37 replies to this topic

[tomdale86]

yeah i removed the circlip dont worry.

ill give it all a good clean and put it back together.

atm though it looks as though oil is simply running out of the central tube through the vacuum holes. so piston trouble i guess.

its confusing as it looks to me as though this would happen naturally and there are no obvious damage marks (apart from on piston dampner, but it leaks without that being in)

i noticed also that the needle can wobble around a bit, side to side, is that normal im thinking rather than the piston being shot, possibly the small piece that seems to hold the needle+spring in to the bottom of the piston.

also, if i need a new part, which carb is it? i was under the impression its a hif38 rather than a hs4

Edited by tomdale86, 10 March 2010 - 01:40 PM.

[jaydee]

Seen the ballbearing only on hif38 carbs..never seen it on Hs series carbs before, should be a later type. If it has the float chamber down the carb then its the hif, the HS type have the float chamber beside the carb.

Edited by jaydee, 10 March 2010 - 01:57 PM.

[tomdale86]

cheers.

right its back together, seems ok.

the reason i took the thing apart is that the car is troublesome starting sometimes, when i thought the carb was using oil (i think i may have been filling it too high )

when i had topped the dashpot up, probably over the top and round the sides leaking out, the car starts much better (first time).

can anyone explain this to me?

[dklawson]

also, if i need a new part, which carb is it? i was under the impression its a hif38 rather than a hs4

Jaydee has given you good advice on how to identify the carb type. Also, go back to the pictures posted by T.Harper earlier in this thread. The photograph (not sketch) he posted is for the HIF type carb. The HS series carbs will have a float bowl "off to the side" of the main carb body.

For the record, there ARE late model HS4 carbs (Waxstat type) that use the ball bearing guide for the piston. I have no idea what they were originally used on but I happen to have one on my Spitfire.

EDIT: Regarding the needle, you have the later type spring loaded needle. It is indeed supposed to be free to move as you observed. Nothing wrong there.

[T.Harper]

Hi Doug! Yes good to be back. I've checked on occasionally over the last few months, but a new job has kept me from the car somewhat! Hope you're doing well too.

yeah i removed the circlip dont worry.

ill give it all a good clean and put it back together.

atm though it looks as though oil is simply running out of the central tube through the vacuum holes. so piston trouble i guess.

its confusing as it looks to me as though this would happen naturally and there are no obvious damage marks (apart from on piston dampner, but it leaks without that being in)

i noticed also that the needle can wobble around a bit, side to side, is that normal im thinking rather than the piston being shot, possibly the small piece that seems to hold the needle+spring in to the bottom of the piston.

also, if i need a new part, which carb is it? i was under the impression its a hif38 rather than a hs4

Well done on giving this a go.

Just to clarify - one more time - we are only filling the thin steel tube of the dashpot piston up with oil (#7 on the diagram) and it hardly takes more than about 20ml.

Are you saying that if you fill just this tube up, oil still leaks down the needle? (Because it shouldn't).

[tomdale86]

no no more leaks now

but same issue with starting; takes 4/5 goes, first one or two does start up, next one or two does start but dies, next one starts and runs fine.

could this be the jet needle worn?

it runs great once its going

Edited by tomdale86, 10 March 2010 - 11:02 PM.

[dklawson]

With the carb oil issue behind you, and knowing that you have taken the carb apart (at least to some degree) it's time to consider a complete tune up to address your engine's starting issues.

Always start with a cold engine and adjust the valves. You may think it unrelated but you have to start with the mechanical and ignition systems sorted before you move on to fuel.
With the valves adjusted, go through the ignition system. Start by inspecting everything. Any cracked, carbon tracked, or other suspicious parts should be replaced. Check the dizzy cap and rotor, the spark plug wires, points, and spark plugs.

Gap your plugs to spec, then set the points gap as detailed in your manual. Condensers do go bad. It's not a bad thing to replace them "just because". However, if the old one seemed to be OK... keep it in the boot as a spare.

With the spark plugs and points behind you, set the static timing to somewhere around 8 BTDC then start the engine and bring it to temperature. When the engine has warmed up, refer to your manual and set the dynamic timing.

When all that is behind you, then you can adjust your cab's mixture. The Haynes and SU manuals do a good job of describing the steps. There are also a lot of Internet articles on tuning SU carbs. If you don't have a manual, be sure to post back here and one of us will walk you through it.

[tomdale86]

so its back together and now the piston doesnt seem to move freely. ha ha ha!

probably needs greasing up following me taking apart, although it wasnt exactly bone drywhen i put it back.

question is, what to use?