7d82adz

new motor with su carbs swapped in last night along with first start..

running lean which i dont like.. also dont think coolant is flowing correctly.
thermostat might be failed/stuck shut, is it ok to remove and flow wide open?
temp shoots to 190 quite fast, oil pressure reads around 25-30ish psi.. not happy with that either. oil level is spot on the 'full' mark on the stick.

n42 block and head, stock internals, new gaskets, e88 intake, su carbs.

first start straight off header.. timing is set on 0.. might have 2 degrees + or -


there is mixture adjusting nuts on the bottom of su carbs.. which way do i turn and how to set those? i got a unisync too for airflow adjustments..

how should i approach this? this is my first time tuning a new motor.. want to break in properly and run a long time..

any advice is greatly appreciated.. thankyou.

beg3yrs

Turning the mixture nuts up towards the carb body will lean them out.

Check out posts 42-44 on this thread: https://www.zdriver.com/forums/240z-...z-39721/page2/

Is the cooling system holding temperature steady at 190? If so, what's the problem? That said, I don't know if it's OK to run with no thermostat (probably hurts overall performance) however, if you're considering removing it, why don't you just replace it? They aren't very expensive and the extra labor effort is tiny. If you don't, later on when you've got everything else running OK, you'll be opening it up again (yet another gasket and/or goup) to put one in. Just do it now IMHO.

High oil pressure could be a concern as it may indicate a blockage. Easiest fix would be for it to be a clogged oil filter and/or dirty oil. Has the oil and filter been replaced recently? I've read that 15psi at idle with up to 60psi at full revs are pretty normal. I've also read that the Z gauges aren't terribly accurate either. Does the motor sound OK? Are the lifters clattering or do they sound like they are happily getting an oil bath?

Timing is in the area of 8 degrees BTDC. IMHO that's a good place to start but each setup varies a little bit. Your motor is already running so that's real good news.

Good luck, please come back and share what you discover.

7d82adz

well good news is ive solved my problems with thermostat and lean conditions.. now i have a power drop off or electrical issue.. or atleast thats what i think i have for a problem.

the thermostat i removed and ran the car without it for a couple drives.. just wanted to ensure that the coolant was moving thru and waterpump was doing its job.. that checked out and i replaced thermostat. opens at around 190.

su's were just poorly adjusted apparently, mixture nuts were too far in.


now i have the car timed and running spot on in the driveway,, go out and put a load down and it hates it.

not running rich or lean, timing is good, alternator was brand new but i swapped that from my other running motor, (no difference)..

my coil throws some serious snappy spark.. all plugs r firing.

i feel as the car cuts out on a couple cylinders.. might be number 1 and 4.
only when a load is put down.. 1st n 2nd gears are fine if you drive normal.. mash the throttle or try driving in 3rd or 4th it chugs like it only has 40 hp.

really wierd.

7d82adz

oh and all the fluids are new.. oil, trans gear oil, coolant, etc.

i may or maynot have a power draw when the ignitions on..
last series of tests.. the car was always running while adjustments were made, and over the course of an hour or 2 of tinkering i lost all power and had a dead battery.

my battery is good.. car was my daily with my raced up motor in it for a year until i jumped timing on that motor and decided to pull stock running gear outve my rusty parts car and run that instead.

did not change anything electrical at all in the swap.. just motor and trans. both are n42s.

beg3yrs

First of all, congratulations! You've made a lot of progress.

I'm assuming by "put a load down" you mean revving the motor or driving it under load. Not sure because you're also worried it could be an electrical problem and you're meaning you've turned on your 1000 watt stereo amp and things die. For now, as I said, we'll assume the motor is revving or driving under a heavier load.

Check your fuel filter(s) and fuel pump(s). You've got the mechanical pump driven by the motor and you may have an electrical one mounted just in front of the fuel tank. BTW, Z-Therapy folk tell me the electric fuel pump is not required with the round-top SU carbs. Hmm... if you've got a high pressure pump back there from fuel-injection days, that would cause problems with the SU carbs. The 260Z and 240Zs with the flat-top SUs used low pressure pumps, three to five PSI. For my restoration, I am just eliminating the electric pump. It's just one more thing to go wrong.

Another possibility is the floats are sitting too low, leaving not enough fuel in the bowls. Come to think of it, if you think some cylinders are cutting out, it might be just one bowl that is low. Although there is cross-feed (each carb does feed something to all cylinders), they might not feed all cylinders equally.

7d82adz

unfortunately i will not be able to tinker on this car for the next few months..

but by " putting a load down" i simply mean take the car on the road and make it go.. and as of right now the car cant handle running evenly on all 6.

could possibly be floats on the roundtop su's..

im very sure that the fuel system and fuel delivery to the carbs themselves is perfectly sound as i have a racing fuel cell in the rear with electric pump regulated down to about 3.5psi before going to carbs...however i havent given much thought as to how much fuel the carbs is allowing into them due to float adjustments.

i do know that this intake setup with the 3screw su's was in good working order on my other engine prior to swapping them the engine im running now.. it free revs great in neutral, cold or up to temp.. go on the road and it hates it. let it idle back down while at a stop and it sometimes snaps outve it if your lucky.. most the time it chugs all the way back to the driveway and stays chuggin until i give up and try the next day and itl do the same stuff..

basically it can start up and run good at first, free rev and run great in neutral, go to drive itl be sluggish but driveable for a mile or 2 then turn to **** until tomorrow... really wierd.

beg3yrs

Lots of heat related problems with the SUs although mostly with the flat tops.

The PO of my car had issues with running OK until he got it on the road. The setup was flat tops and headers, no heat shield between the headers and the carbs. The fuel rail was insulated.

I'm changing mine to round tops (installed on motor but motor ain't in the car yet), heat shield but am going with standard fuel rail as the old insulated one was unusable.

Some of my studying suggests you do everything you can to keep those carbs and the fuel rail from getting too hot. Since you stated that sometimes the performance gets better after idling, this could be the carbs cooling off a bit.

Didn't notice where you are but as the weather cools, your problems might mitigate a bit.

Just something else to ponder....

Steve260Z74

Examine your fuel lines to see if there are any kinks/constrictions that could limit fuel flow. Also, look at the fuel filters going into the carburetors. There could have junk in the lines when you did your build. Catching it at the carburetor filters could be limiting flow.

beg3yrs

Yes. Cleanliness is next to speediness ...

7d82adz

i appreciate the thoughts and ideas on how to improve.. wish i wasnt across the country until next summer.. otherwise id be tinkering.

about the fuel system i have however.. its pretty solid, it was in good clean, working order prior to my other engine spitting the timing chain.. thats why i did a swap with a stock motor i had..

heat is another factor il check into soon as i can, it does have heatshield intact.
while doing all these tests and playing with the car the temp outside was around 70.

i really want to test electrical stuff with the help of a friend someday, and maybe bolt on my fresh set of ztherapy carbs with a 260 intake.. was trying to keep them with a certain motor but if thats what gets me on the road il do it.

i wish i could play with this car some more.. i appreciate the inquirys for help. im happy to have new ideas and approaches once i can play with this car again. so just want to say thankyou to everyone who chimes in with advice

beg3yrs

Wow, that's the same setup I've got on my motor ... only my motor is still sitting on a stand waiting for the body to come back from paint. I'm wondering who will get this done first ...

BTW, you're welcome - folks like you who come back and respond to suggestions are what makes forums like this work. It can be annoying when someone pops up, asks a question, gets multiple pieces of advice and never responds.