Too Weak Idle?

[cuxoni]

Hi,

I've recently rebuilt my first engine, I'm running a GT186 kit with PHBL25, KBA clubman and a ramair remote filter. Everything seems OK apart from 4 stroking at 1/8th throttle. After that it seems pretty good, though cos I've only done 100-odd miles I'm still taking things a bit steady. I've left the jetting as per the standard advice as, but reducing the ilde jet from a 55 down to a 45 with the screw all the way in has reduced it but not got rid of it completely. I thought the choke was sticking on maybe, but it wasn't. I also ruined a 40 slide by shaving bits off with a file cos I thought maybe it was a rich slide, but it wasn't that either. The tickover seems OK but quite fast now, though not hunting up and down so I'm not sure it is too weak, I'm just worried if I drop any leaner I might be in dangerous terretory, if I'm not already. I'm considering an even weaker idle jet or dropping the needle next but I don't want to be making it too lean in other areas when it's only four stroking just off idle.

How lean can I go before I need to worry? Any other ideas would be greatly received....

Main Jet 95
Needle D22 3rd clip from Bottom
AQ266
Slide 40
Pilot 45 screwed right the way in

Bloody scooters.

Cheers

[hullygully]

you shouldn't be screwing your airscrew in all the way, screw it back out between 1 1/2 - 2 turns, your slide (pre-mod seems ok), as are your needle/atomisor combo (maybe move your needle to 2nd from top), when she's ticking over fast does it rev up & settle down with the choke 1/4 to 1/2 on?

[cuxoni]

Thanks. I started out with it 2 turns out but progressivley turned in in a quarter, test drove it, in another quarter, etc until it was all the way in and it seemed a bit better the more it went in. Still a little 4 strokey but less intense than with it out at 2 turns. The clip is 2nd from top I think, which is the same as 3rd from bottom if my counting is right? I'm back on a 40 slide now, the ruined one is on the shelf, I'll give what you're saying a go later and report back.

Cheers.

[CHRIS in MARGATE]

Have you tried it with the filter off?

[bsso78]

Try
X7 needle
AV264 atomiser
Main probably around 100 possibly a bit bigger
Pilot shouldnt be far off but try a 50 and work down
Slide was alright before the file
Mixture at 1 1/4 and see what thats like

I think you are running off the shelf (ish) jetting from Dellorto

[cuxoni]

I tried the putting the choke on a bit while it's ticking over and it just wants to cut out. With the air filter off it's the same. I also had a 40 idle jet which I've tried and it's still doing it. Currently that's on at 1.5 turns out. I tried dropping the needle, that just made it unresponsive when I opened the throttle.

I'll give bsso78's suggestion a go but when I'm googling the x7 and AV264 its saying that they're for a PHBH not PHBL. Am I looking in the wrong place or will these also fit the PHBL?

Cheers

[johnnyXS]

The idle mixture is produced by your pilot jet , air screw and the slide . It does not involve the Atomiser, main jet, venturi or needle at all. leave them alone whilst tuning your idle or you'll just complicate things
At the moment it sounds like you are trying to tune the whole throttle range simultaneously which is impossible.

I would suggest that you tune just the idle mixture first and get your tickover stable and the correct mixture before moving on to your throttle transition .Your pilot and idle mixture has an influence right through the throttle range up to full throttle so you need to get that right first.

If your idle is up at 1200rpm its too high .This is probably why the engine is bogging when you apply some choke on idle ...its too rich. At 1200+rpm the engine is starting to draw fuel and air from the atomiser ventui and needle jet which it shouldn't be.
if you are unable to get your idle stable and lower than 1200rpm by adjusting your idle air screw with a 40/45 pilot jet and your current slide then you probably have an air leak somewhere on the inlet.

Check your inlet carefully , try spraying WD40 between the carb and the inlet and see if the engine reacts after about 3-5 seconds or so which would indicate an air leak.

[2ndtimearound]

Your problem sounds very similar to the one I`ve just had - read my post about 10 down from yours -" PHBL carbs again-sorry".
As jonny XS said, it does sound like an air leak & mine was the MB manifold catching on the cylinder fin & not sealing, but it looked ok, I just couldn`t see it until I took the engine out & cowling off.
Good luck with it, I know it must be driving you nuts, but it will be great when you sort it!!!!

