Amazon: High Idle -I’m on the road

[gothamus]

Hi there- posting from the phone, understand my typos! I took a cruise an hour out of New Uork. Heading back soon. But I have a problem. Car runs so I bet I’ll be home tonight!
My idle is high- first break it was around 2000 rpm. 1/2 hour driving later I’m going 2500 - 3000. Not breaking great in gear! These are SU carbs, rebuilt and good for past 1000 miles.
Looking down the neck I see the rear piston is raised, easy to see needle. Front is low, quite different and what I expect.
Checked idle. Backed screw all the way off lever and idle remains, no change. Checked dashpot oil, topped off for goods sake. No change. Verified jet below, nothing keeping it pulled down. Even with front carb.
My first thought- because this happened a year ago- high idle on front. Turned out to be throttle plate wasn’t closing all the way do to getting oily gunk ( not really seeable) and I used sea foam on it. Cleared up. No repeat.
I have blowbuy. Oil in the chambers under deceleration. I expect during high driving. Just not seeing smoke (maybe the guy behind me does). That is being addressed in my coming project, when it stays warm. ( 4 weeks? 5? Gosh it’s chiily up here!)
Right now, I’m thinking on it hard. Giving a hopeful sea foam shot. Shooting down the throat. I haven’t gone super aggressive there yet. Car off, shot some on the throttle plate, letting it sit for a little.
Any thoughts on what may be causing the carb piston to stay high? Is it possible another part of the system is causing greater pull and piston is responding? It drops about same ( it lands solid, same as front, but a little quieter, always that way). Oh, and it IS touching plate once engine is off.

You guys are probably asleep, right? What am I doing here!

[gothamus]

Looking through some notes I think the cause is pressure crankcase and gasses not escaping. I don’t know if the rear idle is high because of that or because something has dirtied the throttle plates. I’ve set about cleaning the breather and oil cap as best I can. I can’t take that breather apart. It looks like it was glued together. Taking it apart would strand me on bear mountain. So I did an hour of the best I can with curvy things.

Well, I’ll see how things go.

[mocambique-amazone]

Originally Posted by gothamus

Looking through some notes I think the cause is pressure crankcase and gasses not escaping. I don’t know if the rear idle is high because of that or because something has dirtied the throttle plates. I’ve set about cleaning the breather and oil cap as best I can. I can’t take that breather apart. It looks like it was glued together. Taking it apart would strand me on bear mountain. So I did an hour of the best I can with curvy things.

Well, I’ll see how things go.

Crappy mobile too, I won't read your carb thread for this reason.
Are your butterflys with this s h i t t y overflow valves? Like a small coin and with a soft spring reloaded?
Tack them with glue and prob solved. This is emissions crab
Difficult to diagnose from this distance and knowledge about your car.
The breather on side of engine you can't take apart. The breather inside the oil cap is easy to open. Stucked with burnt oil (cole?)sometimes
Good luck, Kay

[Ron Kwas]

gus;

Simply stated...High idle is caused by Engine being allowed to breathe (false) air (See: http://www.sw-em.com/su_carbs.htm#SU_Carbs_False_Air), and not being controlled by Throttles (only)...and the fact that the rear Dashpot is raised is an Effect of this (not necessarily a Cause!...remember, engine drawing in air results in Dashpot rising as vacuum normally BEHIND Throttle Plate is now in Front of Throttle Plate and allowed to get into volume above Dashpot which raises it...so Dashpot rising is a RESULT of something allowing this airflow), but it does direct you to look around that Carb first!
Either Throttle plate itself is not closing (I'd check Throttle Return Spring FIRST (I lost one once which caused such symptoms), but it could be some other linkage issue, which is preventing it from returning fully...LUBE joints and pivots!)...as Kay says, the Throttle Overrun Valve (if late carbs and TOV is present), might be stuck open:

[Source: http://www.sw-em.com/SU_Carb_Throttl...Overrun_Valve]
...but ANY path for False Air to get into intake will result in high idle...a loose Carb or Manifold, including PCV (which should normally be a only very restricted flow path)...to eliminate PCV from suspicion, disconnect it from Intake Manifold entirely, and plug connection into Manifold, (allow PCV to breathe to atmosphere).

Good Hunting at Bear Mt!

Edit: Presence of TOV is visible after removing Dashpot...BUT...if TOV is stuck open is not immediately obvious when viewed from here and without removing carb from Manifold to be able to see TOV from the other side...if a stuck TOV is suspected, try gently manipulating the Spring from the air filter side...this might allow TOV to pop into place correctly on the other side, sealing Throttle Plate as it should (this beats the even more involved work of having to remove the Carb from Manifold).

