Blue Smoke on decel and accel

Information relating to the Matchless G85 500cc Heavyweight, AJS 7R, Matchless G45 and Matchless G50
Member
User avatar
Posts: 823
Joined: Thu Nov 12, 2015 2:22 pm
Location: Florida, USA

Re: Blue Smoke on decel and accel

Postby Expat » Fri Jan 19, 2018 12:40 pm

Hi Marty,

Been following your adventures with interest and fingers crossed there’s light at the end of the tunnel :)

Can vouch for the efficacy of Spriddler’s timing stick suggestion as I made one up to his sketch and find it gives accurate and repeatable results. Use it every time!! with confidence.
Keep shiny side up.

These are my principles, if you don’t like them, I have others. (Groucho Marx)

Member
Posts: 197
Joined: Sun Oct 25, 2015 8:19 am
Location: AUSTRALIA

Re: Blue Smoke on decel and accel

Postby Matchymarty » Fri Jan 19, 2018 7:25 pm

Thanks again Mr SPRIDDLER. Such a wealth of knowledge. Yes, I'm aware of useage of throttle position vs carb pilot, needle and main usage, and it seems that luckily, i've done my first 30 miles this time round with no more than 1/2 throttle, so very little use of the main jet, meaning I've most likely saved the engine from overheating. I can now use more than half throttle with confidence that it's getting enough fuel so will not run hot due to lean mixture.

As for your comments on the timing, thank you for clarification. And yes, that is the method I use, however, I must admit, I've never thought of adjusting timing via the bottom timing sprocket. This makes complete sense, and I'll be doing that from now on, as I often need 2 or 3 goes to get my timing right due to the mag sprocket moving upon tightening. THANK YOU FOR THAT TIP!

That said, I may need to work on some other timing disc method, for at least my knowledge, and, my new Matchless Whisperer, says the compy's with hotter cams require a bit more precise timing.

Cheers!
Marty


SPRIDDLER wrote:Well you do seem to be making progress. Personally (other opinions are available) I wouldn't get too hung up on relatively minor main jet or slide variations vs various bits of documentation as these can be tweaked for best performance once you are satisfied vis-à-vis the smoke and overheating issues. It's worth bearing in mind that up to about 1/3rd throttle opening th'engine is being supplied mostly by the Pilot jet, then Pilot jet and slide/needle up to half throttle, then slide/needle and main jet up to full throttle. Much of the time most of us are running around locally at half throttle or less therefore the Pilot jet setting is important.
You may find this carb tuning guide useful/interesting:

http://www.hitchcocksmotorcycles.com/mo ... to-tune-up

As far as ignition timing goes I have only ever used the 'stick in the hole' approach which I find entirely satisfactory and far more straightforward than faffing about with a timing disc and which isn't as easy to set up on our h/weight singles. On a minor point, with modern fuels and on touring engines I time to 7/16" BTDC at full advance (set points gap first) but to be quite honest if you time to 1/2" BTDC you can fiddle a tad with the A/R lever and experiment whilst out on a ride. My ignition is on full advance when the cable is tight (i.e. pulled) so when I set the timing on an unfamiliar bike I leave a bit of movement (1/4" of cable) available at the handlebar lever so that I have a bit of adjustment to play with whilst out on the road. On some magnetos the ignition will be fully advanced when the cable is slack. There is frequently confusion with new owners as to which way to move the lever for advance and retard. I assume you must have this clear in your mind........?
Not wishing to bore you but when setting the timing it's best to loosen the lower mag chain sprocket to make adjustments rather than the upper sprocket on the mag shaft since it's easier to prevent the lower sprocket from moving when you tighten the sprocket nut.

High tech wire coat hanger timing probe:

CIMG4398_zps5b2c3873 (240x180) (240x180) (240x180) (240x180).jpg


CIMG4402 (480x360).jpg

Member
Posts: 5919
Joined: Wed Sep 01, 2004 12:00 am
Location: WEST SUSSEX UK

Re: Blue Smoke on decel and accel

Postby SPRIDDLER » Fri Jan 19, 2018 8:22 pm

Matchymarty wrote:I've never thought of adjusting timing via the bottom timing sprocket. This makes complete sense, and I'll be doing that from now on, as I often need 2 or 3 goes to get my timing right due to the mag sprocket moving upon tightening. THANK YOU FOR THAT TIP!

