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ADDING TUNING PORTS

Dutchess

Veteran Member
Joined
Dec 20, 2021
Total Posts
102
Total likes
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Location
Tucson, AZ
Adding tuning ports

What is the general thought on adding vacuum syncing ports to the head of a CB450? I am meticulous by nature and like empirical feedback whenever possible, but Honda saw fit to not provide them on this bike. I am about to start final assembly of my head so now it the time to do it if I am going. Thanks in advance.
Lee
 
Just my opinion but I find 2 carbs easy enough to sync without using vacuum gauges, but you can certainly put them in. I don't think that Honda did not see fit to provide them as much as, at the time, only the 4 cylinders had them prior to the 450's transition to the 500T.
 
I looked into doing this on my 350, I believe the 450 also has very “short” intake connections where a port can feasibly go.

Like AD says, you can get a reasonably good sync by hand and feel, which is part of why I decided to not go forward with it.

If you do decide to go this route, I’d recommend trying to mill a flat in where you’re trying to get the port and using a screw and sealing washer while not syncing, so you’re not relying on a vacuum cap to not fall off during your ride.


- 1972 CL350
- 1985 VF700F
 
I have also considered making a temporary standoff that has the ports and removing them after the tuning is done. Not ideal though because it will different than the installed state of the carbs and will also create turbulence which will impact how useful it is. I don't have an O2 sensor or anything so aside from some induction tachs on the coils, I don't have a lot of numbers to work with.
 
I’m the same way re numbers. I loved tuning my interceptor because I have an induction tach and a set of vacuum gauges to work off of.

I haven’t broken out an O2 sensor for the idle tuning on that one because it just feels like overkill, but now you’ve given me a new idea [emoji3061]

Nothing wrong with the route you’re going down, but on the twins you can keep it simple and get it working well.


- 1972 CL350
- 1985 VF700F
 
Hi all
I decided to add vacuum ports to the head of my SL350K1 (the head of my bike is still with a machinist getting other work done, but I got it back temporarily to drill & tap the ports (M6) and add a clearance for the KA Performance tensioner I’m going to use).
The ports are on the underside / inside of the head and I don’t think they will be visible.
I purchased the fittings from 4into1.
Once I have the engine running and balanced I have two options:
1) connect the two ports - ie a ‘balancing’ connection; or
2) connect the two ports as above, but block the connecting hose with a ball bearing - that way, even if there is a backfire, it won’t blow off the rubber port cover which is supplied with the fittings (a tip given by LDR).

DCC13A82-5C56-427A-92E4-AF6BF78F7B51.jpg B5148EC4-DF72-448F-A4E8-AD0331D1E280.jpg

Cheers
Mike
 
I have decided to go ahead and do this as well. I am going to add ports at 4:30 on the right cylinder and 7:30 on the left cylinder, then spot face them for an M5 SHCS, add a copper sealing washer and lockwire the screw to the carb boot flange inboard mounting bolt. It won't be invisible, but it wont come loose either. Spot face tools are pretty expensive so I will probably end up making one.
Lee
 
Nice! Copper washers and a flat will work great.

I don’t know your capabilities very well, but a machine shop might be able to do this for you cheaper than the cost of tools for you, and for less stress [emoji6]

I’ve Got a mill available to me so would give this the old college try, but it’ll be tough to get the flat perpendicular-ish to the bore without the right tooling and alignment.

Just my .02, but if you’re confident with it go nuts - and document it so we can all follow along!


- 1972 CL350
- 1985 VF700F
 
Went ahead and put the ports in last night. Just a quick Gin and Tonic to calm the nerves and 20 minutes later I was all done. I don't like the wrenching surface on the button head screw so I will install the socket head cap screw. It is more visible where I chose to place it, but that was a lot thicker section of the casting. I should have around 6 threads of engagement when the plug screws are installed. Now to fashion and anneal some copper washers.
Lee
Tapped Hole..jpg

SHCS.jpg

Button Head.jpg
 
I think the main reason Honda didn't fit vacuum ports on early bikes was simply that dealers didn't have vacuum gauges, or, if they did, they were the type that fitted directly onto carb inlet.
Honda used brass screws on vacuum ports but it's easy enough to get anodized aluminium screws nowadays as long as you used a 'standard' pitch (6x1, 5x0.8, etc)
EDIT
Just noticed you said 5mm so the aluminium Allen heads for windscreen mounting on sport-bikes will probably be easiest to find (plus available in various colours!)
 
