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Discussion Starter · #1 ·
2013 RG, 103 Stage 4 kit. Bike keeps dying when cold. Discovers vacuum leak at the throttle body where it mounts to the heads. At first it was just on the rear cylinder. Brought it in and they put news seals in. Now both cylinders are leaking. The folks that dyno'd the bike said this is a common problem on the Stage 4 kits. Has anyone ran into this before?? What did you do to fix it. Thanks.
 

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Do you think a 58 is necessary for a stage 4?? I'm seriously considering doing everything but the 58 on mine and not with harley pistons and doing 107 big bore cylinders next winter. My local dealer told me $4900 to do stage 4 and I'm like shit i can get a 120 for $5500. I'm cheap. Didn't do either just cams and a tuner :). 109.87 TQ thats good enough for me for now :). $800 for everything including dyno tuned


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Discussion Starter · #5 ·
It's probably not necessary but it's what was in the Stage 4 kit. I wouldn't have done it either but my dealer had a winter special, $2900.00 including labor. I just have to get this damn vacuum leak sorted out.
 

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Did the dealer give you your old parts back?? If they did then put in the stock 50mm throttle body.
From what I recall the 50mm TB seals and the 58mm TB seals are slightly different in size with the 58 mm seal being the larger seal.
The seals are also tapered so it the seals are installed backwards you may have a issue with the TB sealing to the cylinder head.
The kit you got has the 58mm TB but it looks like the stock fuel injectors are being used so switching back to the stock TB won't be a issue you just need to put the injectors in the other TB. The stock TB will still give the bike plenty of air flow and you will get better low end power and throttle response but you will lose a little on the top end.
The stage 4 will run just fine with the 50mm TB but you may need to re-tune the AFR.
 

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Another reason the TB is leaking is that the TB was installed using the wrong procedure.
If the TB is tighten up when it is tipped down then brought (forced) up to put in the breather bolts it may put a strain on the seals and they may crack.
When you put on the other TB just mount the TB on the heads and leave it loose, then lift the TB and start the breather bolts and snug them up, this will put the TB on the right angle and push it into the right depth, then tighten the TB bolts to the heads and then tighten the breather bolts.
 

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'Running the SE58mm on the 117" (T-Man CVO Street Performer Heads) for >16k now, no issues.

In your case, it sounds like installation technique (Mark's 2nd post). Usually the MoCo has their Kits pretty well dialed in for as much plug n play as possible (idiot proof for the average Tech)
 
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