Amazon: '67 P220 SU adjustment

[gjr0]

Made a little progress today. The engine will complacently idle at 800 rpm while I adjust the carbs. It will idle like that for 10 minutes or more. When I take it for a run up the highway, it idles at 1600 rpm, down from 2500 this morning.

The needle in the front carb is a DX. I suspect that the rear will be the same. The front jet has a yellow band and the rear is red.

I snugged up all the manifold and carb mounting bolts. Spraying carb cleaner on all the gaskets made no difference in the idle speed.

The front jet is 24 flats out but the rear came up a little. It is at about 18. Should I be concerned with them being the same if I get ~50 rpm rise on both carbs when I push up the pin. The rear carb has a slightly lower fuel level at the jet.

Both carbs exhale a fuel mist when I blip the throttle. Should I be adjusting them with the air filters (stock look alikes) installed ?

What is your opinion on using a lubricant like Tri-Flow on the throttle spindles and the jets ?

[Rustinmotion]

I would check the float levels then start from scratch
Disconnect the linkage so each carb is independent
Using a proper carb balancer make sure both are flowing the same amount
Wind both jets in until top is flush with the bridge then back out 12 flats
Do the piston lift test and adjust both carb’s exactly the same
Check the balance
Once your at the point lifting the piston raises the revs then drops back your close, you can try adjusting the jets individually to see if half a flat either way gives smoother idling
Check the balance again

I can say from experience it’s easy to get way out with one carb doing more of the work a proper balancer and a rev counter you can see from the engine bay are worth having
An AfR meter is better but more expensive

[Ron Kwas]

Greg;

High idle after a speed-run suggests linkages are not returning to the idle location...I'd assure all linkages and return springs are well lubed and free to move unimpeded...besides being properly adjusted...!

DX Metering Needle is OK, just be certain it is installed correctly, with shoulder flush with Daspot bottom surface.

Source: https://www.sw-em.com/SU%20Carb%20Service.htm

OK on checking for False Air leaks, but if there were any, you'd likely not be able to bring down idle under any condition...

If it takes four full turns down on the Jet as a baseline, something is very different (wrong?) from the typical nominal adjustment! ...I agree with RiM to check and assure fuel level...also check to assure Jet supply line is not clogged or somehow occluded or fitting at bottom of Fuel Bowl has an issue (such as squished, partially restricting flow)...also verify there is no excessive silt/rust particles in the Fuel Bowl Sumps or even in the Jet Supply Line which is limiting fuel flow (this had me stumped once also...remedied by blasting carb cleaner with a snoozle, back through the Jet!)...See alsu: https://www.sw-em.com/su_carbs.htm#I...et_Replacement

As another thought, assure you have the correct Dashpot Return Spring...it should be Red (if color is ascertainable) otherwise someone can measure and post springwire gauge and freestanding length...SUs are highly configurable and different springs were available for service in different displacement engines, so you must have the correct one installed for our 1.8/2.0L engines.

"carbs exhale a fuel mist when I blip the throttle"...this is called "Reversion"...it is a common effect, (only) during sudden Throttle opening on our SUs...well-known (especially also on DCOE sidedraught Webers! See: https://www.youtube.com/watch?v=Vw1ihxlCIzI ), but nothing to worry about, unless excessive (or you ignite that flammable fuel/air mixture!!!), indicating a Cam/Valve timing issue...carb adjustment is done with Air Filters removed for better access and so you can view relative positions of Dashpots of both carbs...they should be fairly similar in position at all operating conditions (idle, blip, etc), but I always say: Don't make yourself crazy try to get them absolutely identical! Because you will surely make yourself crazy before you get them identical!

I don't so much think that a balancing tool is an absolutely necessary thing when the comparative heights of the Dashpots are right there in plain view when Filters are not in place...in fact, that is what the "bent wire" indicators are based on, except these allow Air Filters to be left in-place...but to use them, Dashpot Dampers are not in place, so Dashpot action when blipping Throttle cannot be checked as there is no damping and enrichment.

I love Tri-Flow where a light lube is called for (see: https://www.sw-em.com/Product%20Reviews.htm#Tri_Flow )...sure you could use it on your SUs and associate linkages, and it will work well, but given elevated engine compartment temps, which will cook it away in not so long a time, so it will need reapplication, I'd prefer a light grease, or even a graphite filled grease, which stick around a lot longer, not to mention the graphite particulates...

...but those 24 flats are still bothersome to me...that would be the first priority to sort for me...

Good Hunting

[Derek UK]

As I said previously I think the nut would have come off the threads before it got to 24 flats. I'll check on a spare SU when I go to the garage next.

Beware if you have to remove a needle. They are often stuck and that makes them easy to bend.

