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CV carb question/theory

  • Thread starter Thread starter north49
  • Start date Start date
N

north49

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Any CV carb gurus out there..?? My '80 GS1000 is very very difficult to start when cold. I read on these pages that blowing in the carb vent pipes will over come the problem. That does indeed work a treat and the bike fires up immediately. (thanks to the member that mentioned it!) OK, the question is......WHY does this work? What is going wrong inside the carbs that they need blowing into the vent tubes? I'd rather fix the carbs than wrap my lips around the vent pipes. Thanks for any info......
 
north49 said:
Any CV carb gurus out there..?? My '80 GS1000 is very very difficult to start when cold. I read on these pages that blowing in the carb vent pipes will over come the problem. That does indeed work a treat and the bike fires up immediately. (thanks to the member that mentioned it!) OK, the question is......WHY does this work? What is going wrong inside the carbs that they need blowing into the vent tubes? I'd rather fix the carbs than wrap my lips around the vent pipes. Thanks for any info......
Click to expand...

By blowing in the vent tubes, you are, in a sense, pressurizing the fuel bowels and forcing fuel into the carbs. The reason that it backfires just after doing so, is thet the carbs return to a lean mixture as a result of a lack of fuel. It sounds like you're in need of a good carb soak and o0ring set. You should be able to start the bike on full choke, without any problems. As the temps (outside) warm up, less choke should be needed to start the bike. If in fact, your bike is not able to do this, it suggests a plugged choke circuit and or a fuel restriction, somewhere. Check the fuel screen on the petcock, inside the tank. Check the vaccume line from the #2 carb to the petcock. Look for a kincked fuel line. AIR LEAKS? Need to check for them as well. Retricted float screens will also cause a fuel delivery shortage, as well. Hope this helps clear up the mystery. :-D
 
I am totally unfamiliar with this theory but I'm guessing that blowing in the vent tubes pressurizes the float bowls which makes gas percolate or bubble into the venturi which gives you a fat mixture to start the bike. It sounds like at the very least, your choke pick tubes or choke pickup orifices in the actual float bowl are clogged.
IMHO.
 
chiphead said:
I am totally unfamiliar with this theory but I'm guessing that blowing in the vent tubes pressurizes the float bowls which makes gas percolate or bubble into the venturi which gives you a fat mixture to start the bike. It sounds like at the very least, your choke pick tubes or choke pickup orifices in the actual float bowl are clogged.
IMHO.
Click to expand...

Good one... :? :-D .
 
I think you can overdo it though. I ended up blowing gas all the way into the air box.
 
I actually did hear gurgling in the tank. That gives me idea, I've got a little dent in the tank, maybe I could pop it out???? LOL:D
 
Thanks Dave.......is there such a thing as a rebuild kit for CV carbs? ie gaskets, o-rings etc.

cheers
 
north49 said:
Thanks Dave.......is there such a thing as a rebuild kit for CV carbs? ie gaskets, o-rings etc.

cheers
Click to expand...

Yes, there is. However, if you're careful, you can pull the carbs completely apart and all you should have to replace is the o-rings. You can get them here: http://cycleorings.com/ You may have trouble with the bowl gaskets and they are also available. The rebuild kits are fine (I prefer keeping the jets factory stock...seems as though there are less problems) but unless you need all the parts, they're a waste of parts, not all of which are the same quality as the factory pieces. Watch out for the air mixture screws, you can strip the heads quite easily. Also, when removing the float pins, I use a pliers and squeeze the pin and the right post (when looking at the carb from the bottom) don't try to "punch" them out or you may break a post off...then you'll be looking for another carb body. Check you slide diaphragms for tears and pin hloes by holding them up to a bright light and inspecting closely. (REMOVE them carefully, they're $80.00 a piece)

Any other questions...just ask.
 
Check the rubber boots between the air box and the carbs, mine shrank and caused air leaks, it wouldn't start in the cold because the fuel mixture was too lean, you could be having the same problem. Also make sure that your air filter is in there snug and no leaks between the base and the airfilter, use silicon if you have to seal it again, replacement boots can be purchased from bikebandit.com or many other parts places if required.

When I replaced my boots I went from not being able to start my bike at 18 degrees celsius to being able to start it right down to 8 degrees celsius, it made a huge difference.
 
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