Doesn't like throttle when cold !

[Sparky]

I have had my 98 Steamer for not quite three weeks now and have ridden it half a dozen times with no problems at all.  Out of the blue last two rides it will start from cold easy and idle nice and smooth with some choke required as it warms up, when you go to ride it will not take any throttle past 3K and falls on it's face and stalls.  If I persist with coaxing it through this flat spot it eventually clears up and runs great for the rest of the ride.  At first I thought it needed more warm up time as I have read these motors don't run good when cold.  I can idle until the temp comes up on the guage but same problem.

The Known
-  Spark plugs replaced about 200 miles ago.
-  Fresh fuel in the tank.
-  Air filter looks clean when viewed through the air box.
-  Air box is stock with the right hand cap in place.
-  Exhaust is stock.
-  Recent coolant flush.

The Unknown
-  Condition of the carbs.

Next step I guess is to clean the carbs as I have no idea when this was last done, am I on the right track and is there anything specific I should look for ?

Thanks
Chris 

[JayDub]

Sounds like the problem I once had - crap built up in the carbs.  Meticulously clean them after a soak overnight in carb cleaner, that worked for me.
Then a sync check. Most people on here have found steamers to be very particular about the cleanliness of their carbs 

[ynotbiker]

stick some prof-fuel in it then ride the tits off it for 20 mile sorted.

[Mustang]

look for water in the gas tank ,your drain is possibly clogged and let's water in under the cap.

what happens when you put it on reserve , better or worse ?

check the filters , there's one in the fuel line right where the line enters the carbs between #2 &#3

seriously though drain your fuel into a catch can and it will be obvious if you have water in it .

Does the bike live in a garage or outside ?

[Sparky]

look for water in the gas tank ,your drain is possibly clogged and let's water in under the cap.

what happens when you put it on reserve , better or worse ?

check the filters , there's one in the fuel line right where the line enters the carbs between #2 &#3

seriously though drain your fuel into a catch can and it will be obvious if you have water in it .

Does the bike live in a garage or outside ?

I tried switching to reserve with no change.

Bike lives in a garage when not ridden.

I'll check the cap drain and drain and clean the tank and see if that changes anything then pull the carbs.  Fuel filter shows nothing unusual.

If it was a clogged fuel filter or water in the fuel would that not create a permanent problem not a very specific when cold problem ?  Once I get past the cold stumbling it runs great.

[Mustang]

go get a can of "sea-foam "from the auto parts store .
dump in about a 1/3 can (assuming your tank is at least half full)
ride the wheels off it and report back ......................
you'll know in about 20-40 miles if it was crap ethanol gumming up the works so to speak .
I got 5 of these bastards to wake up this spring and 1st thing I'm doing is sea foam for the beasts .

[Sin_Tiger]

5  how will I ever keep up, or afford that much profi fuel max.

It does work but the cold thing has me thinking about air leaks again 

[Mustang]

5  how will I ever keep up,

in my defense , 1 of them isn't mine .
Just a good friends whose kitty snuck in with my sleeping beasts .

[nickjtc]

in my defense , 1 of them isn't mine. Just a good friends whose kitty snuck in with my sleeping beasts .

You know they tend to reproduce if left on their own......??

And I concur with the others. Step 1: Sea Foam or some other wonder gum cleaner. Step 2: a nice long ride.

[Sparky]

Alrighty.

These are the Keihin carbs.

Not too bad getting the carbs off and on you guys had me worried reading about Steamer carb removal, good tip on removing the throttle cable at the bars first.

Removed the carbs and gave them a good clean with carb cleaner and compressed air everything looked good nothing obvious jumped out at me.  Drained the tank and refilled with fresh gas. Carb boots look good no visible cracks in the rubber.  Took it for a ride and the off idle throttle response is much better and no stumbling when cold so that problem is fixed.  The problem now is it starts to stumble with any more than 3/4 throttle rpm does not matter just throttle opening.  The main jets I have are 102.5 I checked an online parts place and they show the main jets on the Keihins as 98.  Can anyone confirm the factory jet size please.  I think this thing may be choking on fuel after 3/4 throttle.

[Sin_Tiger]

When you say you drained the tank, did you remove the tap (careful with the screws) and check the filters and for crud around the tank bottom.

Try switching over to reserve when you get the stumbling or go back to 1/4 throttlerfor 10 secs then full again to gauge if fuel starvation might be the issue.

It takes very little restriction for the petcock strainers to collapse.

[Mustang]

.98 is the oem main jet for kiehins and it will run like shit way too lean .
102.5's are good but but 105's are usually fine too .

My solo 98 steamer runs 105's with the needles shimmed up about .050 ..runs like a champ and gets 45mpg

the hacked 98 is running 100's for mains with no shims on the needles . it runs great and gets decent mileage for a hack @30 mpg.

when you say it won't rev past 3/4 is that sitting in the driveway or on the road rolling under a load ?

cuz even when they are perfect they don't like throttle that hard sitting still in neutral , you'll get a serious bog.

[Sparky]

.98 is the oem main jet for kiehins and it will run like shit way too lean .
102.5's are good but but 105's are usually fine too .

My solo 98 steamer runs 105's with the needles shimmed up about .050 ..runs like a champ and gets 45mpg

the hacked 98 is running 100's for mains with no shims on the needles . it runs great and gets decent mileage for a hack @30 mpg.

when you say it won't rev past 3/4 is that sitting in the driveway or on the road rolling under a load ?

cuz even when they are perfect they don't like throttle that hard sitting still in neutral , you'll get a serious bog.

This is while riding the bike rolling under load.  Sounds like the 102.5 jets are not way out to lunch then. 

I did not check the fuel petcock strainer will do that tonight. The problem occurs as soon as you get past 3/4 throttle so I doubt enough time has passed to empty the float bowls in a few seconds of full throttle.  If it pulled strong for a bit then started to bog I would suspect fuel flow as the culprit.

Keep the ideas coming, Thanks. 

[Mustang]

try going for a ride with the gas cap open
just to see if it makes any difference

the tank vents thru the cap, the key slot specifically there is a one way flapper in there  , it could be blocked

[Mustang]

I have been looking at your fuel filter picture
and the  came on

I bet it's starving for fuel on at least 1 cylinder (most likely #1)
gas is trying to flow against the force of gravity
as well as a big empty filter with air in it
by the time fuel finally makes it to #1 being the farthest away fuel delivery wise
the float bowl is damn near empty
at lower throttle it can cope
when it needs the fuel poured in it's starving
I've experienced the same situation with the way your filter and line routing is.

OEM works best .......been there done that