Starts, Idles, and revs but not high revs?

[barrycoish]

Last week took the bike out for a ride and it started causing a few problems. It starts no problem, it runs but I can't get it to rev up like it should it revs like it's at about half throttle and that is it. Thought the carb might have dirt in it but no luck. Took the carb off and checked it out but all looks good. It's one of my 84 200x's by the way incase anybody thinks that matters. Any help would be great.

[smokinp]

give us some more info...what does the spark plug look like?is it smoking or anything?does it have compression,fuel and spark?

[barrycoish]

Thanx John I will check that out when I get home. The plug looks fine, has spark, compression and fire the bike runs but not right. Like I said starts fine, idles fine, runs at low rpms but will not rev up properly.

[smokinp]

try removing the exhaust and see what it does..

[atckowalski]

If you have a fuel filter, it may be clogged.

[wilb67]

Make sure your air filter isn't clogged up with dirt. Coil could be bad. Check timing and your valve clearence.

[barrycoish]

checked fuel filter, no problems found. Took exhaust off still no good. I am going to check the timing and valves tonight, not sure what else to do?

[cliff2302]

I had the same problem with my tecate and after over a month, we finally checked the stator and it was shot. i guess when stators go, they don't usually go away all at once. hope this helps.

[fat batster]

I sure wish that someone would let us know how to fix this problem. I have the exact same problem with my 1986 Big Red 250es. The problem comes and goes. I have tried different carbs, cdi boxes, spark plugs, spark plug caps, rebuilt the engine complete with valve job, new muffler, new timing chain, new fuel tank and petcock and I STILL have this problem. I am lost. The only other thing that I can think of is the pick up coil that is down by the stator. Anyone have any ideas?

[oscarmayer]

tuning?
it sounds like the tune is way off! i bet your runnign lean at the big end. when you are in liek 3rd gear and are at wide open throttle you should have some(jsut a little) black/gray (not blue) smoke comming out the exhaust.

here's what you need to do. use the old plug to let it idle up to warm oeprating temps and when it's very warm, then shut it off and change to a new plug.
take it and rip on it a few times then shut it down and pull the plug. see what it looks like and smells like. if shoudl be a nice carmel color (not a lot but a little but) and smell of burnt fuel. if it's black it's too rich, if it's not colored at all or has a whitish/yellowish coloring it's too lean.

too rich or too lean means re-jetting.

[fat batster]

Thanks for the reply.

I know that it is not the jetting. If it were the jetting it would run bad all the time. The bike will run great for hours and then I might shut it off for a few minutes. Once I start it back up it may or may not run good, its a crap shoot. Sometimes it switches between running good and bad without me shutting it off at all. It is very hard to explain. When it is running poorly, it acts like it is running lean however there is absolutley zero popping or backfiring. If you have ever driven an older car that has a mechanical advance mechanism that is stuck then that is what it feels like. It revs out but it does so slower than normal and with little power. If I upshift to the next gear then it is fine in the low to mid rpm range but once I try to increase the revs it starts struggling again. I am about to pull my hair out.............

[oscarmayer]

hrrm could be an overheating cdi or coil? i knwo on the old carbed hotrods we had issues with heat and fuel vaporization before it hit the intake. we had to put heat hose aroudn the fuel lines to kepe them cool so the fuel woudl not vaprize before getting to the carb from heat. (heatsoaked) i also seen old coils overheat and have issues too.

[beets442]

Sounds like main jet clogged or floats are sticking.
Ran good before this though?

[fat batster]

It still does run fine sometimes and sometimes it doesn't. I agree that it sounds like a float issue and/or a clogged main jet. I keep coming back to that conclusion over and over again but I have cleaned and tested the carb multiple times and it is spotless. I have a new theory that I hope someone can talk me out of. I am wondering if it is a slightly bent or burned intake or exhaust valve. If the valves in these engines rotate during engine operation then it could stand to reason that at some points along the rotation, the valve doesn't seat fully. This would cause a poor vacuum signal through the carburetor which would act just like a lean condition which would cause low power. If this were the case then the valve would eventually rotate around and begin sealing properly again and my power would be restored. If this were the case you would think that I would hear some popping in the intake or exhaust though. Please, everyone rack your brains with this one.........

[PaTriker]

Sounds like a fuel problem.

[oscarmayer]

valves do NOT rotate. the retainer clips keep them from rotating. so that's out.
good thinking though.

do you have a filter between the tank and carb?

oh and the work i was searchign for in my last post is "Vaporlock".

[SCRAMCHARGER318]

if you bent or burnt a valve it would most likely miss at idle and not so noticable a high end, maybe you have a gas cap on the process of going bad? also make sure you clean the gas filter in the petcock(if you havent already) make sure all you vent tubes are clean of mud and debris. if all that checks out then i would agree with oscar and i would say most likely the cause, a electrical issue. if it were a mechanical problem it would most likely do it all the time. get out the ohm meter and check the coil's and cdi box, check all wiring connections and grounds, maybe you have a wire rubbed bare and grounding out on the frame.
hope this helps

[fat batster]

Thanks everybody for chiming in. I agree that it sounds like a fuel issue but everything is new (plastic tank, petcock, clear inline fuel filter, spot less carburetor) I wonder if the main jet sheild that is in the carburetor could be causing this? I have never had trouble before and I know that it is installed correctly..... The problem has to be electrical in nature and somehow tied to the spark advance. I have already checked the coil and replaced the spark plug and cap. The CDI is also new so I guess I will replace the pulse generator and check the wiring. I may replace the spark plug coil as well even though it tested good.

