Spark Plugs, what do you guys think?

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Hi,

Thought I'd start a new thread as the 'Leak Down Test' one has got WAY too long:rolleyes:

OK, I rebuilt the top end, new pistons/rings, new sleeves for the barrels, head rebuilt, all done by Jim C.

Nothing else was changed on the bike.

Carbs got rebuilt about a year ago with new needles, needle jets, stay up floats. Approx. 200 miles on these parts.

Ran the bike for 50 miles on Monday, tuning in the carbs along the way. Lots of on/off throttle action to bed in the rings, kept it below 70mph & 4K revs. Bike back to the workshop, changed oil, torqued head again, re-set tappets.

The pictures below are the plugs after about 30miles, what do you guys think? (they look the same after 50 miles I just didn't take any pics!!)

RH Plug:
Spark Plugs, what do you guys think?


LH Plug:
Spark Plugs, what do you guys think?
 
Sure looks lean. A fresh engine will produce a weak and inconsistent vacuum signal. I suggest turning the idle air trim screws in, raising the needles, possibly get larger main jets to enrich the mixture during run-in. Probably wouldn't be bad idea to consider running colder heat range plugs.

I suggest that you check float height, and, if necessary, change the setting by heating (gently) the float bowel and drifting the float need seat. Yes I know that sounds scary, but it works well and is much easier than it sounds. I have spoken with a number of Amal gurus who consistently say not to bend the tab on the stay-up float.

Best.
 
RoadScholar said:
Sure looks lean. A fresh engine will produce a weak and inconsistent vacuum signal. I suggest turning the idle air trim screws in, raising the needles, possibly get larger main jets to enrich the mixture during run-in. Probably wouldn't be bad idea to consider running colder heat range plugs.

I suggest that you check float height, and, if necessary, change the setting by heating (gently) the float bowel and drifting the float need seat. Yes I know that sounds scary, but it works well and is much easier than it sounds. I have spoken with a number of Amal gurus who consistently say not to bend the tab on the stay-up float.

Best.
Click to expand...

Appreciate the reply.

The air screws are 1 and 1/8th turns out, the needle is on the middle position, the main jets are 250, Needle jet is a 106. Needle is a 928/104 (it has 4 rings at the top) slide is a no.3

Interesting about the float height, the reason I got the stay-up floats was because I could bend the tang! Did the Amal gurus explain why they were suggesting not to bend the tabs on the say-up floats? It's one of the main reasons Amal made them?

I'm slowly educating myself regarding reading spark plugs on 'new' unleaded fuel, the logic seems to be that the 'usual' pictures you see of a sooty plug, or oily plug etc. etc. went out in the dark ages!!

For peace of mind I'll defo. richen up the air screws. Not sure about the float thing! (I'll wait for others to comment!)
I think my main jet is OK, I thought it might be on the big side as it was originally jetted for a 920.

The bike overall was running really well, ticking over like a clock, with good pickup but there was a hesitancy under load up to 1/4 throttle (or a bit less). I've cleaned the pilot jets using a tiny drill & carb cleaner but still have to take the bike out again to see if its made a difference.
 
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I would say the mixture looks okay on the rh plug, complete ring of carbon around the base. Lh plug looks a little lean. That's not very many miles to develop deposits. Might try turning the left hand air screw in a 1/4 turn. May be seeing a timing mark on the Lh plug strap about where you should. As far as the float level's you should measure the fuel level in the bowls per Amal's advice. The level should be at .21" below the top of the bowl. You can measure this with the carbs on the bike by rigging up a U tube using a spare drain plug modified with a barb hose fitting and a piece of clear fuel hose.
 
htown16 said:
I would say the mixture looks okay on the rh plug, complete ring of carbon around the base. Lh plug looks a little lean. That's not very many miles to develop deposits. Might try turning the left hand air screw in a 1/4 turn. May be seeing a timing mark on the Lh plug strap about where you should. As far as the float level's you should measure the fuel level in the bowls per Amal's advice. The level should be at .21" below the top of the bowl. You can measure this with the carbs on the bike by rigging up a U tube using a spare drain plug modified with a barb hose fitting and a piece of clear fuel hose.
Click to expand...

Thanks for the reply.

Yes, I'll adjust the LH air screw in 1/4 of a turn.

From what I'm reading 50miles is not really enough time to get a proper reading on the plugs.

I've got the fuel level 'tool' from Andover Norton so I can check the level with the carbs on the bike, have it set at .21"

I'll take it out for a spin over the weekend and get another 100miles done, it's hard work running in these engines:)
 
I would say the LH plug looks correct. The RH plug looks rich -but both plugs look to be too high of a heat range. You should be using an NGK 8 grade or cooler in your oversized motor.

And the old wives tale that says a larger motor needs a larger jet is rubbish. The jet size is going to be determined by the strength and shape of the vacuum signal seen be the carb. That is determined by the compression ratio, the cam timing and the exhaust system, not the engine size.

