X Flow timing

[Terry Field]

I have now done 1500 miles on my 1700 XF with a 244 cam, and have gradually increased the rev limit.

 

Had a long Blat over two days - 360 miles - and took it up to 5000 rpm. In third it seems happy enough, but in fourth or top when it is under more load, it appears to be 'pinking' as the revs get near to 5000.

 

Valve clearances are fine, and it is timed to 12-14deg btdc.

 

Is the 'pinking' likely to be timing related, and if so, what's the best course of action to correct it?

 

Terry

 

1700XF - Team Lotus with flares.

[I.Mupferit]

Could also be due to a too lean fuel/air ratio or low octane petrol.

 

Brent

 

2.3 DURATEC SV

R 417.39 😬

[Robster]

If I remember correctly, you should retard the ignition a couple of degrees for unleaded on the standard head. With a ported head, you can usually advance it quite a bit again, the smoother surfaces after the porting don't create many hot spots and hence a focus for detonation..I now have around 16 degrees of advance at 940 rpm without any real problems. You should check if you are running lean first, that will heat up the exhaust valves and cause you problems like pinking.

[Terry Field]

I usually use Optimax or similar.

 

I wondered about the mixture, but if anything it seems to have been running a bit rich judging by the plugs, and I have gradually adjusted the carbs to make them leaner and to produce a less sooty plug. I'm still in 'trial and error' mode in this area.

 

I did increase the advance by a couple of degrees when I went unleaded some years ago. This is a new head which is ported, so maybe I will try going closer to 16 deg and see what happens.

 

 

1700XF - Team Lotus with flares.

[I.Mupferit]

Adjusting the mixture screws on the carbs will only alter the mixture at idle as it is running off the idle jets. You may need to look at altering the main jet sizes but beware of going to 16 degrees advance at this stage as it will only worsen the problem.

 

My guess is that you should consider getting it set up on a rolling road as running too lean will ultimately damage the engine.

 

Brent

 

2.3 DURATEC SV

R 417.39 😬

[Terry Field]

Brent,

 

Thanks for the caution. I think a rolling road is the obvious step.

 

 

Terry

 

1700XF - Team Lotus with flares.

[JampJ]

Terry, have you replaced a milder cam? If so you would be advised to get the distributor re-timed the optimum curve will now have changed.

Cheers J&J

 

 

[Trevor Newman]

I ignored the pinking on my 1760xflow seemed to be ok

did a track day and was sorry cost me a stage 3 head 🙆🏻

i was running too lean

got it rolling roaded with a lesser head went better than ever

 

[Robster]

I think you have just mentioned your problem ..."I did increase the advance a couple of degrees when I went unleaded"...you should have moved it the other way..ie retarded a couple of degrees as unleaded tends to detonate more easily (tetraethy lead being an excellent agent to prevent this).

 

[Terry Field]

Thanks for all the advice guys. Rather than dick around for ever, I have booked a rolling road session with Steve Greeenald next week, so I will post an update on the results.

 

Terry

 

1700XF - Team Lotus with flares.