Almost no vacuum

2007 RSV, trying to sync my carbs, but almost no vacuum. When I did my valve clearance I removed the carbs to do the float level check. Got bike back together and it seemed to run fine. It has been sitting for about a month. Now it won't idle and the bars on the carbatune won't move. I set the idle up a little to try and sync the carbs. I used suction and the bars will move so they are not stuck. Any ideas why almost no vacuum from the carbs?

Thanks

Hmmm, had the carbs off...

The first thing that comes to mind is that one or more carbs are not properly seated. The second thing to come to mind is a vacuum hose not connected...

Thanks Bob. Update, cylinders 1 and 2 have vacuum, 3 and 4 do not. Guess I need to take the gas tank off and check for a loose hose.The thing that gets me is I synced the carbs about a month ago but it has sat since then.. The vacuum was not showing really high on the caratune but at least both sides had vacuum. I sure hope I can get this straighten out before the NY rally.

He said it seemed to run fine. Now after sitting for about a month it won't idle. That's more than enough time for untreated fuel to crud up carburetors.

By all means do the checks bongobobny suggested, but I think you're in for a carb cleaning. Do a compression check first to make sure it's not low compression causing the problem.

There is also one oddball problem that sometimes happens. There are two vent lines for the carburetors, each one vents two of them. Sometimes an insect will crawl into one of these hoses and make a nest. What happens is your fuel bowl is empty, and as it fills with gas the air can not get out the vent hose so the bowl never fills up with gas and the bike only runs on 2 cylinders. I am not sure this would affect the vacuum, though, as air is still being sucked thru the carb as normal but no gas is getting sucked into the engine. Anyway, blow through these two hoses to make sure they are not clogged!

I agree with Carl, you DID say it ran fine after replacing the carbs, but hey, you never know! You may indeed have some plugged jets!

Hope you get it fixed before the Rally as I/we are looking forward to seeing you there! Hey, worst case scenario you cage it up, won't be the first time someone has done this...

I am not sure this would affect the vacuum, though, as air is still being sucked thru the carb as normal but no gas is getting sucked into the engine.

It will, but it should make them all uniformly low - the engine will be running to slow for the amount of air the carbs let in so vacuum drops.

I would expect an engine where everything was OK other than the sync to have one or more cylinders with really high vacuum, and some with low vacuum.

A well running Venture engine will pull more than 10" Hg Vacuum. I believe the carbtune is calibrated in CM though. Well running and synced it should read 25 or higher on all cylinders. If none of them are reading 25 or above don't bother syncing until you resolve your other problem(s). In particular, if you have one or two reading 5 or less and the others reading 0 it really doesn't tell you anything about the sync.

Check your carb to intake boots I can almost guarantee one side is no longer seated. they may have been seated just enough to run ok just after you installed the carb's but while sitting they slipped out of the intake boots. It happened to me. What happens is if the carbs are not pushed all the why into the boots, when you tighten the clamps you are actually drawing down on the boot below the carb flange this pushes the carb's up and out of the boot.

Thanks for the great suggestions. After work today I'll take the tank off and check all those things.

Airflow and throttle position are the only things affecting vacuum. You may want to make sure nothing is blocking the air into the carbs, either. Something may have made a nest or somehow plugged your intake.

I took the tank off and the air boxes. I made sure the carbs were seated. Cleaned the air boxes up since they were just a little big oily. Put everything back together. Tried again today and still no vacuum on right side #3 and 4. Cylinders 1 and 2 had a good 24 to 26 cm hg. What I noticed was cylinder #1 was not hot. All the rest were though. But I'm still getting vacuum from #1 and 2. I'll check the right side air cleaner and see if there is an obstruction. If #1 is cold does that mean it isn't firing? Could it be a rectifier/regulator or the ignition coil for that cylinder?

If 1 is cold it's not firing for some reason. Could be ignition or compression or carburetoration/fuel.

Remember, the higher vacuum doesn't show you that cylinder is running, it just means there is more restriction to the air flow.

Assuming the carburetors are working properly the lower vacuum in 3&4 means they are doing more than their share of the work. They'll drag 1&2 along with them.