's a Hail Mary and if it doesn't work the carb may have to come off and be cleaned the old fashioned way.

[FauxRoux]

the carb was fully rebuilt and completely submerged in a carb bath...then each crevice and hole blasted with carb cleaner...but ill try anything at this point.

 

I also have a backup non-CA carb (also freshly rebuilt) I could swap out later if this doesn't work.... if you think it worth a try.

[datzenmike]

I guess spraying is way easier than changing and worth a try. Wear goggles, that shit shots out of the strangest places and stings.

[FauxRoux]

It occurs to me that when I first took apart the carb for rebuilt the primary venturi was loose in the throat....so loose it literally fell out when flipped upside-down.. I managed to break the set screw loose and reset the venturi and can confirm it squirts....I did add a small piece of gasket on the set screw side but could not find the original triangle gasket I was told about, nor was their one in my rebuild kit....As the venturi was being set I did some trial runs before tightening it down and noticed as it tightened the angle of the venturi shifted slightly....could this be the venturi being ever so off angle? maybe slightly blocked off and not delivering properly despite visable squirt?

[FauxRoux]

Sprayed out the idle solenoid..seemed clear and shot out the throat(and everywhere)...now it doesn't want to idle at all...hahaha :rofl: (hahahaaaa ...shoot me) ......looks like its time to pull the carb again I guess

[datzenmike]

I thought you said it cuts out just above idle. The venturi isn't an issue at that point. not until well revved up.

 

It may take some tries to get the carb spray sucked out. It won't hurt to leave it over night to dissolve anything.... and it may work when the gas gets through

[banzai510(hainz)]

OK if you had it at idle why didnt you ck the timming with a timming light.?

[FauxRoux]

OK if you had it at idle why didnt you ck the timming with a timming light.?

my timing light failed and my new one wont be here for a few more days.....I did the valves although there wasn't much of anything to adjust and the PO seems to have adjusted all that right before purchase....new plug wires and all...but as soon as the light shows its first on the list....

[banzai510(hainz)]

if it idles a desent rpm it most likely OK unless the dist is crank all to one side to get it running

[FauxRoux]

So the timing is correct....and ive got the rpm dialed to 600 at idle . I took out the idle solinoid and blew it out...no good. I removed the carb and tore it down again and cleaned out all the Jets and passages thoroughly....no good.... She still falls on  her face when accelerated. I borrowed a compressor and blew all the fuel lines out and it actually allowed me to accelerate normally for about 10 seconds before resuming falling on its face....So I blew out the fuel pump into and found a bit of rust in it.. Still falling on its face.....also when I tested the fuel pump (into a spare jug) it gave a steady amount of gas, but not what I would call a stream. More of a babbling brook. Since it seems she is starved for gas and I can feather to a high rpm....would you guys think it worth replacing the fuel pump and seeing if that helps? It appears to be the original at 127k miles... Or do you think it more likely the carb? (At this point its got to be 1 of them right?)

[datzenmike]

There will be enough gas stored in the carb to accelerate. Look at front of carb when idling. The fuel level should be at the line, about half way up. The pump does not supply only enough gas to run on, it supplies much more that enough and keeps the fuel bowl full. If the pump is not supplying enough gas the carb will empty and the car will quit under load.

 

Did you replace the fuel filter? clogged filter or clogged gas line will not allow the pump to push enough fuel into the carb. Get a container of gas and connect to the fuel pump and put the inlet hose to the pump in it. Crank the engine...does it now have strong surges of fuel??? If still just a small stream the filter or line to tank is part clogged.

[banzai510(hainz)]

once the fuel bowl is filled up the pump goes LIMP. Ever prime a carb once its fill up the fump arm is not pusing anymore gas.

filter plugged usuauly isn't it but more on High RPM issues

 

 

sooner one goes to a weber the better. or finds a rebuild . theser things are over 35years old +

[FauxRoux]

sooner one goes to a weber the better. or finds a rebuild . theser things are over 35years old +

 

I would love to go Weber at this point .....ive never had so much trouble...but im in CA and the truck is a 78....how hard do you guys think the weber conversion using the original air cleaner to pass Visual is? Im currently good for 2 years on smog and with the original air cleaner you cant even see the carb.

