I Need Some Carb Jet Recomendations Please

[240260280z]

3/4 turn iS for old webers. sk/oer is ~2 turns.... same as newer webers.

Edited April 18, 2015 by Blue

[240260280z]

Looks like you are getting closer...keep going!

[grannyknot]

That's good news, maybe I should stop trying to fix what is already working.

[240260280z]

Below 13 is "too stinky"

[grannyknot]

April 19th  I turned the mixture screws back out to where they were last year, 1.5 turns.

I soldered up the 55F8 idle jets and re drilled to 45, undrivable!, way too lean, then drilled them out to

50, driveable but lots of lean pops on slow acceleration and light cruise on a flat was between 14-17 AFR

So today I drilled the idle jets again back to the 55 they were before and no surprise I'm back to 11-12 light cruise on a flat.

It seems impossible that .05 mm would make such a big difference in AFR, but I'm starting to think the mixture screws are playing a part in this that I don't understand yet. The fact is I just don't know how to adjust the mixture screws properly, I have read all the tutorials saying turn them until you find the fastest idle but turning one screw at a time doesn't make that much difference and really, for me it's just sort of guessing.

There has to be some other way to verify that the mixture screw is where it should be other than just by ear?

Chris

Edited April 28, 2015 by grannyknot

[240260280z]

Great exploratory work!

 

When you look a weber idle jet you will note the number and size of air holes and the size of the cavity where the air and fuel mixes/exits vary.

 

Later idle jets have a new 3mm mixing cavity/exit added. I'm not sure what the larger cavity effect is but it is something I wanted to explore.  I have a feeling Weber changed all later jets to 3mm for a reason.

 

You now have 55F8's  running rich at cruise so there are two more areas to tweak:

 

1. You may want to drill out the single 1.2mm air hole on the side of the jet to ~1.5mm first. Then, if needed, drill to  ~1.7mm to lean the cruise.

 

2. You may want to enlarge the mixing cavity to 3mm to see what happens (very exploratory).

 

 

Finally, since the mixed fuel and air out of the idle jet has an awkward trip through the holder, then through passages , then through the progression holes and around the idle enrichment valve, it is difficult to imagine non-orifice changes in the jet will make a big differences when the fuel eventually reaches the manifold.  Changes to the holder (with 4 holes) are also worth exploring.... drilling 8 holes or enlarging the existing 4 holes are possible exploratory items. 

 

 

 

 

 

Edited April 29, 2015 by Blue

[grannyknot]

I measured the side air hole on the F8 idle jets and they were all 1.1mm, it is suppose to be 1.2.

Anyway, I drilled those out to 1.5mm and the idleing at 900rpm is was great at 13.5AFR but light cruise was 15-17 so soldered them up and went down to 1.3mm and the readings were very similar to 1.5.

I realized later, after going back to 1.1mm air holes that the air temp was cooler the day I tried 1.3 so that is where I'll probably end up.

 

So, at the moment, MJ 135, ACJ 210, Idle jet 55F8 with 1.1mm air hole

Idle at 900rpm is 11.5-12.5AFR

WOT 9-12AFR and FANTASTIC

Light cruise 10.5-11.5 but with a little more throttle it comes up to 13.5-14 AFR

for example, 55mph, 2500rpm in 5th gear is 10.5-11.5 AFR but add a bit of gas bringing the rpm up to 2600-2700 and the AFR goes to 13.5-14. I can't figure this last bit out at all.

[240260280z]

Glad the air hole exploration helped a bit in understanding the interactions.

 

I have a theory that small chokes (thick) come in proximity of the partially opened throttle valve causing a venturi effect in that region (also where the accelerator pump sticks out) and pull fuel from the accelerator circuit.  You may wish to close the 3 spill jets with bolts to see if the cruise will be tamed.

 

You could also try lowering the fuel level to lower the rich cruise then address the jets.

[grannyknot]

"3 spill jets" do you mean the 3 progression holes? Those would be tiny bolts.

Or maybe you mean the port in the middle of the Aux venturi?

[240260280z]

The fuel outlets at the bottom of the fuel bowl that feed the accelerator circuit. You have to go fishing to get them our. Just replace with bolts and the accelerator circuit is taken out of the picture.

[grannyknot]

Gottcha, yes, I have those bolts put aside and ready for that test. For anyone following along those are

M6x1.0

But if I determine the accelerator circuit is the culprit is anything really do about it?

 

I'll start with lowering the float level from 26mm to SK's recommended 29mm and go from there.

Thanks for all this help Philip,

Chris

[240260280z]

Glad to help. We are SK brothers!

 

I think it is key to get the cruise first then work out the WOT and idle.

 

For cruise, the progression holes and top of the emulsion tube are the active parts.  Fuel level changes will affect these for "tuning".  It will be good to rule out the accelerator just in case.

Edited May 2, 2015 by Blue