37 replies to this topic

[dklawson]

Tom ! Hey, it's great to see you post again. I hope all is well with you.

tomdale86, take a look at Tom's first picture post showing the cross-section of the carb. As Tom said, note that leader "7" points to the oil in the dashpot. There have been a few threads on this board and others I frequent where people talk about their Haynes manual telling them to fill the dashpot up "all the way" or "1/4 inch above the tube" or some such. All that is wrong. Again, look at Tom's picture and you'll note that the level of the oil (the dotted area) stops BELOW the top of the tube.

Clean out the carb oil as Tom suggested. Wipe the excess oil off the piston and the inside of the vacuum bell. When you put it back together, fill the oil (again referring to leader 7) only to about 5/16" below the top of the tube. When you put the damper back in, you'll see the oil level come up in the tube almost flush with the top. If you add any more oil than that... it WILL overflow and get sucked down into the piston/bell chamber area.

[tomdale86]

Pull it apart. Should only be a couple of screws holding the dashpot (bell housing) down. Be careful as the main piston will pop out and you don't want to drop it as you could damage the needle (there's a big spring that will push it out too).

Take the piston with the needle out, (the shiny bit in the middle here):


Turn upside down and drain the oil out. Try to get a rag and screw driver down the oil tube to give it a wipe. Have a look down with a torch. Try filling the tube up with oil again whilst it's in your hand and see if it's leaking from anywhere (look to see if there are any cracks near the base).

i've removed the bell housing and the piston (silver thing in the middle of the picture). they came out together.

i dont seem to be able to separate them?

also heres a picture of the remainder of the carb on the car:



you can see a bit of soot-like dirt at the bottom. im assuming i should clean this up. is it a signal of anything?

[jaydee]

I wouldnt worry that much, it seems that has never been cleaned propery so has collected all sort of dirt.
Just give it a very good clean using some petrol, then see how it goes.

[tomdale86]

ok thanks, and how do i separate the bell chamber and piston?

[jaydee]

The bell chamber is the dashpot, the piston is swinging inside of it, the piston damper is at the end of the dashpot cap...
Send me an PM if you need the SU handbook.

[tomdale86]

The bell chamber is the dashpot, the piston is swinging inside of it, the piston damper is at the end of the dashpot cap...
Send me an PM if you need the SU handbook.

sorry getting my terminology muddled

how do i remove the piston from the bell chamber/dashpot? want to check for cracks etc etc, give it a clean

also, the piston dampner is scored. is this a problem? i know its not a cause of the leak as it leaks when the car is standing without the dampner in.

[tomdale86]

so i filled the bell chamber/dashpot up (with the piston and needle attached still) and the oil leaked down the needle!

how caused/how fix!?

at least i know where its leaking now!

[jaydee]

You filled up section 7 about and oil leaked throu needle collar?
Thats possible only if piston is cracked..can you post a good picture of it?

[tomdale86]

yeah filled up number 7.

i dont think its leaking on the needle, rather its coming off the base of the piston then onto the needle and then running down.

needle prior to going in:


set up (you can actually see the oil beginnin to run down)


heres the underside of the piston:


It seems to be leaking either from the 'hole' on the left of the needle as you look at the picture, or very close to the hole, and possibly the one on the other side. forms a little drip there which hits the needle then runs down. there are no obvious cracks on the bottom of the piston

what are those holes for?

[jaydee]

The holes are for vacuum.
Revome the dashpot cap. if the piston doesnt fall off the dashpot theres something wrong, it seems to me that dashpot is full of oil or the piston is blocked some how..

[tomdale86]

the cap isnt on! the piston is hanging like that- i dont seem to be able to pull it off.

the piston will move obviously up and down, but it doesnt seem to want to come off.

my piston cracked then?

Edited by tomdale86, 10 March 2010 - 12:47 PM.

[jaydee]

Thas not normal..try pushing it down using a screwdriver through the neck of the dashpot

[tomdale86]

there was a clip attached the top of the piston (the part than you see when looking through the dashpot) that prevented the whole lot from coming out:


this is what the insides look like:




looks fairly obvious that the oil would flow out of those vacuum holes-doesnt seem to be anything stopping it.

[jaydee]

But the oil shouldnt get there, if so the piston damper is shot..

Edited by jaydee, 10 March 2010 - 01:14 PM.

[dklawson]

Thas not normal..try pushing it down using a screwdriver through the neck of the dashpot

Do not use anything to push the piston out. The piston not coming out of the bell is normal on this late carb. This is the type with the large spring and the ball bearing guide for the steel tube on the piston. There should be a small circlip on the top of the steel tube which is preventing the piston from being removed.
This link may not take you directly to the Burlen page that discusses this but start here:
http://www.sucarb.co...tail.aspx?id=76
That should be a page telling you how to dismantle HS4 carbs. Picture 5b shows your later HS4 and the location of the circlip on the steel tube.

If the scoring you noticed is not causing the piston to "hang" or drag in the bell it will be OK as is. You may want to take the pieces apart GENTLY hit the scratched area with ScotchBrite, wipe clean with carb cleaner to remove any debris, then reassemble. The only area that gets oil is the center steel tube on the piston. The outer edge of the piston and the inside of the bell should be dry.

There should be no leak path through the carb piston to/out the needle or those holes on the underside of the piston. Take it all apart, hose it out with carb cleaner, dry with paper towels, and then gently put a little bit of oil in the CENTER of the piston tube. Don't over fill it. let it sit for a while. If you have leaks under these conditions, you have a problem with the piston.