383 240Z is dog slow....confused?

[Guest tony78_280z]

If the engine is idling smoothly, yet lacks power at EVERY rpm, chances are that it's not the carb.

Gonna have to argue with you. Of course without knowing if it is vacuum or mechanical secondaries, but if he is tryin to run it off just the front two tiny q-jet barrels he's gonna have just that. I sluggish, but good running motor. It's not gonna run rich or lean, just not enough flow to satisfy his needs.

 

But like I said, I just look at the carb first.

[TheNeedForZ]

Thanks for the help, 20 replies in a day ain't too shabby, great forum.

 

Tony,

The carburetor uses air-valve secondaries. The air valves open when vacuum overcomes the spring that closes them.

 

Here's what I forgot to tell all of you : The motor was built by its ex-ex-owner and is said to have been driven only 4000km or 2500miles since the build, so it is "less likely"(not impossible) to have very worn cam lobes. The tachometer is not hooked up so no RPM information is available, this just keep getting harder.

 

So how does a manual valve body automatic works? You shift from 1, then 2, then 3. And if you drive with "D" it will start and stay at "3"?

 

Here's I will check on the car this weekend :

 

1. Make sure it's a 350 block

2. Check transmission fluid level

3. All four throttle blades open fully when someone pumps the gas pedal?

4. Secondary opens when heavy throttle is applied?

5. Can car be pushed easily in neutral without e-brake(stuck e-brake check)

6. Test drive again (first drive since K&N filter is in)

7. Test drive as if it has manual valve body (1,2,3 instead of D)

 

I can do 1~7, If it's other than that I'll have to send it out to a autoshop for a once-over.

[Guest WHITEBOY]

So how does a manual valve body automatic works? You shift from 1, then 2, then 3. And if you drive with "D" it will start and stay at "3"?.

 

Yes sir, that's right.

[Guest SC457A]

Here's what I forgot to tell all of you : The motor was built by its ex-ex-owner and is said to have been driven only 4000km or 2500miles since the build' date=' so it is "less likely"(not impossible) to have very worn cam lobes. The tachometer is not hooked up so no RPM information is available, this just keep getting harder.

 

So how does a manual valve body automatic works? You shift from 1, then 2, then 3. And if you drive with "D" it will start and stay at "3"?

 

QUOTE']

 

usually a cam can go flat real fast if it has not been broken in properly! (if not a roller cam). so the miles might not be a factor on the engine in regards to the cam.

 

you got the manual valve body thing right. you shift it. its basically a standard with out a clutch.

 

diagnosing a lack of power is a tough job. take your time, and do not forget the basics. i ran into this problem myself recently on my race car.

[Guest tony78_280z]

The carburetor uses air-valve secondaries. The air valves open when vacuum overcomes the spring that closes them.

VaC2nds. Lighten the spring. I got $2.00 says that is the problem =P

 

My Tranny in my driver went out thursday. (So I got no car with a functioning tranny) so I can't afford more than $2.00 It's tomarrows lunch money so I better be right or I go hungry. - LOL

[Guest dukeZ]

You might want to check the vacum line from the intake to the vacum canister on the passenger side of the transmission. If this is not connected or doesn't have good vacum then it will shift extremely late but doesn't really make it seem it like it doesn't have any power it just make the engine rev really high before it will shift to the next gear.

 

The lack of power seems to be either timing, carburetor adjustments, or spark plug misplacement, or rotor cap. There are numerous factors that contribute to such a problem. It is extremely hard to narrow it down without being there and seeing what it is doing. Everyone here has listed very good troubleshooting techniques. Just try them all and see what happens. It could actually be more than just 1 of the things that have been listed here. Just give the old girl a good look from top to bottom and check everything as you would if it were the first time cranking her after doing a build. Hope my 2 cents help.

[TheNeedForZ]

UPDATE!

 

I picked up a 1980 Q-Jet at a wreck yard for spare and study; I finally can see exactly how a Q-jet works in real life. I am in the process of cleaning it and rebilding it. While I was playing around with the spare Q-jet, I realized there is a secondary lockout lever that prevents 2ndary throttle from opening until engine is hot.

 

So : engine heats up--> choke thermostat coil unwinds--> disengage 2ndary lockout lever--> NOW 2ndary throttle is AVAILABLE for opening.

 

Then I rememberd that my 240Z choke thermostat is not hooked up to anything because the idiots at the shop simply didn't do it. I sent the car out last month to a shop and told them about the problem with the choke system, the stove that provide hot air is not there and choke thermostat is not hooked up to any heat source. After charging me a chunk of change(350$CDN), they gave me a new battery(100$) which did solve the hard to start problem, but they charged me 35$CDN for recharging/testing the old battery that was discarded?!? the air filter(17$CDN) they gave me is the wrong size and the core problem--choke not getting heat--was untouched(about 200$CDN was billed for the carburetor diagnosis/set-up? lol.

