What RPM range is you powerband at?

[Guest Anonymous]

I was just wondering. I got my car running real strong, hauls ass, smokein the **** out of alot of people in my town but after like 4500 rpm's it feels as if its losing power. The stock tach says redline is 6500 rpm and it wont go past 5250rpm at idle if I floor it and leave it floored. Im just confused becuase if I have another 1000 rpm's of power because I want it. If anyone could think of the problem just let me know. Its an l28 with su's.

[Guest bastaad525]

I keep running into this problem on my L28/SU motor too. I think it's fuel starvation. I'm pretty sure it's caused by insufficient fuel reaching the carbs because of clogs or something in the system that just wont allow the engine to rev past that certain point. You have it pretty bad if you can't rev past 5k-ish with the car in neutral. Mine would rev fine in neutral but got to a point that I couldn't rev past like 3.5k on the freeway. Go over the carbs tune them and maybe get the fuel system flushed. Oh by the way, before I had this problem I was running EFI on this motor and had it dynoed, and my power band was between 4300(peak torque) and 5400RPM(peak HP). I know most L28's with SU's OR FI that I've seen or heard about with stock cams have powerbands right around this area. With a cam and triple carbs it moves up a bit higher.

[Guest Anonymous]

my dads car has an L28 with SUs.. it hauls right through.. his fuel system is a really big pump (large enough that you can hear it kick in before ignition) and a regulator up further along so that the SUs dont get blown off!

 

it works extremely well and the car just loves to revv.. maybe something has happened to your pump? have you got an electric pump? that might help a bit

[Guest Anonymous]

I just have the stock mechanical fuel pump. That sounds like a good idea to put an electric one in there too. Could that be it though, its just running out of fuel? If it is then damn this car will haul ass because I just beat an Acura Integra GSR that was all hopped up Also, how much would be a universal electrical fuel pump be and could I use it with my mechanical, and if I do get a electrical fuel pump would it be ok to place it in between the mechanical fuel pump and the carbs or should I have it before the mechanical fuel pump?

 

Thanks for the info!

[Lockjaw]

Well you could have an unbalananced set of SU's too. I would rev the engine up while watching the pistons in the carbs and see what they are doing.

 

I have been in several SU equipped cars that have turned in excess of 7k on SU's. Of course they had cam and a header.

 

What needles are you using? Ztherapy recommends the SM needles, and they are 30 bucks a set I think. You can get them in two days.

 

Check your timing also. The stock 280ZX engine in my 260 was a pig when I drove it, but the SU's were way off, and I am not sure that the needles were in the right position either. I am hoping it will be spunkier when I get it running, hopefully by tomorrow.

 

You should be able to turn past 6000 with the stock cam. I can turn 7k on my stock turbo cam, but that is with lots of boost.

[Guest Anonymous]

You should be able to turn at least 6K on the stock cam and SUs, even on an L28. Are you using the stock FI cam or did you swap over the 240 one? The 240 cam is a bit more aggressive than the other stock cams.

 

Also, an electric fuel pump is a very good idea. Luckily, Datsun was thinking ahead when they designed the car. If you unwrap the electrical tape near the fuel gauge wires, you'll notice that two bullet connectors (one blk (GND) and one greeen (PWR)). These two wires lead back to the main console into a connector. All you need to do is jumper the two wires together at that point, or use a switch so you can control the pump and add some security.

 

Install a fuel pump (the holley red/blue fits exactly where the stock electric fuel pump would mount, even going so far as to use the same mounting holes. All you need are a couple of M6? screws of enough length to mount it. No cutting, or electrical splicing necessary. The only real work is re-routing the fuel lines and installing a fuel regulator.

[Guest bastaad525]

There are aftermarket fuel pumps that AutoZone sells, that pump at 3.5-4.5psi, which is exactly what you need. Mount it as close to the fuel tank as possible. I think with this setup you wont need a pressure regulator. It will just help with pushing the fuel up to your stock pump. I think one big problem is the stock pumps pull the fuel up, and it's much better to push it up than pull. The pump runs about $35. As I said I'm having this problem too, and that pump is the next mod on my list.

[Guest Anonymous]

It's been a while since I posted but I'm having the same problem as well. My 240 is equiped with a N42 head (ported, polished, and performance camed), L28 F54 Flattop block, Headers, 2.5 back to flowmaster then 2.25 into a Supertrap, and running on twin SU's to a E88 intake for now. I've used the mechanical and installed a Purelator ($35) from your local auto store, my advice, don't do it. It was a waste, since the volume was lower then your mechanical. Your better of using ur mechanical or I would spend the extra money and get yourself a Holley Red or a Holley Blue and connect them to a regulator set to 4.25psi.

 

Also, in my pass experience tunning SU, I've found that there are two methods that are most commonly discussed without using a A/F gauge or colortune. Method 1, setting my floats to 9/16 and listening for highest rev possible while adjust fuel mixture nob (source: Ztherpy video). Method 2, disabling one carbs by pushing up the piston and listen to the engine then adjusting fuel nob and repeat(source: Other tunners). I now adjust my carbs by pulling my dome, spring, and piston off the carb and looking down to see where my fuel level is at. It should be approximately 2mm lower then the jet nozzle on both. This method has worked well for me. You may need to re-tune your carbs first instead of buying stuff you may not need.

