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J13 Nikki Carb jet source?


KFunk740

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Hi All,

 

Any idea if I can find different sized jets for the J13 Nikki carb anywhere?

 

Right now at cruising speeds it stumbles if I don't choke it a little.  I suspect that's because the engine was bored out a little and the PO put in pistons with slightly lower compression because that's all he could get.  I think choking it is a little bit of a sloppy fix, and is making it run too rich.

I'd like to increase the size of a jet a little in the primary (?) barrel to fix it properly.  Right now there's a size '60' in there.  I hardly every crack into the secondary barrel, so no idea if its sized right.   

 

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Over boring won't cause this or lower compression. (which is a guess on your part) 

 

 

Check the valve lash is correct and there are no tight clearances. Set the timing to factory. Check that you have the proper range NGK plugs. If cap/rotor and plug wires are old replace them.

 

If it still does the stumble check the primary jet as it may be dirty or partly blocked with sediment.

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Nissan sells them too. 520 had #80 to #90 primary jets.

 

Got a source for part numbers?  I've found some here: http://www.carpartsmanual.com/datsun520/Datsun520521Index/Engine1300J13/Carburetor/ExcLtuToApr68/tabid/1371/Default.aspx

But when I copy the part numbers into nissanparts.cc , it doesn't show up.  Maybe I'm screwing it up.

I was also looking at the wrong jets when I looked at it last night.  I guess I just took out the air bleeds from the top, and for the main jets it looks like I have to get to from the side/float bowl somehow (makes sense now that I think about, it's just set up a lot different from my other carbs). 

 

Good point mike.  I was thinking that the bigger combustion chamber would require more fuel, but vacuum is vacuum and the mix should still stay the same?

But somehow choking it/manually making it richer, makes it run smoother...

 

Most everything on this engine is sparkly clean and nearly new.  It was supposedly rebuilt about 500 miles before I got it, and I've put around 17K on it since then.  Who knows what the rebuilder might have messed up a little, though.  It runs great overall, but just a little out of tune.

 

I was wondering about when I should adjust the valve lash.  I hadn't looked up the specs for it yet or recommended interval, but thats easy to do. 

 

For timing: Last time I looked at the manual, I think it just said adjust it until it pings a little under load, and back off.  That isn't much help... I'd rather get it spot on with the timing light.  Should there be factory marks on the crank pulley?  I haven't seen them.  I guess I could make some, though. 

 

I'll check the plugs again later. I think they were NGK B6 or something like that.  They were black with a little brown on the insulator last night when I looked, but I've been running it choked/rich... 

 

Once I figure out how to access the real primary jet, I'll clean it out.

 

Thanks for the help! 

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Good point mike. I was thinking that the bigger combustion chamber would require more fuel, but vacuum is vacuum and the mix should still stay the same?

That is right. Bigger ccs still need the exact same a/f ratio

 

But somehow choking it/manually making it richer, makes it run smoother...

that is caused by either too little fuel (think plugged jet) or too much air (think vacuum leak)
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I shall work on it.  Vacuum leak is a possibility.  I'll check all nuts in intake tract for tightness.  I previously had an oil leak at the front cover just due to loose bolts.  It seems that any engine that was recently rebuilt should have all bolts checked after some time.  I had quite a few loose on the BMW engine I rebuilt.  

 

Workin on Datsun is briefly postponed, as I finally solved my ignition problem on the BMW.  I've been chasing it for weeks.  Turns out I had a short somewhere on my tach wire, that was feeding positive current into the negative post on coil and messing everything up.   :blush:

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A vacuum leak affects idle more than running. Vacuum is highest at idle but less when revved up and working. As the leak doesn't change size it will have less effect when the motor is revved up.

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A vacuum leak affects idle more than running. Vacuum is highest at idle but less when revved up and working. As the leak doesn't change size it will have less effect when the motor is revved up.

 

Hmmm, true.  Just gonna have to get that jet out from the bottom.  I haven't looked yet, but do I need to take off carb or take off front glass window to get to it?

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OK, I tried pulling primary and secondary jet, but no luck.  In theory, they can be accessed from the outside, but I could not get it.  There are two 12mm hex head plugs, angled downward, below the carb window.  Those are easy to get out.  But, I can't get the jets themselves out.  I can't get a flathead screwdriver angled in there right with enough torque, and afraid of damaging it because I can't see the my screwdriver is in the slots perfectly without a mirror, that I can't even get in the right spot.  It seems I'll have to pull the carb out to get a good straight shot at them....  unless you guys have better ideas.

