Doesn't run while going downhill

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kawagumby
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Post by kawagumby »

It may be that your fuel is foaming too much, throwing float settngs too high, causing lean or no fuel in certain situations. Check to make sure your carb cap is not touching the frame, i.e, it is isolated enough not to hit anything while the bike is bouncing around. It's easy to shove the carb top up against the frame before you tighten the clamps, I've done it myself. You might also try a different pre-mix to see if that helps (if the problem is fuel foaming).

Also check the float hinge pin for free movement in a downhill attitude that mimics the kind of angles you experience before the fuel starvation occurs. It's likely something simpler than jetting IMO.
1994 KDX200, Beta 200rr, yz125, yz250, kx100 modded for adult, gasgas contact 250.
lemmy
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Post by lemmy »

This is possible. The throttle cable (right where it comes out of the top of the carb) is really pressed up against the frame cross bar that goes side to side. I don't really see any way to keep it off of it. It rubs it so bad the rubber boot is completely ripped there.
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kawagumby
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Post by kawagumby »

I doubt that the cable would transmit enough vibration to cause the fuel to foam...but you should be able to rotate the carb a little to take that kind of pressure off the cable in any case.
1994 KDX200, Beta 200rr, yz125, yz250, kx100 modded for adult, gasgas contact 250.
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canyncarvr
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Post by canyncarvr »

Disconnect that Vapor thing. They have been responsible for all sorts of 'it don't run right' problems.

Poo poo that all you want..but you can put it together with, 'How come I get better spark with an aftermarket lighting coil?'

Dont' know why, but...you do.

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kawagumby
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Post by kawagumby »

What vapor thing?
1994 KDX200, Beta 200rr, yz125, yz250, kx100 modded for adult, gasgas contact 250.
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canyncarvr
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Post by canyncarvr »

THIS vapor thing.
lemmy wrote:I just hooked the power up to the light and everything works fine. The tach is very smooth....

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lemmy
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Post by lemmy »

It hits the cable right at the top of the carb though. I am going to try to get it away from the frame, but I have tried that before with no luck.

It was doing this long before I had the vapor, but I unplugged it and it still is doing the same thing.

Right now and I waiting on a new choke plunger, and I am goin to take the carb off with it still hooked up to the tank and tilt the carb forward and shake it some and try to see where the fuel that drips out the front of the carb is coming from.
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Post by canyncarvr »

The throttle housing (covered by the boot) is a close fit to the frame. It shouldn't be so close as to be rubbing hard, but it probably touches the 'bellows' of the boot.

Does the choke have an effect on a cold start? If that part is normal it's an indicator of the choke working as it should.

Normal? Choke on (pulled)..bike idle increases, it won't die. Choke off (down) idle drops significantly, bike probably does die.

That for cold choke starts..not kind'a warm, not warm, and is true for only the first minute or so, and only for a 1/2 fast jetted bike.

So....that part is 'normal'? If so, replacing the choke plunger isn't likely going to fix anything.

I don't recall that (choke cold starts) being mentioned before. If so...then this is all a waste of time.

Neat!!

:wink:

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Post by lemmy »

I just looked at the cable again and it is not touching the frame. It was with the RAD valve that the cable was really hard up against the frame. With the stock reed cage and rubber boot the carb sits more forward. I actually have a hard time getting the air intake up over the carb good so that I can tighten the clamp. So that isn't a problem.

The choke is weird. I do need it for cold starts, but once it starts, I can immediately turn it off and it doesn't seem to have much effect when I do turn it off. However once warmed up if I pull it on, it kills the bike very quickly. So it definitely does something. It has been that way throughout every type reed and jetting configuration.
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Post by lemmy »

I took everything including the jet block apart tonight. I checked every single passage in the carb and everything looks fine. However the jet block o-ring could stand to be in better shape. I am going to order one of those and see if that helps. If the carb is tilted, it could allow fuel to come by the o-ring and either around the needle area or more likely out of the small hole in the bottom of the bore that is closest to the intake. When I tilt the carb and shake it this is the first place that fuel comes out. However it isn't much fuel, so I am not THAT hopeful.
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Post by canyncarvr »

Yes, with the radvalve it does. Yet another reason they suck (besides not working worth a hoot, not lasting for diddle and costing a lot of money).