[Source: Same Link as above.]

[Derek UK]

Also. Check for manifold leaks. If you have a servo, make sure that the check valve is working. With a servo the manifold adaptor for the servo hose should only have a very small hole.

[Ron Kwas]

Richard;

Only after exhausting all searches external to carbs as the cause of a high idle, without success, would I suspect a stuck TOV as the cause...

...because linkage checks, and all other searches for source of False Air external to carb, remove Carb Dome and Dashpot to be able to see spring of TOV, to inspect that is is not somehow dislodged or stuck open (this would be difficult to see as movement is only about 0.10", but it being askew might be more apparent...you could also manipulate it to check for spring action and possibly recenter it with a soft implement like a stick.

Let us know how you make out!

Good Hunting!

[gothamus]

I got home alright last night. And slept in late having gone to bed quite quite late.

The high idle maintains at 2200 to 2500 RPM. Oil squeezing out of the oil pan, front right side (That gasket is probably most compromised there and pressure is being released there). This other symptoms may be too subjective, driving home with some worry and heightened awareness. But it's definitely got a pronounced ping, is weaker on hills and acceleration. Oil (oil and coolant possibly?) was coming out the tailpipe because the bumper has oil spots and smoky hazing I can wipe off. And worst of all- backfire when turning the car off. I turn the key off, engine is off for a beat or 2 and 'pop' and smoke.

Home but I guess something is blown. Let's not mention something being cracked right now. I might start to worry! . The cylinder head needs to come off and I have to plan that. Good thing is I can turn it on and move the car for street cleaning twice a week.

[gothamus]

Delay in my reply. Hurt my lower back the previous weekend. Forgot about that and undid my healing. Smart.

As it was pointed out- the throttle plate must be open for the piston to raise as a result of air being pulled into the engine.

Why? The fast dial screw was depressed by the curb ed choke leaver. If you want to know more about it, here is my wall of text:

I pulled the dome and piston for better inspection and cleaning. Mild blackening in corners but nothing interfering in movement. If the plate was opened, it was not enough to see.

Went to cleaning the SU controls and springs on the throttle and choke and everywhere else. I noticed in 2 spots on the hard metal body what looked like dark glue that was hardened and dried. That was not there last fall. Crud must have gotten there and cooked.

I finally observed the throttle interconnection between the carbs were not in sync. The rear lever, when pulling the central throttle link, contacted the link pin and moved a little bit after the front link. Just a little, but I know they were precise before. Bolts were secure and I saw no condition that would have changed that at the links. That told me the throttle was opened in the rear. Something was causing the throttle to close no further. The rear plate must be kept open past the closed position. A super advanced faster idle. Only 2 spots can keep it open. Idle or Choke.

Idle screw was not touching the idle lever and movement was clear. But the fast-idle screw was touching the curved cam lever. I had backed that off before, but there it was. Screwed it far far out, interconnection was even. I could not see the dark outline of the throttle plate on the neck, which I didn't know should have informed me. That accounts for the raised piston due the throttle plate being open. But how did I miss that if I had backed off the idle before? I don't have a satisfying answer. Maybe I should have backed it off further. I checked the spacing by looking from across the engine, shining a light on the bay wall behind it. Then stuck my finger nail in there.

A few conditions I observed:

The choke cable was pushed further into the engine bay last week while working under the dash. The hood was closing down on the cable. Maybe the movement was enough to impact fast-idle position. It's a reach, but it's a change. And after back fast-idle screw off I closed the hood and ran to the toilet before turning the engine on to check idle. (I'm reaching here, I know. alright?)

The engine has a problem that needs work and it is causing a mess of fluids to be sprayed out through the oil pan gasket to the front, carb side of the engine bay. Fluid spraying forward while cruising at high speeds, random flecks are blown to random locations. Sticky things are ripened and cooked. That may be the hardened gunk found on carb, perhaps the spring or some other surface got some too, and cooked.

That explains the fast-idle. But the conditions that caused that need further diagnosis and planning to address them. I'm going to start that and create a new post about it. I have been planning on pulling the cylinder head this spring. I'm waiting on guaranteed warmer weather. This warm afternoon followed by freezing evening won't do. It snowed a week ago! A few more weeks.

Pictures included, notice some scoring on the piston. It was there when I rebuilt. I don't feel anything but smooth surface. It matches pictures from SU re-build.