POST 10: Blue bike; Cleaning the Exhaust

Once I'd got the bike running I tried to ride it- and literally got nowhere. The bike refused to take up the drive load. Originally I'd interpreted this as clutch slip, but when I realised that the motor wasnt speeding up, I attributed the problem to a lack of power. Lack of power can come from a variety of causes- and most of them I seemed to have- potentially at least.

Firstly lack of compression- my bike is pushing 70-80 psi and should be closer to 120psi. Luckily I did have the rebored barrel intended for the orange bike so I fitted that with its new piston. This pushed compression to 120psi cold- has this cured the problem? Will check later because....

The second likely cause of low power is a blocked exhaust- 2-strokes tend to gum up with carbon from unburnt oil in use. I don't know if mine is blocked or not- it doesn't seem so but unlike other bikes where the echaust comes apart for cleaning, this is a sealed unit and cant be checked inside. Accordingly I decided to clean it while it was off anyway as I was changing the barrel etc. There are 2 methods for cleaning a two-stroke ehaust- burning off any caked-on carbon by heating the exhaust with a blowtorch or trying to shift the carbon with alkali.

The first method is probably best but its also the one most likely to annoy the neighbours as it generates a lot of smoke, and it course is also the method most likely to burn down house and garage! Being a coward I opted for the alkali method. Basically this involves flushing out loose material with water and then adding strong (25%) sodium hydroxide solution and letting it act on the carbon. I didnt have access to sodium hydroxide pellets at the time, and so opted for oven cleaner- a lower percentage of alkali (5%) but a higher concentration of powerful detergent as well. I used this one.

With hidsight 2 bottles would probably be a good idea. I flushed the exhaust with water- it came through clean. I emptied it as best I could- there is an obvious "S" bend internally so its a case of tipping, inverting and tipping again! This cut-away shows the problem.

I could then bung the exhaust in and out pipes - you may need to remove one to allow you to pour the solution into the exhaust. Once the liquid was in- its a fairly viscous jelly, I bunged both tubes and spread the liquid around the inside of the muffler by inverting it several times. I could then let it stand over night first on one side then on the other.

... before flushing the liquid and any loosened carbon out with more water.

A third cause of low power would be a weak mixture- either through faulty carburation or an air leak. I was pretty sure the carb is OK- its been thoroughly cleaned but air leaks are a possibility. Id used an RTV gasket maker round the inlet manifold for instance to try and avoid this so this was also not my top suspicion.

I did however find a bolt missing at the base of the  cylinder head. This bolt pulls the cases together tightly around the spigotting of the barrel, so a missing bolt here could have been a significant air leak and possibly the whole cause of my issue. Anyway- bolt replaced!

I rinsed out the exhaust- repainted it in stove paint before refitting.

Delighted to say all these changes have fixed the problem. When I started up the motor just raced. This turned out to be down to the thtottle stop screw and cable adjustment. Seems both were far too high. I also found that now both the carb air, and throttle screws actually produced a response. Again this sugests that the mixture setting was way out before. Overall Im pretty sure the main part of my problem was the missing bolt and a subsequent air leak. This would have meant that I'd needed to adjust the throttle excessively just to get the bike to run- and of course there would have been no power under load. All of this seems now to be sorted and the bike picks up and moves off well.