hitachi carb problems

[devilsbullet]

so for the last few days my 510 goon has been acting really weird.  acts like its being starved for fuel when the accelerator is punched, has a deadspot where it will die completely, stumbles constantly.  it will start just fine, tho the idle is a bit roughbut not too bad. i have to feather the gas to get it moving, and then it stumbles constantly, doesnt ever seem to really stop stumbling/acting fuel starved.  the fuel pump works, the fuel filter is ok, when watching in the carb while it was running it gets a few decent squirts of fuel and then it turns into a mist and then into virtually nothing. planning on checking for vacuum leaks and making sure that theres gas in the little peekaboo window constantly tomorrow, just wondering if anyone has any other ideas on what it might be. i'm thinkin it has something to do with the accelerator pump so that would be my next route of looking if its not a vacuum leak.  any ideas or help would be greatly appreciated!!!

[DanielC]

It sounds to me like you are on the right track.   Check the fuel pressure, should be 2.56 to 3.41 PSI, and more importantly, the pump should flow 1,000 CC (one Liter) at 1000 RPM, in a minute or less.

 

There is also a possibility you have some water or dirt around the main jets. 

 

this is a wrench i heated up, and bent, then ground the jaws on to reach the front inner nut.  The nut by the float bowl, closest to the engine

[ggzilla]

This is not a symptom of a bad accelerator pump

 

> it stumbles constantly, doesnt ever seem to really stop stumbling/acting fuel starved.

 

Accelerator pump is not used in steady state driving or idling.

 

I suspect water on or near the main jet.

[devilsbullet]

always a possibility, though i'd think the water would evaporate in the week or so its been happening. granted this is the PNW, but i'll check for that and dirt. only question now is...where exactly is the main jet? first carb'd engine, still workin out where everything is. thanks in advance.(if you  happen to have an oic of what i'm looking for that would be even better :thumbup: )

[datzenmike]

Take for a drive and then pull a plug or two. What color are they? Very white would be a lean mixture possibly caused by a blockage of the main jet. Too much air not enough fuel. It runs very hot and the heat burns off any deposits on the insulator.

 

Dump a half pint of methyl hydrate in the tank. It's a form of alcohol that bonds to gasoline and to water. It will absorb the water and allow it to mix with the gas and be run through the carb and burned. If the jet is part blocked by dirt this won't help.

[LenRobertson]

Try everything else first - float level correct looking through the peep hole (maybe watch it for awhile at high idle or faster to be sure the level stays up), and the "gas dry" datzenmike mentioned. If nothing else works and you want to clean the main jet, look at this diagram:

http://www.carpartsmanual.com/datsun510/Datsun510Index/Engine/Carburetor/L16Manual/Aug70ToMay71/tabid/492/Default.aspx#1

I don't know which carb you have, stock Hitachi or a newer Hitachi (if it is a Weber, none of my info will apply), but the main jet will be in the same location. On the diagram, #14 is the main jet. It screws up at an angle into the bottom of the float bowl on the front of the carb (float bowl is what the peep hole looks into). The jet is covered by a screw-in plug #16. This plug has a sealing washer around it which will probably stay on the plug when it is removed. Make sure the washer gets back on or the plug will leak. Depending on your manifold and how much junk is on it, you can probably unscrew the plug without pulling the carb off the manifold. It will drain a bunch of gas from the float bowl down onto the engine. You could unhook your gas line from the filter to the fuel pump (the in line to the pump) and run the engine. This will run the float bowl dry and the pump won't be refilling it. You WON'T be unscrewing the main jet, just cleaning around and through it.  Pull the plug and spray carb cleaner up the hole. If you have a 2 barrel carb, there will be two plugs and two jets, one for the primary barrel and another for the secondary. Primary barrel is the one with the choke butterfly on top.

 

What would better is take the side plate off the float bowl (looks like #19 & #20 in the pic). Three screws hold this to the front of the carb. Depending on how petrified the gasket is, the gasket may tear and will leak if you try to reuse it. Having a carb kit with a new gasket or at least knowing where you can get a kit would be a good idea. Take out the three screws and take the cover off. At the bottom of the float bowl are one or two holes going at an angle down toward the front of the carb. These go right to the jets and with the jet cover plug removed you can blow down this hole and carb cleaner should go right through the jet and out the open plug hole. There is another passage down by the jet that goes up to the nozzle in the top of the carb throat that could be plugged. You could try blowing air or carb cleaner from this nozzle back down to the jet, but the nozzle hole is pretty small and not easy to reach. Hopefully there is something right down at the jet you can blow out. By taking the side cover off the float bowl, you can spray carb cleaner around in the bowl and get rid of any other bits of crap that may be hiding there.

