Cold start hesitation ( 150cc )

[outcrydrummer]

Got a new cart for me and my daughter. Its a 150cc gy6 thats bone stock for the moment.
It will start up fairly easily, even cold, its been in the 20's to 50's here day to day.

I noticed that when its cold it will almost stall before moving. I have to hammer the gas and it really doesn't want to accelerate or get past 1500rpm. After a few seconds of this or letting it sit for a long time to really warm up it won't want to move on its own when its first started.

I assume its weak spark energy since it acts normal once its warmed up enough to promote good detonation in the cylinder.

Just wondering what you guys thought about the situation.

Thanks

PS. Also found the stock carb intake ( hard rubber piece ) is cracked and dry rotted. I cant tell that its leaking yet through spraying carb cleaner around it while running but its probably certainly not helping.

[zman007007]

I would think it is probably carb. related.

[wildbob]

Yup, id replace that cracked/rotten section. I chased carb issues for two months to find the rubber connector from the intake to the carb was torn. The connector would seal fine and look fine when the buggy was still, but once I started riding it would open up, causing all sorts of issues. Plus, if the previous owner lived/rode at different altitudes, the carb jetting may need to be looked at. Just my two cents..

[outcrydrummer]

Same altitude riding and it seems to be fine once warm with no signs of a lean condition. Just doesn't like to do much of anything when cold.

But ive got a cdi....coil...and intake on the way so I will install those and see what we have.

Wildbob how does your 150 perform with the mods you have? Is your carb the mikuni 30mm?

[wildbob]

I love it. I kind of did everything at once, which makes it difficult to say what mod helped the most (and made troubleshooting that much more difficult), but I think adding the four valve head gave the most noticeable improvement. I just recently took off a Keihin type 30mm "pumper" carb and have put a Mikuni 26mm VM26-606 on it. I felt the 30mm was a bit too big (although a lot easier to tune). I'm having to make a custom cable for the mikuni (venhillusa.com) and don't have it jetted right yet, but I think it'll be a better carb. I've been recently thinking about going big with a stroker crank and maybe a 61mm+ big bore kit, but I promised myself that the next think I'd upgrade (and it NEEDS it) is some real shocks like Works Performance or Fox.. I tend to drive with an utter lack of thought for the survival of my buggy..or my back...

[outcrydrummer]

What are you doing with the 30mm carb??? For sale??

[outcrydrummer]

Cdi and coil showed up with the new intake manifold and a cheapo filter.
Well put the cdi in and it didn't start....backfired a lot so I put the stock one back in.
Coil was to short....
Air filter was really cheap lol but I put it on and the new manifold.
Seems to run fine. No improvements anywhere.

[wildbob]

Originally Posted by outcrydrummer

What are you doing with the 30mm carb??? For sale??

I'm going to hold onto it at least until I put the mikuni through it's paces. I gotta make sure I like the swap. I'd probably advise against putting a "pumper" on your buggy until you mod out your GY6 a bit. From what I'm told the stock 24mm is big enough until you really start building out your motor with big bore kits, stroker cranks, etc..

[SYCARMS]

Your stock CDI is best suited for the buggy since it was designed around the heavier buggy. You must realize one thing. Spark does not make any power. What makes power is the amount of fuel and air you cram into the cylinder prior to ignition. A stock engine will only fill a cylinder to maybe 65%. Your power will be made mostly in the head and cam. Your carb problem is due to the lean state these engines need to pass the EPA. You will need to rejet the carb especially after installing the new filter since you will be pulling in more air on an already lean running engine and this will eventually burn the engine up. Rejetting will improve power since you now pump more air/fuel into the cylinder.

[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.

[outcrydrummer]

Originally Posted by wildbob

I'm going to hold onto it at least until I put the mikuni through it's paces. I gotta make sure I like the swap. I'd probably advise against putting a "pumper" on your buggy until you mod out your GY6 a bit. From what I'm told the stock 24mm is big enough until you really start building out your motor with big bore kits, stroker cranks, etc..

Thanks wildbob. Good to know the stocker flows well enough to support basic mods.

[SYCARMS]

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.

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.

[jmansracerocket]

I would start around a 125 main jet for a good exhaust and a good intake. Might need a 38 pilot jet, stock pilot is 35 and the main jets do vary stock but this will get u in the ball park what elevation are you?

[outcrydrummer]

The cheapo air filter us already removed.
Went back to stock. Luckily I have a 125 jet from a kit and I have a uni filter on the way with a cdi from a member here.
Will rejet to 125 main with the uni and see where I'm at.
I'm at or under 700ft elevation.
Thanks for all the info guys