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

[sgallaty]

slides are stuck.

EDIT: hehe ok, well that was my guess before reading.

I'll read it now and respond.

Ok. the 'bwaa' noise is the butterfly valves opening and the engine sounds coming out of the carbs.

Look into your carbs when you open the throttle. when you open the carb you should see the slides move up as that vacuum circuit lifts them. I think your slides are sticking. they take too long to settle (30 seconds).. I think you have some mild adhesion going on there, enough to prevent them lifting (it's a fairly gentle force)

 

[Travis]

It's the tires!!! It's GOT to be since it's the only thing left!

Been watching this thread (like a lot of others on here) hoping the next time I check it the solution is found!

A lot of these types of threads aren't interesting because the poster doesn't give enough information or is inexperienced and doesn't really know what's going on. That makes them hard to stick with. This is not one of those threads and it's nice for a change. Thanks for knowing what you are doing, clearly explaining what you are doing, and keeping a positive attitude about it!

 

[pregrid]

Hmmmmm..............tire pressure..............hmmmmmmmmmmm

 

[xjwmx]

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.

You are wrong.

 

[LilMoney]

If you have a fuse between the battery and the regulator/rec pull it then start her up and see what happens......

 

[sgallaty]

The issue can't be spark advance, because spark advance is reactive to RPM - meaning that you would open it up, the engine would rev to about 2k-2500 and then above that would have no power.

if it idles, you've got spark/fuel/compression.

This has to be the slides not rising in my mind, because the slides are what controls the venturi that determines amount of fuel to the engine. I am guessing you haven't checked what I asked you to check. Look INTO the carbs while it's running and open the throttle and tell me if the slides rise when you open the throttle.

the butterfly valves don't cause your engine to run faster, in a CV carb ... the slides do.

 

[5twins]

The stator died on my SR500. I replaced it with a newer one. The bike would start and idle but not rev up. What I didn't realize was that Yamaha had changed the timing slightly on the newer model by moving the pick-up magnet a little on the flywheel. I had to install the newer flywheel as well and then it worked. I had a dirt bike that suffered a similar problem. I was doing some carb work and inadvertently unplugged one of the wires running to the stator/pick-up. Same symptoms - it would start, idle, but not rev up. So, it is possible for an electronic ignition to function partially - start, idle but not advance. I would investigate the pick-up, magnet, and the wiring related to it.

 

[1974jh5]

I'm with 5twins. Pull the connectors for the coils, pickups etc apart and look for corrosion. Even if they look good, get some contact cleaner (not brake cleaner!), clean the connections and 'tighten' the female plugs before putting it all back together. The TCI box has to 'know' what RPM the engine is running to decide how to advance the ignition so if it's not getting that 'feedback' it won't know what to do.

For that matter, carefully check the ground connection for the TCI box. If it's corroded, all manner of weirdness can happen. Ohming it and the coil etc grounds (and for that matter, ohming any electrical connection) is a start but it doesn't tell you everything you need to know. If you do an ohm or continuity test, all that tells you is you have a ground, it won't tell you how much power that ground is capable of handling. If the wires look good, take the conector off the frame and scrape both the frame and connector until you get shiny metal then reinstall.

For that matter, how's the battery? If it's only showing, say, 9 volts you might be able to get the bike to start but if the TCI box is only getting 9v because the battery's soaking up all the available voltage then it gets its little brain scrambled. You might try disconnecting the battery entirely and then using jumper cables from a car etc to get full +12v to the electrical system.

 

[mouser]

