Board index Flathead Power-Technical Questions, Answers, and Suggestions Knuckles Black Smoke

Black Smoke

Post Thu Jul 27, 2017 7:43 am

Posts: 188
Location: Radolfzell, Germany
Hi Folks,

I know that this topic was discussed at length but I didn't really find anything which helps me further.

My 47 Knuck is running all stock with an original early Pan oilpump. The Topend oilfeed is restricted at the lower fitting of the top-end oilline.
The front cylinder smokes black when opening quickly the throttle (since I am running the bike on 2 seperated pipes I can see which side smokes). Plus the front spark plug is pretty dry-black whereas the rear one is nicely light brown to grey.

Any ideas?

thanks
KLaus

... and Cotten ... no manifold leak (running your peek seals)

Post Thu Jul 27, 2017 3:47 pm
Pa Site Admin

Posts: 6059
Location: Ohio USA

Black smoke means rich. If one cylinder is running black and one is ok, then you have the carburetor dialed in to the one which is ok. In my opinion, that ok cylinder is sucking in air somewhere even though it may not be a manifold leak. The blackened cylinder is starving for air. The blackened cylinder is the sealed one.

Post Fri Jul 28, 2017 1:17 am

Posts: 188
Location: Radolfzell, Germany
Thanks Pa,

where would you look for airleaks other than the manifold?
You dont think it could be over-oiling of the front cylinder head?

KLaus

Post Fri Jul 28, 2017 10:00 am

Posts: 1203
Location: Ojo Caliente,NM,USA
If there's any doubt what smoke is hold a sheet of paper in the exhaust. Examining he paper at leisure under a strong light makes it easier to tell is it's oil or fuel or a combo.
Dusty

Post Fri Jul 28, 2017 12:27 pm
Pa Site Admin

Posts: 6059
Location: Ohio USA

Carb to manifold could be a leak but manifold leak can direct the air to a particular cylinder depending on what side the leak is on.

Post Sun Jul 30, 2017 3:16 pm

Posts: 3321
Location: Central Illinois, USA
Klaus!

Some times it takes more than my blessing.

Please bubble-test again, re-snug the nuts if necessary, and use the full regulated 15 psi.
(Sorry I don't remember, but if you have a very typical late '46-'47 scrap ordinance brass casting, the odds are somewhere around one in five that it might have casting porosities in unbelievable places. Please soap everywhere you can observe, over the entire manifold. Usually I seal them. )

If a drain tube from a front rocker cup gets restricted, particularly the intake, it does that and more. You might blow a little air through it if we find no other culprits.

It's timed perfect and the valves are too, right?

.....Cotten

Post Mon Jul 31, 2017 6:56 am

Posts: 188
Location: Radolfzell, Germany
Thanks guys for your help.

Cotten, I can't find a leak ... tried hard. Your Peek rings are too good ;-)
Timing is all good

DD, how would I see what kind of smoke it is? What would I need to look at?

Klaus

Post Mon Jul 31, 2017 7:37 am

Posts: 3321
Location: Central Illinois, USA
Klaus!

Did you turn the motor through to open the intake valves, and then bubble-test the sparkplugs and headgaskets?

....Cotten

Post Mon Jul 31, 2017 5:56 pm
Pa Site Admin

Posts: 6059
Location: Ohio USA

How about a weak sparkplug or coil ? Reverse the sparkplug wires and see if the cylinders flip flop on each other.

Post Tue Aug 01, 2017 2:36 am

Posts: 188
Location: Radolfzell, Germany
Cotten,

haven't done the test for the head gasket and spark plugs. Will do it this week.

Pa,

what do you mean with "flip flop on each other"?


I run another test ride yesterday and I think it does get a bit better. Plug colour is getting closer (the rear one anyway was always a bit "whiter" than the front. I cleaned the carb and changed some parts. The idle needle looked a bit weird. Unfortunately Palmer's book is not too specific on the proper parts for the M35TP. Will go for another test ride today or tomorrow. I think it is definitely too much gas and not too much oil in the heads!