 

Back to the topic. When I test drove the car last time, I did not realize there is a 2ndary lockout, because the carb book said : some models do not have this lock out. During the test drive the car was probably breathing thru two tiny primaries like Tony78_280z said (No heat to choke thermostat = 2ndary lockout lever remain engaged = 2ndary throttle stay locked.) I have NOT confirmed if this is exactly what causes my car to move like a 4 banger because my other family members took a vacation on short notice. As a result I don't get the extra hand(foot) I need to see if all the throttles open when heavy throttle is applied.

 

HERE'S WHAT I NEED :

 

I've been searching thru many books trying to find a decent instruction/photo that shows how the hot air stove is set up/hook up but to no avail. Apperently those books overlooked the item and chose to show electric chokes only. I have talked to several people in the auto industry and they do not know either. I am looking for a photo/instruction for setting and hooking up the stove.

 

The spare carb(the one not on the car) has electric choke but no other electronic control, which is nice. I will probably go with electric choke in the future but I really want to know how to set up the traditional hot air type.

 

Thanks

[Guest WHITEBOY]

Personally, I would put a spread bore Holley on it, and be done with it. I'd even go with a manual choke. Better yet, an aluminum intake and square flange Holley carb. It would run better, and look better. Best of all, no more nasty quadrajunk to deal with. Good luck!

[Guest tony78_280z]

See what can be learned by getting the right technical manual? The mechanic over looked it, and you figured it out. This type of thing will become more and more common the more you learn. Eventualy you'll quit taking it to the mechanic at all.

 

Then I rememberd that my 240Z choke thermostat is not hooked up to anything because the idiots at the shop simply didn't do it. I sent the car out last month to a shop and told them about the problem with the choke system, the stove that provide hot air is not there and choke thermostat is not hooked up to any heat source.

Having never delt with that insturment, I can not pretend to know what you are talking about. But after reading these few sentences I will urge you to go look for any other things that might not be hooked up. A vacuum leak will definatly kill some horse power.

 

, but they charged me 35$CDN for recharging/testing the old battery that was discarded?!? the air filter(17$CDN) they gave me is the wrong size and the core problem--choke not getting heat--was untouched(about 200$CDN was billed for the carburetor diagnosis/set-up? lol.

Do you feel learnt? I wouldn't bother with them ever again. Sounds realy micky to me. You know, autozone will test batteries & Alternators for free. And if you take your old air filter into the store, they will go get you a matching one from the shelve if you ask real nice.

 

Focus on one problem at a time. Get the secondries to open properly. Have you taken it for a spin since you discovered and solved your posible problem? You should notice a BIG difference in performance. You might be able to "modify" that lock out so that it isn't in the way anymore.

 

Most people (myself included) don't like the quadrajunk carbs because they are usualy as old as the motor and a prone to fail at that age. So most go out and buy a new holley or eddy and think the name brand is far superior. I bet if you were to get a bran new quadrajet it'd run pretty frickin good too.

 

I recomend for your Z a spread bore carb for better economy, Mechanical secondaries for better response, and an electric or mechanical choke. Holley is far more tune able, but I've learned that I do get tired of tuning. Eddy makes some good economy carbs, and you can get a rebuilt quad through jets sometimes for about 180.00.

 

I've got too much time and money rapped up in my Holley I've spent about 450.00 in a profesional rebuild, jetting, springing, and tuning. You gotta buy a "kit" to get the one spring out of 6 that you can use, same with cams. But jets and shooters you get to purchase, try it, purchase another, try it... Holley is a pain. But when you finally get it right.. DAMN!

[Pop N Wood]

During the test drive the car was probably breathing thru two tiny primaries like Tony78_280z said

 

Make sure the carb throttle blades are opening fully, especially the secondaries. Pull the air cleaner, look in the carb and have someone floor the gas pedal (engine off of course). Are all 4 blades fully open?

 

???

 

You never did get back with any info about whether it runs rough or not?

 

Think you ought to take Drax up on his offer.

[TheNeedForZ]

Pop N Wood,

 

Yeah you did said to check all the throttle's. I just haven't got to it yet. If I had the extra person to help me with the checking then your advice would really lead to the cause of the problem. I am theorizing that my car was breathing thru primaries only.

 

Not knowing what you mean by "rough", I think my car idles fine, no black smoke or backfire either.

 

Drax moved his shop to the island and I am located on the mainland(Richmond). I'd have to tow the car and go by ferry, too far...

[awd92gsx]

but they charged me 35$CDN for recharging/testing the old battery that was discarded?!? the air filter(17$CDN) they gave me is the wrong size and the core problem--choke not getting heat--was untouched(about 200$CDN was billed for the carburetor diagnosis/set-up? lol.

 

Learnt? Don't you mean raped?

 

I work at a dealership and those prices even make me cringe!!

[Guest Drive-ability]

Normally if the choke is staying on you will have a higher idle and you will be able to see the choke throttle plate/plates at an angle apposed to fully opened(straight up). I would guess in my opinion this is not your problem. Most often the engine heat under the hood will open the choke after a while. It might take 30 minutes or so but it will open. This doesn't mean your secondary aren't the problem just unlikely a "properly set up choke coil" heated or not would stay closed all the time. You could just remove the screws or rivets and turn it so the choke plates open with the engine cold.

