SU Carb tuning

[Gus Meyjes]

HELP!
   
   Mt car is all done. I took car of the brakes, clutch and oil leak issues. With a brand new pedal box assembly. The pedals operate smooth like a new car.
   
   Brakes are fantastic with the front Disc conversion. Steering is super tight and precise with the steering rack conversion. The car looks fantastic!.
   
   But, in spite of the engine rebuild with upgrades such as a mild comp cam, new pistons and con rods, a ported head, new sleeves, gaskets etc and an increase in compression from stock to 9:1 ratio (according to Robin Woolmer) I can't seem to get power out of this engine.
   
   I've had various widely ranging suggestions on timing with the new cam.
   It is now set at 12 degrees advance and 36 total. the carbs are problematic. They have been completely rebuilt by professional SU guys. But they mostly do twin set ups for MG's. The plugs look good, it's not running lean or rich. But power feels flat. Synchronizing these carbs is problematic, largely I think due to the spring-linkage. The first carb always leads out before the others follow and open up.
   
   Can anyone offer me any suggestions on tuning these SU's?
   
   
   
   Thanks,
   
   Gus

[pls01]

Gus,
   The carb set looks great, nice clean set-up.  I’m no expert on AC’s with SU’s, but here are some thoughts.
   
   The timing values seem in the right range.  Compared with other performance engines, 33 to 38 degrees of total advance is normal.  I’d be surprised if timing was the source of low power.
   
   I would not think the first carb leads the other two.  The throttle butterflies are a “balanced” design.  There is equal butterfly area on each side of the shaft so it takes almost zero torque to open or close.
   
   If the return spring is on the opposite end of the shaft from the throttle linkage, leading could occur.  I don’t see that in the picture.
   
   I use a Syncrotune to tune my Solex’s on the Bristol engine.  It’s available from Moss Motors (PN 386-200) at $29.95.  I disconnect the linkage from each carb and balance the individual carbs very accurately at an idle ensuring all three are on the stops.  I then reconnect the linkage and recheck the balance.  I assume they stay balanced through out the range of throttle openings.
   
   How many miles are on the engine since the rebuild?  My Bristol had similar timing and carb problems but also seemed a little down until about 300 miles.  Around 300, the rings seemed to seat and power improved.  Have you checked compression?
   
   Peter Stanwicks

[Gus Meyjes]

Thanks Peter,
   
   The engine is brand new after rebuild, only 25 miles, so that may be part of it. I did balance the carbs out the way you mentioned, but that was to no avail. The engine is much happier with the choke on, which makes me think I am starved for fuel, even though the plugs had a nice although light,  color.
   
    I hear about people sanding down the needles to get them to allow more fuel in the mixture. I just don't know where and how to sand or even how much.
   
   Do you or anyone have any experience with that?
   
   Gus

[Robin A Woolmer]

Gus
   I have sent you information From Midel in Australia & Burlen Fuels in UK both are SU experts, Midel web is ' www.sumidel.com ' & Burlen is ' www.burlen.co.uk ' They can supply you a range of needles but more inportantly give suggestions as to the original needles & perhaps what you should consider now with your set up.
   The needles have a very precise shape & i doubt you could reproduce this consistantly on three needles.
   The other issue is are you now using the correct choke size? my racing special was set up with 1&3/8'' choke carbs, it would be worth some discussion with other racers!
   I asked Burlen yesterday if they had a formula to size carbs to engines & the various detail parts & they said NO, you could however talk to there experts though!
   It looks as though some level of developement is needed.
   I did send quite a bit of info to Ron Mack on timing etc.
   
   Regards
   
   Robin

[pls01]

Gus,
   If the engine runs better with the choke, fuel starvation is a possibility or maybe a vacuum leak.  If the engine idles poorly, a vacuum leak is more possible.
   
   Peter

[SpqrEddie]

Hello!

anybody would know wich is the correct fuel level for a H2 AUC 700 Carb? (1959 car).

i have found different sources in referecne to the float fork setting.

Should it be set with a 7/16, 3/4 or 3/8 rod across the underside of the lid?

Thanks!

Eddie

[Klassik Metall]

According to the instructions supplied with Burlen rebuild kits for AUC 700 carbs,
a 7/16 (11mm) diameter rod should be used. This measurement is for when the
needle valve is on it's seat.

Regards, Luke.

