Carb conundrum

[GoldenFailure]

Ok. So I finally got a nearly correct carb, its a 376 monobloc, 1 1/16th bore, which is right for the swinging arm model, mines a plunger, so should have the 276, but I'm guessing the engines are so similar that it doesn't matter.

Its got a 3.5 slide, 106 needle, 25 pilot, needle on the richest groove and my drilled out to maybe 230 main jet, but its still frighteningly lean (burnt white plugs) at every throttle opening.

I haven't checked the timing yet but apart from the lean ness it starts and runs fine. Maybe it has scary cams, I have no idea.

My only thought so far is that there is no air filter (missing rubber knee thingy) but its jetted as per the Haynes which probably presumes there is a filter. Would this make such a huge difference? and if it is a lack of filter, is anyone running a similar set up who could recommend jet sizes for no filter, monobloc, and (I guess) standard silencers?

Your continued advice much appreciated.

[beezermacc]

Hi, The lack of an air filter shouldn't make an enormous difference, however going up a few sizes on the main jet is a sensible precaution against holing your pistons. Maybe you have a peaky cam and lumpy pistons in which case the settings should be more like those for a Super Rocket. I have a 1958 A10 Golden Flash in standard trim which I run without a filter and standard jetting and the plugs look OK. The latest iron heads were dsigned to run with a 389 - you can tell which head you've got by measuring the inlet tract. On the other hand the alloy head models have specifications with/without air filter showing a big difference in main jet size, 270 with filter, 410 without. I have a RGS 'lookalike' without air filter and I run the 410 main jet so there is considerable scope for variation and experimentation. I'm assuming you have the correct plugs. I would be inclined to keep going up the main jet range until the plugs are an acceptable colour after a short,fast run then deal with any fine tuning at a later stage, which is broadly what Amal used to recommend.

[GoldenFailure]

Hi Beezermac. Cheers for the advice.

I'm getting closer I think, the RH side plug is tan up to a 1/4 throttle, but then lean all the way after, even with my comedy over sized drilled out main jet, so considering going from a 106 to a 108 needle jet, does anyone have any advice on how big the jump is between needle jets? should I go even bigger?

Also starting to wonder about mismatched timing, as LH plug always looks to be burning leaner, its white throughout the throttle range, which is why I'm considering electronic ignition. And the LH header is blue.

[beezermacc]

I'd try a 107 which is quite a common fitment on monobloc carbs. Re mismatched timing, check for variation in points gap. Quite a few K2F's going through my workshop have imbalanced points, a £30 fix. Much cheaper than electronic! Also, let me know what the numbers are on your carb flange.

[muskrat]

 I'll ditto what beezermacc said. If the timing is the same both pots then you need an anti-bias gasket to even up mixture Sounds lean and or retarded.
Cheers