Jump to content

FCR-MX wideband tuning - Another FCR needle question

Recommended Posts

At idle I get a air fuel ratio of 13.2 and its great until I just about reach 1/4 throttle where the AFR shoots up to 16.2 (noticeable power loss too) and stays lean very briefly up to 3/8 throttle where it drops right back down to 13.2 AFR. From 3/8 to WOT the AFR is great. I tried different clip settings but that affects the whole AFR between 1/4 and 3/4 throttle. If I understand correctly the L1 dimension in the sudco literature is the length measured down from the clip end of the needle and is the point at which the taper starts? I am correct? Does this move the whole taper upwards as it does when you change clip position or does the taper stretch (get longer)? I'm hoping the latter. I was thinking maybe an ELR needle or EGR needle if the taper gets stretched. If all it does is shift the taper upwards like you would change a clip position then changing the L1 dimension will not help me. In that case I might have to try a smaller tapered DMR or DLR.

To me the taper is fine but I think the straight part of the needle lasts slightly too long.

Link to comment
Share on other sites

I have been doing some needle comparisons with the JD Jetting guide spread sheet that I purchased and have determined that in fact changing the middle letter is the same as changing clip position. Also changing the taper E to a D from the spread sheet will probably affect my AFR too much. Instead I would like comments on the NCVR needle which incorporates a 2nd taper that acts from 1/8 throttle to 3/8 throttle but has the same final taper as the EMR. It would seem that this needle might fix my lean condition that I explain in my previous post above. If anyone has comments I would appreciate it.

Link to comment
Share on other sites

i think you are still on the straight diameter of the needle. didn't i see another post where you tried the EMN? did this affect that issue?

Thanks for responding. Yes I tried the EMN needle but the same lean condition existed although it peaked to a lesser extent, see below


throttle - AFR

0 - 13.2

1/8 - 13.2

between 1/8-3/8 - 16.2 peak

3/8-1/2 - 13.2

1/2- 3/4 - 12.8

WOT - 11.8


throttle - AFR

0 - 11.8

1/8 - 12.0

between 1/8-3/8 - 15.2 peak

3/8-1/2 - 13.0

1/2- 3/4 - 12.6

WOT - 11.6

Please note that I am still using a 38PJ and 100 PAJ in both cases and I have no main air jet. The air screw is set at 2-1/4 turns out with the EMR needle and 1-1/2 turn out with the EMN to achieve proper pilot circuit tuning.

I wish I could input my throttle position sensor into the wideband controller so I could more precisely plot % TPS versus AFR. From what I see is the beginning of the EMR straight is good but seems to last too long before the E taper takes over. The taper seems to start taking effect around the 1/4 throttle or very slightly after. The NCVR has a second taper that starts around the 1/8 and last to about the 3/8 throttle. What are your thoughts?

Edited by D0T-C0M
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

  • Create New...