[gjr0]

Last first. The nut did not come off, which I am grateful for, but it is out a long way. The piston return springs do have red markings. The Carb-Tune Model 1A showed that the throttle adjustment screw was off by maybe 1/8 turn on the back carb.

Some guys on the MGA board don't think that the fuel level is absolutely critical in SUs. The problem is that these carbs (originally from a 140 ?) have plastic floats and there are no washers under the seat for the float needles. I could add another gasket under the float bowl cover, but if close enough is good enough, two gaskets doesn't sound like a great idea.

Messing around with the Carb-Tune I was able to keep the carbs in sync (two wrongs maybe) and screw the jets in closer to 12 flats out. As I said before i can get a decent idle sitting in the yard. I'll have to see how it acts once I get it out and run it.

It was my turn to cook tonight so I didn't have a lot of time to fiddle with it. That will have to wait for the weekend. Sunday is supposed to be rainy. I'm leaning towards Ron's idea of something restricting the flow in one or both of the jets.

If you have any more ideas about why the idle is temperature sensitive, please let me know. I'll follow up on them this weekend.
Greg

A bit of back story - My daily driver was an '07 S40. It swallowed a valve in the middle of nowhere Ohio. We were on vacation and I only paid $200 for the car so we abandoned it, rented a car and kept going. When we got home, the '67 went from a project to a daily driver.

It has been good. Now I have a comprehensive list of what needs fixing. I mean, they are never going to be reliable cars until you work through all the problems, right ?

[Derek UK]

A side comment. If Joe Curto rebushed the carbs, did he also refit the shafts, new ones I hope, and the butterflies? Although the fixing screws should centralise the butterflies it can be that they end up a fraction off centre of the choke. This might cause one or both to jam slightly open when the carbs get hot and so increase the idle speed. Also make sure the central zig zag connector clamp is gripping the shafts properly.

[Ron Kwas]

Greg;

...to add to Derek's comment...we will presume Joe Curto et al, knowing their business, installed the correct late Throttle Plates, and correctly, but a well-lit view down the carbs, with Dashpots lifted to allow this, and some manipulation of the linkage would confirm they close precisely:

Source: https://www.sw-em.com/SU_Carb_Thrott...ly_vs_Late.htm
...although it might be difficult to explain how these are affected by temperature...

...also..."...these carbs [are] (originally from a 140..." ...so if JC et al replaced them with the identical original Throttles, these carbs (may) have Throttle Overrun Valves (seen here with the characteristic solder blob):

Source: https://www.sw-em.com/SU_Carb_Thrott..._Overrun_Valve

...and if one or both of these are dislodged, and/or sticking open (partially or more, including intermittently), which has been known to happen, it would certainly also result in an elevated idle...

I've even seen a Throttle with completely missing TOV. leaving a gaping hole (and idle impossible to get below around 2000!)...it was presumably dislodged by a backfire, and later consumed by the engine...that continuous elevated idle was a trick to find (but obvious after the first glance at the holed Throttle!)...remedied by soldering closed the unwanted aperture.

Good Hunting!

[gjr0]

As a quick check, after running errands to get the idle up, the throttle shafts have a little end play ( forward and back in relation o the axis of the car). I'll have a deeper look tomorrow.

[gjr0]

I didn't get as far as I would have liked today. I planned to replace the relatively new but leaky clutch slave cylinder. I had the old one resleeved and installed a rebuild kit. The pushrod between the cylinder and the yoke fell apart when I removed the cylinder. Of course I didn't have a 5/16 fine thread bolt that was 5" long so I had to run to town...

It is really hard to tell the angle on the edge of the throttle plates by looking at them from the inlet side of the carbs. They are new and do not have a 140 style valve. I don't think that they are sticking.

I checked for blockage in the jets, set the jets down 12 flats, etc. Took the car for a drive and had the same elevated idle. So I resorted to reading the manual.

Volvo says 1 1/2 turns down and keep going until the maximum rpm is reached, then one more flat. Another says 2 1/2 turns and adjust the jets up until maximum rpm is reached and then keep going up until the rpms just start to drop. They both say lifting the pin will cause the rpms to drop. 100-150 rpm in one book and 150 -250 rpm in the other.

The Idiot's Guide (by Herb Adler) says start with 2 turns down and lifting the pin should cause the rpms to momentarily rise and then go back to where they were. Burlen says 1 1/2 turns out, adjust jets for max rpm. Lifting the pin causes a slight rpm rise when the mixture is correct.

What do you do ?

[Rustinmotion]

This guide is straightforward to follow the 12 flats should get you in the ballpark
Then adjust both jets in or out to achieve best RPM then do the piston lift to fine tune individual carbs, as long as both carbs are sucking same amount there should not be a significant difference in jet adjustment

Could the mild street cam be causing this? What’s lift and duration? How much overlap?