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Hitachi carb issues (I think) on 100nx


mdb188

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Hi all, stumbled across this site whilst trying to find some sort of nissan 100nx owners club, and this seems to be the only place where anyone seems to know anything about these damn Hitachi cars. 

I bought a 100nx which I was led to believe was a good runner before it was put in storage for 2 years. It is a 1992 1.6 carb engine with cat.

After replacing the fuel, stripping and cleaning out the carb, replacing all vac pipes, and general basic service, plugs, fuel filter distributor cap, rotor arm etc. It does now start and idle quite happily. The only problem, and quite a big one, when you try and drive it it splutters like a misfire like its starved of fuel. The spark plugs are also covered in black soot after it has run. 

Am I correct in assuming this is still a carb issue, I'm really out of ideas so any suggestions would be greatly appreciated. 

If it's any use to anyone, the numbers off the auto choke cover are 2kt60-57

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We started using EFI in all our cars around '82-'83. However a carb is a carb and they all just mix air with gas.

 

CARB...

The carb probably has a glass 'window' on the front? Is the gas level with a dot or line on the glass? This is the fuel level. It should be at the correct height for the carb to work as it as designed. The fuel level is adjusted by setting the float level. If too high it can flood over and drip into the intake making it run much richer than needed.

 

Black is carbon from running overly rich. However if all you have done is start it and not drive it any distance when warmed up the choke is on. The choke is designed to force a rich mixture for running a cold engine until it's warmed up. If you run it till it warms up (about 10-15 minutes the choke should shut off and the spark plugs will get hot enough to self clean while you drive. Possibly the choke is not turning off as it's supposed to. Next time the engine is warmed up take the top off the air filter and look. The choke plate on the primary barrel should have moved from closed to vertical and be fully open.

 

The primary jet is used only above idle and when driving. If it has any obstruction it will reduce the amount of gas going through it and the engine will run lean and lack power and performance. Because the orifices are so small it only takes a very small bit of dirt to cause this. Unfortunately the primary and the secondary jets have the same threads and can accidentally be switched. The secondary jet is always larger and used in the primary circuit will make it run rich.

 

 

IGNITION...

Just to be sure, the firing order is 1342 in the direction the rotor turns.

 

I had a minor problem like this worth checking. The coil had a small crack where the high voltage wire plugged into it. The spark would jump down onto the negative terminal. Check that yours is not 'carbon tracked' and also the top and the underside of the distributor cap.

 

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Hi, thanks for the speedy reply! Just had a look at the side glass, can't see any form of level mark but I can see fuel but it is very low on the glass so maybe the float needs adjusting the other way to let a bit more in, I suppose it's possible it's sucking the carb dry when revved. I'll strip it down again this evening and try blasting that jet with compressed air, it would be nice if it was all just down to a blockage as I can't seem to find a replacement carb anywhere. Checked the auto choke and that seems to be doing its job as it should. Already tried a different coil and there was no difference, also leads, cap + rotor arm so should be able to rule that out. 

Thanks again, I'll update when (or if) I make some progress. 

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Try to locate a FSM a factory service manual (these are produced by Nissan) for  a European model of your year. Amazon or e Bay are good, Nissan might have them but crazy $$$. They will have the specifications for setting the float drop, choke unloader, fast idle etc.   

 

Also to check and verify....

 

Valve lash. A tight valve can leak intake vacuum.

Ignition timing.

Listen for any vacuum leak. Or check every hose connected to the intake for cracks.

 

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Think you're right about the service manual, I've replaced all the vac pipes so there's no leaks on them now, can't hear any air leaks anywhere and I've sprayed carb cleaner everywhere when it's running and doesn't appear to be suckling in anywhere, I've stripped the carb again and everywhere seems clear, one thing I did find though is in the bottom of the carb there looks to be something either missing or snapped off, whatever it did I assume is somehow connected to the main jet as if you blast compressed air through the hole the jet goes in, the air comes from here. Only noticed it because it is shiny brass like something has been snapped off it, I'm sure I saw a photo online that had something screwed in here but can't seem to find it now. It's in the bottom so normally submerged, should really have taken a photo before I put it back together. Or maybe it doesn't make any difference. 

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OK, so I found the pic I was looking for and indeed there should be something in there, if the url works because I can't figure out how to add a photo, it's visible in figure 8.There is what looks like the remains of it but no screw head. Not sure what this does or if it would make a difference... 

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Bit of an update, if anyone's still reading, found the broken part on the nissan workshop manual, turns out it's the primary main jet... Which probably explains the problem looks like part number 16033 if that helps anyone with the same issue. I'll try to get one from somewhere and see if anything changes. Thanks to datzenmike for pointing me in the right direction with the factory manual

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There is the primary and the secondary jets and the power valve between them that are submerged in gas. Primaries are generally stamped in the high 90s or low 100s and the secondary is 155-170 ish. They will interchange so be sure the smaller one goes in the barrel closest the valve cover.

 

WBPIlcm.jpg

 

This carb is upside down and the cover is off the secondary jet, primary is beside it on the right. The jets are very soft brass so be sure to use a thick bladed screwdriver. I had to cut and grind one down just for this. Else the thinner ones will slip out of the slot and tear the metal up. The jets are numbered for size and are simply a way to meter exact amounts of gas to the air. 

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OK bit of an update, after a lot of a faff managed to find the equivalent yamaha jet is apparently no. 109. I managed to drill out the remains of the old jet, re thread to M5 and fit the yamaha (dellorto) jet. The car now runs and drives well, however, the problem I now have is sometimes the idle is perfect and it tucks over like a Swiss watch at around 750rpm, other times it will for no good reason tick over at about 1500 rpm, and then 5 minutes later, it's trying to idle at 250rpm. I'm assuming the fault lies with some sort of idle control valve sticking as sometimes it revs up and down for a few seconds and I can hear a relay or solenoid click. However seeing as the vac pipes were all disconnected when I bought the car, I presume that they may be on in the wrong places. Can't find any clear instructions online anywhere though to check where they should be going. There is one that goes to the top of the air box that controls the flap for picking up warm air, not sure where that one is supposed to go to as where it was seemed to be stuck permanently sucking air from the hot duct, and also the one coming from the top of the map sensor, that was connected to a pipe that goes to the air box but a photo I've found online leads me to think it should be going round the back of the carb somewhere and maybe connecting to something with some vacuum as the pipe that is currently going to it has no vacuum at all. I may well be wrong but if anyone can shed some light on where the vac pipes all go it would be great

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