Carb Issues

[SaxMan]

Oops. After pulling the plugs, I never reconnected the #4 spark plug wire. Amazingly the car started and ran on 3 cylinders. I kept thinking "Boy, she is sure running rough today" as I hadn't started the car in two weeks. But I kept hearing an electrical arcing sound, so I thought "I better check this out before I get on my way". And, lo and behold, the #4 wire was disconnected. The engine ran much better on 4 cylinders. Still have the backfires on deceleration. I'm going to re-check my valve adjustments. At this point, with the motor coming out at the end of the year, I'd just as soon enjoy the car as much as possible and deal with the issues.

 

[SaxMan]

I never quite got the carbs to where I wanted them, but I figured I was close enough that I could take the car out and enjoy it. While these carb issues were going on, I picked up a second set of SUs off eBay for a fairly reasonable price. One of the chambers had a broken off screw that was jammed in that I had to drill out. These SUs came out of a '73 Midget. I decided to clean them up and prepare to swap them with the existing SUs to see if there would be a difference. One thing I noticed, though, is that there are additional lines that attach to the float chamber lids that are not on the '69 carbs. I'm assuming that these are probably emissions related? I figured if I just cap them off, things should be okay?

I've decided to put off the engine rebuild for now. It seems that I'm dropping more oil than I'm actually burning, and my compression numbers aren't terrible. Also, trying to get the '53 Plymouth up and running is eating into my LBC budget.

 

[SaxMan]

Here's a bit of an illustration of my issue. The new carbs are AUD 871, which doesn't even show up on the VB catalog. They go up to AUD 549. I believe my stock ones are AUD 404.

Front carb -- so far so good. One line in, one line out. However, the nipple for the vacuum line from the distributor is not present.
DSC_0079 by David Cohen, on Flickr

Rear carb -- What the? One line in...but what are the other two lines?
DSC_0080 by David Cohen, on Flickr

Meanwhile - this is what is in the car already. Front carb - one line in, one line out and the vacuum line provision near the damper.
DSC_0081 by David Cohen, on Flickr

Rear carb - one line in and that's it.
DSC_0084 by David Cohen, on Flickr

I suppose I could use the float chamber lids off the old carbs, but then I still don't have a provision for the vacuum line. At this point, I just want to A / B the carbs to see if that's where my problem lies.

 

[nomad]

You've got a rear float cover that should be a front float cover. The spare tube is to hook up with a drain tube. Don't consider plugging it since your float chamber needs to be vented. Appears the seller had done some mixing of components

 

[Rut]

You've got a rear float cover that should be a front float cover. The spare tube is to hook up with a drain tube. Don't consider plugging it since your float chamber needs to be vented. Appears the seller had done some mixing of components

Yep, caps are reversed and the extra ports can go to an overflow pipe or to a carbon canister to capture vapors. The port for the dizzy missing is the biggest issue, but even that can be fixed. I’ve got a set soaking in a can of Berrymans while I type this and I’m looking forward to the rebuild...fun project.
Rut

 

[nomad]

No clue what these were used with but having no take off for the vacuum advance would make me think these were meant to be used with a non vac advance distributor. I have a set like this in my parts pile that I just took off my daily driver. The throttle shafts have been narrowed for better flow and it appears to have extra thin throttle plates. Got them in a big parts purchase and would sure like to know their history. Took them off so that I could re-hook the crankcase ventilation system up.

Kurt

 

[drooartz]

There are also setups that pull vacuum directly off the manifold instead of the carbs. Requires a different distributor setup.

 

[SaxMan]

These carbs were definitely off a Spridget, as I have the heat shield, the intake manifold, linkage and a few other pieces that definitely match up. Front and rear lids being mixed up makes sense. I may still try these carbs just to see if there is an appreciable difference, and if there is, try to figure out where the difference lies.

 

[nomad]

I had a 10CC engine swapped into a bug eye that had a non advance dizzy. I think a 23D or something like that. It was missing the ported vacuum take off. When i ran the carbs I mentioned in my last post I ran them with a vac take off on the manifold. Idles much nicer now with the later carb's. Those should work for what you are looking for, David.

