Now Worse After Removing Carbs

Neilr

Member
Still can not get to bottom of this poor running. After suggestions removed carbs stripped and cleaned them. Now it will only run badly with choke out. I need help if possible. Is anyone close to me who would be able to cast their eye over to see where I am going wrong. Also I did notice air bubbles in fuel filter. I am desperate to get to the bottom of this as was looking forward to using soon. Thanks. Have checked dwell and its 24 degrees so this should be ok.
 
OK, here's some instructions I wrote a little while ago on what I do with SU's. it should get you a well running car, but it will probably need further adjustment after this to get it running totally spot on:


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Here us what I do, and it seems to work for me. To set my carbs I do lots of measuring! Please check the books for how many turns in/out everything should be for the base settings, I can't remember them!

I balanced the carbs by removing the dash pot, spring and piston. Mine were rebuilt not too long ago (mileage wise) by me so I know that the gaps on the butterflies when fully closed is correct, which is a key starting point.

Then disconnect the linkages between carbs and wind the stops for both out fully until they are in their full resting position. Now wind each stop screw in carefully so that this is now just touching when closed.

Then add the book figure for base number of turns to each stop screw- I can't remember what it was...

Now you have two carbs that are balanced at idle, but not connected.

Now adjust the connecting rod until it looks like its the right length to not push/ pull anything. Connect it and see if the slave throttle position is moved at all. If it does open the slave throttle, then adjust and try again.

Keep doing this until at rest both are closed. Then operate the master carb and watch the butterflies on both. You will probably find that there is a delay before the slave opens, due to slack in the ball joints on the linkage. Very carefully shorten the linkage by a tiny amount and operate the throttle again. Repeat until both open identically.

Now you have carbs that are balanced through their operating range.

Next is the fuelling. I wound each mixture screw fully in to lower the jet, then raised them by the book figure, which is something like "adjust so flush with the bridge and then turn two and a half turns in ". Use a set of vernier calipers to check each jet is same distance down from the bridge

Now reassemble and start the car. When its at normal operating temp adjust mixture evenly on each carb to obtain highest rpm, and use the lift pin method to check where you are. Once done you can remove the tops of the carbs and check jets with verniers again if you like.

Then setup the choke - I haven't done this properly yet!
 
Thanks Quagmire I am now looking at buying a service kit and needles for both carbs to see if this improves anything. I am getting desperate.
 
Now it will only run badly with choke out.

You need to be certain that everything on the ignition side is perfect before you start on the carbs, but if that's the case, and it won't run at all unless the choke is out, either the idle speed is too low and pulling the choke out increases the idle speed on the fast idle screws, or it's running far too weak and pulling the choke out richens it up.
 
Each original SU service kit comes with a manual or you may look on the SU homepage of Burlen Technical - SU Carburetters
Have done this recently. Was the first time, that I have serviced SU carbs and for the most basic settings some illustrations are really necessary. With the manuals, I´m now sure, that both carbs have the right basic tuning and I can build up here when the engine will fire up again, some day...
 
good luck with poor running . i still have that an dave refurbed both carbs with kits.checked float levels. settings etc timing and replaced dizzy with full electronic. it will now run with choke until warm then idles a bit high . need to check hot idle speed setting again. ( as throttle was altered a bit at pivot point when working on heater in /out ) you ought NOTR to get it bubbles in fuel filter line unless we have just worked on it? ( allowing air entry) am sure you will get there sooner or later but if its anything like mine will be hard fought and uphill battle.
 
Thanks guys. I am going to pull carbs again just to check I have not done anything stupid (always possible) I am also tempted to strip distributor also to see if anything is seized or broken inside. Why does it always happen when weather improves!!
 
OK so pulled carbs apart again nothing obviously wrong. After refitting managed to get her to rev to 4500 rpm on full choke. But this is the only way I can get to do this. I am going too remove distributor and strip this down next as baseplate seems a little too stiff as well as vacuum advance not working. May even try electronic kit back in. Failing that I am going to fuel pump repair kit and see if that helps. Its going to be a slow process of elimination!!!
 
vacuum advance not working.

Vacuum advance is purely an economy device and won't have any effect on performance, and even if the baseplate is seized, it won't affect the centrifugal advance, as the rotor arm moves forward with CA, the baseplate stays in the same place.
 
Bubbles in filter is fine.

HAve you tried just observing into the carbs when you use the lift pins to check things are working as expected?
 
I can see fuel when pistons are lifted. It now seems as someone said like its being starved off fuel. I have ordered fuel pump kit as there now seems less fuel in the filter. I think its just an elimination process now.
 
If it's starved of fuel because of the pump then pulling the choke out shouldn't make any difference. If you had no fuel in the car whatsoever, then pulling out the choke wouldn't make any difference.
 
I understand the theory but I am unable to see any reason for starvation of fuel otherwise. I am sure the filter used to be at least half full before this issue now it only has a little in bottom of filter now. I'm thinking if diaphragm has spilt perhaps this allowing air in also giving poor running.
 
I don't know what you've got lying around but the easiest way to prove it one way or the other is to wire up an electric pump into a slave tank, plumb it into the carbs and see what happens then.
 
By plumbing in a new temporary fuel supply will eliminate any fault with reserve tap.
Seen a few cars where the tap has been in mid travel restricting fuel flow and causing lack of performance.
Clive.
 
Harvey I had thought about this but don't have an electric pump. Seems I will just have to wait. As far as I am aware I can find any air leaks. I even clamped servo hose to see if this made a difference. No Change.
 
I have now ordered an electric fuel pump to check. . I haven't touched reserve fuel tap at all. I there a way to repair fuel tap.
 
Many have never been used so when you pull out the cable to use then push it back sometimes the cable outer cable comes apart not putting the tap back into normal position.
They can leak over a period of time.
Wins sell correct seal to repair.
Not the most easiest thing to get to and better to fix when fuel tank is almost empty + jacking up front of car can reduce leaking. Can leave tap in place remove the small screw and pull out centre of tap with seal.
You will have to disconnect cable to make removing easier.
Clive.
 
Clive thanks another thing to check. Its nearly empty now so maybe the best time.
 
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Did you get a puller pump? If it's a Huco type you won't need the old pump then and you can bypass it.
 
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