Difference between front and rear spark plugs

[gosilver]

Good morning,
I would like to know your opinion, and suggests, about this situation.
I know, for personal choice, that my FL 49 (with stock heads and cylinders) run a bit rich in mixture.
Every time I check the spark plugs, them are with dry carbon deposit. Whit the intention to adjust these facts (without change the air-gasoline mixture) I've tried to run with a different kind of gasoline: shall VPower. This gasoline has 100 octante, but has too addictive that (in teory...) can help a better combustion with cleaner action. I' ve try (but this action I do not belive is significative) to add an addictive "instead of lead". The results are: rear spark plug "perfect" with nut color; front spark plug whit the same dry carbon deposit.
Now....why? And one time discovered the causes...how can I make adjustment?.
Is possible I need a more hot spark plug in front combustion chamber?
Now I run with Champion J12YC.
Thank you all.

[1962FLH]

Intake leak can cause the problem you are describing. Test and repair intake leaks before adjusting carb or changing to different plugs.

Good luck with it.

John

[Mark44]

Good morning,
I would like to know your opinion, and suggests, about this situation.
I know, for personal choice, that my FL 49 (with stock heads and cylinders) run a bit rich in mixture.
Every time I check the spark plugs, them are with dry carbon deposit. Whit the intention to adjust these facts (without change the air-gasoline mixture) I've tried to run with a different kind of gasoline: shall VPower. This gasoline has 100 octante, but has too addictive that (in teory...) can help a better combustion with cleaner action. I' ve try (but this action I do not belive is significative) to add an addictive "instead of lead". The results are: rear spark plug "perfect" with nut color; front spark plug whit the same dry carbon deposit.
Now....why? And one time discovered the causes...how can I make adjustment?.
Is possible I need a more hot spark plug in front combustion chamber?
Now I run with Champion J12YC.
Thank you all.

As already mentioned, check for leaks in your intake manifold -- http://virtualindian.org/11techleaktest.html. Some people check for leaks by squirting a flammable liquid on the manifold while the engine is running, but this is both dangerous and not as effective as pressurizing the manifold to about 10 to 12 PSI (about 69 to 83 Kpascal), and squirting a soap-water mixture. Any leak will cause lots of bubbles to form.

The gasoline has additives, compounds that have been added to it, not "addictives". Heroin is addictive, but not due to additives that might have been added to it. Also 100 octane gasoline is very high octane, close to aviation fuel. About the best we can do here in the U.S. at a regular gas station is 94 octane.

[Bigincher]

Changing the heat range of the spark plugs would be like treating the symptoms, while ignoring the disease.
However- back in the old days, it was common practice to run a hotter plug in the rear cylinder (as I remember it), for exactly the reason you describe. I might be confused about front/rear, hot/cold- it's been a long time since I thought about it...

[gosilver]

Thank you all.
The mainfold has on 1500 miles (Colony). Is brand new.
I can make a pressure test, but facts are strange....
As I've said, mixture is for sure rich, but I can't understand why if before I had two spark with the same kind of dry deposit, only changing kind of gasoline the rear spark plug becames perfect in colour...and only the front spark plug remained whit same dry deposit. Why only changing kind of gasoline (whit an high performance one) rear combusition is pretty good and front combustion is same?
I would like to say that the deposit on spark plug is not heavy. If I work whit a brush on the spark, only with a light job she becomes clean...but has a gray colour (i'm talking about the front spark plug). Is the tipical spark plug working on a rich mixture: not more and not less.
Don't Know the reason, but looking for facts i've think that for a reason I can't understand, front cylinder need a more hot spark plug than rear cylinder. I would like to know, in your opinion and in your precious experience, if is possible and if is reasonable to try to have different spark plugs in different heads, with different (at the state of facts) combustion.
I will try to make pressure test, but I'm quite sure I will not found any leaks. If I will find a leak, ok....but if i don't?

[Bigincher]

If there is no intake leak, why not try a hotter plug in the front?
Try it, it my be the solution. And if so, then I wouldn't hesitate to run with it.
It was common practice years ago, no different today.

[gosilver]

I Know Champion (spark plug brand I'm using and I wont to continue to use) has a a particular code (inverse) to identificate the type of spark plug. Which is more hot than J12YC? thanks for help!

[gosilver]

I Know Champion (spark plug brand I'm using and I wont to continue to use) has a a particular code (inverse) to identificate the type of spark plug. Which is more hot than J12YC? thanks for help!

I Quote myself...
sorry, Champion is the brand I want to continue to use

[RUBONE]

What carburetor are you using? Stock Linkerts with a vertical throttle shaft exacerbate the issue with one cylinder running richer. It is common to all early H-D V-twins.

[gosilver]

What carburetor are you using? Stock Linkerts with a vertical throttle shaft exacerbate the issue with one cylinder running richer. It is common to all early H-D V-twins.

Hi Rubone,
I'm using a Linkert M74B

[steve_wood]

Gosilver,

Is the intake manifold is evenly spaced between the front and rear head? If it isn't, even if it isn't leaking, it can cause result in an imbalance. This happened to me, although it was with the o-ring type of intake manifold. I re-centered the manifold and the problem went away.

[gosilver]

Gosilver,

Is the intake manifold is evenly spaced between the front and rear head? If it isn't, even if it isn't leaking, it can cause result in an imbalance. This happened to me, although it was with the o-ring type of intake manifold. I re-centered the manifold and the problem went away.

Thank you Steve.
I' have to look for...
I can't understand why only one spark plug immediatly change colour (becoming "nut") with another kind of gasoline...
I do belive that Rubone is right...

[Gotnoclass]

Thank you all.
The mainfold has on 1500 miles (Colony). Is brand new.
I can make a pressure test, but facts are strange....

These age or make of the manifold have nothing to do with intake leaks. Even brand new it of the box manifolds have proven to be warped. There are plenty oem out there that you can get, but still need to dress before you put them in - like flat sanding the mating parts and making sure the o ring shoulders are in tact. I also recommend dressing up the phenolic spacer, that gets sandwiched between the carb and manifold. Use good quality o rings, and as other have mentioned here, make sure your cylinders are positioned properly to accommodate the carb and o rings. Bubble testing your manifold AFTER proper alignment of carb in crucial. Make sure to use the barb support bracket, and that no stress whatsoever in placed upon the carburetor. It's a tedious process, but the only one that can achieve best results.