Spark Plugs, what do you guys think?

Status
Not open for further replies.
Just for others who might experience something similar.

I got NGK B8ES plugs and put a quarter turn in on both air screws. I didn't change the MJ, still running a 250. Changed primary chaincase oil, gearbox & engine oil from last outing.

Went out with SWMBO!, bike still had a stumble/stutter coming off idle, approx 1/8th throttle.

Did about 25 miles & had a look at the plugs, they were better but still, to my eyes a bit lean.

With the help of my assistant mechanic (shes a keeper!!!) I took the tank off & raised the needles on the pair of MK1's (clip on the bottom groove). Also noticed that the LH needle clip was in the top groove, the leanest setting! The RH clip was in the middle groove. This would explain why the LH plug looked leaner than the right when I checked the plugs after the last run, as usual operator error!!! (thought both clips were in the middle groove)

Almost night & day difference, stumble/stutter gone, could pull cleanly in 3rd, two up going up a hill. Much better taking off from a stop, previously I was revving quite high just to avoid a stall.

Did another 10 miles, all 'B' roads and checked the plugs again, this time bit of colour on the porcelain & some signs of soot on the ring, much better.

Did another 15 miles of 'B' roads REALLY enjoying the bike & the beautiful day we are having in Dublin. Still keeping it around 4K. Next few outings I'll start creaping the revs up a bit.

So, one happy camper in Dublin on a Norton Commando!

Thanks for all the help lads :)
 
Last edited:
I have a Triumph engine with a 750 kit and tons of other modifications. I first built it in 1992. I have had two sets of pistons and run about four different compression ratios, using different head gaskets and base gaskets etc. starting at 10.8 :1 then going to 10.5, then 10.2, and now about 9.9. Each time there was a noticeable decrease in power. As the compression ratio went down the engine needed bigger main jets to maintain the correct mixture. I think that with the higher compression ratio there is a more powerful suction created. It is a bit backwards compared with what you would expect. (bigger jets, less power) It still lifts the front wheel just wacking the throttle open in first gear even though it is geared really tall. (with the 10.8 though you had to be carefull not to flip it)
 
tricatcent said:
I have a Triumph engine with a 750 kit and tons of other modifications. I first built it in 1992. I have had two sets of pistons and run about four different compression ratios, using different head gaskets and base gaskets etc. starting at 10.8 :1 then going to 10.5, then 10.2, and now about 9.9. Each time there was a noticeable decrease in power. As the compression ratio went down the engine needed bigger main jets to maintain the correct mixture. I think that with the higher compression ratio there is a more powerful suction created. It is a bit backwards compared with what you would expect. (bigger jets, less power) It still lifts the front wheel just wacking the throttle open in first gear even though it is geared really tall. (with the 10.8 though you had to be carefull not to flip it)
Click to expand...


Appreciate the reply, always interested in 'real world' experiences.

I'm finding some of my basic engine 'logic' i.e. bigger engine bigger jets, smaller engine smaller jets is NOT what necessarily works in the 'real world'!!!
 
tricatcent said:
I have a Triumph engine with a 750 kit and tons of other modifications. I first built it in 1992. I have had two sets of pistons and run about four different compression ratios, using different head gaskets and base gaskets etc. starting at 10.8 :1 then going to 10.5, then 10.2, and now about 9.9. Each time there was a noticeable decrease in power. As the compression ratio went down the engine needed bigger main jets to maintain the correct mixture. I think that with the higher compression ratio there is a more powerful suction created. It is a bit backwards compared with what you would expect. (bigger jets, less power) It still lifts the front wheel just wacking the throttle open in first gear even though it is geared really tall. (with the 10.8 though you had to be carefull not to flip it)
Click to expand...
What octane petrol do you run your triumph on?
 
FWIW, compression increases are often assumed to increase power considerably more than they actually do. The advantage to increasing compression is that it makes more power across the entire RPM range as opposed to what cams/exhaust/carb changes typically do - make more power at specific rpm range at the expense of power somewhere else in the range. Higher compression is also more fuel efficient.

