Posted November 06, 2002 - 09:28 AM
Posted November 06, 2002 - 10:55 AM
I took the pilot and main out and cleaned them completely with compressed air. Not just solvent. I also cleaned the air filter and tank. Put everything back and same problem. Bogged badly, missing, backfiring, etc.
I got back home and pulled the seat and tank and put a new plug in and it runs perfect. For some reason, mine seems to foul plugs to the point that they can't recover.
I've heard this happening with street bikes before and obviously 2 strokes but it seems weird to me that a 4 stroke would foul a plug beyond use but it is the case with mine. Anyone have input on this?
Hope this helps.
Posted November 06, 2002 - 12:19 PM
any further than that and im out of my depth
Posted November 06, 2002 - 01:22 PM
I am not sure what the CR9 or CR10 plug would do for me.
I am also at altitude so the higher octane fuel could cause problems as you suggest since it takes more compression to ignite. I normally ride at 7,000-13,000 feet so my compression should be reduced considerably. If my ratio is not high enough at this altitude, then running Super Unleaded would not allow all the fuel to burn causing a rich condition. These are things I already know, sometimes I just need to be reminded.
Posted November 06, 2002 - 02:13 PM
Posted November 07, 2002 - 07:08 AM
At 7,000 feet which is the low end of my riding spectrum, the air density is at 80% of sea level (10:1 ratio)
At 13,000 feet which is the upper end of where I ride, the air density is at 68% of sea level. (8.5:1 ratio)
Atmosphere Table Link
Compression Ratio Correction Link
Posted November 07, 2002 - 07:57 AM
Posted November 07, 2002 - 08:33 AM
They do so much to those bikes it's incredible. Anyway, they had a lot on compression ratio/octane/altitude, etc.
I learned a ton and still had questions.
Posted November 07, 2002 - 08:42 AM
Whatever the atmospheric pressure is outside, your cylinder head takes a volume of 400cc (12,5) at admission and reduces it to 32cc (1) as the piston reaches the top of the cylinder head (12,1:1 ratio) which means that the ratio is not variable because it describes the volume variation that occurs in the cylinder head over the piston during one stroke. Whatever the pressure outside is, the engine always takes 12,5 of what is outside (plus the gazoline) and brings it to 1.
If the ratio is constant, why does a motor breath less in altitude? It is just because the general atmospheric pressure is diminished which means that you have less nitrogen, less carbon dioxide and (very important) les oxygen in that starting 400cc (12,5) volume so less oxygen in the compressed 32 (1) volume. So the ratio is constant but the pressure outside and inside varies with altitude.
Is it useful to bring back that the utility of compression is to heat up these gaz (and the gazoline) and raise their energy level so the oxydation of gazoline (iniated by the spark) becomes possible.
Posted November 07, 2002 - 09:22 AM
Posted November 07, 2002 - 11:39 AM
It is just that I think that the ratio describes what the engine does with what it has access to.
That given, with altitude, the starting pressure (outside) is lowered so the pressure in the cylinder after compression is also lower which causes the bike to breath badly.
Anyway, I think we understand each other very well but just saying things differently...
Posted November 08, 2002 - 07:24 AM
I'm pretty sure though, that when the manufacturers determine what compression ratio they want the engine to have, they are using atmospheric pressure at sea level (1 atmosphere or 14.7 pounds per square inch). When you go up in altitude, atmospheric pressure goes down so you have less pressure within the cylinder at the time of combustion.
With lower pressure inside the cylinder, you don't need as high an octane fuel because the detonation level is lower. For that reason, you can use lower octane fuel which actually has higher potential energy.
Our standard unleaded fuel here is 85 octane, mid is 87 and premium is 97. I know at sea level, standard is 87 octane, mid is 89 and premium is 91 octane.
Anyway, I'm going to experiment a little with lower octane fuel and see if I notice a difference.
Thanks for all the information and help.
Posted November 08, 2002 - 12:14 PM
Your precisions concerning the octane level regarding different altitudes is interresting. I guess that if I was a mechanic I would have know it. But in fact, I'm not a mechanic at all and I'm at sea level so I had never had the occasion to ruminate about that. Lower octane in altitude makes sense since you don't have to prevent a premature (can I use this word here) detonation: pressure is too low.
Ok! Now that beeing said, when do we start that engineering compagny?
Posted November 10, 2002 - 06:06 AM
I realize that the air pressure stuff got off track quite a bit. My fault but I was originally referring to fouled plugs.
I wouldn't touch any carb setting until the plug is changed. Then go from there. Start with the simplest items first, after they are ruled out, move to adjustments.
A dirty air filter could have the same effect that messing with the air screw could since you will run rich from lack of air.
pghwrrider, have you changed the plug and checked the air filter to see if it's clean?
Posted November 10, 2002 - 06:35 AM
Posted November 10, 2002 - 06:36 AM
Posted November 10, 2002 - 09:46 AM
The reason plugs foul to the point of not being useable again was explained to my by a mechanic at work. He told me that once there is enough carbon down inside the plug, you basically get a path for some of the spark to travel back to ground. No matter what you are doing with jets, if the plug is fouled, it will not run right if part of the energy is being grounded.
Jekel, why do you think it is harder to have spark under compression? I haven't heard anything about this so any info would be helpful.
pghwrrider, I had one more question. You said when riding in the first hour, things went bad so I'm assuming that it ran okay when you first started riding. If you shut the bike off and were messing with the throttle, you may have fouled the plug. When I first got mine, my boys were playing on it and twisting the throttle. It would start and die over and over until one of my buddies came by and told me to change the plug. Ran great after that.
Posted November 10, 2002 - 12:58 PM
Maybe I missed it, but no one has mentioned the accelerator pump jet (APJ)...
The 98/99's carb can be modified to mimic the infamous BK mod. Do a search for KL Mod or Taffy mod. 2 different approaches to the same problem.
When I checked my APJ, the squirt duration was > 3 seconds!!
>> The carb is being deluged w/ excess fuel resulting in the bog.
W/ my KL mod, my squirt is down to ~ 0.3 seconds.
BTW: The 99 is NOTORIOUS for crapping up the accelerator pump. Crud goes down the accel pump actuation rod and seizes up the diaphragm and the AP.
You can also do the gray wire mod and blue wire mod. These mods are for improved ignition performance.
Do a search on these as well.