Later
Klaus

Post Tue Aug 01, 2017 11:08 am

Posts: 3321
Location: Central Illinois, USA
Klaus!

The M-35, M-35T, and M-35TP were virtually the same, but for casting differences.
(I have come to believe the TP was '48 production.)

If something looks weird, it probably is.

Pa's diagnostic of switching the plug leads is certainly appropriate.

....Cotten

Post Tue Aug 01, 2017 12:36 pm
Pa Site Admin

Posts: 6059
Location: Ohio USA

If you switch the plug wires around, pull the rear and plug it into the front, pull the front and plug it into the rear, and.....the results fip flop....or reverse....then the coil is bad.

Post Wed Aug 02, 2017 1:52 am

Posts: 188
Location: Radolfzell, Germany
Pa,

thanks. I think I understood what I have to do, I'm just not sure what "flip flop" means. Anyways, the bike runs quite good which would indicate a good coil.

Cotten, have there been different low speed needles used in those carbs. What I find in the WWW is that the needle was always the same but the "head" changed. Is that correct? Is there anydifference in the length of the machined tip? I got 4 needles here and one has a longer and pointier tip then the other 3 tips ... any ideas?

Klaus

Post Wed Aug 02, 2017 6:50 am

Posts: 3321
Location: Central Illinois, USA
Klaus!

Schebler DLX and Linkert 1¼" and 1½" models had LS needles that were 3½" long overall, no matter which head.
Linkert 1" models were 3 1/8" long.

Even with a damaged point, it is hard to imagine how either needle would influence one cylinder over the other.

Is "WWW" something other than "World Wide Web"?

....Cotten

Post Wed Aug 02, 2017 8:23 am
Pa Site Admin

Posts: 6059
Location: Ohio USA

Klaus. By switching around the plug wires, you will be able to inspect the sparkplugs for coloring to see if the switching made a change or a difference. If the black smoke I still from the same cylinder, it seems to me you do have a leak in the manifold somewhere. I am not sure as to how the manifold attaches to the cylinder heads but if it attaches as a flathead attaches, it could be a nipple leak.

Post Thu Aug 03, 2017 1:46 am

Posts: 188
Location: Radolfzell, Germany
yes, Cotten. www is world wide web.
Pa, now I got it ... sorry! I tested it and no change, however, I also cannot find a leak around the nipples.

Post Thu Aug 03, 2017 9:25 am

Posts: 188
Location: Radolfzell, Germany
Hi guys

Just coming back from a test ride. After changing the idle needle and cleaning the carb, the standard idle needle setting was waaaaay too rich (with the other needle it was just fine). So, something changed here. The engine also reacted way better to changes to the needle setting. Obviously the 15km was not enough to clean up the fouled spark plugs. But both go in the same direction. So it seems that both chambers get the same feed.
Unfortunately now I found that the rear exhaust cup is dripping some oil (where the cup is supposed to sealed on the cylinder head. The soldering of the return line is ok). Not so much that I get concerned for now. Anyways don't want to pull the head now.

Guess now I have to go for a longer test ride to see how the color of the plugs "behave".

Any ideas how to best tune the high speed needle? I know the standard procedure but I'm never sure if I got it right ( at what speed does the high speed needle circuit kick in to manage "carburation"?

Later
Klaus

Post Thu Aug 03, 2017 9:52 am

Posts: 3321
Location: Central Illinois, USA
Klaus!

The Armored School Handbook suggests that a small venturi doesn't kick in until ~thirty MPH, so a larger bore needs more.

Reading plugs ain't what it used to be.
Injector cleaners and intake valve deposit additives (IVDs) in modern fuels can make a perfect mixture white on the plugs. Please always start with clean plugs, and take any color at all as significant.

Cup leaks afflict us all with Knucks,... I stopped beating myself up over it.

....Cotten

Post Thu Aug 03, 2017 10:30 am

Posts: 188
Location: Radolfzell, Germany
thanks Tom,

guess we will have to live with some oil dripping ... option would be a flathead ... at least as far as leaks at cylinder heads go.


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