R80ST - Problems, Problems, Problems..

[England-Kev]

My usually reliable ST has aqired a misfire, but it happens right the way through the rev range, so that no matter what speed you sit at, the misfire is there.

The coil is good (Dyna) the leads look Ok, and I pulled the plugs and they both look fine.

Secondly, I think I have a carb problem? I had a play with the Twinmax today, and I noticed that if I adjust the pilot air screw, on the left hand side, nothing changes, either fully in or fully out, but if I adjust the right hand side, fully in kills the motor, and winding out, affects the tickover speed.
Now both carbs were sonic cleaned, and rebuilt with new kits

any ideas?

 

[Solo Lobo]

could be time for a carb strip and clean... pull the float bowl and mixture screw, push up the slide and shoot some carb or brake cleaner through the mixture screw hole... wear some eye protection!

 

[(RIP) Proff]

Change the plugs....
Check no gunge in bottom venturi 'ole [from breathers]
Check the little hole that lets the diaphragms rise and fall ain't blocked
ALSO MAKE SURE YOU AIN'T GOT A TIGHT TAPPET

 

[England-Kev]

could be time for a carb strip and clean... pull the float bowl and mixture screw, push up the slide and shoot some carb or brake cleaner through the mixture screw hole... wear some eye protection!

The carbs have had a sonic clean and full rebuild? I will try what you say though...

 

[(RIP) Proff]

I'll say it again.
check your Valve clearances

 

[JJH]

will it misfire if u have it on the stand? If so u can find the offending cylinder. If its both cylinders it has to be a conom part like a coil. If its on one u can swap parts plugs leads ect until u find the bad part Hope this makes sence and is a help

 

[JJH]

and check the tappets

 

[England-Kev]

I'll say it again.
check your Valve clearances

I have a mind to check the tappets too....

 

[England-Kev]

Sunday morning...

So I dropped of both lids and checked the valve clearances, and they were fine, no tight ones, in fact to be fair, they may have been a little larger than spec, so I adjusted them down to the book, 10 inlet, 15 exhaust. I then set to with the left hand carb, but first I pulled both pilot air screws, the one on the left was bone dry? so maybe there was a blockage somewhere, the one on the good carb was wet when pulled. So I blew, poked, prodded, and cleaned, and it is now all back together, and ready for a run.

more later.

 

[Kenny]

Do them again.....

.10mm inlet and .20 exhaust !!!

 

[England-Kev]

Do them again.....

.10mm inlet and .20 exhaust !!!

That's where they were, I have put them back to factory spec now, actually the bike is quieter. but I still have the mis-fire, so I shall buy some plugs next week, and see if that improves things.

 

[England-Kev]

so what else could cause the mis-fire, any other pointers?

 

[Buckingham]

Misfire

If it has the original rubber moulded plug leads, they sometimes give up. Best to make some up yourself.

 

[Kenny]

Work backwards from the plugs ( cause more trouble than you think ) then plug leads/caps ( make your own but the beemer ones are OK when new )...then the coil and all the wiring etc.....if this cures it then get them exhaust valve clearances back to .020 mm




Good fun though, isn't it?

 

[England-Kev]

why .20

 

[DrFarkoff]

0.1mm inlet and 0.2mm exhaust last update on clearances
it's in Hawksleys forum too in lots of posts

4 and 8 thou for the elder gents on here, if I remember correctly

 

[lurcher]

Is the misfire on one cylinder or both? If its both its a common component, if one then check those components. But you are correct if turning the mixture screw makes no difference then there is a problem with that carb wheather or not its been cleaned.

 

[lurcher]

Also have you checked if the mixture enricheners are returning to their stops and that their gaskets are good?