VM29mm smoothbores question about vacuum/overflow lines.

[Gregory]

I am changing out my 26mm to the new 29mm and notice the 29's have a different fuel/vacuum/overflow tube configuration.

The fuel tube is obvious but there are two other tubes up further- one is on the left side and one on the right side. Does anyone know which one is vacuum and which one is overflow?

 

[TeamDar]

They are both vents. You have to get creative if you want to run a vacuum petcock.

 

[Gregory]

Thanks TeamDar.

Damn that sucks. I know a lot of people prefer to nix the vacuum petcock anyway, but i like it because i will inevitably forget to turn the darn thing off.

How creative will I need to get? Any Ideas how it may be doable?

 

[Nessism]

How about pulling vacuum from one of the sync ports?

 

[Guest]

Yes that's the simplest. Just put a short brass tube on the #2 vacuum port (Z1 sells them or you can make your own) and your good to go.

 

[Gregory]

thanks guys i will check that out today

 

[silverhelme]

That is what I did except I just drilled a bolt with the correct thread size, cut off the head and used a jam nut to set the length then put my hose on it. It has been working fine since Apirl.

 

[Gregory]

Thanks guys. I have brass fittings in my carb sync kit, I can use the short one for it on the second carb. A mystery person from the west sent me a picture of how they did theirs.

I do have a question for both of you, what size main jets are you running with your vm29's? I have pods and 4-1. and am in texas.

 

[Guest]

I have a Marving 4 into 1 and K&N pods with my 29's on my 78' 1000. Mains are 117.5 mikuni's with #25 pilots, using the 1.5 cutouts it came with. Can't remember where my mixtures screws are set but I can look if you want when I get home. Bike runs perfectly at all RPMs. I live at sea level though

 

[Gregory]

Thank you Azr, I sure appreciate the fast response, good timing. These were on a bike from here in Texas, so I was hoping they were right. They are 117.5 mains and 17.5 pilots...so hoping that will be ok. Getting ready to sync them in a few minutes after I do a little refresher on Basscliffs site.

 

[hannibal]

How about pulling vacuum from one of the sync ports?

Aren't the sync ports on the carb outlet? No problem with using an air/fuel mixture to read vacuum? Obviously you sync with this mixture but is sending this behind the petcock diaphragm OK?

 

[Gregory]

To be honest I don't understand what I just read Jordan. Hopefully some of the smarter guys that have vm 29mm will chime in and answer you.

I tried to sync them and found that I needed to block off the two breather hoses with golf tees in order to get any reading out of the carb sync gauges. I also had 3 carbs draining fuel out of the bottom and realized that they were all missing the bowl gaskets. z1 is out but will find some on fleabay.

 

[chuck hahn]

The sync ports are on the intake manifolds..the allen head screws at about a 45 degree at the bottom of the intakes.

In Gregs case, making a vac nipple and inserting it in the manifold will be of no consequence..its blocked off when the bike is running via the petcock is blocking it from being an open vacuum.

Secondly, when he does the sync and puts the carbtune on, hes gonna be using a gravity bottle so there isnt any need to block any ports off. Its a win win for Greg.

All he needs is an adapter and run the vacuum from the sync port to the petcock..done.

I would go off carb intake 1..easy to get at.

 

[Guest]

That's very odd that you had to block off the 2 vents tubes on the carbs to get the vacuum synch to work, I'm thinking there is something amiss inside the carbs. I haven't synched mine for a year or more but pretty sure I didn't need to do that. I'm wondering if there are some more parts missing inside the carb bodies that just float bowl gaskets.

 

[Guest]

Aren't the sync ports on the carb outlet? No problem with using an air/fuel mixture to read vacuum? Obviously you sync with this mixture but is sending this behind the petcock diaphragm OK?

The vacuum ports that are being refered to are on the cylinder head, the ones you use to vacuum synch your carbs. There is no vacuum port on 29mm smoothbores, unlike on the stock 26mm VM carbs where there is one on carb body number 3.

 

[hannibal]

I was thinking that you would be sending air after it was mixed with fuel to the petcock. But it's a vacuum line meaning air flows from the petcock to the carb, not the other way around.

 

[Spyderman]

i have had 29 smoothies on my 78 skunk for 25 years now with no issues at all
i run the factory petcock in prime
i use a on off type 90 degree ball valve inline from the tank to the carbs placed under the seat
#117.5 mains
needle is P-3
pilots are #25
air screws are between 1/2 and 3/4 out from lightly seated
ported and polished head
hindle exhaust
K&N oval filters
this works great for me here in Calgary
hope that helps you out some

and azr is most likely right if you have to plug the vent tubes then you have bigger problems in the carbs

blocking the vent tubes is the cause of the over flow of fuel out the carb bodies if it did that then it also went into the crankcase and you need to change the oil as it has been thinned out with gas and will ruin a bearing or worse
those tubes are there to provide atmospheric pressure to the float chamber so the floats can shut off the fuel supply when needed
blocking them will cause a lack of pressure inside the chamber and you will not run well or at all as far too much fuel will be sent to the engine

 

[Gregory]

i have had 29 smoothies on my 78 skunk for 25 years now with no issues at all
i run the factory petcock in prime
i use a on off type 90 degree ball valve inline from the tank to the carbs placed under the seat
#117.5 mains
needle is P-3
pilots are #25
air screws are between 1/2 and 3/4 out from lightly seated
ported and polished head
hindle exhaust
K&N oval filters
this works great for me here in Calgary
hope that helps you out some

and azr is most likely right if you have to plug the vent tubes then you have bigger problems in the carbs

blocking the vent tubes is the cause of the over flow of fuel out the carb bodies if it did that then it also went into the crankcase and you need to change the oil as it has been thinned out with gas and will ruin a bearing or worse
those tubes are there to provide atmospheric pressure to the float chamber so the floats can shut off the fuel supply when needed
blocking them will cause a lack of pressure inside the chamber and you will not run well or at all as far too much fuel will be sent to the engine

I had these carbs professionally cleaned and put back together, so i dont think anything is missing. Before I plugged up the breather tubes I could not get but a very slight rise out of the morgan gauges. when I plugged them I could read the bars and tell a difference in them.

I think I am quickly becoming frustrated with this bike maintenance.

 

[chuck hahn]

Greg. If you look at carb 3 in the exploded view youll see the spot that would normally have a vacuum like the regular VM26s do. VM29s do not have this and I am not sure if drilling it open will allow a nipple to be put in and supply petcock vacuum or not. I , MYSELF, have never done it and I have never seen anyone her do it.

http://www.sudco.com/Catalog37Digital/index.html#/172/

And if you look at the next page ( page 173 of the catalog ) youll see that item 11 is the vent hose..which obviously says the two nipples are just bowl vents. There is no reason that they should be plugged to get a reading on the carbtune.

Does the bike run right with the carbs on it? Good throttle response, all the pipes getting hot like normal, has power and response when you try to ride the bike??

Does the carbtune respond ( without the vents plugged ) at a higher RPM than at idle??? Try the RPMs set at around 2,000 with the idle knob and then try the sync process.

I messed up on the sync once and she wouldnt settle anywhere. So I took them ( VM 26 ) off and rebenched them and started all over. I had 3 showing great vacuum and one stone cold flat for some reason. Sometimes you just gotta go back to zero and start over.

 

[Guest]

When you are doing your vacumm synch are you making sure the idle is increased to at least 2000rpm? You won't get a reading on the vacuum synch if you're trying to do it at idle, 1000rpm