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Post by markavionics on Aug 24, 2015 20:03:55 GMT -5
Hello Dawgs!
I've been up and down this forum looking for a similar problem...but no luck. I finally broke down and will submit my situation to the community, hope you can help me.
Ride:
- 2008 150cc GY6, distributed by Saga Canada, basically your typical Chinese scooter. Valves adjusted to 0.004/0.006 intake/exhaust. Mostly stock except;
Installed NEW:
- Replaced the stock carb with the same model, but better quality. 35 idle jet / 120 main jet
- Removed the stock air box, installed a Uni Filter
- Installed iridium spark plug
- New battery installed
- Vacuum lines all new
- Fuel filter new
Symptoms:
- Scoot requires several seconds of cranking (5 - 10s) to start. I have to crack the throttle about 25% open to get it to finally catch. More or less throttle and it won't catch.
- Once it is running the scoot seems to run ok, although a little less power than before the new parts were installed. (maybe the main jet isn't quite right?)
- I'm having trouble getting the idle right. Been messing with A/F screw but it doesn't want to idle under 2000 rpm...but over 2000 my drive is starting to kick in.
I'm thinking my A/F mixture is not right when at idle but not sure if it is too lean or too rich. By opening the throttle am I adding more air to lean out the mixture? Or adding more fuel to rich'en it up?
Scoot used to start within 1 - 2s of cranking....not sure what is going on now...I'm afraid I'm going to get stuck somewhere and run the battery down trying to get started.
Appreciate any help you can offer.
Cheers,
Mark.
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Post by JerryScript on Aug 25, 2015 12:13:41 GMT -5
Are the jets the same size as the ones in the old carb? If so, you may need to change them, due to the uni intake. A uni usually allows more air in, meaning you need more fuel. I would start with the next size jet up.
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Post by pmatulew on Aug 25, 2015 12:19:17 GMT -5
Cracking the throttle is letting in more air. So your mixture must be too rich.
If it won't idle down, you need to back it down in steps, (idle stop, mixture screw), until it will.
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Post by lain on Aug 25, 2015 15:10:19 GMT -5
High idle, if not adjusted that way by the rider, is a sign of running lean. Check to make sure there isn't any openeings in the vaccuum lines somewhere, that could let in more air. What did you do with the lines that were connected to the old air box?
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New Rider
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Post by markavionics on Aug 25, 2015 16:42:45 GMT -5
Are the jets the same size as the ones in the old carb? If so, you may need to change them, due to the uni intake. A uni usually allows more air in, meaning you need more fuel. I would start with the next size jet up.
Thanks for responding....I also figured the main jet would need to be up-sized based on other posts in this forum.
Original jets were 35 and 110
Now jets are 35 and 120
Cheers, Mark.
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Post by markavionics on Aug 25, 2015 16:47:12 GMT -5
High idle, if not adjusted that way by the rider, is a sign of running lean. Check to make sure there isn't any openeings in the vaccuum lines somewhere, that could let in more air. What did you do with the lines that were connected to the old air box?
I had previously removed the emissions crap and capped off the lines.
The line coming off the valve cover that WAS going to the airbox is now routed up high and just secured to the frame....this is still open and I can feel air moving when revving the engine.
The line coming off the aft end of the drive (at the rear wheel) is just secured to the body, open to the air.
Thanks for the help.
Cheers, Mark.
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New Rider
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Post by markavionics on Aug 25, 2015 16:49:48 GMT -5
Hmmmm,
pmatulew says I'm too rich....
lain says I'm too lean....
I'm still stumped, but appreciate your comments.
Cheers,
Mark
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Post by pmatulew on Aug 25, 2015 17:24:16 GMT -5
"In theory" below 25% throttle the main jet isn't doing anything. "Should not" be affecting how it starts. Air and fuel should be coming through the idle circuit.
Cracking the throttle to start will let in more air and overriding whatever the choke might be doing. It might also possibly be lifting the needle enough to let fuel through the main jet depending on your estimation of 25%
Really need to get it started and then dial it down so it will idle properly. Sounds like right now it will only run at the transition point. If it's partly running on the main jet then you're going to have a hard time adjusting the idle mixture until you get it down below the transition point.
Maybe you do have a vacuum leak and it won't start until you open the throttle enough to add fuel from the main to compensate.