If, before you tighten the nut on the sprocket to lockit you place a socket :roll: (one which is larger than the nut) against the sprocket and give it a sharp tap it will settle the sprocket quite firmly onto its (clean) tapered shaft. No need to tighten the nut with gorilla force as it only has to drive the mag and resist slipping on the shaft or sudden reversal of direction of rotation if/when th'engine kicks back.

That said, I may need to work on some other timing disc method, for at least my knowledge, and, my new Matchless Whisperer, says the compy's with hotter cams require a bit more precise timing.

He could well be right; especially with a higher compression ratio engine. No harm in having a go with a timing disc, eh?

There's a timing disc here that you can print if you need one:

http://archives.jampot.dk/general/AMC_Timing_Disk.pdf
I poke badgers with spoons.

Member
Posts: 197
Joined: Sun Oct 25, 2015 8:19 am
Location: AUSTRALIA

Re: Blue Smoke on decel and accel

Postby Matchymarty » Fri Jan 19, 2018 8:45 pm

Yes, I usually use a socket over the nut and give it a wack. That sometimes still moves the point block, but as you say, less likely. Thanks for the timing disc. :)
Just got back from a 20 mile ride around my suburb in the cool morning air. Running like a dream, crisp and much more power than it's ever had! It's hard for me to control my right wrist! Feels much better, and the exhaust pipe is clear and no more blue or black smoke that I could see.

Got the fan on the engine, so I can go out again for a breakfast run. Trying to avoid traffic lights as much as possible is hard though! :)

I can't believe the difference in power. I'm absolutely astonished. Is this how it should have been all along? I've owned this '55 G80CS for nearly 2 years, and i've been riding it at 60% of it's power all along and, cooked 3 pistons in the process!

Will report back again soon. Will also try and get my hands on those Carburettor settings data for the use of this FORUM! ;)

Member
Posts: 57
Joined: Mon Jan 01, 1990 12:00 am
Location: NORWAY

Re: Blue Smoke on decel and accel

Postby bjorn » Fri Jan 19, 2018 10:08 pm

Marty,
Glad to hear your problems with the 55CS appear to be getting resolved. Always good to have a knowledgeable local guy to assist.

To try to shed some light (or more confusion?) on carburettors for the 1955 Competition singles, the following can be found from spares lists and instruction manuals:
The same cylinder head was used for the 1955 G80C (rigid frame trials) and the 1955 G80CS (sprung frame scrambler), with an inlet bore of 1 3/16”. The 1955 G80S had a different head with an inlet bore of 1 5/32”. The carburettor fitted to both the G80S and G80C was an AMAL monobloc 389/1 with a bore of 1 5/32”. The G80CS (your bike) will have been originally fitted with an AMAL TT carburettor with a bore of 1 3/16”. The TT is a racing carburettor.
The jetting data that can be found for the 389/1, main jet 260, etc. is for the fitting to the G80S and G80C, which both have mild cams.

The 1955 G80CS is a different beast, with race cams (SH as fitted to yours). Although a long-stroke CS, it has much more in common with the 1956 G80CS, which has a monobloc 1 3/16” which uses a 440 main jet with an open pipe and a 400 with silencer. Jetting, as your “MW” friend has pointed out, should be in the same range.
As you are now finding, performance of these “old” bikes is quite good. If you intend to use it to the full, timing and carburetion need to be correctly set, along with at least 97 octane fuel and a spark plug with an appropriate heat rating.

Here in Norway, in addition to scrambles, the G80CS’es were used for long track dirt racing in the fifties in the “standard” class. Winners were either Matchless G80CS or BSA Gold Star.