 

[LenRobertson]

I'd lost track of your thread and just found it again tonight. Sorry to hear you are still having serious problems. I skimmed through all 5 pages and may have missed some details, but didn't you say you have a non-Cali carb you can swap on and try? That sounds like a relatively easy thing to try. Probably a non-Cali Hitachi is easier to get past a smog inspector than a Weber. I've never had to deal with smog testing so I don't know how much time they spend on visual inspection. However we tend to want to think inspectors are stupid and easy to fool which may or may not be the case. I think there is a thread in the How To section on modding a stock air cleaner to fit a Weber. I guess if you go with a Weber and get caught you can always remove it and sell it. Do they put a sniffer on the tailpipe to check for emissions? I don't know if a Weber would pass the sniff test but maybe. I would want to see posts from Cali folks who have passed smog with a Weber before I spent the money on one.

 

Someone within the last few months posted that he got a rebuilt Hitachi from somewhere but I can't remember any details. Maybe someone else does. "National Carburetor" is running through my head. You might try a search here on Ratsun and see if that name brings anything up.  I don't even know if the rebuild solved his problems. I'm suspicious of rebuilders but if you can find his post and his rebuild worked well that might be something to consider. But I would try the other carb you have first.

 

Len

[NoMoneyZ]

I've been following this as I'm having issues with my 77 idling like crap and not passing CA smog also. I haven't had much time to fiddle with things but I need to go back through your thread and try everything before pulling the carb off. I hope you get it figured out.

[FauxRoux]

I'd lost track of your thread and just found it again tonight. Sorry to hear you are still having serious problems. I skimmed through all 5 pages and may have missed some details, but didn't you say you have a non-Cali carb you can swap on and try? That sounds like a relatively easy thing to try. Probably a non-Cali Hitachi is easier to get past a smog inspector than a Weber. I've never had to deal with smog testing so I don't know how much time they spend on visual inspection. However we tend to want to think inspectors are stupid and easy to fool which may or may not be the case. I think there is a thread in the How To section on modding a stock air cleaner to fit a Weber. I guess if you go with a Weber and get caught you can always remove it and sell it. Do they put a sniffer on the tailpipe to check for emissions? I don't know if a Weber would pass the sniff test but maybe. I would want to see posts from Cali folks who have passed smog with a Weber before I spent the money on one.

 

Someone within the last few months posted that he got a rebuilt Hitachi from somewhere but I can't remember any details. Maybe someone else does. "National Carburetor" is running through my head. You might try a search here on Ratsun and see if that name brings anything up.  I don't even know if the rebuild solved his problems. I'm suspicious of rebuilders but if you can find his post and his rebuild worked well that might be something to consider. But I would try the other carb you have first.

 

Len

The non-cal carb is another I rebuilt ...honestly it looks rougher then the original and is my last ditch option that Im about to try. I know the problem has to be in the Fuel circuit...Does anyone know anything about Chicago Carburetor? National seems to not have any in stock as the link to the 78-79 Hitachi's is dead on their site. Is a 720 L20B Hitachi 340 usable?

 

Also im wondering if anyone knows the likelihood of a line being clogged even after blowing them out with 120 psi? They seemed pretty damn clear to me...and are there any diaphragms in the fuel circuit that could have possibly been damaged by rust passing the fuel filter? Or am I still looking for some nook or cranny that could be clogged in the carb? The main jets are definitely clean...as well as the line behind the idle solinoid...

 

To those helping im sorry for the intermittent work im able to do. My wife and I are in the middle of tearing our house down and moving and its a huge undertaking.

[LenRobertson]

Since I'm kind of gun shy on the Cali carbs with the self loosening venturis I still like the idea of swapping on the non-Cali carb and see what happens. I know, easy for me to say since you are the one doing the work of swapping.

 

I'm puzzled by what looks like two phenolic spacers under the carb. Seems like that adds the need for another carb gasket but maybe if you go to just one spacer you run out of threads on the base studs. It looks in one of your pics like you have a flat heat shield between the phenolic spacer and intake manifold. There should be a new gasket between the heat shield and manifold just to eliminate a possible vacuum leak. Someone in another thread posted pics of a new spacer he bought somewhere if yours aren't good. So they are available.

 

As to a passage in your idle circuit still being plugged, yeah that sounds like something that is possible since you got rust into the carb. I would suspect those tiny idle holes in the primary bore of the cast iron base. But to do it right you probably need to remove the base from the rest of the carb, soak in carb cleaner, then blow both ways as best you can through the passages. All of which may be a huge waste of time if that isn't your problem.

 

When you had the carb off, did you set the position of the primary throttle butterfly to the spec in the FSM? This is kind of the beginning point for setting the idle and I think can only be set correctly with the carb removed.

 

I don't think it has anything to do with your problem, but you posted your fuel pump may be weak. Probably a good idea to replace it so it doesn't give you trouble in the future. Also replace all the rubber fuel lines with new if you haven't already. I know there is a type of gas hose now that is supposed to ethanol resistant. I would definitely get that kind.