 

But maybe you will get lucky and some gas dry will fix you up.

 

Len

[ggzilla]

> i'd think the water would evaporate in the week or so its been happening

 

Nope. Gasoline evaporates faster than water. Also it could be a tiny bit of crud in the fuel bowl. I've been through this many times with various carburetors. Sometimes happens to webers to.

 

No need to remove the carburetor or "rebuild" it. With a stock 510 carb, just remove the jet plugs on bottom of carb to drain the fuel. Make sure the engine is cold.

[datzenmike]

I've done this and, at least on the L20B, was very hard to get at. The 12mm covers for the jets are removed more by feel than seeing them and I had to cut down a wrench to make it easier. I used a stubby screwdriver with the sides filed down so it would fit up inside to get the jets. A-series carbs may be easier but the L series doesn't leave much room. 

 

Do one at a time if doing both. The jets will interchange and you don't want that.

[devilsbullet]

already tried using some gas dry on it before, didnt help the problem.  checked plugs, they're black as the night and burnt out, so i replaced those. started it, still doing the same thing, float level is good stays even when under load(what load i can get it to go under). pullin out the jet plugs now to try and clean those out with carb cleaner.

[ggzilla]

It's not so much cleaning the jets as it is emptying the fuel bowl. For this reason you might have to do it more than once, but you should Immediately see improvement if that was the cause of your symptoms.

[devilsbullet]

still doing the same thing. it runs beautifully at idle but starts stumbling once the accelerator is pushed down.

[ggzilla]

Well, start with the basics. After you've done these things, let us know what results you get.

 

1. Drain the fuel bowl

2. Do a fuel pump flow test

3. Inspect the fuel level

4. Visually test the accelerator pump (engine OFF)

[devilsbullet]

ok, i somewhat lied. went back and started it again, still has the dead spot and stumbles a little when trying to smoothly rev up, but not as bad. no longer backfiring thru the carb or tailpipe. fuel level stays good, not sure how to do a fuel pump flow test or if i even have the capability to do it(my dad and i are doin this all at his machine shop). accelerator pump squirts a decent amount of fuel with the engine off, cuts off after a few seconds but i'm assuming thats what its supposed to do. dad and i are hungry so its time for food and we'll be back at it tomorrow morning. i dont have a computer at my house at the time but i'll check up and in on this when we get here in the morning, so any ideas will be appreciated.  and thank you much to everyone thats been patiently helping out!

[ggzilla]

If draining the fuel bowl made it run quite a lot better, but not perfect, I would drain the fuel bowl once more. After you change the fuel filter and clean the carburetor inlet filter, whatever crud got down into the fuel bowl needs to be washed away.

 

Fuel flow test is very easy, only special tool it takes is a watch or clock with a seconds indicator. See Fuel pump Volume test.

[devilsbullet]

got it drained out again, messed with the mixture screw a bit. its runnin better, its at least semi-driveable, can sputter its way thru the dead spot (before it was just dying at the dead spot) drove it around made it up a few hills. changed out the fuel filter.  thinkin we're gonna try and take off the float plate later tonite or tomorrow(got family stuff to attend...) and clean the inlet filter.  curious as to whether i need a carb kit or if i can get away with just some gasket material or sealant/glue type material in case the gasket rips. especially since i cant find a number anywhere on this thing to even begin looking for a kit. thanks again all for your help, and i apologize for the lack of oics in this thread, my phone doesnt like downloading onto computers, and mines dead anyways lol.

[LenRobertson]

Good to hear you are making some progress. If you have water &/or gunk in the fuel, it may take awhile to get it all out. Gas dry in the tank may not get forward into the line and carb until you run awhile. So taking the side plate off the float bowl still may be worth doing. If you are carefully and lucky your gasket may be reusable. The problem with making one is it is a really thin gasket that fits into a recessed area. I've never had anything like silicon gasket sealer hold up very well to gas. Maybe someone else knows a product that works to seal gas. If you can find an autoparts that stocks a kit, you could buy a kit only if your gasket tears. If your gasket doesn't leak when you put it back together then you'll be good. I've had at least one cover gasket that would seep just enough to drain the bowl if it sat for a couple of days, so it took a bit of cranking the engine to refill it. But it was drivable down the road. I would say any 510 kit will be close enough, except if your '68 is the original carb, it may not be the same as later 510s. I don't know if you could find a pic on Google Images for a '68 and see if it looks like yours, then post a link to the pic.

 

You still could have an accelerator pump issue, but until you are sure the water/dirt possibility is eliminated, maybe don't fool with that yet.

