GSX 250 spluttering over 45 - 50 Carbs ? elecs ?

[ukjules]

I have a problem.

Currently it runs poorly at higher speeds .... 45 plu ..(ho ho)
(It has only a few weeks ago run ok all the way up the power band so this is a new issue)
When it was running fine i noticed petrol leaking out of the carbs air inlet
when i stopped. to fix this i started looking at the petcock and carbs etc.
I am now at this stage with all ok bar this spluttering at mid range speeds?


start up and tick over it is absolutely perfect - it sounds spot on.
It as if it is cutting out or running out of petrol above 50mph ? like it does when it
needs to be out on reserve. Or the electrics are cutting out ?

I have taken the carbs off at least 10 times this week to fix this and am completely stumped.

-Valve clearances spot on
-plug gap ok - and a spark on both
-Carbs removed, dismantled and cleaned 3 times now in one week.
Various new bits stuck in.
-Tank removed - chemically cleaned and washed out - petcock not leaking and cleaned out.
-coils checked - both primary - 4.25ohms both sec - 11000 ohms without plug on
- both plug caps ok

what next do you think ? ATU , pick ups ? coils ? carbs ? HELP

 

[hampshirehog]

Does it run ok on half throttle at 50?

 

[ukjules]

At present:
Yes it is ok at half throttle at med speeds 40 -50.
As soon as i try and open it up it hesitates as described ?

Are you thinking the various circuits in the carb ? By pure chance it is blocked again on a jet somewhere ?

 

[hampshirehog]

Yes, it sounds like a fuel problem so either the carbs (a blockage somewhere) or the tap isn't delivering enough fuel.

 

[ukjules]

would you think

a) remove petcock and put new seals etc on (i am yet to do this as a single
tank to petcock seal solved my initial problem with a air blow out)
Test
if still issue
b) off with carbs again and clean ....

 

[hampshirehog]

If your tap has got a prime position that stays on prime by itself (rather than using a vacuum to set it off) I would try running it down the road to see if the problem occurs. Also check, by pulling the fuel pipe off, that there's plenty of fuel coming out.

Another thought, your tank breather could be blocked and you could be creating a partial vacuum in your tank. You can test this by running without the filler cap on.

 

[ukjules]

I have tried it down the road over 3 miles and it happens probably over a 1/4 turn on throttle.
The idle is as perfect as have known it !

will try those tests tomorrow , cap off and check the prime (it is screwed in)
the thing is this did work ok 2 weeks ago. I did a 30mile run on it
and it behaved ok.

 

[ukjules]

-Stripped down carbs again cleaned out and there was again dirt about
and pilot jet was blocked and needle valve seat filter had dirt under it
-Off with petcock and cleaned.
There must have still been dirt somehow in the tank ?

rode down the road, running on one cylinder (remember both have good spark)
the minutist turn of the throttle conked the bike out.

Stripped bottom of carbs down again - pilot jet blocked - but carbs clean
Engine started and fired on both cylinders - perfectly.

Went down the road and again it hesitates over 5k revs ?
also with the fuel cap off no difference.

when i am stationary it revs freely to 5,6,7 revs no probs.

How can it be when driving it along it hesitates at 5k upwards ?

It is not in me to clean the carbs anymore , there simply cannot be any more dirt anywhere ?
Or do i ?

 

[Gorminrider]

petcock troubles- if the bike works ok running on prime (you are testing this) ? but if not
It still sounds like a fuel issue. Don't some 250's have fuel atomiser screens? Does yours? are they missing? check fiche.....if ok, Dirty jet seem most likely, seeing that you still have Crap showing at the fuel tap and jets .....confirm that you are actually removing and cleaning main jet.Cleaning just the bottom of carb is not cleaning it, given your symptoms, IMO... You need to disassemble vacuum diaphragm and pull slides out to push the main jets up and out. Tiny holes block easily. Use a tiny strand of stiff wire (destranded fine wire cable can work or the finest welding-tip cleaner) to clear these without enlarging them.

when i am stationary it revs freely to 5,6,7 revs no probs

I'm not sure about that high , but Motors can rev up pretty high unloaded and lean but still gasp under load. The more you open the throttle, the more you are lifting the main jet needle ,drawing gas from main jets. .... If pulling the "choke"enricher improves things when riding, that indicates not enough fuel at one or both carbs main jets ... perhaps in some cases raising the needle a notch if someone has tinkered with these previously....and....do you have "pods"? =wrong jets?
OR even timing. rare, but Check your spark advance mechanism.

