This is a discussion on Hello everyone within the NEW MEMBERS READ HERE! forums, part of the Caferacer.net Forums category; So I cleaned the rotor rings. First I took a scotch brite pad to it, and then i polished them to something close to a ...
I might be completely wrong, but assuming your carbs are balanced, your idle circuit may be too lean. When you cut the throttle, the sudden switch to the idle circuit causes a lack of fuel and kills the bike.
Once you give it a twist of the throttle the RPMs climb up nicely, however on their way down they go way below the normal idle speed and the engine can die if not let off the RPMs gently.
You can kind of see this happening on the carb balancing video linked above
Any ideas what might be causing that? I think it has something to do with idle jets, but I also think that it needs a good proper thrashing which it didn't get basically since I bought it.
Originally Posted by alwhite00
CV carbs are a pain in the ass.
Originally Posted by 46lukasz
If your float levels are off that could induce the problem you described, unfortunately several other CV fuel circuit issues may also be the cause of the problem including fuel delivery pressure.
#2 carburetor probably has some kind of fuel pump thingy on it yes? That could be an accelerator pump or it could be a decelerator fuel pump. You might want to research that part because it seems to me they added a decelerator pump to some motors to deal with over-lean operating conditions when the throttle is chopped.
You have to remember that on a CV carb your throttle cable controls a butterfly valve but that valve precedes the vacuum operated slide valve. By design there is a lag time between the operation of the butterfly valve and response to open the slide valve. On closing the throttle both valves slam shut very effectively, fuel circuits were added to the design of later CV carbs to accommodate that operating condition, your carbs could have as many as 5 fuel circuits to control air and fuel ratios throughout normal operating conditions, blockage in any of those tiny passages is a common problem.
Last edited by TrialsRider; 03-26-2019 at 06:57 AM.
I'd just get some CR smoothbores and be done with it
Originally Posted by alwhite00
A little bit happened since the last update:
Shortly after balancing the carbs I noticed that the throttle is sticking open, so I replaced the push pull throttle cables with new ones.
One of the old ones had a kink in it and it was causing the problem. I lubed the new cables nicely put some grease on the bars underneath the throttle tube.
I also got a new tachometer cable just because.
It was a very noticeable improvement, throttle was very smooth, and after adjusting the idle speed slightly I could take the bike off choke in about 20 seconds so that was great.
I started playing with carbon fibre and epoxy resin, just out of curiosity of how you work with this stuff. It comes out really nice and i might do something cool for the bike soon.
I'm also slowly buying/preparing equipment to repaint the bike.
I plan to go for deep metallic black with a red stripe running down the middle.
There will be a chrome-looking Honda sticker with the wings on the tank, and a red CB750F on the side cover.
The side cover stickers I got are reflective stickers, i don't know if its a good or a bad thing yet, but i like them.
I did a mock up on the computer just to see how it would look in black (just inverted colors) and I am happy with it.
So I was really happy, bike running best I ever saw it run, just the paint job and the project is complete, but then disaster struck!
I fired the bike up and noticed that fuel is pissing out of one of the overflow tubes at the carbs. Small tear-down to take out the bank of carbs with the airbox.
I also noticed that the fitting at the top of the airbox which is the input of the crankcase ventilation system has this yellow goo on it. What could that mean?
I took off the float bowls, and saw that they are really quite clean on the inside. No fuel turned into varnish anyway!
With the carbs and float bowls off, I poured some fuel into the input tube, and tested the float valves individually, by keeping 3 closed and opening one at a time by hand.
None of them was leaking! So I'm not sure what was going on (maybe one stuck open). I guess it works as expected and it would be fine now if i threw it back on the bike.
One other thing I'm going to check though is maybe one of the overflow tubes that stick up in the bowl is cracked along the sides or at the bottom. If that's the case then the fuel doesn't have to reach the top of the tube to go into overflow.
And because its taken off now I thought I might as well take some time and clean it up a bit later. Any tips on this?
I was quite surprised to see that there is no diaphragm underneath the top caps of the carbs. Instead, they use a metal puck and very tight tolerance to make a seal and work in the same way as a diaphragm (vacuum created on intake pulls the puck with the needle up etc).
I have a couple of questions:
1. Should I use some lubricant between the puck top ring and the inside of the top cap to make a better seal? Maybe polish the two surfaces?
2. Should I also use some lubricant on the slides that go up and down inside the throats? There seems to be a lot of rubbing action there, and the slides of carbs 1 and 4 have visible scoring marks on engine side. 2 and 3 are very smooth
3. Could someone explain what's the function of the air cut-off diaphragm? there is one on each carb.
4. I totally don't have an accelerator pump on the #2 carb. I also cant see an accelerator nozzle anywhere in the throat of the carb. I thought these bikes came with one. Is this normal?
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