 

I don't know if anyone mentioned the fine mesh screen inside the banjo fitting on top of the carb where your rubber gas line hooks up. Maybe you have already taken the bolt out and looked at that screen. Often they are missing anyway, but it is worth checking if you haven't.

 

Len

 

 

 

 

[ggzilla]

A repair kit is not needed. The L-series carburetor uses a reusable rubber seal for the float bowl. But why take that off?

 

The inlet filter screws into the carb.

[LenRobertson]

A repair kit is not needed. The L-series carburetor uses a reusable rubber seal for the float bowl. But why take that off?

 

The inlet filter screws into the carb.

I suggested taking the side cover off the float bowl to be sure there wasn't any water or crap inside that didn't drain out when the jet plug was removed. If only the plug is removed (and not the jet too), everything has to drain through the jet itself which is a pretty small hole. But I agree it may not be necessary to take off the cover. Just that it is easy to do and see if there is anything in there which might plug the jet. It once removed a float bowl cover and the gasket was so petrified it broke in two places and wouldn't reseal, so I mentioned the possibility of that happening. But hopefully won't happen. The Hitachi I currently have torn down now has a good rubber gasket like you mentioned and should be reusable. Having had a gasket break that once made me gun shy I guess.

 

Len

[devilsbullet]

got the front cover off, made sure inside the bowl was clean. now trying to re-adjust the float. it seems to either want to fill the bowl all the way, or not at all. good times, good times :crying: .

[ggzilla]

Oh no, not re-adjust! You can only do that with the drop method (with carb off). You shouldn't mess with it when it was OK before. Carbs are too easy to make worse.

[LenRobertson]

There is a possibility there is something causing your needle valve (#21 on the carb exploded view) to stick open resulting in the float bowl overfilling or not opening enough and starving the engine for fuel. Sticky needle valve isn't really common, but most carb kits come with a new valve needle and seat, so it must happen often enough. I don't know if you have taken your float out of the carb. It just slides sideways off the shaft in hangs on. Some carbs have a tiny piece of tubing on the shaft to keep the float from rubbing the cover (#18 on the diagram). Be careful not to lose this when you pull the float off. Sometimes a tiny spring hooks the needle to the float. The needle part of the float valve will fall down into the float chamber once the float is removed. But whether you will be able to see anything wrong, I don't know. Spraying carb cleaner up into the valve where the needle comes out of might dislodge some dirt. If you take the banjo fitting off the top cover of the carb to access the fine mesh screen filter (if it hasn't been damaged and thrown away already),   it is a straight shot right down into the top of the float valve, so you can spray cleaner from the top of the valve. There may not be any problem with the float valve, but it is easy to take apart and clean so worth trying.

 

If you have the float out, and the plug over the main jet back in, try sticking the wand to your spray carb cleaner in the hole in the bottom (the hole on the primary side) of the float chamber. Hold the tip of your finger or a piece of cloth over the hole to seal the wand in and give it a squirt. Carb cleaner should come out somewhere in the carb throat if the passage from the main jet is clear.

 

Len

[devilsbullet]

carb wasnt fine before, thats why we started with adjustments. we cleaned out the bowl, put it back together, went to start it and it filled the bowl completely, causeing the same exact feel/sound it was doing before. this combined with the black as night plugs i pulled out earlier are starting to make me think that something started going out of adjustment for whatever reason. and i cant get the top of the fuel inlet filter off, its frozen on there. can get the bottom part to spin but the arm that has the fuel inlet nozzle on it sticks out too far.already sprayed carb cleaner up the hole seeing if i could dislodge anything. i'll try the wand in the main jet len, see if that does anything.  if we cant get this figured out by the end of today i think i'm just gonna give in and get a weber, already had plans to get one since this hitachi is pretty old and worn, its just a bit sooner than i expected. but fingers crossed that it'll get fixed and i wont have to spend the money just yet :thumbup: .  and thanks again for all your help guys.

[ggzilla]

If the Hitachi is worn, then by all means replace it. Do the same for any Weber that is worn. A kit does not fix a worn carburetor.

[devilsbullet]

my thoughts exactly. i know the engine was rebuilt a bit before i got the car, but it originally had a weber on it from what i understand. and the guy i got it from had a literal yard full of datsuns and datsun parts, i've got a feeling that the carb hasnt had anything major done to it in 30+ years with the amount of grime on the outside of it. i know all the holes and jets are clear, i can see where the carb cleaner sprays out when i spray into them. we're still messing with the float some trying to get it adjusted, but probably wont be at it much longer before we call it a day and order a 32/36

[devilsbullet]

sdo we went out and bought a new float, it wasnt moving at all no matter where we adjusted things at. messed with the mixture screw some more and seem to have it at least idling ok again. gonna install the new float and see if that fixes our overfilling state.