Hi everyone -

I've been reading everything here on the white spacer mod, carb adjustments, backfiring, afterfiring, etc.  I can't figure out my particular issue. This has a lot of elements, so bear with me:

I just finished a Ryca build...so I have the shorty pipe with a K&N filter. The bike ran great before I took everything apart. I went up a size to 52.5 and 155 pilot and main jet. I did the white spacer mod with washers...currently I'm running a single, thin washer.

1. The bike won't start without the choke.  Once it has started, though, I have to turn off the choke within 10 seconds or it starts a loping, missing, slow idle and dies. So - I pull the choke out, start it, then after 10 seconds, put the choke in and it ALMOST dies, but then it picks up to a nice-sounding idle.

2. When I'm riding it, it has great power and sounds great under acceleration in all gears.  The second I let off the throttle, it starts crackling and popping and if I close the throttle and pull-in the clutch (coasting to a stop) the idle rpm drops way down for 2-4 seconds, then comes back up to normal (1200-1300)...sometimes the idle drops down so low after closing the throttle/disengaging the clutch that it dies. It drops, and then it recovers...every time I pull-in the clutch/let off the gas. If I don't pull-in the clutch but rather let it engine brake, the pipe starts making a loud "brrrappping" sound as soon as the throttle is totally closed.

3. I have adjusted the idle mixture screw up/down a bunch until I get the smoothest/highest-speed idle I can when the bike is warmed-up. The idle screw it turned-out 2.5 turns.

Here's what I don't get - If the idle mixture is TOO LEAN, I would think that the bike would idle better with the choke pulled-on...or at least for awhile...but if the bike is running and I pull on the choke, it IMMEDIATELY dies (even when it's cold).  BUT I need the choke to start it for just a few seconds.

If the idle was TOO RICH, I would think that I could close the idle mixture screw all the way down and it would run better...but it doesn't - if I close down the idle mixture screw, it idles rough and then dies.  It idles best with the mixture screw turned out 2.5 turns.

I have sealed the pipe/header with exhaust sealant.  I have also checked for vacuum leaks using carb cleaner all around the carb.

Any ideas out there from you carburetor experts?  The carb has a new gasket, new main and pilot jets, and a new diaphragm/slide assembly (b/c I couldn't get the little screws out of the old one, no matter how hard I tried .

thanks everyone!

delaPlanet

Quote:


If you didn't clean the carb before, most likely you have a dirty TEV (the little triangle plate on the side)
I wouldn't adjust the spring, but cleaning is good.

If you just put a pod filter on if can be difficult to tune because of inherent problems.
1. pod filters sometimes has a tall step on the inside that closes off the eyebrow inlet.
2. this carb likes a lead in duct.

brrrappp on max engine brake is normal.

Interesting...OK.  If I turn in the idle mixture screw, it idles very badly, though. It lopes and misses and dies. I will turn it into the borderline of running and see if the throttle roll-off drop is any better, though.

TEV looks perfect on mine - I cleaned everything in the carb before putting it all back together.  I tried running with a 47.5 pilot jet and it ran about the same as it does now...maybe worse.

What is a "pod filter"?  I'm using a K&N "puck" filter that plugs right onto the carb...it's only like 1" away from the carb.

Thanks a bunch for the suggestions, guys -

delaPlanet

Check to make sure your float needle is shutting off when the float is raised. Also check your float level. Remove the float bowl and With the gas on (reserve if it still has the vacuum petcock) the fuel should dribble out until you raise the float parallel with the carburetor body (where the float bowl mounts) then shut off.  Make sure you put a cup under the carb to catch the fuel in.  If it's to low will be lean if it's to high it will be to rich. And be careful gas is explosive!

It may need a new float needle and seat assembly.

Good question on the washer - I tried 2 washers and it wasn't idling well, so I went down to 1 washer. Maybe I should go all the way back up to 4 to start with...it's sounding more and more like everyone here suspects the idle mixture is too rich.  Still, though, I can't help but counter that opinion by noting that when I turn the idle mixture screw IN, it dies.

Question for you guys - Is subtracting washers on the slide the same thing as turning the idle mixture screw out?  Don't both of them just enrich the idle mixture?

The number of washers on the needle should not have any effect on the mixture at idle.  The Pilot Jet circuit controls the idle mixture - the needle does not allow any fuel to flow until the slide begins to rise.....and that does not occur at idle speeds.

The needle (and number of washers) begins to have an effect at about 1/8th throttle.....the kind of acceleration and speed that would occur when you slowly leave an intersection where a Police car is watching you!

The fact that the engine will stop when you turn the Idle Mixture screw in is a very good sign....you know the mixture is not too rich.  The ideal Pilot Jet size is indicated by the best idle smoothness occurring between 1.5 - 2.0 turns from lightly seated.  If you have to go out more then 2 full turns - it is time to try the next larger pilot jet.

I don't know for sure what that RYCA style air clean does to affect the mixture - but I suspect it has almost no effect at idle where the air flow is very low.  A #55 pilot jet is way more fuel flow than a carb in good condition requires....it sure sounds like there is a carb issue that is causing this problem.

Is the rubber adapter and O-ring between the cylinder and carb in good condition?  Those can get old and crack and provide an air leak.  The problems you describe sure sound like you have an air leak between the carb and the cylinder.

My 2007 ran fine and it never wanted any choke to start and run....and even after I used the O2 sensor and gauge to jet the bike - it still never wanted any choke.  The 2002 Rescue bike was jetted nearly the same, and it liked the choke to start and for just a few minutes of warm up.  I really don't know why the two bikes were so different. (Both carbs had #150 mains, the 2007 had a #50 Pilot and the 2002 used a #52.5 pilot)...and both bikes idled best with the mixture screw between 1.5 - 2 turns.


 

Thanks!  I actually did a vacuum leak test with carb cleaner awhile ago - I couldn't detect any leaks.

Interesting - I just went down in size on the pilot jet to a 52.5 after looking at the plug and seeing that it was all sooty.  Going down to a 52.5 produced no change whatsoever.  I didn't even have to mess with the idle screw.  It runs the same as it did with the 55.  This doesn't make sense.