problem

[Roman Tasel]

I started my truck and after about a few minutes of 3000rpm idle speed the truck drops to 2000rpm ( iguess normal since the engine warmed up) but it shoots back up to 3000 and repeats untill it dies. My engine is sooooo screwed.:( About the high rpm, i adjusted a few things and it helped a little. since i thought it had vacuum leak, asprayed wd40 on the base of the carb. No vacuum leak:rolleyes: I was told it could be idle selenoid not working. How far does the mixture screw have to be turned out from the bottom of a hitachi carb on my l18? Just wondering, i know thats not the problem.

[datsunfish]

If your sure its not a vacuum leak I would suspect that the secondary throttle plate may be sticking. Whats the history on the carb? Those old hitachis had iron bases not aluminum and can rust up. Also there could be a problem with the secondary vacuum circuit. i doubt your engine is shot. You would be suprised how many datsuns we get for cheap up here because people think their shot when they just need carb or ignition/timing work.

[Roman Tasel]

Actually, the carb was rebuilt 3 months ago and was driven once. What exactly is the secondary vacuum line?

[ggzilla]

There are tons of places for vacuum to leak, not just the base of the carb. It sounds like either a big vacuum leak, or the adjustment is just waaaay off.

 

Is the choke closing all the way? Are you pulling the choke out all the way?

[datzenmike]

The secondary vacuum is internal and can't be gotten at. Get a flashlight and look down the secondary barrel. If it isn't closed you'll see it cracked open.

 

Is the choke fully off? If on the fast idle cam may be on giving a fast idle (what else). Maybe the fast idle cam linkage is stuck/not adjusted. Who rebuilt it? A friend who's done it a thousand times??

 

Is the throttle linkage adjusted? If too tight the throttle can't return to idle.

 

BTW, your motor isn't screwed, it just has an idle problem.

[Roman Tasel]

The choke works perfect. In the morning when its cold before i start it, its closed all the way. Once the engine is heated up, it opens. I had my carb rebuilt by rods carb shop. It was recomended by alot of auto parts stores. The shop might be local i am not sure.

[datsunfish]

Intake manifold gasket,pcv valve,vacuum advance port,power brake booster lines and fittings,carb base section gasket(the hitachi breaks down into 3 sections) all possible vacuum leak points to inspect. Make sure the throttle linkage is assembled correctly and the release lever for the secondary is not stuck or engaging it.