General & Model Specific Technical Forums > Twin Cam

Modify Big Sucker or trash it?

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Nebraskarider1:
For some reason I can't get the o-rings to seal on my Big Sucker a/c. I was thinking about cutting off the stands for the breathers and either getting seperate breathers like a Mikuni carb uses or a tube like the F.I. SE Evo a/c uses where both are hooked together and they have one hose hookup. I am thinking sinces it uses the factory throttle body support that all that would be hanging off the 3 a/c screws would be the backing plate and filter and cover and the throttle body would be supported by the factory support. My question is would the 3 screws handle the backing plate, filter and football cover? Don't want to have a new set of problems. I think the chrome plating or rough machining under it, on the Big Sucker is why its not sealing. Its about to hit the scrap pile.  :banghead:  09 Ultra  I can't return it since I drilled it for external breathers, which I don't think are distorting it btw since they are about midway in the stands. Thanks in advance.

ViennaHog:
The newer versions of the 2008- BS back plates require the factory bracket to stay in place. The new BS versions can be identified by small ribs on the outward facing surface next to the breather holes.
SE versions with the round back plate require removal and the TB is supported by the back plate alone without issues.
Looks more like a stacking problem to me. Make sure that you have only one gasket between the TB and the BS plate. We have seen the strangest things and very popular a mix of parts between BS and SE that dont really fit.

Nebraskarider1:
It is a newer one with the factory tb support left in place, I'm positive I only have one a/c-tb gasket but will double check it tomorrow when I take it apart. Gonna see what I can figure out with some feeler gauges too.

Nebraskarider1:
Well I took it apart this morning and did some checking. Judging by the paint worn off of the throttle body bracket where the o-ring sits it was only fitting tight on the upper half. I took the o-rings out and checked it with the backing plate to throttle body gasket in place and there is a gap without the breather bolts tight, and when snugged up a little I could fit a piece of paper in on the bottom side. If I take the throttle body to a/c gasket out the o-ring surfaces contact. I measured the gasket and it measured .018 where it had been compressed. So I made a gasket out of some gasket paper I had that measured .012 new and tightened everything up without the o-rings and it seemed to fit better. I put the o-rings in and put it together and will see what happens.

Nebraskarider1:
Has anyone else had a problem with the o-rings? After putting in a thinner TB-backing plate gasket it sits flatter at the o-ring surfaces now. Only rode it about 75 miles so far but they seem to not be leaking.

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