hi guys, i have a set of brand new SU's carbs on my car, they ran good for a while, but now they have started acting up.

The problem i have is that the car will run great until operating temperature or a bit above. I notice it the most when I get on the highway, or sustain rpm above 2000 for any length of time. as long as my revs are up, this problem persists, if I stop and let the car idle rough for a couple minutes it smartens up and runs nice again.

at first i thought it was the stock mechanical pump not being able to keep up with the 2.9 stroker. I saw a lot of air inside the lines, it was boiling the fuel in the lines so I decided to install a carter pusher pump at the tank. this resolved the fuel boiling issue but my car still isn't running right. I've thrown a good bit of money at it now and nothing has changed.

I have checked and rechecked the carbs for dirt, engine bay fuel filter was just replaced, and last chance filters are spotless, fuel pressure is right, bowls are staying full, and float levels are correct (I checked them right after it started acting strangely the last time)

2 things that i have not had the ability to check are carb synch and timing. But I can't see those being intermittent problems. It runs so happily when it decides to run right. I did back off the timing a bit to see if that would help with the backfires (lean) but it didn't do much.

I'm contemplating selling these things and just getting a holley manifold and 390 carb. I can't stand being so frustrated with this beautiful machine.

Edited June 5, 201410 yr by azriel_strife

So you are advanced now already?

What dizzy model are you running and what's your static timing

I don't know how to tell, i'm assuming it's a stock 240z dizzy, it's a points unit. I read that 32 degrees was a good place to be with locked timing. just trying things at this point because I don;t have any information pertinent to my particular setup.

Try taking measurements and filling in the list below to help us help you

Advance measured with VAC connected:

Idle:____________ (degrees)

1000:___________ (degrees)

2000:___________ (degrees)

3000:___________ (degrees)

Idle RPM:______________

Max Advance RPM:_______

Advance measured with VAC disconnected:

Idle:____________ (degrees)

1000:___________ (degrees)

2000:___________ (degrees)

3000:___________ (degrees)

Idle RPM:______________

Max Advance RPM:_______

Try taking measurements and filling in the list below to help us help you

Advance measured with VAC connected:

Idle:____________ (degrees)

1000:___________ (degrees)

2000:___________ (degrees)

3000:___________ (degrees)

Idle RPM:______________

Max Advance RPM:_______

Advance measured with VAC disconnected:

Idle:____________ (degrees)

1000:___________ (degrees)

2000:___________ (degrees)

3000:___________ (degrees)

Idle RPM:______________

Max Advance RPM:_______

Idle: 10-11 degrees (mark jumps around)

1000: 15 degrees

2000: 25ish degrees

3000: 30ish degrees

The vac hose being connected didn't make any difference to the readings, so all of this is with vac disconnected.

Max advance is right around 2800rpm, I cant see any difference after that no matter how high i rev.

My good timing light kicked the bucket, so my replacement doesn't do offset.. I can't see beyond 15 degrees on the indicator for the pulley. so anything beyond 15 degrees is a best guess based on distance.

If I advance any farther i get knock at low RPM high load. it;s likely my increased compression ratio from the F54 with flat top pistons and the N42 head.

The amount of advance i am getting is quite high, wich leads me to believe i have a crappy emissions distributor, maybe I should consider getting a 280zx distributor instead.

If anyone has an e12 80 ZX distributor available for purchase I will buy it right away.

Edited June 25, 201410 yr by azriel_strife

So i was looking and I didn't see it before, the flywheel and block have been painted so the markings for timing on the flywheel and block were almost invisible.

To my surprise each tooth on the block for timing is 2 degrees, what i thought was 10 degrees initial timing at idle was actually 20. it seems that my timing is way too far advanced. it also seems that the spot i thought was zero on the toothed indicator on the block is not zero at all. i need to go have a look again.

ok, so i have set my total timing to 34 degrees at 3000rpm, and the car seems to hesitate under light throttle (vacuum) at 3000+rpm. Seems like it's getting too much vac advance. Other than that it is running and idling happily.

If I unhook vac advance, it doesn't seem to do it anymore, but I lose a noticeable amount of torque on initial pedal press.

I may have to check and make sure my balancer hasn't spun on the rubber. is there a good method of doing this?

Great stuff.

You may be able to remove the vac advance but give it more initial advance to compensate.... say ~ 17 to 19 at idle. This should help the mid RPM problem (from too much vacuum advance). However the small print side effects of no vac advance are: It may be more difficult to start and, you will loose fuel efficiency at cruise.

The vacuum advance canisters are adjustable but you need to chip off the epoxy blob to access the limit screw.

Edited June 28, 201410 yr by Blue

http://www.classiczcars.com/forums/electrical-s30/34559-adjusting-vacuum-advance-zx-distributor.html

Great stuff.

You may be able to remove the vac advance but give it more initial advance to compensate.... say ~ 17 to 19 at idle. This should help the mid RPM problem (from too much vacuum advance). However the small print side effects of no vac advance are: It may be more difficult to start and, you will loose fuel efficiency at cruise.

The vacuum advance canisters are adjustable but you need to chip off the epoxy blob to access the limit screw.

It does run better without the vac advance plugged in, but it seems like it's still lacking timing under light load with no vac advance. If i advance the timing up to 38-40 degrees total advance it seems happy. This is what makes me think my balancer may have spun on the crank.

Should i use the old screwdriver in the #1 cylinder to find tdc trick and compare it to the marks on the balancer?

My distributor is an old points unit, so i'm not sure if i can adjust the vac advance on it.

A non-points distributor is a great upgrade....especially at high rpms'

yes get the piston at TDC then check the marks

I ordered a hot spark electronic conversion kit for my distributor today. my car doesn't have the ballast resistor either, so it should be an easy swap over.

Ugh i really dislike the stock ignition.. some weird things today.

-set the points, they were well above 25 thou, set them to 19 thou

-reset timing to 34 degrees total, no vac. I lost almost 10 degrees of advance from setting the points.

-Checked coil voltage, there is no ballast resistor on my fender, but coil voltage is 8.8 volts roughly.

-Checked Coil resistance, 1.6 ohms.

All seems to be in order, but the car is running worse than before, i get misfire and very jerky throttle response in low rpm. Advancing the timing seems to resolve this. I might just give up on it until my electronic upgrade conversion arrives.