88 SB50P - Low Power, 16 mph top speed

[tony.kelbert]

I’ve got a 1988 SB50P with little to no power. I weigh about 220 lb and I can only go about 16 mph on flat ground. If there is even a slight incline that drops to ten, and I have to push it up hills steeper than a slight grade.

Is this typical? If not, where do I start troubleshooting?

Another symptom; when the engine is cold and I drive it down hill it will start sputtering like it is is misfiring on every tenth or so rotation. Any ideas what that might be?

Haven’t done a compression test yet. I have cleaned the carb with carb cleaner but I don’t have a vacuum gauge so I can’t say for certain whether the carb is the issue.

Coil, wire, plug are all new as are the bystarter and air filter.

Two cycle engines hate me, but I’d really like to get some more power out of this one. First moped I’ve ever owned (I’m 34) and even though it tops out at slightly faster than a jog it still makes running errands fun. Any help is appreciated. I can share video of a stop to 16 mph acceleration if requested. It takes about 20 seconds if I don’t push at all.

[vintagegarage]

That is not typical. A 1988 Elite E should top out at about 25 mph, and a 1988 Elite ES should run off the end of the speedometer.. 35+ when running correctly. Cold sputtering is normal though as the mixture hasn't yet become correct until the engine warms up. The bystarter starts to close once the engine starts, and the fuel mixture won't be perfect until the bystarter is fully warm. Once warm there should be no sputtering. Make sure that your factory stock airbox and air filter (clean and correctly oiled) are in place, and that your exhaust system is not plugged up with oil and sludge. Make sure your bystarter is fully closing when warm. The procedure to check it starts at 4.6 in the workshop manual at:

http://www.motorscooterguide.net/manual ... Manual.pdf

Weight limit on your scooter is around 180 pounds. It will always be slow off the line, and even when running properly, won't be able to start up a hill from a standing start with you on it. You will probably have to continue to "Flintstone it" to get it moving from a standing start on any significant hill. Once rolling, your scooter should have plenty of zip. Acceleration when going from 20 to 25 mph should be brisk. It should easily be able to climb slight hills at 20 mph.

[tony.kelbert]

Thanks for your reply. I was sure that this performance was way below what it should be and having someone else agree makes it easier to justify putting more money into this. I intend to start with cleaning the exhaust and oiling the air filter and we’ll see what happens.

[tony.kelbert]

I am pretty sure I found a big part problem. Did a compression test with engine cold...90 psi. I think I remember reading that this should be more like 120 psi. I ordered a new piston/cylinder and we’ll see how much that helps.

I cooked the exhaust on the grill for a few hours as well. It smoked a little, but it doesn’t appear that was the issue because I still had terrible performance even after I took the exhaust off.

I don’t know nearly enough about carburetors so I can’t say for sure if that is part of the issue or not. Does anyone sell a carb kit with gaskets, floats, pins and jets?

[nateberrier]

If your compression tester is accurate and you did it correctly, 90psi is the low end of what you need to be able to get it to run.

If the bike is new to you and has some miles on it, its probably a good idea to get a new belt

A new spark plug will probably make a difference also.

Also it never hurts to tear down the carburetor and clean it up. I dont know the specific carb on your scoot, but im guessing you wont find a total rebuild kit, but you can look up part numbers and find stuff on ebay usually. Treatland.tv might have gaskets for you also

[vintagegarage]

Tony.. I don't know if there is a carb kit available, but none of those parts you mentioned will make your scooter run faster. Measure your belt and see if you need a new one. Once you get up to 25 MPH and want to go faster, then search this forum for tips. Look for SB50 topics. Make sure your mainjet is a #68 and not a #65.