[High end power loss, need some input]

damn, that was what i was thinking... that there isnt enough timing to make any kind of power. ill throw a can of 110 in it and pull the timing up..

 

thanks

[High end power loss, need some input]

That's really high compression for an L engine. I would suspect detonation issues unless you are using high octane gasoline.

 

i have a knock sensor hooked up and its not reading anything. it knocked at 12 degrees initial, back it down to 8 and its fine.

 

 

Is this a new problem?

Lack of fuel or plugged exhaust will cause these symptoms.

 

Mongo

 

ive got 3psi at the carbs at WOT and the exhuast isnt plugged. ive got a full msa header, straight pipe to a magnaflow chambered muffler.

[High end power loss, need some input]

ok, i havent posted on here in a long time, so thanks for looking.

 

with my Z, the motor just doesnt have as much power as it should. its got a f54 with flat tops and a mn47. one of the local guys figured its about 11.2:1 compression. so i will say it drives just fine under part throttle. 1/4 throttle driving it runs just fine. and at half throttle it moves real well. but anything past half throttle doesnt go any faster, just a quick as half throttle. Is this a carb turning issue? or a timing advance issue?

 

im lost and im not sure what im doing wrong here.

 

 

thanks in advance

[The build of a 240Z by 310z]

wow thats a wicked build. really like the wheels

[carb jetting, too rich? too lean?]

IIRC the DGVs have 2 venturies, but one of them is only opened when "floored" - in other words, like a secondary on a holley 4 barrel. It sounds like you are fine until the second venturi opens and then it falls flat. I don't think we can tell for sure if you're lean/rich from what you've said, but you might want to start by making sure that basics are all ok, such as that you have proper fuel levels in BOTH sides of the carbs, that the floats move properly, etc. Also check to be sure that the jets for the secondaries are installed and match.

 

When I bought my DGVs used a long time ago they were in horrible condition and none of the jets were in the correct locations. They're pretty easy to rebuild and there's lots of documentation on the web about reassembling them (including diagrams) so it's not a hard project. This is only a guess, but I suspect you will find that there's something wrong with one or both of the secondaries.

 

 

 

well at WOT it runs hard and just fine up till 4000ish rpm.

 

and i checked the float height and travel on both carbs and its right where the manual says they need to be. Ive checked the jetting and they are what is recommended for a 240z. not for a 280z.

 

 

Ill take a video later today, maybe it will help diagnosing this thing.

[lets see your 240z-260z]

not quite finished, almost there though. motor is in, runs ( kinda) and drives.

 

 

Now i just gotta get teh front lip re painted ( i ran it over at 80+ mph ) and re mounted..

 

 

 

 

 

 

[carb jetting, too rich? too lean?]

so i finally got my Z to run well. off idle stumbles a little bit due to the cam and lack of vac

 

but part throttle and cruise are great. off idle to 2000 rpm feels great, part throttle and wot.

 

2000-4000 part throttle and wot are good as well.

 

 

but 4000+ part throttle is good but WOT feels heavy and is very sluggish. its hits a wall at 4500 and just stops reving. i have to back off the throttle to get better acceleration.

 

 

so would that be a case of too rich or too lean? and since its a higher RPM range i need to change my air correction jets right?

 

and for info, i have a l28/mn47 stage 3 msa cam, weber dgv's

 

Thanks for the help

[Carb tuning, need some help. Fresh built and runs like garbage.]

Fuel level isn't the same as fuel pressure. Have you tried any adjustments at all to the mix screws?

 

whoops i read it as fuel pressure...

 

 

i have. i checked the jetting in the carbs and they are spot on.

 

 

the way i set them is like so: screwed them out to high idle to my vac gauge then backed them in 1/4 turn

[Carb tuning, need some help. Fresh built and runs like garbage.]

i think im just going to set it on fire and call it a day

[Carb tuning, need some help. Fresh built and runs like garbage.]

still stuck...

[Carb tuning, need some help. Fresh built and runs like garbage.]

ive got 3 lbs of fuel pressure at the T where it splits into both carbs

 

 

id like to go back to SU's or tripples but money wont allow it since i just re built this motor.

