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Vaccum issues..


Jerrod R
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Hey what's up guys, just bought an 84 Venture 1200 Royal. Got it running, even idling. But I know I have some sort of Vacuum leak it's Backfiring out over 3 of the Carbs, and it seems to be revving kinda sluggish. But the strangest part is when I put my Filter and Airbox lid on it causes it to rev up and idle at like 3000 RPM. This makes absolutely no sense to me lol. Has anyone delt with anything like this?

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These V4s don't like to go out without a hat on, so in other words, air box and filter need to be in place.

Next I would check to make sure all the carbs are properly seated in their boots. Sometimes,,, like most of the time,,, a fellar needs to seat these things back and forth a few times to get them to stay.

If that don't help, fire it up and then go around the intake area with an open unlit propane torch and see if you notice any difference in the RPMs, if you do you can now dig for an intake leak.

Then come back here and ask some more.

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You may also have the idle set too high, and if it were me I would look at that closely and then try to do a carb sync if I could get the idle low enough, but you will need a carb sync tool for that.

There is no gasket material in the carb boot setup. Under the carbs the ports slide into a ringed rubber boot and above the carbs the airbox has rubber boost. Most common is having the lower boots not sealing on the carb ports.

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I'm talking between the Head itself and the Intake Boot. And your Right there was no Gasket's, just little rubber seals. And someone had used some sort of Gasket Sealer at some point. Seals seem to be ok so I'm getting all the old Gasket Sealer off before re-install...

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Oh, and what's happening is the Motor will be idling ok with no Filter or Cap, but when I drop the Filter on and install the Cap it instantly Revs to like 3500.. If I just put my Hand over the the Intake where the Filter goes it will cause it to Rev up.. Makes absolutely no sense, at least not to me lol.

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The reason putting the air filter lid back on makes a difference is that they are constant velocity carbs and need the vacuum created by the air filter box to make the diaphragms work properly. They will idle a bit but wont rev up must past 3K without having issues with the lid off. Also there isnt a gasket for the carb boot for its seating surface for the head. It uses an O-ring for that. 

What you can look for is as mentioned before, make sure the carbs are seated properly in the boots and the clamps are in the correct position and tight. Also check and make sure that the vacuum caps on the vacuum ports for carbs 1, 3 & 4 are tight and not cracked and leaking air.  Carb #2 has a hose connected to it that run up the the ignition box for vacuum advance. If the bike is idling at 3K, there is a knob on the left side of the bike, under the left side carb rack that adjust the idle speed.  Also check the 1st Gen Forum Library and under manuals, you can download a copy of the service manual for your bike.

Hope this helps.

Rick F.

 

 

 

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I've cleaned off all of the Gasket Sealer or whatever it was the PO put on the Boots, made sure the Seals were seated properly and reinstalled. It was 3am before I got everything back together so the moment of truth is gonna have to wait till Morning. 

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  • 1 month later...

Hey guy's, so I pulled my Carbs and was looking them over and discovered that the Pilot Screw on my number 2 Car had been tightened all the way up. I could see the tip of the needle protruding. So I pulled them all cleaned everything then set them at 2 turns out from closed.. Getting ready to reinstall and give the Starter button a little tickle, any Suggestions before I do?? Any advice would be appreciated..

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Closely check the pilot screw to make sure it doesn't have a indent ring close to the end where it might have made hard contact with the seat. If there is a ring it would be suggested to get one that is in better shape. Will it run with an indent? Probably but not as nice as it should.

As you install: with the carbs out and upside down install the return cable, then flip them over, shove half way into position and install the pull cable. Make sure that the return cable is on the right side of the shaft with a nylon spacer on it. Do not install the cable to slide on the nylon spacer.

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Copy that, and no it didn't appear to have any damage.. But I plan on ordering a Rebuild kit at some Point either way. I do know that I no longer believe this thing Ran great when the P.O parked it 2 years ago..

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 I got problem's now. It's oil Fouling the Plugs and Stalling out in under 2 Minutes. And it still won't Run with the Airbox lid on. As soon as I put the lid on it instantly Revs to like 5000 RPM without the Carbs opening. I have no idea what's going on here.

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As stated in an earlier post this bikes do not run well with the air box off if at all. but if it runs at 5,000 rpm once you put the air box on you may want to check the idle speed screw setting its on the left side of the carbs and it has knob on it so you can turn it with your fingers, it could be screwed in too far. Throttle cables may also be adjusted too tight or may even be seized or binding. Balance screws may be way out of adjustment as well.

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Oh, sorry I thought I responded. I had checked it before I even Posted. I actually have it fully retracted. It's doing this with the Butterflies fully closed, which has me thinking some sort of Vacuum leak that's why I re-seated the Carb Boot's.

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But I have really no idea, never seen anything like it. So that issue is on the Back Burner, and I'm getting ready to Pull the Heads to find out why a bunch of Oil is finding it's way into the Combustion Chamber's. And if I'm Lucky I'll stumble across what ever is causing the idle issue along the way.

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10 minutes ago, Jerrod R said:

Oh, sorry I thought I responded. I had checked it before I even Posted. I actually have it fully retracted. It's doing this with the Butterflies fully closed, which has me thinking some sort of Vacuum leak that's why I re-seated the Carb Boot's.

Keep in mind that the carbs tend to pop out of their boots on the one side as you seat the other side, and then all the clamps have to be placed properly so that they seal the boot to the carb, sometimes all that looks good but then on final inspection you might find that things are't as seated as you thought they might be. The carbs will actually make a popping sound/action when they seat properly, so if you don't get that, then keep pushing, and then check and check again.

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4 minutes ago, Jerrod R said:

But I have really no idea, never seen anything like it. So that issue is on the Back Burner, and I'm getting ready to Pull the Heads to find out why a bunch of Oil is finding it's way into the Combustion Chamber's. And if I'm Lucky I'll stumble across what ever is causing the idle issue along the way.

Maybe  a dumb question, but how do you know you have oil getting into the combustion chamber?

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4 hours ago, Jerrod R said:

But I have really no idea, never seen anything like it. So that issue is on the Back Burner, and I'm getting ready to Pull the Heads to find out why a bunch of Oil is finding it's way into the Combustion Chamber's. And if I'm Lucky I'll stumble across what ever is causing the idle issue along the way.

Make sure your oil level is not to high or that the crankcase venting is not plugged before you pull the heads.

4 hours ago, Jerrod R said:

I have a Compression Tester, but I bought it for my XJ-750, and it won't work with the Venture.

Most universal compression testers with different spark plug hole adapters will work.

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