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carb starting problem

  • Thread starter Thread starter s watson
  • Start date Start date
S

s watson

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hi .im just putting my gs750b back together.ive stripped the carbs .no problems clean.and it will not start.fuel is getting to the float bowls but not the engine.turning over but no fuel on spark plugs ....help
 
If you only looked in the carbs and possible spritzed some spray around, they are NOT clean. Time to take them off and do them right.

Two other items that will prevent starting are improper technique and mis-adjusted valves.

.
 
Scroll down on the right side and find the CARB REBUILD tutorials. You dont say what year and I would ASSUME a 77 or 78??? If so then you want the VM tutorial.

http://members.dslextreme.com/users/bikecliff/

1 oring kit from our member Robert Barr does the full rack. And see the parts about intake orings and order them as well. New bowl gaskets will be in order as well.

http://cycleorings.com/

1 can of Berrymans from Walmart to soak them..full 24 hrs per body. Take the plastic basket out and you can do 2 bodies at the same time in there.

And the starting procedure is as follows. Full choke. DO NOT twist the throttle and hit the button. Twisting the throttle ruins the vacuum in the venturis and she will not fire or get fuel.
 
ive now bought new carb to air box boots ..these are nice and soft and fit very well .not like my old ones which were hard. and did not fit well.im going to fit all new jets .and set to factury specs.i live in the uk whats the best make of jets to buy..many thanks for your help .
 
hi tkent02 ..what do you think was my problem was as I have not try to start it yet .many thanks
 
Can you give us a rundown on how you cleaned your carbs? A visual inspection does not guarantee anything internal is actually clean and allowing fuel to be drawn through to the combustion chambers.
 
What bothers me is we are still at the same problem as in post 1. Then we linked the rebuild tutorial and we arent seeing anything stating that ws done..and we are still at the original problem. Dont figure.
 
hi bigd-83...I took the carbs off the bike.stripped them .and visible checked them they were clean after putting the carbs back on. tried to start it .will not start. fuel is at the float bowls.but not being drawn through which makes me think its a vacuum problem.. many thanks
 
​your carbs are clogged up!!!!!!! Go back to post 4 and follow the links i added..is that plain english enough for you to understand??????????
 
Hi watson,
These guys are suggesting that you thoroughly clean the carbs, not just inspect them. The tutorial that was linked to provided great instructions for me. Only differences I found on the GS750B carbs were the need to remove the tops to pull out the throttle shaft and I'm pretty sure our carbs don't have a spring on the pilot fuel screw. I used electronic duster normally used to clean computer keyboards since I don't have an air compressor. After soaking in the carb dip, I cleaned every passageway I could find with the carb cleaner. Then I used the compressed air to blow every passageway. On one carb, I had a piece of debris fly out. That one blockage could cause the carb not to function properly, and I may have never seen it if I haven't dipped, then cleaned, the blew out the carbs.

I'm learning that carbs don't break. You either have incorrect size jets or a clog somewhere. Even with the wrong jets, the bike should idle poorly, or at least try to start. Lack of vacuum as you describe points to a clog that's preventing the motor's vacuum from reaching the fuel bowl.
 
s watson said:
hi bigd-83...I took the carbs off the bike.stripped them .and visible checked them they were clean after putting the carbs back on. tried to start it .will not start. fuel is at the float bowls.but not being drawn through which makes me think its a vacuum problem.. many thanks
Click to expand...

Not to thwack you with too big a stick, but the previous advice is most likely correct. With these bikes, there is no shortcut. You should pull the carbs again, and clean them as in the tutorial. It's not likely to be a vacuum problem, and most likely to be clogged passages in the body of the carb; you will not be able to gauge that just by looking at the shine inside the float bowls. After that, if you are still not getting fuel through the carbs then you should start investigating other problems.
 
Last edited:
hannibal said:
Lack of vacuum as you describe points to a clog that's preventing the motor's vacuum from reaching the fuel bowl.
Click to expand...

Now that's a novel idea... NOT.

He doesn't have a vacuum problem he has either a fuel problem related to clogged passages or an ignition problem. So far I haven't seen any verification of ignition and no confirmation that the carbs have been THOROUGHLY cleaned as in the manual. Seems like the OP likes to beat his head against a brick wall.
 
Vacuum in the fuel bowl is necessary to draw fuel out of the bowl and into the carb, isn't it?

I never suggested his motor wasn't making vacuum, just that that vacuum wasn't reaching the bowl. I was trying to tie his observation of no vacuum in the bowl to the recommendations that a thorough cleaning would allow this vacuum to reach the bowl and suck up fuel.

Please correct me if I'm misunderstanding the way carbs deliver fuel.
 
When the piston goes down on the intake stroke it sucks air into the face of the carbs. This makes a low pressure center inside the venturis..which in turn lets the fuel come up via the needle and needle jets. The vent nipples allows atmospheric pressure to now push fuel up thru the carbs.

There isnt any vacuum produced in the bowls..its all in the carb throats via the low pressure formed there. You have low pressure in the carb bores and high pressure going down the vent tubes. The high pressure just pushes the fuel out of the bowls..its that simple.
 
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