Author Topic: Lean? Rich? Or just OK? (Read 2581 times)

Erny · « **on:** March 23, 2018, 11:07:05 AM »

Live from garage - can you give your opinion by these plugs? Is it ok or lean or rich?
Also notice differences between them - they are in order as cylinders - from 1 to 4 (left to right)

Paintedseat · « **Reply #1 on:** March 23, 2018, 11:10:22 AM »

2 and 4 look a little lean

sinister902 · « **Reply #2 on:** March 23, 2018, 11:19:36 AM »

I would say 1&4 are closest to stoich being that they're the most brown in color. 2 looks a little lean and 3 looks like it is rich or it was lean and the white residue knocked off.

have the carbs been sync'd? are the mixture screws all set the same number of turns out?

Erny · « **Reply #3 on:** March 23, 2018, 12:07:38 PM »

PO told me sync was done, screws I do not know yet.

TwoTired · « **Reply #4 on:** March 23, 2018, 12:46:48 PM »

All except one look lean. Or, very new.

Run conditions matter. Under power? Low speed? High speed? What predominant throttle position?

POs lie. If you haven't performed the 3000 mile tune-up check list, or synched the carbs yourself, you have an unknown, and are just wasting yours and everyone's time.

Nice you told us what mods have been made to the bike. Thanks.

Cheers,

Deltarider · « **Reply #5 on:** March 23, 2018, 01:12:53 PM »

I don't know how you guys manage to draw conclusions on plug noses with nowadays gasoline. Ever since the introduction of leadfree I certainly can't, not without adding a spoon of castor oil to the fueltank prior to running and reading. BTW, smells nice too. Then there's a myth that's passed on over and over again: that one needs new plugs. Not so. As long as the plug functions OK, deposits help you determine as they 'tan' and new porcelain doesn't. All I can say about the plugs shown in the pic, is that they're new.

Erny · « **Reply #6 on:** March 23, 2018, 05:23:44 PM »

Quote from: Deltarider on March 23, 2018, 01:12:53 PM

I don't know how you guys manage to draw conclusions on plug noses with nowadays gasoline. Ever since the introduction of leadfree I certainly can't, not without adding a spoon of castor oil to the fueltank prior to running and reading. BTW, smells nice too. Then there's a myth that's passed on over and over again: that one needs new plugs. Not so. As long as the plug functions OK, deposits help you determine as they 'tan' and new porcelain doesn't. All I can say about the plugs shown in the pic, is that they're new.

This is exactly true - plugs are new, approx 30 km done on them

Paintedseat · « **Reply #7 on:** March 23, 2018, 05:36:52 PM »

2 and 4. Porcelain color is not the only way to tell. The ground electrode is an indication. There should be a slight color change at the bend. If it looks like yours it is lean. 2 is leaner than 4.

Erny · « **Reply #8 on:** August 24, 2018, 02:22:33 PM »

I have update on this topic

Bike is now after full point settings (dwell, advance...) by strobe, carb hand cleaning and sync. It idles far better now (when it is warm).

I measured compression on warm engine too all cylinders were very close to 55-60psi (4 bars). Is that OK? (Isnt it too low?)
Engine is 100% stock, never opened, 9000miles from new

Pics of plugs now after 20mins ride attached

Deltarider · « **Reply #9 on:** August 24, 2018, 11:13:50 PM »

What made you decide to do the test? I myself never managed to do a compression test right. I would get readings like yours. I must have done something wrong. Decades later bike still performs as it should. So no worries, stop playing the mechanic and enjoy riding.

robvangulik · « **Reply #10 on:** August 25, 2018, 12:37:49 AM »

Did you do the comp. test with wide open throttle?

TwoTired · « **Reply #11 on:** August 25, 2018, 01:15:09 AM »

Are you using a small engine compression tester? Or one intended for larger displacement engines? The engine FAQ explains why the later gives you false readings.

And, you need to have the throttle wide open as well as the choke wide open, too.

Cheers,

dave500 · « **Reply #12 on:** August 25, 2018, 01:27:43 AM »

50-60 is way #$%*ing low,as mentioned already was the throttle held wide open?id like to see at least 140-160 psi,the length of the hose don't matter it just takes a couple more cranks to fill it so long as it has a lower end one way valve.

Erny · « **Reply #13 on:** August 25, 2018, 01:30:09 AM »

Aha.. I did not know that.

When I did comp test, trottle was closed

Tester is this one http://s.aliexpress.com/3MrUjuQ7?

I'm not saying something is wrong with the engine, I just wanted to check it (plugs, comp) after engine tune up and carbs cleaning.
At least having all cyls the same comp is good from my point of view

Note: mixture screws are all set to basic settings only. Here I wonder if I should do something with them.

Just to add - I think engine pulls nicely, especially up from 4-5k RPM, I have no other CB750K to compare with. I can reach 100mph and if I try to bend to tank I can go to 110 (tacho readings)

david 750f · « **Reply #14 on:** August 25, 2018, 02:24:47 AM »

Those plugs look fine. If you can run 110 mph (with a GPS), everything is great.

Scott S · « **Reply #15 on:** August 25, 2018, 03:34:38 AM »

I don't know if you have ethanol in your gas, but ethanol laced gas seems to make plugs appear leaner, in my experience.

Erny · « **Reply #16 on:** August 25, 2018, 04:05:24 PM »

yes, all fuels sold in Slovakia contains ethanol...

flatlander · « **Reply #17 on:** August 26, 2018, 12:48:25 AM »

is there a problem that you are trying to solve? if yes, can you describe it?
if not, then stop fiddling around and ride the thing

ekpent · « **Reply #18 on:** August 26, 2018, 04:46:26 AM »

Quote from: david 750F on August 25, 2018, 02:24:47 AM

Those plugs look fine. If you can run 110 mph (with a GPS), everything is great.

I agree with David and they sure look a lot better then most we see posted around here.

Stev-o · « **Reply #19 on:** August 26, 2018, 06:56:47 AM »

We have a very famous saying in America:

"If it ain't broke, don't fix it!"

Erny · « **Reply #20 on:** August 26, 2018, 09:53:41 AM »

Thanks to all responses

Just wondering if/how to tune mixture screws (now they are all in basic settings only). Could these further tune engine? If so, what''s best way to tune them?

Note: for my curiosity, I'll redo comp test with open trottle (I suppose on 1 cylinder will be enough, knowing all have apprx the same value with closed trottle)

dave500 · « **Reply #21 on:** August 26, 2018, 12:48:54 PM »

do the compression test again fully not just one cylinder youll have all the plugs out anyway,#$%* its only a half baked job otherwise,write the readings down you can check them a year later.

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Author Topic: Lean? Rich? Or just OK? (Read 2581 times)