Author Topic: Lean starting when cold?? (Read 5044 times)

Trusty2stroke · « **on:** November 19, 2015, 03:15:49 PM »

One issue that i have with my bike that I have found only occur when the weather is pretty chilly. On the first start of a cold day the bike starts lean and has a very high idle then after about 30sec it will then start to run like normal. The motor is a fresh ported stock cylinder with 300 sleeve, cool head with a pump gas dome, carb is a 36mm pj and I know my jetting is a bit on the rich side at 165 main, 48 pilot, needle clip on 2nd from the top. Once everything is warmed up it runs fantastic and gives me zero issues. I will try to upload a video of a cold start and maybe that will better explain what im trying to describe haha.

Hurley250R · « **Reply #1 on:** November 19, 2015, 03:30:59 PM »

I don't think that is uncommon. I try to prime my cylinder by kicking it through the stroke a few times slow with the ignition off first.

Trusty2stroke · « **Reply #2 on:** November 19, 2015, 08:44:13 PM »

I do that aswell, It just doesnt seem to make a difference. Im really just wondering why it does it haha, it just bugs me

supernutt · « **Reply #3 on:** November 19, 2015, 09:46:07 PM »

Both my Hondas do that also. I just toggle the kill switch to keep the rpm down until they idle normally

Skeans1 · « **Reply #4 on:** November 19, 2015, 10:05:16 PM »

Do 3 prime strokes and then kick it like a zilla.

rablack21 · « **Reply #5 on:** November 20, 2015, 10:14:05 AM »

Are you already using the choke when you do this? If so, you're saying it's still lean even with the choke on?

Jerry Hall · « **Reply #6 on:** November 20, 2015, 04:45:08 PM »

This is very common in cold weather. The cold start tables on fuel injection units are many times 400% to 500% richer at 0 deg F than a 80 deg F for the first few second of engine operation and then taper off to a value that more closely fits the calculations that correlate the air density with proper fuel flow.

There is a starter jet in most float bowls that regulates fuel flow to the enrichening circuit (choke) on most two stroke carbs. The four strokes enrichening jet is usually next to the pilot jet.

The jet in most float bowls can be drilled to make the engine start easier in extreme cold temperatures but will usually be too rich during the summer.

We drill the enrichening jet in the float bowl when we do an alcohol conversion to keep the air/fuel ratio correct during starting using alcohol.

The starter jet is not the only thing that needs to be richened when it is cold. You probably also need to richen the pilot. main and needle to keep the mixture optimum and prevent the piston from overheating and failing.

havinnoj · « **Reply #7 on:** November 20, 2015, 05:09:13 PM »

Quote from: Jerry Hall;61148

There is a starter jet in most float bowls that regulates fuel flow to the enrichening circuit (choke) on most two stroke carbs. The four strokes enrichening jet is usually next to the pilot jet.

The jet in most float bowls can be drilled to make the engine start easier in extreme cold temperatures but will usually be too rich during the summer.

On a PWK, is there the said "starter jet in most float bowls"?

Jerry Hall · « **Reply #8 on:** November 20, 2015, 05:49:24 PM »

Quote from: havinnoj;61149

On a PWK, is there the said "starter jet in most float bowls"?

On the PWK style of carb the choke jet is a brass jet that is pressed into the upper carb body on the spigot side of the carb. The choke jet is about 5 mm in diameter and hangs down 22mm below the gasket surface from the upper carb body into the float bowl. The fuel flow flows through a .033" hole inside of this brass press-in jet. I usually enlarge this hole to .035" to .040" for gas and .046" to .050" for alcohol depending upon the temperature.

CAUTION:

It does not take much of an increase in diameter to make a difference.

Trusty2stroke · « **Reply #9 on:** November 20, 2015, 07:07:19 PM »

Yes. Its lean with the choke on and seems to rev higher upon startup with the choke on.

Trusty2stroke · « **Reply #10 on:** November 20, 2015, 07:09:54 PM »

Quote from: Jerry Hall;61150

On the PWK style of carb the choke jet is a brass jet that is pressed into the upper carb body on the spigot side of the carb. The choke jet is about 5 mm in diameter and hangs down 22mm below the gasket surface from the upper carb body into the float bowl. The fuel flow flows through a .033" hole inside of this brass press-in jet. I usually enlarge this hole to .035" to .040" for gas and .046" to .050" for alcohol depending upon the temperature.

CAUTION:

It does not take much of an increase in diameter to make a difference.

Does a standard 36mm pj have this starter jet?? or is this only a feature in a pwk?

Jerry Hall · « **Reply #11 on:** November 20, 2015, 09:02:53 PM »

Quote from: Trusty2stroke;61151

Yes. Its lean with the choke on and seems to rev higher upon startup with the choke on.

The jet's flow area may be reduced due to a layer of varnish inside the jet or the jet may have some debris reducing the flow when the enrichening circuit is activated.

Jerry Hall · « **Reply #12 on:** November 20, 2015, 09:14:05 PM »

I think that the PJ carb's enrichening circuit has a very small metering rod that is part of the enrichening plunger. I believe Keihin over-engineers some things on many of their carbs, omits some features that other carbs have so that the whole carb has to be replaced when some circuits ware out and I think that some features are just stupid.