my bike starts,runs,idles perfectly but will not rev!

Thanks every one for your input. Here is the whole story. 2 yrs ago I put this bike on it's side at about 40 mph..I was banked hard in a right hand curve and my front wheel ran over a piece of plastic about a foot square and it caused a speed wobble and down I went. I slid with it until it stopped and broke my left hand. I brought it home and started it up a couple of days later. It ran fine and I parked it, being unable to ride it.
It sat for a full year. I picked up the parts to replace those I wrecked in the accident.
Bars, instruments, master cylinder, kickstart, tire, seat, etc. and installed them last summer about this time. The bike ran fine still.
I found that I still was unable to use the clutch effectively because of the hand so I put it away for the winter. This spring it still started and ran normally and I drove it up the road and back a couple of times, but I found that calipers etc needed servicing from sitting so I tinkered with all that stuff all summer then decided to put it on the road last week. That is when this problem started.
Short of draining my float bowls and putting fresh gas and plugs in it I did nothing to the engine since the spring, four months ago, when it ran perfectly...
It starts and runs better than it ever has but will not do anything but idle perfectly...
In 44 years playing with dozens of motorcycles this is the first one that has me absolutely stumped......BUMMER!
Today I will again remove and disassemble the carbs for the third time and look for clues! If that doesn't work I will try to hire an exorcist!!!
 
I don't want to insult your trouble shooting abilities, but I have to ask; when you twist the throttle does the carb shaft with the butterflys actually rotate?

I've run out of ideas, but I'm sure there is a solution.

Don't be one of those guys that never reports back here after the real problem is found. The members here all want to see your bike running properly again, so just keep at it:)
 
I will definitely keep posting. Thanks for your interest ! No insult taken.! :D The butterflys function perfectly.
I might be onto something now!. I just started it up...first kick as usual ..without the air filter pods on an looked into the intakes as it was idling. I have never done this before and am not sure what would be the normal behavior of the slide.
What I just observed is that when I open the throttle the slider goes up about 1/2 way and then vibrates rapidly up and down about 1/8 inch and fuel in the form of rather large droplets sprays and bubbles up from where the needle goes into the jet and actually sprays out the intake!!!!!
What's up with that!!!
 
That doesn't sound right. Fuel mist should come up but not large droplets like that. I think you're flooding out when you apply the throttle and that's why it won't rev up. Inspect the needle jet and the hole it mounts in. The needle jet is a push fit into the body and is sealed in with an o-ring. If that o-ring has gone bad, gas can flow up around the outside of the jet instead of just through it. Before pulling the needle jet out, place your finger on top of it and see if you can wiggle it in the hole. If you can, the o-ring is shot.

There's also an air feed jet (marked with an "M" on your carb set) that supplies air to the needle jet area. If that's plugged, you would be getting only fuel .....

BS38AirJets.jpg
 
I've run into this symptom many times on cars with a dropped baffle in the muffler or a plugged converter. You've got to get the old exaust out before new fuel can be introduced into the combustion chamber. With a partially plugged exaust the engine will idle but will not take revs as the exaust gasses cannot, well, exaust. You said you were gonna try it with the exaust removed, have you tried that?
 
Not just the o-ring. Look up through the passageway that the needle jet plugs into. There is a hole entering from the side. That's where the air from the air jet enters to mix with the gas being pulled up from the main jet. If that air jet is plugged, you're pulling straight fuel up from the main and there's no air being let in to mix with it.
 
You said you changed spark plugs, did you use Resister plugs or not? Depending on your ignition setup you may have used the wrong plug perhaps. For instance I have converted mine to use 5/8 plugs and I changed the connectors to compensate for my plug choice.

But I tend to believe you are now on the right track with the blow-back and the non emulsification of the fuel from the main jet.

By the way when you took off the exhaust did you remove the headpipes? You may want to just to check for mouse nests or mud wasp nest in or near the exaust port.
 
