SB50P Carb Help!

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SB50P Carb Help!

Post by wiliamJ » Tue Jun 30, 2020 1:06 pm


I have been working on getting a 1988 Honda SB50P Elite E scooter running and have been having issues getting it to run right. I am wondering if you know of any way that a rich condition can be caused other then by jets? The manual mentions clogged air jets but I am not sure what that is referring too.

When Air Filter is on: it will only idle at full throttle. when the gas is turned off and it uses most of the gas from the bowl it will all of a sudden run right for like 30 secs then die, I assume this is the point when gas gets low enough to allow additional air through the pilot tube?

When air filter is off: Runs and can be ridden getting to 15mph or so (bogging of course at full throttle).

The jet is stamped as a #65 and doesn't appear to be drilled out.
I replaced the air filter foam(stock)
Needle is at middle position.
All passage ways are clear in the carburetor (I have cleaned it multiple times).
I have confirmed the bystarter is working as expected. I also tried plugging the bystarter inlet and output holes to see if it changed how it ran and it experienced the same issue.
Float height is correct at 12.2 mm
Float needle is in good condition, and seat has been cleaned to ensure it is sealing correctly.
Does not apear to be flooding, when removed I have atatched gas (turned on) and confirmed no gas drips.
Pilot circuit is clear (small hole in venturi is not clogged)
I installed a manual inline petcock since the auto petcock was not working properly.
New spark plug and battery.

Just in case I am ordering a #68 and #65 carb jet from the honda dealer.

While I wait however I was wondering if you guys had any other ideas on what would cause the scooter to run rich?

I have 100PSI compression.

I am at a loss, and this is probably something super stupid that I am forgetting about.

Thanks in advance for all your help!

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Re: SB50P Carb Help!

Post by motormike » Tue Jun 30, 2020 2:45 pm

You've given an excellent report of the bikes status williamJ.
Newbs should take note. :thumbwink:
Now as for the rich issue, first instinct says go to the emulsifier tube above the main jet and clear all the holes.
if you haven't and there is a tube present...I'm not familiar entirely with the carb present on your model.
One other thing I would do: attach clear hose to the bowl drain, point hose toward the sky, fasten hose securely, and observe the float level.
Since the float levels aren't adjustable, and measuring the float height doesn't guarantee the level to be accurate,
this method gives you a visual check under operating conditions. edit; the hose shoild be directly next to the bowl giving a level that is equal to the level in the bowl. Fluid will always seek it's own level is the theory involved.
Hope one of these ideas help you back to 30mph.

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Re: SB50P Carb Help!

Post by wiliamJ » Tue Jul 21, 2020 11:21 am


Just an update, I got the scooter running!

The issue was the Pilot tube, once pulled out and compared to the pilot tube from a parts carb it was clear that the pilot tube was drilled/reemed out. Whenever there was back pressure (air filter was atatched) gas was being sucked through the pilot tube and dripping out the pilot air inlet which was causing the rich condition. Once I replaced the pilot tube with the pilot tube from the parts carb it has been running well =)

Thanks for all your help!

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