86' Spree Bogging and Low Torque with Throttle

[takota]

Hello all, I'm absolutely stumped by an issue I've been having with my 86' Spree for the last few months and I'm hoping the gurus here on the forum may have some ideas.

Spree idles fine but when throttle is applied the scooter bogs down and has very low torque. It will also somewhat randomly throttle up without the throttle being applied.

Troubleshooting Action:
Swapped carb (& thoroughly cleaned multiple times)
Swapped vac petcock
Swapped clutch assy
Swapped igniter
Cooked exhaust over fire & wire cleaned
Installed new top end & piston
Inspected reeds (they look OK)

I'm almost out of things to replace. Could it be an issue with the crank arm seals? final drive gears?

Thank you for reading!

[noiseguy]

Bogging sounds like intake side issues. How are the air filter and filter box? Those in place?

The "random throttle up" is an air leak, most likely in front of the carb (either intake or the thermal decoupler between the carb and the intake.)

[takota]

Thanks NoiseGuy

Took a look at the airbox and made sure everything was fully seated. I found that the intake to carb connection was a bit loose and tightening that up looks to have solved the "random throttling issue".

Rode around and was still running into the bogging issue when throttle is full wide. Sprayed some starter fluid around the carb area while running but the engine didn't throttle up, so seems like it is leak free.

Also added a video to give an idea of the behavior; I was holding full throttle the whole time: https://imgur.com/a/xqCrDtX

[noiseguy]

The bogging issue is usually related to issue from the air filter. Spree, for some reason, are really sensitive to changes on that end. For example, a pod filter will do exactly the same as what you describe.

So, is the air filter in place, oiled, with the air filter cover on and screwed down?

[takota]

Air filter is oiled with cover and screwed down. Whenever you let off the throttle it goes back to idling nicely so I also tried removing the vac petcock and supplying fuel straight to carb, thinking it may be a fuel delivery issue, but didn't make a difference.

[ss800]

i dunno, my '86 spree starts/idles/accelerates perfectly. Last carb clean performed was 2024. I also added Stabil 360 to the fuel tank. Note it does do a lot of sitting as well.

[noiseguy]

Check every gasket in this set and make sure they're OK on yours. https://www.ebay.com/itm/142207616725?_ ... ust+gasket

The crank seals are the other things going on these bikes, 40 years after production, and should probably be replaced too.

[takota]

Finally got around to replacing thing! I've installed new crank seals and ended up finding the final drive/transmission bearing in pretty bad shape, which I also replaced. This seems to have solved the issues I was seeing with inconsistent throttle response and random bogging.

Exhaust, reed and carb gaskets are the next task on the list, but I'm not totally convinced those are the bad based on the behavior I'm seeing:
I'm getting very little low end torque, and when throttling up the bike wants to die on there is anything but flat/downhill ground. When the bike is on the stand, there isn't any issue throttling up or bogging. Its also totally fine when you can get up to higher speed, and can maintain full throttle without bogging/seizing (fan shroud is installed); feels like it struggles to get revved up and then takes off once at speed. Once you let off the throttle though, it doesn't want to get going again.

Maybe a clutch issue? I swapped in a clutch assy from a junk engine I picked up and noticed similar behavior, but that might not be a "known good" sample...

Would love to get your thoughts - I'm a bit stumped

[noiseguy]

Check your main jet size if you haven't yet. Should be 65 or 68. I assume you've already cleaned the carb, since the usual issue is they won't idle if the carb's dirty.

Revving on stand doesn't tell you much in my experience. They run completely different unloaded.

Check the spark plug boot (plug wire to plug boot). These unscrew from the wire. If wire's in bad shape, cut 1/4" off the end and screw it in again.