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Post by mdscoot on Jun 12, 2022 11:40:25 GMT -5
Ok, I've got a new carb on the scoot.
The backstory is that this scoot has always been a bit hard starting and had some erratic behavior but it always pulled hard when it did run.
No matter what carb I have on the bike it starts hard, sometimes requires WOT. The spark plug is sparking. The spark plug is wet, indicating that fuel is in the ignition chamber.
I need to perform a compression check. I did find that the reed valves had a pretty good gap. I flipped the reeds and this closed up the gaps a lot but still not 100%. This time the scoot started much more easily and it would idle but still had almost no power. Not rideable like this.
So, before I waste money on a reed valve assembly I'll perform a compression test. If it has enough "oomph" I'll replace the reeds.
Anything else I should check?
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Post by aeroxbud on Jun 12, 2022 17:56:53 GMT -5
Sounds like the reeds definitely need replacing. They are pretty cheap and will definitely make starting harder if they are not sealing correctly.
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Post by mdscoot on Jun 16, 2022 10:09:42 GMT -5
Sounds like the reeds definitely need replacing. They are pretty cheap and will definitely make starting harder if they are not sealing correctly. Hi aeroxbud, I performed a compression check yesterday. 105psi. I'm aware that 150psi is normal/optimal and I think 90psi is the minimum. Is it worth installing new reed valves with 105psi? |
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Post by aeroxbud on Jun 16, 2022 14:01:57 GMT -5
There could be other reasons for the low compression. But I would definitely change the reeds.
You can just buy the reed petals and replace the ones in the assembly. No need to replace the whole thing.
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Post by mdscoot on Jun 29, 2022 14:44:25 GMT -5
Ok, replaced the reeds. A tiny bit better but not enough to matter. Hard starts and when I crack the throttle it bogs out and dies.
I pulled the plug. It's an NGK BP7HS. It's old. The spark is present, but yellowish rather than blue. I cleaned it and it made a tiny improvement so I'm off to buy a new plug right now. If that doesn't help, I'm stumped.
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Post by mdscoot on Jun 30, 2022 9:23:51 GMT -5
Alright, let's recap:
Comrpession: 105psi
New carb
New spark plug
New reed valve assembly
No vacuum leaks that I can find
Scooter starts somewhat easily now. It idles smoothly but pretty low and sometimes runs down and stalls out.
When trying to rev it up, it just bogs and dies immediately. I managed to ride it around my house once, blipping the throttle to keep the RPM's high enough.
The scooter starts more easily if I choke off the venturi with my hand. I guess what I'm trying to figure out here is if the scooter is flooding or starving?
Any thoughts?
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Post by pinkscoot on Jun 30, 2022 10:02:35 GMT -5
It sounds like the carb needs a good cleaning and tuning.
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Post by Lucass2T on Jun 30, 2022 10:24:33 GMT -5
Did you check both crank seals?
And did you pressure test it like you do when rebuilding an engine?
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Post by mdscoot on Jun 30, 2022 12:42:14 GMT -5
It sounds like the carb needs a good cleaning and tuning. It's brand-new. Can the float be mis-adjusted out of the box? |
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Post by mdscoot on Jun 30, 2022 12:42:46 GMT -5
Did you check both crank seals? And did you pressure test it like you do when rebuilding an engine? I didn't do either of these things. Sigh. |
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Post by pinkscoot on Jun 30, 2022 14:32:17 GMT -5
It sounds like the carb needs a good cleaning and tuning. It's brand-new. Can the float be mis-adjusted out of the box? I always clean new carbs because there can be little machining debris in them that will clog a jet. Throwing a new carb at the problem might not be the solution. They still need to be jetted and adjusted properly. What carb did you use to replace the stock carb? |
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Post by aeroxbud on Jun 30, 2022 14:39:03 GMT -5
Is the new carb the same as the old one? Have you tried changing the jetting?
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Post by mdscoot on Jul 7, 2022 7:15:07 GMT -5
Hi guys, I bought this carb: www.amazon.com/dp/B09MY25BWN?psc=1&ref=ppx_yo2ov_dt_b_product_detailsFrom my research, the Kymco Buddy 50 engine and several other models used the same engine as the Big Max 50. I really couldn't find an identical replacement carb by searching "Big Max 50". Well, I did find one but it was $200! I still have the original carb but the behavior is still the same. Question: How can you tell the difference between flooding and fuel starvation? Question: What is the "base" starting position of the adjustment knob on the carb? What am I looking for? I can get the scooter started but when I attempt to rev it, it often quickly bogs and dies. I can't tell if I'm flooding or starving it. |
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Post by Zino on Jul 7, 2022 12:46:44 GMT -5
What size jets do you have ?
And what type ?
Thta looks like a keihin carb
What main jet is in it what idle jet and where is the needle
Rich sounds deep blub blub and struggles to rev
Lean sounds high pitched zingy and revs but no power
If it idles fine and then falls on its face going wide open go up 5-10 % bigger on the main and see if that gets better or worse and then work your way down from there
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