i have the same problem as this guy. it always happens when going down a long steep hill off the throttle, then going into a hard right turn at less than 3k rpm.


https://www.superhawkforum.com/forum...stumble-17677/


i have been thru the carbs twice, sync'd them, cleaned them, TPS, new OE air cleaner,adjusted fuel screws with the idle drop method from the manual....all the obvious things. this just started happening recently, so it makes me thing something is worn, something has changed. i have been working on this thing for almost 1800 miles now trying to diagnose this problem. i work on it one night, then the next night take it out for 100 mile hell ride. last night it never missed a beat until 75 miles into the ride, and then got a stumble from the downhill, right turn thing. i thought i had it fixed, i was so damn happy too, then i happened again.

my float needles do have a wear mark on them, although i would not call it damage. i'm really starting to think that the bowl gets too full b/c the needle does not seal quite well enough, and when i go into the turn the vent gets submersed in fuel and then it hiccups. do the needles seal faces have to be pristine? there does not appear to be an elevation change on the sealing surface of the needle, just a smoothed witness mark where it hits the seat.

other than this one issue the bike runs perfectly. i have stock jets, needles shimmed up 0.5 mm.
bike has 50k miles on it.

 

Do the float bowl vent lines still cross between the carbs? If so remove them from the carb stays and route them so they just point straight down.

 

so i would pivot the air fitting in the carb and point them down, probably make the hoses shorter too, or just get rid of the hose?

i will do this, but can you tell why that works? there is still 1 atmosphere of pressure at the end of the hose. does some of the fuel leak out of the vent and stop of the tube for a short time, and this mod lets the fuel fall out instead of becoming trapped in the horizontal section of vent pipe.

 

Well it's from a service bulletin that was released in '98 and generally only effects the earlier bikes but what is happening is the hole through the carb stay is a touch undersized.

What this does is very slightly pinch the vent line. So what happens is when you are going down hill, on the brakes, the rear carb pukes a bit of fuel into the front carb and you end up running on one cylinder until it clears out.

The bulletin stated to just remove the vent lines from the carb stays (where they cross each other) and just point them down instead of going through the stay. You can cut them down or whatever you want.

Sounds pretty simple but it really does work....

 

my vents are not linked together so i don't think one overflowing vent would allow fuel into the other carb's vent.

but they do travel horizontally them make a 90º bend and then into the holes in the carb stay.


any chance you could tell where to find that service bulletin? i would like to see some pics. when i first bought this cali model bike back in 99 i immediately removed all the PAIR and carbon can junk. so i have no idea what the float bowl vent hose routing for a 49 state model looks like.

yes mine is a very early model, it has SN# 43, yes the 43rd chicken ever produced

damn i hope this works, sure is a simple fix.
BIG thanks for the advice.

 

The vent lies are not hooked together...... it comes from the throat of the rear carb, up the long stack and into the short stack......

No I have no link or pics, just a good memory.....lol and all the bikes (49 state or not) have the lines routed the same way. It was fixed in the later models, so it is only on the earlier bikes that you need to do this.

 

Well not sure what part of NoCal you are located at.... it is kind of a big place..... but if you are near the Bay Area you could always bring it by and I can figure it out for you if you still have problems after you reroute the vent lines.....

 

i'm not too far from you, i'm in the santa cruz mountains. my guess is you do some riding around here.

ever go to alice's for breakfast?

 

Look at www.SuperHawk996.net

 

Though the one I saw had you reroute both lines......

 

Haven't been there in a while. When I lived in La Honda I was there all the time. Though things have gotten pretty bad over there on the weekends with all the squids and the popo they bring with them.

So I tend to spend more time on Mines\Mt Ham anymore when I do get a chance to go for a ride.

 

oh yeah, lots of squids and chp, hence on weekends i only go out at 6 am, do 100 miles or so, and am back home by 10 am. weekend evenings are great though. i railed down hwy 9 last night about 7, had the whole road to myself, my own personal track it seemed. i think i made from 35 to BC in 15 mins, damn it was fun.

planning to do hamilton/mines very soon, haven't been up there in a few months......how is the road? last time i was up there quit a bit of sand and gravel going up hamilton, mines was wonderful as always. love that road, never crowded and always a challenge.

 

Well I haven't had a chance to just go out and ride for around 1 1\2 months now but maybe in the next couple of weeks. I'll let you know if and when I'll be out there as there are a couple of other members asking about that ride also....