Good Luck,

[Guest Zpeed]

on a stock cam u won't see power above 5500 i think it is... but it sounds cool...

 

ur engine should not let u go past 6500 or whereever the redline is, i forgot... if it doesn't then something is wrong.. but u should feel a power loss with the stock cam after 5500rpm.. maybe u won't feel it, but if ur racing and the car next to u is gaining on u at that time, thats when u should change.. thats how i learnt.. i also heard that reving past the power line, wears ur engine faster

[Lockjaw]

Well I have come up with a couple more options. First, make sure you have the right distributor support. I have a 260 with a zx engine, and you have to use the distributor support from the 260 unless you use the zx distributor.

 

My timing was way off. Also, your balancer timing mark may not be in the right place. Mine is not. Evidently it s common for those to move after time.

 

I would also get rid of the mechanical pump. The are just not up to feeding a bigger engine. I have some sort of loud electric on mine, likely a holley, and a regulator, and I picked up a 240 fuel rail and plumbed the return line, and it keeps my fuel filter full, there is not any air in there. The fuel stays cooler too.

 

Get your SU's set and then see what happens. Could be time for a cap and rotor to.

[Guest Anonymous]

Ummm this might sound stupid but what would happen if my return line for the fuel was not hooked up? I looked all over for it and can't find it. What does it hook up to?

 

Thanks

Lance

[Z-Gad]

My daily driver flat top L28 w/ Shaved N42 and SU's has no problem pulling into the red. I am using a stock E31 head cam and only the stock mechanical fuel pump. I am leaning more toward your ignition rather than the fuel problem. Getting rid of the points and going w/ an electronic ignition (79-81 ZX distributor for example) has worked wonders for my upper RPM's for spark (no point bounce), but first check your timing marks. Get the #1 to TDC, pull the valve cover and check the alignment markings. Also check that the rotor is just hitting the #1 cylinder plug on the cap. It sounds like the timing may be retarded.

my .02

[Guest Anonymous]

Ive been trying everything and still can't find whats wrong. Im leaning toward ignition right now. My spark is red, my shop teacher told me that it should be blue. What causes a red spark besides a bad coil.

 

Thanks

Lance

[yo2001]

Originally posted by Lance Wert:

Ive been trying everything and still can't find whats wrong. Im leaning toward ignition right now. My spark is red, my shop teacher told me that it should be blue. What causes a red spark besides a bad coil.

 

Thanks

Lance

bad wires may be? Check the ohm of the wires. Check the point too

[awd92gsx]

Before diagnosing this, I need to know...what exactly happens that it won't let you go above a certain rpm? Does it start to cut out and miss on you? or does it just not rev that high but still run smoothly?

[Guest Anonymous]

Ok in neutral I can rev it all the way to about 5250 rpm fine. It's load as hell but it runs smoothly. If im in a gear gettin on it at about 4500rpms it starts cutting out really bad, it has no power, its not backfiring it just sounds like theres no fuel getting there. I checked all my plugs which only have about 200 miles on them and they are completely black with carbon. Im about to go get a 4 bbl intake manifold and throw the S.U.'s in the trash.

[Kevin Shasteen]

My first Z was a 73 w/the dual carbs. It had no problem reaching the red on the tach; it got there rather quickly too I might add.

 

Bad spark can be one thing or it could be a combination of problems.

 

If your spark plugs & wires are new then you should check out your points for proper adjustments (if you're still running a points dist). Your coil could be bad; most Aisian coils rarely go bad...but it is possible/get your ohm meter out & check your coil for tolerance-whatever the repair manual says it should be is what it should be.

 

Also check both fuel filters; dont forget you have a second fuel filter located almost directly behind the passenger rear tire back at the fuel tank.

 

I would say since it doesnt backfire that it isnt a spark problem and that it would be fuel related; but sinc you did say your spark is weak-then it could be a combination.

 

Sounds like you have enough fuel and spark for your engine to run & run appropriately as a daily driver; but, you are not getting enough fuel & spark to "Race" your car at higher rpm's.

 

Keep us advised-sounds like a mystery indeed.

 

Kevin,

(Yea,Still an Inliner)

[awd92gsx]

Lance,

 

Have you tried new wires? Sometimes wires can ohm out good but still be bad (they tend to break down under load).

 

If you haven't tried new wires go get yourself a cheap set of wires and start there.

 

Sometimes you can use electrical tape and insulate (wrap) the spark plug boot to help with diagnosis.

[awd92gsx]

Any luck getting it figured out?

[Guest Anonymous]

Well not really i just moved to college and havent much time to figure it out. I really think that it is the spark plug wires because that is like the only thing that i have'nt changed on my wholoe car. Im also in the process of patining to so ill get there. I would just like to thank all of you for all your help becuase i dont have internet acess down here. So thanks and ill talk to you guys later.

 

Lance