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113" SE Twin Cam Problem
Old 06-03-2009, 06:35 AM
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Default 113" SE Twin Cam Problem

Hi, Im new on here so here I go...... I built a Flhtc 113" over the winter
1: Se cnc heads with custom pistons to match the heads
2: Se 4.375 fly wheel 4.06 cly
3: Se Big bore intake with a 45 mm Mikuni
4: Se 258 cams
5: feuling pump
6: the cranking compression is 205 static is like 11:25
7: True duels with pig pipes 1.75 baffles
8: Dyna tc88-2p

My problem is I had the bike dyno it made 103 hp and 119 tq
the rear cly a/f was right on but the front was 11.5 a/f between 2700 and 3600
and from 4500 to 5800 it was 10 a/f with the right baffle in
we took the right baffle out and it fliped 2700 to 3600 it was 10 a/f 4000 to 5800 it was a/f 11.5....... with out the baffle it had a big dip from 2700 to 3000
with the baffle it was a nice curve 2500 98 tq .... 4000 119 tq 5000 98 tq
i need to scan these and send them
so if I'm right with the right cly a/f correct i would pick up some hp and tq

Thanks Larry
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Old 06-03-2009, 10:36 AM
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Mike Mike is offline
Join Date: May 2005
Location: Oregon
Posts: 3,506

The pipes are definitely holding the peak power back. But, as you've noted, as you remove the back pressure to gain peak numbers the 2700 rpm area starts to suffer (baffle removed). The single stage true duals will not allow higher end/rpm numbers so there really is not a great concern to go after those numbers. Tuning the low/mid will give better usable results.

You're also facing a a typical carbureted tuning situation. Since it is a signal based system, it relies heavily on the exhaust to create those signals (as evidenced by the "flip" in the fuel curve when the baffle was removed). As is often the case, a good compromise between the front and rear cylinders may give the best overall power/performance. I.E. a slightly lean rear with a sltighly rich front. It also becomes a compromise in fuel curve, down the rpm line, where a rich condition at 2500 may not be completely tuned out due to a lean condition at 4500 going lean to the point power drops. Adding two degrees of timing to the rich cylinder, vs the rear, can also help (if the igntion system allows this).

A tip with the Mikuni is to aim the accelerator pump nozzle to favour the lean cylinder (in your case the rear), the residual fuel can find its way well into the fuel curve, down the rpm line.

Its all about the best balance.
Mike Stegmann
Performance Consultant
Team Latus Motors Harley-Davidson

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