Dyno graph feedback

[Jeff_H]

Hey guys. Thought I would post a couple dyno graphs from last year to get some feedback on my jetting work. '98 900CR with ported heads, 944 kit, FCR 41's and pod filters. The original run (blue line)was done in July with the FCR jetting at : 155 mains, slow air 1 1/2 out, EMT needle and clip on 5th position. I had some big lean spots and some detonation at full throttle under load. I spent a few weeks tuning the carbs by making individual needle and jetting changes, putting in new plugs and riding it on the same road over and over. I went by the seat of my pants and the color of the plugs. Not very scientific, I know. I ended up with 162 mains, slow air 1 3/4 out, FMR needle with clip on 4th position.

The second dyno run was done in the fall and is represented by the red line. I have a couple rich dips but the detonation is gone and the throttle is smooth everywhere, with no lugging or surging. I'm very happy with it, but thought I would post and see if anyone had constructive feedback regarding tweaks I could make if necessary. I figure a little rich means better life for the engine, yes?

...and the attachments disappeared! Standby one.

Regards,

Jeff

[Jeff_H]

...and here. Hopefully.

[LeoLegend]

Looks good! hopefully I'm somewhere in that range. FCR's, hicomp pistons, open air filter.

I think I'm running the stock mains and about 1 1/4 turns out.

The only thing I've been fiddling with is the pilot jet, I moved down to a 56 I think but still need to go lower to get the off idle throttle just right.

Any idea what your pilot jet is?

[Jeff_H]

Is the pilot the "slow" jet? If so, it's still at 60. Maybe I should consider bumping that down a smidge as well. I might try a 58 and see what that does for me. It is a tad rich at idle, but that seems to help when the weather is cooler. I suspect I lost a tiny bit of HP by going to the pod filters, but it makes working on the carbs so much easier, it was worth it.

Regards,

Jeff

[LeoLegend]

slow jet yes I believe it's the same things. I tend to "load up" a bit at idle and part throttle is a bit lean. Problem with these carbs is the transition areas, 1/8 to 1/4 etc.. trying to get the part throttle stuff sorted.

Did you have different dyno runs at different throttle angles? or just full?

[Jeff_H]

All my runs have been full throttle. When the dyno trailer comes back to town I'll ask about doing runs at different throttle settings. Wish I had thought of that...

I tried really hard to smooth out the transitions with my jetting choices, but seat of the pants is only going to work so well.

[rond944]

Pretty good-looking curves . I've got pretty much the same setup . The 60 pilot sounds rich to me . I'd go gown in 1 step increments and see what happens . I think mine are around 55's or something like that . Also , be advised that the pilot jets seem to have a big effect on fuel mileage , so smaller will help in that regard too .

What kind of pod filters ? I heard from one seemingly knowledgeable tuner that you need to get the filter media away from the carb throat as much as possible . You can do that with filters with a long neck ( like the K and N RU-1750's) ,but I think a better solution is to use some velocity stack-like filter adapters ( K and N PN 85-3000 ).

Lastly , I'd be worried about running a hi comp 944 with stock ignition timing . Noted Ducati tuners Doug Lofgren and Brad Black have written extensively on this subject . Probably the easiest and best way to do it is with an Ignitek box . But you could also remove the flywheel and file down the leading edge of the ignition timing trigger lump to retard the timing about 3 degrees or so . Go to Brad's website and read up on some of the things he's tried .

[icycold]

Looks great

[Jeff_H]

Thanks guys! The ignition has been retarded by 2 degrees by sliding the timing bar, but I'm considered going with 3-4 for longevity. Jeff Nash from AMS ported my heads and he said 2-4 degrees, same with Mr. Meyers, who also recommended milling the flywheel lump. There is a Nichols flywheel on there now, so I'm not sure if I can alter it or if I have to have the stocker lightened and milled.

I'm running the RU-1750 filters right now, but was considering trying some foam pod filters from a company called MWR. Kind of pricey though. I'll research the velocity stacks a well. Thanks!

I'm definitely going to put some 58 pilots in and see how she does.

Regards,

Jeff

[Joe-B]

Jeff, are your FCRs racked or split singles?