Carb Issues

[SaxMan]

To much timing advance can contribute to a higher idle.
Is the choke completely off?

Choke is fully off. Was thinking it may be a timing issue. I have a strobe gun, but I don't think they took into account that the timing marks are at the bottom of the engine and the battery was in the back of the compartment. Part of me wanted to take a shot at adjusting it by dead reckoning, but the other part decided that I might be opening a can of worms that way.

 

[dklawson]

For the timing marks, consider the tape kit made by Jeff S. at Advanced Distributors (link below).
https://advanceddistributors.mybisi.com/product/1275-midget-sprite-timing-tape-kit
You can always extend the leads on your timing light using jumper cables.

Always make all the ignition settings/adjustments before touching the mixture and going through carb adjustments.

If your timing is advanced it can certainly influence the idle speed. However, if you back the idle screws out all the way it still ought to slow down. I know you said the choke is released. However, make 100% sure that is correct.

On the assumption you are running twin SU HS2s, the two little arms on the choke linkage rod should both be loosened so they can slide on the rod. Look carefully at the linkage that lowers the jets (particularly if these are the flat metal linkage arms... as opposed to the ball/socket linkage on later HS4 carbs). The flat linkages can bind. When they bind, the jet does not return to its full height and that in turn makes the carbs behave like you are giving the car choke or throttle.

 

[SaxMan]

For the timing marks, consider the tape kit made by Jeff S. at Advanced Distributors (link below).
https://advanceddistributors.mybisi.com/product/1275-midget-sprite-timing-tape-kit
You can always extend the leads on your timing light using jumper cables.

Always make all the ignition settings/adjustments before touching the mixture and going through carb adjustments.

If your timing is advanced it can certainly influence the idle speed. However, if you back the idle screws out all the way it still ought to slow down. I know you said the choke is released. However, make 100% sure that is correct.

On the assumption you are running twin SU HS2s, the two little arms on the choke linkage rod should both be loosened so they can slide on the rod. Look carefully at the linkage that lowers the jets (particularly if these are the flat metal linkage arms... as opposed to the ball/socket linkage on later HS4 carbs). The flat linkages can bind. When they bind, the jet does not return to its full height and that in turn makes the carbs behave like you are giving the car choke or throttle.

Installed the kit. Needle is still there, but the sticker that went on the crankshaft pulley fell off -- poor preparation of the surface on my part.

The choke arms may be the issue -- when I replaced the jets, I tightened up the screws a fair amount. I will try that.

 

[dklawson]

I am posting some picture links below to illustrate the choke linkage parts that may be causing problems. None of these pictures are mine, I just found them on the web.

The first link below is to the linkage rods and arms themselves. Small arms bolt to the rods with pinch bolts so the two carbs can be set to respond in unison to the throttle or choke. When setting the mixture and the rough idle speed during the initial setup the pinch bolts on the choke linkage arms should be completely loose. In the picture linked below the arms are shown totally removed form the rod.
https://sucarb.co.uk/media/catalog/...e5fb8d27136e95/s/u/su_image-2997_original.jpg

In the next picture link a set of carbs is photographed from below. The "jet link" is shown attached to the bottom of the red jet. You will see there is a Phillips head screws attaching the Z bent sheet metal jet link to the red jet. The Z shaped link can get bent out of shape and create binding which holds the jet "down". That in turn can cause high idle speed. Likewise, the Phillips head screw should be left slightly loose so the Z bent sheet metal link can pivot freely on the screw.
https://ccts-inc.com/SPITFIRE/DSC04418.JPG

The final picture link shows the rod shaped jet link that replaced the sheet metal part on later carbs. To the best of my knowledge these rod jet links were used on all carbs with Waxstat jets (left carb in the picture link) but as shown in the picture they were also used on some carbs with "traditional" jets (right carb in the picture link). The rod type jet link is much less likely to bind than the Z bent sheet metal part.
https://farm6.static.flickr.com/5251/5489810839_a7f7c91cd3_b.jpg

 

[SaxMan]

Thanks for the pics, Doug. My gut is that it's the Phillips head screw, as I cranked them down when I put the new jets back in. Only issue I have now is we're going through a stretch of rainy weather over the next couple days in Maryland for me to try it out.

 

[SaxMan]

A surprising break in the weather allowed me to take Baby Blue out today. No change from before. Still idling around 1300 - 1500. The one odd thing is that when idling, when I depress the clutch, the revs dip 100 - 200 rpms. I'm thinking that's a vacuum issue?

