kolts

I've just recently purchased a 75 260Z. The car is in prestine condition, and has only clocked 68,000km. The engine is basically stock, but the previous owner replaced the original carbs with a set of SU's and RamFlo air cleaners. The exhaust too has been replaced from the standard manifold backwards with a mandrel bent 2.5inch dynomax system. The car runs like a dream, and revs smoothly all the way to 8000rpm when asked to. The only glitch is the car has no bottom end torque, and will do nothing at all with less than 2000rpm. The engine also tends to spit a lot when cold, again when running under 2000rpm. I only use petrol with a 96 octane rating or higher. Can anyone advise me as to what I can do to make the engine more tractable at low revs. Also is the spitting a result of poor Australian petrol quality?

Kolts
Perth - Australia

L0ki

1. Extractors will give your car a bit more go over the original exhaust manifold in my opinion.

2. See if you can get a set of original 240Z SU's ... they seem to be the best of the SU's for Zs

3. Are you crazy or do you have a really big cam in the car ? 8000RPM !?!?!? You will bend valves etc revving your engine that hard take not that the Zed Tacho is not accurate at those kind of revs. I have bent valves in an L26 and L28 from over revving them. If your car made a poping bang sound at 8000rpm that is the valve spring hats poping off the rocker and the valve hitting the piston top!

4. Sounds like the car does have a cam in it. I have a slightly mild cam that lets my motor pull all the way to the 6500rpm yellow line and doesnt really make much until 3000rpm... I dont rev it to 6500 very often. Does your car still even pull at 8000rpm ?

5. How many litre was your last engine ? Its not a V8 ... L26 is a pretty small bore engine they have to be revved a bit to make their power. The only time i drive under 2000rpm is doing 60km/h, and if i want to over take someone drop it back to 4th. The car is designed to idle around 1000rpm so you want your car to make heaps of power from idle ?

6. I don't think in 1975 Datsun ever thought of running the zed on Optimax so im sure the fuel isnt a problem. It supposed to run on 85ron Leaded. Optimax and BP Ultimate are the only fuels i would run in a Zed motor in australia ... LRP is EVIL !

7. When you start your car do you use a choke ? Also you have to let the car warm up a bit ... it helps a lot

8. Ways to get more torque:
Change the points if needed
240Z Su's (top end as well)
Electronic Dizzy
Lighten Flywheel
Extractors (for more top end)

L0ki

Edit

4. Your car may have a cam in it.

I cant edit my posts

AlansZ

All (most?) L series engines are dogs when they are cold- I can tell you mine has bout 5000 miles on it since the last rebuild and when it is cold it coughs and splutters, misses and backfires, but when it is warm it runs like a dream, you just have to get used to it. Jake is right about the torque of the L26- both the L24 and L26 revved higher, but the L28 has more torque, so you could swap that in if you want, it's pretty easy. And I wouldn't rev it that high as well- I rev mine to 6500 when gunning it, and I don't go any higher than that

Alan, Australia

AlansZ

I can't edit either- what's up with that? I've got 'cookies' enabled in the netscape, but it still won't let me

Alan, Australia

AlansZ

I forgot to say my engine is an L28, so you should be able to rev a bit higher than me

Alan, Australia

kolts

thanks for all the help guys. I shall keep what Loki said in mind, and refrain form revving it too hard. However, the engine pulls beautifully all the way up, with a marked increase in acceleration from about 4,500rpm onwards. I choke the engine when starting it up, and then let it sit a idle for couple of minutes to get the oil moving and the engine warmed up.

cheers for the tips

kolts

Zpeed

i have 240z SU's on the L26and when its cold its perfect no problem at all... i worked out the choke to work perfect... alan make sure your choke is working as mine used to cough sputerr and all that before i got the choke working... make sure it pulls the jets down to let more fuel in, when starting cold, it should sputter for around 0.5secs then be perfect, this is only on morning starts 10degrees or less, it should be i click over 1 second then it cranks beautifully. or else something is worn or wearing out...

Zeds don't have power below 2200 i think it is around... well thats when i feel the power come in on my stock cam L26...

over 3500rpm.. all i feel is back presure.. thats with 240z SU's (k&Ns), extractors 2 1/4 exhaust and electronic dizzy, thats all i got and its killer..

<font color=blue>76 260z</font color=blue>
The NiteRider

AlansZ

How do I check that my choke is working properly? How long should I leave the choke on for as well?

Alan, Australia

Zpeed

to check it if works.... put the choke in off position (for me its most forward (closer to radio) then look at the carbs, the 2 choke levers should be on the lowest position, pull the choke cable towards the hatch, full extention, the levers should now be all the way up, thats to check if the levers and cables are working...

remove the carb bowl and piston with needle.. see where the position of the jet (i think thats what it is called) should be around 1-2mm down from the flat area, that is with the choke off, when it is on, the jet should go alot more down, so it puts in more fuel

i usually leave it on untill i see my temperature guage move to 1/4 -1/2 of the guage (usually sits at half on temp guage when at proper temperature)

also when the car is running, on startup when you pull the choke the revs should rise to aound 1300-1500rpm and if that doesn't happen that means something is stuffed... this is on 240z SU's when i got the carbs the choke wasnt working so it could be just nor connected properly.. .also check that the cables are connected at the right distance... usually takes a bit of fiddling around but its worth it..


<font color=blue>76 260z</font color=blue>
The NiteRider

L0ki

i wouldnt leave the choke on that long because it uses too much petrol

and my revs dont increase by that much either

Zpeed

i set my choke to go to 1300rpm most of the time anyway, higher on colder start ups... 1300 is where most new cars sit so i put it there...

i feel its alot easier to drive no hickups if i leave the choke on for a short time, doesn't use that much petrol... i do turn it off quickly..

<font color=blue>76 260z</font color=blue>
The NiteRider

kolts

I find that if I start my car on a full choke, leave it for about 30 secs, and then gradually turn the choke off and use the gas pedal to hold the revs at about 1500rpm for just a little while gets the engine up to temp. Also, I was told by the guy I bought my car from to rum the choke for as short a period as possible, as the rich petrol mixture would bugger my plugs? To what extent is this an issue?

L0ki

dont go for a drive and forget the choke's on extent

AlansZ

I leave it on for about 300 metres, then just use the accelerator so it does stall while stopped

Alan, Australia

Zpeed

yer.... i do the same.. but when i stop at a light, i put it on just a tad so it stays above 750rpm..

<font color=blue>76 260z</font color=blue>
The NiteRider