1988 Elite E (SB50P) bogs down only when warm

[fizl]

I have an '88 Elite E (SB50P) which I bought about a year ago for some short puttering around town.

When I bought the scooter it ran well. Started first kick, idled well...etc. I took it for a ride around and island near me (gravel covered roads), got about 3 miles into the trip and the scooter died. I was able to restart it but the engine was running really rough. I was able to limp back home with motor sputtering, surging and stalling.

I had the scooter serviced. The mechanic cleaned the carb, air filter, replaced all the fluids..(typical maintenance stuff). The scooter ran better but was still not at 100%. It seemed to bog down when under load (for example, going up a slight hill). It would also bog out if I ran it near full throttle. The engine would sort of sputter, the RPMs would drop, the scooter would decelerate (as if i had quickly grabbed the brake) and then accelerate again. Very unnerving.

I brought it back to the mechanic and he noticed that the airbox had come detached from the carb. He fixed that and the bike ran great!

Excited, I took it out for another short spin around town and it indeed seemed to be running well.

Yesterday, my son took the scooter to pickup some stuff at the grocery store (about 2 miles away). I got a call 15 minutes later saying that scooter had died.

When I got to the scooter I was able to start it on the first kick...the bike will purr at idle but if I give it any gas (even a tiny amount) the motor will bog down almost to the point of stalling.

It seems that the scooter runs great when it's cold. Starts right up, idles perfectly, engine sounds great, no smoke. It accelerates well and goes pretty fast for a 26 year old bike. (I've had it up to 35mph and I'm 220 lbs) However, after a couple of miles (or ~15 minutes), when the engine gets warm it bogs down to the point of barely running.

Here's are some ideas that I've got from reading other posts on this forum:
1) vacuum leak causing fuel pump to not work
2) carb not getting fuel (burning up whats in the bowl, gas not getting replenished)
3) bystarter getting stuck or activating (dumping more fuel into carb) when warm
4) exhaust needs cleaning (back pressure)
5) gas cap not allowing air into tank
6) carb set up with proper enrichment setting but improper run(?) setting

Any ideas? It's a great little scooter and I'd like to be able to ride it for more than 1 to 2 miles at a time.

Thanks.

[fizl]

I stand corrected. It's not just when the engine warms up. It's now all the time. Can start the scooter. It idles great. Try and it give it gas (small amount)...engine speeds up. If I hold the throttle, about 15 seconds later the engine will bog. WFO causes immediate bog/stall.

So, to recap. Scooter was serviced, ran great. Starts first kick, idles nicely, almost purrs, no smoke. Good acceleration. 30-35mph top speed (stock bore).

Son takes it to store (~2mi trip)...15 minutes later, scooter barely runs. I'm going to blow out the carb this weekend (on the off chance that some crud from my gas tank found its way in there).

Other than that I seems like my scooter tune ups have about a 30 minute shelf life. Tune up/clean out...runs great for about 30 minutes of riding time...then, bammo!...crapsville!

[Rip_City_Spree]

Id clean the carb and check for airleaks. not an expert by any stretch but thats where Id start. its running at idle so thats a good start.

[swimmingfree]

next time it bog just open the cap on the tank and see what happens ..that will tell you if the vent on the cap is working... the by starter ( choke) is not what i is going on its worm a nuff it may not be engage at all.... pull the plug and look at the color it shood be the color of a candy bar .. set the gap at 25 ...
swimmingfree

[Pete M]

Remove the emulsion tube and clean it. You have a dirty/clogged main jet. The only reason it runs correctly at times is the fuel enrichment circuit in its cold state is making the the mixture rich. As the engine heats up, the enrichment circuit closes and reduces the fuel to the normal amount of fuel. Follow the carb cleaning instructions in the Wiki and you should be fine. Greg could you please post the link for me. Good luck! I have 2 SB50p's.

[patthesoundguy]

Remove the emulsion tube and clean it. You have a dirty/clogged main jet. The only reason it runs correctly at times is the fuel enrichment circuit in its cold state is making the the mixture rich. As the engine heats up, the enrichment circuit closes and reduces the fuel to the normal amount of fuel. Follow the carb cleaning instructions in the Wiki and you should be fine. Greg could you please post the link for me. Good luck! I have 2 SB50p's.

I agree with this and add to it the possibility of maybe the screen in the oil tank being clogged. Maybe its just not getting oil like it should. I'd pull the carb and pop the main jet out and the emulsion tube out and clean them as pets suggested then see how it goes. Try a tank of 35:1 premix after you get the carb in and the problem is still there see if it solves the problem. If that. Doesn't help you may have to dig further into the whole thing. Like new crank seals or a hidden air leak.

[Trafficjamz]

I think an air leak is the most likely culprit.

The air box must be tightly sealed up 100% to run correctly.

Those elite e and spree carbs get stripped out pretty easy. The bolts that secure the carb to the intake can vibrate loose and cause a small air leak too.