Cold Start Problem on SU's

M

moonraker_tom

Well-Known Forum User
Hi there

I have fitted a pair of 2" SU's (HS Type, from a 4.2 Jaguar) to my 260Z, and finding when starting from cold, the engine turns over for about 20seconds and then ‘catches’, with the occasional backfire from the rear carb.
When the engine is warm, starting is on the button.

The vacuum pipe runs to the rear carb (beofre the butterfly), and appears to be blocked, before I remove the carbs, should this be clear? From previous experience this should be, but the carbs were fitted to another 260Z, and ran perfectly?

There is fuel in the filter & no evaporation from float chamber (checked when engine is cold). The carbs are balanced (by ear).

Apparently, the carbs have racing needles, not sure if this makes a difference.

Has anybody got some advise as to what else I can check/do?

So far I have;
Rebuilt the carbs, put the needles in the float chamber the correct way up as there was flooding before. (Starting the car before the rebuild was worse).
Timing – this has been professionally checked
Points – checked
Points, Dizzy, plugs etc replaced about 2,000 miles ago

Thankyou
Tom
:confused:
 
Are both carbs choked? Only one of mine is and I have the same symptoms.

I must sort that out. :rolleyes:
 
Take the dashpots off, remove the piston/damper assembly and pull on the choke lever then check that the jet assembly is actually moving down far enough below the bridge of the carb to give a richer mixture on cold start.

I ran 2" SU's on my 240 and cold starting was instant, I do have an electric puel pump fitted though, are you still running the mechanical one?
 
zbloke said:
I ran 2" SU's on my 240 and cold starting was instant, I do have an electric fuel pump fitted though, are you still running the mechanical one?
Click to expand...

I have an electric pump too and it helps, especially if the engine hasn't been started for a few weeks. I can hear it filling the float chambers before I start 'cranking'. Don't 260s have an electric pump as well as a mechanical one - not sure how this arrangement works.

After a long break my car doesn't start on all cylinders straight away, but if it's only left a couple of days it's fine. Hot starting no problem.

Vaccum pipe - as long as it's connected to the dizzy it wont be affecting starting whether is blocked or not. I don't have a pipe on my car.
 
Rob Gaskin said:
Don't 260s have an electric pump as well as a mechanical one - not sure how this arrangement works.
Click to expand...

No, but my late one had wires at the back that were live when the ignition is switched on, but don't know if early ones had this.
It might have appeared when they made the 280z.
 
Apologies for not replying earlier, been in the shed re-arranging bench/tools etc, as Noah was visiting today. Is anybody else feed up with this rain!

Thankyou, I will check the dashpots and needle movement (weather permitting) tomorrow.

My 260Z appears only to have the mechanical fuel pump. The fuel level in the filter looks good, approx third > half full whether the engine is running, or the car has been stood for 3 or 4 days. New pump and filter were fitted about 4,000 miles ago, and had no problems on the old carbs.
 
Quote:
Originally Posted by Rob Gaskin View Post
Don't 260s have an electric pump as well as a mechanical one - not sure how this arrangement works.
No, but my late one had wires at the back that were live when the ignition is switched on, but don't know if early ones had this.
It might have appeared when they made the 280z.
Click to expand...

It depends where the 260z went market wise in the world whether an electric pump is used. You will find that in Australia and I think the US too (or maybe just which State) the two pumps are used. I think this is to overcome the hotter climates where the flat top carbs are used, where fuel pressure is critical to them to work well. Wiring already on the car, definately on a late 260z.

Wiring for an electrical fuel pump is there on say, a 240z for the North American market. Whether the wiring was fixed to a rear mounted fuel pump again depends on which country/market .. though have not got to the bottom of who got what. Maybe wiring there on UK spec 240z? probably...as I think the wiring is also there on a Z432 as well... and the 280z was definately a electric pump.....on all S30's then?

Nissan produced a lovely fuel pump bracket for the rear mounted pump, which the modern Facet pump, a lot of people are using, fits onto lovely and just a bolt on (e.g. threaded holes in chassis).
 
Last edited by a moderator:
Ian mis right about this, i dunno about specefic UK cars, but on all US cars are the wires there, they come out along with the gas tank sending unit and are wrapped with blue tape, the wiring is also there at the fuse box, i believe the 260Z have a relay put in between the fuse and pump, regarding the pump, i have read that Facet have been taken over the company that made the Z pumps and it should be the exact same.

Chris
 
Hi there,

OK, checked the dashpots and the choke cable moving the jets, and hey the rear carb jet does not move down.
Will take the carbs off and find what screw/fixing is missing.

Tom
 
OK, choke cables re-aligned (rear choke cable was not activating the choke mechanism on the carb). The engine now fires straight away at cold.

However, just one backfire out of the rear carb this time.

Now off to re-balance and set the fuel mixture.

PS - For those with SU carbs found an excellent site that allows you download (in pdf) the SU specs in detail, under the 'Technical' section

http://www.sucarb.co.uk/


THANKYOU to all help.

Another Z on the road (pending MoT!)

 
Hi there mate,

Are you running the 2" SU's on the 2.6 engine?

Do you notice any significant improvement over, say, 1 3/4" 240z SU's? I'd be interested to know as I've read and heard different things. Are the 2" SU's too much for a 2.6 as they were for Jags with bigger engines?

Cheers all
 
Hi there,
Apologies for not responding earlier, been on holiday.

The 2" carbs where fitted to another 260Z for tracking, and he had no problems.
Certainly, I have had no problems (with the exception of this thread topic).
My only remaining problem is to fit the correct needle size. I did speak to Burlen (SU carb dealer in Salisbury - really recommend these guys for info/advise/parts) and they said that I would have to get the correct setup determined on a rolling road, but they did not recommend fitting the original needles for a 4.2litre Jaguar set up.

As far as performance goes, I feel the SU's are an improvement on the original's, acceleration (this maybe in my mind, as I always enjoying making the fuel needle drop fast) the start up, running, setup and spares availability.

My opinion, for what its worth, SU carbs are found on Merlin (Spitfire), Black Shadows, through to different sized engines from BL (Mini, Healey, MG etc) so they should not be a problem with the carb size versus the engine size, the key is the needle size.

If you are in the Southampton area, more than happy to meet up and discuss further.

Hope this helps
 
Many thanks for the reply mate...interesting...

I was going to get rid of my 2.6 in favour of an N42 2.8 but as the engine had under 25k on it from new, I thought it would be better to keep hold of it and eventually (and reluctantly) let my N42 2.8 Z go.

I've been considering various options and I think that the 2" SU on the 2.6 road will be the one to go down. Are your running any other mods?

I'm in the North Birmingham area so miles away! If you are ever passing Junction 9 of the M6, feel free to drop by for a brew!
 
Hi there,
The car is not running any other mods, the car is standard except for the 2" SU's, the stereo! The air filters are K&N with trumpets.

Thanks for the offer of a brew, it will have to be without the other half, she can talk cars but after 30 mins gets bored! and then wants to go shopping!

Good luck
 
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