timing advance ea81

[asra]

Hi allgot a problem with the ea81 in regard to timing. Time it at 8 Btdc starts fine. manually adjust timing at 3000 revs for best revs lovely smooth as silk. idle back to stop and shes a right b**ch to start. Checked the advance both mechanical and vacume both appear to be working ok. I will try opening the slot to allow more mechanical advance. I was wondering if anyone else has run into this problem? or if anyone has fabricated a means of manually retarding the dizzy ie cable / push pull rods instead of the vacume mechanism. I think this would be able to be done fairly easily but im not sure of the risks involved apart from the obvious one of linkage failure.Any thoughts on the subject would be appreciated. Motor is stock with twin su carbs on fabricated inlet manifold

[adrian_clince]

does the engine back fire when you stop it?

[chook]

Greg, manually adjusting the timing is fraught with danger. (pre ignition - overheating and holes in pistons)The manufacturer goes to a lot of trouble to get the rev/timing range exact for not only engine power efficiency but also emission standards. If you look at the algorithm tables for most newer computer controlled distributors you will find that they are 3 dimentional and look like

[asra]

Thanks guys Adrian No the engine doesnt backfire on stopping.Chook appreciate the responce thats what I was looking for ie the hidden dangers in operating a manual advance mechanism.I have found the culprit: Not enough vacume with the twin carbs. One carb has a vacume take off point the other doesnt. I had it hooked up to one carb. Hence not enough or not consistant vacume given one carb runs 2 cylinders.

[Brian]

Incredible isnt it, you think the problem is in the distributor /timing and is actually in the carbs !

[asra]

Chopperhad to scratch the noggin to figure it out.

[Dewie]

GP The vacuum tube would not make any difference to starting, just set

[tonydenton]

i probably should know[ but i don"t ] what my timing advance is . i"m sure its set . there isn"t any vacume advance either . it was blocked off with the standard sub ea81 carby and when i myself put the dual su carbs on, it definetly doesnt have vacume advance. actually i know what i"ve been told what the advance is set at , and fairly high . based on the fact that its always running between 4000 to5000 rpm . starts easy too.

[chook]

Dewie remember that the vacuum advance also prevents "hesitation" when you crack the throttle open quickly in a car. I know you"re an old (i use the term old endearingly!) bike racer and after I put this post down went out to refresh my memory on how my kwakka 900 used to over come the hesitation problem in the manual. No reference to it so I can only assume that the revs picked up quickly enough because of the lighter crank and flywheel configuration on bikes.

[Darrell Jones]

HI Greg, email me your landline phone number, I"ll have a chat about the timing.

[Dewie]

I have found the culprit: Not enough vacume with the twin carbs. One carb has a vacume take off point the other doesnt. I had it hooked up to one carb. Hence not enough or not consistant vacume given one carb runs 2 cylinders.