VM29mm smoothbores question about vacuum/overflow lines.

[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.

[azr]

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

[Gregory]

Thanks guys.

Chuck I don't mind using the sync passage for the vacuum line. When I first started it u it had some backfires and sputters, but I did get it to idle at higher revs.
AZR if I am remembering correctly, my gauge wasn't hardly moving at all (until i plugged the breather tubes). I thought had it up around 2-3k, but maybe that was after i plugged the lines.

I wonder if sucking air through the bowls would cause it to not move the gauges?

I will re-address all this again after I get my bowl gaskets in, then report back.

[Agemax]

dont mean to hijack the thread but as it is a relevant question, i was wondering if you HAVE to use a push/pull throttle cable assembly on the 29mm smoothies? i know they say you have to on the 33's but i have been running my 28's with a single cable with no problems and as the 29's have the same strong return spring set up, is there a real need for the push cable?
TIA

[Gregory]

I was told by an old timer here that you can just use one cable. Since my setup had a two positions, I just went with the two cable system.

[Agemax]

I was told by an old timer here that you can just use one cable. Since my setup had a two positions, I just went with the two cable system.

Thanks Gregory, i thought it would be ok but just checking.

[Sandy]

As far as I know you should use a return cable with any non CV type carb. There is a possibility of the slides hanging and the only way to close it is with the cable. With only one return spring and one bracket there is no redundancy built into the return mechanism other than the return cable. I guess it's there for a reason. I've also heard on big motors flowing a lot of air that the flow can be high enough to actually hold the slides up or at least delay their closing, maybe the air flow binds the slide in the bore. That might just be myth, I'm not 100% sure on that.

[Fjbj40]

Yes they will hang, I found that out the hard way!

So I guess the 29's do not have the vacuum port between the #3-4 carb like the 33's do?

[chuck hahn]

No vacuum ports on 29s. One thing i was thinking of is the small hole in the back of the jet block being blocked by spider nests or something. I was the one that rebuilt them for Greg and I am sure they were very good when i was done. They were done about 1 1/2 years ago and have been setting around since far as I know.

Theres a tiny hole in the back of the jet blocks and the gasket has a corresponding hole..which I am sure i lined up correctly. I think I would take a e wire ( paper clip or whatever fits in the jet block hole ) and poke it thru to see that the gaskets hole is clear too. Take a light and look at the back of the jet block and youll see the hole. bend a wire and stick it in the hole to be sure its not clogged and the gasket hole is there.

[Gregory]

Will do, I may even give you a call when I get around to them when the gaskets arrive. I had them wrapped in a large plastic bag inside a box here in my office.

[Gregory]

Thanks for the help on the phone today Chuck. I got the new gaskets in and re bench synced the carbs. I put them on and the first thing was the breather hose between 1 and 2 started gushing gas as soon as I hooked the gas line up. I tapped on the bowl and started it, and it seems to have cured that. I had a little popping but it seemed to smooth out some as I synced the carbs....

BUT......I had a very slight reading on the gauges so i got them where they were all about the same height across. then i revved it and noticed that the bars would not go up when revving but seemed to go up as it was settling back down.

Anyway here is a video. I am sure something is wrong because these things usually read a lot higher than this. Also I notice in the clip they are not level but they were originally before I pulled out the camera.

https://youtu.be/mVvadxyLXr8

[chuck hahn]

So..does it run good and not have hammering sounds like its all out of whack or smooth??? The exercise isnt how high the gauges goes its how even tha bars are. Sometimes as the slides are moved a lot youll see the bars go higher lower..and youll,hear the RPMs follow that change.

If its steady and seems to sound right I wouldnt worry too much. I dont have speakers on this old laptop so I could actually hear it..thats why i ask.

And Yeah ive seen my gauges do the same as the RPMs come down...the bars will flex up and then settle back.