 

I suspect the 720 L20b carb National lists is essentially the same as the slightly older Hitachis, but don't really know for sure. Might have different jet sizes or something. I can't tell you a good source for a rebuilt Hitachi. I mentioned National since someone here on Ratsun mentioned them. They may do a fine job of rebuilding but I just don't know.

 

Another random thought is air bleeds or something have been switched around although this may not have a thing to do with the idle. But it might help with the dying out coming off idle. Your FSM should have a table of what sizes go where.

 

Getting tired. Going to find my cat and go to bed and read a book (NOT a Datsun FSM. Those give me nightmares :lol: ).

 

Len

 

 

 

[FauxRoux]

Since I'm kind of gun shy on the Cali carbs with the self loosening venturis I still like the idea of swapping on the non-Cali carb and see what happens. I know, easy for me to say since you are the one doing the work of swapping.

 

I'm puzzled by what looks like two phenolic spacers under the carb. Seems like that adds the need for another carb gasket but maybe if you go to just one spacer you run out of threads on the base studs. It looks in one of your pics like you have a flat heat shield between the phenolic spacer and intake manifold. There should be a new gasket between the heat shield and manifold just to eliminate a possible vacuum leak. Someone in another thread posted pics of a new spacer he bought somewhere if yours aren't good. So they are available.

 

As to a passage in your idle circuit still being plugged, yeah that sounds like something that is possible since you got rust into the carb. I would suspect those tiny idle holes in the primary bore of the cast iron base. But to do it right you probably need to remove the base from the rest of the carb, soak in carb cleaner, then blow both ways as best you can through the passages. All of which may be a huge waste of time if that isn't your problem.

 

When you had the carb off, did you set the position of the primary throttle butterfly to the spec in the FSM? This is kind of the beginning point for setting the idle and I think can only be set correctly with the carb removed.

 

I don't think it has anything to do with your problem, but you posted your fuel pump may be weak. Probably a good idea to replace it so it doesn't give you trouble in the future. Also replace all the rubber fuel lines with new if you haven't already. I know there is a type of gas hose now that is supposed to ethanol resistant. I would definitely get that kind.

 

I suspect the 720 L20b carb National lists is essentially the same as the slightly older Hitachis, but don't really know for sure. Might have different jet sizes or something. I can't tell you a good source for a rebuilt Hitachi. I mentioned National since someone here on Ratsun mentioned them. They may do a fine job of rebuilding but I just don't know.

 

Another random thought is air bleeds or something have been switched around although this may not have a thing to do with the idle. But it might help with the dying out coming off idle. Your FSM should have a table of what sizes go where.

 

Getting tired. Going to find my cat and go to bed and read a book (NOT a Datsun FSM. Those give me nightmares :lol: ).

 

Len

I haven't switched them yet because the check ball, pump discharge is stuck in the non cali-carb and with multiple soaks isnt coming out..... not sure how to approach that 1

 

There are all new gaskets under the heat shield and in between the spacers...I used both spacers because its how I found it...the base studs are long... but the spacers ARE chewed up good...I would love a new one(s).

 

There is also old orange ATV stuck under the carb in the manifold between the wall and the plate down there....im contemplating using some fine tweezers and pulling it out....But given I know just enough to screw myself I hesitate before I try things like that. :rofl:

 

When I soaked the cali carb (twice) I hit it with a can of carb cleaner after...my neighbor has since offered his compressor so maybe I should make another go of it and try 1 more dip and a proper blasting out...

 

The Primary butterfly is set to 1.4mm from the bore per spec, set on the bench...or as close as I could get it which would be a frogs hair off if at all...

 

The truck idles fine at 600 rpm at this point...and I can feather her up to high speeds....but any attempt to properly accelerate and she falls flat on her face and dies pretty much instantly is the current issue....

 

Thx for the advice Len...enjoy the cat, book and bed.....with my upcoming move I doubt I will get much of those luxuries this month haha :D

[datzenmike]

I haven't switched them yet because the check ball, pump discharge is stuck in the non cali-carb and with multiple soaks isnt coming out..... not sure how to approach that 1

 

 

The discharge BB is below a small spring under a brass cover plug. Try a magnet. With carb disassembled, gently strike the carb downward against a block of wood to dislodge it. Can you see the BB? it may be mission.

 

This should not prevent you accelerating normally from mid range on up.

