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Discussion Starter · #1 ·
I've been talking about installing a carb sync port for quite some time and tonight I performed the mod.

As I see it, there were two way to perform this modification. I could drill the rubber intake boot and install a port of some sort. The "some sort" was what I didn't have. I could have removed a fuel intake port from an old carburator but I didn't have an old carburator. Assuming I did have an old carburator, then I'd have to somehow glue/secure the port to the rubber boot. If I get through those two steps then there is always the chance that through vibration, age etc., the port joint might crack and then I'd have an air leak to deal with.

On the other hand, I like drilling aluminum and tapping things so I decided to drill and tap the head. The downside to this mod is that if I screw it up it means removing the head and getting it welded or replacing the head. Hmmmmmm.....I decided to drill and tap the head. The other downside is the bike will never win a classic show for most original. :)

First things first. If you're using a Craftsman tap, don't pay attention to the "tap drill size" that is listed on the 5mm tap. It says to use an 11/64th's drill bit but that is probably 1/64th to big in my opinion. The resulting threads are a little loose. I'm going to try them but if it doesn't work, I'll redrill it for a 6mm tap since I have two sets of ports for the Morgan Carb Tune, 5 mm & 6 mm.

First you need to locate a position for the port. I wish I could tell you all the engineering theory that went into my choice but I can not. I picked a spot that was close enough to the carb and still allow me to room to drill and also allow me to install a 5mm screw without any interference.

When drilling any hole with a precision location, always, always, always use a center punch. I've drilled a bizillion holes for every rivet in my kit airplane and I still use a center punch for most holes.

Center punch both intake tracks in the same position.



After installing a towel or something similar to stop chips from going into the motor, drill both holes.



Next...and this is important, admire your handiwork. :)





...and the final step is to tap the hole and install the 5mm screw. Unfortunately I forgot to take a picture of the taping process but you get the idea. There are still two issues to deal with. The pictures just shows a SS washer and I'll be replacing that washer with a sealing washer. Also, the screw was a little long (I think it was a 5mm x 10) and it sticks into the intake track by a few threads. I'll be cutting off the additional threads so it sits flush.



Here is a shot of the vacuum port attachment. I suppose you could install the port and then use a rubber plug like some of other bike models but I decided to use the screws so I don't have to purchase another set of ports for the various bikes I might need to use the tool for.



Enjoy the rest of the evening with the beverage of your choice.
 

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Discussion Starter · #4 ·
NE350 said:
Mike, Forgive my ignorance, but what exactly will the carb sync port do?

Matt
It will allow me to hook up my Morgan Carb Tune and synchronize the carbs. With a vacuum port the accuracy of the carb sync is much less difficult and more accurate.

I haven't read it lately, but I think the manual says to put your hand over the exhaust to "feel" the pulses when sync'ing the carbs. Other people remove a plug cap, check the rpm, then do the same to the other side. That may/may not be accurate.

In my opinion, it just allows me to use the right tool for the right job.
 

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Ditto on the 350. Plus, sure would be nice if there was an after market ported intake boot.
 

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MNellis said:
NE350 said:
Mike, Forgive my ignorance, but what exactly will the carb sync port do?

Matt
It will allow me to hook up my Morgan Carb Tune and synchronize the carbs. With a vacuum port the accuracy of the carb sync is much more difficult and less accurate.
think you meant Without
one trick the guys on the xs650 site do is to run a permanent vacuum line link between the barbs after sync, smooths it out that last little bit, tried it on my 74 650 after putting in barbs and it does work
 

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MNellis said:
Other people remove a plug cap, check the rpm, then do the same to the other side. That may/may not be accurate.
The vacuum gauge will allow you to balance flow of air into the carbs in the best way possible. But it is quite possible that (with twins cylinder bikes in particular) to balance the entire 'process' of getting two cylinders to inhale and exhale in "balance" - to work together - that vacuum alone may not account for all other variables. Carb vacuum is like timing, valve setting, compression, carb condition, etc. and are input variables to the process. Rpm or actual speed of operation is a summary of all the inputs.

Most of the old Beemer tuners will use the "short one cylinder" method and balance rpm's on each side of the motor. From a stock bench setting, if one side wants to run (for example) at 1K rpm and the other at 900 rpm, then one cylinder is pulling the other along while the other is dragging and does not make for balanced operation in toto.

However, keep in mind I have yet to tune up one of these puppies :?
 

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Discussion Starter · #9 ·
go_hercules said:
Hey Mike, have you thought about how to do something similar on the 350?
It looks like I missed a few messages in this post.

I have thought about doing this on the 350 but I'll have to do it differently since there is so little extra meat to work with on the head. I'll probably have to do something with the rubber boot or maybe drill the carb itself but I haven't gotten that far. I'm dealing with carb problems on the Gold Wing right now and then it's onto the completion of the 450. After that I've got this cool seat foam to try and install on the 350 first. :)
 

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I used a couple of pieces of 3/16" (.187) brake line tubing, drilled my intake boots and JB welded the tubes into the boots it has held up well, the 650 intake were about a 1/2 inch thick there so plenty of material to hold the tube, use a 11/64" (.171) drill for a tighter fit if the intake is thin
 

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Great write up! I'm having trouble finding a metric barb to sync the carbs on my 1982 CB450SC engine, so i've been thinking about doing this same thing myself. This question is about your engine though. What is that thing protruding out from where i'm used to just seeing the cam chain tension nut? What's it do, and if i get one.... will it make me go faster?! Thanks for the words of wisdom on this mod!
 

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You can use this tool, by placing it over the carb mouth, with the air cleaners removed: http://www.amazon.com/UNI-CARB-SYNCHRON ... +sync+tool These were used to balance multi-carb setups(Corvairs, hot rods) and such, back in the day. Compare the readings, at the throat of each carb, and adjust as required.
 

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Does anyone make a pre-fabricated intake boot for the cb450 that already has a sample port installed? I want to be able to sync my carbs more accurately, but am scared to start drilling holes and break something that is not broken.
 

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Noob question here. The stock carbs don't have a port already? I figured most carbs would have somewhere to plug into since syncing them is pretty standard operation.
 

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WooHoo! I knew I'd find what I needed here. I just got the head reassembled and valves adjusted and was thinking about how to add a synch port to the engine. Thanks for the great write up.

John
 

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Well my carbtune only had the plastic barbs and I am not real patient so I took a shortcut. Hope it doesn't bite me but I don't think so. I got some 3/16 barbs from Lowe's, trimmed them to fit and JB welded them in place.






John
 
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