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I've got a flat head screw driver with a flex shaft, that allows it to bend and get in to areas like that.  Sometimes it's like shooting pool with a rope, but other times it works wonders.

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I have a feeling that once its loose, it'll be easy to get with a stubby screwdriver.  I just figure the last guy torqued it in way too hard. 

 

I've got a rebuild/gasket/pump jet kit for the carb ready to go, so maybe it wouldn't be a bad idea to go ahead and take off the carb and go through everything.

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Best to remove the carb. As for a screwdriver, I had to grind the sides down to allow it to get in there yet have a large enough blade to fit the jet properly.

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Well, I finally pulled the carb to get jets out.  It was getting worse, and I have a lot of mulch to haul, and only a short time to fix it.

 

I still didn't manage to get the primary and secondary jets out.  I got them loose (they may have already been loose from last time, oops), turned it upside down and shook it, and they won't come out.  I tried opening fuel window and pushing them out with a little screwdriver, and still they won't go.  They're catching on threads or something.  So, I settled for blasting them with compressed air from the outside with them still in place.  I think I may have cleared a clog in the primary jet.  It seems to run fine in the driveway now, we'll see how it does on the road tomorrow when I gotta go back for another load of mulch.

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OK, it'll actually cruise now without stumbling, and without choking it at all, so that's an accomplishment.  However, after you get a full load (~2/3 cubic yard of wet mulch filling most of the bed), at half-throttle it stumbles real bad.  If you go full throttle and open the secondary barrel up, it does great.  Maybe this is the way it's supposed to be, but I do not know.  It also dieseled a little bit after I shut it off, which is weird, because I've never had that before.

 

By the way, I did check ignition timing the other day.  It was pretty damn close to 15 degrees BTDC at 600 rpm, just as my manual states.  It may have been a slight hair retarded (14.5 degrees?), but not enough to warrant messing with it at the time (a buddy had my timing light out using it on his car, and I just took a few seconds to check mine out of curiosity).

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I once worked for a German mechanic who had jet reamers.  I had the same problem you had with my Nikki carb on my Datsun L320 Pickup.  I slightly reamed the jet but it still stumbled.  Years later I found out that the primary venturi that screws in had pitting under it and I had to clean it up and epoxy the pits and install a new O-ring under it and reinstall.  Now, because I reamed the jet, it runs slightly rich and can't find replacement jets.  So, check the main nozzle in the primary for corrosion under it before rejetting.  It just unscrews out (2 screws) and inspect it and the O-ring under it.  I was a parts man for years at Datsun and Nissan dealers and I believe the OEM carb for the 520 was a Hitachi, not a Nikki.  Is your carb an after market carb?

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  • 2 months later...

I once worked for a German mechanic who had jet reamers.  I had the same problem you had with my Nikki carb on my Datsun L320 Pickup.  I slightly reamed the jet but it still stumbled.  Years later I found out that the primary venturi that screws in had pitting under it and I had to clean it up and epoxy the pits and install a new O-ring under it and reinstall.  Now, because I reamed the jet, it runs slightly rich and can't find replacement jets.  So, check the main nozzle in the primary for corrosion under it before rejetting.  It just unscrews out (2 screws) and inspect it and the O-ring under it.  I was a parts man for years at Datsun and Nissan dealers and I believe the OEM carb for the 520 was a Hitachi, not a Nikki.  Is your carb an after market carb?

 

Hi Norman,

 

Thanks for the tips, I'll look into that whenever I get the truck back out.  It's currently hibernating due to scary road salt.

It's been running OK, but still running best/smoothest with the choke pulled just a bit, so it needs a bit of something.

 

I think some 520s got Hitachi carbs and some got Nikkis.  See the 520 parts manual here that has diagrams for both:

http://www.carpartsmanual.com/datsun520/Datsun520521Index/Engine1300J13/Carburetor/tabid/1370/Default.aspx

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  • 4 years later...
  • 2 weeks later...

Ansza messaged me, and I'll also update on the thread here for the record, that there is no update!  Sorry, never got around to messing with it anymore.  I still drive the truck regularly and choke it just a bit.  I've now got two young children, and minimal time to mess around in the garage. 

I guess I still haven't peaked into that venturi.  My 3 year old loves looking at the engines on my cars, so maybe I can manage that sometime.  

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