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[sudburys]

Thanks for all the input everyone, I haven't been rude and ignoring you all but I just haven't had a spare minute to check in.

I might get a chance tomorrow to look at the bike and change the bellow too. Not too see what and where the map sensor is....

[sudburys]

Ok, so I managed to change the bellow today and have a look for any other leaks but couldn't find any. I checked all sensors were connected properly and even undid and cleaned the sensor going into the top of the exhaust (it was filthy with soot).

Unfortunately it made no difference to the bike except on my way home, after sitting at the traffic lights it spluttered and refused to pull away properly before kicking in and blowing black soot out of the exhaust. It then decided to violently judder forwards then stop and did it again like it was trying to throw me off like some raging bull!

Anyway, I limped it home and tried revving it a few times but the throttle seemed almost delayed.

Sod knows what's up with this thing... I'm gonna have to get it to a garage and hope they can put the computer on it to find a fault.

😢

Suds

[jefrs]

There is a long and possibly contentious thread re plug fouling. Imo the stock oem Bosch-India plug is poor quality and that you should try the NGK BPR6ES (lawnmower) and BPR5ES (car) plugs. The NGK 6 is heat equivalent to both Bosch 7 and 8, and the NGK 5 is heat equivalent to a Bosch 8 (which is what the CGT uses), the two plugs are practically the same heat range, a slightly hotter running plug should help burn soot off itself a little better. The "R" means resistor so HT cap should be non-suppressor type. The fouled plug will have by now thoroughly sooted up the motor. I got rid of that sooting by running a liberal dose of RedEx through the tank, double what it says on the bottle to decoke (a clean engine doesn't need it), plus italian tune up (thrash it). This soot is loose and soft so a RedEx decoke does work; it did. Do check your HT cap is good because the oem metal job on mine fell apart and may well have caused the plug to miss sparks, which would cause it to foul. Once a plug gets fouled it misses sparks so there's unburnt fuel left over which causes it to foul up more and soot everything up. Good luck

[sudburys]

Thanks jefrs,

I'll give the redex a go.

Come to think of it, a while ago my bike was in a garage (I later found out to have not such a great reputation) and I noticed they had put a new spark plug cap on, a ngx one.

Could this be defective in anyway as to affect the spark plug and its burning off capabilities?

[jefrs]

They may have found the oem HT cap was NBG. I replaced the broken metal job with a non-suppressor NGK type from our hosts, all good.



The HT lead on mine was a little short, I had to reposition the coil to give it more slack. I felt the tightness could pull the lead from the cap.

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Missing a spark leaves some unburnt stuff in the cylinder so the next time it fires it will be rich. Soot.



First fix the sparks. I am using a NGK BPR5ES (5) which may be a trifle hot for your bike. One uses a hotter plug when the engine is not thrashed hard. A colder plug runs cooler, which means it may not get hot enough to burn crud off but if one races the bike everything gets hot etc. I tried the iridium plug but it has a tiny pinhead for an electrode and it fouled up quickly.



Secondly clear the soot out of the system. One can strip down and decoke but this soot is soft and loose so I use RedEx. I suggest a liberal dose for a RedEx decoke, at least twice what it says on the bottle for 'regular use'. It took 2 or 3 tank fills but it did it. I even took the exhaust pipe off and inspected the port, soot gone.



Thirdly, check the plug colour. There used to be colour pictures in the Haynes joke books. A fuel injector will return a paler colour than a carburettor does. Don't pull the plug too often, once it is burning nicely it's the right one and leave it alone. Stop using the RedEx when done.

[Rattlebattle]

The symptoms your engine is displaying are similar to those I had a while ago. The bike became steadily worse until it was virtually unrideable. In my case it turned out to be a disconnected tps. It is not unknown for the tps connector not to have been pushed fully home at the factory. Presumably the same could happen after some home or dealer servicing. Basically mine had run so rich that eventually it completely fouled up the plug.
Have you checked for fault codes? This should indicate which, if any, sensor/connector is faulty. Just ground the spare wire attached to the ECU and read the number of long and short flashes. What they mean is in the w/s manual, or do a search. Sooty plugs are seldom to do with the plug itself - you need to find the reason for the rich running.

