Running (nearly) Properly....Carburation Question

[Pete D]

Chaps

New plugs and rewiring the coils has pretty much done the trick.  Filled up with some premium petrol today and taken the old girl out for a gentle blast.  Pulls beautifully above 3k RPM, but has a tendency to 'fluff' a bit under that when applying small throttle increases.  Larger inputs makes her lift her skirts and head for the horizon - really smooth as silk beyond 4k.

So, my question, do they all 'bog down a bit at lower RPM/gentle throttle openings' when trying to 'waft along'?  I plan on getting the carbs ultrasonically cleaned and rebuilt over the winter anyway....but would hate to try to cure what is a 'feature'....  I ride a day to day older BMW, and that has a fair amount of what may seem odd traits, but all of which are 'normal'.

Now just that pesky minor oil seep to sort.....and a slightly weepy petcock.......small stuff....

What a lovely bike though!

If I sound rather happy.....I am!

Cheers

Pete

[Rob B]

Hello Pete,

They pull well from about 2,000rpm as long as the cush-drive rubber has been modified to eliminate transmission snatch, which it has been on your bike, and everything is setup properly. Have you got a carbtune or similar carb balancer? The HESKETH loves to have precisely synchronised carbs but otherwise is a total pig at "poodling around" speeds. Yours is a quick engine once you get the revs on but watch it in the wet though!

Cheers,

Robert

[Pete D]

Hi Robert

I don't have a carbtune yet........but will have very shortly. As ever, astonishingly quick and sound advice. Thanks for the gen on the upgraded cush drive. Getting there..... I'll check the plugs to assess mixture when the old girl has cooled down a bit.

Pete

[Pete D]

Both plugs a mite sooty.......

If I can source any, I'll try some new air filters before I mess around.....however, it only had a 15 mile gentle run, so might need a little 'throat clearing' too....

Cheers

Pete

[Miti]

Well done Pete..!!

The sootyness is almost certainly the accelerator pump settings... Mine are WAY to enthusiastic and I'll be backing them off to a half-bucketful per throttle twist ASAP...

Dave H (Snr) and Rob B have done lots of work in this area and there is info here on the forum... Try the 'Search' link above...

Jeff

[Pete D]

Hi Jeff

Another thought that struck me was that as the snag occurs at only partial throttle openings, I should trawl the HOC Forums re idle mixture setting. Having found a very useful exchange between yourself and Robert re 1.5 turns out or less, I checked just the front carb on mine, as it is a bit late in the evening and Mrs D would like my company in the house.

Result......2.25 turns out. No wonder the old girl is running rich!  I'll check both tomorrow, but will set them at 1.25 turns out as a starter for 10....

Once again,I am grateful to you both for such expert support over the past couple of weeks. I feel I am making significant progress.

Cheers

Pete

[Pete D]

I'll look into those accelerator settings next. One step at a time.....

Pete

[Pete D]

Carbs set with mixture screws 1.125 turns out. Slides balanced by ear, but results pretty good. Another 10-mile test ride today; the Old Girl pulls really cleanly above 2500 RPM.  Still a bit 'fluffy' under that when 'lugging' slightly, but pulls fairly cleanly if a bit more throttle applied.

I will leave the settings be to let the bike settle for a few more miles, before pulling the plugs and tweaking any further. Bless her; she's been running on one for quite some time I expect, so deserves a bit of stability.  I'll change the oil and filter again before the winter lay-up, exhaust replacement, tank and plastics re spray etc.  Must pace myself.....a lifetime of nurturing means I don't need to rush..

Once again, thanks to those who have helped me get the Old Girl back on an even keel. Hope to meet you in the next year; with any luck, she'll be oil tight by then, albeit is only marking her territory with a couple of drops each stop.

Cheers

Pete