[Guest tony78_280z]

Properly placed zip ties will hold those open pretty good. =)

 

Reply and let us know if it works. I need that $2.00 =)

[TheNeedForZ]

Will do,

 

I got a free weekend this week.

 

I emailed the ex-owner about the gear shift and he said just use "D" to drive.

 

So "manual valve body" is crossed off the list.

[TheNeedForZ]

Hi, all

 

First let me start off with a question : When I try to start my car eqipped with a Q-Jet, do I have to pump the gas pedal once to reset the fast-idle cam?

 

Now here's the update :

 

I brought a stick of crazy glue with me to troubleshoot the 240Z. I was hoping to use a tiny bit of glue to temporarily glue the 2ndary lockout lever to a stem so it woudn't lock the 2ndary, but the carb is full of gunk just from the looks of it so I didn't even bother to try the glue.

 

Then I proceeded to start the car. I had problem starting the car at first, so I messed around a bit. Then I tried to hold the throttle open slightly as I turn ignition and the engine fired up.

 

Since the 2ndary lock is not disabled, I had to somehow test the 2ndary manually. With the engine running, I opened the air valves and used a screwdriver to push open the secondary throttle gently. I pushed the 2ndary throttle open, heard the engine sped up a bit, which is expected. When I stopped doing the test I hear the engine gradually speeding up faster and faster !!! Freaked out, I dashed back into the car and shut off the engine immediatly. I didn't know what's going on. I went back to checked the 2ndary system to see what the heck just happened. Turns out the air valves are stuck open when I opened it with my hand. Since the air vlaves are stuck open and the 2ndary throttle are slightly open too, there was a steady supply of airflow to keep the 2ndary throttles open a bit. That explained the gradual speeding up of the engine.

 

With the engine off I checked the air valves again. Indeed, if I open it fully with my hand, the air valves will stuck at full open position. The entire carb has just too much gunk. The air valve tension is also too tight to my liking; I doubt it will ever opens as is. Once the air valves are closed the engine acted normal again. Obviously the 2ndary system will work nicely once the throttles are unlocked.

 

I took the car for a bit of test drive in the alley with the 2ndary system still locked. Somehow the car feels very different than last time(last time I used a crooked air filter. This time I used K&N Xtreme so perhaps air metering is correct) I'd say the car is much faster than my VW Jetta even though it is only running on primaries. This time I had A TON OF FUN in five short minutes because I KNOW the car can easily be better if I unleash the power hidden inside the 2ndary system. After the test drive I let the engine cool and spent 10 minutes looking at the car from different angles. It is such a sweet looking car with such awesome power!

 

With a silly grin on my face I covered the car up with waterproof tarp and went back into the house.

 

Conclusion :

 

-The carb on my 240Z desperately needs a thorough cleaning. Fortunately, I just finished a practice cleaning of my spare Q-jet

 

-Electric choke will be installed.

 

-Air valve spring tension needs to be lightened.

 

....I still have that silly grin on my face. To think retrospectively, I almost gave up after having trouble starting the car this afternoon. I am glad I kept on trying.

[Guest tony78_280z]

See how much you've learned already? Fun isn't it? Learning a skill and putting it to use...Troubleshooting and diagnosing and solving the problem.

 

You'll have a lot less trouble and a bit more success if you just buy a new carb. You wont learn as much as you will fiddling with and fixing this one. But, It'll save you time and get you out in the street quicker. Also, this carb has proved to be undependable, and a carb is not something you want to go out on you leaving you stranded on the highway or worse, leaking gas onto a hot engine. Also, being a holley guy, I don't have much to offer your in this particular carb or this particular problem. If you choose to get a new carb, I figure you'll want at least 750cfm Double Pumper with Mechanical secondaries. Perhaps a bit bigger even. You'll probably spend 300.00-500.00 depending on model, vendor and extras.

 

If you choose to stick with this carb try to find some more info on rebuilding the carb or a person who has knowledge about them. You may end up needing to rebiuld it to be reliable. Look into rebuild kits for that carb. Keep tinkering with it

 

So are you pretty sure it's the carb? So I win my $2.00?!

 

Gotta love that silly grin. I sport that look alot too. =)

[Guest 305240]

You can do the Ghetto rebuild. I've done this to a few cars and it worked fine for me. Get a couple of cans of good carb cleaner. take the carb apart slowly, being careful not to tear any gaskets. Clean the chit out of everything. then put it back together. Or, get a carb kit. I usually get a Jiffy kit. Follow the instructions the letter. set your air jets with a vacume gage and tach. You want the highest vavume reading you can get and the highest reading you can get on the tach. That should get you on the road.

[Guest Drive-ability]

That must feel good!! Really the Q-Jet is a basic carb and rebuilding it is simple. You likely just need to disassemble, clean and reinstall. The secondary lock out can be removed, just remember not to nail the throttle until it runs a while.

[Guest GillSS1]

Might even look into the Torque converter.