GSXR750 G starting probs...and only firing on 2 cylinders?

[Mudskipper]

Bear with me please, I have done a search but can't see any posts with my specific issues.

Got a new battery for my slabby, fully charged and also trying to start with a booster pack.

Will start eventually on full choke, when it does it idles but hideously roughly and cuts out shortly after or if choke or throttle are touched.

All 4 plugs spark outside the engine, but none look particularly strong (not entirely sure how big the sparks should be). They are new plugs. HT leads all seem in good condition and snug fitting.

When it does start and is run for a min or two, exhausts 1 & 2 (from left) are hot, 3 and 4 are stone cold. So on 2 cylinders, probably why the idle sounds so rough (and then cuts out?).

Fuel tap is on, gallon of fresh fuel in tank, not sure of condition of carbs but has been stood (with occasional attempts at starting) for about 6 months now.

What should I be looking at/testing next? Coils? CDI unit? Straight to carbs? Anything I've overlooked?

Cheers
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CBR125|||GSXR400|||CBR400|||CBR400|||CB250RS|||GSXR750|||CB250RS
"You're clumsy, you eat too much and you behave like a 12 year old boy. But you know what? Every once in a while, you find a thumb."

[lonner]

personally id go straight to the carbs
check and a good clean is best imo (have you looked at the diaphragm's lately as they could be perished on an early gixer)hth

[Kickstart]

Hi

Those 2 cylinders are fed by different coils (or should be, check the HT leads are on the right way round), which probably counts out the ignition system.

Worth doing a compression check to ensure that the head gasket hasn't gone between those 2 cylinders.

But most likely I would hope would be something preventing fuel getting to the 2 carbs on that side.

[NiteMare]

if it's still got the original carbs then as Kickstart says they'll be flatslides (no diaphragm)

most likely you have two HT leads on the wrong cylinders, 1 and 4 are fed by the same coil, as are 2 and 3 are fed by the other coil (wasted spark system) swap the leads on plugs 3 and 4 being as they're the cold ones....

if it's not that then your tank should have three pipes coming from the tap, one is the vacuum pipe, the other two feed fuel to the carbs ...

you "possibly" have a blockage in the pipe that feeds carbs for cylinders 3 and 4 (unlikely but not unheard of)...

check the HT leads are on the correct plugs first ...

if that doesn't solve it then check the fuel is flowing correctly when the tap is put on "prime" (use the carb drain screws)...

finally bung up a side on photo of the bike (so we can see the carbs) then there's enough of us here to help a little more if needed
____________________
it ain't broke...

i ain't fixed it enough

[bootsbiker]

i got 1 of these with a similar problem. I think my problem is the low voltage of the old battery.. =12.15v at most.. turns engine but not enough to get a nice blue spark..

I think it is funny that 2 of the carbs don't work and think that a block is where i would look.. maybe a kink(can i say that) in the pipe more then a blockage(same thing)..

Anyway i been thinking about taking of the carbs and cleaning them.. They look like a nightmare 2 remove.. I think that the inlet manifolds need to be removed.. Question is do they go into the airbox..?

[NiteMare]

[bootsbiker]

i took out the sparks and cleaned them.. They look good.. Got my mate around with his transit and tried to jump it, wouldn't start and it was down to no-spark.. First i cleaned the connect to the CDi.. YUK.. That wasn't the problem.. a connector come lose from the CDi to the coils. DUH

Replaced it now and i getting a dull spark, but a spark.. Problem now is m8 has gone home Tomorrow is a new day..

I am 100% sure the battery is a gonna. Can tell just by the way the starter motor turns..

"flatties from a slabby" not use to the jargon,, think I know what u mean

If any1 can tell me to remove the carbs without to much brain power would help.. I hate doing things blind..

cheers Boots

[NiteMare]

if you really want the best possible source of information regarding your slabby i suggest you register with "old skool suzuki" ...

introduce your self in "general" then dive into "oilcooled" with your question of "how to remove carbs", there'll be plenty of folks there that'll be able to tell you exactly the procedure

P.S.
i wouldn't remove them until you've tried jump starting it again, there's absolutely no point in making work for yourself
____________________
it ain't broke...

i ain't fixed it enough

[NiteMare]

just an extra to my previous posts regarding "flatties" ...

apparently they rattle quite loudly, this can vary quite a bit depending on wear but they rattled from new ...

so don't get too panicky about the strange noises
____________________
it ain't broke...

i ain't fixed it enough

[Kickstart]

Hi

I second OldSkoolSuzuki for stuff on oil cooled ones (amoung other stuff)

[Robby]

If it was running ok previously then the HT leads shouldn't be a problem, unless you put them on wrong when you put them back.

Remember 90% of carb problems are in fact electrical.

So, we know coils are working. Give the HT leads a good spray with WD40 and make sure they are connected right.
You have a charged battery and a booster pack, so we can assume enough power in the system regadless of whether the alternator is behaving.

