720 engine races.

[azorr]

Hi Guys, I am new here, found your forum from a link given to me on nissan4wheelers. I have been offered an 83 720 with the z24 engine. However, the engine on the truck "idles" at about 5000 RPM. The story on it is that my Dad got the truck when he purchased an estate, we got it running by replacing the fuel pump relay, and it ran really well. However when my brother was driving it (he admitted that he was flooring it) something happened and now the engine races without pressing the accelerator. First thing we checked was if the accelerator cable was stuck, which its not. So they took it to a semi professional mechanic who said that a flooder valve in the carb was broken (or something like that, I can work on cars but don't know anything about carbs). Does that sound like a reasonable diagnosis to you guys? My father says I can basically have the truck if I can fix it... however its a couple 3 hours away so I am going to need to go fix it to bring it home.

[PEZi]

It is a very reasonable diagnosis. But before digging in so deep, be sure to check all the vac lines for leaks. They can cause the same thing and it is a much easier fix.

[azorr]

It is a very reasonable diagnosis. But before digging in so deep, be sure to check all the vac lines for leaks. They can cause the same thing and it is a much easier fix.

Thanks! Any suggestions on the best way to check them? I assume the carb cleaner trick won't work since the engine is already at high RPMs. Maybe I will just pick up a bunch of hose and replace them all.

[PEZi]

It is never a bad idea to replace them. Start by looking for something that just sticks out... it could end up being right in front of your face, but possibly not.

[breadbox]

Also I'd check the timing with a timing gun and see how far advanced it might be.

Also could be off a tooth compounded by other issues.

Z24 has a vacuum advance distributor. So After making sure your Vac situation is great.

How does it react to advancing or retarding the dizzy? Spray around with some carb spray once you can drop the idle a bit, see if the idle changes and find some leaks.

[azorr]

Ok, I will try that too once I get a free weekend to go work on it.

[tricknasty84]

My truck did the exact same thing. We replaced all the vacuum lines and that seemed to take care of it. (kind of) It still idles high but if you're sitting at a stop light or wherever and it's idling high, you put it in first, foot on the brake, and let the clutch out almost to the point of stalling it. Push the clutch back in, and it idles fine. Not sure why, has to do with vacuums considering I just replaced the carb. That's what my truck did when I replaced all the vacuum lines, so just keep that in mind. Good luck!

[Bulwyf_fjyr]

I had that issue. For me it was a combination of vac leaks and an old throttle cable that I had to replace