Took the cam off, tried it, and sure enough it works fine..the spring is not broken but does feel kind of loose, like maybe it wasn't wound around the cam tight enough, any thoughts?

sectionecho wrote:Took the cam off, tried it, and sure enough it works fine..the spring is not broken but does feel kind of loose, like maybe it wasn't wound around the cam tight enough, any thoughts?

Review the rebuild thread. It shows how the end of the spring inserts into a small hole. You can test to see that it operates correctly by pulling it back a little and watching the spring pull it back to the correct position (like the photo). I suspect that the person who rebuilt it may have not put things back as they were originally.

I'm glad to hear that it functions properly.

I wanted to drop a thanks to fastboatman for this rebuild tutorial. It carried me through my Hitachi rebuild flawlessly 3 days ago. The old girl has new life now. I regularly rebuild carbs for lawn tractors and mowers, even the tedious 2 cycle carbs for chain saws and weedeaters, but this baby was a whole new level. I don't think I would have been able to finish it as quickly or efficiently without this thread. Thanks again.

busterone wrote:I wanted to drop a thanks to fastboatman for this rebuild tutorial. It carried me through my Hitachi rebuild flawlessly 3 days ago. The old girl has new life now. I regularly rebuild carbs for lawn tractors and mowers, even the tedious 2 cycle carbs for chain saws and weedeaters, but this baby was a whole new level. I don't think I would have been able to finish it as quickly or efficiently without this thread. Thanks again.

You are very welcome. We need to keep these cool trucks on the road. I'm glad my DIY helped you tackle the job.

First I would like to thank fastboatman for an amazing post. I am currently rebuilding my fathers 1984 720 as a "thanks for not killing me as a kid, dad". I started work on the carb last week after finally getting the motor to start. It was having some major issues with the fuel pump lol. Anyways, I was about halfway through the carb repair and was removing the plunger mechanism on the middle section when I lost the BB that's located under the spring. I heard it hit the floor and never found it. I spent two days looking for it with shop magnets and a vacuum with a sock over the nozzle. That thing is gone.

My question, is it a critical piece to the carb? And I would like to replace it but can't find it on a parts schematic anywhere, does anyone know what size that BB is? I'll just order a steel BB the same size off some site if I can.

That is the accelerator pump mechanism. Yes, I think it needs the BB. Wasn't there a new BB in the rebuild kit? If you still can't find the BB, send me a PM with your address and phone # and maybe I can locate one.

Jay

Unfortunately my kit did not come with a replacement BB. The only shop that had the a kit in stock was Autozone and there kit seems to be a little lack luster (part:96-527).
Looks as though I can't send PM's yet as I just signed up for the forums last night, even if you were to only provide me with the dimensions in MM would help greatly.

I can open up an old carb and send you the BB.

So my family and I took a very long weekend and went camping and we just got back last night, as I was unpacking all the gear and bringing it back in the house, a glint of something shiny on the garage floor caught my eye. TADA! There was my missing BB.
So I apologize for not getting back to you sooner but it looks like I no longer need a replacement and now have a perfect working carb! Thanks so much for your help. I'm now one step close to getting my fathers pickup back to its former glory.

That's great news. Glad to hear another truck is staying on the road. Have fun with it.

Happy New Year everyone,
Thank you fastboatman29212 for the detail rebuild. I have a question before I start the rebuild process. My 1986 Nissan 720 starts and runs fine in the summer when the weather is warm. However, whenever cold winter starts (about the last 3 years), the truck starts with lots of white smoke like the the engine is flooded with gas as it runs so rich. From far away, it looks like my house is on fire! When the engine runs warm after about 5-10 minutes, the smoke goes away and the truck runs normal. Would you let me know what the problem is? Should I do a rebuild of the carb or need to do something else? Thank you very much.

PS. Before I found your post, I purchased a carb rebuild kit from Rockauto.com by Kemparts 15792B (some of the gaskets from the photos that you posted are not appeared to be included in this kit. I wonder if the ones included in this kit will have sufficient parts for this rebuild. Any thought?)

The correct carb kit is not very expensive, so I recommend getting the one I listed. It should have everything that's essential.
The white smoke sounds like it could be coolant. Check the radiator and oil when you do an oil change. Black smoke would be too much fuel from a stuck choke. You definitely need to diagnose the smoke problem before you spend time rebuilding the carb.

fastboatman29212: Thank you for the fast response. My correction: the smoke is black colored. Would you show me how to fix the stuck choke problem? Thanks

The choke is controlled by a heat sensitive choke mechanism. You will check the choke mechanism during the rebuild. The choke mechanism has a spring inside the choke case. Yours might not be working. See the rebuild instructions on how to check that. The black smoke makes sense and sure seems like a choke problem since it clears after it warms up.

Very excellent post! Thank You.

I'm trouble-shooting a low-idle problem. In other words, the engine runs fine when cold, at normal operating temp. it idles fine at (around 800 - 900 rpm) for about a minute or so, then it will start to stumble and the rpms drop to 500 -600. I've checked thoroughly for vac leaks, pcv and replaced most vac lines (didn't do the ones marked with yellow bands that seem to have something inside for who knows what?).

I've moved on to fuel and discovered the sight glass on the front of the carb (don't know why it took me so long to notice) and something is amiss. First, I couldn't see the fuel level (because the chamber was all of the way full (not right). After revving the engine, I've had the level at slightly above and below the mark but never right on the spot. So, I'm thinking a rebuild is in order which brings me here. I've done my share of auto repair out of necessity but I'm no mechanic so I'm a little worried about a carb rebuild (so many little parts to keep track of) but, with this guide I'm feeling more confident... so I really have to let you know how much this info. is valued.