Otherwise, the car continues to run well. First "real" tank of gas this season yielded around 28 mpg, which is pretty much where I was when I put the car away. Engine runs nice up to 4500 rpm. As before, past 4500, I tend to get more noise than speed increases, and with the motor going sour, I'm really reluctant to push it past 4500. I discovered my daughter likes the feeling when the car on the higher part of the torque curve and really feels like it's pulling.

 

[dklawson]

A drop in RPM when pushing in the clutch while idling is not necessarily vacuum related. More likely, you have drag on the thrust bearings. Keep your eye on it.

 

[Bayless]

Also may be worthwhile to check the crankshaft end float.

 

[SaxMan]

When I get back from a drive, I have to idle for a moment while the garage door opens. This is the mark that is left on the ground after I pull in. This one was after 17 miles of driving on an 82 degree day:
Soot by David Cohen, on Flickr

The soot from the exhaust would lead me to believe the carbs are set rich. But when I am driving and decelerating in gear, I still get some random backfire pops in the exhaust, which would be indicating that the carbs are lean. Thoughts?

 

[JPSmit]

I am going with too rich. From the spot marking.

Ms Triss pops all the time when I decelerate - especially as I still have some of last year's gas in the tank.

If it is too lean, the popping is in the top of the engine (pre ignition) not the exhaust - you can hear the difference it really does come from the front of the car not the back.

 

[dklawson]

But when I am driving and decelerating in gear, I still get some random backfire pops in the exhaust, which would be indicating that the carbs are lean. Thoughts?

Actually not. When you get backfires on deceleration, that typically indicates an air leak into the exhaust and a rich mixture. Backfires out the carb when trying to rev are signs of a lean mixture. Set your mixture a bit leaner, look for open joints on the exhaust, and drive the car a bit more.

 

[SaxMan]

Actually not. When you get backfires on deceleration, that typically indicates an air leak into the exhaust and a rich mixture. Backfires out the carb when trying to rev are signs of a lean mixture. Set your mixture a bit leaner, look for open joints on the exhaust, and drive the car a bit more.

Got it. Any thoughts on how many flats to back off? I was thinking 2 to 4 for starters?

 

[dklawson]

I am not good at guessing carb settings or needle selections. Assuming your needles are close to correct, I would use the lifting pin method to get the mixture close.

 

[SaxMan]

Finally had a chance to get the car back out again. I ended up leaning out the mixture considerably. Engine still runs up to 4500 rpms smoothly and the idle is now back down between 900 to 1100 rpms. Idle is still a bit uneven, but not bothersome.

I also discovered how well the brakes work when a pickup truck backed out of its driveway right in front of me. I sort of expected his move, so I was already slowing down. I take the motorcycle philosophy of assuming you are invisible to everyone, and in this case, apparently I was. I kicked the brakes hard enough to send everything in the car flying. It didn't feel like I locked the wheels, but there was enough tire screech to scare the **** out of the pickup truck driver. Once my adrenaline settled down, I was pleasantly surprised at how fast the manual brakes brought the car to a stop.

 

[SaxMan]

Much warmer weather seems to have helped in slowing down the idle. There was one rather unexpected side effect to the carb issues: As many of you know, my daughter Jessica is autistic-non verbal, and she is often prone to making various verbalizations, the most typical one being "You-ee you-ee" and various derivations of that like "Uh You". Lately she was making a new verbalization "Boomp" and my wife and I were scratching our heads where this came from. Sometimes Jessica pics up other verbalizations from her classmates, but none of them made this sound. I found the answer one afternoon when I took her out in the Sprite and was decelerating in 3rd gear, which triggered a couple of exhaust backfires. Sure enough, when the car's exhaust starting popping, Jessica chimed in with her "Boomp" verbalization.

 

[SD Bugeye]

You may want to replace plugs
judging by that soot on the concreate
they may be fouled
at the very least pop i out and take a peek

 

[Jim_Gruber]

I believe your car is a '69. My buddy's, bought new '68 Sprite, had those same issues when the Gulp Valve aka PCV Valve malfunctioned. You may want to change out that diaphragm on the Flying Saucer PCV Valve. And or check that there aren't any leaks there.

 

[SaxMan]

Just put new plugs in over the winter. PCV valve is long gone. Someone put a plug on the line. I still have the oil breather. I was told I have air entering the exhaust which is causing the popping, and given the cars compression numbers, it's probably coming in past the rings.

 

[SD Bugeye]

Leaving a spot mark like that just saying they may now be fouled

 

[SaxMan]

I pulled all four plugs and they were fouled to varying degrees. 1, 3 and 4 all had black soot on them, with #1 cylinder being the worst, that's consistent with the rich condition. Cylinder #2 had white ashy deposits, indicating it was lean. I'm really not sure how that is possible. Could that be a valve adjustment issue?