rich mixture

roby_59 · Mar 15, 2017

Hi everybody,

My ST has always shown low gas mileage (approx. 14,0 Km/lt average ). Recently (due to wather-hose) change) I've removed the carbs, cleaned the bowls and jets, replaced the bowl gaskests and the boots, Everyting looked good and clean, but the consumption is just a little bit higher than before:

the engine runs smoot at any rpm.
Start is fine with choke in cold weather
Above 15 C no choke is needed
The plugs are black and dry
the main jets are 148
air filter is K&N

Where to start ? :bow1:

Bush · Mar 15, 2017

roby_59 said:
air filter is K&N

BINGO! Are you using the foam sleeve on it? Too much oil? Try an OEM filter and see if your mileage improves.

roby_59 · Mar 16, 2017

Bush said:
BINGO! Are you using the foam sleeve on it?

NO

Bush said:
Too much oil?

NO

Bush said:
Try an OEM filter and see if your mileage improves.

I tested a commercial air filter and the consumption rised a bit

Brant · Mar 16, 2017

roby_59 said:
Hi everybody,

My ST has always shown low gas mileage (approx. 14,0 Km/lt average ). Recently (due to wather-hose) change) I've removed the carbs, cleaned the bowls and jets, replaced the bowl gaskests and the boots, Everyting looked good and clean, but the consumption is just a little bit higher than before:

the engine runs smoot at any rpm.

Start is fine with choke in cold weather

Above 15 C no choke is needed

The plugs are black and dry

the main jets are 148

air filter is K&N

Where to start ? :bow1:

Well, you didn't state whether the idle mixtures were correctly re-set first, THEN a carb sync. done, in THAT order

. If NEITHER done, in that order after carb installation, that pretty much explains excessive fuel consumption. After doing BOTH these tuning procedures, my 92 ST consistently got 48-52mpg. at 80mph. Hope that helped

.

roby_59 · Mar 17, 2017

Brant said:
re-set first, THEN a carb sync. done, in THAT order.

1) in the manual i't's just the opposite

2) Do anyone know easy achievable tools suitable for the purpose ? :tools1:

Jim Van · Mar 18, 2017

QUOTE : " .... my 92 ST consistently got 48-52mpg. at 80mph. Hope that helped ".

That's great mileage. At 80 mph, I consistently get about 42 mpg. At lower speeds it is much higher. At 58 mph, around 56 mpg.

To compare, see Fuelly ST1100

afrymoyer · Mar 18, 2017

I'm thinking you may have made a typo error? You've stated that your main jets are #148. If this is truly the case, then this is your problem. Your bike should have either #128 or #125 main jets, pending your country's emission standards. More than likely you meant to say #128 mains?

roby_59 · Mar 20, 2017

afrymoyer said:
I'm thinking you may have made a typo error? You've stated that your main jets are #148. If this is truly the case, then this is your problem. Your bike should have either #128 or #125 main jets, pending your country's emission standards. More than likely you meant to say #128 mains?

Right ,when I did the work I was shure that the jets were correct,128 I suppose.I hope not to be forced to check them again....

Any suggestion for an easy-to-find angular screwdriver to set the idle screws ?

roby_59 · Mar 20, 2017

Another question: do the screw needles control the air or the fuel ?

afrymoyer · Mar 20, 2017

roby_59 said:
Right ,when I did the work I was shure that the jets were correct,128 I suppose.I hope not to be forced to check them again....

Any suggestion for an easy-to-find angular screwdriver to set the idle screws ?

I wished you would have said something before you put the carbs back in. I could have helped you set it up better.

Being an Italian bike, I have no idea what you have for mixture screws. It's either the "D" shape emission head, or the "international" Phillips head screw. You may get lucky and find someone there with a factory tool you can borrow. You might find one to purchase in the European spares market.

To answer your other question, these are Keihin VD series carbs. The idle mixture screw only controls the "fuel" for the idle circuit.

Brant · Mar 20, 2017

roby_59 said:
Another question: do the screw needles control the air or the fuel ?

