I've noticed that at about half throttle the bike will get this kind of jumpy kind of motion.. It's like it's starved for fuel at half throttle.. Any ideas?

welllll... i'm no engineer!! ... but reckon a carb clean or jet inspection may be in order .. just to see whats what ...

i rather expect the people with lots of real experience will be along shortly to see what may be up with your throttle/fueling/carbs .. or just some other advice...

its probably a good idea to heed the advice of the people with current hands on experience... rather than the 'i used to' .. works out better ... nothing like keeping the knowledge fresh in your mind by actually doing the maintenance from day to day .. (eh Addy!)

What year bike?  Stock exhaust?  Air filter?  Carbs?

I don't want to threadjack, but I'd like to jump in as I think I have a similar issue. 

• 1993 500EP
• Stock Airbox
• Stock Muffler [BUT, it looks like it was opened up at the end by a PO if you follow me.]
• I cleaned the carbs last year, used stabil over this winter, did a valve job and a half-assed carb. sync. in the spring.
• For carb settings I'm on 1 #4 washer and 3 turns out.
• The mix looks good as far as I can read on the plugs, but I'm a little new at this.

I'm getting just over 60 mpg. and the throttle seems nice on either side of the flat spot.  If I feel it losing power when I'm rolling-on I open it a little more and it zips right through it.  I can hear the engine respond nicely through the exhaust sound when I get on it a little bit more.

OK good we are talking about throttle position and not about rpm ...

Alright both of you - is the issue @ steady throttle or when you're opening the throttle and revs are raising through that range.

If its @ steady that = lean.
If its opening and revving up when you have 1/2 throttle - like you've opened from 1/4 to 1/2 and its climbing and you have issues, that = rich.

Cool.
Buddha.

Quote from: 007brendan on September 20, 2013, 12:12:27 AM
What year bike?  Stock exhaust?  Air filter?  Carbs?

I'm riding a 1997 gs500 everything is stock except for my Uni foam air filter but this was happening before the airfilter

Quote from: The Buddha on September 20, 2013, 07:55:17 AM
OK good we are talking about throttle position and not about rpm ...

Alright both of you - is the issue @ steady throttle or when you're opening the throttle and revs are raising through that range.

If its @ steady that = lean.
If its opening and revving up when you have 1/2 throttle - like you've opened from 1/4 to 1/2 and its climbing and you have issues, that = rich.

Cool.
Buddha.

Mine is when opening the throttle.. And I'm guessing mine is running rich.. But why does it seem like it's starved for fuel?

Quote from: newbie1993 on September 23, 2013, 08:52:37 AM

Quote from: The Buddha on September 20, 2013, 07:55:17 AM
OK good we are talking about throttle position and not about rpm ...

Alright both of you - is the issue @ steady throttle or when you're opening the throttle and revs are raising through that range.

If its @ steady that = lean.
If its opening and revving up when you have 1/2 throttle - like you've opened from 1/4 to 1/2 and its climbing and you have issues, that = rich.

Cool.
Buddha.

Mine is when opening the throttle.. And I'm guessing mine is running rich.. But why does it seem like it's starved for fuel?

Its momentarily appearing @ 1/2 throttle when you say - open from 1/4 to 3/4, as the revs climb and you are @ 1/2 throttle it could cough or act up ... then clear out and keep going ...

You may be rich in that case - and I suspect a high float in that situation.
You could be lean every other location .. I'd set floats and retry, and if its lean now, do 40/125. Stock bike should wotj with 40/125, if floats are not off .. or they may be off in 1 carb.

Cool.
Buddha.

Quote from: The Buddha on September 23, 2013, 09:22:40 AM

Quote from: newbie1993 on September 23, 2013, 08:52:37 AM

Quote from: The Buddha on September 20, 2013, 07:55:17 AM
OK good we are talking about throttle position and not about rpm ...

Alright both of you - is the issue @ steady throttle or when you're opening the throttle and revs are raising through that range.

If its @ steady that = lean.
If its opening and revving up when you have 1/2 throttle - like you've opened from 1/4 to 1/2 and its climbing and you have issues, that = rich.

Cool.
Buddha.

Mine is when opening the throttle.. And I'm guessing mine is running rich.. But why does it seem like it's starved for fuel?

Its momentarily appearing @ 1/2 throttle when you say - open from 1/4 to 3/4, as the revs climb and you are @ 1/2 throttle it could cough or act up ... then clear out and keep going ...

You may be rich in that case - and I suspect a high float in that situation.
You could be lean every other location .. I'd set floats and retry, and if its lean now, do 40/125. Stock bike should wotj with 40/125, if floats are not off .. or they may be off in 1 carb.

Cool.
Buddha.

What do I set floats to? And another thing is that when I last cleaned my carbs one of my pilot jets were stuck... It was stripped out.. Any idea how to get that out?

