bike wont accelerate past 40. help!

[spanish]

I'm trying to help my lady friend get her 1980 gs250t running perfectly again, since she doesn't know anything about mechanics. It starts up fine, it runs fine, and it accelerates fine...until it gets to 35-40. That's when the problem starts. You can open the throttle up all the way, and the bike just won't go any faster. The gas is clean. The spark plugs are brand new. Both pipes get hot, so it's not a combustion problem. I'm not a master mechanic, but I just can't seem to think of a reason for this. Someone give me some ideas please

 

[BigD_83]

A slipping clutch seems likely.

 

[Big Rich]

+1.

If you give it more gas, does the motor rev higher but the speed does not? That would be the clutch. Either the cable needs adjusted/replaced, oil needs changed, or the clutch plates & springs need replaced.

 

[Steve]

Shift to second gear? :-\\\

.

 

[Seana23]

Hi babes.

Freshly oiled.pods - too oiled.
dodgy Condensor (if points fitted)
Timing not advancing...
Dirt in carb...
Blocked fuel filter...
Blocked Needle jet...
Or blocked Main jet...
Fuel tap diaphram perished...

Or as Steve said....
....change into second gear..........

Hope that helps some.

Xxx

 

[Guest]

Or possibly a frozen ignition advance unit?

 

[tkent02]

Clogged exhaust pipe had my GS 1000 down to where it would only do 50 down a hill. Some tard had put a big ball of steel wool into the collector for whatever reason. Pulled the steel wool out and it goes 140 or so just fine.

Maybe you have a mouse house in your tailpipe.

 

[spanish]

i'll check the exhaust first, that would be about the best problem to have haha. When I'm riding I can rev the bike into higher rpms, but when it hits 40 it won't go any higher than about 5k. I know it was just a joke, but shifting gears doesn't change anything. The rpms go up and down, like they should when changing gears at the same speed, but the speed stays about the same. Even with the throttle opened all the way

 

[terrylee]

hjfisk is probably right, had same problem with wife's 450, advance was rusted and not moving freely(should turn easily by hand). Took it off sprayed down with PB and broke it loose, been working fine ever since. The bike loves going as fast as you want now! terrylee

 

[musicman]

Wildly different cycle, but I had a Honda Passport (hotrod baby!) that would barely start, spent a lot of time trying to figure it out, I had fuel, spark, and compression, still wouldn't go. Had a bee's nest inside the muffler, which wouldn't blow out, broke it up with a screw driver and that tiny little 70cc engine came to life. Ya never know what you'll find in your exhaust! Might be worth investigating just to make sure.

 

[7981GS]

Wildly different cycle, but I had a Honda Passport (hotrod baby!) that would barely start, spent a lot of time trying to figure it out, I had fuel, spark, and compression, still wouldn't go. Had a bee's nest inside the muffler, which wouldn't blow out, broke it up with a screw driver and that tiny little 70cc engine came to life. Ya never know what you'll find in your exhaust! Might be worth investigating just to make sure.

Good point!
Mud daubers and wasps like to build nice nests made from clay.

Eric

 

[tkent02]

I have had several clogged exhausts on cars and bikes, thy all run the same, terrible.

One had an internal muffler baffle break and lodge against the outlet, one bike had the PO's daughter sticking toys in the exhaust pipe, many animal induced clogs.

 

[spanish]

Ok...so I took off both mufflers, nothing inside either one. The header pipes look fine too. I also checked the ignition advancer. Its moving freely. Keep throwing me ideas if you have them. Remember, the spark plugs are brand new, and both pipes get hot, so the plug wires are fine too. The bike runs perfectly fine up to around 40, then it refuses to go faster

 

[Guest]

Good point!
Mud daubers and wasps like to build nice nests made from clay.

Eric

Same thing happened to a friend with his outboard, mud dobbers clogged the port with clay.

 

[Guest]

So, what happens when it hits 40 and you hold it wide open?

Does it bogg,

Does it want to die out

If you get it up to speed again and pull the clutch in lightly while holding the gas does the engine want to rev up or just stay the same maxed out rpm.

I'm trying to figure out if its just dragging brakes or engine related.

If it wants to rev up quickly and it should as soon as you touch the clutch than I would lean towards other things, starting with loosening the back brake a bit and see if that helps.

If the engine simply rev's slightly more and doesn't go any higher than there is a test you can do.

Its a plug chop essentially.

Get some new plugs or use those if they are not colored too bad. Get it up to that speed, hold it wide open for about 5 seconds and then let go of the gas while pulling the clutch in and hitting the kill switch all at the same time.

Take the plugs out and take a look at the color. If you got the engine to shut down quick enough, the plugs will show you how it was running right at that point.

If they are white than its running way too lean. If its black its too rich. If its tan, move on to other things.

 

[brad020]

Similar problem

Similar problem

I am resurrecting a 250T as well, sounds similar. I can hit 50mph or so, but the engine seems like it's bogging above 5500rpm. You can feel a slight hesitation, like a (bigger) bike going from 4 cylinders down to 3. I would think if a twin dropped a cylinder, it would be more noticeable. I'm wondering about a valve spring floating or out of adjustment, poor mid-high range jetting, or an intermittent spark miss. Interested to see where this leads...

 

[Nessism]

Are their any modifications on the bike such as leaving the airbox off?

 

[brad020]

I am resurrecting a 250T as well, sounds similar. I can hit 50mph or so, but the engine seems like it's bogging above 5500rpm. You can feel a slight hesitation, like a (bigger) bike going from 4 cylinders down to 3. I would think if a twin dropped a cylinder, it would be more noticeable. I'm wondering about a valve spring floating or out of adjustment, poor mid-high range jetting, or an intermittent spark miss. Interested to see where this leads...

I was able to raise the jet needles, there was a spacer on top of the snap ring that should have been below the snap ring, and it helped a lot. I still feel a slight hesitation at high revs over 50mph, thinking maybe richen it up more and re-check the floats, and I should be all set. By the way, I have pod filters and stock exhaust, pilot jetting has been richened up.

 

[Guest]

What about the main jet?

Raising the needle didn't fix anything, more like the main is too small and your compensating by making the mid-range richer with the needle.

What does your plugs look like when you chop at high rpm?

 

[Billy Ricks]

Have the valves been adjusted and carbs properly cleaned. You need to start with the basics.