High idle when warm, sluggish at top, getting a bit stumped.

[mike-s]

The GSX250 is still a pain in the arse, the compression thing has been sorted and it runs reasonably well at part throttle considering the tuning has gone to shit.

I have two separate, but still semi related problems here, the first i am trying to tackle is an idle when warmed up issue. It continually rises in revs to about 3-4k, which says to me that idle is running lean. I have got the idle screws out to about 1.75 turns out, i might try and progressively see if putting them out to 2.5 or even 2.75 turns out to see if this fixes this (naturally trying in 1/4 turn increments). If it doesn't, i'm going to start getting very confused very quickly. I would be very surprised if this turns out to require a larger pilot jet, even though i have a more free flowing exhaust than it did when i got it.

Once i sort that out i am going to work on the mid to top-end problem. Currently it runs to redline (10k redline) in 1st and 2nd, albeit with a bit of popping and farting at about half throttle, which it recovers from and goes to the top), but 3rd it runs slightly short to about 9.5 and in 4th I'm having a hard time convincing it to go over 7k or so, with 5th and 6th being equally dismal in behaviour. This problem seems much more tightly related to throttle position than it does to revs as around half throttle or more is the "magic point" where things go to crap.

The carbies are new (to me), the only reason i swapped them is that i managed to cock up and strip a couple of threads on it with some of my ham-fistedness. These new carbies have been given a clean-out and I'm reasonably happy with the job done, however I have moved the idle and main jets from the old carbies (they were pristine in condition) as they had been given a thorough clean-out and i know are ok. The Diaphragms are ok as they are acting like these as opposed to these and don't appear to be displaying any leaks upon holding them up to an extremely bright light.

The emulsion tubes have been removed and cleaned out (no problem looking through the cross-drilled holes or through from bottom to top. The carb intake manifold/boot was replaced a little while ago and i have only just replaced the o-ring between the head and manifold last week. Inspection of the manifold showed no cracks or splits at the edge nor anyway along the internal or external part of the intake tract.

The carbs came with 117.5 main jets, which i swapped down to my original 115's in case that was a contributing factor, despite the fact that i would have thought 117.5's more appropriate due to the much improved exhaust the bike now has.

I have also removed the airfilter and let it use just the built in mesh on the airbox, with no improvements observed.

Three courses of action i am considering are:
1) Checking the mechanical advance to make sure that it is operating within spec (20' advance at 2000rpm and the maximum advance of 40' chimes in at 4000 &* stays there all the way to redline).
2) swapping the emulsion tubes for that from my old carb, as i said, the only thing that was broken on the old ones was a stripped external thread, the symptoms are that it's receiving too much fuel, which work emulsion tubes would certainly provide.
3) Swapping the spring diaphragms & needle to the ones from my old carb as although not perfect were known to be good (and frankly it's easier to swap the whole assembly instead of removing the needle from the old sliders, as even the haynes manual i have say that this is a bastard of a thing to do).

Is there anything obvious that i am missing? this bike has been the spawn of satan for so long but is so close to working right it isn't funny.

[oldman]

With new carbs it's hard to tell but you have the classic symptoms of a vacuum leak, (air by-passing the carbs and going directly into the intake). This could be from several things; a disconnected vacuum hose, leaky carb gaskets, carb bolts not tightened properly etc. If it is that, you can find it by spraying something that smokes when it burns such as wd40 around the obvious places around the carbs. When you find the leak you will notice smoke plus an obvious change in idle, (Haha, 3000 rpm) speed. It could of course be just farked carbs but I would try finding a leak first. Jim Beam always assists in trouble shooting carbys. Just not more than 12 or 20 shots.

[mike-s]

Mr oldman i have probably killed my fair share of rainforest with spraying WD40 and other chemicals in an effort to see if i can identify the cause. I have to agree about the airleak symptom, finding it has proven to be a royal arse-ache however.

I have two candidate spots it could be at 1) the vacuum measuring points on sides of the head (they elected not to use mounts on the carb like every other bike i've ever had ) and 2) the vacuum hose/petcock

I have gone over near every other possible airleak spot permutation i can think of and have. I have recently replaced the hose for the vacuum switch, however foolishly i haven't tried testing the bikes running abilities with the vacuum hose pinched & the petcock on prime. Might try that in the afternoon tomorrow....

