Loss of power after high speed run

[Murph]

This afternoon I took the zed for a bit of a blat down a nice straight empty road in the middle of nowhere. Went quite nicely up through 2nd gear, then 3rd, 4th, then just after hitting 5th at about 160km/h I see car in the distance, so hard on the brakes back down to 80km/h or so.

Now when I got back on the accelerator the engine was loosing power, sort of pulsing on-off-on-off a few times a second much like when it's not getting fuel with vapour lock problems. Over the next few k's it seemed to go away, till I got home and found it wouldn't idle anymore. It'd drop to about 500rpm and splutter away.

While driving it still feels ok, but sounds pretty sick/lumpy at idle. It isn't blowing any smoke or anything like that. It's lowish on fuel at the moment, but probably still 15 or so liters in the tank. It's definantly still firing all it's cylinders.

Any ideas what could be causing this? It's been about 3 months since it was last tuned (carbs were rekitted then) and has been regularly driven in that time.

Btw, it's a 260Z 2 seater, basically a stock L26, with 240Z carbs and and electric fuel pump that bypasses the mechanical pump.

Any help is greatly appreciated,

Justin

[McZ]

Do you think that maybe some trash or gunk in the bottom of the tank might have moved and blocking the fuel pick-up inthe tank?

[Murph]

It's quite possible I suppose. Tomorrow when I get a chance I'll get under there and check the fuel filter for gunk (just before the elec pump).

[Murph]

Something of interest I noticed this afternoon while having a play with it when I got home, was that when you pushed the piston up in one carb, revs would increase, when you pushed it up in the other they would decrease. This would suggest a tuning problem wouldn't it? Sorry for the complete noob question but I was brought up on EFI, still have a lot to learn about carbs!

[ZmeFly]

Thats another thought in itself. You may just have a sticking piston in the carb, causing them to become unbalanced.

Clean your carbs up too while your at it.

[Murph]

Both pistons seemed to move quite freely.....and they should considering they were both completely cleaned out three months ago.

[Murph]

ARrrrrrhhhhhHHHH!!!!

It's all getting more confusing!

Today I made two new gaskets for the balance tube between the inlet manifolds as one was leaking, and the other fell appart while handling it. Now when I've fired it up, it's blowing blue smoke again, a problem it's had on two occasions a over the past few weeks. Previously I attributed it to a stuck PCV, however I have verified that it is working fine atm.

When pushing the piston lifting pins, revs will increase a bit then drop back down to about the same revs but running very roughly. It does this for both carbs.

Using the hose in ear trick I had a listen to the air flow into the carbs and while the overall volume sounds about the same, the front carb has a lumpy pulsing sound to it, where as the flow in the rear sounds totally smooth.

Any ideas what is going on? I'm somewhat stumped now.

About a week ago a compression test came up with 150, 135, 110, 130, 120, 120. Doing a wet test they came up by about 10psi, so I can be pretty sure the valve guides are somewhat worn. I might try another compression test later....see what it gets.

[datto_240z]

Im only 15 so i dont know too much. Sounds like fuel. Mayme somewhere along the line its been kinked or dinted. If not it sound as if its in the carbs. Im pretty sure that revvs arent ment to disvrease on one carb and not the other. Maybe one of the filters in the carbs is blocked up, or a bit of crap has gotten thru the system... I donno.:stupid: I know a wee bit about m/bike carbs(watched my dad) but not much about car carbs...

Cheer'z'

[Murph]

A little bit more info. Just took it for a drive and the smoke cleared up after about 30 seconds or so. Still a little puff on gear changes as per usual.

At about 700rpm the airflow in both the carbs sound fairly equal, however if I crank the fast idle up a bit, say 1200-1500rpm, it sounds like there's more air going into the front carb. Can't be sure though.

It did drive quite nicely though.

[HKSZ]

Might be time to check valve clearances, I find when you give a motor a caning thats not used to it you end up with alot of valve train problems

steve

[Murph]

I did 7 runs at the drags a week ago, so it should be used to a caning.

Wasn't reving it past 5k when this problem started either? I will look into the valve clearances though, no hard.

[Alfadog]

Your car is 30 years old.

Did you check your fuel lines? Very common problem, easily flushed...

Sounds more like tired carbs though. If a 50 year old is made to run as fast as a 20 year old, he'll probably need medical attention afterwards. You know what I mean?