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Discussion Starter · #1 ·
1968 CL175. Can anyone see any reason why this extra line from the filter to the power jet would have been added? Obviously this is not a stock setup, and I’ve been running it without. But I’m wondering if it could possibly serve any purpose? Maybe some elder tuning trick from way back?
 

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That’s really interesting! There is obviously a bleed screw into the carburettor but it’s above the slide? So where does the other end of the pipe go? It looks like into the air filter... but that won’t make sense because it’s a cable operated slide not a vacuum slide. It’s pre 1970’s so it’s not an emissions control.
That’s a good one.
 

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Discussion Starter · #3 · (Edited)
There are two "power jets" on these carbs, once where the tube is attached and another behind the screw just to the right of it. Someone obviously went through the trouble of finding these unique pod air filters with a hose inlet on the back of them, so they must have at least thought there was a good reason?
 

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The pods aren’t standard. Back in the day they were known as K&N filters.. at least in the UK. it was a make; and the motorcycling press had loads of letters saying “I’ve fitted K&N filters but my bike won’t run right how can I get it to run properly?”
And the reply was usually to change the jetting... which didn’t help most 17 yr olds who couldn’t afford to change the jetting; let alone understand what effect that would have on their bikes they just knew it would liberate (At least 3 horse power!!!) which for a 50 cc bike producing nearly 4 HP was absolutely fantastic. And they believed that guff!
I’m still none the wiser why it was fitted, but are the carburettors on your bike working? I’d just live with it...
 

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The CB72 had similar power jets on the carbs (PW22). There was a tube that was designed to connect the power jet to the stock air filter, which had an extra outlet on it just for that tube. The CB77 with PW26 carbs didn't have it. It was there so crap didn't get pulled into the power jet.
 

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Discussion Starter · #6 ·
Yes I know this isn't standard, that's why I'm so miffed that someone would go through the trouble to do this :confused:. I've actually not run the bike WITH this tube installed because it seems so odd. Bike runs great.

The pods aren’t standard. Back in the day they were known as K&N filters.. at least in the UK. it was a make; and the motorcycling press had loads of letters saying “I’ve fitted K&N filters but my bike won’t run right how can I get it to run properly?”
And the reply was usually to change the jetting... which didn’t help most 17 yr olds who couldn’t afford to change the jetting; let alone understand what effect that would have on their bikes they just knew it would liberate (At least 3 horse power!!!) which for a 50 cc bike producing nearly 4 HP was absolutely fantastic. And they believed that guff!
I’m still none the wiser why it was fitted, but are the carburettors on your bike working? I’d just live with it...
 

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Discussion Starter · #7 · (Edited)
Another possibility....although I'm not sure what the point would be? Wouldn't it be "vacuuming" in the wrong direction?

Is that simply a vacuum line attached to a float bowl vent?

My first thought when I saw that was something I saw on the CycleX page a while back... It was a carb jet added to the main bore near the air inlet side, it had a hose connected to the float bowl drain. Their site is changed since I saw this, but there was a pic back when.
 

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Well, not really vacuuming in the wrong direction if it's pulling a vacuum on the float bowl vent. The way I understand it the vent is there so that air or fuel vapor can be displaced as the float bowl fills, and air can enter as the float level drops.

I wonder if the vent allowing a little air in to the float bowl as float level drops is less important than getting the air out when the float valve opens. Could this vacuum help increase the amount of available fuel in the float bowl at any given time as opposed to gravity feed controlled only by the float valve and fuel level?

This way when the float valve does open, could it possibly top off the float bowl in less time before the float valve closes again?

A sort-of vacuum assist to the float valve's function.

I wonder if something like this would help performance at high altitudes or something, the PO put it on there and left it there for a reason.
 

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A quick search turned up more info, none relavent to this bike. But the idea of float bowl vents connected to an airbox seems to be common for many applications.

I wonder what the PO was using it to accomplish and if it worked?

Concensus seems to be that vacuum on these vents will help the float valve to close and may reduce fuel flow through all jets.

Could this help with efficiency or performance at WOT?
 

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After some research I find that this arrangement is used in many cold start systems, using a valve the vent is switched to atmosphere or to airbox depending on engine temp to allow faster warm up times. There was some reference on SOHC4 that it's mentioned in Hondaman's book to place the vent hoses into the bottom of the airbox. I don't have the book or know the exact context therin, but it's possible the airbox inlet is an area of less turbulence than other areas behind the engine, this would allow the 4 carbs to behave more in unison...
 

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The early sloper cl 175 came with Pw22 carbs same as the cb72 but with different settings iirc the power jets are there to control the float bowl pressure /vacuume. As they lead to the bowl their air line came from the air filter to keep the fuel clean . Later designs removed the power jet and dropped the carb size to 20mm
 

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Discussion Starter · #12 ·
Lots of interesting stuff. Yes if memory serves I have seen this configuration on (something) before...can't exactly remember what but almost certain it was an inline 4.

My sloper has 20mm carbs AND power jets, so yet another configuration in the mix - unless of course they were changed at some point.
 

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I believe this may be a fuel vapor feed back into the filter. Think old school EGR valve.

Sent from my SM-G920V using Tapatalk
 

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On the early Kawasaki ZX-9 that had ram air induction, there were tubes that went from the air scoops to the float bowels. These were to equalize pressure in the carb intake and float bowls. If these tubes came loose from the air scoops, the bike would not go over 90mph. However, I seriously doubt that is what is going on here.
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