Mixture Setting

[Guest]

Hi I have a 1982 gs750E. Ive rebuilt it and it has run fine until id done about 70 miles. Then it wouldn't tick over, stopped and would not start for 20 mins. Took out the plugs and they are black and sooty. Too rich a mixture Im assuming. The idle mixture adjustment seems straight forward and was set at 2 turns, but can that effect the plugs when the bike is being driven, if not is it the jets that need changing ?. Ive also read about changing the position of the clip on the jet needle can be used. Would that change the mixture ? Is there any other mixture adjustments I can make. Any help would be appreciated.

[tom203]

What you got for airfilter/airbox ? Yeah, you can fiddle with needle position (but most guys want to raise it to richen things but you seem to be running rich already), What brand of spark plugs? Of course, none of this explains why it stopped and wouldn't restart

[AJ]

Probably better to post this over on the Carb/Fuel/Exhause section.

If you didn't change your needles, then they are probably ok. Plus, needles will show up more as you're tuning the upper ranges of the throttle setting.

Agree with Tom above about the filters. If you have an original paper filter, it may not be flowing enough air, or a foam filter could be collapsing.

Are you sure you didn't leave your enrichener circuit ("choke") on?

[ned-999]

Hi thanks for the reply's . The air filters are the k&N type. Ive checked the choke and its not sticking. I changed the idle to 1 1/2 turns from 2 turns and been a few miles and they are not as black as before. Think im going to take the carbs off again and check the needle position as the PO may have changed it. Where is the needle suposed to be ? Also I have cleaned them properly twice but I still get a strange residue in the float bowel when I strip them again so il check that too.

[tom203]

....Also I have cleaned them properly twice but I still get a strange residue in the float bowel when I strip them again so il check that too.

The residue might be clogging the idle circuit passages which would explain your no start condition (but not the black plugs). How's your petrol tank look inside?
How did you actually clean these carbs?
Did you note mainjet size? maybe a PO got creative

[ned-999]

I have no idea what the residue was but it doesn't look good. I cleaned them by taking them all apart, put them in the hot jet cleaner at work, cleaned all the holes and connecting holes with mini drills and carb cleaner, and checked all the passages were clear with compressed air. Put them back together, about a week later (no riding just starting i found the stuff in the float bowls as per picture. looks like grease to me, but I have no idea where from.

Il check the main jet size later. I did notice they were plastic which I have never seen before !!

[ned-999]

Here is my bike .

[mvalenti]

nice scoot... that gunky gunk looks gross.... whats the inside of your tank look like? do you have an inline filter somewhere?

[ned-999]

The tank was brand new and I had an inline filter. I don't get it as there is also filters on the needle valves on the inlet to the bowl so it cant have got through there. I have no idea really unless it was some sort of reaction with the fuel !!

[Crank]

The tank was brand new and I had an inline filter.

Steel tank?

[Old guy]

Rinse your tank with gas. Use that gas in the lawn mower.

[ned-999]

Yes it was a steel tank. Is that where it came from then some sort of cleaner in the tank ??

[Nessism]

The problem is not the pilot screw or needle setting. You are running obnoxious straight pipes and pod air filters, and the carbs are not jetting correctly. The valves may be tight and starting to burn too.

[ned-999]

Well when I got the engine it had an 4 into 1 straight through exhaust that was about 24" long.... Would 4 straight through be any different. Il have a look at the jet sizes.

[AJ]

Very clean looking scoot, Ned. Always nice to see people's bikes.

Fouled plugs occur from:
1) too much gas (rich mixture)
2) too little air (rich mixture)
3) poor ignition system (weak spark)
4) poor oil sealing (oil fouling)

3 & 4) Verify that the ignition is good and that you're not burning oil.

1) Too much gas: If you're running stock jets and haven't raised the needles, that's probably not the problem. Plus, open pipes and/or higher flowing air filter usually help you flow more air, requiring you to increase the main jets and possible change or raise the needles to enrichen the mixture back to correct levels.

2) Too little air: Real K&N filters are a bit of a pain. If you over oil them, they won't flow enough air, thus acting like a choke and making the mixture overly rich. You may need to wrap those filters in paper towels to remove excess oil. Or, if those are Chinese copies of K&N filters, then they are regular paper filters and probably should not be oiled at all! If they are indeed paper filters and you did not oil them, did you ever get them wet? Paper fibers swell after getting wet and the filters will be ruined even after they dry out.

Given your descriptions above, I'd recommend replacing (or cleaning) the spark plugs, verify the ignition (strong spark), then remove the air filters and see if the condition improves. Running without filters is not a great idea, but running around for an hour won't hurt too much.