Power loss problems

Answer to most of the common technical questions

Moderators: BRONZEE, Z Club

Post Reply
RPV1
Posts: 53
Location: Wellington

Power loss problems

Post by RPV1 » Sun Aug 22, 2010 8:07 pm

My L28 powered 260Z (see http://www.zclub.org.nz/viewtopic.php?t=922&test=test ) isn't long out of the rust spa. It hasn't been used a lot in the last 18 months and gets a run about once a month at the moment.

It has three 40mm Weber DCOEs and they seem set up very nicely - good torque low down and spins out nicely at the top end. Until recently.

First symptom was a loss of torque then a 'running-on-five-then-four' feeling on a long, sweeping uphill left-hand bend north of Upper Hutt. Slowing down, stopping and idling for a while sorted it and the rest of the trip would be fine. Float chamber levels need looking at I thought at the time. A friend whose opinion I value suggested tank scavenging and more general fuel feed problems. The problem however, only appeared on that VERY corner (coincidentally the Northeast end of the little-known 'Hutt Triangle').

Last weekend it occured on a long straight flat! The tank is however, only just above 'E'.

Has anyone come across this before? In the dim recesses I recall a similar 'power starving' event in my old Hitachi/SU 240Z. Half an hours idling fixed it then and I nver gave it another thought. Is the answer perhaps:

a. Don't be a dick! give it a full tank of gas and a tuneup!
b. You don't deserve a car like this! It has to be ridden hard and put away wet! Regularly!
c. Webers are Divas! If you haven't spent thousands on her recently you'll never get her to perform!
d. Common problem. The simple fix is....

Chaps? (please be gentle)

R

User avatar
us2
Z Club Member
Posts: 1876
Location: Weymouth by the sea.Auckland.Don't dream it ,be there

Post by us2 » Sun Aug 22, 2010 9:56 pm

Sitting awhile? Dirty fuel springs to mind. Rusty tank? :?

(A) sounds about right Ross.
!972 240z
Retirement is great. Growing old sucks.

User avatar
asyado
Posts: 275
Location: Carterton, Wairarapa

Post by asyado » Sun Aug 22, 2010 10:19 pm

What type of fuel pump are you running, mechanical or electrical?. I'm sure I've read a thread somewhere that the guys with turbo's use a fuel scavenge tank so there is never a chance of running out of fuel when the car/motor is under certain G-forces. I can't say I ever had a problem with my flat top hitachi's and I used to run on near empty all the time. My 260z would get thrashed on the Rimutaka's, she would howl like a cat with a banshee after it, lol. My first thought would be to install a fuel pressure gauge in the infeed line to carbs to see whether it is indeed starving of gas, although it would be hard to check while moving. A more remote one, there is water in the fuel tank and being heavier than fuel, is only sometimes getting picked up from the tank, more so on empty and will only show when the car is going up or down hill or under G-forces, it would explain coughing and feeling like not on all cylinders. Water not gone thro carbs, thro motor will sit in the bottom of carb fuel bowls. I had a mate who was a fuelquip tech, he got av gas from Palmy airport once to run his car. We headed away for a ski trip and I ended having to tow him up each bloody steep hill, we pulled into Mangaweka and looking at carb site glass found bowl 2/3's full of water, we drained all of fuel tank, lines and carb bowl. It would run perfectly on flat straights because fuel was sitting horizontal in bowl, steep hill it was a 50/50 mix of fuel and water. Hope you find the cure soon, happy zedding. Nigel
Insanity is only one gear change away!!!

User avatar
old_datto_fan
Z Club Member
Posts: 940
Location: Kapiti

Post by old_datto_fan » Sun Aug 22, 2010 11:05 pm

Definitely B!!!!!

I doubt it is A - I have found I only get scavenge problems if I have 1/3 tank or less and giving it heaps around corners at Manfeild. Although if it is the corner I think you mean then it is quite long and steep and being that you are going uphill, don't forget that the front of the car will be above the petrol tank and of course you are going to have trouble getting petrol up there! I think you should go up there in reverse and then you will be fine!

Actually, I am jealous. If I left Upper Hutt with any less than half a tank of gas I would be wondering if I was going to make Masterton to get another dose of 98 especially if I had a clear run over the hill.

If it is doing it on the flat then the dirty fuel or water in the fuel ideas sound likely to my limited mechanical knowledge!

And I take it then that just in case it happens again that you won't be driving over the Rimutakas to meet us at Haywards and then cruise back again when you join us on our cruise next month.

RPV1
Posts: 53
Location: Wellington

Post by RPV1 » Mon Aug 23, 2010 8:37 pm

That's amazing analysis! Thanks guys!

Nigel, I'm leaning to your dirty/wet fuel theory. The pumping mechanism is standard as far I know (electric at tank and mechanical up front?). The mechanical pump was replaced in ChCh by my coachbuilder (who took it for a huge wrack on the Canty plains to get it moving again)

Image

So, it runs anyway. In the photo above there's a poor view of the fuel return line arrangment - things that are unfamiliar to me are the cannister-type filter (just to the right of the oil cap) and a return line looping above it with a pressure limiter (I think) on an aluminium flange extending from the RH strut tower. Short of tearing it to pieces, I have no idea what the setup was meant to achieve - except that on a good day it goes like stink!

Mike I may not be meeting you at Haywards when there's such good coffee & food at Cornucopia Cafe in Featherston - but we WILL meet you there and join the cruise. I may have rescue vehicles in tow and I'm hanging out to see Nigel's 260Z in Carterton!!

Thanks again chaps. I may have to drain the tank

User avatar
asyado
Posts: 275
Location: Carterton, Wairarapa

Post by asyado » Mon Aug 23, 2010 10:21 pm

An easy way to check for water in petrol tank is to remove drain plug at bottom of tank. If water is present then it will drain out first then petrol after it. If you run on empty all the time then draining won't be a problem, lol. I would have gone with option E all of the above pmsl, just kidding. Nigel P.S. If you have an electrical fuel pump at the tank then you wouldn't have the mechanical pump installed on the motor as well, there would be a blanking plate where the pump used to be and the electrical pump would be pumping straight to the carbs with a fuel filter and in your case pressure limiter in between. When the carbs don't need refilling with fuel(fuel floats have shut off fuel infeeds to carb bowls) then there should be a return line back to the tank as a bypass. When you come over I'll have a closer look at those lines, abit hard to see from that angle.
Insanity is only one gear change away!!!

Post Reply