Running Rich ??

[jonboylaw]

I just had the MOT done on the Caterham (passed with flying colours). As it is a '92 car there was no requirment for emissions but out of interest we plugged it in the machine.

 

So at idle I am at 6% CO rising to 9% at 2.5k rpm.... So I guess I am running a little rich 😳

 

That might explain the less than impressive fuel economy.

 

So, any tips on where to start? I guess, I should 1st look at the jet sizes or just take it for a RR session with good carb man.

 

1800cc xFlow on twin 40s with Megajolt.

 

 

[Billyboy]

I used to have the exhaust on my xflow powered cars in the past a nice biscuit brown but they were all on downdraft webber twin chokes.......they were hard enough to keep in that tune, doubt you will achieve that on twin 40's but I think you could improve a lot on what you have......

 

Best bet is to learn how to do it yourself and keep it in fine fettle on a regular basis......this for me would be the fun of having an xflow in a 7, along with the overrun show 😬 on those night blats

 

I used a cheap exhaust gas meter at the time to assist, but the running and the colour of the tailpipe / spark plugs told me more, along with how well it pulled through the gears and the general feel.........

 

 

Happy fettling

[Roger King]

If it's at idle or low revs it should be nothing more than the adjustment of the idle screws. The main jetting will have no effect whatsoever on this.

 

Edited by - Roger King on 2 Jun 2011 17:25:55

[jonboylaw]

Hi Roger,

We took it through to about 4500 rpm and is was showing high through the range (not dipping below 6%) but I don't think we spent enough time to really see what it was showing. Will get it back down there later this week to get a good feeling of what is happening, then maybe splash the cash on an RR session.

 

 

[skeetsy]

Quoting Billyboy: 

I used to have the exhaust on my xflow powered cars in the past a nice biscuit brown but they were all on downdraft webber twin chokes.......they were hard enough to keep in that tune, doubt you will achieve that on twin 40's but I think you could improve a lot on what you have......

 

Best bet is to learn how to do it yourself and keep it in fine fettle on a regular basis......this for me would be the fun of having an xflow in a 7, along with the overrun show 😬 on those night blats

 

I used a cheap exhaust gas meter at the time to assist, but the running and the colour of the tailpipe / spark plugs told me more, along with how well it pulled through the gears and the general feel.........

 

 

Happy fettling

 

I used to use the exhaust colour as a guide to how well the carbs were set on my cars in the past but since they stopped selling leaded petrol I've never seen an exhaust tailpipe which is anything other than black .

 

With twin 40's (as Roger says) if the thing is running rich at anything above idle then you will need to sort out the main jets, emulsion tubes and possibly choke sizes to tune it and this can be done quickly at a rolling road trying to sort it out yourself, although possible, is time consuming and expensive since you will need to trial a number of different types of each component, if you speak to someone in the technical side at Burton Power, or Burlen Services they should be able to give you a good idea of what jet, and choke sizes you need together with what emulsion tubes will work, however, for best results the only way is to take it to a rolling road

 

All the best

 

Richard

[jonboylaw]

The engine is one of Roger's 160 spec xflows (1800cc). I had it down at Northampton Motorsport a few years ago and they upped the mains and did a few other things, but we were not able ot get a power run in as the dizzy was not advancing. Now running a Megajolt so it should be simple.

 

Does anyone (Roger maybe?) have recommended jetting for this engine I can use as a base line?

 

 

[Roger King]

Can you let me have the engine number or the name of the original owner who had the engine work done?

[jonboylaw]

Hi Roger,

The Engine number is: VR 9306158

I believe the original work was carried out for Peter Murphy.

 

Cheers

[Roger King]

Jonathan,

 

I've had a look at the records and the last time I had that engine on the rollers was in May 2002. The jetting we finished up with was as follows:-

 

Choke 34

Main 130

Emulsion tube F16

Air 140

Slow run 50F9

Pump 35

 

The above is pretty much what I would expect for an engine of that spec and was giving 5% - 6% CO all the way up the rev range on full throttle. You would expect lower CO figures on part throttle, but I'm assuming you were using a tester that was taking readings with the engine under no load, even at 2500rpm, which is something you wouldn't normally do in the real world, so your figures might be a little academic.

 

A couple of points. There is a note on the rolling road sheet to the effect that I recommended the carbs be fitted with overhaul kits due to slight wear of the needle valves, etc. Secondly, it is very common (and perfectly legitimate if done properly) to drill jets out to larger sizes. I always had a policy of filing off the original size markings if I did this but a lot of people don't bother which can lead to misidentification of the jet size. The only way to be sure is to actually measure the jets.

[jonboylaw]

Thanks Roger,

I really appreciate your time to look this up.

The carbs were overhauled last year and new needle jets were fitted as part of that.

 

I think the best thing for me to do is to get a rolling road session booked and see what we get.

 

Out of interest, what power did the engine make then?

 

Regards,

 

Edited by - jonboylaw on 31 May 2011 23:08:42

 

Edited by - jonboylaw on 31 May 2011 23:11:02

[Roger King]

It made 118bhp at the wheels at a relatively low 6000rpm. This engine was built to run on 95 octane fuel so it has a relatively low compression ratio of 10.3:1 and the cam timing is optimised for the mid-range rather than top end power. Of course I have no way of knowing if it has been altered since so I can't guarantee it's still OK on 95 octane.

 

Rolling road readings are notoriously difficult to compare due to differences in the road itself, the testing technique, the weather, what gear it is tested in, etc, so the figure is relatively meaningless. As an example, I could send you to a rolling road not far away where that figure would be at least 30bhp higher.

 

Typically, an engine to this spec, but with a higher compression ratio and different cam timing would show 120 - 125bhp at the wheels on the rollers I was using.