I just bought an 84 and I am trying to get it up and running. The engine was replaced by the last owner but it hasn't run right since then.

Here is what I have so far.
The car idles just fine. When you press on the gas it will rev up to 2500-2700 and then cut out.
If I rev it up to 2500 and then manualy push open the secondaries then it will rev up higher.
At first I thought the acuator for the secondaries was bad but I tested it with a vac pump and it works fine.
So then we tested total vac on the engine and discovered a problem. From idle up to 2500-2700 it has great vac but then it drops to zero.

SO, my question is what happens at the 2500-2700 mark that would possibly fail and cause a leak?

Thanks for your time,

Josh Gesler

 

bump

 

Pop the cover off the secondary actuator diaphragm. Check the diaphragm for leaks and make sure the spring is there. If you raise the rpm's real slow will it rev beyond that 2700?

 

I pulled the whole actuator off and tested it with a vacuum pump. It didn't leak any vacuum so I would assume that it is ok.

Even if I try and sneak slowly past the 2700 mark it still won't budge. I think I will try and remove the rats nest this weekend and eliminate some possibilities but I think it is kind of an odd problem.

 

We have a car that is doing the same thing. We have removed all the EGR stuff and installed block off plates and vacume caps. It'll rev to about 2500 but when you put it under load it'll make a loud rushing air sound and choke out. If you leave it floored, eventually it'll just kick it and go to rev line like there was nothing wrong. It's very weird, almost like it's choking on fuel temporarily. If you tap the gas it'll run better, which I'm guessing is the pump shot kicking in.

 

Hmmmmm
I am trying to remember if we tried just holding it. I probubly just assumed that if I held it then it would die. I'll have to give it a try. Let me know if you figure out what's wrong with yours.

Did you do a vacuum check on yours?
Does your vacuum drop at 2500?

 

Sounds almost like your secondaries are slamming open, creating a super lean mix and killing the motor, or at least causing a major bog. Ask any of the guys who run mech secondaries on their Nikki's. They do exactly that if you floor it. a WAG
a- your secondaries are either intentionally or unintentionally mechanically being actuated.
b- your sec spring in the actuator box is gone/missing.

 

Are you saying that you cant see the secondary throttle open? Thats normal. Only 2 ways to actually see that puppy in action. On the dyno or on the flowbench.

Or remove the hood and lay on the engine while some else drives at high enough speed to make them work.

 

Rig up a venturi-cam.

 

So you are saying that the secondaries do not open if I am sitting in my driveway and reving the engine?

Well that's ok I guess but that still leaves me with a vacuum leak @ 2500 and no revs past that.

Does anyone know if a selonoid opens or something at the 2500-2700 mark that isn't hooked up right?

 

Actually you probably could.

 

Yes thats EXACTLY what Im saying.

Not that I know of on the solenoid. Try this, tie the secondary arm from the box to the strut tower so the secs wont open at all. Then drive it. Itll have low power but at least youll know if its some weird vac leak, or your secondaries slamming open too soon.

 

I was kidding about the venturi-cam until I thought about it a little bit, and you know, it actually could be done pretty easily. That'd be HAWT!

BTW, you CAN open the secondaries in the driveway, you just have to push on the lever with your finger.

 

It definately sounds like your secondaries. I modded my carb to allow the secondaries to open sooner and had to play with the air fuel mixture quite a bit afterwards plus it ate a lot more gas! after the initial mods, mine did the same thing until I figured out the air fuel mixture and the fact that the mod wasn't actually working all that well.

 

Yea, I bought a mini cam for the racecar. I bet I could mount it in the air cleaner. Hmmmm.......


Real funny smartass! I said "in action".

 

Just get one of those little fiber-optic type lenses and drill a little hole in the top of the aircleaner lid. Then the little camera mounts wherever you want.

This post brought to you by the word "little".

 

If the secondaries aren't going to open in my driveway then why won't it rev past 2700 in the driveway?

I am pretty sure that the accuator for the secondaries is working properly because it works with a vac pump.

If removing the rats nest doesn't fix anything then maybe I'll just have to rebuild the carb. Argh!

 

Accualy I tried this, I rev the engine up to 2700 and then push the secondaries and it revs up great.

 

Then convert it to mechanical secs and test drive it.

 

I guess that is probubly my best bet at this point.

Am I going to loose anything with mechs?

 

Just takes a little getting used to.
Gotta fight the urge to pop 'em open too early.

 

Hmmmm
Now I am going to have to think about this.
I wish I could just figure out what the problem is.

If I was my car I would just go mechs and not worry about it, but it is my wife's and I am going to have to explain why the car doesn't move if she slams on the gas.

I guess I'll just remove the rat's nest, and check for vacuum leaks again. If that doesn't make a diff then I'll go for mechs.

 

Well I was saying to do it as a test. Make sure thats your problem. If it is great, then concentrate on why. You dont need to keep it that way.