But within the usual range of street engine compression the actual peak HP change with a compression increase of 2 points - with no other changes - is only around 6%. Frankly, (IMO) that's not enough to bother with considering the cost/effort involved in changing pistons/milling the head/whatever. Typically, of course, other changes are made along with the compression change. Few builders (none?) would build a "performance" engine by taking a stock engine and simply increasing the compression alone. It usually goes along with cam/intake/exhaust/ignition timing changes.

Some modern street engines have as high as 13.5:1 compression but the computer and related mechanical systems ensures optimum fueling, ignition timing, valve timing, induction system volume (air mass, not noise), and exhaust system volume.

We built conventional engines with up to 13.5:1 compression though engines at that level were built for off-road, not street use. Of course, people used them for whatever they wanted to use them for and some of them were used on the street. Frankly about 10 minutes in one of them on the street was more than I needed! ;)
 
I had the same look on my plugs recently. One of the newish resistor plug caps was normal, and the other tested way high out of range and that side was very rich.

I had happened to also have a problem with the factory float height on the opposite side, and thought that I couldn't get that to come right so was chasing fairies on that instead.
 
On topic - never assume identical settings for two Amal carbs, but instead fine-tune each as needed. Mind you this was my experience with chopped Monoblocs from a 650ss but I find it applies to all Amals as a rule.

Off topic - I always break a new engine in using a single carb (Amal; Mikuni) and used header pipes. Once everything is rosy, I move to the dual carb and put in my fresh pipes for proper bluing.
 
MexicoMike said:
FWIW, compression increases are often assumed to increase power considerably more than they actually do. The advantage to increasing compression is that it makes more power across the entire RPM range as opposed to what cams/exhaust/carb changes typically do - make more power at specific rpm range at the expense of power somewhere else in the range. Higher compression is also more fuel efficient.

But within the usual range of street engine compression the actual peak HP change with a compression increase of 2 points - with no other changes - is only around 6%. Frankly, (IMO) that's not enough to bother with considering the cost/effort involved in changing pistons/milling the head/whatever. Typically, of course, other changes are made along with the compression change. Few builders (none?) would build a "performance" engine by taking a stock engine and simply increasing the compression alone. It usually goes along with cam/intake/exhaust/ignition timing changes.

Some modern street engines have as high as 13.5:1 compression but the computer and related mechanical systems ensures optimum fueling, ignition timing, valve timing, induction system volume (air mass, not noise), and exhaust system volume.

We built conventional engines with up to 13.5:1 compression though engines at that level were built for off-road, not street use. Of course, people used them for whatever they wanted to use them for and some of them were used on the street. Frankly about 10 minutes in one of them on the street was more than I needed! ;)
Click to expand...

Aware of the extra CC's not necessarily giving you more power unless you 'mod' other parts. I know the Norvil 920 conversion at the time (at least 9+ years ago) was marketed as a 'touring mod' as opposed to a performance mod. It lowered the revs for highway speeds and gave a nice increase in torque low down but didn't necessarily change the top speed, just how the power was delivered.

Thanks for the info. above I'm getting a Master's degree eduction each time I ask a question on this forum :-)
 
gortnipper said:
I had the same look on my plugs recently. One of the newish resistor plug caps was normal, and the other tested way high out of range and that side was very rich.

I had happened to also have a problem with the factory float height on the opposite side, and thought that I couldn't get that to come right so was chasing fairies on that instead.
Click to expand...

I've chased my fair amount of fairies around my workshop!!! They have a tendency to avoid capture just when you think you have them cornered :-)
 
Jdub said:
On topic - never assume identical settings for two Amal carbs, but instead fine-tune each as needed. Mind you this was my experience with chopped Monoblocs from a 650ss but I find it applies to all Amals as a rule.

