Topic: Anyone with poor running at low RPM

[knudsenuk]

I posted a while back about poor running and hesitancy in the low rev range. I have tried every thing such as, strip and reassemble carbs, replacing worn parts. Changed the exhaust which had some small holes in the muffler/can. Set the points gap, checked ignition, new plugs (without resistors), gapped them etc etc, compression test.... the list goes on. What no one has mentioned and this could be the problem for some others on here, is pre-ignition.  Mine only runs poorly when up to temp. So the symtoms of mild backfiring into the airbox are indicatve of pre-ignition from some lump of glowing coke in the cobustion chamber. it also runs only a little worse if remove the ht lead from the suspect cyclinder. It was bought form an old boy so I dout it spent much time above 3k and has become oiled up. Any thoughts on removing the carbon deposits effectively? Will update once the treatment has been administered..

[Gordon]

If carbon deposits in the combustion chamber is the problem, the only way to clean it out is by hand.  This is a pretty easy job as long as you aren't talking about a 750.  If it is a 750, then it requires pulling the engine to get the head off.  If it is pre-ignition, you should be able to hear it when the engine is under load.  You may have an intake valve problem on that cylinder. 

[TwoTired]

Have you compared your spark plug tip conditions to the pics at:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

This ought to tell you your combustion conditions.  Usually preignition is accompanied by white spark plug deposits, the result of burning rather lean, usually.

What were your compression test numbers?

You say you suspect a particular cylinder.  Which one and why?

Are all the head pipe temps the same?

Decarbnonizing the cylinders can be done by feeding a steady stream of antifreeze into each carb intake while running.  Anyone who's seen the combustion chamber of a water cooled engine with a head gasket blown into the water jacket can attest to how clean the cylinder can be.
Anyway, put the bike on the centerstand, warm up the engine to op temp (put a fan in front to keep from over heating), and then squirt anti freeze into the carb intakes while the bike is reving mid to 3/4 RPM.  A small steady stream or mist is what you want with out stopping the engine, and all kinds of crud will come out the pipes so be prepared for that.  The only way I know to check when you've done it enough, is a borescope in the spark plug hole.  But, your plugs ought to come out pretty clean.  And, when the pipes stop spitting chunks, you are probably there.

The only alternative I know, is mechanical removal of the carbon after dissassembly.

[Bob Wessner]

Hope I never need to do this procedure, but for clarification, is the antifreeze introduced at 100% strength or 50/50 mix with water as is usually found in cooling systems?

[TwoTired]

The last time I did it was about 5 years ago.  I had some old, used, antifreeze, (Prestone and distilled water mix) that had sat for a year to settle out the sediments until it was clear, or transluscent anyway.  I guess I don't know if pure anti freeze would work as well, or perhaps better.  I haven't tried it straight in a running engine.

I do know that glow engines bathed with straight antifreze in a crockpot, cleans them as new, including the combustion chamber.  But, that's a different fuel, too.

I should warn those who have moded the engine for higher compression.   That, too much liquid in the chamber can blow the head gaskets.  Liquids just don't compress.  I used a squirt bottle, I think it was an old, emptied, 409 cleaner sprayer.

Here some who did it with straight water:
http://forums.s-series.org/viewtopic.php?t=34007

Marine 2 cycles are also decarboniized while running using something called Mercury Marine's Power Tune.  Don't know what, exactly, is in it though.

[Badboy]

I have heard that plain water will take the carbon out. Spay a small amount into the engine when it is hot and running. As for anti-freeze,it will burn [suger based] and can leave some deposits that are not too  good for the engine,so don't overdo it. Yes,an engine with a blown head gasket does have a clean chamber,I think due to the water in it. I have heard that hytrogen can be made
by spraying water on hot carbon,I do not know just what the reaction is ,but I guess it is true.

[dusterdude]

back in the old days we used atf

[knudsenuk]

I have taken the head off and note the following:

Dark/black, dry, hard deposits around the edge of the head/squish zone, every where black and sooty except one valve (outlet on number 2) which is pale pink/very light tan.

Any comments 

[Badboy]

It sounds to me that you are running to rich. What do your sparkplugs look like? Did yoiu mean the exhaust valve? That would not build up so much carbon  [hot gasses going out] keeping it cleaner than other parts of the head. Have you checked your float levels, choke working okay,etc? It could that it has just not been run hard enough to keep it clean. I have been a machanic for about thirty years,and sometimes I think we should go back to horse and buggy!

[Tim.]

At least when a horse quit working, you could eat it 

[eldar]

Well I dont think I have a carbon problem but when I think a quick clean is done, I dump in some seafoam. that seems to work wonders and is available at hardware stores. I have used it in my bike and my vehicles with no problems ever. Just dont dump a whole bottle in your bike tank.

[dusterdude]

good stuff,eldar

[eldar]

Anything that makes working on my bike easier is good

[Badboy]

Has anyone tried horsemeat?

[Bob Wessner]

Seems to me I read somewhere that horsemeat is eaten in many other countries outside the U.S.

[kghost]

Went to a Beer festival in Malta once........

Band was singing the "Rawhide" theme, in Maltese.

All the while, my freinds where eating horse meat across the table from me!

Pretty hard to "Keep them Doggies rollin" when you eat the friggin Horses.

True story,