I did the standard free mods this evening. carb parts, drilled muffler baffle, and did the crankcase breather mod.

It fired right up after going back together. Sounded and ran great! I took a little rip down the alley and all was fine. Great throttle response and a lot more power.

Anyway... I decided to take a longer ride. I got about 3 miles from the house and the damn thing went.... BRRRPPPPPPPP. I could feel something give or let go through the throttle cable. The bike would idle just fine, but as soon as I gave it any gas, it would stall out and die.

I got home by turning up the idle as far as I could and just limped back to the house. Giving it any throttle at all would start to stall the bike.

Any ideas on what happened??? I have to be at work in five hours, so I haven't torn back into it yet. Bugs the hell out of me. Don't think I'll sleep too good tonight.

Willum
TC

 

I wonder if it might be possible that a shaving of plastic from the crank case breather mod maybe got sucked into the carb and is lodged in there somehow? Just a stab in the dark, really ...

 

Sounds like something blocking the air pathway. Friend of mine left a rag in the airbox once had similar symptoms.
Good luck

 

Check the diaphram. It sure does sound like you have a tear in it, sorry to say.

 

Thanks for the ideas guys. I sure hope its an obstruction in one of the jets or something simple like that. Marty, If I did tear the diaphram, how could it have happened? I think if I tore it during the installation, if would have never started to begin with. Maybe I have it pinched or something and the throttle/slide action finally tore it after so many up/down cycles.

I don't know man, I'll let you guys know what I find when I get home from work this evening.

If I did tear the diaphram, who has them cheaper than bikebandit.com? Theirs is $104.


Willum
TC

 

In a Keihin carbed bike, it will start up and run just fine. However there is no throttle since the diaphram is what causes the slide to lift and let the air / fuel mixture into the engine.

The diaphram gets it's "signal" from the engine via the little hole in the slide that sits closest to the intake of the engine. When you open the throttle, this "signal" is presented to the diaphram which raises the slide. You will never get more slide open then there is vacuum. Basically with a Keihin carb you will never give the engine more fuel mixture than it needs. That is why this type of variable carb is used on so many motorcycles. It is automatically adjusting for many altitudes based on it's design.

If the diaphram is not seated in the groove, or if the carb lid is forced in place, that might have pinched the diaphram and after a bit of riding, it simply tore.

Now, if you had the Keihin 40 mm carb - found on the KLR650 - you could go to your friendly Harley dealership and buy the slide and diaphram for the Sportster for about $40 and be done with it.

Sure did like the look on the H-D parts guy when I went there to pick up a diaphram / slide for a friend's KLR650. He asked me what year Sporty I had and I told him, I don't have a Sporty, this will be going into a Kawasaki KLR650. Immediately I got this "WTF?" look from the parts guy that made me wish I had a camera to capture it with. "Why would you put a Harley-Davidson part into a Kawasaki KLR650?" . . . . . . . . . Now, this is where complete self-control comes into play . . . . . . . . I was surrounded by H-D guys that all of a sudden were very interested in my answer. There are so many things that I could have / would have / should have said, but I didn't want to have to fight my way out of the parts department of the local H-D parts department.

Let me know what you find.

 

Thanks Marty for the carb lesson. This is my first bike with a Keihin carb. Mikuni and Tillotson I'm a little more at home with.

Sure wish I could ditch work and go home to work on it.

I'll let you guys know what happened so that someone might learn from my errors.

Willum
TC

 

I'm with Marty on this one. Torn diaphram. Sucks.

 

I found this on another website...

http://www.nightrider.com/biketech/hd_cv_mods.htm

Assembly Tricks for the diaphragm

The diaphragm is easily mis-aligned or pinched. This is a common source of problems after carburetor modifications are performed. The diaphragm frequently has the appearance of being too large to fit into the groove. The repeated up and down movement of the diaphragm causes it to stretch, making re-assembly tricky. Try using the cap to position the diaphragm. It will allow you to evenly push the diaphragm into the groove. You can "wiggle" the top and feel when the diaphragm is properly located. A damaged diaphragm will have the symptoms of the engine being able to idle, but will not accept any throttle. If you think the diaphragm is damaged, check for any pinholes with a bright light behind the rubber, pulling on the edges to stretch the diaphragm a bit. If you find any, the entire slide/diaphragm assembly must be replaced.

It sure is looking like that's what it is.

Willum
TC

 

Well, I took off work early for the three day weekend! Yeah!

Here's the latest... I removed the top of the carb (with the carb on the bike) and took out the slide/diaphragm assy. It looks fine. No rips, holes or other anomalies to be found. I held it up to a bright light to look for any small pinholes, etc. Nothing found.

I put it back together without actually fixing anything. It seems to be working fine again. Maybe a tad rich, but it pulls great up to 9000.

I've got my 16 year old out riding it around in the field by the house. He's young and can push it home if needed.

I'm a little gun shy at this point, but so far, so good.

Willum
TC