Running problem advice needed

vpulsar

Well-Known Forum User
Hi guys, I'm getting a bit of an intermittent running problem with my car and I can't quite put my finger on it :confused:.

It appears to be running on less than 6 cylinders at low revs maybe even higher up the rev range but that may be being masked by the exhaust noise, It seems to come and go, Last night it was fine today it sounds like a bag of bolts.

I was thinking it must be a problem with carbaration because everything else is new, I'm running an MSD type A ignition box with the big racing MSD coil as well as a rebuilt 2.8 electronic dizzy with new 8mm leads and new plugs.

As well as running rough it doesn't pick up speed quite as fast as it should, I've removed one of the carbs recently to adjust the float level, Would an incorrect float level cause problems ?, How about an air leak between the carb and manifold ?.

Its been a long while since I've worked on an old car like this so any advice regarding this problem would be greatfully recieved, I'm tempted just to chuck my new webers on and see what happens :devil:.



Rob
 

Nigel Brook

Well-Known Forum User
The ignition module on the side of the dizzy is known to give problems as you describe. I assume as it has been rebuilt there is a good clean earth between the module and the dizzy body. Also condensers can give similar problems as can the wrong coil. If you have a 280zx coil I'd try that on its own as well.
 

Rob Gaskin

Treasurer
Staff member
Site Administrator
All you can do with the ignition is to check all the Low and High Tension wires/leads for bad connections, poor insulation etc. And rev counter wiring (is that swinging about all over the place or steady?).

I've been having a similar problem - started the morning we left for Le Mans. But the car was ok when hot so I assumed it was carburation. It's not it's ignition.

I have an OMEX Rev Limiter and if I disconnected that it runs fine. Been in contact with OMEX and they say they usually work fine or fail completely. They suggested interference from HT leads. My Rev Counter was swinging around a lot as the engine misfired (less of a misfire actually more a on/off situation).

My HT insulation was poor at the coil - I got a good 'belt' when messing with Low Tension wiring whilst engine running. So I fixed the insulation (rubber cover) but also discconnected the Rev Limiter before Mallory Park last week - it ran fine. I now need to put the Rev Limiter back in circuit and check again.

Just a thought - do you have oil in your carb dashpots?
 

vpulsar

Well-Known Forum User
Thanks Rob I'll check over the wiring, I did top up the dash pots but I did take one of the carbs off the other day and can't remember if I lost any of the oil out of it. I check in a minute to see.

The coil should work fine as it's the one recommended by MSD to work with the ignition box I have on the car, My rev counter is stable no jumping about all over the place.

Thanks everybody.



Rob
 

vpulsar

Well-Known Forum User
Things SHOULD always work fine Rob but never assume anything.

Well seeing as it's not showing any symptoms of not working fine mate, I'll feel free to assume away if that's OK with you :rolleyes:.

I'm 99.9% sure it's a problem with one or more of these old 240 carbs so I'll have to take a closer look at them, It's more than likely something to do with the one I took off the other day seeing as I was just guessing about what was needed to fix the problem I was having with it :rofl::lol:.




Rob
 

rallymanDP

Well-Known Forum User
Have you replaced the needles in the Carbs - if they are the original ones, they could be slightly bent and/or worn at the point where they meet the venturi.
New ones are available through MJP at a very reasonable price, but go for the SM spec type for improved performance.
Have the Carbs been cleaned and properly balanced ?
 

vpulsar

Well-Known Forum User
Have you replaced the needles in the Carbs - if they are the original ones, they could be slightly bent and/or worn at the point where they meet the venturi.
New ones are available through MJP at a very reasonable price, but go for the SM spec type for improved performance.
Have the Carbs been cleaned and properly balanced ?

I pulled the old needles out last week and replaced them with as you say some very reasonably priced SM needled from Mike ;), The carbs where set up by a so called local expert in all things old and decrepit, But he failed to notice just how far out the float was in one of them :confused:, He told me he had to strip them down but I dont think they did anything other than spray some carb cleaner through them :(.

I'm going to rebuild the buggers I jut ordered two kits from mike, Thanks for answering the phone so late mate :thumbs:.



Rob
 

vpulsar

Well-Known Forum User
All sorted now thanks to some new carb filters sent speedily by super Mike lol, I spent an hour of two rebuilding both carbs this morning and found the small gauze filters to be completely blocked in the back carb and not a lot better in the front, Gave everything a good clean fitted new filters/gaskets and she now runs spot on.

At least I can sell the 240 carbs on in the knowledge everything works fine once I've fitted the webers soon hopefully.

Just to add to this I'd already been charged good money from a local tuner to have the carbs set up and was told he'd had to clean the carbs out to get it to run properly, Which just goes to show us all what a load of lying bastards their is out there these days, And just makes me wish I'd done it myself in the first place.


Rob
 
Last edited by a moderator:
Top