Tapping carb boots for vacuum ports?

B

bobjohnson

Coast to Coast
Ok, so im finally sick of tuning my new bikes carbs by ear. I built a manometer last year and got spoiled big time ;D So i want to install some sync ports on the carb boots, any ideas on how the best way to go about this is? I tried searching here and on google but could only find one guy who tapped the head. I dont really want to do that, since if i screw up, it means replacing the head or getting it welded.

So what i was thinking was getting some threaded inserts and some gasket maker, drilling a hole in the boots, coating the insert with gasket maker (on the outside), hammering it into the carb boot. Then i can get some small screws to fill in the hole when im not using the sync gauge adaptors. Only problem i can see here is where im going to find 5mm ID threaded inserts... Good idea? Bad idea? Better ideas?
 
i say go for it...

if it were me i would tap a hole in the outlet of the carbs. I feel like tapping into rubber will just get ripped out eventually.

steel is the real deal.
 
Well, ideally id like to tap the head but i dont want to for 2 reasons. First is i dont have a garage, so its kinda hard to tap steel when i cant use all my tools. Second reason is because im super prone to screwing stuff like that up, and if i tried, i see welding in my future. Which kinda leads back to the first point ;)

I think tapping into the rubber boots will be ok, because there willl never by any actual pressure on them. Ill block off the ports with screws when not in use, and when im actually using them, ill have a tiny brass port adaptors attached.
 
What bike / boots / carbs? I've seen carb bodies drilled/tapped for barbs. You can buy boots with barbs (my Mikuni boots have them). On the XS650 there is even a way to drill/tap the cylinder head into the intake port to put barbs right on the engine.
 
Its a 71 cb450, running the stock keihin CV carbs for now. There is a really nice spot to drill the head for ports but i dont have the garage to do it in. I was just out in the parking lot looking at the rubber boots, i think i could tap them pretty easily, if i can find some 5mm inserts. That is unless some toronto DTTer with a tap kit and a drill wants to let me come over and tap out some 5mm ports in the head for me ;D
 
Won't work in your rubber boots. First.....trying to thread and seal a metal barb'd fitting into rubber is begging...no...pleading for vacuum leaks. Plus.....that's almost 40 year old rubber. Look into fresh carb adapters...likely you can find something that'll serve that already has the fitting in place....
 
In that case i think ill just wait and get some mikuni slides. I was going to do that anyway, but i figured if i could add some sync ports itd solve a few of my problems and maybe save me 200+ dollars.
 
You don't need to buy new carbs - just new carb boots - bet you can get Mikuni boots with barbs to fit your current carbs.
 
Yeah but the mikunis are way more adjustable, and i like the slide carbs better than CV carbs. So i might as well go the whole mile.
 
Pretty sure it already has vacuum ports on carbs, but, its a long time since I worked on CB450 (maybe 30 yrs?)
They also used a lot of different carbs on different model year/markets

PJ
 
Nope definately doesnt have them. I think maybe the later ones where they added the spring and the diaphram to the slide have them, but im not sure.
 
If you remove carbs you could fit a flanged piec from inside boot.
If you cant find anything suitable, I'm sure I can invent something with 5mm thread for plugs, (in fact, I already thought of something)
 
Do it! You could sell a ton. Ill be happy to test the prototype for you ;D But seriously i would happily send you some money if you came up with something to add sync ports.
 
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