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 .

[John Park]

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

gsx250 pic.jpg