 

[ukjules]

Ok all taken on board.
Ill have news imminently after this test run ....

By the way i was "completely dismantling" the carbs - completely top and bottom over the past few days.
Normal air filter

 

[ukjules]

Work done:
Petcock removed , cleaned (but was clean)
there are no fuel atomizer screens ..

Both Carbs removed, dismantled "totally", new needle jet, main jet , pilot jet, float valve and float valve holder put in.
cleaned out top and bottom and blown out.

Initial run it went fine.

Took it for a 20 mile run and it started (not as bad as before though) to hesitate again.
Petrol put in and it went better.
It now goes ok but does hesitate on occasions. I simply cannot guarantee it not
to start hesitating but never below 30 , low throttle.

Note: have yet to test it with the prime on (unscrewed on my bike)
I have tested the bike with a external tank when working on it and it runs fine.

I will do the prime test tomorrow and take i for a 10 mile run and see if this
changes anything.
Ill also check pulling the choke on when it does this "hesitation"

It is not as bad as it was though ! I dont know what this fact makes it point too - fuel still i think.
Plugs , valves , Carb sync, coils ....... all spot on.

timing however - it is set ok when looking at the camshafts as per manual but with my timing gun
it is not right. Ill check again tomorrow .
the issue here is there is no big changs you can make here - you cant rotate the pickups much.

 

[ukjules]

Test:

7 mile run and again it was very mildly hesitating.

Use the choke when it is "hesitating" - It went worse (someone told me to try this)
This is what I would have expected anyway.

Run on prime - For 4 miles back I did this and I am sure it went a lot better if not perfectly.
The prime screw unfortunately leaks (out of the screw) when in use so could not use it too long.
(The petcock repair kit does not come with new washers and minute seal for this screw)

For the last 3 miles i put it back to normal and it went i would say as good as it could go.
No different to prime but for the first time.

Clearly something has happened with this mass of changes .... I wish i new what !
Will test further with a long run today and inform.

 

[Gorminrider]

...but you are making progress! I am suspecting the petcock given your comments. so I'll pontificate on it at length, if you can stand it! Petcock issues are very common. I have had these same symptoms from bad petcocks.

,For the last 3 miles i put it back to normal and it went i would say as good as it could go

. the bike will run/coast quite a long way after filling the bowls up on PRIME,but petcock is still faulty...These bikes sip gas. Petcocks can be intermittent. Fuel level can make a difference in the most finicky cases....ie: full tank has more pressure against the tap. You haven't fixed it by accident, IMO.

A replacement can be bought, but they are really expensive and I would try to fix it temporarily to confirm the $ is well spent. Also, DO YOU HAVE THE SQUARISH TANK? the replacements offered often seem to have the outlet going the wrong way and on my GSX400E, the bike frame is in the way of the fuel line. Something to check... Can be worked around but better not to if possible. You also have to be careful with rebuild kits. The diaphragm might be is larger on yours...


"Plumbers string" can be very handy. It's just cotton string you might try around the threads to stop the drip while testing. I'd try string first. but you can also take the tap apart and disable the vacuum operation for testing by several ways... removing the spring,or putting it on the wrong side etc to keep the valve open, but then you have no shutoff. Be sure to keep the diaphragm and the fibre washer in order if you disassemble. You need to ensure the floats and needles are working too, of course.

Of course you can test the vacuum tap by attaching a tube to the vacuum port and sucking on it but this is not a guarantee of correct operation ...it doesn't duplicate what actually happens ...it actually pulsates with the piston .... ONE successful fix I think I have found for my own intermittent "vacuum plunger" is to replace the tiny o-ring with the next size up if you can find a hardware or fastener shop that has a drawer full of o-rings. I can't remember what the PRIMEscrew has for sealing (mine works) but again you may find it locally cheap.