Fuel........rule of thumb is if mixture screws are on air cleaner/intake side of carb intake......air mixture adjustment. If idle mixture adjustment screws are on head intake side of carbs.....fuel mixture adjustment

.

roby_59 · Mar 21, 2017

afrymoyer said:
IIt's either the "D" shape emission head, or the "international" Phillips head screw. You may get lucky and find someone there with a factory tool you can borrow. You might find one to purchase in the European spares market.

not exactly Phillips, they have two perpendicular slots, like that

afrymoyer · Mar 21, 2017

roby_59 said:
not exactly Phillips, they have two perpendicular slots, like that

Roby... It maybe just an illusion on my part. I'm not wearing my glasses.

But in that picture you've posted, it appears that the top mixture screw has the metering needle end snapped off? If so, this could be your problem of running rich....

And Yes, those are the "international" Phillips mixture screws. More than likely you have the #40 pilot / slow speed jets too.

roby_59 · Mar 22, 2017

afrymoyer said:
Roby... It maybe just an illusion on my part. I'm not wearing my glasses. But in that picture you've posted, it appears that the top mixture screw has the metering needle end snapped off? If so, this could be your problem of running rich....

It's just a picture from the internet, my screws are perfecly shining and do have the needle, anyway the four plugs aree equally black. Actually I've to solve the tool issue before triyng the screw setting. When I cleaned the carbs I set th screws 2 turns out.

afrymoyer · Mar 22, 2017

I feel that two turns out from lightly seated is a little too much for were you are located. 1 1/2 - 1 7/8 range would be best for you. Granted it would be convenient to have the proper factory tool. But at this point, it might be faster to pull the carbs, set them all at 1 3/4 and put it back together then synchronize. Only takes about two hours.... Did you reset all the float heights to 7mm while you were in there?

roby_59 · Mar 23, 2017

afrymoyer said:
Did you reset all the float heights to 7mm while you were in there?

no I didn't. I only cleaned the bowl and the jets, changed the gasket and re-assembled, anyway the mileage was low even before the cleaning.

afrymoyer · Mar 23, 2017

roby_59 said:
no I didn't. I only cleaned the bowl and the jets, changed the gasket and re-assembled, anyway the mileage was low even before the cleaning.

Just making a suggestion here... I recommend that you remove the carbs again, open them up and set everything properly before you go any further. You don't know what the floats are set at, the idle mixture screws are a little out, and your trying to diagnose a rich condition. After everything is set up properly and synchronized, then we'll move on from there.

Bush · Mar 23, 2017

Going back to Roby's first post, he claims an average mileage of 14 km/ltr. If we do the math, the 28 litre tank is giving an average of 392 km. Since we don't know what kind of riding this involves, the assumption of low mileage may be premature, as the best mileage I can ever expect with mostly highway riding is close to 500 km (300 miles) to an almost empty tank, with maybe a litre left in it.

With a mix of stop and go city riding and highway, I generally get about 400 km. This, I believe, has been found to be quite standard amongst the 1100 owners.

So I go back to my original point that possibly the K & N is causing the black plugs. Rather than pulling the carbs again, it would be far easier to definitely rule out the K & N as the problem by buying a Honda filter and giving it a try.

TerryS · Mar 23, 2017

Some excellent points made above.

I generally don't do highway riding, most of mine is twists and turns with braking and accelerating. 400km to the low fuel light (23L used) or around 16km/L is pretty much all I get, although if I do have a steady highway run that number would be more like 18-19km/L.

Adam's suggestion about the float heights is a good one; I was having some over-rich running and resetting the floats to exactly 7mm made for some improvement. Previously if I set the fuel screws to 2 turns out, I had a problem with plugs fouling during idling. Since the float setting was corrected, this problem has not re-occurred.

Highwayman · Mar 23, 2017

If you're going to take the carbs back out, Adam Frymoyer's 2014 tutorial on carburetor clean and adjust (on this site at http://www.st-riders.net/index.php?topic=10249.0) is excellent. Couldn't have done mine without it. I agree with everyone else that you should go with genuine OEM everything on these bikes (air/fuel/oil filters, etc). When I got my '93, it had some kind of car air filter Mickey Moused to fit under the lid. That was the first thing to go. Also, you don't mention what plugs you're running, but obviously they shouldn't be black. Again, use the recommended NGKs (CR8EH9) or Nippondensos (U24FER9), and make sure they're gapped correctly - .031-.o36.