Get a round tipped, flat surface punch and a small hammer. VERY VERY carefully peen the buggered parts of the slot back down where they were and make sure you get the best fitting screwdriver you possibly can that fits the slot perfectly. Mount the carb solidly so you can put a good amount of force on the screwdriver. You may even want to get a box end wrench or vise grips on the shaft of the screwdriver so you can get good torque.

The tapping with the hammer and punch will break the corrosion bond between the jet and carb body. I have had virtually 100% success with this method, even on a 70 year old Stromberg 48 carb on a 1937 Ford.

I would bet that primary jet is most of your problem. On my 89 I made sure the primary jets were clean, didn't even pull the plugs out of the adjustment screws and it runs perfect.

regards
Mech

Quote from: Old Mechanic on September 23, 2013, 06:57:07 PM
I have had virtually 100% success with this method, even on a 70 year old Stromberg 48 carb on a 1937 Ford.

   

The pilot jet is brass.
The carb body is cast impure aluminum that has a shiny coating that keeps it from oxidising - forget what its called - parkerised maybe. Whatever that is, if it was dipped i nalkali it will come off, the carbs will be dark grey and will oxidise into white powder easy ... but not otherwise.

I really dont think there is "corrosion bond" between the 2.

I use a left handed drill to pull pilot jets that have got boogered ...

Setting floats - you do it by bending that prong the needle sits on, make sure your needle spring is active and set it accordingly ... it should end @ the top of the bowl, no more, no less ...

Cool.
Buddha.

Quote from: Old Mechanic on September 23, 2013, 06:57:07 PMThe tapping with the hammer and punch will break the corrosion bond between the jet and carb body. I have had virtually 100% success with this method, even on a 70 year old Stromberg 48 carb on a 1937 Ford.

This is how I had to get my gas cap open when it got grossly corroded. Put the key in and apply a slight torque while tapping on the gas cap with a hammer. Took a few minutes, but it has never failed me. I call it the poor man's impact wrench (usually hammering on a breaker bar).

Quote from: RossLH on September 24, 2013, 10:43:29 AM

Quote from: Old Mechanic on September 23, 2013, 06:57:07 PMThe tapping with the hammer and punch will break the corrosion bond between the jet and carb body. I have had virtually 100% success with this method, even on a 70 year old Stromberg 48 carb on a 1937 Ford.

This is how I had to get my gas cap open when it got grossly corroded. Put the key in and apply a slight torque while tapping on the gas cap with a hammer. Took a few minutes, but it has never failed me. I call it the poor man's impact wrench (usually hammering on a breaker bar).

Yea but there is steel parts in a lock that slide against each other ... so there can be corrosion between them levers.
Now you do know you may have had the same effect pressing down on the front of the locking part of the cap - you're unloading the tounge that does the locking. Or squirting penetrating oil in the key slot. Either of these will do the same ... clean out corrosion/lube/unload the plunger etc etc.

Cool.
Buddha.

Pressing down on the gas cap would relieve pressure in one direction--don't you think I tried that? Tapping the cap with a hammer introduced vibration into the system, which in this situation helped a whole lot more than any combination of penetrating oil and pushing down on the cap.

Yea sure, but you have steel parts in that thing not to mention its exposed to the elements, so rain, dust, bird crap etc etc all make their way in.
Cool.
Buddha.

My problem was lots and lots of corrosion. All better now though.

Aaaand back on topic...you get my standard answer: check the floats. Which is currently something I need to do--my bike recently developed a problem of falling on its face past 1/4 throttle. It runs great right up until then, but any more throttle and it just flops and refuses to rev any higher. Only happens under load, switching it to prime and/or opening the choke doesn't change anything. Need to get it fixed....it's supposed to be 75 and sunny for the next week at least.

Quote from: The Buddha on September 24, 2013, 08:08:23 AM
The pilot jet is brass.
The carb body is cast impure aluminum that has a shiny coating that keeps it from oxidising - forget what its called - parkerised maybe. Whatever that is, if it was dipped i nalkali it will come off, the carbs will be dark grey and will oxidise into white powder easy ... but not otherwise.

I really dont think there is "corrosion bond" between the 2.

I use a left handed drill to pull pilot jets that have got boogered ...

Setting floats - you do it by bending that prong the needle sits on, make sure your needle spring is active and set it accordingly ... it should end @ the top of the bowl, no more, no less ...

Cool.
Buddha.

I repaired and reused the same jets.

regards
Mech

Quote from: Old Mechanic on September 24, 2013, 05:31:36 PM

I repaired and reused the same jets.

regards
Mech

I never (almost) never reuse pilots, firstly, I am asked to replace them by people who send me carbs for rejet - so its going up a size.
Ergo, they are junk no matter what. Secondly, unless the thing comes off clean without shaving/beveling off the slot it will get progressively harder and harder to get out. I had a big collection of stock size jets, ones that came off perfect ... so in case I needed a stock, I have 50 lying round just in my driveway ...

Anyway, these are cheap jets not worth it.
Cool.
Buddha.