Done deal....fixed!
I knew this wasn't a carb thing!!!!
I went out yesterday morning and was going to perform carb surgery again then decided no way...I've been at this bike game for 40+ years and know what a good carb looks like...
So I thought back to what was the first thing I fiddled with when the issue started and decided to start there...first I changed my plugs then when It didn't start and I didn't have spark.....The Magic box.....at that time I plugged in a spare TCI I had and got spark so I made assumption #1....the box was to blame. But that time instead of taking the plug out for the spark test I plugged the cable onto an old plug I had taken out earlier and had great spark. Assumption # 2...that the new NGK plugs I had just installed were good..
That is when the problems stated..I made assumption #3!!! That the spare box I had was good! Now I was in deep!!! Now I had replaced the black box with a defective one and put new plugs in....one of which is defective!!!!!..during all of these issues I had put the old Champions back in...now I had two good plugs but a defective box...
Three carb removals and inspections later.!!!! Hours of cleaning and testing wires and connections later!!!!! Days of frustration later!!! I dug the original box out of the trash, plugged it in.....bike instantly starts, and runs better than it ever has...
I kicked my own arse up and down the driveway for being so stupid and then spent the day riding!
I cannot begin to express my gratitude to you folks for the help and advice you have offered. Because of it I now have the cleanest, most perfectly tuned carbs in the world, Electrical connections that would work on the space shuttle they are so perfect, and have re-learned lessons that I thought I had already learned....
Never make assumptions!!! Never overlook the obvious! And never ever!!! buy another NGK spark plug.
Ride Safe! Keep it shiny side up!
Thanks again...

 

[pregrid]

So did this epiphany come to you on the boat?

 

[mouser]

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!

This quote is what turned it around for me......I owe you!!!
Brilliant ...and sound advice!!!!!

 

[retiredgentleman]

Well done to sort that out.................we knew you would do it

A good trouble shooting rule to live by.......................when any mechanical or electrical device goes defective on you, only change one thing at a time.

 

[xjwmx]

Do you know how unusual it would be to have a bad brand new plug? It's the carbs...wait and see.... They're bubbling and frothing raw gas, remember?

 

[pregrid]

This quote is what turned it around for me......I owe you!!!
Brilliant ...and sound advice!!!!!

Nah, glad you got it worked out.

 

[pregrid]

Do you know how unusual it would be to have a bad brand new plug? It's the carbs...wait and see....

if I had a nickle for every bad brand new spark plug I've run across I'd buy you a 12 pack of your favorite beverage. and a massage!

 

[xjwmx]

^What are the odds then? One in three? One in three million?

 

[5twins]

I hope you also learned to never throw old parts away. lol.

 

[1974jh5]

Glad you got it fixed!

I know what you mean about going through everything only to find it was fairly simple; when I finished the rotary swap in my Jensen Healey race car reversed wiring on the crank position sensor drove me completely bugshit for about a week. It would not start, my noid light showed no injector pulse but the spark would pop about once every ten engine revolutions. I was leaning on the workbench, drinking a beer feeling sorry for myself and looking at the connector layout part of the wiring diagram when it hit me... and no I had not reversed the wiring at the plug!

 

[xjwmx]

Better to throw old parts away than new ones. I'm not ready to accept that a bad new plug was the problem. Many things are more likely, including bad connections, which may turn up again. Yes I'm sure bad new plugs are as common on the message boards as feathers on a goose. But. Ponder the specific odds of the ,many potential causes. I wouldn't get on that plane.

First thing I would do is swap the plugs twenty times and each and every time it has to follow your prediction.

 

[Mark19]

Well!!! many hours later!!!!
I tried the Reg / Rect and found it made no difference. I tested resistance in the pickup coil. It is fine.
I cleaned and tested every electrical connection. I completely disassembled cleaned and tested my ignition switch. The primary circuit and ground on the coil test ok.
I even tried spraying fuel into the carbs when it is running.,no change in the RPM!!! just over rich fuel exhaust..white smoke..I tried manually choking both carbs when running , still no changes from a perfect idle. RPM stays at idle. It will idle easily from as low as 6-700 rpm up to I'm guessing 1200-1300rpm after that......nuthin. I tried a new set of NGK's and a new set of Champions and put the used plugs it last ran on.
I checked my compression, valve clearances, and cam chain and intake manifolds.
I am at a complete loss as to what to try next.! This one has me stumped!
44 years biking and building bikes and I have never come across this problem or any thing like it.
Anything I'm missing gentlemen???
Thanks for your input....

I amcurrently having the same issue with a 1980 XS650 special II. I did the same things and still having the issue. Had the carbs off three times looking and cleaning. People advised me off the advance but it is a electronic ignition dont know where the advance rod is.