12 replies to this topic

[jezjsa]

Hi.
So my 998 with hs4 carb, aau needle with maniflow twin box exhaust had a flat spot when accelerating.

The spark plugs were quite white in colour.

I’ve tweaked the air fuel mixture to now be richer which has almost got rid of the flat spot but I now get a popping sound when accelerating which I think is from the exhaust.

I’m not 100% certain but I feel this is mainly at speed rather than at 30 through the village.

Is the mixture too rich now? Or something else I need to tweak?

Cheers

[Quinlan minor]

Check the exhaust for leaks.

[jezjsa]

Ok so a bit more information as these are probably related…

Flat spot when accelerating… has got less noticeable as I’ve made the mixture richer.

At speed I get misfires or popping through the exhaust.

Rev counter needle bounces when at speed.

When go to turn the engine off it try to keep going a while longer…

Any help/suggestions…

Cheeers again.

[DeadSquare]

Ok so a bit more information as these are probably related…

Flat spot when accelerating… has got less noticeable as I’ve made the mixture richer.

At speed I get misfires or popping through the exhaust.

Rev counter needle bounces when at speed.

When go to turn the engine off it try to keep going a while longer…

Any help/suggestions…

Cheeers again.

That is more likely to be ignition than fuel.  The timing may be a little advanced.

 

Mark the distributor bowel and the clamp, in line, so that you know where you started.  Slacken the clamping bolt, not the two that hold the clamp to the block.  Carefully rotate the distributor about 5 degrees ANTI-CLOCKWISE to retard the ignition.  Re-tighten the clamp and try it

[cal844]

Ignition system. I'd put my money on the coil needing replaced BUT first check and clean the connections and then road test.

Rev counter bouncing is the low tension circuit breaking down or a loose connection on that circuit

Edited by cal844, 17 September 2023 - 09:17 AM.

[68+86auto]

Check the dwell, condenser and then coil. The richer it is the lower the KV required from the ignition system to ignite the mixture which could be why making it richer improves it.

[jezjsa]

Thanks for the replies guys.

OK so if i do need a new coil, after checking and cleaning connections, I'm thinking at the same time i may as well change the distributor to an electric one.

What about this combination - or should i be looking at something else?
 

59D distributor Top Entry Electronic with 998cc curve (D10-98)

 

HIGH ENERGY Lucas DLB 198 Coil (Silver)

Silicon HT Leads

[DeadSquare]

Thanks for the replies guys.

OK so if i do need a new coil, after checking and cleaning connections, I'm thinking at the same time i may as well change the distributor to an electric one.

What about this combination - or should i be looking at something else?
 

59D distributor Top Entry Electronic with 998cc curve (D10-98)

 

HIGH ENERGY Lucas DLB 198 Coil (Silver)

Silicon HT Leads

What ever you choose, buy it all as a complete kit from one person.

[jezjsa]

Its all from the PowerSpark website
https://simonbbc.com...ic-distributor/

[68+86auto]

I would NOT change the distributor unless you can find a fault with it, it would be a waste of money and add more potential issues into troubleshooting your issue. Although those ones are listed per engine size (unlike many) there still should be many advance curves per engine size. The vacuum advance should I believe also be different as some had manifold vs ported vacuum.

[68+86auto]

Thanks for the replies guys.

OK so if i do need a new coil, after checking and cleaning connections, I'm thinking at the same time i may as well change the distributor to an electric one.

What about this combination - or should i be looking at something else?
 

59D distributor Top Entry Electronic with 998cc curve (D10-98)

 

HIGH ENERGY Lucas DLB 198 Coil (Silver)

Silicon HT Leads

That also appears to be the incorrect coil for that distributor. The correct coil will work on a points setup (non ballasted) too so I would suggest doing that first.

Edited by 68+86auto, 19 September 2023 - 03:59 AM.

[coopertaz]

just fit powerspark coil and matching module into ditributor, running these on mine for years with no problems, engine running due to incorrect mixture so sort ignition problem first then running on as a a seperate fault. rolling road session will take guess work out of mixture setting

[jezjsa]

Turned out to be issues with the distributor. Needed to replace the Lumenition electronic ignition kit and the vac unit for it as well.

Other than that the carb was running too rich.

Drives really well.

Now just a vibration through the steering wheel to resolve when at idle.