Mixture Setting Problems

[MinorOCD]

That’s a good result. Nice to find a place that can still tune carbs, especially custom needle adjustments. Worth every penny penny.
All the best,
Paul

[svenedin]

Thanks yes. The rebuilt engine is in good health. I had been a bit disappointed as the performance could be rather flat in certain driving conditions and sometimes the engine would hesitate, if only very briefly, and not spin up as I would like. It seems this was due to under-fuelling and those spark plugs were not lying!

Stephen

[svenedin]

That’s a good result. Nice to find a place that can still tune carbs, especially custom needle adjustments. Worth every penny penny.
All the best,
Paul

Yes definitely especially as Burlen are charging £20 for a needle. They are just too expensive to buy to experiment and find you have to try several before you get the desired result. Even then, the home mechanic can only road test and that isn't really very scientific.

Stephen

[Blaketon]

I had an interesting morning at Sanspeed tuning in Bexley.

Well worth getting a rolling road tune done if there has been a major change such as an engine rebuild. There is a limit to what can be done at home. You can get the idle fuel mixture spot on but you can't really judge whether the fuel mixture is correct up through the rev range.

Absolutely. I am setting up mine now, so that I can use it while I bed in the newly rebuilt gearbox. In addition to the gearbox/clutch job, it now has twin HS2 carbs, so I have used Gunson's Gas tester to set the idle (I need some richer needles), just to give me a starting point. I'm not going to be caning it and certainly not with the gearbox newly rebuilt. Once that is bedded in, I'll get it set on the rollers.

Best part of forty years ago, my father fitted a Holley carb to his MGB GT V8 and nobody could tell him, for sure, that their air filter would clear the bonnet. In the end, he made his own airbox. At the time, we knew a retired engineer, who had work for Ford, developing diesel engines. He told us that whatever you do has to be proved on the dyno, even when you know what you are doing!! As it turned out, the air box worked well on the rollers but we were working on the basis of not wanting to alter the bonnet. I remember experimenting with cardboard templates; now I have a hand held endoscope camera, which would have been very useful then. I only got it when I dropped a washer that I couldn't find and I concluded that it must have somehow fallen in through the starter motor hole (Of the Traveller). It had but if I tried to get it to do so again, I'd never do it!! The endoscope enabled me to see where it was and to fish it out with a piece of welding rod.

[Bill_qaz]

[/quote]

now I have a hand held endoscope camera, which would have been very useful then. I only got it when I dropped a washer that I couldn't find and I concluded that it must have somehow fallen in through the starter motor hole (Of the Traveller). It had but if I tried to get it to do so again, I'd never do it!! The endoscope enabled me to see where it was and to fish it out with a piece of welding rod.
[/quote]

I bought one that comes with attachments that clip to the camera head. A magnet, a hook and a mirror. Very handy for recovering small lost items, looking in cylinders and down drain which i initially bought it for. One of those tools you don't use often but pays for itself when you need it

[svenedin]

Purely out of curiosity I tried an H6 needle to see if I could have got the mixture right without taking the car for a rolling road tune. The answer was no. The mixture was far too rich with an H6 instead of the custom modified AN. To my surprise, the H6 is quite obviously different to an AN even just looking at it without measuring.

Stephen

[panky]

You can compare needle profiles on here

http://www.mintylamb.co.uk/suneedle/

Click on the two that are already there to get rid of them then pick the needles you want to compare from the drop down menu

[svenedin]

Thanks. Yes, I have actually used that comparison tool and doing so appears to show the AN (standard) and H6 (rich) to be fairly similar but they are too far apart in practice for my needs. I will need to find some needle tables to find something just fractionally richer in the mid to upper range.

Stephen

[svenedin]

I bought a copy of the SU needle tables. The website graphs are useful but you do need to know which of the very large number of needles you want to compare.

Looking at the graphs, H6 is quite a lot richer than AN. Of all the needles I looked at, the one that gives just a smidgeon more richness is CE but the curve is a little strange. I might try that if I'm bored but at £20 a needle not very likely!

Stephen

Mintylamb SU Needle Compare-o-rama.png (318.5 KiB) Viewed 5520 times

[svenedin]

Minispares had an "AC" at £8.10 (not £20 as Burlen charge) so I will try that for my own amusement.

Stephen


AN standard SU HS2 needle
H6 rich SU HS2 needle

According to the SU needle reference table booklet:

Needle stations:

1&2 Idling
3,4,5,6 Pick up top gear 20-50 mph
2,3 Cruising 30 mph
5 Cruising at 50 mph
7,8,9 Full throttle
10,11,12,13 Not used with 1.25" carburettor

Mintylamb SU Needle Compare-o-rama.png (317.87 KiB) Viewed 5483 times