14 replies to this topic

[BenLAST]

So, after having enough of my car struggling to do 70 comfortably, i decided to change some parts to make it a little normal for a 998.

So after sourcing a stage 1 head (or stage 2, he's not sure) from munnracing, and a Maniflow exhaust and manifold also from munnracing, we went about fitting them. Turns out, there was a good 4" hole in the top of my original backbox, the manifold was perhaps half the size of the new one, and the old head had a cracked valve!

Now, after fitting these, we eventually got it running. Drove home, it was fine. Then it suddenly dropped to 3 cylinders, and after drying was of the plugs (which was soaked) it ran normal, but after literally a few seconds dropped back to 3. We then changed all the plugs, and it seems to be alright for now, but there is an aweful amount of smoke coming out of the back, which sticks of petrol. Could the mixture, which will hopefully be adjusted asap, cause the 3rd spark plug to get wet and drop to 3 cylinders?

Thanks, Ben

[Ty4815162342]

have you tuned the car since you added the mods? as this may be why

[BenLAST]

have you tuned the car since you added the mods? as this may be why

No, this is what i'm asking. It will be rolling roaded asap, but as a temp. fix, will a simple mixture adjustment sort this out?

[1984mini25]

Sounds like, especially if you’ve fitted a new richer needle that it’s running rich enough that’s it’s fouling up the plugs, so would need the mixture leaning off.

It’s also possible as the engine has been played with and your previously lack of performance problems (my standard 998 can do up to and slight more than a ton if pushed) could be down to a weak spark not being able to burn off all the fuel/air mix, so might be worth going through and checking the ignition system.

[Pie]

From what you've said you haven't uprated the needle! If you havent, do a search, and order a stage 1 needle.
As for uprating the head, not much point unless your uprating the cam at the same time.

Only things needed for a stage 1 are; exhaust, manifold, air filter, and carb needle.

[BenLAST]

Stage 1 rich needle, and a Pipercross filter have been added also. But i've taken the rich needle back out as it was running too rich, but it still hasn't quite sorted the problem.

Ingnition wise, all HT leads and plugs were changed, and i'm going to get an electronic ignition off a friend tonight and fit that also.

What cam would you recommend to pair with the head then? Wasn't planning on doing so, but if it was get more performance out of the head, it may be worth doing before a rolling road.

[Marky Tizz]

sw5 cam on a 998 imo google swifttune.
hope that helps....

[BenLAST]

This then? As i was looking into 1.5 roller rockers also.
http://www.swiftune....ghlift-kit.aspx

[1984mini25]

Stage 1 rich needle, and a Pipercross filter have been added also. But i've taken the rich needle back out as it was running too rich, but it still hasn't quite sorted the problem.

If you tried to adjust the mixture with the stage/richer needle then the settings will be out once you replace it back with the original, you can try setting the mixture up with a either a co tester or a colour tune kit which will be a lot better than guess work.

[BenLAST]

We tried adjusting with the standard needle in as it would hopefully be closer to a leaner mixture. But as i am complteley new to adjusting mixtures and what not, i'm awaiting my uncle to do it who works with carbs day in day out.

[mini_mad69]

If its just one plug that is geting fouled up I would say its not a fueling issue, maybe that plug has weak spark causing it to get fouled and no combust fuel. Adjusting the mixture to compensate for one plug being wrong will do nothing, if it was a fueling issue all of the cyinder would be effected. I would check your ignition system if I was you.

After refiting the head, did you reset the tappets?

[Pie]

This then? As i was looking into 1.5 roller rockers also.
http://www.swiftune....ghlift-kit.aspx

no no no no no!!

1.5 rockers are overkill on a 1275 let alone a 998!!
Pressed steel rockers is what you need to look for. Their good enough for upto 150 bhp!
As for cam, get a Kent, either 266 or 276. Kent do the best cams about for the a-series, no doubt about it.

[BenLAST]

If its just one plug that is geting fouled up I would say its not a fueling issue, maybe that plug has weak spark causing it to get fouled and no combust fuel. Adjusting the mixture to compensate for one plug being wrong will do nothing, if it was a fueling issue all of the cyinder would be effected. I would check your ignition system if I was you.

After refiting the head, did you reset the tappets?

3 different sets of spark plugs have been used, and after running fine for 2hours or so, it dropped back to 3 cylinders. Just tried some performance leads i've nicked from a mate to see if it was that particular lead getting warmed up and not sparking enough.

[mini_mad69]

Tried cleaning rotor arm? dizy cap?

[BenLAST]

Checked points and put a new condensor in there, and cleaned it all out to no effect. I have an electric dizzy here anyhoo so i'll try that tomorrow night.