xflow very poor performance over 3,000rpm

[twobone]

I just finished replacing my battery, checking my timing advance and balancing my carbs on my 89 crossflow kent.

Now my car will not accelerate hard over 3,000. I get a horrible misfire/backfire.

I noticed I now have a fairly significant exhaust leak at the connection between the headers at the join for the 4 into 1 exhaust system.

At high revs will that exhaust leak be the culprit to my poor running?

[Incorrigible]

Sounds more likely to be dodgy electrical, somewhere along the line. Re-check the timing and advance. I would guess at the king lead next (I assume it's running electronic ignition, if not check the points)

[smeagol]

Hi, Just a few checks. I had with a poor running xflow (Wesfield but don't hold that against me ;-).

I presume you have twin webbers? and electronic ignition.
The exhaust leak will certainly not help but it should be ok, except if your ignition system uses some kind of lambda sensor (I don't think yours will) then its fueling/timing will be all over the shop.

I have points (no vacumm advance) and bike carbs. I had a leaking exhaust and performance certainly improved when i fixed the leak (top tip - I used firegum as a "gasket glue" on the exhaust manifold and it worked a treat, ie take off manifold coat the gasket both sides with firegum and bolt together sealed nicely)

With webbers you might be overchoking (ie running far too rich) My original webbers were chucking in far too much fuel and had a similar problem ie >3000rpm naff, I took it to a garage where the guy "cut his teeth on xflows" he found that someone had been mucking around with the carbs and even had some jets missing - hence the move to bike carbs.

However the first port of call is certainly ignition and timing. I would check you are getting a decent tick over to start with and then hold at 1000rpm increments listening to how the engine is. I have heard that often xflows are not advanced enough at higher revs (especially dizzy electronic ignitions with no vacumm advance) as when you advance it enough they are harder to start. It may be that you just need to advance it a bit to get the performance back. ie sacrifice a lumpier tick over for a nice system where you need it.

Hope that has helped. If you can give more details about the car I might be able to give a few more suggestions.

[geoffd]

I had a similar problem which turned out to be a broken spark plug. Easy to check!

Geoff

[twobone]

Thanks.

I rerouted the plug wires the other day. Perhaps I damaged a plug lead. Let me check

Thanks guys for all the possible suggested culprits.

[twobone]

Best to start from a clean slate.

For 200 quid plus shipping, Caterham UK will supply an Aldon distributor with an ignitor built in as well as all new plug and coil wires.

Hopefully this will fix up my ignition to the point at which all future issues will be fuel related

[gsewell]

Is the poor performance consistently above 3000rpm - or just the first time after going through a village/town at just above idle. I had a problem where the B8ECS plugs were fouling and would misfire on exiting a village (slow area). So, for road use only, went to the hotter BPR7ES plugs from the 1600 sprint engine.

Again, check carb balance and idle mixtures to ensure that you do not run fuel over-rich even on one carb.

[twobone]

turns out it was primarily float level.

I replaced my needle valves and bodged my setting for the float level. My mechanic sorted it. That combined with a proper Aldon distributor has it running quite well. Just some hesitation now in transition between idle and main jets, but I should be able to tune that out myself