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Post by scootypuffxl on Jun 25, 2020 16:04:13 GMT -5
Hi, new here, been messing with scooters for a while now. I have a 2008 vitacci 49cc with 50mm bbk with head, a9 cam, 20mm carb with 98 main jet, aftermarket cone filter, and aftermarket exhaust. Just finished the break in on bbk and decided to open her up. Picks up speed to wot, but then I have an intermittent bog after 20 to 30 seconds. Still haven't been able to hit 40 mph, like with my 2012 taotao that has the same set up but no big issues of bogging at all. My question is, is it possible I'm losing vacuum to my petcock at high rpms or is the 98 main jet still too small? I live in st Louis mo. And have no idea the elevation here, just quite perplexed to have 2 scooters built the same, one runs great one is being a beeotch. Have been searching forum most of today and I'm not seeing anyone with this problem.
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Post by FrankenMech on Jun 25, 2020 19:55:32 GMT -5
About 466' per google. Vacuum loss is one possibility. Remove the petcock and run a direct line. Then check your carb tuning. |
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Petro
Scoot Enthusiast
Posts: 149
Location: Gothenburg, Sweden.
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Post by Petro on Jun 26, 2020 0:09:28 GMT -5
Hi, new here, been messing with scooters for a while now. I have a 2008 vitacci 49cc with 50mm bbk with head, a9 cam, 20mm carb with 98 main jet, aftermarket cone filter, and aftermarket exhaust. Just finished the break in on bbk and decided to open her up. Picks up speed to wot, but then I have an intermittent bog after 20 to 30 seconds. Still haven't been able to hit 40 mph, like with my 2012 taotao that has the same set up but no big issues of bogging at all. My question is, is it possible I'm losing vacuum to my petcock at high rpms or is the 98 main jet still too small? I live in st Louis mo. And have no idea the elevation here, just quite perplexed to have 2 scooters built the same, one runs great one is being a beeotch. Have been searching forum most of today and I'm not seeing anyone with this problem. I had the same problem on an old scooter I had. When I BBK'ed it, it did the exact same thing when the tank was half emtpy or less... I cuted the too long petrol line so it pointed more downwards to the carb and the problem disapeared. Gravity couldn't do it's job properly, air pockets in the hose/line was building and that in turn didn't fill the bowl on the carb, after say 30 sec full throttle the bowl was empty... |
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Post by GrumpyUnk on Jun 26, 2020 10:21:04 GMT -5
Maybe check the needle position in comparison to the one that works better.
Does it feel as if it is running out of gas? Such as, cruising, open the throttle, and nothing happens... OR does it feel as if something happened, as in it started to stumble mumble and use swear words? The former would be like running out of gas, the latter would be the condition if it was too rich. At least that's what I am trying to differentiate.
I thought for a 50mm you would need a main size over 100. Something along the 105 range.
tom
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Post by mikehailwood on Jun 26, 2020 11:05:37 GMT -5
I've been experiencing a similar problem with a newly installed 72cc kit - cylinder and piston upgrade only. With about 100 miles on the new set-up I'm beginning to push the speeds to 34-35 mph. When I hold that speed for about 1/2 mile the bike slows down as if it's not getting fuel. If I pull over and let it sit for a few seconds it will take off and run fine. After reading petro's recent comment on this subject I filled my fuel tank to within 1" of the top and took it for a spin. On 2 separate runs at sustained speeds of 34-35 mph for 1/2-3/4 mile stretches I experienced no symptoms at all. I'll take a closer look at the fuel delivery hose when I get a chance. It may be worth mentioning that I've never been comfortable with the fit of my petcock vacuum line. It does not feel as snug as I'd like. But I have no idea how critical this is.
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Post by GrumpyUnk on Jun 27, 2020 9:42:27 GMT -5
You will have less manifold vacuum at high speeds. With any leakage, the vacuum could be dropping low enough to partially restrict fuel flow(allows the petcock to close or partially close).