[LenRobertson]

I recall having a stuck BB and using either a really small jeweler's screwdriver or tip of an ice pick to pry it loose (sprayed carb cleaner on it first). You might try compressed air from the accel pump chamber, but obviously need to hold a rag over the discharge chamber or reinstall the plug to keep the BB from going into orbit.

 

I found the thread where someone bought a new phenolic spacer. Unfortunately it was one for an A-series carb

http://community.ratsun.net/topic/69511-hesitation-upon-accelerating-from-a-stop/page-6

I believe he got it from RockAuto. I looked at a couple of years of L20b engines on their site and didn't see where they listed spacers for them but you might look more carefully.

 

It sounds to me like you have a problem now in the accelerator pump on the Cali carb. And changing to the non-Cali carb may have the same problem. I maybe got lucky when I switched to a different carb and solved my accel pump problem. I still want to do an autopsy on the carb with the bad accel pump and see if I can find exactly what the problem is. I'm guessing a tiny piece of something blocking the discharge nozzle.

 

I've also wondered if the seats for the BBs could get pitted so the BB didn't seal. I've thought about putting the BB on the seat and tapping it with a long skinny punch, the idea being it might flatten any pits on the seat. But I believe I sprayed carb cleaner down on top of the BBs and they didn't seem to be leaking (at least not leaking fast).

 

It would be nice to rig a small flexible tube to compressed air to be able to blow back through the accel pump discharge nozzle. Swapping carbs worked for me so I never pursued the idea.

 

The worst part of screwing around with carbs is it so time consuming. If you are in the process of moving that is one thing you don't have. I can understand buying a rebuilt carb being attractive in saving time. One of those time vs money situations. I saw AutoZone and RockAuto have rebuilt Hitachis but they are about $300. It may be worth it to you to spend that much. My fear is if you happened to get a bad rebuild the seller would give you a thousand reasons the problem is something else on your vehicle, not their sleazy rebuild. But I tend to be overly cynical and suspicious.

 

Len

[datzenmike]

Len the BB doesn't have to seal perfectly at the bottom of the accelerator pump. In fact slight leaking is preferable and here's why... If you step into the carb slowly some fuel will push back into the fuel bowl and less squirts out... and this is fine as you are stepping down rather slowly. If you suddenly floor it a small amount will push back but the majority will be under higher pressure and go out the nozzle. In a way the accelerator pump give more when it's used quickly and less when used slowly.

 

Lost the BB for the bottom of the accelerator pump today while rebuilding/cleaning. Had old bicycle pedal and the BBs in it are perfect. BB showed up while putting tools away.

[LenRobertson]

Len the BB doesn't have to seal perfectly at the bottom of the accelerator pump. In fact slight leaking is preferable and here's why... If you step into the carb slowly some fuel will push back into the fuel bowl and less squirts out... and this is fine as you are stepping down rather slowly. If you suddenly floor it a small amount will push back but the majority will be under higher pressure and go out the nozzle. In a way the accelerator pump give more when it's used quickly and less when used slowly.

 

Lost the BB for the bottom of the accelerator pump today while rebuilding/cleaning. Had old bicycle pedal and the BBs in it are perfect. BB showed up while putting tools away.

datzenmike - The idea the check balls don't need to seat especially well is Important News to me. Seriously, this is something that has long bothered me, that the balls weren't seating properly and I didn't know what to do about it. So now I can worry that maybe they are seating too well! :lol:

 

Also it is useful info there is a source for replacement balls. I think some carb kits include new ones but many don't. I have enough spare carbs I can rustle extras from that I'll probably never need replacements but still good to know.

 

I intended to mention in my last post when I suggested a jeweler's screwdriver to loosen a stuck check ball - tools I use a great deal are cheap imported jeweler's screwdrivers, seldom for loosening screws but for poking down into small holes and scraping in small recesses. Also Harbor Freight has sets of mini seal picks - four different shaped ends that are quite useful for probing and poking stuff. Finally I can hardly work without my telescoping pocket magnet since I'm constantly dropping nuts and screws. If something falls down when I'm working on an engine I usually don't bother to look for it. I just wave the magnet under the car until I hear the click of it picking up something metal. Installing carb base washers and nuts I lay the magnet across the manifold so if I drop a piece there is a chance the magnet will grab it.

 

Len

[datzenmike]

The Weber uses a diaphragm and no matter how slow you push the pedal the same amount comes out, even if not needed.

 

Have that Canby carb on and it is totally different than the others. Above idle is perfectly smooth and balk free. Revs to 2.500 and then there is a problem. The primary should take over from the slow speed circuit but nothing comes out the venturi and it bogs and will stall if I hold it at this point.