PCV/oil breather and carb linkage ?s

Scooter311 · 06-15-2004, 06:27 AM

I know this has been gone over, but after seeing some old posts I still have a question about oil breathers -
For carbs, is it OK to run the vent hoses from the heads to the flashback valve, then to the PCV valve, or will this not let any relief to the atmosphere?
OR Should I buck up and buy the oil breather box (EMPI, Bugpack style) and run the vent hoses the same way (heads to box, box to PCV)?

Also, I have a hexbar linkage from CB that has no throttle cable bracket. Grrr, can I buy the bracket somewhere, or do I have to cobble together some disaster that will break off and leave me stranded somewhere.
Grrr, indeed
Thanks for the patience!
JEFFRO

lapuwali · 06-15-2004, 09:05 AM

None of the CB linkages come with a throttle cable bracket. You're expected to buy one extra, or fabricate something. Which bracket you use depends on how you set up your linkage (there are two ways, both correct), and which throttle cable you use (try to use the stock EFI cable, or have a shorter one made up), and how you route it.

If I had a digital camera handy, I'd show you a photo of the one I made up in 10 minutes that's now worked for several months.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Cough up for the breather box, or you'll be sucking oil in where you don't want it.

--DD

balthazar · 06-15-2004, 03:46 PM

Here is a picture of the linkage. The mounting bracket was fabricated. The cable bracket was in a box of carb stuff I bought. I am using original fi cable. I wish it was just a few inches shorter.

balthazar · 06-15-2004, 03:51 PM

Here is a picture of the crankcase vent. The pcv valve is one off the shelf at autozone. A toyota pcv grommet fits into a hole in the air cleaner. No more fumes from crankcase...

lapuwali · 06-15-2004, 06:20 PM

Interesting linkage. Can't say I've ever seen one that looked like that. It's not a CB Perf style linkage, which has a solid cross-bar mounted to the bottom air-filter plates and three arms, one for each carb and the third for the throttle cable.

Scooter311 · 06-16-2004, 05:15 AM

Thanks for all the replys so far, and the pics as well. Since my post, I called the vendor, and he was surprised the kit didn't come with a bracket, so he's sending me one - very nice guy. I also found a real nice breather box ass'y - I'll have it by the week's end.
So I'm assuming the correct hookup would be; head vents to breather box, breather box to PCV valve?
Balthazar, I had the same push-pull linkage on my 1.7, and my new carbs came with the same setup - err, I should say, what was left of it, all bent up. Do you have head vents, and if so, where are you venting them to?

balthazar · 06-16-2004, 05:44 AM

This is the only linkage I have any experience with. It's pretty hard to balancce the carbs with it.

I have been gathering the parts for a CB perf. linkage for awhile now, and I am just about ready to go. As soon as possible, the current linkage goes byebye...

The motor is a 71' so the heads are nice and sealed. You could prolly just vent the heads in a similar way, just put in a T. Put them before the PCV valve though.

Kevin Powers · 06-16-2004, 03:18 PM

drawing through the filter base looks messy. this linkage eliminates the cable holder issue completely.

balthazar · 07-04-2004, 01:31 PM

***I am updating this thread with some content from another, similar thread***

Link:http://forums.pelicanparts.com/porsche-914-914-6-technical-forum/170673-crankcase-vent-tube-carburated-engines.html#post1392818

update

Well, I just had some more ideas as to what is happening with this setup. My Father and I took the car out for a little spin just now and we made some observations that may explain a little better what is going on here. The pertronix konked out, but that is another story...

The effects are magnified because of the size of my engine. The 1.7 is almost too small for the 40IDF carbs. Even running 115 mains (thanks Jake), there is a very narrow band where AF is correct. I am either too lean or too rich.

Taking the above into account, the added air from the breather on the left side is causing a lean condition at high revs. I was really into the throttle today, and I got a little hesitation at around 5k rpm.

When at lower rpms, say 1500 to 2k, the AF is richer, and the carbs will load up. This is what causes the drop in revs. At idle, the air from the breather drops off, and has no effect on the AF, allowing for a text book idle...

Maybe I'm running headlong into a cam issue here? Perhaps the added lift and duration of a "carb cam" will fix this or at least smooth it out a little, so the "sweet spot" is broader?

Eric Fry · 07-09-2004, 12:50 PM

On the carb linkage issue, I have worked on the linkage with the bell crank in the middle type and the hex crossbar type and have never had luck with getting the tuning to hold. There is just too much slop that can't be taken out and/or the set screws never hold for long, constant maint. Take a look at the one that Triad West sells, the one in Kevins post, all high quality hiem joint pivots, nice piece. The cost sounds a little steep, BUT, how often do you want to mess with the carb adj. Driving is a lot more fun. Check out the web site www.triadwestperformance.com or give Dave a call in the evening @ 360.412.8021

Eric

Kevin Powers · 07-10-2004, 06:08 AM

hi eric. why would the breather hose cause a lean condition? the cost compared with a cb that had to be slightly "modified" and cobbing up a cable holder made the Triad unit a bargin. aside from not tightening down one of the jam nuts on the cross bar enough, i've never had to "fiddle" with the linkage after setting it up. when you figure out using the drop link on the pass side carb to match the flow, not using the idle adjust screw, things will get simpler in a hurry.

kevin

balthazar · 07-10-2004, 08:54 PM

Kevin,

I think your question was directed at me?

"why would the breather hose cause a lean condition?"

When the engine is at idle, there is a pop-pop-pop sort of airstream coming from the breather. When the engine revs, that pop-pop turns into a strong and steady stream. Simply put, this air flow is enough to alter the A/F in the left carb, un-balancing the set-up. Any imbalance is magnified because the engine is so small, and has an weak cam. The end result is that the car misses at high RPM's.