I took a look online for the rebuild kit you recommend. On the Walker site its Hitachi #151000B and at first I was puzzled because there is a picture of all of the gaskets and rebuild components but no way to add the kit to the shopping cart. Then I realized you can click on each item and order it. Now, I wonder, is it better to buy a kit or just the parts that are needed. Of course, this probably more a matter of individual choice but I thought it might be useful for some to know you can get the components of the rebuild kit piece-meal. Here's the link: https://buy.walkerproducts.com/carburet ... nents.html
Any thoughts, insights or observations before get my hands dirty?

Get the kit. Try local auto parts store or RockAuto.com. I'm not certain you need a carb rebuild. Maybe the choke isn't working?

Thank you for the response. I checked the choke as per the instructions in the Haynes man. It works. The fuel in the float chamber was very near the bottom of the sight glass before I started the engine. Within a minute I was seeing fuel level on the dot. The engine idle speed was just slightly under 2000 rpm according to the on-board Tach. In about three minutes the level in the chamber was near the top. If you drew a line from 11:50 to 1:10 on a clock you'd have about the right picture of where the fluid level was on that round sight glass during high idle. At about 10 minutes the idle speed dropped to 1500 rpm for a minute then revved back up (on its own) to 2000 rpm where it stayed. The choke valve started at all of the way closed and opened by degrees during this time period. At about 15 minutes, she was warmed up. I goosed the throttle to get her to go to low idle which she did. The choke valve opened all of the way, the fuel level in the float chamber went temporarily below the mark then rose to the correct level and stayed there while she idled perfectly at about 900 rpm for another 15 min. when i shut her down.
No problem right? This has happened before though as I worked through some of my vac leak suspicions. I fix something, get her running perfectly in the driveway and, later experience the stumbling at low idle problem when out on the road. It's weird.
After this test though, I would agree that I may have been following a false lead on the carb rebuild notion. Thanks again, I'll post if I learn something more.

The RPMs you are getting seem very high. I would think they should be closer to the 700-800 range. Perhaps the fast idle cam is not properly adjusted or has a broken spring (return spring). Perhaps a previous owned tinkered with the idle mixture screw to get it to run better when they had a vacuum leak and now that you have eliminated the leaks it just need to be adjusted again? Just thinking out loud here.

Yes, I did have the idle mix screw a quarter turn clockwise. I've set that back now and the low idle sits at roughly 800 rpm (using the tack in the vehicle). I continue to see fluctuation of the fuel level in the float chamber (above the dot), but I haven't had the stumbling problem in the last few test drive. In fact, she's running really nice. The only thing I've done (and doesn't seem to make sense that it would be related) is I replaced the fuel shut-off relay. I repaired this part a couple of years back when the PU was dying intermittently and without warning from what appeared to be fuel starvation (which was the case) and I found this article after going through the fuel pump thoroughly:
https://axleaddict.com/auto-repair/The- ... t-Tell-You
I soldered the part as described in the article and the problem went away. Since I knew the part was bad once I decided to replace it now just for the heck of it. I don't really understand how this could have solved my current problem but, like I said, so far she's not misbehaving.
I'm still wondering why the fuel level in the float chamber is so high. Maybe a float adjustment will fix that problem but I'm reluctant to dig in to that while she's running just fine. I'll keep you posted if things change.

Yeah, that's a well written article. I've replaced mine twice. Recently I heard mine clicking like a mad cricket whenever I was at an idle. The clicking would go away as soon as I started driving. I thought about it for a while an then realized it was related to low voltage. Sure enough, my alternator was ready to go. It barely made 12 volts with the engine at idle. Driving made more voltage. Just enough to keep it from clicking off and on like it did at the traffic light.
New alternator, problem solved.

As far as your irregular idle issue, maybe the float is bad or the carb has some trash in the bowl that occasionally obstructs the float needle?

I can now say for sure that the fuel shutoff relay has nothing to do with my current low-idle problem. Your last sentence (in your previous post) sounds right on. I was at a stop light nursing the throttle to keep her from dying then, two minutes later I pulled off and let her sit and idle. I checked my watch just to see how long before she started stumbling. For ten minutes she sat and idled perfectly. I gave up and drove off, but she has acted up a few times since.
I have the rebuild kit you used and I'm thinking about doing the whole carb since I'll have it off the vehicle. I will definitely be looking at the float, float chamber and the needle first to see if anything is obviously wrong there.
I'll be following your guide every step of the way and feel very fortunate to have it. Thanks again and I'll let you know what I find.

Gotta give Kudos to you Fastboatman. You called it.

I found some rather large debris in the float chamber. It looks like it could be from a gasket or hose that deteriorated. The float is fine and just needed a bit of adjustment. I didn't rebuild the whole carb since time was limited and I felt confident that I found the problem. I did replace the (rubber) fuel lines under the carb and installed an additional in-line filter on the feed line. I also put on a new distributor cap and rotor on only because it looked a little cruddy and I was under the hood anyway. I've been testing for a couple of days now w/o a single problem and the fuel level in the float chamber is on the dot all of the time. I'm gonna knock on wood and say she's running purrrfectly now.

I'm wonder where I might find a replacement rubber seal (gasket) that fits on the air cleaner housing and forms the seal around the top of the carb as mine is in bad shape. I don't really even know what to call this part. Is this something that I would have to get at a wrecking yard?

Thanks again for the expert help with the diagnosis which was the hardest part of the job.

Best Regards

Not sure where to get that seal for the carb/air cleaner connection. Maybe you could cut a piece of thin floppy rubber vacuum line in half length wise to make it half round and use it. Then use some RTV to glue it to the proper location.

Glad to hear you have it running right. Mine runs like a little sewing machine, No smoke and 218K so far. Lacks power but I just drive it anyway. Need to do my brakes next.