Couple ZS 175 questions

[mrv8q]

Hello, BCFers, I'm doing a light rebuild of my 175 carbs, and a couple questions for those who've been down this road before. In my TRF carb rebuild kit, there was no inner gasket for the bypass valve; Nelson Reidel shows one on his 3 part rebuild PDF, as seen in my photo,

(the one w/ the brass-colored ring),but it's not present in either of the rebuild kit; The one in there now is quite stiff...I guess a call to TRF is in order...

The second questions is a little more perplexing to me: I want to at least see if the o-ring on the needle adjust screw is OK; I'm able to get the needle/carrier out, but the the adjusting screw/o-ring, and 6 prong retaining clip is held fast. (I have the correct tool).

Nelson talks about tapping it out w/ a steel rod, but won't that clip score the air valve guide rod as it comes out, and how do I know how far to tap it in when I reassemble it?

I'm guessing the o-ring is OK, as it's holding damper oil in the guide rod, but as long as I'm here in the neighborhood... Thanks for all comments, and God bless Nelson Reidel!

 

[TR3driver]

Nelson talks about tapping it out w/ a steel rod, but won't that clip score the air valve guide rod as it comes out,

Yeah it does, a little. If it's really bad, you might have to clean the damage up some, but I didn't have to touch mine as the scoring was very light. The damper piston isn't all that snug a fit anyway, and as long as it fits easily in the bore, you should be OK.<div class="ubbcode-block"><div class="ubbcode-header">Quote:] and how do I know how far to tap it in when I reassemble it?[/QUOTE]Just keep going until it stops; then check how hard it is to turn the adjustment screw. If it's really hard to turn without the needle carrier in place, tap it back just a bit.<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I'm guessing the o-ring is OK, as it's holding damper oil in the guide rod,[/QUOTE]Then I'd be inclined to leave it alone. Easy enough to go back later, since it's just 4 screws to pop the dome off, you don't need to remove the carb or linkage or anything.

BTW if you don't happen to have a suitable steel rod handy, an ordinary wood pencil works fine, too.

 

[poolboy]

hey Kevin. The part that you want to know about in the Throttle Bypass Valve is called by Moss the "throttle bypass diaphram". If you get the Diaphram Kit for about $11.00 you will get it along with another couple of regular gaskets.
If your's is brittle and stiff, a fresh one will certainly be noticeable in deceleration and probably your idle as well.
Adjusting the spring tension on the brass part of the diaphram is key to getting a new one to work properly. Too little tension and it won't seal at Idle and your idle speed will be a couple a hundred rpms higher than you want. Too much tension and it may not open during down shifts etc. and you'll hear the popping of gas explosions in your exhaust.

 

[mrv8q]

Thanks, Randall and Poolboy, good suggestions each. I was able to pop off the restraining clip using Randall's pencil tip... worked like a charm, and no scoring involved:

Strangely, all the square shouldered o-rings in the kit are too large, and the correct sized o-ring is of course, circular; doesn't seem to match what's on the adjusting screw, or in Nelson's picture of same. Further perusal of the Spare Parts Catalog is in order. Poolboy's suggestion of the bypass valve diaphragm is ZEBPV56. Thanks again!

 

[TR3driver]

It's my belief the original O-ring started out round, and wound up square due to abrasion and heat. At any rate, I used round rings and they seem to work fine for me. If you look at the end of Nelson's third carb article, you can see he used a round one, too.

 

[DrEntropy]

The O-ring is tiny and ~should~ be included in the kit. It will look too small to fit if it's in the kit. Additionally, cleaning the old ring out of the land it seats into should be scrupulously done. "Hospital Cleanliness" done.

And now it's too late to heed Randall's comment to leave it be, so you need to find the replacement. Clean the bore into which it seats with "Q-Tips" and Brakleen or carb cleaner too. Oil the ring with whatever you use in the damper on reassembly.

 

[DrEntropy]

It's my belief the original O-ring started out round, and wound up square due to abrasion and heat. At any rate, I used round rings and they seem to work fine for me. If you look at the end of Nelson's third carb article, you can see he used a round one, too.

It's round.

 

[mrv8q]

It's my belief the original O-ring started out round, and wound up square due to abrasion and heat.

Ya know, I wondered if that was the case..... anyway, I do have some round ones, Doc, at will give those a go. Thanks to you both....

 

[mrv8q]

So for fun, I ordered just the o-ring separately from TRF, to compare what I'd get, as opposed to the what's in the rebuild kit. The "solo" o-ring is the more purple-colored one:

Carbs are buttoned up, onto the third an last chapter of Nelson Reidel's epic, <span style="font-style: italic">"TR250-TR6 Carburettor Overhaul"</span>

 

[tdskip]

Go Kevin, go Kevin, go Kevin!