SU needles 3.8 Series 1

[chuffer]

I've recently been experiencing a slight hesitation when picking up from idle, no load, and have not been able to discover what's causing it - checked oil in dashpots, pistons not sticking, etc, so decided to check the archives, both here and on JagLovers.

My attention was quickly drawn away from this initial problem when I realised that because I had an ITG air filter, similar to David Jones's (whose archive postings were most helpful), and tubular exhaust manifolds (though the engine is not tuned in any way) perhaps having the original UM needles was not the best set-up.

Based on what I read, I decided to try UB needles with the option of going to UE later if necessary. They arrived from Burlen today and I fitted them. Wow! It goes like whatsit off a shovel now! That's got to be the best 20 quids worth I've spent on the car.

However, the hesitation on pick-up is still there, even after getting the Colortune out and setting it up. I still think it's fuel, but I'll begin to look elsewhere tomorrow. Any ideas anyone?

Ray

[christopher storey]

I have found that this problem often is caused by just a few degrees retardation of the ignition . A problem with these engines is that the timing pointer is not always accurately positioned. It is best to check TDC with the aid of a dial gauge in cylinders 1 or 6 and set the pointer accurately, and then retime the ignition

[Heuer]

Ray

I only use super unleaded fuel (Shell V-Power or BP Ultimate etc) - the small extra cost is more than compensated for in better performance at all revs. The various SU needles have different profiles so you may need to go to the UE ones if the problem is still there after you have followed Christopher's advice. Worth buying the SU Caruretters Tunig Tips & Techniques book from Brooklands (?9.95) as it really helps understand the difference in the various needles and getting the carbs setup properly.

[chuffer]

Many thanks for the advice. I think I've cured it by being a little less heavy-handed on the mixture screws - setting the carbs up by using a Colortune at idle is fairly coarse and it needed bit of fine tuning.

I had hoped that Christopher's advice would work when I found the ignition advance was only 8 degrees, but setting it to 10 unfortunately made no difference. I did notice that when I removed the vacuum advance from the front carb, there was no apparent suction on my thumb when I put it over the brass fitting on the carb. Should suction have been apparent?

I think I'll stick with UB needles for the moment, because the profile of both UM and UB are virtually identical for the first three stations of the needle, so won't affect my problem as this appears just off idle - where I assume the needles are the same. However, I take the point that UE are slightly different throughout the entire profile.

I'm only confidently stating that because I found this website on JagLovers which is excellent for comparing needle profiles, though perhaps not as good as a book which explains what the profiles mean!

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

It's interesting to put in and compare all at once UM, UB, UE and the ones David received with his air filter, UO.

cheers
Ray

[christopher storey]

Vac advance port : no suction is there at idle . The suction only appears as the chamfered edge of the throttle plate passes the inner point of the vac port .

Are you sure that your problem does not arise from using UB needles whcih are too rich, and then setting the mixture too weak to compensate ? Moving away from idle with a blip of the throttle you will be going well beyond stations 1 to 3 on the needles .

Or another thought, have you checked float levels? - a first and easy way to do this is to see if you can see fuel in each jet perhaps 1/8 inch down . Another check which I now make is to check the jet depth settings before doing any adjustments at all , using a digital depth gauge . A nominal starting point of about 60 thou down on each jet is a reasonable start if the float levels are anything like correct, but I have found often that the depth varied considerably between carbs, which immediately suggests something is amiss with the tuning

Edit : Have you tried a vacuum gauge on it - I use the servo take off to attach one ? It should pull at least 17 inches and preferably nearer 20 inches at idle , and if it is less than these figures, or varies, you have an air leak

[Heuer]

Great site that Ray. All sorts of calculators for not only SU's but also diff ratios, power to weight ratios, wheel and tyre ratios etc etc. I have added a link to the Library. This is the Automotive homepage: http://www.mintylamb.co.uk/?page=auto.htm

[chuffer]

Whilst I thought I had cured this hesitation in July I was wrong. On a trip to the Lakes last week the darn thing returned - runs OK from say 600 rpm up to 1000 then coughs through to 1200 and then OK again. Once moving, it even pulls away from 600 rpm on the level in 5th. So all my work setting up the mixture and timing has improved something!

But I've now found it! Hooray!

I unscrewed the acorns in the distributor cap and found one of the brass (?) washers had come away from the splayed ends of the wires and was sitting end-on alongside the terminal in the dizzie. The wires poking out of the end of the plug lead were just aiming vaguely at that terminal. So I guess the spark jumped at certain revs but baulked at the idea at others. Must have been like that all the time I've had the car.

So I'm now a happy bunny :D with a car that is finally tractable and easier to drive after rebuilding the engine, fitting the new T5 (sorry Paul, T5 derivative) smaller diaphragm clutch, new side frame and speedo cable. I now need to drive it whilst we still have dry weather........only thing stopping me is the fact that my wife broke both her ankles on August Bank Holiday Monday so I'm head cook and bottle washer for the forseeable future. Well there's always next year.

Hope this unusual fault description and rectification helps others.
cheers
Ray

[Tony]

I had a similar problem, not with the e type but my Westfield. It missed on accelerating through 1000 to 2000 revs. Drove me mad for months.

Stripped car, played around with jets, filters, getting a spark which it did through the range when stationary.
The same as yours it turn out to be the HT leads separating at a poor join on acceleration.

It's funny when you do solve the problem even though you have wasted time a money. You are so pleased you forget all the bad bits.

The annoying thing is the problem was simple with afterthought

[chuffer]

It's funny when you do solve the problem even though you have wasted time a money. You are so pleased you forget all the bad bits.

The annoying thing is the problem was simple with afterthought

You are so right on both counts. Fortunately I didn't waste money but I now have a thorough understanding of the carbs and can remove them in my sleep. This investigation led me to change the needles for the better and to discover that the timing was out.

Very happy....

Ray