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Post by svint1 on May 4, 2022 8:55:19 GMT
Hi all,
Still working on my Polini130 (steel) equipped 90Racer...
New BGM fast flow fuel tap. New float in the 19/19 carb. New float needle in the carb. Carb and jets cleaned. New fuel filter in the carb inlet.
BUT still issue with the fuel flow to the carb.
It hardly pours any fuel into it, and when filled up, it will not fill up in the fuel-line above the float level.
So when riding, it empties the fuel line, and hardly anything flows into the carb and the engine stutters. -but helps with pulling the choke.
Any suggestion on whats wrong?
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Post by vinrouge on May 4, 2022 11:08:26 GMT
Sounds like fuel delivery to the carb, I guess you've checked the usual suspects, breather hole blocked in the tank cap, fuel line to long, kink in fuel line etc.
Does the BGM tap have a reserve, do you have an inline fuel filer, have you checked on the flow from the tap.
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Post by svint1 on May 4, 2022 11:25:31 GMT
Sounds like fuel delivery to the carb, I guess you've checked the usual suspects, breather hole blocked in the tank cap, fuel line to long, kink in fuel line etc. Does the BGM tap have a reserve, do you have an inline fuel filer, have you checked on the flow from the tap. Yep, checked all the usual suspects. -breather hole is "wide open" -fuel line is as short as it gets. -no kink in the fuel line. So still searching for potential causes for the issue....
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Deleted
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Post by Deleted on May 4, 2022 11:56:20 GMT
Can only be breaher hole surely... if you remove tank, put a litre in tank and secure cap,turn tap on whats the flow like? As that will be true delivery rate.
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Post by tzsteve on May 4, 2022 13:51:04 GMT
A bit like the last post form @matteastwood Try a run with the cap unlocked. Then take the tank out and check the flow with no carb connected , Could be an obstruction in the tap
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Post by svint1 on May 4, 2022 15:10:00 GMT
A bit like the last post form @matteastwood Try a run with the cap unlocked. Then take the tank out and check the flow with no carb connected , Could be an obstruction in the tap I’ve tested the fuel line with the tank out of the frame. -flowes nicely both with cap open and closed. The issue is only there when fuel line connected to the carb. There are air in the fuel line that does not travel upwards when fuel line connected to the carb…
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Deleted
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Post by Deleted on May 4, 2022 15:49:31 GMT
Have you checked the float level?
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Post by tzsteve on May 4, 2022 16:49:45 GMT
I bet its driving you mad, Have you tested the carb away from the scoot with no float needle
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Deleted
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Post by Deleted on May 4, 2022 17:10:57 GMT
I bet its driving you mad Drive a man to drink does a vespa....
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Post by svint1 on May 5, 2022 6:19:59 GMT
I bet its driving you mad, Have you tested the carb away from the scoot with no float needle U bet! Tried to hook up the carb to the tank without needle and floater/bowl on, and the fuel ran nicely....
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Post by svint1 on May 5, 2022 6:21:27 GMT
Have you checked the float level? No, I haven't... The thing is that I rebuilt the engine 3 years ago, and it ran smoothly since. But I bought the scooter this winter, and the seller told me that it wasn't runing properly. -but it ran fairly good with the choke out... What height is the float level to be on?
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Deleted
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Post by Deleted on May 5, 2022 8:14:02 GMT
Have you checked the float level? No, I haven't... The thing is that I rebuilt the engine 3 years ago, and it ran smoothly since. But I bought the scooter this winter, and the seller told me that it wasn't runing properly. -but it ran fairly good with the choke out... What height is the float level to be on? I have no idea on the precise method of float height setting. Its easy to diagnose by removing the bowl, blowing into the fuel line while holding the carb flat and level, while blowing slowly raise the float until you cant blow anymore and the valve is closed. Itll be obvious if the float angle is way out - as in valve closed and float at 45 degrees. Then a bit of trial and error bending (ever so slightly) the metal tang that operates the float valve.
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Post by vinrouge on May 5, 2022 9:54:34 GMT
Could the breather tube in the fuel tap be blocked, not allowing air to escape?
Do you have one of the those small auxiliary petrol tanks, just to try and eliminate the tank and tap
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Post by pitadavespa on May 5, 2022 10:21:00 GMT
Hi,
Maybe a stupid idea, but, since pulling the choke helps, can it be a partially blocked/clogged idle jet?
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Post by svint1 on May 5, 2022 12:30:43 GMT
Could the breather tube in the fuel tap be blocked, not allowing air to escape? Do you have one of the those small auxiliary petrol tanks, just to try and eliminate the tank and tap Could very well be the breather in the fuel tap. -I've been thinking that myself... That said, it is a brand new BGM fast flow, so kind of ruled out that. Guess I've to try a another fuel tap.
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Post by svint1 on May 5, 2022 12:32:10 GMT
Hi, Maybe a stupid idea, but, since pulling the choke helps, can it be a partially blocked/clogged idle jet? Not stupid at all, but have had the carb out twice and cleaned it and the jets properly, so we can rule out that. And it runs fine from start, but when carb bowl is nearly empty, it runs only with choke due to marginal flow of fuel in the line.
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Post by tzsteve on May 5, 2022 12:58:39 GMT
If it runs ok with no float needle fitted it mist be the float height, I aint used one of those carbs since 1982 so i dont know what the float height should be
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Post by jbcollier on May 5, 2022 15:06:59 GMT
If it runs better when the choke out then fuel supply is not the issue. Something is plugged or partially blocked.
It is normal for there to be air bubbles in the fuel line at high spots.
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Post by svint1 on May 5, 2022 16:19:00 GMT
If it runs better when the choke out then fuel supply is not the issue. Something is plugged or partially blocked. It is normal for there to be air bubbles in the fuel line at high spots. The air buble is not on a high spot. -it is just above te fuel banjo on the carb. And the scooter runs perfect in all revs until the fuel in the bowl is used. -then I can only run it on low revs with low fuel consumption without choke… So that’s why I suspect the fuel supply.
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Yoshi
100 Sport
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Post by Yoshi on May 5, 2022 18:40:43 GMT
I see you have replaced your float and valve needle. Was the problem also present with the old ones or were the parts faulty somehow?
Just thinking if the new ones are someway slightly different than the original ones.
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