[oscarmayer]

is the spark advance itself in good shape? are the springs broken? is it locked up? are they worn out and loose?

[fat batster]

This is a 250es which has no advance mechanism. It is built into the CDI.

[Tri-Z Pilot]

Just test your stator coil with a multi meter before buying new. No need for new parts if your old ones are fine. Have you checked that your floats are set right, or are they plastic, I cant remember.

[boosted96cobra]

Have you undone the gas cap just to check it when it does run poorly? My friends 185 did this and so did my daughters 125m. Air has to go in and replace the fuel that has been used inside the tank.

[fat batster]

Yes, I have tested the stator and it is good. I have also tested the pulse generator and it tested good but all that means is that it is not shorted out since you are only measuring the amount of resistance between the wires....it could still be "lazy". The float in the carburetor is plastic and non adjustable. Yes, I have checked the fuel cap. It is a new plastic cap.

[BigRed_Ryno]

Have you undone the gas cap just to check it when it does run poorly? My friends 185 did this and so did my daughters 125m. Air has to go in and replace the fuel that has been used inside the tank.

That was the problem on my little '70

It'd run great, then would start to bog, even by taking the cap off, it was too late the engine would die. New cap = Kushty :D

[fat batster]

UPDATE:

I think I figured out the problem. Everytime that I would strip down the carburetor it would be clean so I would put it all back together and it would be fine until a few weeks later (the next time I rode it). I finally broke down and pulled the carb off again and I found evidence of what I believe was causing the problems. I found a few small pieces of trash hanging out in the bottom of the float bowl. When I rubbed them between my fingers they turned into a powdery mess. Rust you say?.....nope, I have a plastic tank. The problem appears to be the sealer that I was using on the float bowl gasket. I know, I know....you shouldn't use sealer at this joint but my gasket is 22 years old and had flattened out a bit. I made sure to use a non-hardening type sealer that was supposed to be unaffected by gasoline. Turns out it wasn't. After a few weeks, some of it would flake off and fall into the float bowl. From there it would clog up the main jet just enough to lean it out to the point of power loss. Eventually it would be sucked up through the jet and my power would come back and the bowl would be clean for a bit. This is why it was so hard for me to catch it. I actually hooked up a clear drain line to the bowl and routed the open end into the fuel tank/side panel grommet. The same method you would use to check the float level....anyway I did this and left the carburetor drain screw very loose. I rode the trike around like this for a while and thats when I noticed the small bits of trash beginning to accumulate in the clear tube. It just goes to show you, even if you think everything is spotless..........check again........and again......and again...............................

[oscarmayer]

haha not that's funny!!!!

i use hi-temp black silicone to hole the new gasket in place while puttin ghr blow together. (very very thin amount.) why don't you spend a few buck on a carb rebuild kit like suggested? they come with AL the gaskets and seals for the carb. off ebay it's liek $20 shipped to your door!

[fat batster]

Figured I’d chime in on this old post that I’d hijacked (sorry about that) and share that I finally found the real issue…only took a little over a decade haha.

To recap, my 86 250es had an intermittent low power issue. There was no rhyme or reason to it but when it acted up, it just ran flat for lack of a better description. It would start and idle fine but wouldn’t rev out. I’d suspected a timing issue but could never catch it in the act of messing up when my timing light was around. Finally, the stars aligned and I was able to confirm my suspicions. At idle, the timing was spot on but when revved the timing was actually retarding instead of advancing. I tried to take a video but I could barely see it myself and the camera was unable to capture it.

I swapped to my spare CDI and the problem disappeared. Then, I swapped back to the “bad” CDI and the problem wasn’t there. I suspect that the issue is actually a poor connection at the CDI and not the CDI itself. It’s weird because I’d swapped CDIs before and the problem persisted which furthermore leads me to believe it’s just a poor connection. I cleaned the pins as best I could and doused them in WD-40 and so far so good for the past year.

Hope this helps someone…

[350for350]

Wow! It's awesome that you were finally able to figure this out. It sucks that it took so long for the stars to align for you though. Merry Christmas and happy triking!

[ATC King]

I cleaned the pins as best I could and doused them in WD-40 and so far so good for the past year.

There are products for cleaning and improving electrical connections. The good ones aren't inexpensive by any means but they're what the automotive and other industries have relied on for years to fix some serious and perplexing issues that came down to bad connections.

Here's one: https://wurthusa.com/Chemical-Product/Cleaning-and-Care/Electronics/Stabilant-22A-Electrical-Contact-Enhancer-15-ml/p/0893622

A less expensive product is https://caig.com/deoxit-gold-g-series/