10 replies to this topic

[andychell]

Hello, I'm hoping somebody can help please.
I've got a 1989 Classic, registered as a 998cc. It's running a stage 1 kit, 1/2" SU carb and quite new electronic ignition. It's also got NGK tri- electrode spark plugs and this is where I've got an issue.
I took it to a rolling road last week and whilst happy with the results, I decided to check the spark plugs today. Cylinders 1 and 4 looked lovely, just as I would like to see, lovely brownish pink. But cylinders 2 and 3 were really black wurh carbon, as if it is running rich. I've not seen this before so would appreciate some advice as what would be causing this please. Many thanks. Andy.

[wile e coyote]

Generally completely normal with a single carb....

[andychell]

Really? Blimey, my very novice logic expected them to be all the same.
Many thanks for that, put my mind at rest!
Andy

[cal844]

Yup very normal, how does the car run?!

[KernowCooper]

Siameese Inlet ports not uncommon but it could be a tad rich

[Mini Manannán]

Wind the jet up a 1/8 turn and drive around, chop the plugs after that.

[andychell]

Car runs really well. Rolling road tune up was great, but they did not check the plugs, which I thought was surprising. They said it was running lean at idle, which does not seem to bear out with the colour of the plugs.

Interesting and really useful comments, many thanks.

I'll have a play around with the jet setting at the weekend, but it's running well. 49BHP for a 998 on the rolling road was better than I was expecting!

Cheers. Andy

[Jordie]

Id be less tempted to mess with the jet if its been rolling roaded.

 

I would put a new set of plugs in and monitor from there, if its driving ok.

 

I assume they would have set the fuel and timing to get the best possible, so changing it might give you poorer performance/economy.

[Alpenflitzer]

Cylinder 2 and 3 -  Cylinder head gasket has burned between the 2 a bridge ?

[sledgehammer]

Cylinder 2 and 3 -  Cylinder head gasket has burned between the 2 a bridge ?

 

I wouldn't think it a 998 would make 49 bhp with 2 cylinders down

 

but have been wrong before

 

as above I would think the colour difference is due on inner cyl's being closer to carb

 

the only way to stop this - is twin carbs - which unless you are very lucky , always seem to go out of tune after a while

 

(all the twin carbs I have had , always seem to go that way - may be just me)

Edited by sledgehammer, 27 October 2014 - 06:14 PM.

[KernowCooper]

Whats the spec of the engine for 49bhp from a 998 ?