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Hippysmack 5th November 2019 20:21

What's that go on bustert?
I'm still a little fuzzy on timed breathers.

Before the new umbrellas, I lost 3-3/4" (7-1/2" WC) and the engine died when removing the oil cap.
I checked today and I still lost 2-1/4" (4-1/2" WC) when removing the cap.
But, I only lost a slight pitch in the engine and not a noticeable amount on the tach.
No frothing in the oil tank now with the cap removed at idle.
So it does look like the rear umbrella was on the way out.

I had (previous to any testing) set the A/F mixture by the Idle Drop Method:

Today I moved the mix to and fro and found no difference on the slack tube.

I tried to get to 6000 while testing in the shop and it won't do it.
But on the road, easy peasy.
Do I need to go back into the carb?

Hippysmack 6th November 2019 03:04

Summaries from Slack Tube Testing
I'll update this post as I go to keep all this info in one place.

A. Before changing to new umbrellas;
1. The rear umbrella was more stiff than the front one which was 'like new'.
2. I pulled the oil cap off at hot idle and the engine stumbled or died.
There was oil frothing in the oil tank when I pulled the cap off.
The frothing got less when the cap was 'slightly' off.
It didn't have any affect pulling the cap at cold idle.
3. There are app. 1/4" fluctuations in the pressure readings at 1000 and 2000 RPM.
The fluctuations are relative quick changing.

B. After changing to new umbrellas;
1. The engine loped a little better.
2. There was no noticable change in RPM with the oil cap removed.
3. There was no frothing of oil in the tank with the cap removed.
4. Engine sounds / lopes better with new umbrellas.
5. Residual vacuum was decreased with new umbrellas across the RPM range.
6. The engine flipped over to positive pressure at a lower RPM.
7. There was less gap between the pressure changes from 1000 and 2000 RPM.
8. Fluctuations of pressure at 1000-2000 RPM are much slower.

C. After restricting both breather bolts to 1/8" openings;
1. The smaller bolt holes actually reduced vacuum.
2. They also offer more control of CC pressure throughout the RPM range by creating lower pressure swings.

Other testing:
1. The air/fuel mixture did not have an affect on CC pressure.
2. There was no difference in pressure with the air cleaner on or off during testing.
3. Timing changes did not have an affect on CC pressure.

Other Notes:
There was no oil spewing / puking out the A/C before or after changing the umbrellas.
There was no extra drag on the motor before or after changing the umbrellas.

bustert 6th November 2019 14:11

how was the throttle acting at the 6k shop run?
6k on a free wheeling engine is diff with one that has a load.
was it 4 cycling (blubbering)
or if you backed down a tad, it would stabilize out?

Hippysmack 6th November 2019 16:00

I guess blubbering would be a good way to explain it but it seems to be RPM related.
It originally didn't start until around 5500, now just higher than 4000.
I back down from 4100 and it stops. I move past there and it stops until I get around 5500.
I think I'll recheck the float level.
I have the longer aftermarket float valve in it and it was difficult to set.
I had to suck on the inlet hose slightly to feel when the valve actually closed then set the float based on that or it'd leak.

bustert 6th November 2019 22:37

sounds like it is going rich, hummm which is funny because i run a 45/200 setup which is on the rich side
still have the vac petcock? i gutted mine so i would not pinch off on wot
i could have pulled it to 7k but no one rides there.

Hippysmack 7th November 2019 00:15

Yes, vacuum petcock. I don't think the petcock is a problem but I'll keep it in mind.
I decided to go ahead and reduce the breather bolts and that went OK except my memory went South on the 04-up hole size. :doh
I drilled 1/8" holes instead of 1/16".
But, it's still a restriction. The new assembly doesn't hinder the A/C.

For lack of having fine thread 5/16” bolts, course thread SS (5/16“x18) bolts were re-threaded to 5/16”x24. This works fine and re-threads easily.
But it's easier to go and buy the correct bolts.

The holding block was needed to keep the bolt straight while boring a hole through it.
You could use a block of wood, plastic or steel. The hole drilled was .2720“ and tapped 5/16”x24.

Each bolt was screwed into the hole, corner to corner lines drawn across the head to find center and the center punched to keep the bit from wandering.

An O-ring was added under the head to seal off the original hole.
The factory threads were chased with a 5/16“x24 tap to straighten warpage and clean the threads for the new bolts to be inserted.
Normally, marking center on both ends and sending the drill bit in just over half way from each end will make a more straight thru hole.
But this just being a test, the hole was drilled thru from one side.
The hole ended up off center in the thru end but this is not a critical point in this application.

So now, at least I'll get to see what affect smaller holes has inside.
I may re-drill more bolts to 1/16" if this shows a reduction.

60Gunner 7th November 2019 04:06

Not sure what difference it actually makes but shouldn't the exit holes be bigger?

Hippysmack 7th November 2019 04:25

I figured I'd just see if the restricted hole itself has an affect on pressure on the inside and if so how much.
I realize the restricted hole is on the inside end of the newer bolts.
I just want to see where I'm at here.
I have limited equipment now. If I still had access to the machine shop at the university, I'd just make some.
I could try to reverse these but I'm not sure if it'd make a whole lot of difference past the restriction anyway.
And given there will be a hose on the end of the vents later, not sure if flipping them is important, but it may be.

I don't plan on using this setup for anything else other than testing.
I don't have 04 breather bolts that I can use although I've been looking at some on Ebay.
That would probably make it easier for me to upgrade from.
Depending on what I come up with on the slack tube from where I'm at now, I may look into getting some 04 ones.
I'm still debating on how I want to run vent lines.

And yes, debating the Deimus mod. :hidechai

60Gunner 7th November 2019 04:34

I was going to say, vent from the cam chest. ;p

Hippysmack 7th November 2019 04:51

Well, in order to bring this little experiment full circle, I'm gonna have to eventually test cam chest venting also.
I've started from OEM breathing, then I'll go to external lines, then external breathing all from the heads.
Then I'll go to cam chest breathing.

We've done the theories and now the natural progression is hands on.
Thanks again to bustert for introducing me to the slack tube.

FourSpeed, if you're still reading this, is there a soft rubber sheet that can be purchased, cut round with a bolt run thru the center and a small washer underneath that would suffice for a replacement in the 86-90 baffle tube?

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