Mechanical issues - obscenely tight valves could make it difficult to start, but if it was running ok prior to being stored then they don't have any reasons to have changed.

So for once I would go with the idea of checking carbs. I'd just clean the jets out to start with. If you're very lucky you may be able to get the float bowls off and the jets out from underneath without removing the carbs. Look through the jets and see if they look blocked, or have deposits of varnish on.

Secret option number 3 - Keep on trying to start it, and keep it running for as long as you can. A little heat into the engine and suddounding area, with some fresh fuel running through your carbs, could clear any blockage or dry out any dampness.

If you have to do this for a while, follow up with an oil change. Putting lots of neat fuel through a cylinder than isn't burning it could end up with fuel seeping down into your oil. If it's been laid up and you're putting it back on the road an oil change is a good idea anyway.

[bootsbiker]

cool thanks Keith..

I found a book in the WWW from Haynes about carbs but haven't looked at it yet but will... That is a good start..

[NiteMare]

[bootsbiker]

I wasn't going to use it for the bike... Just out of interest and nice to have free info etc... I like the pic as well..

We covered carbs in college but only just.. Fuel injection was the topic(cars)..

Bit off subject... are all new models of bikes fuel injected now or are they putting in carbs still in new models??

You r right through should just find a manual..

[NiteMare]

i've no idea to be honest about new models although i suspect most that are produced 500cc or less will still be carbed for another couple of years ...

but i doubt it will be for too much longer as even harley are fitting fuel injection now due to the emmission laws
____________________
it ain't broke...

i ain't fixed it enough

[Kickstart]

Hi

Few bikes are still carbed (eg, Aprilia RS125, although it is an electrically controlled carb), but pretty rare now.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[lonner]

[Ichy]

FWIW.

My old GSX used to do exactally the same if it was left for any time. It would be a pain to get going and then only run on two cylinders for a few minutes with loads of back fires.

I used to connect it to my car battery then either heat up or swap the plugs on 3 and 4 and they would eventually fire up and run fine.

I'd definately do what nightmare suggested and make sure the plugs are connect correctly, done it myself plenty of times.

New plugs can work wonders.

I've owned loads of bikes over the years and have only needed to clean the carb once due to varnish blocking the jets. That bike hadn't moved for 8 years. My old GS wasn't used for three years and started up in minutes with a gallon of petrol, warm plugs and a car battery.

Are you running pod filters or standard?
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[bootsbiker]

sorry Mudskipper for butting you thread but didn't want to start 1 myself.. this is more of an update

ok.
Mate came back and we hooked up the transit and if by magic it started with 15s.. I did spray some easy start (i didn't say that) but that was yesterday so i reckon it has vaporized over night.. c how it goes with it's own power source..

It was only running a few minutes and cut out but we unhooked it etc.. Was coughing a bit but hasn't run for a while and its cold.. will put a new battery in and then run it for a while on idle.. would go 4 a ride but no tax or mot..

I joined that forum but havin asked about the carbs yet.. Still would like to clean them but it can wait..

now the forks seals.. god damn the rain..

[Mudskipper]

Thanks everyone, all very helpful stuff.

I will definitely check the HT leads are the right way round first! It's very possible I've done that. Just need to recharge battery & power pack first. Will check for obvious kinks in the fuel line too.

[bootsbiker]

to heat up the plugs=== i would put them in the oven.. not the microwave..

[damz]

i had the same problem as my fzr

bassically start it up, wont start for a sec or two then will idle badly for about 15 secs then cut out, then if you turn the throttle it cuts out instantly.

at first i thought it was a flat battery as it hadnt been used in a while so tried to jump start it from my other bike and blew a few fuses, after sorting that out i started it again and same problem after charging the battery with a new battery charger.

i just kept my thumb on the starter button while it was idling roughly with full choke on and it kept running and after a min or two it was fine.

been riding the bike all afternoon and seems fine now so my guess was spark plugs.
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Current Bikes RVF400 - 94
Cars: RX7 FD, Eunos Roadster
Former Bikes: FZR 250R 89, ZX7R 98

[NiteMare]

i just use a blowlamp on plugs (forget about wasting oven gas ), if you haven't got a blowlamp use the gas "ring" on top of the oven ...

obviously you take the plugs out first, then play the flame onto the threads/metal body of the plug....

i heat plugs until they're almost too hot to hold and have to keep rolling the ceramic in my fingers to stop it from burning me ...

then just drop them back in the holes and nip them up with a socket/box spanner...

be a little careful of overheating the starter motor by just keep spinning it over, give it a chance to rest and cool the windings off, we don't want you asking how to change the starter next :p

Damz...

it sounds more like your bike was struggling to get fuel thru even tho the choke was on, once it had caught on all four pots it made it easier to draw fuel thru as the revs picked up slightly
____________________
it ain't broke...

i ain't fixed it enough

[Bikeless]

I used to get the odd cold exhaust pipe,only on idle though and worked out it was a blocked pilot jet.

[bootsbiker]