Yamaha Eleven Special Issues

[Bike Extreme]

Hi,

I am a newbie. I have required recently a 81 model Yamaha Eleven Special. It have the following problems that baffles me.

Problems :

Can't set idling lower than 1800 rpms otherwise bike dies.
When you ride her under 3000 rpms no power and than when you go over 3000 rpms sudden surch of power.
There is a constant blow back of air through airbox.
At times she gives blow back down so heavy that it blows out the little plastic seal on top of the timing tensioner.

What I have done so far :

Cleaned and set carb according to workshop manual.
Replace both fuel hoses and vacuum hoses.
Replace sparkplugs.

Please help!

[slow mo]

you moght try the pick up coil fix ,,look it up on the forum it,s common and an easy fix ride safe and welcome ,,,slow mo!

[natemoen]

Check your valves and make sure they are in spec and you absolutly must vacuum sync the carbs.

[GLoweVA]

There is a constant blow back of air through airbox.
At times she gives blow back down so heavy that it blows out the little plastic seal on top of the timing tensioner.

This is the statement that concerns me the most.
If you've got pressure building up inside the case, then it's due to blowby past the pistons.

Compression tester is your friend. Check to make sure that all 4 are even (within 10% or so) I've heard that some have been as high at 150, and some will even run as low as 60psi but the key is that no single one is too low.

[TopCatGr58]

Hey there Bike,

Like George said, a compression test will help with diagnosis. Remember to do it with throttle held WIDE OPEN, and after the engine has been warmed up,but I would suggest 1st cold. Just turn OFF the fuel, and remove ALL 4 plugs at the same time to lessen the resistance and making it easier on the starter motor. The values should be within 10% of each other. You could repeat the test after it's warmed up, and if they are lower, then that will indicate too small valve lash/lifter clearance=reshim, see FSM!

The way these engines age/wear, the valve tolerances actually get closer, and so can eventually cause a valve to not fully close=blowback, and will get worse when engine warm.

Other problems could be carbs not fully cleaned...we have a phrase "triple clean", because folks often don't get ALL of the small pilot/idle circuit passages fully cleaned the 1st time around. Also, hopefully you didn't use caustic carb cleaner/dip and soak the bodies in the dip...it can damage the butterfly shaft seals=vac. leak! Running strong over 3k rpm is when you are getting into the mains, so the low rpm throttle response also points to the pilot circuit not thoroughly cleaned.

But another problem can be if you used a carb kit...with replacement pilot jets....K&L jets in those kits are known to NOT be correct and cause overly rich running, untunability, poor throttle response and such....best to get real Mikuni jets from local dealer. Good luck, let us know what you find.

T.C.

[skids]

Worn out or inappropriate exhaust systems can cause exhaust to back into the carbs. This can cause a lot of heat in the carbs and other problems. You can get the opposite of "exhaust scavenging" occurring at certain ranges of rpms.

[Bike Extreme]

Thanks guys for all the info so far. I have started to open her up today. As I progress and get new hiccups I will shout.

[MaximPhil]

Welkom Bike Extreme. You have found the right place to get all the help you will need to get your bike running. Many have started with bikes that did not even run so you are well on your way.
Phil

[Bike Extreme]

Thanks Phil, I appreciate your well wishes.