FWIW, take a look at the filter also. If it is restrictive(too) it can slow fuel flow also.
The key signal(evidence) was that higher level of fuel in the tank==higher pressure at the outlet, which would cause better flow even through a restricted outlet.
tom
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Post by mikehailwood on Jun 27, 2020 14:35:01 GMT -5
"You will have less manifold vacuum at high speeds. With any leakage, the vacuum could be dropping low enough to partially restrict fuel flow(allows the petcock to close or partially close). FWIW, take a look at the filter also. If it is restrictive(too) it can slow fuel flow also. The key signal(evidence) was that higher level of fuel in the tank==higher pressure at the outlet, which would cause better flow even through a restricted outlet. tom" I checked the fuel line which has a little extra length which is horizontal for about 3 inches but I doubt that this is significant. I pulled the vacuum line because it was never as snug as I thought it should be. 3.5mm fuel line fits nicely. BUT...I did notice that each end of the vacuum hose was a little wet which could indicate a failing petcock diaphram. Any opinions? .5 |
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Post by GrumpyUnk on Jun 28, 2020 10:10:00 GMT -5
What did the 'wet' smell/taste like? If you have a section of vacuum line, you can apply suction using yourself or a vacuum tool(mityvac). Some have a gauge, and will indicate if there is leakage. If you taste/smell gasoline, not good. It does not take a lot of vacuum to open the valve. Most times if the diaphragm is leaky, you will get dripping or strong odor of fuel.
tom
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Post by mikehailwood on Jun 28, 2020 14:43:18 GMT -5
What did the 'wet' smell/taste like? If you have a section of vacuum line, you can apply suction using yourself or a vacuum tool(mityvac). Some have a gauge, and will indicate if there is leakage. If you taste/smell gasoline, not good. It does not take a lot of vacuum to open the valve. Most times if the diaphragm is leaky, you will get dripping or strong odor of fuel. tom Tom, I've no idea how much vacuum is generated at the manifold of these scooters. Putting a Mityvac on the line and pumping to 15", the gauge dropped to 10" after 1-1/2 minutes. After 2-1/2 more minutes the reading hit 5". I could see a tiny mist of liquid (gas as it turns out) at the connection of my clear tubing to the scooter vacuum line. I'll source a new petcock unless someone can convince me that what I have is acceptable. Thanks for your comments. |
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Post by GrumpyUnk on Jun 29, 2020 7:38:56 GMT -5
Ain't spozta be gasoline on that side of the diaphragm. The leakage rate is not bad, but any fuel is an indication of a leak. The diaphragms being made of some sort of rubber-ish compound, they likely have an age limit where they get stiff and crinkly, and start to fail at their 'fold' points(flex?). My bet is it is on its way out and it is only a matter of time before it starts to allow major amounts of liquid fuel to be fed directly to the intake. That's no fun.
tom
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Post by mikehailwood on Jun 29, 2020 11:22:39 GMT -5
Ain't spozta be gasoline on that side of the diaphragm. The leakage rate is not bad, but any fuel is an indication of a leak. The diaphragms being made of some sort of rubber-ish compound, they likely have an age limit where they get stiff and crinkly, and start to fail at their 'fold' points(flex?). My bet is it is on its way out and it is only a matter of time before it starts to allow major amounts of liquid fuel to be fed directly to the intake. That's no fun. tom I'll order one. Given the situation, it does not seem urgent. It would be interesting to know which happens first: vacuum too weak to open the valve enough to let fuel to the carb OR hole in diaphram so large that fuel "runs" into the intake. I hope I never find out. |
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Post by FrankenMech on Jun 29, 2020 13:03:19 GMT -5
I'll order one. Given the situation, it does not seem urgent. It would be interesting to know which happens first: vacuum too weak to open the valve enough to let fuel to the carb OR hole in diaphram so large that fuel "runs" into the intake. I hope I never find out. I think you know now. The added fuel causes a misfire which bogs out the engine which lowers vacuum, etc.
Replace the petcock, Now, not later.
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