[Carb tuning, need some help. Fresh built and runs like garbage.]

can anyone help me with this one?

[Carb tuning, need some help. Fresh built and runs like garbage.]

So i recently built another l28 for my Z after my last motor lost the head gasket ( thank you fresno 112 degree weather.)

 

so my problem, my instinct tells me the carbs are too rich. they flood on idle super easy. if its sitting at idle for more than 2-3 mins i can see the primary throats lined with fuel and it starts to choke and will soon die.

 

part throttle they run just fine but my eyes burn like hell and it smells of unburned fuel. under WOT it sounds like its drawing enough air but its sluggish and gutless.

 

off idle to WOT it just pops up the carbs and spits fuel back up and out.

 

so any help would be greatly appreciated.

 

 

and to let you all know what ive done. im on dual weber DGV's i checked the main jets, idle jets, air correction jets, venturi's, everything and they are all what is reccomended from weber and other members on this site.

 

this is what ive got so far

 

http://i43.photobucket.com/albums/e355/raceme54/240z/DSC02155.jpg

[Brake bias problem ( new valve installed, still problematic)]

aww sheet! kragen has them down the street..

 

 

>.<

[Brake bias problem ( new valve installed, still problematic)]

it was mentioned in another thread that the fittings were m10x1.25

 

i have not taken it off and tried. might be worth a try

[Brake bias problem ( new valve installed, still problematic)]

yeah i very much so agree with that.

 

 

and where did you find the m10x1.25 unions? i cant find them anywhere

[What's the stupidest thing your previous owner did?]

Well ill start off i thought i had the worst case ever of shitty past owners but you guys got some bad ones too...

 

so when i got it, shoe laces were holding everything including the battery in place,

 

 

 

the alternator lead wire was just twisted together and bare...

 

 

and every last bit of wiring was just terrible.

 

the gold speaker wire you can see is the wire for the fuel pump

 

 

 

 

and i thought that was bad, then i found the lug nuts were standard, forced onto the studs.

 

the rear struts were WELDED to the strut towers. they cut the cables to the footwell vents, welded the radiator to the core support. it was just a messy hell.

 

lucky today its got a lot more love...

 

[Brake bias problem ( new valve installed, still problematic)]

Guys... THERE IS NO REAR PROPORTIONING VALVE ON A '73 240Z!!!

 

Remember that!

 

I've seen this happen over and over again, where owners of earlier Z's advise later Z owners to just gut the prop valve, assuming it's still located at the rear of the car. Bad idea!

 

Here's why... I'm not sure exactly when it started, but probably from the beginning of the '73 model year, Nissan moved the proportioning valve to the firewall.

 

 

Furthermore, it does not operate in the same fashion as the earlier valves. With the '73 and later (not sure if this includes all model years for the 280Z), the brake pressure to the front, right caliper modulates the pressure to the rear brakes.

 

 

 

If you GUTTED the valve on the firewall, you've tied the front right and the rear brake lines together! This is not good!

 

What you need to do is REMOVE the valve, and splice the gap in the lines together. Make you you tie the correct lines together. The top lines connect together, and the bottom lines connect together. You can see this done in this picture linked to earlier (look at the brass fittings splicing the brake lines together on the firewall) ...

 

 

 

The brake pressure switch that others are talking about is located on the inner driver's side front fender, below the master cylinder. Don't touch that. If you've gutted it, then as mentioned, you will have also tied the front and rear brake lines together.

 

Nigel

'73 240ZT

 

 

 

THATS IT!!!

 

i gutted the valve on teh firewall as pictured. no wonder it wont work for ♥♥♥♥.

 

 

yeah i know the valve in the front should be left alone...

 

 

well now i feel dumb.. after i patch the two lines together should it all work properly?

[Brake bias problem ( new valve installed, still problematic)]

anyone else have any ideas?

[Brake bias problem ( new valve installed, still problematic)]

I have the same setup as you if you're using 300zx rotors in the rear, but I find that unless I use a rear pad with a higher coefficient of friction than the front, even with the prop valve all the way open, I get front lockup first.

 

While I don't see how the stock prop valve could cause the rears to lock first, still I'd remove it just to get one more variable out of the equation.

