Dual Weber IDF 40s, Carb Rookie question... Options

[PatMc]

Compression test on an engine that overfueling will not be very accurate because the fuel is washing down the cylinders. I wouldn't concern yourself with the compression numbers right now

[930cabman]

Rich, find out why. floats, mis adjustment, needle valve. So long as there is some compression the engine will run

[rhodyguy]

If you verify the floats source new gaskets first. If it’s apart, get some.

[malcolm2]

Was this a newly rebuilt engine?

Compression test should be done on a warm engine. Also, I rarely do compression tests anymore even on unknown engines. I get more info from leak down tests.

Yes a 1.8 from a 914 in northern Alabama. I upped it to a 2.0 with bus pistons.

[malcolm2]

This float setting does not seem to be accurate. I see videos with the dude hold the plate vertically, the floats bounce back and forth and he sticks a mic on it and says it is not right.

Sorry, but I don't see the exact second when he is measuring a moving float.

ACN says they set mine at 12mm.... I can move the plate around and say BOOM... 12 mm. is that right? (IMG:style_emoticons/default/barf.gif) THis guy suggests 10mm. i can't tell.



https://www.youtube.com/watch?v=54uPwTZ3DJw

[malcolm2]

OK... the more i putzed with it, the more I could see where he was measuring.

Tilt floats down and they open fully.

Tilt slowly backwards and the floats will STOP moving.

Tilt more backwards and the floats touch the gasket.

I measure at the STOP point. I got just about 12mm, just like ACN said. Does this group agree that 12mm is good? the video above the dude wanted 10mm.


https://www.youtube.com/watch?v=jJ4UhNCru5s

[r_towle]

10mm is correct. Not sure where 12mm came from

https://www.dellortoshop.com/contents/en-us...loat-level.html

[r_towle]

Curious to know the differences you find between the two carbs.

[malcolm2]

The floats on both carbs are 12mm. Post #11 has the spec sheet that ACN gave me with my carbs.

12mm from the plate to the top of the float would result in LESS fuel in the bowl than if they were set at 10mm from the float to the plate, correct?

It seems that my situation is, or might be OVER FUELING. So the bowls are LESS full per the float at 12 vs 10mm, correct?

[r_towle]

In theory you are right.
The proper specification is 10mm, but you can set it as you choose.

I would suggest you verify the needle valve is seating properly with no dirt or obstruction then you are done with this step.

Remove and verify your jets are correct, and properly seated.
Then move to validate your accel pump, gaskets, settings etc.
The pump needs to be right

[r_towle]

The collective experience we have all had is that new carbs are not always setup properly and you can get two carbs that are different.

[cgnj]

Based on video at idle you have at least one dead hole Look how much it is rocking. Carb on 2-3 bank has pump jet circuit problem. Should look like #4

Can this car idle without blipping the throttle? If it can pull the plug wires off one at a time. Idle speed drops = good hole Move to next one. Check all of them.

[malcolm2]

In theory you are right.
The proper specification is 10mm, but you can set it as you choose.

I would suggest you verify the needle valve is seating properly with no dirt or obstruction then you are done with this step.

Remove and verify your jets are correct, and properly seated.
Then move to validate your accel pump, gaskets, settings etc.
The pump needs to be right

I removed the floats and dropped the needle valves, I see no dirt in the needle valves. Jets have all been removed and verified with the spec sheet.

I did remove the pump cover and checked under the pump. Springs are there. It seems to activate the jets nicely on the bench.

Someone mentioned the pump adjustment is set with the threaded rod and nut, but Number of threads??? Is that the check? how many?

While on the bench, I loaded the bowls with carb cleaner and activated the throttle. The pump jets were straight and true, I saw no leakage.

[Superhawk996]

The floats on both carbs are 12mm. Post #11 has the spec sheet that ACN gave me with my carbs.

12mm from the plate to the top of the float would result in LESS fuel in the bowl than if they were set at 10mm from the float to the plate, correct?

It seems that my situation is, or might be OVER FUELING. So the bowls are LESS full per the float at 12 vs 10mm, correct?

Don’t get hell bent on the exact number - people have their own preferences.

What you want to know is where is it at and is it in the ball park within a couple mm - your answer to that is yes - OK

The reason you want a baseline. Higher fuel level in the bowl from your baseline = runs richer. Lower fuel level in the bowl runs leaner.

[malcolm2]

The collective experience we have all had is that new carbs are not always setup properly and you can get two carbs that are different.

That is why I paid extra for the "set-up" from Air Cooled.net. So going thru this exercise has confirmed that they did what they said they would do.

[Superhawk996]

I should have mentioned 10mm correlates to a higher fuel level in the bowl as you correctly inferred.

FWIW - 10mm seems too high to me. CB Performance IDF guide suggests 14mm. That seems low but again it’s all relative to what your engine wants.

You need to figure out why your plugs are black.

I’m guessing . . . but assuming . . . you don’t have idle mixture screws and throttle plate position set properly as you’re trying to tune idle. If your idle speed screw is holding the throttle blade above the 1st transition port, you’re going to pull in too much fuel at idle and lose throttle response.

Once you get closer to an ideal tune, then float level can be used to tweak slightly richer / leaner but at this point - let it go. You’re close enough.

[Superhawk996]

Since you were looking for a book and the Tomlinson books aren’t readily available - I highly recommend reading this - the Weber tuning manual that was put out by Weber.

This doesn’t have the IDFs but the way the idle circuits woek and the transition from idle to mains is the same. Pay special attention to the diagram on page 10.

https://www.lainefamily.com/images/WeberTuningManual.pdf

[Superhawk996]

In theory you are right.
The proper specification is 10mm, but you can set it as you choose.

I would suggest you verify the needle valve is seating properly with no dirt or obstruction then you are done with this step.

Remove and verify your jets are correct, and properly seated.
Then move to validate your accel pump, gaskets, settings etc.
The pump needs to be right

I removed the floats and dropped the needle valves, I see no dirt in the needle valves. Jets have all been removed and verified with the spec sheet.

I did remove the pump cover and checked under the pump. Springs are there. It seems to activate the jets nicely on the bench.

Someone mentioned the pump adjustment is set with the threaded rod and nut, but Number of threads??? Is that the check? how many?

While on the bench, I loaded the bowls with carb cleaner and activated the throttle. The pump jets were straight and true, I saw no leakage.

(IMG:style_emoticons/default/smilie_pokal.gif)

So you know that isn’t the problem - go back to the tuning basics - best idle, balance airflow, sync carbs. Don’t mess with the accelerator pump linkage - if you’re spraying a steady stream on the bench - it’s OK and the issue is elsewhere.

Although I didn’t pick it up in the video - take the prior suggestion to heart that Member CGNJ mentioned. Make sure you’re running on all 4 cyclinders. That is assumed before any attempt to tune

[930cabman]

I run 12+mm on my 40IDF Weber floats. I prefer to have the fuel level a bit lower as opposed to higher. Is your fuel pressure in the 1 - 3 psi range? I run around 1.5 and seems to work just fine.

[malcolm2]

I run 12+mm on my 40IDF Weber floats. I prefer to have the fuel level a bit lower as opposed to higher. Is your fuel pressure in the 1 - 3 psi range? I run around 1.5 and seems to work just fine.

That is my next recommendation.... As I started doing test drives around the hood, it was suggested to run at 3.5 psi.

Recently, it was recommended to drop to 2.5, so once I get the carbs back on and the idle adjusted and sync'd, I will drop the pressure.

Whole thing started when I noticed the pressure was 1.5 not sure what happened with that, but since then, I have made enough changes to pretty much start from scratch.

So here I go...