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Hoses From Petcock, How Do I Run Without The Fuel Tank?

  • Thread starter Thread starter d.loseth
  • Start date Start date
D

d.loseth

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Hi guys, 1978 GS750. Attempting to sync my carbs, gonna use a separate tank with a hose to run it while I do it. My question is there are two hoses from the carbs to the petcock, a larger one and a smaller one. I assume its the larger one that is the fuel line as that is the nipple that the fuel comes out of if I turn the petcock to RES. The smaller line I assume has something to do with the vacuum system. So if I take the tank off and connect a temporary one for the purpose of syncing, do I need to plug one of those lines? I'm assuming I connect the temp into the larger hose, can I leave the smaller hose as is or should I plug it? Do I have this all wrong?
 
Put a piece of tubing with a bolt in it on carb 3 nipple that goes to the vac side of the petcock. Then hook your gravity tank to the carb fuel line. I have a double ended 1/4 inch barb fitting from my IV botttles line that pushes into the fuel line from the carbs.
 
Smaller hose is the vacuum and unless you use that as one of your sync hoses then you will need to plug it. You can typically use an M6 bolt for this.
 
hillsy said:
... unless you use that as one of your sync hoses ...
Click to expand...
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Can't say how many times I have cussed the screw in the #2 sync port on the CV carbs.

This is ABSOLUTELY BRILLIANT. :encouragement: :dancing:

.
 
Thank you for all the info, I really appreciate it.

Got it to finally turn over and run today, but only if I'm holding down the throttle. This thread is morphing into a off topic thread now, but I figured you guys that posted might know the answers to these questions instead of making a new thread.

It will start up but it idles really low, too low, so it stalls. I started with the pilot fuel screws 3/4 out and my air screws 1.5 turns out. I fiddled with the air screws and couldn't get it to help. I turned the pilot fuel screws to 1.5 turns out (the screws on the bottom of the carbs) and the air screws 2 turns out. I think that was even worse.
BTW, the main throttle adjuster is all the way in in an attempt to get it to idle higher. I adjusted the adjustment nuts on my throttle cables to try and make up for it as well.

What should I do? What will adjusting the pilot fuel screws actually change? Also, what does adjusting the air screws actually change? How can I get it to idle right without the main adjustment turned all the way in?
 
The idle knob being all the way in makes me think the carbs are WAY WAY out of sync. I would take them off and rebench sync them. Just touch the idle adjuster to the throttle linkage and then add 1 full turn in, bench sync, and try it again.

Use a small wired paper clip wire as your feeler gauge while doing the bench synch. get all 4 as close to identical as you can and reinstall them.
 
Sorry for my ignorance, but how do I bench synch? I get where to adjust ( top of the carbs) but what am I measuring with the wire, and am I lowering that top screw or raising it?
The whole thing seems odd, I've never adjusted those top screws (syncing) and it was never this bad in the past. Unless I did take that all apart when I took the carbs apart and put it back together out of whack. It was a couple years ago and I had a couple bikes so I'm not completely sure.
 
From the bottom of the slide to the bottom of the Venturi ( the carb throat bore ) Set the wire in the venturi and loosen the lock nut on each slide. adjust with the screwdriver till all 4 slides are resting gently on the wire. This is called bench syncing. Its purpose is to get the slides aligned good enough for it to run and accept some throttle..then you do the gauge syncing with the engine running at around 2,000 RPMs to balance all 4 to a running engines requirements. Measure from the engine side of the carbs
 
Wow,if I'm envisioning this right, that gap that should be the thickness of that wire is currently closer to 1/4" or so
 
There ya go..should be like 15 or 20 thousands.

Touch off the big idle knob to the throttle linkage and go IN 1 full turn and reset the slides. Then as you turn the idle knob out youll see the slides drop down a little and stop. Next touch the idle knob to the linkage and go in about 1 1/2 to 2 turns. This will give it enough idle setting to get it to start usually. you may have to go in a little too...just depends on the engine.

When it starts the RPMs may even be up like 2 G or so..no biggy. Just turn the idle down with the knob.

And hands off the grip when starting. Full choke and hit the button. RPMS will be high with the choke on so easily take some choke away till it settles in around 2g and let the bike warm up well before doing the gauge sync. Set a few fans in front of the bike on high speed to get air going accros the engine so it doesnt overheat.
 
Thanks so much for this info man, this is the best direction I've come across yet.
I just need to clarify what you mean by the linkage talk.
So you're saying 'unscrew' the main throttle knob back until it loses contact with the throttle part where the cable is attached? Then move it so it just touches it, go in one turn, do the paper clip adjustment on the slides, then back the throttle knob off again so its just making contact, and this time go in one and a half turns instead of one and try and run it?
 
So I bench synced the carbs, hooked it back up with the specified throttle adjustment turns, got her running, warmed up, hooked up the sync gauges, and its staying in the zone on my gauge that says vacuum leak or heat riser leak or something like that. My hoses seem fine, but what the heck is the heat riser?
Anyway I tried adjusting the slides while it was running and hooked up, I tried half a turn on 1,2 and 4 carbs, with relatively no difference showing. When I adjusted #3 the RPMs shot up and got real lot, little smoke (I think some fluid is leaking at the very front of the engine) and I shut it off. According to the gauges, its really out of whack.
Fuel pilot screws are 3/4 out and air mixture 1.5 turns out.
I'm starting to wonder if there is another problem.
 
What gauges you have?? Pics will help get answers that are more accurate. Where in Canada are you???? May be a member nearby with syncing experience that could come by if they knew where you are at.
 
RPMs will change as you go from carb to carb and youll be adjusting the idle knob a few times..its normal. Did the gauges react when the RPMs went up too???
 
Make SMALL adjustments.

If you try to close a slide and it's already fully closed, the other three slides will open instead. That's why Steve's advice about setting the idle screw before bench syncing is important. You need room for each slide to go up or down.

There is no correct order to adjusting the individual carbs but I think the common advice is to start with the carb furthest out of sync.
 
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