 

Also, I would suggest you pay more attention to the pads you choose. My own limited experience is that the pad materials have MORE EFFECT on the overall brake performance than the calipers and rotors. If you don't know what brand of pads you have front and rear, then that could also be an issue, although if turn the rear pressure down with the prop valve, it should prevent the premature locking you describe. If that doesn't work, then I think you have to go back (again) and really confirm that you have the adjustable prop valve in the rear circuit and not the front.

 

 

well i know there just generic semi metalic pads IIRC "prostop" brand.

 

 

 

and i put my prop valve very similar to this setup

 

http://i51.photobucket.com/albums/f380/rontyler/Pro1.jpg

 

but i used the line out of the splitter like this

 

http://forums.hybridz.org/attachment.php?attachmentid=11342&d=1231570198

 

 

 

 

I guess ill just take a picture later when im home.

[Will +20 offset fit with spacer. Searched.]

as long as the spacer you get is hub centric and the studs are long enough, a 1 inch spacer would make them fit ok.

[Brake bias problem ( new valve installed, still problematic)]

Ok let me start off with thanks for all the replies...

 

What you're saying here doesn't make a lot of sense. The valve doesn't apply the brakes. All it does is change the pressure going to the rears. If you cranked it up then it should reduce the pressure going to the rears when you step on the pedal. It sounds like you have something else funky going on.

 

thats what i was thinking but there wasnt any problem before this.

 

The proportioning valve is relatively sensitive and by dialing the valve all the way in one direction, you should be locking the front brakes not just reducing the input to the rears. What are you using for master cylinders? Do you have separate ones for front and rear? Was the valve new when installed? Have you tried to re-bleed the brakes?

 

right, its just limiting the pressure. im using a new oem master cyl. valve is brand new. re bled the master cyl and the brakes.

 

 

Do you still have the stock proportioning valve in line?

 

no i do not. i "gutted" it by instruction of a local grassroots racer.

 

 

Wait a minute... you didn't put it in the front brake system, did you? If so, take it out and put it in the rear brakes. You DO NOT want a prop valve in the front brakes.

 

no its in the rear section.

 

 

You have 240sx calipers in the rear but are using a 280zx rotor? What bracket did you use to attach the caliper? This swap commonly uses the 300zx rear rotor with the 240sx calipers.

 

You say MSA Stage 2 front brake upgrade, is that with vented or solid rotors?

 

What brake pads are you using?

 

Did you remove the stock proportioning valve located in the rear of the car?

 

modern motorsports caliper adapter. it might be 300zx rotors. its been a while. front rotors are drilled/slotted. pads are standard semi metalic pepe boys pads. i did not remove the prop valve in the back of the car. only the one on the firewall was "gutted"

 

 

Thanks again for the help.

[Brake bias problem ( new valve installed, still problematic)]

So on my 73 Z, ive got a msa stage 2 front brake setup ( toyota truck binders, large spaced rotor, stainless steel lines) and in the rear ive got 240sx calipers and 280zx rotors.

 

now it was too rear biased when i put the 240sx rears on and i got myself a wilwood bias valve.

 

i installed it and went to tune it and with the knob half way in teh rear brakes were locked like i had the parking brake on. so i dialed it all the way out and its almost right but its still too rear biased, when the tires lock the rears lock up first?

 

 

any idea on why this is still too rear biased or a solution to my problems?

 

 

Thanks in advance

[Tt Sho 240z]

Stock fire wall, coolant neck has to be cut down and a hose bead added to except a 1.5" tight 90 hose.

 

i cant wait to see progress. best build imo.

 

but thats cuz im a sho owner and a z owner.

 

mad props to you dude

[Very Low charging (dim lights)]

ok well its a 73 240z.

 

here is something that might help find my problem. sometimes when im driving the interior lights go off.

 

and the other night the bad ground went away, it all was ok. then seconds later it came back.

 

i checked all my grounds, ground wire from the batt to the engine. ground from the harness to the alternator, ground on my ignition box.

 

where is the major grounds on the 73's?

 

ill take apart my headlight switch and hope i can find something