Re: ..choke is weird...

A bike that needs no choke to start...or very little..is generally a bike that has too rich a pilot circuit. The, 'Starts first kick every time!' is not as good a deal as the person saying it thinks it is. There is likely a performance hit 'cuz it's too rich.

Musing....but the '..kills the bike very quickly...' part isn't real good, either. IF...the bike is on the rich side of things, then the bit added by the choke would more likely kill it than if it wasn't. Still....your bike should be able to run for quite awhile with the choke on. Not well...4-stroking and blubbering, but it should run.

You were running a 45 pilot, correct? Given the 'jet by mail disclaimer' (it doesn't work)...that's on the rich side. I suggested changing it some time back...don't know if you ever did......

Ron Black told you he thought it was a jetting issue, correct? I would suggest taking his advice. At the very least explore the options.
Someone wrote:21mm level, 40 pilot, and a 'C' taper needle....and put the 152 back in while your there. Maybe even a 150.
Good luck! You'll get it sorted out.

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Post by lemmy »

At one time I had a 35 pilot, C taper, and 152 main but the level was at 17mm. The choked acted the same way it does now. It seems that nothing I do to the pilot circuit changes anything except the air screw. When I get that o-ring in, I am going to try it with the existing needle with 40 pilot and 152 main and see how that does, then I am going back to the C.
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Post by canyncarvr »

I'm getting the Keihin mixed up with some Mikuni carb I'm sure..but I'll ask anyway. I'd much appreciate your input..your PWK being in pieces.


Mikuni's (some) have a washer between the main jet/needle jet. It's not hard to get that washer mis-placed on re-assy (no..it wasn't me!). The PWK has a washer there? Seems it's maybe swedged into the body?

The Mik needle jet drops out the top of the carb when the main is removed..thus it's easy to get IT (needle jet) misplaced on re-assy, too.

The PWK jetblock is held into the body with a couple of torx screws, isn't it?

Point being...there is no way to put the main/washer/jetblock/needle jet in the PWK 'off' (not seated, crooked) such that it leaks?

You can in the Mikuni.

Just wonderin'.

Thanks!

**edit**
Another btw..but your carb IS sitting with the cast key in the downstream throat aligned with the slot in the boot? It's not hard to get that out of place..and that causes carb leakage.

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Post by lemmy »

I can remove the main jet, but the needle jet doesn't seem to be able to be removed. I don't see any washer in my carb or in the exploded diagram. Yes, the jet block is held in by two security torx screws. They had blue loctite on them. The only source of leaks I can see is around the o-ring for the jet block. I am going to post some pictures so you can see what I am talking about. I am getting a new o-ring, however I turned the carb upside down and filled the cavity with fuel with the jetblock installed. Some leaked into the main throat, but very little. Of course any leaks had to be coming around the jetblock o-ring since there are no other passages up that high in the carb.

Yes, the cast key is firmly inside the slot in the boot.
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Post by lemmy »

I have taken some pictures and typed up how I think things work and a summary of the passages on this carb. I figure it might help someone else trying to troubleshoot problems, and help me in pointing out an area I am talking about. I am sure I have some things wrong, so please point out screw ups.

Bottom:
Image
Jetblock1:
Image
Jetblock2:
Image
Airbox:
Image
Intake:
Image

Choke circuit:

The air comes from A on "airbox" picture and the fuel comes from the brass C on the "bottom" picture. When the plunger is down, it blocks both passages, but when up, the fuel and air come out of B on the "intake" picture.

