I have just received a shiney new SU carb rebuild kit and am hoping over christmas to rebuild the carb on the elford. It currently feels like it is running a bit rich so most likely the needle/jet is a bit worn. Have no idea what sort of power the engine is putting out but being quite an old car I imagine a few of the pony\'s have escaped.
I know a few have rebuilt these carbs before. I imagine they run fairly rich as new to help cooling with the non intercooled setup. Any tips on set up or rebuilding tips?
ken have a read of this, http://www.rx7fb.com/viewtopic.php?f=4&t=86
Ian has rebuilt his SU.
Dibs
Have a look at Ians thread on the other forum.
I couldn\'t get Miss January tuned right both at tickover and full throttle. One or the other but not both. Decided it was just air leaking in so did not buy a new needle, just the Burlen rebuild kit that Ian recommends.
We did mine on the back of Ians write up, and it proved both easy and successfull. More power and about an extra 7 mpg!
If you get a new needle as well I would be interested to know which one you go for and how it turns out?
John
Hi Ken,
From years ago I found that three full turns out on the adjusting nut under the SU body was a good place to start tuning,
As you would know there are all different needles for these carbs but "if" you find you cant get it rich enough if you start by putting a very small flat on the side of the end of the needle but not right on the tip with a needle file you can start to richen it up this way accordingly,
Cheers for the responses, looking forward to getting it on the go. May even chuck it on a dyno to get it tuned correctly. Anyone ever measured CO or lambda?
Emailed SU and they suggested a BFS needle. I have yet to open it up to see if a BFS is currently fitted so will wait and see.
A 7mpg improvement sounds good, currently getting 16, 20 on a good run.
Quote from: kenwhiteside;802119A 7mpg improvement sounds good, currently getting 16, 20 on a good run.
Yep. we went from 17/18mpg to a normal 25mpg. Managed 28mpg at a speedo 80 on the motorway down to Oxford and back yesterday.
John
Well finally rebuilt the SU and found a few horrors including a machine screw replaced with a wood screw and also a missing seal. The carb also had a BFS needle fitted as standard and as recommended by SU.
Got some new plugs in as well so have to muck around with the mixture a bit to get it running better. The plan was to lean it off as much as possible then go back rich 1/4 of a turn or so.
It seems people are running really rich (like 11 to 1). Seems excessive to me. Does anyone have any actual data on how these carbs / engines should be set up (afr or co)??
Hi,
Well the SU is rebuilt and fitted but struggling to tune it. Spoke to Tim White at RX motors and he advised the following:
- Set to approx 7% CO at idle (massively high!)
- Take it for a drive for fine tuning, apparently what elfords would do was to run full load in 3rd gear, high rpm and lift off / de-clutch, if the engine fell to idle and stalled it needed to be more rich, if it did not stall you could lean off
The problem I am having is that I cannot get the CO to stay stable at idle. Once set I rev it up and it runs massively rich.
As per the above post I am running the BFS needle that was what was fitted before the rebuild (although a new needle). The replacement \'green\' spring was also slighlty longer than the one I had fitted. Apart from this the main jet, seals and damper were all new. It ran OK before rebuild but there was room for improvement.
So I think there are two possible things going wrong
[LIST=1]
- I am letting it sit at idle for too long and fuel is gathering / pudelling in the turbo compressor, when I rev it up the fuel is sucked through causing it to go rich
- The spring / damper is too stiff so that the slider is not moving up fast enough when I rev it up causing it to go rich
Planning to refit the old spring and damper this weekend and have a go at retuning, also going to make sure to rev it up to clear any fuel out of the compressor every 60s or so.
Any thoughts / ideas / comments appreicated. Spent four hours trying to tune it so far and still nowhere near right.
Thanks,
Hi.
My Elford - Miss January - is still running fine, but unfortunately I am not enough of an engineer to say what is wrong with yours. eg, I don\'t know what needle I have - it is still the original - how could I find out?
Next time it goes for MOT I will ask them for some CO2 figures, but since CO2 is not measured for FB MOT\'s I have never paid any attention.
I can vouch that there is significant low rev surge on Miss January, particularly on light throttle and overrun, which might fit with some of the fuel symptoms you mention - so maybe we have that in common. I just run with a fairly high tickover and avoid low revs and gentle overrun.
Where are you? maybe we could meet up and compare notes? I am just south of Birmingham....
John
Gidday John,
Thanks for the reply. I am down in Brighton so not terribly local. The needle has a code printed on it so you have to disassemble it to get to it. Probably not worth while.
Had some success today by putting the original spring back in the carb and changing the damper oil from 20w to 3in1. I can now easily set the idle speed and it responds much more nicely.
Going to get it back on the CO meter hopefully tomorrow and try to set the mixture to 7%. Would love to know what yours runs on the meter as a comparison. Might even stretch to chucking mine on a dyno and get a good AFR reading through the engine speed range.
Cheers,
Tim
There\'s a blast from the past Tim, had I but remembered it.
Not put my spoke in here because I know nothing about Elfords and the SU set up.
But in a previous century, a couple of motors that I owned needed 3 in 1 for the SU dashpots, not engine oil. Your post just flashed a memory up in my mind.
(The twin SU\'s were always going \'off message\' on the couple of TC\'s I had).