sprint doesnt idle, any ideas?

[Rudi]

hey there good fellas,
my sprint doesnt hold idle...but runs great besides that (80 kph easy)
doesn't seem to be the idle screw, cause turning it clock wise, doesn't make a difference
Don't think it has to do with the mixture screw either

I suspect low compression.... (but then, engine only has 7000 km on it since overhaul)

i still havent really checked it out, but until then, any ideas?

thanks.

[sbwnik]

Have you checked the points? Always a good place to start with older scooters.

[Rudi]

Thanks, but I dont think it's points...cause it runs super fine from every above-the-idle rpm
anyway the problem just went away the other day...
I have no idea what is going on ....

[kru251]

Sounds a classic case of a bit of dirt/tank rust getting into the idle jet. The holes are tiny so it takes very little to block them partially causing the symptoms you refer to. Once the throttle is 'opened up' the main jet can come into effect so no issues. A quick strip and a blow through with an air line can clear what often can't be seen with the naked eye! The carb built-in fuel filter really will only stop (realtively) large debris getting through.
Glad it's seen fit to pull the 'dirt' through and is now working!!!!!

[Rudi]

thanx
yeah, most likely its the idle jet...

what about a paper fuel filter, will that cause any flow problems?

[kru251]

What's the fuel line's internal diameter/bore? I know my PX fuel line has a large bore and most paper inline fuel filters have a smaller bore than the PX. Not sure about your Sprint though.
I certainly use a filter on my Royal Enfield 500 'Bullet' and that has been very effective at trapping the little, annoying pieces of tank rust that inevitably form.
Good luck!

[Rudi]

thanks

[sbwnik]

I've used inline filters a couple of times and they've led to fuel starvation in both cases. Just bear that in mind - I know others that have used them, but my experiences weren't great.

[colin4255]

99% sure it will be a blocked idle jet. Had the exact same thing on my PX last week, ran like a top until it dropped to idle. Cleaned jet, all fine now. Like sbwnik says, leave filters alone, not the best idea with 2 strokes as they clog up really quick.

[kru251]

Colin4255.
Filters clog up with what? If it's rust/dust/dirt then it's doing its job and you wouldn't have had your idle jet issue last week IMHO. Most filter housings are clear you can see exactly what's happening and catch potential issues of tank rust etc early. These are seen as disposable items so they can be changed on a regular basis if required. Better to trap the stuff where you can see it rather than just use the large mesh carb internal one which you can't see unless you undo the carb fuel inlet housing and perhaps have your idle jet blocked at some point (as your turning right at traffic lights and it dies halfway across the slow moving junction perhaps)?
Anyway, each to their own I guess.

[sbwnik]

I never had any particular problems with them becoming blocked, just with them slowing the fuel flow down. My SX225 had one for a while and holed pistons for fun until someone suggested that the filter may be part of the problem (You can jet up as far as you want, but if there's no fuel there in the first place......). Once removed it took a while to jet it back down to where it wanted to be, but it improved things no end.

Still used to blow pistons occasionally, but nowhere near as oftern (from pretty much fortnightly to once every fw months.)


She was a bit highly strung, but fast as hell

[kru251]

Oh I surely agree that if the flow rate is being restricted by any filter then you're in trouble! My take on it is as long as the surface area of the filter is much larger than the supply pipe's bore size and the intake/exit bore of the filter housing itself is at least equal to the fuel pipe then you won't do any harm and only do good. Now block the flter with fine sediment or use too small a bore inlet/outlet then there'll be tears before bedtime as my mother used to say!!! ;D

[Rudi]

Vespa started acting up at throttle opened too, so I decided to open the carb
found lots of particles and things...no wonder i had leaks and all these idle problems.. that were to come and go every now and then (thats why i didnt do it sooner, always thought- ah its fine now...)
I think I will fit a filter sometime soon...

[sbwnik]

That'll be the problem then....