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rothon
09-02-2004, 10:41 PM
I have a 280zx with a 6 -1 header fitted 240z carbs.

Problem being the car can't drive, just fitted the carbs but if you keep the throttle about 4000 it starts to loose power, fuel pressure is good. Looks like itís the jetting at fault. does anyone know how to come around this problem or do you think the carbs are faulty. :confused:


any suggestions welcome. or do you have the bits I need to fix this problem.

Tony 260Z
10-02-2004, 02:53 AM
That's pretty much the same spec as my 260 - P90, 240 carbs, nismo 6-2-1. Could be the float setting not letting the bowls fill up fast enough, or carb inlet valve sticking. May even be the little filter in the top of the float bowl banjo getting cruddy and not flowing enough. My carb inlet valves used to stick and sometimes I had to get out of the car and tap the top of the bowl with a screwdriver handle to unstick them. Two or three light taps and hey presto she ran again.

Another problem I had was with the pipes that go from the base of the float-bowl to the jet. When they get old they deteriorate inside and a) won't flow properly, and b) lose crud into the jet which blocks it!

Have the carbs been refurbished/rebuilt? Do you know how they were set up before you put them on your car? Is this a problem only at 4000 (ie: it clears up above that, which would baffle me), or is this a problem that appears at 4000 and gets worse until the car tries to stall, or does it appear at 4000 and then clear as the revs drop (which might tie in with the bowls not refilling properly).

I don't know much about swapping 240 carbs onto a ZX engine that had FI before the carbs. Is there a tie-in between the injection and the ignition, that a lack of feedback from the FI sensors might mess-up the ignition? It's time consuming, but when I have a pain-in-the-ass fault I usually work on the old elimination method to pinpoint the problem!

Good luck!

TL

The Z Farm
10-02-2004, 09:39 AM
Think that Tony 260Z has got the likely problem identified - the inlet valve needles are sticking in the closed position, and/or some crud is in the bottom of the float bowl, preventing full fuel flow getting in from the pump.
Remove each float bowl carefully ( undoing the 12 mm head half nut securing the spindle which goes right through the main carb body ), and slide the float bowl out. Undo the top, taking care not to break the gasket as you do so, and clean out the bowl with thinners and blow through with an air line.
Also, remove the inlet valve and clean with a rag with some thinners - the cone-shaped valve becomes coated with a hard varnish from all the old fuel over the years, and thus sticks when closed.
Check the opening/closing spring mechanism works as per your Haynes Manual, and carefully reassemble everything.
Also, another thought, have you changed your fuel pump over to the 240Z/260Z mechanical system or retained the 280ZX F/Injection pump ? Hope not, otherwise you'll be feeding 30 psi into the carbs ! Also, have you fitted a fuel return system as per the 240Z set-up ? The 240Z carbs need to be fed at about 2/3 psi - have you checked that the pump is doing that ?

Hope that one of these works for you.

Mr.F
10-02-2004, 12:53 PM
The inlet banjo bolts on the inlet side of the 240Z fuel bowl also have some fine gauze filters on them - worth checking to see if these are clogged - one of the few parts still available for 240Z carbs.

rothon
10-02-2004, 09:04 PM
Getting the little filters and needles from Mike (cheers) the car starts to die off when holding the revs at 4000, revs just drop and the car loses power. I have changed the pump to a small facet at the moment which supplies enough fuel, done a flo-test to make sure there was enough fuel supplied. Carbs had been aparently tuned before we bought them. Have used full system from the 240 including the fuel return pipes. Car can only do 30mph at the moment.

Will try cleaning out pipes and see how it goes with the new needles and filters. Thanks for all the ideas, will get to work now!!