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Vaccuum port/s

  • Thread starter Thread starter jizracer
  • Start date Start date
J

jizracer

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Just reassembling carbs and thinking.....(new bike)(new old bike:rugby:)Hey whats this rugby ball doing here? that's a NZ sport!! COOL. Anyways.....
Number 3 carb has the vacuum hose. Number 1 carb has nothing. Number 2 and 4 have vacuum brass pipes, But the P.O has them blocked off (2&4) with a bit of fuel line and a M6 screw in the fuel line.
Is this OK or do they need to be vented or something? Its a 78 750

:rugby::rugby:RUGBY:rugby::rugby:

P.S Im one of the few NZers that's not into :rugby::rugby: Im a petrol head. Still Cool but.
 
Last edited:
Not to sure about the carbs for an early 750 but generally...

The ones with the bolted up fuel lines need replacing with something like this.

http://www.dimecitycycles.com/vinta...s-vacuum-intake-port-rubber-caps-11-4972.html

The fuel tap vacuum line is normally run from carb 2 or 3 (not usually an outside carb.

No1. should be the same as 2 and 4, i.e. with removable caps. The purpose of these is so that (with the vacuum line removed also) you can fit a set of vacuum guages to all 4 and get them balanced.

Hope this helps.

p.s. don't mention rugby again.
 
Number 1 shouldnt have a brass nipple..if it does you have the carbs in the wrong order. Best way is to look at the side mixture screws. 1 and 2 should face to the left of the rack ( from the airbox side ) and the nipple will be on # 2. the screws will face to the right on 3 and 4. both will have brass nipples. BUT carb 4 will have the big hole that looks like the fuel tee hole blocked off on the outboard side...follow me here ??

The one on carb 2 is a vent and it stays UNCAPPED. Carb 3 is the one that goes to the vacuum on the petcock. Carb 4 is also a vent and stays UNCAPPED. The bowls need the ability to breathe some atmospheric air to equalise the inside pressure of the bolws to the atmospheric pressure outside. If you cap the vents they go into a "vcapor lock" of sorts...and sometimes they will even overflow and have fuel coming out the airbox side.

Get some normal vacuum line that fits the nipples and run the vent tubes over the top of the stock airbox and down the back side of the box..stuff the ends between the engine and the swingarm. Cut off about even withn the bottom of the oil pan.

If you dont have the stock box and run pods, just gather them in the center of the tranny area and stuff down and cut them off.
 
This is what you should see. Be sure to face the bowl drains the right way too.

001cts.jpg
 
Here is where to have the calipers when checking float hts. Note there is no gasket and the depth pin rests on top of the ridge. Look at BOTH floats for correctness and be sure they are straight up and down..not leaning on the hinge plate.

009zq.jpg


24 mm is the center of the service manuals stated range...

005ffb.jpg
 
Set bottom pilot screws at 7/8 out from lightly seated and leave them alone. set the side mixture screws at 1 3/4 out from bottom. This will be very good for initial restart. Once valves are done and carbs are back on, youll do all fine tuning with the side mixture screws. Turning the. IN will richen the fuel to air ratio..and out will lean the ratio.

Once all the maintenance is done and you do some fiddling youll probably wind up being about 1 1/4 to 1 1/2 out on the mixture screws as youre ending point. I have a Colortune which makes setting the mixtures as easy as pie. But if you dont have one youre plugs are your guide. Sooty puffy black is a rich condition so adjust the mixture screws out at 1/8 turn intervals, clean off the plugs and repeat till each cylinder looks good. Might go thru a few sets of plugs in the process. If plugs run an ashy grey then turn the screws in and recheck them at that setting.
 
chuck hahn said:
Number 1 shouldnt have a brass nipple..if it does you have the carbs in the wrong order. Best way is to look at the side mixture screws. 1 and 2 should face to the left of the rack ( from the airbox side ) and the nipple will be on # 2. the screws will face to the right on 3 and 4. both will have brass nipples. BUT carb 4 will have the big hole that looks like the fuel tee hole blocked off on the outboard side...follow me here ??

The one on carb 2 is a vent and it stays UNCAPPED. Carb 3 is the one that goes to the vacuum on the petcock. Carb 4 is also a vent and stays UNCAPPED. The bowls need the ability to breathe some atmospheric air to equalise the inside pressure of the bolws to the atmospheric pressure outside. If you cap the vents they go into a "vcapor lock" of sorts...and sometimes they will even overflow and have fuel coming out the airbox side.

Get some normal vacuum line that fits the nipples and run the vent tubes over the top of the stock airbox and down the back side of the box..stuff the ends between the engine and the swingarm. Cut off about even withn the bottom of the oil pan.

If you dont have the stock box and run pods, just gather them in the center of the tranny area and stuff down and cut them off.
Click to expand...
Hey thanks for the replys. Makes sense to me, I was right thinking they need to be vented.
You say a float height of 24mm? my manual says 25-27mm.
 
Let me recheck. I may be thinking of my 1000s..If so I apologise. I have the 77 750 and I had the 78 750 E.
 
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