SU Carbs - I Can't Win

[Curtis]

The engine would rev on up with the old carbs after I changed out all the ignition parts. It was obvious though that the throttle shafts were worn and it just wouldn't idle decent. Idles well with the new carbs. Just has the flat spot mid range.

Engine has been port matched at the manifold and has a mild cam.

I'll get it, eventually...

[greydog]

Im sure you will Curtis.
Ill bet that once you establish a solid baseline you be able to get it sorted out.

Sounds like it outta be a strong runner once you have it dialed.
Dan

[Curtis]

Im sure you will Curtis.
Ill bet that once you establish a solid baseline you be able to get it sorted out.

Sounds like it outta be a strong runner once you have it dialed.
Dan

It goes.

[Linda]

The Colortune is another tool you might like.
Linda

[Curtis]

The Colortune is another tool you might like.
Linda

I have one.

[Linda]

And ...more to fiddle with, Tom's latest mod, might want to experiment on a spare set:
viewtopic.php?f=3&t=30765#p282393
Linda

[Curtis]

And ...more to fiddle with, Tom's latest mod, might want to experiment on a spare set:
viewtopic.php?f=3&t=30765#p282393
Linda

Oh no, no messing with them. I'll just put the single throat 45 webers on I have.

[Linda]

So, don't you have to fiddle around with Webers too? I know nothing about Webers or Solexes.
Linda

[Curtis]

So, don't you have to fiddle around with We ers too? I know nothing about Webers or Solexes.
Linda

I suppose, but one of the guys on here bolted these on his stroker, adjusted them a bit and off he went.

[JT68]

Webers are exactly like Mikuni, Solex, Delortos, Holley etc, . Dialing them in properly is exactly the same level of complexity. Any can have flat/weak spots, rich/lean idle issues, require accelerator pump calibration, jet changes etc. O2sensors/dynos/EGA's are all very helpful. There is no magic carburetor.

[Curtis]

Webers are exactly like Mikuni, Solex, Delortos, Holley etc, . Dialing them in properly is exactly the same level of complexity. Any can have flat/weak spots, rich/lean idle issues, require accelerator pump calibration, jet changes etc. O2sensors/dynos/EGA's are all very helpful. There is no magic carburetor.

These are a one off type weber that apparently have little in the way of adjustment. They are sold as a replacement carb for Triumphs and such. Maybe you can tell.

[nismou20]

Those are interesting Webers. 38 mm ? Like the R engines?

[Curtis]

Those are interesting Webers. 38 mm ? Like the R engines?

45's

[keith0alan]

Curtis,

Try this. Attach a service tach if your tach is not very good. Set the engine speed to 2000RPM and verify that the carb air flow is balanced. If not, then sort that out. Adjust the mixture knob on the bottom of each carb to maximize the RPM. You can also lift the slide a little. The RPM should drop off if you either pick up or push down the slide. Once the carb mixture is adjusted at 2000RPM then drop the engine speed back to idle. Check the air flow balance at idle. Fix if not balanced. Double check the 2000RPM balance. At idle raise the slides just a little. If the engine speed picks up then you are rich at idle. Do not fix this by adjusting the mixture knob as you will mess up the 2000RPM mixture. To adjust the idle mixture you can move the metering needles out a few thousanths of an inch. Loosen the needle grub screw and slide the needle out a little bit. Lay a feeler gauge on the face of the piston and use a straight edge to push the shoulder of the needle flush with the feeler gauge. Try .010" to start. Reassemble and verify that the 2000RPM mixture is still good(it should be). Then go back to idle and check the mixture again. A couple trys and you should get the 2000RPM and idle mixture both good. Once the mixture is sorted then go for a drive. If it stumbles on acceleration you need thicker carb oil. Stock is about 10w but I have had to go to 30wt. You want the thinnest oil that stops stumbling on acceleration. If at cruise you have a stumble then one or both of the carbs are lean. richen both about 1/4 turn. Check the spark plugs. If 1-2 or 3-4 are black then that carb is rich. Lean that carb by 1/4 turn.

After all this the carb adjustment should be pretty close. I would expect that the ADQ needles will work better than Nissan needles.

[Curtis]

I ordered a tach I can use since the one in the car is crap.