Bike doesnt rev past 4/5k rpm

[Ant132]

Replaced the rocker-cover gasket today in hope of curing a small leak. This involved taking off just the tank and the rocker cover, so job done and i re-assembled it, topped up the oil level and started the bike back up, no problems.

I was taking it around the the block so i could come back and re-check the oil level, but when i got on to the main road i opened it up to find that the bike wont move above 4/5000 rpm, it wont rev above that and comes to a halt until i knock it up a gear and come back down to the lower revs.

It starts and idles fine and in low revs its the same, but open it up to anything near 4/5k and it wont budge.

What have i done now?
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1980 Suzuki TS50 ~ 1984 Honda CB400N ~ 1992 Triumph Trident ~ 1998 Suzuki Bandit 1200

[nightshaddow]

sounds to me like maybe the choke is stuck on what bike is it i have the 125 cc super dream and when you take off the tank there is twin carbs on mine, maybe one of them (if you have 2) has become disconnected or the choke system cable has seized/ stuck in the closed position. presuming you havent touched anything else the only other thing it could be is fuel flow, check the tank tap and maybe even the inides of the tank tap could be a blockage reducing fuel flow to the carb
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"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

[Jamie S]

Not ever so slightly trapped one of the fuel lines ?

[Ant132]

[nightshaddow]

ok when you check your oil is it high or low and also does it hiss when you release the cap????? you could be building up pressure in the gearbox also check and clean your plugs as well as making sure they are sealed properly.

one thing did she run ok befor you changed the rocker cover gasket, if you also check it fireing on both cylinders the same the easy way is to check the down pipes to see if one side is hotter than the other,

it could be several things i just keep going till we sort it, i going to check the book of lies now to see if i can dig up any more
____________________
"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

[nightshaddow]

also just noticed in your reply you said there is only one tube to lh carb is there a fuel line to the right hand carb????? if theres not there is your problem maybee a pic would help if you can
____________________
"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

[Ant132]

The oil is fine now, but when i checked it, it was on the low side so i went and bought some from the garage. Now, the oil level is just under the max mark.

Would the level of oil have any effect on the problem i am having, could it be a cause?

Checked the plugs and the caps and lubricated the wiring, coil eith WD40. Just been out again and the exact same thing is happening, runs fine and when it gets to 5k rpm in an gear it splutters and theres like no more engine noise just like a bang bang bang, pop pop pop kinda thing. Hard to explain really although i tried to power out of it as if it might be a blockage but it was having non of it.

Ran great before the gasket change, only a few weeks ago i use POR-15 on the fuel tank and its immaculate inside, all new fuel tubing and carbs were cleaned. I went out this morning and it felt fine as usual.

Both cylinders are equally hot and theres only one fuel tube supply to the LH carb, no RH one

Thanks alot for your help mate.
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1980 Suzuki TS50 ~ 1984 Honda CB400N ~ 1992 Triumph Trident ~ 1998 Suzuki Bandit 1200

[nightshaddow]

ok how is the fuel fed to the second carb ie the RH one, i am thinking when you took the tank off what did you do mine has 1 line out of the fuel tank followed by fuel filter followed by a splitter (2 into 1) and one going to the LH carb one going to the RH carb i am thinking maybe a blockage or air trap some where so if we figure out the fuel feed i may be more help
____________________
"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

[Ant132]

[c-m]

i broke a bolt off in my rocker cover and the bike did the same. It would idle fine, low revs fine but when i wanted to go anywhere it would bog down.

Obviously a hole in or gap in the rocker cover allows gasses/oil etc.. to escape

[Ant132]

[nightshaddow]

definatly worth checking, though with these they are ohc and only 2 bolts required, check that the fuel tap fully open as i still think fuel or air flow problem have you checked the air box for possible blockage,

just as an after thought does it rev in neutral or will it not go above 5/6 k in neutral too
____________________
"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

[Ant132]

[Jamie S]

Although the revs sound way to high to be this, but could it possibly be a faulty side stand switch, if the bike is fitted with one ?

[Ant132]

[Ant132]

Just a though about what Jamie said about it being electrical maybe. The CDI is just above the rocker cover and sits inside the tank attached to the frame. If, for example, i'd accidentally knocked it and dislodged a connection or two could this be a possible cause?