[AE 501]

I had the same problem with my Healey some time ago (only 2 carbs). He asked for a slightly pulled choke to run equally. At the end it was a loosened screw wich fix the needle in the piston. The shoulder of the needle should be flush with the bottom of the piston. It was about 2-3 mm the needle had come out. Easy to control or to fix - just open the bell housing on the carb and pull the piston.

Regards, Chris

[AEX 31]

Hello Gus,

I have been running AEX 31 with an engine that sounds similar to the specification you have, for 7 years.

Ignition setting also sounds the same.

I have also experimented with a number of needle sizes but have found that the engine runs best with the
standard DW needle and the top of the jet adjusted 1,5 mm down from the bridge.
Which needles do you use?

Please let us know how it goes.

Regards Jonas

[SpqrEddie]

According to the instructions supplied with Burlen rebuild kits for AUC 700 carbs,
a 7/16 (11mm) diameter rod should be used. This measurement is for when the
needle valve is on it's seat.

Regards, Luke.

Tahnk you Luke,

I set them up as you suggested. and then tried to tune them, but i dont seems to be able to get them right.\
They remain quite rich, and very strangerly the first two pistons work at 200 degree less then the other 4... (100' vs 300).
And this dont change even by changing the carburettor settings to the extremes. very strage. may be there is a leak.
Also despite the cylinder work, when i disconnect the plug of it, it doesnt seems to badly affect the engine running.
i can see it works as when pulling the plug out you can see there is combustion.

On another note, when checking the igition with a strobo light, i can not see any sign on the flywheel.
The maual says 1/6 should be seen. I will try again and eventualy alter the timing.

Best,
Eddie

[nicksonsticks]

Hi,
I've read through the posts with intetest and can see you've had lots of great advice, just a thought though as it's easy overlook some the basics and assume you've got carb problems. A quick check with a vacuum gauge will give you some good indications of what's going on, expect  steady reading of approx 18 to 20 inches of mercury, a fluctuating reading would indicate a mechanical fault, e.g. valve clearances,  seats, etc, a steady low reading might indicate ign timing or valve timing etc. As a test you could even try rotating the distributor with the vacuum gauge connected to see if this improves your reading.
If you suspect you've got an induction air leak have a Google of a tool called smoke pro. I've used a snap on version of this for  years and it is unbeatable for finding induction leaks.
Hope this helps a bit.
Kind regards Nick

[SpqrEddie]

Hello Nick,
thank you!!
it is the first time i work on a car, but i come from motorcycles and with my firends we always say that 80% of Carburetor issues are electrical!

i was able to get a rough carburation yesterday, the car doenst smoke or miss beats. As well after cleanign the jet (and the rusted spring!) of the first carburator, al the cylinders run around the same temperautre.So despite the mixture skrew completely open it was running lean. Now it should be ok.

As well, this time instead of starting tunign them from one turn and and half out, i started the tuning procedures with the mixture skrew completely in. The standard one and an half turn out was already too rich.

Today will try to check the timing. But still not to sure what i should see on the flyweel as marks. now i dont see any, so i am definitely out.

I will consider that Smoke Pro, and unfortunately the syncorniser i bought never arrived! so i am using the hiss method for alligning them.
i am considering as well and exhaust gas analyser.

And defintely a full rebuild kit for the carbs!!!!! i dont know i will get any closer to a good carburation with these worn parts.

Eddie

[SpqrEddie]

Hello!
anybody would know what i should see with a strobo light for a Weller engine?

I can see three markings on the flywheel: a "5", a bar "I", and a "1 I 6"

With the strobo lamp i can see the "I" with the motor running very slow, then it disappear...

At what should i aim?

Thanks! and sorry the manual is not very helpful on this!

Eddie

[kicksey]

I had exactly this problem last year!   just going out now,  but give me a shout and I can talk you through our process of resolving the issue which may help

Regards
Chris
07557 304376

[SpqrEddie]

The bar "I" is just a few centimiters before the "1 I 6".

"1 I 6" should be the TDC for Cylinders 1 and 6, so i belive that the bar "I" is the firing point at 12.5 degree before TDC.

Anybody can confirm this? what's are your flywheels marking on a CLB engine?

Thanks!

And Thanks Chris for your availability and time at the phone today!

Hello!
anybody would know what i should see with a strobo light for a Weller engine?

I can see three markings on the flywheel: a "5", a bar "I", and a "1 I 6"

With the strobo lamp i can see the "I" with the motor running very slow, then it disappear...

At what should i aim?

Thanks! and sorry the manual is not very helpful on this!

Eddie