mixture emergency!! was running rich, adjusted it, now wont start.

[big_dave_1992]

Hi all, I have a 79 gs750L. I just got it going and had a mechanic adjust and sync the carbs...but it was running super rich right out of the shop...so rich it was spitting black smoke and fouling plugs. It left me stranded on a roadtrip. I tried emergency adjusting on the side of the road. The carburetors have 112.5 main jets, 4 into 1 kerker pipe, factory air box and foam filter. current settings I got fromanother forum are: air screws on top, 3/4 turns out. Fuel screws on bottom, 1.5 turns out...cleaned the plugs and gapped, put it all back together...now it gives me nice gunshot backfires and wont start unless I have the air filter out of the air box, and then it wont idle and doesnt really respond to throttle...I was just trying to lean her out. Smells very much like gas. Im at a loss...I could take it back to the shop but I was hoping you guys could help.

 

[Steve]

"The shop" set it up like that, ... and you want to take it back????

If you do, you deserve what you get. :-\\\

First of all, you need to reverse the settings on the screws. The fuel screws (the ones on the bottom) should probably be about 7/8 turn out from LIGHTLY seated, the air screws (the ones on the sides) should be double that, or about 1 3/4 as a starting point.

Next, stock mains are 100. Unless your Kerker is wide open (no baffle), 112.5 might be a size or two too large.

.

 

[big_dave_1992]

"The shop" set it up like that, ... and you want to take it back????

If you do, you deserve what you get. :-\\\

First of all, you need to reverse the settings on the screws. The fuel screws (the ones on the bottom) should probably be about 7/8 turn out from LIGHTLY seated, the air screws (the ones on the sides) should be double that, or about 1 3/4 as a starting point.

Next, stock mains are 100. Unless your Kerker is wide open (no baffle), 112.5 might be a size or two too large.

.

Thank you for the reply, what jet sizes would you recommend going with? Is there a general kit I can buy or sizes for all the jets that you think could work with this setup?

 

[Steve]

The jet size will be suggested by reading your spark plugs, once you stop fouling them with your severely over-rich pilot mixture.

I mentioned the mains "might be a size or two too large" which should lead you to either a 110 or a 107.5, but your plugs will tell you when you are able to do some plug chops. Start with your 112.5s, see what the plugs look like, then adjust from there.

The size of the main jet required will depend on the flow characteristics of your header. As mentioned earlier, if it is a quiet street baffle, the 107.5 jets might work. If you have the Competition baffle, a 110 or your present 112.5s might work. If you have NO baffle in there, my personal suggestion would be to run the smallest jet possible so you blow up the engine, which would then bring some quiet back to the neighborhood. (You get the idea that I don't like LOUD pipes? :-k) In reality, a straight pipe will probably need something in the 115-120 range.

.

 

[big_dave_1992]

It's got a pretty quiet baffle in it. It's definitely always been a cruising bike, I don't think anyone ever went with speed or noise on the old thing, just a nice normal rider. I'll use your settings when I go pick it up tomorrow and start from there. Bike is currently still in my gf's garage an hour and a half away from me haha. One guy, a mechanic I talked to yesterday, said I should have the fuel screws at 2 and 3/4...I thought that just sounded ridiculous.

Also, sorry for cluttering the other post, I'm still getting used to forum ettiquete and use.

 

[megatwin]

Might want to check your float bowl levels,too.
If you have a fuel over flow problem,you could have fuel in the crank case,which will let the carbs suck it back through the vent.
If your oil is over full,that is a good indication.

 

[big_dave_1992]

Do you know any good links or threads that could instruct me on the float adjustments, megatwin? I drained the oil the other day, the level wasn't bad, so I don't think the engine is washing. I think my air filter might be over-saturated. It's pretty oily...clean, but oily. I haven't seen a whole lot of gas back in the air box, not enough to drip from the drain tube or to really notice in the top, there has been just a little bit though.

 

[Steve]

One guy, a mechanic I talked to yesterday, said I should have the fuel screws at 2 and 3/4...I thought that just sounded ridiculous.

He might not realize what carbs you have. :-k

Starting with the '80 model year, the GS models that didn't already have CV-type carbs got them. THEY have pilot (mixture) screws that need to be turned somewhere between 2 and 3 turns out for proper mixtures, but the VM carbs on your bike have separate fuel and air screws. Stock setting on the fuel screws is about 5/8 to 3/4 turn, and the air screws are usually about double the fuel screw setting, so 1 1/4 to 1 1/2. With your header, you will want that just a little richer, about 7/8 turn is a decent starting point.

Also need to note that turning either screw out (left) will increase what it's controlling, but the mixture goes in opposite directions.
Turn the fuel screw out (left), the mixture gets richer.
Turn the air screw out (left), the mixture gets leaner.

Generally-speaking, setting the fuel screw will determine how much mixture is added to the intake stroke. Setting the air screw will determine the 'quality' of that mixture.

.

 

[Big T]

Do you know any good links or threads that could instruct me on the float adjustments, megatwin? I drained the oil the other day, the level wasn't bad, so I don't think the engine is washing. I think my air filter might be over-saturated. It's pretty oily...clean, but oily. I haven't seen a whole lot of gas back in the air box, not enough to drip from the drain tube or to really notice in the top, there has been just a little bit though.

All the information you need is at New Members, click here! in the GS Owners section.

Don't take it back to that shop, ever. Learn to do it yourself, which is what we are here for.

Clean and lightly oil your filter (K&N?) and reset the screws as Steve suggests than see how it runs

 

[big_dave_1992]

It's the UNI foam filter.

 

[megatwin]

All the information you need is at New Members, click here! in the GS Owners section.

Don't take it back to that shop, ever. Learn to do it yourself, which is what we are here for.

Clean and lightly oil your filter (K&N?) and reset the screws as Steve suggests than see how it runs

As Big T says,go to that topic,and read up.
You have to get the baseline set correctly before you do any fine tuning.Start at the beginning,with all of the maintenance,including valve adjustments,and while you are there verify your timing marks are correct,then move on to the carbs.Do it as the thead suggests,and you will figure it out,while getting a bunch more familiar with your machine.

 

[big_dave_1992]

Used your settings steve, plugs are still coming up black. How much should I back the air screws out at a time? 1/4 turn between test? I dont think I over oiled my filter, but it could be possible.

 

[Steve]

Adjust the air screws (the ones on the side) with the engine idling. You will hear when the engine speed starts to fall, due to a too-lean mixture. Stop there, turn the screws back in about 1/8 turn, move to the next carb.

Do this with a warm engine, have a fan blowing on the engine to keep it cool.

.

 

[big_dave_1992]

Will a box fan keep the engine cool enough?