Long shot i know
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1980 Suzuki TS50 ~ 1984 Honda CB400N ~ 1992 Triumph Trident ~ 1998 Suzuki Bandit 1200

[Jamie S]

[nightshaddow]

i dont think it would be the cdi it would work or it wouldent basicaly i never heard of one half working though on the other side is the coil or twin coils depending on which it is it is more a possibility that these are breaking down, to me it still sounds like fuel starvation,

first before anything underneath the carbs are drain screws, open both in turn and let flow for a few seconds to a minute catch the fuel make sure you let drain more than the bowl could hold, maybe even tap the bottom of the bowl gently at the same time to dislodge any crap, then give her a rev also take out the plugs and give them a clean with a wire brush, also check the gap, i belive it should be 0.7 gap, trying never hurt
____________________
"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

[Ichy]

Check the carb bowls incase some bits of rubbish got dislodged when you removed the tank.

No reason why its not electrical. For instance, Viragos are notorious for cutting at a about 4-5k due to the vibration affecting the side stand switch connection. I would certainly check all the CDI connectors and the coils.

Try turning the choke on when it starts cutting out.
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https://www.metacafe.com/watch/1972097/how_to_behave_on_a_forum/

[Ant132]

[Gaz-t1esto]

I had a similiar fault with my motorcycle, unlikely that this is the fault on your bike but maybe worth reading...

Recently when i opened throttle even just a touch i would hear sparking noises from around the spark plug area and engine revs would drop and the bike would cut out. took me 2 new spark plugs and a month of trial and error before i found my spark plug cap and wire were faulty and sparking due to the thread being damaged.

Maybe worth checking that the spark plug and surroundings, other than that, i agree with the other posts as i had to check all of above for my fault before i noticed the sparking noises from the bike.

Regards

G

[Ant132]

Had the carbs off today, they were really clean but cleaned them regardless. Got them back on, quite hopefuly but took it out on the road and the same happens. Re-traced everything i did yesterday and i cant find a thing wrong or different. Cables, tubes, pipes, oil level, carbs - everything.

I've got the rest of the week off anyway, so i think i am now going to order the parts in for a top-end overhaul that i was planning for the near future.

So, i am just going to order a top-end gasket set and piston rings, if needed. In the hope that all will be solved with regard to the oil consuption and leaky-ness. Needed doing anyway, this has just given me more of a reason.

Thanks for the help everyone!
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1980 Suzuki TS50 ~ 1984 Honda CB400N ~ 1992 Triumph Trident ~ 1998 Suzuki Bandit 1200

[Finglonga]

Take it the first thing you did was remove the tank again to make sure you hadn't trapped or kinked any cables/breathers. . . . .
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Andy Sez....
F.Y.Y.F.F.

[Odie]

God almighty do some of you talk a load of "arse cheese"
The rocker box on a 250N does not hold pressure in only oil so it wouldnt effect it!
Yes it could be the CDI but more likely the generator, wont go past 4,000 / 5,000, ignition not advancing.
The carbs only have one feed to them, they feed the other carb internaly.
Check carb rubber (ask Kal about them!)
any problems give me a bell, Kal has my number (needs to stop pissing about and get his engine done )
odie
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You are so ugly when you were born the doctor said "I?m gonna drop it, if it falls is a rat, if it flies is a bat."

[Ant132]

Finglonga - full checked everything!

Odie - Thanks for replying, If im in, say, 2nd or 3rd gear it will rev fine up till about 4,000 and that when you notice something is wrong and it will gradually find its way to 5,000 rpm exactly when it stops and loses power.

When i knock it up one, it will have the exact same symptons but just minus 1,000 rpm i.e. it does it at 4,000 until i knock it up one again and thats when it will continue fine at 3,000rpm.

Very frustrating, just been out and checked all wires and connections to the generator and everything is fine and connected. Have you a way of confirming the generator is at fault mate?

When i had the carbs off earlier, the right hand carb rubber (going to airbox) had a small split in the bottom but i wasnt too worried about it, the rest are fine. What kind of difference will this make?

Just as an after-thought and a reply to nightshadow, I came in after re-testing it and i was in first gear with the clutch in and it revved freely over 5,000. It went upto 7,000 when i backed off.

Thanks for your help
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1980 Suzuki TS50 ~ 1984 Honda CB400N ~ 1992 Triumph Trident ~ 1998 Suzuki Bandit 1200