Hello All hope you’re well
Had a day tinkering with the Scott and having gone through all the tips given I finally swapped over the sparkplug leads. This has resulted in a few bangs etc but as yet not fired up. Are the bangs an indication that the leads were the wrong way round or a reason that they are now the wrong way round…any advice would be great
i was getting nothing prior to this
Bangs/Pops usually mean that the leads are on the wrong way round. I have often been able to get an engine to do this whilst it won’t do anything with the leads the right way. First thing to test is the compression and then look round for air leaks.
Hello Michael, I did the compression this morning and it was 110 on each cylinder .the engine was cold as haven’t got it going yet so I guess actual compression is probs nearer 125
I’ll look for posts on how to find air leaks
Hi Tom. I have had brain freeze on a few occasions when starting my bike after a rebuild and thought that the problem was X when it was Y. To my unlearned eye it was also hard to know which timing mark works for which lead and whether pushing the timing lever away from the bike was full advance or not. They seem simple things now but as a modern bike person it was new to me.
I set my timing to 5/16 BTDC and usually there is a mark on the flywheel there from previous owners. The mag should be on full advance when you set the timing, if the points end of the mag is on the left side of the bike, and full advance is when the mag is the furthest point clockwise. On my bike I pull the lever towards me and the mag arm is on the left to set it.
I have taken the transfer ports off before and poured quite a bit of oil into the crankcase. As far as I understand this provides the seal to get the suction from the crankcase to pull the fuel in.
Air leaks are from where the carb bolts on to the engine as the ears tend to bend if done up too tight (I had to grind mine flat), the transfer port doors and the crankcase doors which I remove, put a smidge of fine grinding paste on and fit them that way with a rag stuffed inside to capture any rogue paste. And a final gasket. If you undo the bolt and remove the crankcase door strap and the door falls off on its own accord it is not sealing. It should take a kick or two to blow the doors off.
Fuel height, don’t know for your bike but if your plug is wet then I would say that there is enough fuel for starting and that I am inclined towards saying that fuel height affects running more than starting as long as you actually have fuel. You could set you float bowl in its highest position by rotating it backwards to ensure there is indeed enough fuel if you like, but as a last resort. What about sticking the plugs in the flame of the gas cooker and then trying it then. Does pouring a capful of petrol down the plughole do anything? Do you have a sodding great hill nearby?
Air screw 1 turn out and see how it runs once started and make sure that the slide in the carb is fully down to the screw as a stuck open slide will mean there is too much air for it to start. I had this on my Yam at the weekend on one side and the cable had come out of its locating sleeve because it needed lubricating.
Saying all that, it is likely to be none of those. If you remove the plugs and earth them on the frame does it spark?
Apologies if all that sounds like I am insulting your intelligence and knowledge Tom and I hope that what I have written is right in the first place! These are the things that have flummoxed me before. Sounds like you have good compression anyway.
Hello just read this post which is very helpful, still new to Scotting. I have indeed got it starting regularly now but only on one cylinder , things are never simple. Swapped the plugs so know it’s not that. I have a spark on the lead which looks the same as the other. I wonder if the piston is not sealing to draw the fuel through so I guess that’s the next test. Not sure how I’ll do that as yet but will have a look on the forums etc,
thanks for the reply
Tom,most likely cause of it running on one cyl.if you have a good spark is a massive air leak,the cause of this is usually is a sticking gland on that side when the tongue of the gland overides the slot it has worn in the flywheel key slot .sometimes a temp fix can be done by giving the crank and or the flywheel a sharp blow to dislodge it. Good luck Potty.