Hi, recently picked up a clean, running JDX6. Sled had an inconsistent idle and at higher throttle power would come and go.
Changed plugs and found #1 cylinder too rich/black and wet. pulling the #1 plug wire would also have only small impact on idle quality - pull #2 and it wants to die though can stay running on #1 only with heavy throttle.
Compression test yielded over 120psi on both cylinders
Swapped coil and plug wires from #1<>#2 however problem remained on #1 cylinder, ruling out ignition.
Decided to replace the points and condensers anyway as diagnosed lighting coil was dead and wanted to replace, get it over with while apart. Visual inspection of the primary coils and they look fine, resistance within spec for both as well. also replaced mag and pto crank seals for good measure. No leaks noticed elsewhere. Replaced secondary coil for #1 with new to rule it out, along with new plug wires,fuel and impulse lines, and fuel filter. Timed engine to factory specs (thanks for the info in tech, btw!) with dial indicator and light.
Still same behavior. #1 cylinder only richer/plug wants to foul, mostly running on #2 at idle, and at high throttle full power is normally there then randomly drops out. Obviously the #1 cylinder 'working' then not. #2 cyl still running perfect and nice color on plug. Swapping plug and coil wires with the new parts and problem still remains on #1. Also ran it with sled side of harness disconnected to rule out anything there. When the power is there the sled really runs fantastic.
Any suggestions on what to go onto next? Nice that the tach and lights work now with new lighting coil but I really want it to run perfect. I was thinking of pulling the intake manifold and inspecting the reed cage assy for #1 - could a bad/sticking or dirty reed(s) for one cyl cause this type of issue? Thanks for any help!
Jdx6/kec400/22 Weak cylinder and intermittent power
Re: Jdx6/kec400/22 Weak cylinder and intermittent power
Could very well be that the reeds are sticking open on #1.
Todd Schrupp
Milbank SD
Milbank SD
Re: Jdx6/kec400/22 Weak cylinder and intermittent power
Did not have enough light to pull the manifold and inspect the reeds, but I decided to fool around with it some more and found my problem is not limited to cyl #1 as I thought. I had previously been testing only with air box installed. I tried running it with the air box removed, and the exact problem moved to #2 instead. Reinstalled air box, problem back to #1. Tried this back to back several times with same cylinder switch result each time - so now I'm getting a little stumped with this thing.
Airbox and tube were pretty clean but there was a few tiny bits of junk in the box. screen is long gone too.
When it is idling on both cylinders, it is silky smooth at around 2krpm. After about 30 seconds of running, the idle will drop to around 1k rpms which is when one of the two cylinders is weak and I can pull the weak cyl plug wire with little impact on idle (cyl # depending on airbox on or off as noted before) It seems to want to stay like this unless revved up. Revving it up a bit and the idle will again sit smooth at around 2krpm for about 30 seconds before dropping back -repeat-
Maybe I need to do some more tweaking with the carb, idle quality is perfectly smooth when running on both but that doesn't last long obviously. Hoping leaning it out idle some more will help. IIRC idle is a hair over 1turn out right now.
Not sure why the air box on or off is switching which cylinder acts up, guess it effects the airflow in some strange way that #1 may be getting loaded up with fuel from rich mixture when it is installed. ??????
Plug color was always a nice medium tan on #2 (with airbox always on) so the high speed has to be close.
No snow so I can't actually drive it around to test under load at higher throttle with air box on and off right now, just revving it on a stand.
Still plan on pulling reed cages to clean and inspect them, already have the gaskets anyway and there were a couple pieces of crud in the air box which means potential of debris on the reeds. Just want to keep ruling stuff out at this point.
Thanks again!
Airbox and tube were pretty clean but there was a few tiny bits of junk in the box. screen is long gone too.
When it is idling on both cylinders, it is silky smooth at around 2krpm. After about 30 seconds of running, the idle will drop to around 1k rpms which is when one of the two cylinders is weak and I can pull the weak cyl plug wire with little impact on idle (cyl # depending on airbox on or off as noted before) It seems to want to stay like this unless revved up. Revving it up a bit and the idle will again sit smooth at around 2krpm for about 30 seconds before dropping back -repeat-
Maybe I need to do some more tweaking with the carb, idle quality is perfectly smooth when running on both but that doesn't last long obviously. Hoping leaning it out idle some more will help. IIRC idle is a hair over 1turn out right now.
Not sure why the air box on or off is switching which cylinder acts up, guess it effects the airflow in some strange way that #1 may be getting loaded up with fuel from rich mixture when it is installed. ??????
Plug color was always a nice medium tan on #2 (with airbox always on) so the high speed has to be close.
No snow so I can't actually drive it around to test under load at higher throttle with air box on and off right now, just revving it on a stand.
Still plan on pulling reed cages to clean and inspect them, already have the gaskets anyway and there were a couple pieces of crud in the air box which means potential of debris on the reeds. Just want to keep ruling stuff out at this point.
Thanks again!