Quote:
Originally Posted by outcrydrummer
I understand a cdi swap isn't going to net me anything. I thought the sluggish performance when cold might be to a weak spark ( bad coil etc ).
What style jets do these stock carbs use? Any idea what the stock jetting might be?
I have a few jets laying around from a few assorted jet kits I did on my supermotos.
And I would have to disagree that spark doesn't make power. Better / hotter spark or more duration or in the case of aftermarket ignition systems such as msd mallory etc use multispark for cold starts etc.
While obviously the volume of fuel/air into a cylinder makes power the efficiency in which that fuel/air is burned is just as important.
And I also believe that stock volumetric efficiency for a good operating engine is around 85% if I'm not mistaken.
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The jets I'm not sure which style but believe they are Mikuni type. All CV carbs use this jet. As far as the coil goes if it was weak you would have issues through the entire RPM range.
The hotter performance coil on a stock engine will have no added effect over the stock engine since the stock coil is designed to operate efficiently on a stock engine. The coil is just a wound copper wire that stores electrical power, the more winding the more intense spark. If you smoke you use a lighter to lite whatever is smoked and not a blow torch. Sure a blow torch will work just fine but it is overkill. The spark duration is controlled by the ignition, in this case the CDI and not the coil. However you usually need a higher capacity coil to supply the longer spark. Now to VE. In the average stock motor your cylinder will fill anywhere from 50% to 65%. This is purposely done so to keep the drivability within reason for everyday driving in all conditions. In these cases the stock 15KV coil is just fine. To fill that cylinder above the average the only way is to allow for the engine to pull in more air /fuel which will mainly be accomplished in the head, cam, intake and carburetor. The average racing motor will achieve about 93% VE and some reaching as high as 98% but usually with the use of a turbo. 100% and above will require a supercharger. In these cases a hotter and longer spark is necessary to ignite this added air/fuel more efficiently. Of coarse elevation and other conditions such as temperature and water grains will effect the VE as well. What I was trying to say in my last post is that due to EPA regulations these old school engines are required to run much leaner in order to pass EPA. Back in 2005 the GY6 come stock with a 114-116 main jet and a 35 pilot jet. The enrichment jet was much larger as well. Today the average main jet used is a 90 and not sure of the pilot since it seems they are no longer marked but the last several I have done, the pilot gauged around 30. Since 2008 these buggies with the GY6 as well as the 110 and 125 old school engines have a more difficult time starting in cold weather due to their lean mixtures. On your stock motor with an exposed air filter you will need around a 125-128 main jet and a 35 pilot jet. Also you really need to scrap the cheap filter and go with a quality open filter. The open filter will allow more air to pass which increases the potential of sucking in what the engine does not like. Many of these cheap no name foam or paper filters do not trap as many contaminants as a quality filter will. It doesn't take much to wipe a set of rings out in these motors.