I was up until 12:15 last night building a "new" set of two-bolt SUs out of parts and jets that I have on hand. The jets and pistons springs are matched pairs as were the carb bodies. The KN needles were brand-new. It took a while to get the jets centered, but it went relatively fast otherwise.

I went with a two-bolt pair because the forward carb has a small vacuum port for use with a vacuum-controlled Dizzy (like my BL33). I have it capped right now and I did test it with a vacuum gauge later.

So, this morning I removed the 68's 3-bolt carbs and installed the 2-bolt carbs. I was immediately faced with significant fuel pouring from the reservoir/jet connections and this took some time to get that correctly sealed up.

Now I know what that sort of problem looks like... scary. The 68 was not previously leaking fuel there. That's for sure.

Anyway, I got the repaired two-bolt carbs on and ran the motor for some time to warm it up. I tried to get them both down to baseline, but found that even using a "Unisyn" it was a chore. The engine was rocking quite a bit when I finally got the mixture and vacuum in sync.


I followed Cam's directions carefully - adjusting the flats as suggested. I think I got these new carbs pretty straight. The mixture is quite a bit "leaner" than when I had the 3-bolt SUs on there, but I'm not so sure about the engine rocking. I'm also not sure if I got the idle down to the grumpy idle that was described. The idle did definitely slow as I leaned it out, but it did seem to plateau after a bit. I was pretty close to the top.

I've had the issue (recurring with most of my carbs) that the one will adjust just fine, but the other usually runs high, even when the throttle screw is all the way out (touching nothing). I've never been able to figure that out.

I took to car for a drive and found that I had plenty of power, but it hesitates somewhat suggesting that it is still not quite right. I strongly suspect that the system is out of sync even after using the unisyn and checking individual mix with the lift pin. It also has this behavior when I rev the engine while tunning. I'm not sure what to do for that.

I also hear some faint pops in the exhaust noise, even when idling. Maybe still too lean... seems different than my other experiences...

I did re-check my timing after adjustments and re-adjusted it after I got the carbs tuned for a test-drive.

This has also been a chore since the cart's Smith Tach ceased to read correctly some time back. I have to sorta go by idle sound and memory of what 900 rpms sounded like. My tach only reads up to about 1500 even at full throttle. It also drops down to almost 0 when the car idles. This makes is hard to really do this right. I have a small 240-gauge on it's way and that should help.

So if any of you can tell me what's probably going on with the engine shaking and the hesitation at initial acceleration, please let me know.

Thanks.

Oh yeah, the 68's 3-bolt carbs had KN needles, but at least one was showing some wear/damage. This was probably a contributor to my problems, but does not seem like enough to explain it all.

you are likely burning that gas up due to improper carburettor settings. Timing could do it too, but I doubt it could have that much affect if the car is otherwise running OK. If it were leaking, you'd have smelled it, and/or burned your car to a crisp by now.

Only leakage that I can fathom that you might not smell...

Please remind again what carbs and airfilter setup you are using.

If you're using a later type black box (140 type) air cleaner assembley with the float vents tubed into that black box... then a float overflow situation would end up in the box. I've seen that on HIF6 carb setup on my '71 a time or two. Even there though... the likelyhood of running a gallon of gas through that box every 10 miles is slim to none...

You need to adjust them carbs. simple as that. A tiny adjustment in the rich/lean can make a huge difference.

A gallon every 10 miles..from a leak...., you'd smell it. Oh yes. You would most definitely smell it.

And get a fire extinguisher and keep it handy.. to be safe.

Take it to a shop and have them do an emmission test... I think you'll find your car pegging the meters.



--
-Matt I ♥ my ♂

Jack,
Put a timing light on your engine and see if it advances when you speed it up.
Should start from around 20 and go to around 35°.

Make sure your float level is not too high. If it is, it will suck a LOT more
gas at speed than at idle.

And do NOT try to estimate mileage by using the gas gauge. Fill it up, run it
until it is low, then see how much it took to fill it again and check the miles.

These comments are in addition to what the other guys posted.

Unless your trips average half a mile or less, you should be getting over 20 mpg. I have gotten over 30 on long trips in a wagon with no stops, and it was
a big-bore engine.
--
George Downs, Bartlesville, Heart of the USA!

personally, I've had fuel leaks in the following places:

1. By far the most common, in my experience, is from the overflow vent at the top of the float chambers on both carburetors. this has happened on both B20's I've owned. It's a very common problem with SU's and is well documented on this board and elsewhere. It is especially common on engines that have sat for a while. In my experience, I've always been able to smell the gas leak as I drive down the road, and I've been able to watch it happening by watching the running engine with the hood up. If you haven't already- run your engine, and while carefully inspecting the carbs, rev the engine at different speeds, manually moving the throttle linkage. The leak might only occur in a specific RPM range because of the dynamics between spring-dependent (variable) fuel pressure, and different levels of fuel demand being placed on the float assemblies. There are many simple ways of troubleshooting this, but sometimes a persistent leak will require new float valves.


2. I recently discovered that the original short flexible section of fuel line that connects the hard line to the fuel pump was leaking. It was the original, which is rubber with a fabric sheath around it. The sheath masked the fact that it was leaking and I believe I've been living with the condition for some time. It's interesting that it was on the non-pressurized side of the fuel circuit- before the pump. Also, it was a pulsing leak. I suspect that the pump would draw fuel from downstream, and at the moment the pump stopped "pulling" the inertia of fuel moving down the line was enough to force small amounts of fuel through the cracks in the 40 year old hose.


3. I had a fuel pump develop a leaky diaphragm. Fuel was spraying out the relief hole that's designed into the side of it. Again, this was detected by smelling raw gas whilst driving down the road.

My '67 220 had a leaking rear jet. There was absolutely no question where the fuel was going - you could smell it from feet away when the car was parked and from within the car when running. However, you couldn't really see a leak since it was dripping right down on the exhaust manifold.

I can't imagine that you're leaking that much fuel without smelling it.

There's a vent hole in the float chamber cap--directly under the tube. Fuel can spill out there if the needle valve gets overwhelmed (what kind of fuel pump do you have--SU's don't need much pressure) or stuck open (not likely given the otherwise good running). Leaks at the tube connecting to the jet would just plain leak and you'd know it. Could there be something other than motor related--dragging calipers or overtight rear shoes? Ignition timing (not enough advance at speed--the mechanical advance can get gummed up and not work). Pop the distributor cap and twist the rotor counterclockwise -- it should move a noticeable amount and then spring back when released.