Coughing and spluttering at full throttle

[swbarnett]

I've noticed recently that when I wind on to full throttle my GSX750F coughs and splutters. Ease off a tad and it's back to normal. Any ideas as to what could cause this? Do my carbs need an overhaul, perhaps? The bike's nearing 90,000km.

[gammaguy]

While your at it check your coils and leads and plug caps

[F5 Dave]

Start at the start. its a suzuki of the vintage where a number of factors could be playing.

1. find a meter for measuring volts & put it over the battery & rev it. If it stays well under 15V you're ok.
2. Turn the switch to Gnohms & check the plug caps from pair to pair should be 20k or under (each cap would be 5-8k)
3. replace the plugs
4. Clean the carbs out. there will be debris that a filter won't stop as the fuel tanks rust slit. blow through the small pilot jets
5. Foam airfilter should be totally cleaned & lightly oiled with real airfilter oil

if done all above, then come back & tell us about the nasty 4-1 & pod airfilters you are running.


edit just noticed age of your bike is younger than I first thought. Oh well same may apply to lesser extent.


Hmm, while you are checking the plugs lets know if the plugs are black in one or more of the cylinders, it'll have those Mikuni flatslides that wear the emulsion tubes

[cbfb]

Does it do it in all gears?

If it does, ignore me.

If it's only in top, mine was doing this too, turned out to be a blocked fuel tank vent.

[F5 Dave]

Tanks rusting can cause people to add inline filters (which often kink the fuel line enough to stave flow) or to run some tank sealer (which blocks the vents).

[Mom]

I've noticed recently that when I wind on to full throttle my GSX750F coughs and splutters. Ease off a tad and it's back to normal. Any ideas as to what could cause this? Do my carbs need an overhaul, perhaps? The bike's nearing 90,000km.


Start at the start. its a suzuki of the vintage where a number of factors could be playing.

1. find a meter for measuring volts & put it over the battery & rev it. If it stays well under 15V you're ok.
2. Turn the switch to Gnohms & check the plug caps from pair to pair should be 20k or under (each cap would be 5-8k)
3. replace the plugs
4. Clean the carbs out. there will be debris that a filter won't stop as the fuel tanks rust slit. blow through the small pilot jets
5. Foam airfilter should be totally cleaned & lightly oiled with real airfilter oil

if done all above, then come back & tell us about the nasty 4-1 & pod airfilters you are running.


edit just noticed age of your bike is younger than I first thought. Oh well same may apply to lesser extent.


Hmm, while you are checking the plugs lets know if the plugs are black in one or more of the cylinders, it'll have those Mikuni flatslides that wear the emulsion tubes


Steve, I have a multi meter if you want to take a blat up here we can check the voltages. Can probably replace the plugs too if you do the spanner work, I only have one operational hand.

I will call this a battery issue as a starting point.

[swbarnett]

Start at the start. its a suzuki of the vintage where a number of factors could be playing.

1. find a meter for measuring volts & put it over the battery & rev it. If it stays well under 15V you're ok.
2. Turn the switch to Gnohms & check the plug caps from pair to pair should be 20k or under (each cap would be 5-8k)
3. replace the plugs
4. Clean the carbs out. there will be debris that a filter won't stop as the fuel tanks rust slit. blow through the small pilot jets
5. Foam airfilter should be totally cleaned & lightly oiled with real airfilter oil

if done all above, then come back & tell us about the nasty 4-1 & pod airfilters you are running.


edit just noticed age of your bike is younger than I first thought. Oh well same may apply to lesser extent.


Hmm, while you are checking the plugs lets know if the plugs are black in one or more of the cylinders, it'll have those Mikuni flatslides that wear the emulsion tubes
Thanks for the advice. I can check all but no. 5. If it becomes necessary I'll let my mechanic handle that (it's my primary transport and I can't afford to have it off the road whille I figure out how to put the carbs back together (or pull them apart for that matter).

Oh, frogot to add that I'm running iridium plugs. Been in for about 40,000km

[swbarnett]

Does it do it in all gears?

If it does, ignore me.

If it's only in top, mine was doing this too, turned out to be a blocked fuel tank vent.
More than just top gear. When I noticed it at the beginning of the week I dropped down a couple and tried again with the same result. Might check the vent anyway though (once I look up where that is).

[swbarnett]

Steve, I have a multi meter if you want to take a blat up here we can check the voltages. Can probably replace the plugs too if you do the spanner work, I only have one operational hand.

I will call this a battery issue as a starting point.
I have a meter I can use. Thanks anyway.

[nzspokes]

Service time mate. Wouldnt hurt to chuck new leads and plugs at it anyway with those ks on it.

[swbarnett]

Service time mate. Wouldnt hurt to chuck new leads and plugs at it anyway with those ks on it.
Just had a service. At that stage I'd just noticed a slight hiccup when winding open the throttle fast. This was cured with a slight richening of the mixture.

[The Reibz]

If its carb related, full throttle problems would relate to the main jet. Overhall them anyway. New jets are about $10 a peice from cycletreads.

Also with that amount of KM's the emulsion tubes are prob very well worn which would have been causing your mid range issue. Making the mixture more rich is a temp fix. They should really be replaced with OEM or after market nickle tubes from FactoryPro.

286992286993

[F5 Dave]

I've never known jap carbs to wear mains. Emulsion tube yes.

40k is old for plugs. Obviously

[swbarnett]

40k is old for plugs. Obviously
They're Iridium; suppposed to last upto 80,000km.

[98tls]

I've never known jap carbs to wear mains. Emulsion tube yes.

40k is old for plugs. Obviously

And plug leads,TL ones caused problems years ago.

[F5 Dave]

Check em anyways it's not a corolla. ESP if the carb emulsion tubes are worn they could be toasted in a tank of gas.

[swbarnett]

I went for a blat down '22 yesterday. To start with the problem seemed much deminished (went to Whakatane and back on Monday/Tuesday). By the time I got half way to '23 it had gone completely. It seems that my only problem was 6 months of 120km a day of Auckland motorways almost always at constant speed and not much else.

Thanks all for your help anyway.