Advance non-adjustable? Here's how to change that :) AND is there a replacement out there?

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dan filipi

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When Honda put the vacuum advance together they evidently figured there would never be a reason to adjust it.
They did a good job at preventing any kind of adjustment to it by setting the vacuum advance unit where they decided it should stay by using a special set screw with a allen head that would "snap off" once it was tight.
This effectively prevented any future adjustments to the advance because once the allen head snapped off, it left a threaded screw with a flat head and no way to loosen it.

We're about to change that the CGW way :cool:
Here's what to do.

This mod is much easier done with the entire pickup assembly removed but slabghost was able to do it with it still on the bike through the rear after removing the rear tire, plastic fender, and gas tank.

First a shot what the assembly looks like:
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Cut a slot in the rounded smooth cap like surface:
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Now you can get a screw driver on it and unscrew it.
You can stop here if you want, there's no need to go any further because you just made the advance adjustable!
All that's actually needed is to loosen that set screw enough so the vac housing will rotate. The screw has to loosen about 1/2 way to disengage the dished recess in the vac housing (in the pic below) but once it is the vac housing can be rotated right and left.
Right would shorten the rod length which would advance the ignition timing, left would lengthen the rod which would retard ignition.
It looks to me like the vac housing can be rotated while in the bike though I need to verify this.
By replacing the Honda set screw with a 8 or 10mm hex head screw there should be enough room to get a wrench in between the gas tank and the screw to turn it. Maybe a modified wrench but it looks doable. This way once everything is back together the ignition timing would be adjustable, He, he!

I'm going a little further with it because these vac units were only sold as a complete assembly together with the pickups and housing, I'm looking for a off the shelf replacement because those Honda assemblies are no longer available.

Once it's unscrewed all the way out, the vac advance housing slides out of the main housing:
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It's important to count the number of turns as you unscrew it from the threaded rod.
They are usually threaded 11-13 rotations (if you forgot to count it).

Here's a shot with the vac unit removed. (Note the little spring on the rod will fall out and go bye bye):
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Vac removed:
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A shot of the original set screw:
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The vac unit is fairly soft metal. Re seating the set screw after turning it left a dimple in it.
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So there we have it.

If this little gem of a vac unit looks familiar to anyone as coming off some other vehicle please let me know so I can look more into it.
 
Very good post Dan, I can and will confirm that someone can set their timing spot on the money while the engine is running, I have done it several times, you loosen that screw and turn the canister right or left until you put your marks spot on using your timing light sight cap [inspection cap] while doing this,,,Joe Drum insisted I could do this, I didn't listen at first but I thought about it and he was right, all I can say is this, if those marks are spot on and your vacuum advance is working proper your motorbike should run perfectly..Great post...
 
realy good thread ...i usaly just grab that snap bolt with a real decent pair of channel locks ...its always come loose for me doing that ....these are rare pictures of the iggy unit they real hide well ....iwouldnt call it the easiest adjustible iggy ... like the 1000 is but its doable ...its always doable at CGW and the wingnut madmen
 
You're assuming, of course, that the threaded rod has not rusted itself to the vac. unit....like mine is. If the rod is rusted, and unable to unthread from the vac can, you'll wind up damaging the advance plate some, twisting the rubber diaphragm in the can, OR popping the tiny widdle snap-ring right off. Either way, your day will be ruined.
It's a dang good idea, tho, and worth the effort, if it corrects a timing issue. It's pretty much like setting the timing on yer old Chebby, basically. :good:
Thanks for all that ventured into the unknown on this! :thanks:
 
Good point there Joel.

Once your in far enough to cut the slit or remove the set screw, also remove the ignition cover to look at the condition if it to see if it will even screw either way so as not to damage anything.
 
Just a few more points. The vac bulb is designed to adjust in only full turn increments. You'll note there is only one dimple for the retaining screw. Not a big deal if that were the only thing. As Dan has shown the dimple can be made with the screw. As seen in the sixth picture. You can also see the dimple made by the screw is just a bit further in. This is caused by the alignment pin that fits into the base of the vac bulb through the gasket. Note the tiny holes. So if you plan to adjust in less than a full turn you'll need to cut down that alignment pin so it just engages the gasket and no more. You'll also need to be sure to keep the bulb pushed up tight against the housing while you are adjusting it. This is both to seat it against the gasket and to assure accuracy. It is possible to adjust by simply pulling it out a bit. But that would allow crap to get past the gasket to foul the pickups or mechanism.
 
I noticed that pin hole for what appeared to be for alignment but there was no pin in this one. Odd. Only a shorter pin to hold other end of the gasket.
As soon as I loosened the set screw the vac would rotate.
Wonder someone been in this one already or never had it.
 
Looking at this closer it appears the way the set screw is designed to engage the vac unit it will pull the vac housing tightly against the gasket as the set screw is tightened.
I don't know what one rotation of the vac unit would be but watching the ignition backplate as it's turned it appears to be less than 1 degree so one full turn I'd think would be best to use.
 
I currently have mine off the bike for overhaul.
I had a lot of crap inside the advance mechanism and the vacuum portion would only move sometimes due to dirt and corrosion.
With all the gaskets and sealed up the way it is I was confused as to where the crap came from.
I finally realized that when the diaphragm has a hole in it the entire assembly has a constant vacuum on it and will pull moisture and dirt inside through any imperfections in the seals of the unit.
:doh:

I wonder if there is any kind of spray on rubber that could coat and refresh the entire diaphragm without making stiff areas?
 
Now this is way out yonder, Never tried anything like it so don't hold me to it, what about that stuff they sell as "liquid rubber in a can", Flex-Seal. It's high price, bout 12.00 can. I noticed the other day that Walmart started selling it. Also saw it at Atwood's which is a farm and ranch supply place like Tractor Supply Co. They said it's flexible a bends and waterproof after you spray it on. Thinking outside the box here.
 
hmmm ...thats a different veiw on how to fix it .....there nice when they work right ...when gov and corporation catered to each other ...the customer was totaly left out ...and you get this kind of realy stupid engineering ....just think how gas could have saved by having access to time the thing right and keep it up to par ...
 
Someone would have to sacrifice a diaphram to test it, to see how flexible it would be after sprayed and whether the chemicals in the spray would react with the rubber when applied. Might be worth a shot.
 
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