Question about Honda CB 750 Motorcycles

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Honda CB 750 carb overflow

Hi, l have a CB 750c which is overflowing on the no. 4 carb only a drip but it won't stop, I have replaced needle valve but no luck. Any ideas?

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Hi, Louis and the usual suspects are:
1. Damaged or restricted fuel tank venting system.
2. Loose float bowl screws.
3. Damaged float bowl o-ring.
4. improper fuel level in the float bowl.
5. Worn or dirty inlet valve or seat.
6. Damaged or leaking float assembly.
7. Particle contamination in inlet fitting cavity.
8. Damaged petcock diaphragm allowing fuel to flow through the vacuum line into the combustion chamber.
For more information about your issue and valuable "FREE" downloads that you will need for viewing or printing please click on the blue links below. Good luck and have a wonderful day.
Carb is leaking from overflow Why
1981 Honda 750 carb leaking
Honda CB750f2 Manual
Honda CB750F2 Owner Manual

Posted on Aug 09, 2017

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Posted on Jan 02, 2017

SOURCE: 2003 WR250 F - eng. won't idle down and carb starts to overflow

Hi Jwelden,
Have you checked the float level in the float chamber?
I guess you may have to reset the float pin adjustment, its allowing more gas to pass through thn required and thus the overflow!
Not bad too, when you are working on the float assembly take the opportunity to blow out the fuel line from petcock to the carburator via the seat for the float pin,any foreign particals there would stop the float pin to seal up and thus overflow.
Fit in an inline fuel filter , this will help keep out the dirt or whatever.
Hope this helps.

Knight (Yamaha Seca XJ750A 1981)

Posted on Feb 13, 2009

  • 190 Answers

SOURCE: Cleaning Carb Jets

not to a trained ear also go by rpm and spark plug color

NOTE: use copper wire to clean jets, sync is just thottles are same position as all carb's just leave them adjustments alone will be fine if are out use a 1/8 drill an place in between piston/butterfly to carb bore to sync/calibrate

better use a manometer for adjusting screws

depends on condition of org parts

worn = richer running

new = lean an clean

also if changed the exhaust system need to
re-calibrate carbs for max performance

Posted on May 09, 2009

  • 1 Answer

SOURCE: 1999 polaris magnum fuel comming out carb

i have no spark

Posted on Oct 26, 2009

  • 4 Answers

SOURCE: Rebuilt Carb #632641 on Toro model 38170

Is your rubber seat possibly sideways?
Also take the float back out and see if has fuel in it.
sometimes the foat has gas in it and it drops down and the gas keeps coming in the carb.

Posted on Oct 26, 2009

Testimonial: "Found that the float was defective, replaced same also replaced seal in fuel inlet again set fl;oat 11/64 new bowl seal still leaked gas from overflo."

  • 9 Answers

SOURCE: mg midget 1275 [1974] runs very lumpy..wont run

check distributor advance mechanism(below points)the weights and springs could be stuck or broke

Posted on Nov 18, 2009

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1 Answer

Gas pouring out of overflow tube, gas in crank case

Definitely a carb. clean problem. Gas is more than 6 months old & has float needle stuck. Clean carbs. & always replace the float needle valve assy\'s & bowl gaskets. There is nothing you can put in the gas tank to clean carb correctly.

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it can be very hard to correctly trace a gas leak.. Start with the petcock at the tank - make sure its not leaking, carefully move your way down towards the carbs..

If it is indeed the carbs - you will have to pull them and clean (possibly rebuild).. Either the floats are flooding / sinking and not blocking the incoming fuel, or dirt has stopped the needle from sealing properly, or you might have an external leak on the hoses / orings etc..

It might be your tank overflow - is the tank completely full when this happens?

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Sticking floats or worn float valve needles or incorrect float height, tap float bowls to see it overflow stops (sticky float), remove and clean float bowls and fuel inlet passage with carb cleaner and compressed air, check float valve for wear to the rubber tip. Reset float height by slightly bending the metal tab on the float to adjust the closing height of the valve measure from the carb bowl mating surface to the top of the float when fitted then re adjust 1mm at a time higher untill fuel doesnt over flow.

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this is an oldie need carb rebuilding new needle seats and check the floats for leaks ( put them in water see if they sink.
do a thorough carb cleaning job on them and you need to check specs for float level setting.

Apr 27, 2010 | 1972 Honda CB 250

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I have zl 1000 had petrol going into sump afer haveing new camchain fitted,told it,s a carb problem,by same shop,what do you think

hi,this problem is normally caused by the float needles inside the carb bowls not sealing properly,which will allow the carb bowls to keep filling untill they overflow,once they have overflowed the petrol will make its way through the inlet manifold past the valves in the head and then down to the pistons,past the piston rings and into the sump,it is not difficult to replace the needle valve seats once you have the carbs off,all you do is take the carb bowls off (4 screws),pop out the pin that holds the floats in,the needle valve is connected to the floats normally by a little spring type clip,unscrew the needle valve seat(brass) and remove,screw in the new one..job done..replace the needle valve as well..hope this helps...cheers

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