[cuxoni]

OK, I had the air filter running though a normal type air filter rubber mount, I think maybe there was a leak in that somewhere. I've also made double sure there are no others by dropping the engine, taking off the manifold, making sure the gaskets are good, put a bit of grease on them, back in and tightened right down.

I can now get a more consistant tickover using a 45 idle jet 1.5 turns out - I dunno if this is the correct way to count the revs but i'm counting 4-5 'pops' per second, so does that make it 300 RPM? Is that pretty low? Should I be going for a faster one? I'm not sure how fast/slow it should be.

Pulling off seems a bit better, but there's still some richness, I looked at the plug and its pretty oily and it's still not 100% smooth pulling off. Should I try going a bit weaker with the idle? Or Maybe order a propper leaner slide than butchering my own?

[johnnyXS]

well done thats good progress.
There had to be at least one air leak from your description.

45 pilot and 1.5 turns out sounds just about perfect.
Your idle speed might still be a little high but without a video its impossible to say. Don't be afraid to experiment a bit with the idle. its really crucial to get it right as it makes everything else easier to tune in.if you get the tick over too low it will just keep cutting out or sound unstable so you'll know when you have it right.

Oil on your plug is not a sign of richness its more likely to be the result of a leaking oil seal in the crankcase . Only a pressure leakdown test will tell you that.
What spark plug are you using ? you might need to change your plug for a hotter one which will help burn the oil off.

You need to clean the plug carefully and go for a good run to get the engine up to temperature and see what the colour of the ceramic part of the plug looks like then.You are looking for a light tan to coffee colour .tell us how the throttle performs if there is any bogging when snapping the throttle open or any surging when cruising speed etc

[cuxoni]

Thanks for the help. I'm hoping it's not a leaking seal cos it's brand new from the rebuild. It might not be oil, it was just really black looking. The plug is an NGK B7ES. I rode it to work just now, I was in 2 minds as because I've got the RAM filter directly on the carb now it touchs up against the side panel but I took it round the block first and it seemed ok. The only issue when I snap open the throttle is if I open it right up from low speed/revs, as it builds it starts to choke a bit - a sort of lumpyness. I guess that might be air starvation now the filter is been restricted a bit, I'll try it with the panels off. In fairness I'd never ride it like that normally anyway so maybe I'm better off with it straight on the carb rather than through the rubber as it seems like a bit of a bodge doing that anyway. If I build speed in a normal way and keep it revvy it seems fine.

I can probably put up with the 4 stroking but it's be really nice to get this one little last issue sorted. It makes the whole bike vibrate when I'm filtering through traffic which is a bit of a pain!

[johnnyXS]

that bogging you get when snapping the throttle open is often caused by too much air rather than too little.
When you snap your throttle open the engine suddenly creates a huge vacuum which lifts your slide and needle and sucks fuel from your Atomiser into the venturi.

The larger the venturi the less strong the suction (think of hose pipe and straw) so the less fuel is delivered at that precise moment hence the bogging.
You can check this . When the engine is next warmed up try removing the air filter and snapping the throttle open a few times . Then partially cover the carb venturi and snap the throttle open again. Vary the amount you block the venturi and You'll probably find a spot where the engine will pull strongly and cleanly without hesitation.

That said the initial idle to 1/4 throttle is controlled by the pilot jet the air screw and the cutout in the slide.
If you have a good stable idle with the 45 pilot and 1.5 turn air screw setting then I suspect that it is your slide that is now creating this particular problem.
I seem to remember you 'modified it ' a little ?

Try rolling on the throttle slowly and pulling away gently...how does it perform? If the engine still tends to die initially then your slide is probably too lean and you may need a richer slide. To prove this try the same test with half choke on and if it improves you know the mixture is too lean.

if the engine splutters but keeps going the slide is likely to be too rich .

if its too lean you could try installing a 50 pilot and readjusting your air screw and see if the snap throttle improves.

I don't know enough about these carbs especially used with Ramair filters so I'll let others advise on trying a different slide.

[cuxoni]

It's certainly more spluttery than weak. It doesnt slow down or seem weak, just splutters a bit but keeps moving. The 'modified' slide was replaced with a new one a while ago when I realised I'd screwed it up. I went out at lunch and It definately seems a little better now the air leak is repaired, I might just see how I get on for a bit and then try a leaner slide if I decide I want to spend 35 quid on a tiny peice of aluminium. It isn't causing me a major problem it's just an annoyance. Thanks for the advice.