Kurt.

 

[SD Bugeye]

JMO
ported vacuume was for emissions on another car I have
crappy cam low compression you get the picture
I think you can make manifold vacuume work

 

[SaxMan]

My car was converted to Pertronix. I'm wondering if there was even a need for the vacuum advance? From what I recall the vacuum line was actually disconnected when I first bought the car. I don't know if that was an accident or by design.

 

[nomad]

Without vac advance fuel mileage suffers and if your car doesn't have the correct advance mechanism I think performance could suffer as well. The ported vac advance is really only effective at idle to give you a smoother one. At all other speeds connecting the vac advance to the manifold does the same as ported does. If your car has a newer Oriental made Pertronix distributor there is a good chance your vac advance doesn't work anyway. Try sucking on the tube and see if there is a hint of the diaphragm moving.

Kurt.

 

[SaxMan]

It would certainly explain the idle issues. I have the second set of carbs cleaned up and ready to install. Just need to find a day where I can slap them on and tweak on them for a bit. I may go back to the factory choke cable while I'm poking around, since the friction lock on the replacement gave up the ghost, and the replacement VB unit looks and feels like a cheaply made part. If I'm going to have to stick something behind the knob to hold the choke open, might as well use the original unit.

 

[SaxMan]

One of the pieces of advice I impart on younger musicians on how to troubleshoot when their gear is giving them problems is "Usually the obvious problem is the correct one". I should have followed my own advice when it came to the carb issues.

I put the new set of carbs on and fired up the Sprite. It immediately took off to 3500 rpm without choke. I stopped it and backed off the idle screws -- no change. As I'm looking I notice the throttle linkage is bumping up against the heat shield. When I adjust it, the idle comes down, but it's clear the Sprite really isn't very happy with these carbs. I swap back the old carbs and look at how I set up the linkage -- same problem. When I made the adjustments and fired the car up, it came to life at 1500 rpm with the choke engaged, numbers I haven't seen in a while.

I'm kicking myself a bit, but there was one positive that came out from it. By capping off the vacuum line from the distributor, which apparently was inoperative anyway, it closed up the source of my vacuum leak. Even dead cold, the Sprite was idling baby butt smooth. Now I just need to do some fine tuning to get it really dialed in.

 

[Bayless]

I love it when a plan comes together.

 

[SaxMan]

Continuing work on the car, my cold compression numbers actually improved from last winter 160 / 150 / 150 / 165. I'm guessing that means that I did a better job adjusting the valves. Leakdown testing yielded consistent results across all four cylinders, around 50% which is high moderate. There's no doubt the motor is getting tired, but it seems like it has more life in it than I thought. I suspected that I've been leaking more oil than burning, and the results of the tests tonight seem to confirm that.

 

[nomad]

Nothing wrong with those compression numbers. I think it would be good for quite a while before needing work.

Kurt.

 

[SaxMan]

After all that, on the first nice day, I ended up with a dead battery. Battery had been with the car at least 7 years, so it was time. It took me a few minutes to figure out how to get the battery out. At first I just had the hood open with the prop rod, and I could not get that battery out. I began to think I needed to take the hood off. Then it hit me that the hood can come open further than just the prop rod. Using a large piece of wood that I had previously employed on the '53 Plymouth, I made B.B. "Open wide and say aaaah". Battery came out.

New battery in, and it fired up. Couldn't believe how fast the starter motor was actually turning with a fresh battery. Now, I just need some decent weather!

 

[SaxMan]

Found this old thread. I did my spring carb tuning, and think I finally nailed the mixture and synchronization adjustments. It only took almost 10 years to get it right, lol. Really happy with the way the motor is behaving this spring. Baby Blue still likes idling at around 1200 rpm, even with the idle screws completely backed off. I could lower the idle by really leaning out the mixture, but I think that would be the greater of the two evils.