Bonneville America Forums Forums Technical Forums General Tech Vacuum Mod...best 15 cents you can do to you bike

Reference the below post...if you haven't done this cheap and easy mod, you're missing out on probably the best thing you can do for improved drivability, especially in the city during stop and go riding. I did it this weekend and it made a HUGE difference in the smoothness of idle.

http://www.bonnevilleamerica.com/forums/...;gonew=1#UNREAD

Ok, just to clarify, before I get really excited and go buy tubing. You guys are running a hose from the vacuum port on the Intake Manifolds??? Or are you running a hose between a port on the carburetors themselves?? My CRS carbs have this funny bowl vent deally Bob on the carb body, and I've seen pictures of people running hoses off of that, is that the same thing like what ya'll are talking about??

I ran mine on the intake side, Matt ran his on the carb side, and I believe we accomplished the same thing. I don't think it really matters...

I only did it because of the stock carbs rolling up and down at idle (and occasionally stalling). Do you have this same issue with the CRSs?

Thanks for the Comeback, yes, occasionally the idle starts going a little south, and is not quite as smooth as I would have liked. Normally, the thing manages to avoid stalling, but really sounds like it wants to. I wish I could say that it had occurred to me to try this trick but it never did, my normal response to these little hijinks is to start messing around with the air screws and / or turn up the idle speed a little bit. These two responses normally have debatable results, so I tend to not start screwing with the things until I've gotten really annoyed.

Round,
The hose trick does work good. Phil, or was it newt?, gave nme a chunk of the hose and I installed it on my carbs. It makes the idle balance and hum now.

I'll do that tonight then, and most likely will be kicking myself for either not thinking that up or doing it like 9 months ago. If I'd wanted a rough idle, I'da bought a Hardley! Thanks again, Guys!!

I ran mine carb side. Went to auto zone and asked the guy for 10 inches of hose...which he gave me for free. I figured it was worth 15 cents. I ran the hose through the larger hole in the brace that angles down just in front of the carbs.

Errr.. uhhh... for those of us that are not mechanics nor play ones on TV... does any one have pictures?

Thanx,
Soren

Sorry, didn't take any pics, but on the engine side (or front side) of your carbs are two large rubber vacuum plugs...hard to miss them. You can pull them off with your fingers. Take the cap off both carbs and then use an 8 to 10 inch piece of vacuum hose to connect the two plugs.

I'll definitly do that then. Especially since you referenced a thread I started:) Someone in there also mentioned using some of the hose that you take out when removing the AI stuff...

Just did this mod after work, ended up using about 1-1/2 feet of small stuff routed under-over each manifold, due to all the clutter near the ventral engine mount (the triangular one with the big hole in it), and without taking Her out on the streets, the idle seemed more steady (both exhaust and valve lash), and seemed to hold more consistently on the tach. I'll keep the original vacuum caps just in case, but seems to be doing me good. Thanks Again Guys!

Just did it myself, had some black vacuum hose in my box. Ran mine carb side. Thanks for the tip, missed that one!

My old '77 had a plastic tube that ran in-between the manifolds. I did have to replace it, because after time it constricted considerably. Age or heat maybe. I'm curious as to why the engineers on the new bikes didn't do the same.

Did you secure the tube in-place some how, or just stick it on?

I used fuel injection hose clamps when I put the hose on, the hose I had wasn't too tight of a fit, so I cranked down on those, and everything seemed good.

I used the tube from the AI removal. Seems to be working fine. It just balances the vacuum to both intake sides so the pressure differnce on each side should be small if the carbs are balanced and tuned correctly. Definitely helps with the idle. I saw this quite a while back on the old board and jumped right on this tough little mod.

Soren,
I'm not a mechanic either, nor did I stay in a Holiday Inn Express, but if my cyber skill still works, there should be a picture here of how it looks....



Also there is some evidence of what your bike looks like after riding home from work in the rain, 3 nights in a row...

I routed the line up over the rear engine mount that fastens to the cylinder head. That keeps it clear of the throttle linkage.

I took 2 rides Sunday after doing this. The first ride I noticed the improved idle, and things seemed a little better overall.
During the second ride, starting out, the right side seemed to be "loading up" a bit. Eventually it seemed to clear up.

I have a gut feeling it may be wise to re-balance your carbs after hooking the 2 manifold ports together. Then again, having this line installed will probably affect that in some way. It's time for the fuel gurus to chime on in here...

In order to balance the carbs, you need the vacuyum caps back on, the crossover will give you the same readings on both sides, that's the purpose of doing it.
Sync the carbs FIRST, then put on the hose.

Thanks! I thought that maybe that was the way to hook it up, but didnt want to take any chances without seeing any pictures first.

I take my bike in for it's first service tomorrow, so maybe this weekend I will give it a go.

Soren

soren,
note that you can use either set of holes, the ones on the front (like the picture) or the rear ones, on the carbs themselves.

I figured that was the case.
Ran some errands today and the bike now seems to stumble a bit till it's completely warmed up. I'm going to take the line off and put the plugs back on and see if that goes away.
I had just synched the carbs a few weeks ago and they were nearly spot on - only needed a pubi-meter adjustment.
Methinks I have a gremlin somewhere.....

I was just looking at my carbs and there is already a line running between them on the air box side of the carbs. So I would also add one after the carbs?

Nevermind I was just taking another look at grumps picture he posted and noticed that he had the line before the carbs too. I should pay closer attention.

Yeah, I've already ran the hose off the manifold vacuum ports, the CRS carbs don't have their own ports that I can see unless I've gone totally blind. And I've also been tweaking on the balance for the darned things prior to this hose deal, the balance went a little outta whack when I put the new rubber intake boots on about a month back, so the balance should be good. The AI was already removed when I bought the bike, otherwise it would have been a real nightmare with hose and wiring harness every which way from sunday! Anyways, had the hose on for a day or so now, I'm pretty happy with it! Thanks again!

Sniper, thanks for the reminder. The guys were talking about this in Georgia and I planned on doing it when I returned but forgot by the time I got home.

Hum, So I would say that if we run this rubber hose we will have to remove it before we balance the carbs.

Also, what are the odds that the AI system performed a similar task as this balancer hose, i.e., smoothing the idle? Thought I would throw that one out there.

Edited...Just read Pat's Post about syncing.