Once that is done i hope i get it working well and am going to start really crossing my fingers about getting this sonnavabitch running. I hope the airleak identifies itself, and once it does, the mysterious carb shitness magically fixes itself, otherwise there might be a suzuki on fire in the spectator area at the next Eastern Creek trackday, plus me with a jerrycan in one hand and molitov cocktail in the other..

[oldman]

Jim Beam will give you patience.

[P4nza]

Mike bring ur gsx around and we can fix yours and mine together ... well, try anyway!

[mike-s]

Sealing the synch stb holes did nothing. I've thought it through and the only thing that is still there from the past wonky setup is the intake boots. I also got a slight rise in revs when spraying around the r/hand boot base (the bit attached to the engine head) so i suspect theres a leak in the general visinity of those bits of gear. Metro wreckers have a couple spare for a good price, so i think i know where i'm heading tomorrow.

[mike-s]

This is how i spent my afternoon after it turns out aus-post are the useless dicks i expected them to be & didn't get the brazing rods to me today (though i must admit i was a bit optimistic for them to get here this quickly).

Have been dicking around with this for a bit, trying different options, at last i think i've made some headway. Pulled plugs left & right while running and it seems that my early suspicions were right, the left side isn't running well at idle, as pulling that HT lead made near no difference to the sound of the exhaust, except stopping a bit of popping and farting. Checked with a timing strobe and both cyl's are firing ok.

Took carbs out and did a ground up check of everything.Made sure both of them had every single passage cleared & figured out what each passage did & where it went. Both sides are fine. Out of curiosity i did a leak test, wearing a latex glove (i always wear gloves working on the bikes) i covered the intake venturi,and sealed the various fuel & vacuum plugs with fingertips and blew down the butterfly side as hard as i could. The cylinder that wasn't firing had no leak, however the one that was "working" had a micro small leak coming from the pilot needle as well as between the cv cap and the body. This was confirmed with soapy water & bubbles being blown by the leaky bits.

First i need to get new o-rings for the idle needle on both sides, then i'm going to figure out this cap thing. Sometimes putting things away for a while and coming back helps. I'm hoping this is the case here. So as it turns out, it's looking like the carb boots are a-ok which is good, as i've been given a 6 week lead time on getting them from suzuki

[oldman]

Have you done a compression check? I realize that compression or a lack of will not cause a high idle. But it is an easy test and you might be chasing two problems and don't know it.
Another thing a lot of people don't know is that when checking compression, four shots of Jim Beam and a brew make the compression higher, (drink it, don't pour it down the carbys).
This is an old family secret so please keep it to yourself.

[Strika]

If it's only idling high when warm, it has to be an air leak or the slides holding up.

FYI, Oldman, mike has done a comp test already.

[mike-s]

Redid the comp test for the sheer sake of it while i did all that, 140psi right on the button left & right.
Just called bike shop, suzuki-aust has exactly ONE of the o-rings i need in stock. Good enough for getting things sorted, bad in that i have a habit of replacing all of one thing simultaneously to give it the best chance of working correctly and this goes against that. Oh well I can live with just the one then.

I've decided to be as methodical as hell about this as it's turned into suck a royal "see you next Tuesday" of a trouble to track down. O rings & caps on the carbs first, with a thorough clean of every orifice in the carbs and moving the old emulsion tubes to replace the new (and not yet proven as any good to me) parts in there. We'll see where that leads.

[mike-s]

Fixed the Mutherf*cker. There WAS an airleak between a cv cap and a carb body as well as a slight airleak on the o-ring on the idle needle on the same carb. As this made the one cylinder run well before the other it made the idle sync all fucked up and impossible to sort out. Also it turns out that the throttle cable adjustment was out a bit as well, which was my cockup .

Looking forward to payday so i can re-register it & take her out for a blast .

[P4nza]

Wanna buy another one? with spares?

[mike-s]

God no, two bikes are enough for me and i think the wife would kill me if i took you up on that offer.

[Strika]

Glad to hear you have it sorted mate!