Rough running

[maton_acoustic]

Hi, I'm having issues with my 1978 Datsun 260z. It's been sitting for 5 years during welding repairs and what not. Managed to get it to pass an MOT today but it's back firing and stuttering and generally doesn't pull well at all. The carbs are hs4's from a Volvo which the po installed. I've installed an xr700 electronic ignition kit and a ps90 coil. New plugs and leads. New fuel line and filters. Changed the su needles and jets and float valves and springs. The float levels aren't adjustable. Fuel bowls have been 3/4 full when I've checked them. I've set the timing to 10btdc with vacuum advance connected and it does advance when I blip the throttle. Checked for vacuum leaks and compression is good. The dash pots do seem to leak oil quickly though.

When I adjust the car by the colour of the fuel mixture using a colourtune the mixture nuts are around 3 flats out and if I lift the carb lifting pins it sounds like it wants to stall and rpm decreases. I've tried the car at 12 flats out and it does seem to run better and smell less, engine rpm stays the same when I lift piston. I can get it to idle ok But still similar when driving. All and all quite contradicting to me.

Im doubting wether these carbs are suitable for the vehicle at all. I'm trying to find a specialist at the moment who could take a look but there's a lack of them here.

Any ideas appreciated

 

[Tony 260Z]

If memory serves then HS4 makes them one-inch carbs which is pretty small - more suited to a mini or an MGB. I think the Hitachi's on a 240 are equivalent to HS6 which is an inch and a half. It could be a lot of things (I hope more knowledgeable members will chip in at this point) but I'd probably start by sourcing a set of 240 carbs and refurbing them.

 

[maton_acoustic]

My mistake, they are in fact hs6

 

[chrisvega]

If memory serves then HS4 makes them one-inch carbs which is pretty small - more suited to a mini or an MGB. I think the Hitachi's on a 240 are equivalent to HS6 which is an inch and a half. It could be a lot of things (I hope more knowledgeable members will chip in at this point) but I'd probably start by sourcing a set of 240 carbs and refurbing them.

HS6 and equivalent Hitachi SU fitted to Z are an inch and three quarters

 

[STEVE BURNS]

Dave
see you are based in Cardiff
Dont know if they can help you but try and PM
s2k_adz and big rex2
as they might be able to help as in your locality and you might be able to have your own little meetup and chat

 

[maton_acoustic]

the bore size is the same but the float level is fixed and it has an offset needle that doesn't need to be centered. BBR .100in needles

 

[maton_acoustic]

Ok, thanks Steve

 

[Tony 260Z]

HS6 and equivalent Hitachi SU fitted to Z are an inch and three quarters

Ahhhh yes.... sorry... it's 8ths of an inch plus one inch isn't it?!

My **** memory.

Good to read they're HS6's though - that's a good start!

 

[Farmer42]

Sounds like an ignition timing problem to me. It sounds like it is firing late. Might sound like a daft suggestion but have you checked the leads are in the right firing order and the rotor arm is in the right place at the right time?

I had a similar problem last year and it turned out to be dodgy condenser causing late timing & misfire under load. As you have changed to electronic that shouldn't be the case unless you still have it connected. Was this happening before you changed to electronic ignition? If not, you might want to check the installation or go back to mechanical points & condenser to get it running right before trying to reinstall.

Otherwise try disconnecting the vacuum pipe on the dizzy and advancing it.

 

[maton_acoustic]

Sounds like an ignition timing problem to me. It sounds like it is firing late. Might sound like a daft suggestion but have you checked the leads are in the right firing order and the rotor arm is in the right place at the right time?

I had a similar problem last year and it turned out to be dodgy condenser causing late timing & misfire under load. As you have changed to electronic that shouldn't be the case unless you still have it connected. Was this happening before you changed to electronic ignition? If not, you might want to check the installation or go back to mechanical points & condenser to get it running right before trying to reinstall.

Otherwise try disconnecting the vacuum pipe on the dizzy and advancing it.

Yes, that makes a lot of sense. I wasn't confident fitting the ignition system because the instructions didn't have a dizzy that looked like mine. Can you confirm the firing order and does anyone know of a good Xr700 installation guide so I can start again?

Thanks!

 

[toopy]

Not that it should cause the problems your having but, have you removed the ballast resistor?
Its only required for points distributors and helps to stop the points burning out too quickly by, i believe lowering the voltage once the engine is running.
Chop it out and connect the two wires/ends together.

 

[maton_acoustic]

Not that it should cause the problems your having but, have you removed the ballast resistor?
Its only required for points distributors and helps to stop the points burning out too quickly by, i believe lowering the voltage once the engine is running.
Chop it out and connect the two wires/ends together.

I didn't remove the ballast resistor because it said only remove for the xr3000?
Are you supposed to install a different cap and rotor when installing this ignition? I recall the rotor arm sitting a lot higher after the install.

 

[jonbills]

Cap and rotor shouldn't change, so shouldn't sit higher.check the rotor is properly located.
Are the carbs correctly balanced?

 

[jonbills]

Oh and how old is the fuel and how old the fuel filter?

 

[Farmer42]

Yes, that makes a lot of sense. I wasn't confident fitting the ignition system because the instructions didn't have a dizzy that looked like mine. Can you confirm the firing order and does anyone know of a good Xr700 installation guide so I can start again?

Thanks!

The firing order is 153624.

Haven't used an XR700 so can't help with any guides. I have an E12-80 electronic distributor from a 280ZX and it runs sweet. It certainly cured all the misfire & spitting problems that I had.

The other thing I found with the old mechanical dizzy is that springs for the centrifugal weights inside were very weak causing a huge advance when revved up under load. If you have used your old dizzy for the electronic conversion, it may be too worn hence the possible timing issues.

If it all fails, try to get hold of a 280ZX dizzy and ditch the other stuff.

 

[maton_acoustic]

Just a quick update. It was a timing issue after. The metal washer on the xr700 shutter had spun seperately to the plastic part somehow. I also noticed the shutter doesn't allow the rotor arm to seat properly so it was rubbing on the top of the dizzy cap.. I had to cut a couple of mm off the bottom of the rotor arm.
Thanks for the help.

 

[Farmer42]

Glad you managed to solve the problem.

Now time to get out and enjoy it whilst you still have the weather