Off topic - I always break a new engine in using a single carb (Amal; Mikuni) and used header pipes. Once everything is rosy, I move to the dual carb and put in my fresh pipes for proper bluing.
Click to expand...

On topic: Yes, I've had the carbs adjusted differently in the past, still getting to know this new setup I have!

Off topic: Interesting about changing the twin carbs for a single, I can see how this would make the whole process of initial start & running in a bit simpler & more manageable, thanks for passing this on.
 
Did another 130miles today on the new pistons/rings etc. total now about 250 miles.

Mainly 'B' roads and a little bit of motorway at 75mph. 4K revs = 70mph. No full throttle runs yet! Once I get to 500miles and use my mates private road, I'll let it rip;)

Recap: New 880 pistons & rings, B8ES plugs, 250MJ, Needle clip on lowest ring (needle highest position, rich), new stay-up floats, fuel level checked with fuel tube attached to the drain plug (approx 4-5mm from top of bowl measured in the middle where the jet is)

Rock steady tickover, good clean pull from standstill. I know it's difficult to read plugs from photos due to differing colour casts, monitors etc. but here you go:

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


LH Plug:

Spark Plugs, what do you guys think?


Shot of the bike today:

Spark Plugs, what do you guys think?
 
Last edited:
After all you've been through with that motor, the nicest thing about those very nice plugs is a complete lack of oil!
They look great to me, I wouldn't mess with it unless the fuel mileage is poor, just enjoy.
If anything , it might be running just a tad rich, which is the safe way.
What is your imp. fuel mileage on a gentle cruise at 60 mph?
If it's below 50 I would try dropping the needles a notch, if above 50 then best as is.

Glen
 
Last edited:
worntorn said:
After all you've been through with that motor, the nicest thing about those very nice plugs is a complete lack of oil!
They look great to me, I wouldn't mess with it unless the fuel mileage is poor, just enjoy.
If anything , it might be running just a tad rich, which is the safe way.
What is your imp. fuel mileage on a gentle cruise at 60 mph?
If it's below 50 I would try dropping the needles a notch, if above 50 then best as is.

Glen
Click to expand...


Thanks Glen, lack of oil is nice, long may it last! No stats on MPG yet but thanks for the tip.
 
Click, your plugs look pretty good.


Gortnipper ,that right one does look a bit hot. The carbon on the side electrode is burned clean all the way to the base of the threads.

Make sure your timing is not too far advanced. You don't have a thread insert in that hole do you?

Raise the needle one on that side.

B8ES plugs are a little safer than a BP8ES. They are not as likely to glow the side electrode and pre-ignite.
 
Timed to 28 @ 3k, no insert.

My TS is wired directly to that RH coil, and then a jumper to the LH coil. Would swapping that jump around have any effect?
 
gortnipper said:
Timed to 28, no insert.

My TS is wired directly to that RH coil, and then a jumper to the LH coil. Would swapping that jump around have any effect?
Click to expand...

No, that shouldn't have any effect. What ignition?

I would probably just raise that needle and see how it looks. As long as you don't see any pepper flakes on the insulator your not hurting anything -but your probably not too far away from it. Jim
 
Trispark.

Note that these plugs were pulled after a good ride, finishing with a WOT uphill run when I chopped the ignition.
 
gortnipper said:
finishing with a WOT uphill run when I chopped the ignition.
Click to expand...

Then the side with the hot looking plug might appreciate a bigger main jet, if you are sure there’s plenty fuel flow from the tank.

Don’t raise the needle and change the jet. Test one change at a time.
 
Status
Not open for further replies.

Similar threads

Norcoastal
  • Locked
Where do you guys find your bolts?
2 3 4
Replies
66
Views
7,072
Bernhard
B
nick's_Cafe
What do you guys think.....
Replies
0
Views
1,014
nick's_Cafe
nick's_Cafe
B
  • Locked
Parts and Services, what do you think?
2
Replies
25
Views
2,313
bwolfie
B
Back
Top