I wouldn't worry about the timing. Not the problem, given you have it going ok some of the time....I just tossed it in in case the centrifigal advancing weights behind the pickups were rusted solid or stuck on a badly routed wire or something. Someone recently had this .

 

[Guest]

I'm no petcock expert, but the early ones had a one way vacuum check valve with a bleed so they took a while to shut off and also took far less vacuum to hold open. I figure if I could go 115 mph with an 850 sucking on it, the thing should easily keep up with a twin. The later ball valve style petcocks are cheaper to make but either they left the one way valve out or I've never had one that worked.

I just gave up on the new and improved style and run the original type; no problems. If it runs okay on Prime and starves under load on On then you've got a problem. I've also seen the little spring on the diaphragm stretched out by idiots trying to cure a leak; that'll do it for sure.

On the old ones you can fill in the curved recess on the selector plate with epoxy and then leave the spring out or whatever. That gives you Res, On and Off. The new style one would require plugging the small passage in the ball. You lose prime, but On becomes Prime if you sabotage the vacuum valve.

 

[ukjules]

Excellent advice and I will act on this tomorrow and inform how it goes,
The hesitation issue did continue today but I have again cleaned the carbs and will do another test tomorrow.
I have not touched the petcock !
But the hesitation over 4-5k was definitely present in both prime engaged and not engaged.
It is not any better and the carbs are clean.

Many thanks.

I will add some pictures tomorrow as I am sure this is going to be a troublesome fix.
The bike type is as in pic

 

[ukjules]

Took the bike out for a test run this morning full of hope.
- again anything over 4500 revs it spluttered and hesitated

Pulled the petcock off - put plumbers tape on the prime screw thread.
For the first time the tank did not leak when off in the standard position.
I was hopeful at this point.

-Took the bike out and again exactly the same issue
-unscrewed the prime and exactly the same issue - hesitation

It is beyond me this one - how can a bike be in perfect tune below 4500 revs
and when on the road anything above it it starts to hesitate / splutter ?

I have ordered another petcock off eBay (second hand so a risk)

I did leave the spring out to see what would happen but it simply poured out
of the fuel pipe. This is what was wanted but i could not get it connected quick
enough without getting soaked in petrol.

I am beginning to return to the cdi unit ?
I wonder if it is the wrong one ?

anyway ill try the other petcock when it arrives.
consider the cdi unit ?
if this fails ill buy a new petcock

if that fails i am totaly stumped

 

[Gorminrider]

CDI looks to be very similar to mine on GSX 400's. Looks like it has been replaced from a wreckers given the painted label....Does it indicate the Previous owner had the same problem and has followed the "faulty CDI" path already?

Another easy way to be too lean is leaking rubber carb boots at the intake manifold...but I think the "symptoms" would be the case at lower rpm too, when you are starting off.... it's not an issue I have had so someone might chime in..
Also, Confirm for us you don't have "pods"? and that the bike has stock airbox .

if that fails i am totaly stumped

Don't say that. It's just something wrong on a list that grows shorter. Often on these threads, it's something simple that you discover all by yourself. Consider us to be blind men in a dark room with only your verbal clues coming in via speakers.

so, some eclectic problems it might turn out to be:
-the resistors inside the spark-plug cap, (but I readon another thread you have replaced these caps? hate to say it, but sometimes the last thing you did is the first place to revisit )
-stuck advance weights,
-faulty spark plugs (You should change these now if you don't know how old they are because I bet you will when the bike runs perfectly anyways, so why not do it now?)
-a loose or leaky power connection with a symptom that you might not bother to tell us or haven't noticed yet ie: headlamp dims/flickers because key switch poor

 

[ukjules]

Notes:

-My bike has the standard airbox on it , a foam filter.
-carb - cylinder head inlet rubber i am sure are ok and give good seals - will double check
-looking at the cdi unit it is the right one but as you say someone has changed it - unknown why and if it sorted the issue.
-the plugs i renewed but used ngk instead of what was in there (one was faulty)
-Valve clearance all within limits
-Good compression stats
-No electrical issue i can think of

Remember it runs as sweet as you can imagine ticking over and up to 4000 -4500 revs.
It then jutters and stutters and if i am annoyed i thrash it and it clears and runs ok from 6500 - 9000 revs.
(I dont like doing this though and this too might be intermittent.

