There has to be vacuum there if its running. Where is #4 vacuum line tapped into?
If it is tapped in correctly, it has to be the nipple is plugged or the stix.

 

you can stick your finger on there to test for vacuum.

Or if your real adventurous you can use your tongue like on a 9v.

 

Guys,
The header pipe on #4 is as hot as the others get. I have tested the Carbtune by attaching it to number 4, getting no reading then attaching the same hose from 4 to any of the others and the carbtune reads fine on that particular rod. So it looks as though the Carbtune is fine and the carb itself seems to be working ok. I will try the aero start idea in the morning and see how that goes. Where abouts do I check to see if there is vacuum ? I'm not sure as to where the vacuum line for number 4 is to be attached as I know nothing about carbs. If you could tell me where and what I am checking I'd appreciate it. Thanks guys.

 

Hey Bordo,

With the checks you have done thus far, it (IMHO) shows that the vacuum nipple is blocked - as someone (Sprock?) mentioned earlier - probably from the fragike foam in the air line filter breaking up.

So somehow, we have to unblock that nipple. This is the one that the carbtune line goes onto. I think this just goes into the venturi of the carb, which with air speeding up through the 'choke' causes the vacuum (which the carbtune is measuring) to be formed.

If that is so, and I'm happy to be corrected (Damn Toilet Duck - not sure you were right TK), you may be able to unblock it with a fine piece of wire.

I'd like someone to second my opinion before you attack the carb with wire Sprock? Naga? Shadow? TK/JK? 4...............3...................2............. .1


Cheers, SB

 

I'm with you on the blocked vacuum pipe SB.
Dunno about trying to clear it with wire tho, unfortunately Grey Ghost is at my place in Hawkes Bay about 4 hr from here but checking out workshop manual I wuld think that a quick blast of compressed air into the pipe would clear it although I would probably recommend removal of carbs before I did that (it isnt that difficult really) and also its a good oppurtunity to give everything a good clean anyway.
The alternative could be to give the vacuum pipe a squirt of aerosol carb/injector cleaner to try to dissolve whatever is causing the blockage.
The chances are that whatever is causing the blockage is either soluable or not too hard eg metal or stone etc so a squirt of cleaner/ solvent applied with the engine running is unlikely to produce anything that would cause any damage if it were to be ingested into the engine anyway.
Probably just a bit of dirt crud or a spider or some such thing in which case it serves the little bu99er right for taking up residence there in the first place.

Seriously I think Squirt with solvent,start and run engine, give it a rev and as you back it off (creating maximum manifold vacuum)give it another squirt in the vacuum pipe. This should clear any blockage.Maybe leave for a while after first squirt to allow blockage to soften before startig engine .
Sorry if I sound a bit vague as I'm just thinking this through as I'm scratching at the keyboard.
Worth a try anyway I really cant see it being anything likely to cause any damagegoing through your engine.
Good luck
JK

 

Okay so I know you said it's a 92 ............so I'd take it the carbs are metal capped
and the carb rack is v shaped ? if so there's air nipples on the front top of each carb

If however and it sounds like this to me - potentially - they are plastic capped and the
carb rack is straight they are MK 3 carbs ---------- the nipples are on the head
under the intakes and require a whole different approach.
So depends which style of carbs you have Bordo ?

 

Exactly Sprock!

On my '94 there isn't a nipple. There is an allen head cap screw in the head in front of the rubber boot. That needs to be removed and an adapter for the vacuum line goes in. The screw is hard to see if you don't look up between the frame and engine.

That can't be plugged as the cap screw is keeping debris out.

Here is the low down on mine. This is all done on the head, under side of the intake header.

#1- I pull the petcock vacuum line and plug my sync line in. I then use my vacuum brake bleeder to keep fuel flowing.

#2- I pull the black port cover off the nipple and plug the sync line in.

#3- I pull the black port cover off the nipple and plug the sync line in.

#4- I remove the allen head cap screw and install my line adapter, install sync line.

 

Guys,
The vacuum nipples are on the top of the carbs as per the Mk2 setup ( metal caps and V shape as you say Sprock ). I will try the aero start thing tmrw when I get some time. I'll do that in conjunction with some fine wire and see how that goes. I'll also check that the rubber boots between the airbox/carb and the carb/block are tight and not perished etc. I'll do all that and if still no vacuum I'll get back to you all with what to do next. If it comes to it I'm happy to pull the top of the carb off and see if I can see what the problem may be. Thing is the vacuum point from what I could see last night isnt a part of that top metal cap anyway,but I may be able to see how to get to it. Thanks again.

 

I pulled the top of the carb off of # 4 and checked the rubber part underneath the top cap. There were no holes in it or anything to suggest a leak. I started the bike and did feel a fluttering in the top of the carb to suggest there is air there and possibly a vacuum. I also put some fine wire in the nipple and did the aerostart thing. I still cant get a vacuum reading on it. As the bike seems to be running fine and is only going to be a possible commuter bike, I don't think I'll bother any further with it at this stage. The bike will never be any further than 20 km from home so if I do have a problem I can get it back without to much drama. On a brighter note I did the carbs on the 89 yesterday and they were perfect and within 1 HG of measurement of each other. No need to touch them at all. I'm heading out now to put the swin garm and shock back in the 89 after waiting 2 weeks for the rubber chain guide..... Thanks for the info regarding the carbs guys. I appreciate it.

 

I believe my 90' is the same carb as your 92'. I have my carbs off as I am lapping the valves. I have 66K miles and thought it would be easy. Anyway, here is a picture of the capped sync port on my carb #4. It appears to come from a large hole above the throttle plate, on the engine side of the throttle plate. I think it is virtually impossible to clog it. Also notice that I put red nail polish (ha ha, it's my wife's) on the sync screws as they are impossible to see with the tank up and the engine running.


Can you try one last thing for me? With your bike on the sidestand and the right side cover off, anyone with a screwdriver, long fingernail, pocket knife, or thin coin is going to try and tighten the mixture screw on carb #4. Here's a picture of it. Just begs to be tightened.


Try and screw the screw in lightly until it bottoms. I think it already is. Then turn it counterclockwise 2 and 1/2 turns out. Then start your engine and see if you have vacuum on the sync port.