Dommi 99 tuning

Previously Phil Hannam wrote:

I would suggest looking at the electrics first. Possibly you have a magneto pick-up brush that is not working correctly. Check the slip ring inside the body for a lumpy track. How good are the pick-up brushes? Do they retract into the housings easily? Check the earth brush at the other end of the magneto.

Next head for the plugs and leads and look for loose or poor connections. Have you got the correct plugs and caps for a magneto? You do not really want either with resistors built in.

Lastly, check out the carb. It could be the float sinking due to Ethanol in the fuel and thereby flooding the engine. Are you jets, needle and slide all the correct spec for your engine? Possibly they are all gummed up and just need a good clean.

Thanks for the advice Phil, I previously stripped the carb and all appears ok. I have suspected the Mag for some time, so at least I now have something to look for.

Previously anna jeannette Dixon wrote:

Previously peter_coates wrote:

having just put my dommi 99 on the road, 1st time since 1986, I find that there is no accelleration with lumpy running.

the magneto timing is set to the recomended 32 degrees btdc, as far as I can tell the carbureter is original, I can attain a tick over, although lumpy,

It will only rev to any degree with the manual choke fully closed and the spark plugs are indicating a rich mixture (black), I don't know if it is the magneto or carburation that is at fault.

anybody any ideas?

Pete

Hello now witch way round have you timed the Magneto , has there is a right way and a wrong way, , Now the right way is from the Drive side Left cylinder first this is set in Stone, and the ignition lead for this cylinder is the one farthest away near the Battery Box the points should look up ward the cam is at near the bottom there are two cams inside a magneto set at 180 to each other but fire at 360 one is a lost spark in sparks in between the strokes has a four stork engine only fire once every 720 degree or two turns of the crankshaft, a parallel twin is like a split single and fire every 360 degrees or so the magneto can be out by 6 to 8 degrees on its cams .and I have known pistons too be shattered because of this out of timing on one side or another, some check the timing factors and the lead are on the right way around, right hand lead nearest too the back of the barrels the left nearest to the Battery box This is the right way around and its SET IN STONE By Lucas, I have there big sevice manual that tells you every thing you need too know, and its the same way round for the Distributor too , so do not get it wrong like so many have . and say it does not matter , but they all way have ignition trouble and still blame something else, and ignition and Crankshaft balance are all related too having a smooth running engine, next is the carburation mixture . black plugs can mean many things one over rice mixture two wrong plug type , too cold a plug . but try over rice mixture first its manly the float and the float valve not seating at the right time, or getting suck in its seat, or the float bowl level is too high ie flooding the float chamber something that needs careful looking at . make a clear float chamber end plate so you can see how far the fuel level is, and if its flooding inside running though the main jet and air holes . hope this put some small light on things yours anna J

Thanks Anna, I'll let you know how I get on.

Pete.

Previously Phil Hannam wrote:

I would suggest looking at the electrics first. Possibly you have a magneto pick-up brush that is not working correctly. Check the slip ring inside the body for a lumpy track. How good are the pick-up brushes? Do they retract into the housings easily? Check the earth brush at the other end of the magneto.

Next head for the plugs and leads and look for loose or poor connections. Have you got the correct plugs and caps for a magneto? You do not really want either with resistors built in.

Lastly, check out the carb. It could be the float sinking due to Ethanol in the fuel and thereby flooding the engine. Are you jets, needle and slide all the correct spec for your engine? Possibly they are all gummed up and just need a good clean.

Thanks Phil, I'll keep all this in mind.

Pete

Previously David Cooper wrote:

If you must have the slide down to get it to run then I suspect those mysterious pilot air galleries in a neglected. They can get blocked up if left unused for years. Sounds exactly like my 16H being started again after a 30+ year layoff. As for "which lead goes to which plug?" - that must be a matter for concours judges. The mag is symmetrical and doesn't care which plug it feeds. Mine has been both ways round over the years and it didn't make a ha'p'orth of difference to me. Good luck! David

Thanks Dave, but I have to say thats not what Anna says ?.

Previously paul_standeven wrote:

Another thing which needs checking is the functioning of the ATD. If the timing chain is too tight, it will prevent the ATD from doing its job, even if it is otherwise in good condition. Check that it opens smoothly and snaps to retard when you let it go, and is not sloppy.

It would also be worth checking the actual range which it advances over. On some bikes, the advance range is better reduced, due to the different characteristics of modern fuels with ethanol in them. I am just at the beginning of recommissioning my 88, and will be checking on this...

Thanks for that Paul, watch this space for future developments.

Pete

Previously Colin Fairall wrote:

Previously anna jeannette Dixon wrote:

Previously peter_coates wrote:

having just put my dommi 99 on the road, 1st time since 1986, I find that there is no accelleration with lumpy running.

the magneto timing is set to the recomended 32 degrees btdc, as far as I can tell the carbureter is original, I can attain a tick over, although lumpy,

It will only rev to any degree with the manual choke fully closed and the spark plugs are indicating a rich mixture (black), I don't know if it is the magneto or carburation that is at fault.

anybody any ideas?

Pete

Hello now witch way round have you timed the Magneto , has there is a right way and a wrong way, , Now the right way is from the Drive side Left cylinder first this is set in Stone, and the ignition lead for this cylinder is the one farthest away near the Battery Box the points should look up ward the cam is at near the bottom there are two cams inside a magneto set at 180 to each other but fire at 360 one is a lost spark in sparks in between the strokes has a four stork engine only fire once every 720 degree or two turns of the crankshaft, a parallel twin is like a split single and fire every 360 degrees or so the magneto can be out by 6 to 8 degrees on its cams .and I have known pistons too be shattered because of this out of timing on one side or another, some check the timing factors and the lead are on the right way around, right hand lead nearest too the back of the barrels the left nearest to the Battery box This is the right way around and its SET IN STONE By Lucas, I have there big sevice manual that tells you every thing you need too know, and its the same way round for the Distributor too , so do not get it wrong like so many have . and say it does not matter , but they all way have ignition trouble and still blame something else, and ignition and Crankshaft balance are all related too having a smooth running engine, next is the carburation mixture . black plugs can mean many things one over rice mixture two wrong plug type , too cold a plug . but try over rice mixture first its manly the float and the float valve not seating at the right time, or getting suck in its seat, or the float bowl level is too high ie flooding the float chamber something that needs careful looking at . make a clear float chamber end plate so you can see how far the fuel level is, and if its flooding inside running though the main jet and air holes . hope this put some small light on things yours anna J

I feel I must correct Anna on this.... A magneto does not have an 'idle' spark !! The magneto rotates at half crankshaft speed. Therefore a spark every firing stroke on both cylinders. The wear in the two-lobe cam, or the points assembly mounting can cause timing errors on one cylinder. If there is an error take the average between the two. If the mag is in good condition, point gap can be between .010" and .015"The correct spark plug cap on each cylinder will be indicated by the fact that if it's wrong the engine will bang in the exhaust and not start. The right way it will run fine. Hope this helps...Colin

Now I'me getting confused, but I can see the logic.thanks Colin (back to you Anna).