Hitchcocks Forum

Case: The engine has been running rich for the last 6000 km, but maybe much more if it did so also with previous owner. Black, sooty plug every time I have checked, but otherwise running well, easy start, consumption within what is expected etc., so no big issue really. For some strange reason I have only checked that all jets are correct, which they are, air filter OK, tested warmer plug (without any improvement) etc., but not until yesterday got the idea of lowering the carb needles one notch. (Stupid, I know! Never assume anything is correct just because the book says so.) (I may also have mixed up 2nd notch from top and 2nd notch from bottom....).-.-.-.-.-.-.-.-.-.-.-.-.-

Anyway, I lowered the needles one notch, and no more sooty plugs! But I can only guess that the rest of the head and piston top is rather full of carbon too. .-.-.-.-.-.-.-.-.-.-.-.-.-

Question: So what should I do about that?.-.-.-.-.-.-.-.-.-.-.-.-.-

Option 1: Take the heads off, decoke, and at the same time check valve seats and lap them in again if needed etc..-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

Option 2: Add some Redex (or similar product that claims to clean the engine and remove carbon deposits) and "run like mad" one tankful to burn it off? .-.-.-.-.-.-.-.-.-.-.-.-.-

Option 3: Like 2, but only the "run like mad" part of it?.-.-.-.-.-.-.-.-.-.-.-.-.-

Option 4: Do nothing?.-.-.-.-.-.-.-.-.-.-.-.-.-

Of course, the like the engineer I am, option 1 is the only really good solution, but it taks some effort etc. etc, and may not be needed..-.-.-.-.-.-.-.-.-.-.-.-.-

Maybe option 2 would be OK? I am thankful for any inputs on this!.-.-.-.-.-.-.-.-.-.-.-.-.-

Regards, Anders F. R..-.-.-.-.-.-.-.-.-.-.-.-.-

PS. The bike in question this time is actually a 1956 BMW R50, but as the question might apply to any old, carburetted engine I take my chances here!

I'd go for option 4 and do nothing. The carbon build up will raise the compression ratio so you just get a a small efficiency bonus. The wide open throttle maximum power might be a touch down simply because of the valves being coked up but that might not matter to you anyway. Engines needed de-coking years ago because of the raised compression ratio caused them to pink badly on the very low octane fuel and also some "ran on" after switch off if the carbon remained glowing, but as you can stop the engine by decompressing, that won't matter. If you have a correct fuel mixture now, a full bore blast for several miles will burn most of the carbon off.

Thank you for your quick reply!.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

What you say is go for option 4 but maybe a little of option 3 as well. That is probably what I will do, considering the very little effort i have to put into it. And besides: This doesn't rule out going for option 1 later, if I need it for other reasons..-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

As said, the engine is easy to start (first kick normally), is running well, doesn't use more petrol than might be expected (approx. 0,52 l/10 km = 54 mpg), stops immediately as I switch off the ignition (no decompressor on this boxer twin), and has always done so. I took it for a 25 km (approx. 15 miles if you like) ride yesterday, and noticed that it runs even smoother now. Plugs were not black anymore but medium grey. No blueing of the exhaust, only the usual slight straw colour. So in all it seems that the engine is happy now. .-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

Checked valve clearances and ignition timing last week. Valves were spot on as usual. Timing was not, as usual, but can't be corrected completely on both sides simultaneously because of some wear in the auto advance or thereabout. Doesn't seem to matter much, anyway..-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

Well, option 4 with a touch of 3 it is then! Thank you for your input!.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

Regards, Anders F. R.

Hi Anders, After I posted my reply I remembered you were referring to your BMW and not your Bullet and your bike has no decompressor, but too late to change my post. I guess the Redex might help soften the carbon if left for at least 12 hours. I can remember years ago that many car owners used it and created huge clouds of smoke that filled the streets, and some owners poured the stuff directly into the carb with the engine running, which could not have done much good apart from making even more smoke. It was that image I thought you were referring to when you said "run like mad" ....I thought you meant run away to escape the smoke!!!......So perhaps your options of 2 or 3 would be best and save option 1 for a Winter overhaul. (I must learn to read more slowly and carefully!) I never used to like the old boxer BMW's but nowadays I can see the BMW R50 and R60's are beautiful machines, and would like one myself.....Best regards...Les

Hello ANDERS --------- nowt wrong wi' Boxer twins, appen !! As our good colleague LES H has got it pretty much wrapped up , then might I just add that standard convention for describing needle position is in Nos. with No.1 being at the top; needle pointy-end downwards. Generally speaking you'll find 5 slots with the clip in the No.3 position for starters (ie at the mid-way point). Hope that helps ??

Use redex, nothing to lose. No need to decoke with heads off unless or until it becomes absolutely necessary. Get the engine nice and hot on a run, plugs out 5ml of redex down each bore, (teaspoon), cover plughole with rag and turn engine vigorously on kickstart 2 or 3 times, plus back in, wait 5 min then start and retreat, see people marvel as you vanish like merlin in a huge cloud of white smoke,
After thus, dude the tank and just run it as normal with maybe a spirited burst or 2.

Plugs back in and dose the tank, (smartphone autocorrect is too smart for it's own good!)

Thanks again, all of you!-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

I will try some Redex, if I can find some. It doesn't ruin my personal economy, nor does it involve much work. It may even help.....-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

About that "run like mad" part: I meant "ride like mad". Really get the engine good and hot and help burning off deposits. But I remember now that I once tried some sort of engine cleaner in a Sachs 175 2-stroke. Off with the air filter, run the engine warm and pour the contents of a little bottle slowly into the air intake. O-boy! Did that smoke! I nearly had to "run like mad" to get some air after a short time. If it made the engine go any better? Nope! But no additive can fix worn crank seals in a 2 stroke, I guess.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

Anyway: Off to buy some Redex tomorrow. Have to get home by train today because my daily transport (BMW F650 GS) is beeing serviced. (And getting a new rear tire, and fixing a leak from the water pump, and renewing the chain and sprockets...... All that after ony 30000 km! And it's gonna cost more than I like to think of right now. Oh, how I like the Model G and the R50. No fancy electronics or water pumps or injection that may fail. Automatic chain lubrication on the G (the crankcase breather) and no chain at all om the R50. I just love shaft drive!)-.-.-.-.-.-.-.-.-.-.-.-.-.-.-

Again: Regards, Anders F. R.

-----------have a look at this}---http://www.cleanburn.co.uk/power_boost. ... ----------

I've heard of a method called the "Italian decoke", which involves driving everywhere at full throttle for a while. A couple of days ago I needed keep the throttle pinned to keep up with a group I was in, and did that for at least 50 miles on motorways and dual carriageways. The bike is now a bit noisier than it was, but it doesn't half go -- the top speed is up by 5-10 mph. I take no responsibility for your engine blowing up if you try this