This is the colour of my plug after about 3 hrs of riding at a range of throttle openings the 1st time out after new piston rings replate of cylinder bottom end clean out with new main seals standard timing setting water ways perfectly clear with new impeller inner clutch case cleaned exhaust clean air filter and standard jetting.

I put in 70ml of Rock oil strawberry trial 2 in to 5L of Shell Super unleaded.

With the bike warmed up the idle was still increasing in speed with the screw out 3 turns from closed so I am going to put a 27.5 pilot jet in the carb it's got a 30 I there at the moment which is standard and the main jet is 150 with needle clip in the middle position.

The colour in the picture is a pretty good example of the actual colour and it looks a little grey to me.

1 thing I know isn't 100% right is the positioning of the head gasket it's been fitted in the 1-2 o'clock position instead of the 12.

What do you think?

Is the plug a bp5es, if it is not and you have the stock plug, it will run to cold if you are in the Uk!

try going in half a turn on the air screw

and stop biting your nails

Edited December 22, 201312 yr by nelly1

I`d leave the 30 at least during the winter months. But I would fix the head gasket while still new. The coolant flow will be wrong. The holes are smaller in places

Grey is a weird thing and it doesn't mean anything to me

The only way to read plug color is on the trail, you cannot way any time period, it must be done hot

I prefer the burn pattern on the piston crown, if you can get a carbon spot in the middle of the piston that extends to within 6mm or so of the ring land you are getting good combustion temps

Is the plug a bp5es, if it is not and you have the stock plug, it will run to cold if you are in the Uk!

I'm in UK and running the 5

try going in half a turn on the air screw

and stop biting your nails

I had it out 2 turns from closed and I had nails like Flo Jo pre this bike!

I`d leave the 30 at least during the winter months. But I would fix the head gasket while still new. The coolant flow will be wrong. The holes are smaller in places

Your right I've a new head gasket on order

Grey is a weird thing and it doesn't mean anything to me

The only way to read plug color is on the trail, you cannot way any time period, it must be done hot

I prefer the burn pattern on the piston crown, if you can get a carbon spot in the middle of the piston that extends to within 6mm or so of the ring land you are getting good combustion temps

I didn't know you have to look at the plug as soon as you stop the engine I will get a picture taken of the crown when the heads off

The plug on the photo looks way too rich, the base ring (the bit next to the threads) looks like tar, it should be tan to chocolate brown. The fact that the centre and earth electrodes are much cleaner suggest the plug is hot enough to burn the deposits off, perhaps too hot.

I am always reluctant to suggest leaning off the mixture via the internet because of the consequences of going too lean. I would start by checking the carburetor float valve, float level and that the cold start enrichment is seating / sealing properly.

There is a lot of misleading advice about carburation / plug colour.

The carburation is mainly judged by the colour of the base ring and the part of the centre electrode well up inside the plug (hard to see - needs magnifier and strong light). The heat range of the plug is judged by the colour of the electrodes and insulator near the spark area.

Dad of two. The head gasket is off from center, which is blocking proper coolant flow. I would not re-jet until fixed.

2nd that , and the grey color may be from a additive in the fuel .

I've got a new head gasket and taken the head off and this is what the inside looks like also when I rode it it was muddy, I didn't think at the time but I had quite a lot of mud built up on the front pipe which probably wasn't a good idea whilst breaking a new top end in.

Can someone explain why Betas neeed a hotter plug in the UK? Temperatures are similar in other parts of the world. UK bikes come with flywheel weights but I think that would be more load on the engine and actually increase temperature slightly.

That explains the gray. Have you checked the impeller and fan all working ok? MCMAN, I`ve ran a 5 in all Beta`s since `89.

That explains the gray. Have you checked the impeller and fan all working ok? MCMAN, I`ve ran a 5 in all Beta`s since `89.

Yes fan was coming on and I will check impeller spins freely whilst coolants drained.

The grey was caused by the mud around the exhaust? Fair enough.

The reason I was going to try a 27.5 pilot was because the idle speed keeps increasing when turned out 3 turns and I read elsewhere rightly or wrongly that if it increases in speed past 2.5 turns out a smaller pilot jet is required.

If anybody would like to enlighten me further feel free .

I think a trials bike is probably a hard engine to get jetted right, might be different for different people

I would be happy with a carbon spot of almost any size on the piston crown, yours is clean or washed down

The theory is for power reasons you need your combustion temperature and therefore piston crown temperature to be high enough to burn the fuel mix onto the crown

Rich means cooler temp, lean would put carbon to the edge of the piston

Obviously this is easier on an engine run at full throttle at controlled temperatures and atmospheric pressures, loads etc

There are about a million variables making jetting a very unique to location and rider kind of thing

And compounding this you need to set your main first and then your needle, your pilot always flows fuel but only has a minor effect on needle and main circuits

At least 20 seconds at above 3/4 throttle with moderate loads and pull your plug immediately should put you on the right path for main jet setting and then same time at 40 - 60% throttle to set your needle

Make a mark on your throttle housing and grip with whiteout so you can judge opening

Take your time and enjoy

Hate to tell you, but only after 3 hours of riding that cylinder and head should be clean as new. Hard to give advice over the internet, but have someone that knows check it out.