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Vintage SU sticky dashpot?

AndrewNance

AndrewNance

Amateur hour!
Joined
Oct 24, 2011
Location
Winston-Salem, NC
The front HS6 carb on my 142 seems to be hanging on the dashpot. Usually follows a heat soak but it?s done it even without that happening. If I pull the dashpot out the piston moves nicely so I?m positive the large diameter section isn?t sticking inside the dome. I swapped dashpots between the carbs and it stayed with the front carb so it seems to be inside that smaller diameter section that slides up around the dashpot.

Is there a way to remedy this? Is it ok to spray carb cleaner in there? It feels a little gritty/rough when pulling the dashpot up and down - not smooth like the rear one. I have a spare set of dashpots from my HIFs that I might try but it really feels like it?s in the carb.
 
You can spray carb cleaner inside. I would remove the top and clean it all out inside. Do not use any kind of sandpaper to clean the metal. just use a good stiff brush if needed. That is a precision machined surface that you don't want to affect.
 
dl242gt said:
You can spray carb cleaner inside. I would remove the top and clean it all out inside. Do not use any kind of sandpaper to clean the metal. just use a good stiff brush if needed. That is a precision machined surface that you don't want to affect.
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Right on. Just wanted to be sure it?s okay to spray inside the dashpot where the oil goes. Might be worth it to check and make sure it?s straight and hasn?t been tweaked somehow. Just to be clear, the piston doesn?t seem to be sticking on the inside of the dome. The action there feels very nice.

StanleyR said:
Upgrade to FI and be done with SU.
You can thank me later
;-)
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It?s on the wish list for sure. I?ve accumulated a few parts that I?ll need for MS but I?m not planning on starting that for a while. Got a few other car and house projects I?d like to finish up.
 
They do get gummed up, you can always wear gloves, spray some carb cleaner on a rag and wipe down the inside of the pot directly. It would leave very little residue and would avoid diluting the oil with carb cleaner. Are you using ATF or carb oil in your pots ?
 
I’m using 15w-50 in mine. I’ve had a bottle for a long time and it’s always worked well for me. Once upon a time I had an actual bottle of SU oil but it was used up and I couldn’t find it anymore.
 
Sometimes the jet isn't centered and can cause wear against the needle. That can also be felt as some resistance. I'd suggest going to atf or something a bit thinner like 30w oil. 15-50w seems a bit thick viscosity for SU carbs.
 
If the jet is not centered the needle will stick, take out the needle and see if it is better. I use ATF in the dash pots.
 
I cleaned both dashpots and switched to straight 30w oil. It seems to be working much better now. I let it heat soak and drove it some more and all was good. Gonna test it by driving 400 miles this weekend :-P
 
I had problems with the plunger (screw-in thingy) binding up from time to time, so check and clean that also.

BTW, I found running ATF worked best for my motor, but it really depends on the engine (head, cam displacement, intake manifold), needles, springs in the SU, and lots of other little things.

-John
 
Did ~375 miles and I didn’t have a single issue with sticky pistons or dashpots all weekend. I did however have to deal with both jet assemblies falling apart and leaking fuel twice. I had to disconnect the choke linkage, cobble my fuel hoses back together with rubber hose, and zip tie the jet in place but I drove it 150 miles back to my house that way.
 
Those tubes are some infuriating nonsense.

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Pretty much worth taking the carbs off the car for better visibility, less fumbling around underneath the carbs, etc.

*cough*cough* Also a half-decent reason to start looking for some DCOE's.
 
planetman said:
Do you want a new set of jet tubes?

I only sell original SU jet tubes for the HS6 carbs.
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I do need a new set for sure. I?m guessing these weren?t installed properly because I never touched them and the rear one just fell out this weekend. I was poking around the front one to see how it goes back together and then it fell out too. I need some other parts too and I?m working on a list right now. Let me see what I?m ready to buy and I?ll shoot you a message later.
 
JohnMc said:
Those tubes are some infuriating nonsense.

Pretty much worth taking the carbs off the car for better visibility, less fumbling around underneath the carbs, etc.

*cough*cough* Also a half-decent reason to start looking for some DCOE's.
Click to expand...

:lol: I want to fix them for now but MS is definitely on the list for this car in the future. Maybe well into next year after I?m driving my 122 some more. I want to be able to take my time with it and learn something.
 
I meant taking them off the car just for better visibility while fixing those tubes (other than joking about DCOE's). It's a horrible design - you need to hold that tube into the hidden inner portion of the hole (while a spring tries to push it out) while you tighten the nut until it smashes the o-ring enough to hold the tube in place. And even after you tighten it, that's really all that holds the tube in - a compressed o-ring. It's a rather passive sort of design. Depends on non-intuitive assembly tricks, and that nothing ever really gives even a gentle tug on the tube after.
 
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