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Post by scooter on Aug 25, 2015 17:41:15 GMT -5
Hello Dawgs! I've been up and down this forum looking for a similar problem...but no luck. I finally broke down and will submit my situation to the community, hope you can help me. Ride: - 2008 150cc GY6, distributed by Saga Canada, basically your typical Chinese scooter. Valves adjusted to 0.004/0.006 intake/exhaust. Mostly stock except; Installed NEW: - Replaced the stock carb with the same model, but better quality. 35 idle jet / 120 main jet - Removed the stock air box, installed a Uni Filter - Installed iridium spark plug - New battery installed - Vacuum lines all new - Fuel filter new Symptoms: - Scoot requires several seconds of cranking (5 - 10s) to start. I have to crack the throttle about 25% open to get it to finally catch. More or less throttle and it won't catch
- Once it is running the scoot seems to run ok, although a little less power than before the new parts were installed. (maybe the main jet isn't quite right?) - I'm having trouble getting the idle right. Been messing with A/F screw but it doesn't want to idle under 2000 rpm...but over 2000 my drive is starting to kick in. I'm thinking my A/F mixture is not right when at idle but not sure if it is too lean or too rich. By opening the throttle am I adding more air to lean out the mixture? Or adding more fuel to rich'en it up? Scoot used to start within 1 - 2s of cranking....not sure what is going on now...I'm afraid I'm going to get stuck somewhere and run the battery down trying to get started. Appreciate any help you can offer. Cheers, Mark. Try this short video. See how he adjusts the carb, what he's listening for, and he discusses when to rejet. . |
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Post by markavionics on Aug 25, 2015 18:01:08 GMT -5
Thanks Scooter...I have a look and give it a try tonight.
Cheers,
Mark.
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Post by markavionics on Aug 25, 2015 18:28:30 GMT -5
"In theory" below 25% throttle the main jet isn't doing anything. "Should not" be affecting how it starts. Air and fuel should be coming through the idle circuit. Cracking the throttle to start will let in more air and overriding whatever the choke might be doing. It might also possibly be lifting the needle enough to let fuel through the main jet depending on your estimation of 25% Really need to get it started and then dial it down so it will idle properly. Sounds like right now it will only run at the transition point. If it's partly running on the main jet then you're going to have a hard time adjusting the idle mixture until you get it down below the transition point. Maybe you do have a vacuum leak and it won't start until you open the throttle enough to add fuel from the main to compensate. Thanks pmatulew.
This "theory" is interesting. I do find that if I give it too much throttle (50% or more) the engine won't crank over as quickly and it won't start.
So, assuming I'm too rich - opening the throttle a little adds more air to lean it out; but opening it too much and I start to introduce more fuel as well from the main jet circuit making the mixture too rich again....
I'll have another look over the vacuum lines tonight.
Cheers, Mark.
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Post by markavionics on Aug 26, 2015 10:25:48 GMT -5
So I removed the Uni-filter to view the needle assembly during start. What I saw was the needle/air valve bouncing as the engine cranked, due to the vacuum being generated I assume. It would seem to me that my mixture is too lean with the throttle off and by opening to about 1/4 the vacuum is causing the needle valve to open briefly, introducing more fuel to the mixture. Appreciate any thoughts on my theory... Cheers, Mark.  |
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Post by JerryScript on Aug 26, 2015 11:23:44 GMT -5
I agree, as I said earlier, a uni often requires up-jetting.
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Post by lain on Aug 26, 2015 12:20:37 GMT -5
You may also benefit from adjusting the needle position.
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Post by scooter on Aug 27, 2015 0:09:53 GMT -5
So I removed the Uni-filter to view the needle assembly during start. What I saw was the needle/air valve bouncing as the engine cranked, due to the vacuum being generated I assume. It would seem to me that my mixture is too lean with the throttle off and by opening to about 1/4 the vacuum is causing the needle valve to open briefly, introducing more fuel to the mixture. Appreciate any thoughts on my theory... Cheers, Mark. Know this: Your vacuum pressure will be at its highest when the throttle is closed, and you will lose vacuum pressure as you open the throttle. It may drop from 15 in/Hg at idle, down to less than 1 in/Hg at top speed. (However this is despite the fact that fuel pressure will rise as RPM goes up, indicating a difference between vacuum pressure, and the rate at which it is applied. That is to say, a lot of little pulses are still more powerful than a few big ones.) The vacuum level on a gauge will jump up and down at idle. The air slider will jump up as the piston is sucking air into the intake, then it will drop back down while the piston is compressing and exhausting. As we rev the engine, it reads a steady reading as throttle is applied, dropping almost to zero at WOT. It would appear that, at least until the idler circuit shuts off, that you are getting fuel from the idle circuit AND from the running circuit as well. Because of this apparent intermingling of circuits, which is beyond my learning, it would seem best to set the main jet to make the bike run fast, but cool, and then go back and work on the idler circuit while NOT adding throttle. Or vice versa, the point being to isolate the problem to one circuit or the other. Perhaps try determining the starting problem this way: Set the idle down to around 1500-1600 RPM while the engine is running, then shut it off, or let it die if it's going to, and try to start it without throttle. If it won't start, then close off some of the filter with your hand, or something, and try again. If it then cranks, then you needed more fuel to your idler circuit. If not, then it would seem you need less fuel or have some other issue. |
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