QuestionQUESTION: My idle has climbed in 2 days from 900 RPM to now its at an unbearable 3500 RPM – its like riding a runaway pony. I cannot find anyone who has a clue. Mechanics shaking their heads at me.
What I know and have done: I have set the car to full rich, mid way and lean with no effect.
The idle screws are out and in the magnetic tray so they are not the problem.
Throttle cable checks out and is fine.
Throttle is closed (raised) to lowest idle position (highest physical position)
Butterfly valve functioning correctly to my visual inspection.
The diaphragm inside is clean and intact no perforations or tears.
The water choke valve is not stuck in a position and can be moved by inserting a finger into the little rubber cover (throttle held open with other hand for access).
No visible vacuum leaks by hose.
EGR valve working. (very minor vacuum leaked at EGR fittings (2) apparent with carb cleaner sprayed on fittings.
No leak on back of carb where the spitfire is mounted to the Zenith Strom.
Runs smooth and strong – just to fast idle. What do I do or look for next?
HELP????
ANSWER: Chris,
What condition are the plugs in? Bright white insulators or sooty black?
Typically an erratic idle is caused by a vacuum leak. Are you sure the manifold is sealed to the cylinder head?
And does there seem to be any power at all if you try to drive the car, or does it want to stall?
Cheers,
Jim
---------- FOLLOW-UP ----------
QUESTION: Plugs are clean. New Plugs still look good. The manifold is sealed to the cylinder head with no leaks found with carb cleaner. And driving it with the idle at 3600 is an adventure. Lots of power. Going is not the problem its slowing down. I had to shut down at stop lights. It has been running rich, but this is out of control. Its idling at 70mph on the freeway in 4th.
I have taken the choke apart and made sure it is sealed upon assembly. It also seems properly aligned.
I have tried to adjust the gross idle and fine idle out of desperation but no effect.
I have checked and tightened, and sealed every hose I have.
The choke idle screw had been backed off and is out and the idle screw is pulled all the way back.
I tuned the rich /lean anticlockwise as far as visually max. It seems to spin without stop anticlockwise. But clockwise (rich) it has a stop.
What about the air pump – could it have any effect? Or the timing / dwell?
It revs even higher with the stock Air cleaner on, and with a custom it settle at about 3600.
It also wants to keep running after the key is off.
Anti Run on screw is set full stop.
This is a gremlin.
Thanks - Chris
ANSWER: Chris,
Check the timing. If it's off it can cause the idle to climb.
Still, if the plugs aren't sooted up it really sounds like a vacuum leak in the system.
Cheers,
Jim
---------- FOLLOW-UP ----------
QUESTION: I broke down the carb and the butterfly in the throttle body was not seating closed. The spit runs rich – a problem I can not solve either – and between the rich mixture and the stuck throttle body the spit was a runaway train. I am back to 900 rpm idle and am still very rich. But that wont kill me.
Thanks
Chris
ANSWER: Chris,
If you're having trouble getting the needle adjusted properly it's possible to swap in a new carb piston. Unlike the SUs the Stromberg doesn't rely on a close match between piston and cover.
If you are anywhere near Carlisle Pennsylvania this next weekend is the import swap meet. If not, keep an eye on the classifieds at www.vtr.org or www.nasshq.org. Or of course any of the Spitfire parts vendors can supply new pistons/needles.
Cheers,
Jim
---------- FOLLOW-UP ----------
QUESTION: If I loosen the set screw on piston holding in the needle can it be adjusted downward to allow a leaner fine adjustment with my 1/8 allen?
ANSWER: Yes, that's the proper process for adjusting mixture. One word of caution, there's a special tool for adjusting the needle, if you'll notice the top of the piston has two grooves cut into it across where the allen wrench goes? Stromberg had a special tool that would fit the slots with the allen wrench in the middle, it keeps the piston from spinning when you adjust the needle.
Otherwise you tear the diaphram.
The obvious workaround is to remove the piston completely from the carb body before adjusting.
Cheers,
Jim
---------- FOLLOW-UP ----------
QUESTION: Yes, that is how I have done it in the past. I pop out the 4 retaining screws on the top of the Stromberg, lift out the piston and work visually. I was happy to discover the diagram is keyed to I am sure of its replacement position.
However the allen adjusts to a stop moving right (clockwise -rich) but the left (anti clockwise - lean) it just spins forever. When the piston is out you can visually see the right adjustment raise the mixture needle. However, left after a couple of turns it just floats – or bobs (in a max lean position?). Is this normal?
If so, then my question is in regards to the needle where it is inserted into the piston and held in place. There is a small setscrew that holds the mixture needle into the piston. As I cannot lower the needle enough to effectively lean out the mixture – can the setscrew be loosened and the entire mixture needle and adjustment allen be lowered slightly to give me the bit more depth of needle I would need to adjust the mixture control by use of the center allen?
Thank you for being here. It is very kind for you to take the time to help like this.
AnswerChris,
Now you've got me wishing I had either my manuals or a spare carb sitting here at work....
If you look at the piston, as the needle moves "down" into the jet that's lean. I don't remember the Stromberg adjustment being left hand threaded, but it's been 15 years since I messed with one. I got tired of the problems and converted to a single 1.5" SU on my '73.
Cheers,
Jim
