Most peculiar
 

Hello all, is it me or has petrol quality/composition changed over the past fortnight here in dear old blighty?

Been using the St4s for daily 120 mile round trip to work, and over the past fortnight its' developed a quirk, to-wit
after a longish spell at motorway speeds when the throttle is then shut off quickly it will maybe stall, or spit back through the intake or both.
The normal running temp is up by @ 2 degrees at 73 (C) ,
and I'm getting better MPG, on standard 95 unleaded.
It also likes full 'choke' now to start, rather than 1/2 as before.

All of which would seem to indicate the old girl (26,000 miles) is running lean, but I haven't had any of the settings changed, that I know of.

I've got a few days off work now so I'm going to check the air filter and ducts for leaks just in case.

What do you think?

I think that petrol vaies from supplier to supplier. Are you judging a level field here with fuel from the same garage?

I hired a petrol van once and the yard was behind a Fina garage. It had no fuel in it so I had to fill up there. It ran rough as hell all the way down to london and used a tank of fuel to do it (just over 100 miles). I filled up at services there and it ran like the proverbial **** off a shovel all the way to Bournemouth and got far better mileage. Needless to say, never used Fina again! Cound have been dodgy fuel from any of them though really.

My ST4 was idling low in hot weather here and sometimes stalling in traffic. Took it to the dealer and he was going to adjust the idle, but instead he shot carb cleaner into the air intakes and also used some carb conditioner (foam) to clean them off. I got an instant 200 rpm increase on idle. he said that slow speed running can build carbon up near the air intakes of the injector and that is what slowed the idle down. COuld this be similar to what is happening to you?

Here's an update, took a look at air filter etc, all ok in there,no split inlet trunks either.
I'm using petrol from the same source,which I've used for past 2 years now because of problems with dodgy supermarket petrol previously.

Its' working out at 132 miles round trip between fill ups, and working out at 46.15 mpg which I'm not complaining about with current price of petrol.

However,to my mind something still not right. I'll give it a shot of carb cleaner and see what happens.......

Pete

strangely I've had my st2 popping on engine braking, thats only been the last couple of weeks O_o Obivously coincidence.

Check your fuel filter, it may be causing you to run a little lean.

be scientific. do one thing at a time and check the results before moving on.

A couple of years ago I was geting erratic running on my ST4, which actually caused a finger numbing vibration through the bars. In the end it turned out to be sticky/gummed injectors.

I treated it to a good dose of Redex just before a motorway trip and it cleaned it out and cured the vibration.

I now put a shot through every so often to keep it clean.

I dont think that petrol has the shelf life that it used to and is certainly more prone to gumming up the cabs on my singles. Now if I am not going to use a biked for a while I drain the carb, before I put it away.

I have just picked up an early Pantah for renovation and I have had to throw float needles and some jets away as the gummed on petrol wont come off, even with carb cleaner.

[Edited on 8-9-2005 by ChrisBushell]

This is an unwanted byproduct of current unleaded petrols. Before consigning your carburator parts to the bin try leaving them immersed in cellulose thinners for a few days. It usually softens the gums and lacquers left by dried up petrol.

How much Redex and how often do you squirt it in, is there only one flavour, thanks.