Z wont go past 55mph!

[2k2wickedspecv]

I have a 1971 240z, with practically all drivetrain/engine dual carb etc. original. Im having problems going past 55mph.. It seems to just not want to rev anymore.

I Know its not the tranny, or the clutch or of that sort. It was recently fixed for a clutch for and new clutch was put in. I have a new air filter, new spark plugs, spark plug wire, no compression problem according to the mechanic.

once i hit 55 the car just doesn't seem to want to pull or go any higher. It almost feels like if it were a rev/speed limiter. Its getting fuel, it can rev first and second, but when it comes to third gear it only goes to abut 4k. and stays there, four gear cant go past 3k.

So im stumped. Some help would be appreciated.

[MikeW]

Its getting fuel, it can rev first and second, but when it comes to third gear it only goes to abut 4k. and stays there, four gear cant go past 3k.

I think it may be getting enough fuel to make it rev but not when under load. I'd first check the condition of the fuel filter.

[EScanlon]

Just on a hunch, from previous posts: Distributor Advance Mechanism. Specifically the vacuum advance pot.

2¢

E

[2k2wickedspecv]

I think it may be getting enough fuel to make it rev but not when under load. I'd first check the condition of the fuel filter.

it has a new fuel filter.

[2k2wickedspecv]

Just on a hunch, from previous posts: Distributor Advance Mechanism. Specifically the vacuum advance pot.

2¢

E

What is vacuum advance pot? Sorry im kinda new to all this.

[thefastestz]

its a vacuum hose that connects to your distributor...geez i wish i could remember...but check out to make sure all your vacuum lines are okay.

[EScanlon]

I'm going to let the real mechanical guru's step in on this. I'm a bodyman / electrical. The true grease-work as this is, I leave up to the experts.

But to answer your question as best I can, the vacuum advance is a system attached to the distributor to advance the timing (point of detonation) within the engine based on the amount of vacuum the engine is developing. The more vacuum you generate, the more the timing needs to be adjusted. Usually this is under acceleration as opposed to steady speed, although when the engine is revving quite high there is a lot of vacuum being generated.

The Z's are notorious for the mechanical advance that is attached to the vacuum solenoid for going bad. This will result in a situation where the car simply can't / won't accelerate past a given rpm and othertimes of running as if it simply didn't have two or more cylinders igniting.

But, this I've gleamed from the real guru's here.

E

[2k2wickedspecv]

I'm going to let the real mechanical guru's step in on this. I'm a bodyman / electrical. The true grease-work as this is, I leave up to the experts.

But to answer your question as best I can, the vacuum advance is a system attached to the distributor to advance the timing (point of detonation) within the engine based on the amount of vacuum the engine is developing. The more vacuum you generate, the more the timing needs to be adjusted. Usually this is under acceleration as opposed to steady speed, although when the engine is revving quite high there is a lot of vacuum being generated.

The Z's are notorious for the mechanical advance that is attached to the vacuum solenoid for going bad. This will result in a situation where the car simply can't / won't accelerate past a given rpm and othertimes of running as if it simply didn't have two or more cylinders igniting.

But, this I've gleamed from the real guru's here.

E

Thanks peeps, Im gonna go try this out... hopefully i can figure it out...

[2k2wickedspecv]

ok,, i just went to the car, and pulled the hose to test it, it is so old its dried and cracked... I easily came off the distributer part without even trying... i tried pulling the other end off.. and well it just broke off too.

Anyways.. thanks again..

Just one more thing... If i want to remove emissions parts...can anyone tell me or post something showing how.. Maybe a pic of the emission parts on the engine not needed?

[nealkeith]

Sounds to me like fuel starvation. May be a bad fuel pump, or trash in the fuel tank.

[wfl_colorado]

What is you setup now? Stock 71 w/ stock SU's?

[Pir0San]

As wfl_colorado said, what is your setup? On my '72 with the stock SU's, I removed the smog pump, plugged the spot on the rail that the hose that goes to the smog pump, and removed the hose that goes from the pump to the back of the air cleaner housing.

The picture isn't great, but here's a pic of my engine bay. The part circled in yellow has a cap on it, which used to go down to the smog pump. The rail goes from the anti-backfire valve on the exhaust manifold, back into the air cleaner. I plugged the end circled in yellow with a marker end, the part that holds the ink in the marker itself. If you want to use the same thing, make sure you use one of the cheap off brand markers, not the crayola ones. My marker plug may seem weird, but you can't even tell what it is, and it fits perfectly.

The part circled in red is the anti-backfire valve itself and all of it's associated pieces. I know alot of Z people remove the valve itself and cap off the exhaust manifold where the valve used to go. I left mine on, and it still keeps the engine non cluttered and nice and neat. I'll get another pic of the engine bay a little bit later, to give you a better idea of what I've done.