Thread: Low RPMs
07-21-2011, 11:16 PM #1
Here is the story, it has been going on for some time now.
I have constantly had low RPM issues with this setup for a long time now. Several have given me ideas thru PMs during this time, just have not come up with a solution. The RPMs have been low at the first of the year with 8260. I installed the 15/20 I have that was pitched for similar mods to this except, I had a Rude1 charger. To get the 15/20 to 8520, I had to add roughly 4mm to the impeller and switch from a 81 to a 83mm ring. At 8520 RPM I see right at 78.4 MPH. Previously with these mods, impeller and Rude1 I had a best speed of 84.6 and numerous 84 mph runs.
The problems started along the time I switched to a Rotax Racing 4224 camshaft for a short time. When I was installing the new cam, I also added a RRFPR and new Delphi 50# injectors and had the bung installed on the Jpipe.
Along in this time also, I added the new ride plate modified by Jim. Did not care for the way the welded skegs worked and removed them.
Any ideas ?
Last edited by DaveC; 07-29-2011 at 09:47 PM.
07-22-2011, 08:45 AM #2
All them mods with stock fuel pressure regulator I would start there you have no way to tell whats your base psi wot psi etc. do you have a afr guage? Gets some readings
07-22-2011, 08:52 AM #3
Generally a stock X charger being used with a Riva ECU and 48# injectors is known to be safe. But guess there is only one way to know for sure.
Last edited by DaveC; 07-29-2011 at 09:51 PM.
07-22-2011, 08:55 AM #4
Dave i know you checked BUT i would triple check all your timing components.....If this started acting up when you switched cams ill bet theres something amiss in that area..jumped tooth or something silly..
07-22-2011, 09:09 AM #5
07-22-2011, 09:09 AM #6
Dunno Scott, I used both the cam/crank locking tools. I also verified TDC of the crank with a dial indicator and found the locking tool position to be spot on within the last two days.
07-22-2011, 09:13 AM #7
07-22-2011, 09:14 AM #8
07-22-2011, 09:18 AM #9
With the cam/crank locked, the sprocket sits in a slight retarded position as in, you can just barely see the slot on the left side of the bolt. I tried it with a little more advance, not max but more. Found it to be sort of soft feeling in the mid range RPMs and ended up with about the same 8520 RPM.
07-22-2011, 09:21 AM #10
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