I can now take the carbs off , strip them down totally and replace in 1 hour as
I have done it so much.

Next:
1)I will get new plugs an check again ht leads and coil as it is simple.
I wil get the other type - x277esr-u if i can

2) Another petcock has been posted and will try that one

3) i do have a loose connection that i thought / think i have fixed.
It is on the starter solenoid and "occasionally " when i switch on i have to jiggle the wire !
"I hear you all gasp now .....!"
I sorted this last night but again my electrical connections skills are crap.
It is the live from the battery through the fuse and on.
Thinking about it if i tugged on this going along it might give that very fault ?
But why every time at 4-4500 revs ?

4) AtU i am sure is ok and moves freely.

 

[Guest]

It's possible that the needle is in the wrong position. Once you get the slides up and it's on the main jet it runs but the middle rpm, partial slide up, may be lean. Or way rich. Do you have a spec for the stock needle position, or are you just assuming that where it was when you got the bike is the original setting?

Suzuki also was very proud of their 'twin swirl's' ability to run on lean mixtures; remember, this was the 'lean burn' era. So probably the same guy set up the stock carb settings as did the GSX400 and they are on the edge of lean surge. Raising the needles a notch from stock - whatever that was - is usually a good move, especially in view of modern gasoline which tends to be rather 'lean' - read adulterated - to begin with. I find that if you're on the edge of mixture, even a change of brands of gas can put you over. Modern feedback loop FI eliminated the reason for the oil companies to get too fussy. Even my Honda lawnmower will surge on anything but ethanol free 94. A difference in gasoline density or viscosity will throw your carbonation off.

If it's like the GSX400 carb, there will be some spacers in there and you need to get it all in the right order, but the results can be measured by comparing the needle projection from the base of the slide. IOW, take notes. It looks like you're moving the needle a lot, but as a percentage of how far the slide moves it's not that much.

The nice part is that you only have to take the top off the carb to access the slides and needles; easy stuff. Glad to hear that it does 6500 to 9000.

I'm kind of a 250cc light bike fan, but in Canada we never got the GSX250E because the insurance cutoff was at 400cc. I've always wanted to thrash the daylights out of one?..just because. I'd buy one in a heartbeat and see how low and light I could get it?.

 

[Gorminrider]

Ok, well, I went back and listed things

-a few weeks ago run ok all the way up the power band so this is a new issue

-When it was running fine i noticed petrol leaking out of the carbs air inlet

- soon as i try and open it up it hesitates as described...it happens probably over a 1/4 turn on throttle

-Carbs removed, dismantled "totally", new needle jet, main jet , pilot jet, float valve and float valve holder put in ...Initial run it went fine. Took it for a 20 mile run and it started (not as bad as before though) to hesitate again....Petrol put in and it went better.

-(applied) the choke when it is "hesitating" - It went worse
-unscrewed the prime and exactly the same issue - hesitation

There were also petcock troubles in the mix but that can now be worked around....The first is the very important- Something has changed since you got the bike. Otherwise given new info of bike running ok above 6500, perhaps the slides are sticking or there is trouble with the cv diapragm. DID you take care to replace it correctly? You can test for proper operation of CV slides by lifting slides with your finger and plugging the lozenge-shaped hole on the air-box end with your thumb. Slides should fall very slowly. At least that's how mine work on two well-running bikes and the spare carbs I have. It is a pretty ez test if you can get at them. On my bike airbox can be wobbled back aways especially if I unbolt the section of rear fender there and shift it off the knobs...hard to explain but the bodywork on my GSX400E is identical to yours, I think.

and John Park mentioned needle settings a good possibility especially if people have been in and out of there a lot. I have a set of spares so I can check out what is stock setting if my 400's carbs are identical, but given they are identical , is there a possibility 250's would be set a step leaner or richer? to allow the same carbs to be used? (Beyond my paygrade,this... )