yes, especially since there is not much material.
Hi all,
I’m using a product called Tefgel to deal with the stainless bolts / aluminium corrosion issue.
I can’t really vouch for the product as there hasn’t been time for corrosion to take effect, but I know boating people who swear by it.
Check out the website for info…. tefgel.com.au
Cheers
Mike
 
Not something I am overly worried about as I live in the desert and galvanic corrosion is a much bigger concern in marine environments. I'll put a little anti seize on the threads and isolate the head with a copper washer. Also, this bolt will be removed every 1,500 miles for service tuning. Here is the nipple I ended up making as I couldn't find a metric one and the set I have for my girlfriend's CB360 appears to be an M6 x .8 (or maybe .75). I chose to use an M5 x .8 as the nut was the correct size to fit inside the spot face. Not sure how visible it is, but when installed, the threads on the nut are bound and sealed and there is an oring between the nut and the head.

A note about tefgel, years back, I did some consulting work with a company who made marine aluminum hull bolts with 100% 316 stainless hardwares. Tefgel was used any fasteners #8 and smaller, but standard locktite was used for larger fasteners. We learned that it provided good resistance to vibration induced loosening, but in larger fasteners tended to wick out. I can only imagine that in a vacuum or solvent envirement, it would draw out into the intake manifold. I doubt it would hurt the engine, but I doubt much would be left after a few hundred miles. If people are curious, I can install some in the vacuum chamber and see what happens.
Lee
Tuning Nipple.jpg
 
It's M6x0.75, I used to make them as a service for 360 owners and made hundreds for CMC.
A cheap substitute which is better than copper anti seize for stainless into aluminium is ordinary plumbers Teflon paste. (around $7.00 at 'home centres)
I'm guessing Tefgel is a Teflon Gel?
Being for boaters adds at least 100% to the price (in my experience of a DT400MX, piston came from Yamaha Marine)
 
I'm just curious -- what is the reason for trying to hide the vacuum ports by putting them in the least accessible position (i.e. underside / inside of the head)? They look a lot less obtrusive than those unnecessary in-line fuel filters that so many people use. Are you embarrassed because they are not supposed to be there?

I like the stock appearance on my bikes too, but I cannot imagine the trouble it would be to uncap the fitting and put on a test hose if the port was placed above, and angled toward, the cam chain adjuster housing. Is there a reason to do that?



The Motion Pro Synch Adapter is available almost everywhere, including eBay for $3.99, and it will work just fine. I think anybody would be hard pressed to make them for less than that.

https://www.ebay.com/itm/1736699983...AyO5mu9_KEF-g9n51ZtjHURUehvnZIFYaAlx7EALw_wcB

The hard fibre washer that comes with the adapters work just fine. There is one problem though. The vacuum cap that comes with it will melt in very short order in this application.



My original intention was to leave the adapters in place, and to use the caps that came with them. I soon realized that would not work, so I would remove the adapter when finished synching, and install an M6 button head screw. That was a pain in the butt. I chased down some silicon caps and they work just fine. Silicon caps won't melt, and they come in a variety of colors. My CL350K3 is blue, so I use color coordinated vacuum caps.





They don't exactly stick out like a sore thumb. They have been on there for a long time without melting, or falling or blowing off. I kind of like them.

By the way, anybody who says these are not necessary has never used them. I thought I had my carbs synchronized perfectly till I finally installed these ports and used them. It makes a world of difference!
 
Motion Pro are cheap, but they don't work on 360 as it's 6x0.75mm pitch. 6x1 just doesn't go in without something breaking.
When I started making the adapters they were not available anywhere and Honda had discontinued them at least 30 years earlier. (more than 40 years now)
The genuine Honda adapter is actually very short and adapts the 5x0.8mm thread adapters in genuine Honda vacuum set, has 6x0.75 drilled through and tapped 5x0.8. I always thought it a bit weird.
 
Motion Pro are cheap, but they don't work on 360 as it's 6x0.75mm pitch. 6x1 just doesn't go in without something breaking.
When I started making the adapters they were not available anywhere and Honda had discontinued them at least 30 years earlier. (more than 40 years now)
The genuine Honda adapter is actually very short and adapts the 5x0.8mm thread adapters in genuine Honda vacuum set, has 6x0.75 drilled through and tapped 5x0.8. I always thought it a bit weird.

Until I read this, I had no idea that the 360 carburetors had vacuum ports. Looks like you were providing a valuable service for 360 owners. Since the 350s had no ports from the factory, I just drilled and tapped my cylinder head to accept the Motion Pro adapters. I understand now why you were producing them.
 
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