TheSamba.com :: View topic

Tue Jan 11, 2022 4:47 pm

I have a 1766 I am trying to tune, it has a 120 Engle cam, 1.25:1 CB Rockers larger valves and the ports have been opened up quite a bit.

I have been trying to tune these with DUAL EMPI HPMX 40's but have been having quite a bit of trouble (mostly with the quality of these HPMX units) the butterflys on my Dual HPMX seem to stick and one of the carbs refuses to close all the way, despite my repeated adjustment, I am starting to lose hope with the HPMX and am tempted to purchase the CB Weber 40's as I have had good success with those in the past.

In regards to jetting, I have been trying to follow the standard 1600-1835 jetting guide that is referenced online. But from my understanding, the opened up top end on my engine would change the jetting requirements quite a bit.

So my questions are:
Recommended Jetting for 1766, 120, 1.25:1, ported on Dual IDF40's
Recommendation for other/better carbs to use, im open to everything.
Other ideas? EFI?

I would go to a single center-mount carb, but have heard a few bad things about Icing, especially as I don't have heat risers.

I live in NZ, so relatively warm climate, temperatures range from 2-32 Celsius and im very close to sea-level most of the time.

Thanks, Alex.

Tue Jan 11, 2022 4:50 pm

What does it have for an exhaust?

Any idea what the compression is? Deck Height?

Small engine, larger cam, big ports, and low compression is gonna be a pain to tune.

Brian

Tue Jan 11, 2022 4:56 pm

It has a EMPI Single Quiet Pack, running Stock heater boxes (yeah probably a-little restrictive for 1 and 3, I have some J-tubes I can swap too also.

Im unsure on deck height, 9:1 compression ratio from what ive been told. Im unsure on deck height exactly.

I purchased this engine which was built by someone else, I have checked it over, it runs fine, just cant get it running amazingly (again, hesitation with carbs, and one carb wont "close" completely, so struggling to balance with the snail tool)

Tue Jan 11, 2022 6:24 pm

What venturies and jets do you have now??
And did you try those first??

If one side is not closing your linkage is off, balance the carbs then set the linkage.

Tue Jan 11, 2022 7:59 pm

28mm Venturies

1.30 Main (I have 1.15, 1.4,1.5 and 1.6 available)
2.00 Air
F11 E/Tube
.52mm idle jet (I have .60mm available too
.50mm pump

Its not the linkage, it wont close properly (with or without) the linkage attached.

Another sign something isint right is I did a compression test with closed throttles, and the numbers were similar on 3 of the cylinders but one was way lower. Whereas at wide open, the test was the same on all 4 cyls.

What does everyone think of the CB Webers VS Empi HPMX?

Tue Jan 11, 2022 8:40 pm

Might help to post pics of what ‘closed’ looks like. Both butterfly closed and the throttle arm.

Tue Jan 11, 2022 8:49 pm

Do the throttles close correctly if you remove the linkage adapter from the throttle shafts? I had a similar issue bench setting carbs recently and it turned out that the linkage adapter plates weren't bent completely correctly causing them to bind when actually installed on the throttle shaft and tightened down. I had to re bend the angles a bit to clear the carb casting at the bore for the throttle shaft when bolted down.

Wed Jan 12, 2022 1:20 am

First.
Replace the exhaust system to a 1½" and use a muffler that will handle the power.
There are several how to´s on the Tube as to how to go through a set of Chinese IDF clones.
Do that and your jetting should be somewhat easier.

Wed Jan 12, 2022 7:43 am

Fix known problems first. You can't set up the carburetor if it isn't operating correctly.

Wed Jan 12, 2022 6:41 pm

Check to make sure the linkage arm on the carb is not hitting the intake manifold.

Also, improperly adjusted pushrods will hang a carb open like that.
You should have one rod loose and be able to spin it with your fingers to find the place where both carbs can sit on the idle speed screws.

Have you moved the left side adjusting screw to so you can see both and adjust both without having to reach behind the carb?
That's an important step many folks miss.