Does this plug indicate too lean

[Paulnobodyimportant]

Over the last 50 miles, since my re-lined and tuned Monza barrel has been running, I've been doing plug chops up to half throttle and the colour is always consistent with the photo's below. Its an AV266 atomiser with X2 on 2 clip.

Its slightly 4 stroking upto 1/2 throttle and bogs out if I turn on my choke. I get the sense that I could fine tune that out by putting the clip at the 1 and 1/2 position. However, thisd new plug does look on the lean side.

I do note that CamLam now recommend an AV268 atomiser, so I will try that next before I do any damage, but any feedback would be appreciated on the photos below.

[CHRIS in MARGATE]

To me that looks lean.

[johnnyXS]

well the main issue that you have there Paul is a far too rich idle

The pilot jet, slide and atomiser selection have a profound effect on your fuel mixture from idle to half throttle and acceleration whereas the main jet and needle have very little !

I would concentrate on getting your idle mixture correct so that you can see what is going on before looking at your main jet and needle combo.
Don't know what plug you are running but you would probably need to consider using a hotter plug (longer nose) to burn off some of those deposits . Make sure you haven't got a slight oil leak too.

[MickYork]

what slide you running ? possible air leak ?

[Paulnobodyimportant]

Thanks for the feedback, its convinced me its lean. Tickover is rich, so I will get that right this morning and then go for a short run and play around with needle setting. Plug in the photo is a B8ES, but thinking about it, may put a B7 plug (is that advisable) in for now because I'm only doing shortish run in runs up to half throttle to sort out the settings for this range, but I do blip up to 3/4, cant help it.

Current carb settings are (30PHBH with Open Mouth)
Main Jet 130
Power jet 30
Atomiser AV266
Needle X2 P2
Pilot 50
Slide 50

Before I had the barrel tuned it ran correctly with Av266 and X7 on 1st clip, but had a ram air filter, this was on a series 2, but now the engines in a GP, all felt a bit squeezed, so its now open mouth.

Did think about air leak so have PM'd Darrell Taylor for his air testing kit. Should have done it earlier while this engine was on the bench as I've procrastinated for this over the last 2 years.

Oil leak, no real evidence and I replaced the drive side oil seal around 1500 miles ago, but there again, mileage is no testament these days as the drive side oil seal has gone in my TS1 after a similar amount of miles


Once I get the jetting more or less there, I'll taker it for a dyno to give me that final level of confidence.

But thanks for the feedback.

[bsso78]

If you intend to take it to a dyno why bother trying to do it yourself?

[Paulnobodyimportant]

bsso78

If you intend to take it to a dyno why bother trying to do it yourself?

Trouble is I don't have a van, so will have to ride the 25 miles there, hence need to get my jetting more or less right.

I have plenty of mates who do have vans and scooters, but don't want to put them out.

Plus, its all part of the learning curve on changing your carb settings. Last 2 times i have had engines dynod, they didn't need to change anything.

[Captain Pugwash]

My best guess or two is slightly pre ignition rich at lower speeds or/and a contaminated mixture, possibly a very slight drive seal leak.

But that's only my guess and it's most likely very very wrong

[Paulnobodyimportant]

Oh dear Captain, that was a curved ball, not that I understand cricket. But the pre-ignition may be a point. Have a look at the graph below on my setting 8 for a tuned Monza barrel. Where my timing is at near enough 25 degrees till it drops at just over 4000 rpm.

Mind you, this curve 8 ran ok before I tuned the Monza barrel.


As for oil leaks, must get full mashing viton oil seals from Readspeed next time.

[Knowledge]

Your ignorance of cricket is obvious: curve ball is an expression from baseball. Don't worry about it and just accept that England winning the Ashes was a good thing.

The viton seals kit demo Readspeed were a good investment. Saw me to Austria and back with no issues. I put much of this down to the sealed bottom end