Spark plug probs

[evil_yoda]

Replaced the spark plugs in my 2000 1150 the other week as part of the 24000 mile service. Since doing this I have been getting the occasional backfire, not the usual pop on the overrun but proper gunshot types where people run for cover!

I've just taken the new plugs back out to have a look and they are different from the old ones.
The old ones are: NGK - BKR7EKC
and the new ones are: NGK - BKR7EKC-N

They came as part of a service pack from Motobins.

The gaps are smaller on the new ones. Could this be whats causing my problems??

Also noticed recently that I get a small "pop" when the revs fall through about 1500rpm and I get a 6 inch blue flame from the exhaust

Is this normal??

 

[littleredrooster]

Y-piece?? Catalyst?? End-can??? Or are you completely standard?

 

[evil_yoda]

OK. When I 1st got the bike, it have a y-peice and revolution on and there was no cat code plug. It surged a bit so I did the "Steptoe link" and it improved the surging. All was well!

After a while I got a bit annoyed with the noise so I decided to keep the y-peice and refit the standard silencer. I wasn't sure what to do about the cat code plug, so I left the Steptoe link in place and everything seemed to run fine. No noticable loss of power, just quieter!

All untill I replaced the spark plugs. I tried removing the steptoe link and this has improved the backfiring, but it now seems to surge more!

 

[Sergeant Pluck]

Did you reset the Motronic when you took Steptoes link out? From what I can gather from much research here and through plenty of experimentation is that if you run a y-piece and standard can - NO cat-code plug gives the best mixture, whilst if you have a remus can and the y, steptoes link is best. I have never been able to stop backfiring under any exhaust/CCP/TPS setting configuration on 2 different bikes and I'm personally pretty sure it's not actually possible (because of the way the y-piece manufactured)*. I have noticed that how well you adjust your valves and also type of spark plug and the gap you set can have quite an affect on the 'ferocity' of your backfiring. Oh, and the ambient temperature too!

*edit: this is the bit where you all come on and tell me how you've been running y-pieces etc for years and have never experienced backfiring

 

[evil_yoda]

Yup, I've reset the motronic everytime I've messed with the cat coding stuff.
It's now running with no ccp and as I said, seems to surge a bit. Somedays seems to surge worse than others.
The valve clearances and throttle body balancing is next on my list, but I wanted to make sure there wasn't a problem with the spark plugs 1st.
Does anyone know what the difference between 7EKC and 7EKC-N is?

 

[Bronco Billy]

Yep I know......


N

 

[evil_yoda]

Yep I know......


N

Actually it's "-N"

 

[Bronco Billy]

Actually it's "-N"

I know but the..... - Key on my keyboard is missing..

 

[littleredrooster]

Yup, I've reset the motronic everytime I've messed with the cat coding stuff.
It's now running with no ccp and as I said, seems to surge a bit. Somedays seems to surge worse than others.
The valve clearances and throttle body balancing is next on my list, but I wanted to make sure there wasn't a problem with the spark plugs 1st.
Does anyone know what the difference between 7EKC and 7EKC-N is?

Plug code guide here
I would have thought that a change of plugs would NOT cause your backfiring. Summat else must be amiss. FWIW, when I ran a Y-piece + std. can, the backfiring was present all the time, even with a Techlusion fitted and careful sealing of all the joints.

 

[evil_yoda]

It just seems strange that the bike was running fine with the standard exhaust and y-peice for a couple of months up until I changed the spark plugs. The only other thing I changed was the air filter. Just a standard filter though.

It had always popped a bit on the overrun, but this is a proper backfire!

 

[pomm001]

What happens when you put the old plugs and air filter back in,
is it OK again ?

 

[evil_yoda]

What happens when you put the old plugs and air filter back in,
is it OK again ?

That sounds like a really logical idea. Must have been far too obvious as my highly evolved brain did'nt think of it, so I might give it a go at the weekend and see what happens!

Now that the CCP is out, the backfires are almost gone so I might leave it and see what it's like after doing the valves and throttle syncing.

Matt