[jefrs]

Electrical connections on the bike are pretty shoddy and no, the plug does not cause fouling in itself but once fouled they only get worse. The cause of mine fouling was missing sparks. First fix the sparks, your cause may not be the same as mine. I traced mine to mainly the HT cap (tracking down outside the plug was a big clue), we do know that the bike has received a new HT cap.



I have also had minor glitches with corroded oem fuses and cheap spade connectors too thin with poor plating. So TPS (throttle position) connection would not surprise me at all.



The box connectors used on the bike are however pretty good, similar to those on a Suzuki &c, provided they are pushed in properly.

[jefrs]

I may have given the impression that changing the plug will cure the problem, it won't, not in itself.

However once the bike starts missing sparks it will run rich because there is some unburnt fuel left over from the missed firing(s). There are two problems to cure: fix the sparks and clean up the mess.



The stock twin electrode WR7DDC4 is not a Bosch but something made for RE from a company Bosch-India bought out. It is roughly equivalent to an NGK BP6ES or BPR6ES. The twin electrodes make it a peach to clean and set. The CGT's hotter WQR8DC likewise but this is equivalent to a NGK "6" or NGK "5". The CGT has enlarged ports but otherwise very similar head to the C5/B5, interchangeable bits and clearance.

NGK make the BPR6ES as a lawnmower plug but make the BPR5ES as a car plug (Vauxhall Nova), the "5" looks very much better made, we used to have a Nova and I just happened to still have some unused plugs. The 5 is only a half step hotter than a 6, there is little information on them, back equivalence gives the 5 equal to a Bosch 7 or 8. My bike does have free-flow, K&N and Power Commander, so it is possibly not working as hard to provide the grunt, running cooler - like the CGT and so needing a slightly hotter plug.



Choosing the plug is about tuning the bike after fixing the sparks. I found the 5 to run a better colour and cleaner than the 6 after fixing the sparks.

[Rattlebattle]

I have a pack of four NGK BP6ES plugs bought years ago for a car I used to own; I don't now recall which one but certainly at one time it was sold as a car spark plug. I have been meaning to replace the original plug cap on my C5 LE Despatch for a while now. As I had a couple of other minor jobs to do on it I finally got around to replacing the cap today with a Champion one from our host. I decided to cut about 3/8 inch off the end of the HT lead as there didn't seem to be much copper visible in the hole vacated by the original plug cap. I made a nice firm connection with the new cap. Lo and behold, when I reassembled the bike it started first kick, something it hasn't done for a while, though it always starts quickly enough on the starter motor.
FWIW many owners of BMW oilheads used to replace the original Bosch twin electrode plugs with NGK (or better still Autolite) single electrode plugs. These engines used to surge quite badly; putting better pliugs in helped some. The twin electrode idea was primarily to avoid the need to set the gap so often. They didn't spark any better because electrical current takes the line of least resistance, so most of the time they only spark across one gap. When erosion has made that gap bigger than the other they then spark across the smaller gap. A solution to a problem nobody raised really....

[jefrs]

The current C5 has the HT lead captive with the coil - to replace the HT lead you have to change the coil (?). My HT lead is decidedly short, there's not a lot of spare to cut off. An old dodge was to shove a bit of solid copper wire up a suppressor lead to find the carbon string before screwing it into the HT cap. I did not need to do that.



The BP6ES could well have been a car plug, the V.Nova is a thing of the past now too. Looking at the NGK BPR5ES and the BPR6ES they do look different. The ceramic of the 6 is more creamy than the white of the 5, the printing is smudged and the ceramic not moulded as finely, it's as if they were made in different factories.