I bought my 1956 G80CS in 1969. Acceleration was identical to my friends Norton Atlas 750 up to 160km/h which is about the maximum on the street when running a silencer. Acceleration and top speed also the same as a friends Honda 450 Scrambler, except he could jump ahead at start due to a low first gear.

Regards and happy riding
Bjørn

Member
User avatar
Posts: 886
Joined: Sat Jun 20, 2015 8:38 am
Location: Chester, UK

Re: Blue Smoke on decel and accel

Postby clanger9 » Sat Jan 20, 2018 9:43 am

So glad to hear it's finally running right, Marty!
I would never have suspected an over-lean main jet from your "smoking" symptoms, but there you go.
On a high-comp engine, a lean main jet will destroy a piston quite quickly. Far better to be over rich than over lean if in doubt...
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

Member
Posts: 5919
Joined: Wed Sep 01, 2004 12:00 am
Location: WEST SUSSEX UK

Re: Blue Smoke on decel and accel

Postby SPRIDDLER » Sat Jan 20, 2018 11:44 am

Marty. Just a suggestion that since th'engine has been running seriously hot it is essential to change the deteriorated oil.
Your comment about overheating and using a fan when you leave the bike after a run set me thinking about Aussie weather. Pure amateur theory, but I found several references on t'web that an air cooled ali m/bike cylinder 'normally' runs at a surface temperature of around 65 to 120 degrees C (seems rather low to me but the web isn't always reliable) so if you have been tinkering with the carb etc. in what? an ambient of 30 or even 40 degrees C ? it will overheat very quickly, and also affect carb tuning.
As an aside, I read that a chap in Finland had ongoing seizing issues which he traced to the extremely cold temperatures (plus wind chill effect when riding). It seems that since from a cold start the piston expanded more rapidly than the cylinder the piston running clearance was lost. Not that I or you would ever (want or need) go out in such weather. Just a thought to ponder..............
I poke badgers with spoons.

Member
Posts: 197
Joined: Sun Oct 25, 2015 8:19 am
Location: AUSTRALIA

Re: Blue Smoke on decel and accel

Postby Matchymarty » Mon Jan 22, 2018 2:58 am

Spriddler,
Thanks... and yes. Actually I changed the oil after a ride this weekend. It had only done 50 miles. That said, i've now tightened down the head, changed oil, adjusted pushrods and checked things over. Seemingly all ok for the moment. Hoping to do some decent miles and get things bed in. Unfortunately, I had a terrible ride on sunday, heading down to the coast and chose the wrong way to go , leading to many sets of traffic lights and associated idling at such. I'm now freaking out that I've done damage. Fingers crossed.
Luckily it was only 26-28 degrees and the air was coolish when riding along.

SPRIDDLER wrote:Marty. Just a suggestion that since th'engine has been running seriously hot it is essential to change the deteriorated oil.
Your comment about overheating and using a fan when you leave the bike after a run set me thinking about Aussie weather. Pure amateur theory, but I found several references on t'web that an air cooled ali m/bike cylinder 'normally' runs at a surface temperature of around 65 to 120 degrees C (seems rather low to me but the web isn't always reliable) so if you have been tinkering with the carb etc. in what? an ambient of 30 or even 40 degrees C ? it will overheat very quickly, and also affect carb tuning.
As an aside, I read that a chap in Finland had ongoing seizing issues which he traced to the extremely cold temperatures (plus wind chill effect when riding). It seems that since from a cold start the piston expanded more rapidly than the cylinder the piston running clearance was lost. Not that I or you would ever (want or need) go out in such weather. Just a thought to ponder..............

Member
Posts: 378
Joined: Wed Oct 12, 2005 9:45 pm
Location: FRANCE

Re: Blue Smoke on decel and accel

Postby JEAN-NOEL » Mon Jan 22, 2018 5:10 pm

Hello Marty,
Just a thought : you have runned in your engine with max 1/2 throttle. User's manual recommend only 1/3 throttle max for 1000 miles. This could explain the seizures you have experienced.
J.N.

Previous

Return to Competition / Racers

Who is online

Users browsing this forum: No registered users and 1 guest