Please help my '84 720 idle better!!

[brex]

Hey all,


I'm a newbie here, but I have done a lot of reading through the forum and many of your posts are extremely helpful. I have an '84 720 4X4 stock carb and the vac line system is intact as far as I can tell. I just bought a new dizzy from O'reilly's b/c I thought I needed a new ICM inside the dizzy and it was cheaper to do it that way (the store on ebay.com said they ran out of them After I had ordered one!). Long and the short of it is, I checked the ignition relay, it's fine, all the fuses are fine, the new dizzy w/ICM is in correct and I just timed the engine. All the plugs/wires are new/good, and it runs as long as I have my foot on the accelerator. Unfortunately, it dies when my foot is off the gas (Related: at one point, I noticed the accelerator went really "touchy" or slack but no longer feels as loose).

I'm wondering if after all of this troubleshooting my problem still comes down to possible leaks in my vacuum lines?? I know of several that are splitting a little at their ends and the vacuum port control switch that sits in water/coolant (the 3-pronged stump that screws in vertically w/3 vac hoses hooking into it) is broken and is held together with some e-tape....IF SO, would it be easier for me to delete the vac system, or put all new vac lines in?


or is it possible that my carb needs cleaning? It doesn't feel like a carb problem to me, but I don't have a ton of experience with these mid-80's nissans yet...

would it run well at higher rpms w/my foot on the gas, but then just die if there was too little pressure in the vac system??

ANY/All help is very welcome and much appreciated!!!!

Thanks,

Ben

[brex]

sorry for the long post^ but I wanted to make sure you all had as much info as I could remember off the top of my head....!

Thanks again.

[breadbox]

Depending on how loud your truck is there are two simple ways to find a vacuum leaks.

stethoscope or carb spray.

Grab a tube and put it to your ear and go around the vacuum system and intake gaskets listening for sucking noises.

Or spray around with carb spray and because it burns it will affect the idle when it gets sucked in.<--- what I usually do.

Read through the carb rebuild thread, lots of stock carb info. its in the stickies at the top of the first page of this 720 forum.

Also there is an in depth Vacuum thread, replace the lines one by one by following that and then you can hopefully eliminate vacuum as an issue for a long time.

[brex]

^Thanks a lot for the advice. Yes, I am planning on replacing all the vacuum lines starting tomorrow, and I'm hoping that it will be the final solution...thanks again!!

[brex]

Ok, so after installing a new thermal vacuum switch (valve) in the top of the thermostat housing, Completely replacing all of the vacuum lines, putting all new plugs in, my truck is running better, but still not where it should be. Re-timed it with the light and it's fine now...but overall running-wise still not quite there. Idling around 1,000rpm but not smooth like it used to.


I also drained all of the fuel, checked the filter, bought 92 non-ethanol and put some Seafoam in with about 4 gallons of the non-ethanol stuff into the empty tank....It sounds a lot better than before, but I decided to try driving it and it doesn't have the right amount of power and still sounds like it's searching a little bit....So now I am thinking it may need a good carb-cleaning/possibly a whole rebuild (I hope not)

also, it only runs when I disconnect the vacuum line entering the carb on the driver's side..I will try to post a couple pics to try and show what I'm working with here.There is good pressure on most of the vac-lines that I have tested...but now I'm getting closer to wanting to just delete them!

It feels close..


I think the next thing I am going to do just to double-check is some compression-testing on the cylinders...something is just not right and I'm getting a little desperate (?)

Any more advice would be much appreciated!!

[brex]

Ok, so I did a compression test and my cylinders (front to back) are: 175, 175, 170, 175....

so now, i'm just stuck with the thought that I need to rebuild my hitachi carb...I have read the rebuild thread from fastboatman...very helpful with tons of pics! I am just not sure I have the time to do it.

Is there anything else that anyone suggests checking before I resort to the carb-rebuild/cleaning?

I just can't think why all of a sudden my little truck goes from running fine to not even idling....then after fixing the no spark issue in half of my plugs w/a new ICM, why it still is running so rough?

[brex]

https://plus.google.com/photos/11710789 ... 2bSVwNODXg

https://plus.google.com/u/0/?gpsrc=ogpy ... 7339858306

[marbuf]

I know this is over two years old but, I didn't see any other posts from you on possible causes. I'm having the exact same issue. Did you ever find out what was causing the problem?