I was convinced this morning that I had it beat thanks to suggestions from both 5 twins, pregrid, and the rest of you kind folks.
Yesterday I removed my exhaust completely...right to the head...no change...the exhaust is absolutely fine.
I know the passage from the needle jet chamber is clear...and unrestricted in any way.
Today I removed the carbs again.....boy am I getting good at that job lol...I pulled out the needle jet which had the tiniest bit of movement. Every time I had taken them apart before I had visually inspected the o rind but was afraid to actually remove it for fear of damaging it. I live in a very remote area and a small thing like that can take you off the road for a week or more..
This time i took them off the shaft and sure enough they were still intact but pretty ragged looking. I managed to find new o rings locally, strange but true!!!!, I blew cleaner thru every thing. then compressed air.. and probed the three tiny holes in the throat and made sure they were open.
After reassembling them I saw a discrepancy in the throttle flaps. every time I worked on these carbs I removed the angle iron piece joining the two bodies because it got in the way of removing the bowl gasket. This time I put it back on before I checked my flaps. I noticed that the flaps weren't set the same. This explains why this bike always came up black looking on my left cylinder during a plug check. Never enough to worry about.
Well now I was so confident that my problems were over I put my boots on got my helmet and filled my gas tank. It started first!! kick!...Sounded great!...better than it ever has!!! and did exactly the same thing! It will idle from 600-1200 rpm then spits gas out the intakes and will not rev up! This time however it did not have the gas bubbling up out of the needle valve...I suppose the new o rings fixed that. The droplets appear to be coming from much deeper in the carbs ...like near the float flaps...
Can this be my coil breaking up or something of that nature. I've tested it with a meter and it appears to be good. I've tried two black boxes that both do the same thing but I don't have a spare coil or any other electrical spares to try.
 
I did change my plugs and have tried new resistor plugs, new non resister, and the Champions that were on it when it last ran fine.... I am confident that it is not the plugs!
Thanks for asking glenpd I appreciate your input.
 
I'm having pretty much the exact same problem! My bike 1983 starts great, idols and revs up to 3000rpms perfect. Then it feels like it hit a rev limiter and chokes. As soon as I let off the throttle, it returns to idol great.

My mechanic said that my TCI unit is messed and it isnt advancing. I just bought a used TCI - an '81 part # TID12-01B 4M4-10 and the bike turns over but doesn't even start. My old TCI looks older, part # TID12-01 3GI. That one starts great.

I have a feeling I have the wrong TCI unit. Sounds like a need a 5V4 version for an '83. Not sure what else to do but try and track one down. Hopefully you come up with a fix! Crosses fingers.
 
son-of-a-bitch! where's that emoticon giving the sign of the cross? Prolly need to walk away for a while and let the diagnostic gods think on this for a while. I turned wrenches professionally for over 40 years and from time to time I would run across a problem like this one that would test my confidence in myself. Almost always, if I would walk away from it the answer would come to me or I would see something I missed the first 20 or so times I had looked at it before. The answer is there, waiting to show itself. Walk away, but stay with it (if you know what I mean). You'll figure it out, and we'll all celebrate!
 
Well if it is any help JohnnyAction, that is the part number on both of the units I have tried on my '80. That is stock # for that year. Both of them do exactly what you say is happening to your bike too. I think it highly unlikely that two of mine would both be messed up identically...I'm not buying a third one just yet...Keep me posted if you discover something.
 
Pull the carbs. Leave them together. Drain the gas from the float bowls. Find a shop vac and a vacuum hose that is close to the diameter of the carb outlet. Fire up the shop vac. Place the vacuum hose at the engine side of one of the carbs, With the shop vac running, rotate the throttle shaft. If your slides and diaphragms are working correctly, the slide will rise. The more you rotate the throttle shaft the further up the slide will rise. Repeat this test on the other carb. This the only test I know of that will let you actually see the slides rise by air flow. They must pass this test. If they fail this test you have a slide, clogged port or diaphragm problem.
 
I think your brass floats leaked and sank in the two years it was sitting, making it run super rich now. That's the only thing that can really explain the gas bubbling out of the main jet :D Pretty obvious.


Could be the needles and seats too I guess, but it's one or the other.
 
I'll try that test you described Purplezinger ...I refuse to give up on this one! I've fixed, worked on, and lived bikes for over 40 years. this is the first one that truly is challenging me....!
 
As obvious as it my seem xjwms. The floats are absolutely not to blame on this bike. They are perfect and are adjusted and function perfectly. the needles, seats, diaphragms, and slides are immaculate, as is every passageway for air and fuel. It ran perfectly only 4 months ago...I'm still guessing electrical....I've checked everything else but my tire pressure.. Thanks for your input however, I will keep you posted. I will get to the bottom of this...now I'm absolutely determined to find out what's up ...this is a first!
 

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