Welcome to our Site for MG, Triumph and Austin-Healey Car Information.
Triumph TR6 - SU BLUES
I've got ZS carbs on my 6 and the car is running great. A friend has just installed SU's and although they seem to respond faster than the ZS carbs we can't get any vacuum off them on the line going to the vac advance on the dist. When I pull my line off, my idle increases and the end of the hose sticks to my finger tip with the vac...on his there is no difference in idle nor suction on the hose. There is also no suction at the carb end.
Anybody else have this experience with their SU's ??
I run with the vac to the distributor disconnected and the nozzle on the carb blanked normally, but I removed the blank from the fitting behind the dashpot on the rear carb to try it and the vacuum is quite strong there so I can only assume if you are talking about the same connection that maybe it's blocked??
they are brand new carbs but we will look into that possible blockage
|Charlie, I run SU,s on my 6 and I do not have any suction at idle from them either. I can run it connected or disconnected and it does not seem to matter.|
Should have said the vacuum's quite strong at running speeds, at tickover it's almost non existent!!
.that will save us wasting time...now to look for that hesitation somewhere else !! hahaha
|Just found out the butterfly valve on the ZS are at a slight angle and do not block the vac hole therefore you have vac at idle and with the SU's the valve is more vertical and blocks the hole at idle and only gives vac at acceleration.|
thanks for the help guys
|Further to the above list I have some questions regarding SU carbs. I run a used set off ebay from New Zealand and cannot get them working correctly. When the engine is cold and the choke is on it runs great lots of acceleration etc but once it warms up and the choke is off it is sluggish and seems too lean. At operating speed (2000 RPM) if I pull out the choke it works better but then is way too rich to idle. I am suspecting I need a different set of needles so my questions are:|
how do you identify exactly what kind of SU it is?
how does one determine the needle that works the best? is it trial and error? I am located in Northern Ontario Canada elevation of 653 feet above sea level. Any suggestions would be appreciated.
One of the first things you might do is find out what needle is currently in there. Armed with that, and the part numbers on the float bowls, call Joe Curto in New York state. He diagnosed my problems 3000 miles away, having never seen the car or carbs. If the carbs came from a sedan, the engine sits nose high (someone said 15 degrees) and the float bowls are different depths to compensate. Don't matter how many times you set the float level....
The Needles that keep coming up are BAG, BAX, and Joe Curto recommended BAL for me. Check the archives for SU needles, lots of info there. Mine is doing great... went to the Oregon Coast early June, 1700 mi. round trip, 25 MPG average. Joe's a genius!
Good luck...happy moToRing!
|Also......if the float bowls are to the front of the front carb, and the rear of the rear carb, you have HS6's. If the float chambers are enclosed in the 'body' that would be an HIF6.|
Hope that helps.
Your description fits the probelem I had to a T (R6) haha.sorry
Mine used be the same...I was always moving the choke in and out when pulling away from a stop even when warm also had poor acceleration and a bit of a miss on a regular basis....what I found was ..
1 A tiny hole in one diaphragm
2 timing was off
3 Mixture to lean
I replaced the diaphragm, adjusted timing, bypass valve, ( 9 turns from fully clockwise ) balanced carbs,and ran them fully rich for a while then back about an 1/8 .
It's been about 7 weeks since that and it still runs great.
If I set my needles to the middle position she runs lean so I find I have to be more on the rich side ...maybe my needles need replacing ?? but I don't think your symptoms are just needle related.
|Thanks guys! From the information provided by Rod it would appear I have HS6,s which is kind of what I thought. I will check out the numbers on the needles and fuel bowl as well. I also recall that when I first installed the carbs I had a fuel bowl overfill problem on the rear carb and readjusted the level. Maybe there is a problem in that area.|
I have tried every kind of timing confiquration possible and it does not change things alot. I have the crane electronic ign. Last night I took it all apart again and balanced the carbs and adjusted the mixture, same problem. It just seems like it is starving at cruise. I suspected the fuel pump but my theory is that pulling out the choke would not make a difference if there was insufficient fuel to the carbs. As a last resort I will reinstall the ZS carbs.
I will keep you posted, thanks again
Several check points about SUs;
Check the float level and the condition of the needle valve.
Check the butterfly spindle for wear.
With the air filter off check that both damper assemblies fall freely and at about the same rate.
If there are spring loaded valves through the butterfly either solder them shut or better still remove them and blank the hole.
There are two types of HS6, one with a fixed needle [early] and one with a spring loaded needle [later] if you have the spring loaded needle type a good starting point is BDM needles and red damper springs.
There is also a type of SU with a waxstat on the jet assy which is not really recommended for the TR6 due to the heat from the exhaust manifold affecting it.
It is also well worth getting the SUs completely reconditioned by a knowledgable carb specialist if you are willing to spend the money as they are a far superior carb in most ways to the Stromberg.
|Ok Thanks for all the help, I checked the archive and found some excellent data on needles and then checked mine. Reccomended ones are BAG,s and I had BDB, which according to the chart are considerably thicker therefore allowing less fuel to flow. I also thought that if the fuel float and bowl will porduce enough fuel when the choke is pulled the problem had to be in the needle. Knowing I had the wrong needle anyway and being a bit impatient waiting a week for a new one I put the needle in the drill press and filed it down while spinning it being held in the pointed small end. I did both trying to get the as close as possible to each other. I do not have a micrometer at home so I did it by feel. I installed them warmed up the car and went for 20 mile ride. It performs like a new car, no hesitation, full RPMs no back firing etc. I will run the hand done ones until the new ones arrive. I also checked all other functions and everything check out OK. I am going to try blanking the small sping valves on the butteryfly as well. Thanks a million guys, what a great help!|
If you're into reprofiling needles its worth shaping the needle so its profile is slightly concave rather than just a straight taper, this gives a noticable improvement in acceleration at the expense of economy.
|Thanks Rod I will try that. I am also curious about the little spring valve on the butterfly. what was it supposed to do and what removing do?|
|Following on the above I contacted Joe Curto for some needles and true to the above comments he had me check the pn on the bowls first and one was from a sedan. He suspected that because I got them from New Zealand and indicated they were from a sedan. He is supplying me with the correct bowl, gaskets and some BAE needles that are very close to the BAG(he was out of those). What a guy! I would highly reccomend him for parts and trouble shooting here in the colonies. Phone 1-718-762-7878 www.geocities.com/jcurtoinc/|
I think the little spring valve was an anti polution device to reduce the vacuum on the overrun, apart from the fact it causes popping on the overrun it doesn't exactly do much for the air flow through the carb.
Nowadays in the UK if you send an SU back to the makers for refurbishing they automatically replace the butterfly with a blank one with no valve
|That thing sounds like the "by-pass valve" on ZS carbs....|
|Ken, I am really impressed with your initiative to just try doing a mod like this by yourself, especially by feel. And by your luck(?) in getting it running so well right away. These cars really do respond well to fiddling, don't they? That fact, I think, is what makes them so close to our hearts. (Besides how fun they are to drive)|
This thread was discussed between 01/07/2004 and 10/07/2004
Triumph TR6 index