So if everything else is exactly the same [not the case in your motor] a larger motor may in some cases create a stronger carb signal and therefore require a smaller jet to make the correct mixture. Jim
 
Don't be fooled by the soot on the metal part of the plug. The bit you are looking for when doing plug readings is right down inside on the porcelain where it meets the metal. There should be about a 2mm black ring. It depends on the heat range of the plug and it is probably only relevant to full throttle running - the main jets. I have never used plug readings to set the needle jets or idle circuit. It is too unreliable. If you have identical jets in twin carbs, the plugs should look the same, unless you have flooding or starving in one carb, or an oil problem. If you are using a single carb and the plugs look different, I would suspect the ignition system. That can also happen with twin carbs, but it is rare in both cases. It is possible to have one needle hanging loose in one of the slides. There was a previous topic where one of the guys had this happening. In most carbs the needles are held down by the spring seat which might be a disc or a clip.
It is unusual to start burning valves or pistons when you are not using full throttle, so I always run main jets a bit richer than needs be for best power. If you are too lean in the midrange, you should know it. The bike usually becomes a pig to ride.
 
comnoz said:
I would say the LH plug looks correct. The RH plug looks rich -but both plugs look to be too high of a heat range. You should be using an NGK 8 grade or cooler in your oversized motor.

And the old wives tale that says a larger motor needs a larger jet is rubbish. The jet size is going to be determined by the strength and shape of the vacuum signal seen be the carb. That is determined by the compression ratio, the cam timing and the exhaust system, not the engine size.

So if everything else is exactly the same [not the case in your motor] a larger motor may in some cases create a stronger carb signal and therefore require a smaller jet to make the correct mixture. Jim
Click to expand...

Thanks Jim.

Interesting I didn't know about running a cooler plug in an oversized engine! I'll track down some NGK 8's

Also interesting about the main jet size, you hear some things so often you take it as fact without any real experience!!!
 
acotrel said:
Don't be fooled by the soot on the metal part of the plug. The bit you are looking for when doing plug readings is right down inside on the porcelain where it meets the metal. There should be about a 2mm black ring. It depends on the heat range of the plug and it is probably only relevant to full throttle running - the main jets. I have never used plug readings to set the needle jets or idle circuit. It is too unreliable. If you have identical jets in twin carbs, the plugs should look the same, unless you have flooding or starving in one carb, or an oil problem. If you are using a single carb and the plugs look different, I would suspect the ignition system. That can also happen with twin carbs, but it is rare in both cases. It is possible to have one needle hanging loose in one of the slides. There was a previous topic where one of the guys had this happening. In most carbs the needles are held down by the spring seat which might be a disc or a clip.
It is unusual to start burning valves or pistons when you are not using full throttle, so I always run main jets a bit richer than needs be for best power. If you are too lean in the midrange, you should know it. The bike usually becomes a pig to ride.
Click to expand...


Thanks for the reply.

I was aware of reading the base of the porcelain tip & looking for the black ring, which is quite difficult!
Thanks for your other insights
 
comnoz said:
I would say the LH plug looks correct. The RH plug looks rich -but both plugs look to be too high of a heat range. You should be using an NGK 8 grade or cooler in your oversized motor.

And the old wives tale that says a larger motor needs a larger jet is rubbish. The jet size is going to be determined by the strength and shape of the vacuum signal seen be the carb. That is determined by the compression ratio, the cam timing and the exhaust system, not the engine size.

So if everything else is exactly the same [not the case in your motor] a larger motor may in some cases create a stronger carb signal and therefore require a smaller jet to make the correct mixture. Jim
Click to expand...

I found this with my 1360. It was way too rich with the correct jetting for the same engine in 1200cc size.
I had to go down 2 sizes to get the AFR right.

Glen
 
worntorn said:
I found this with my 1360. It was way too rich with the correct jetting for the same engine in 1200cc size.
I had to go down 2 sizes to get the AFR right.

Glen
Click to expand...

Your lucky.
I learned it the hard way many years ago when I installed a 1900cc low compression engine in place of a 2000cc high compression engine.
The 1900 cc engine was used and well broken in but when I installed it with the carbs from the 2000cc engine it burned the pistons and seized the first time I took it up to road speed.
 
I had a bit of advance info from an old-time Westwood racer/tuner . He told me that the bigger engine would probably tune up with smaller mainjets, so I figured starting with the 1200 cc sized mainjets was relatively safe.
I guess you were going the other way, that's not so forgiving!

Glen
 
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acadian said:
Since we're exposing our plugs
View attachment 10062
Click to expand...

Those look non/pre-ethanol in color...or aviation fuel.


Click...it’s hard to make an accurate call...as the responses indicate. Every screen is different as is the eye of the interpretation.
My Ipad screen says RH normal to slightly rich with LH lean. My big monitor looks like the RH is rich and the LH has been wiped off.
 
Really appreciate all the responses, this is my take away:

1. I seem to be running a bit lean

2. My main jets could be too big, I've gone from a 920 to an 880, I'll drop at least one size.

3. I'll get some BP8ES plugs and see if the cooler plugs work

I'll try the main jets first & richen up the LH air adjuster

More anon!
 
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