Pilot:

The fuel comes from B in the jetblock2 picture (pilot jet is inserted in this hole). This comes up to C in the jetblock1 picture. This passage is also connected to D in the jetblock1 picture. A in the jetblock1 picture is an air passage That comes through the jet block and also out of C. B in jetblock1 comes in to the area around E, not sure what this is for. Fuel/air mixture coming out of C in the jetblock1 picture goes through the small hole D in the bottom picture. This D hole comes out A in the intake picture. A in the intake picture is the first place fuel comes out when tilting the carb forward. I think fuel is leaking around the jetblock o-ring (seen in jetblock1) and out the hole A. B in the airbox picture shows the air screw. The hole B is connected to B in the jetblock1 picture. The C in the airbox pictureis a passage that the air screw goes in to and this passage comes out A in jetblock1 (which goes around to C jetblock1 as already mentioned).


Bottom picture:

A - goes to vent hose.
B - goes to the other vent house.
C - fuel pickup for choke/enrichment
D - hole for fuel delivery for pilot/idle circuit (pilot jet size determines the amount of fuel)
E - Air passage for pilot circuit (passes through jet block)
F - air passage that goes around needle jet (passes through jet block)
G - fuel inlet from petcock. Needle valve goes here to shut off fuel supply when fuel level is high enough in float bowl
H&I - jet block torx screw holes to attach jet block to carb body


Airbox picture
A - air intake for choke/enrichment circuit
B - air intake that goes around needle jet (comes out of F in "bottom" picture)
C - air intake for pilot circuit (comes out of E in "bottom" picture). Can't see passage in this picture, the end of the air screw fits in to this passage.
D - air screw adjustment
E - fuel hose attachment

intake picture
A - fuel mixture outlet for pilot/idle circuit (connects to D in "bottom" picture)
B - fuel mixture outlet for choke/enrichment.


jetblock1 picture
A - air intake for pilot/idle circuit. Source of air is C in airbox picture, air comes out C in this picture
B - air intake to area around needle jet (E), source of air is B in airbox picture.
C - fuel mixture outlet for pilot/idle circuit
D - also connected to C, not sure of purpose
E - needle jet

jetblock2 picture
A - main jet (main jet is removed in this picture)
B - pilot jet (also removed in this picture)
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canyncarvr
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Post by canyncarvr »

Great! Thanks!! Excellent pics and notation.

Inda: This would be a good stickie to Jets and Needles
A reference for the PWK carbs...


Re: Jetblock-2 'A' That's the swedged in (staked, whatever) washer I was thinking about. It's loose in the Mikuni's I've fussed with. Being loose, it can get cocked..then the main jet doesn't seat. Setup like that, it leaks a lot. :wink:

Did that jetblock gasket come from Sudco? You got the other gaskets, too? Some are air..some air/fuel, but might as well replace them if they're available. That's all part of the 'do not take apart' diagram of the PWK on Sudco's website.

Dang! Fine documentation job. MUCH appreciated!!

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Post by lemmy »

This morning I placed an order with MXSouth for the Jet Block O-ring (021.532) and a couple of other small carb parts (vent hose and drain o-ring). The Jet Block O-Ring was $4.41. I orded other stuff like a knee brace and No Toil Air Filter. I get an email that small carb parts will deley the order unless I wanted to pay the $20 manufacturers minimum order fee. So I called the place that I ordered some jets from a few weeks back (Carbparts.com) and the guy said that O-ring was never available except that there was such demand, Keihin USA had a batch made. Then Keihin Japan made them not make anymore because of liability issues. Something about if it isn't in right, it could cause sever problems. Personally I don't see what problems it could cause any worse than a bad o-ring. Anyway he said that the distributor (I assume Sudco) has two left and there would never be anymore made. He said the price was $21. I think I am going to call Sudco. The only thing from Sudco that is listed as available from Sudco besides standard stuff on the exploded diagram is this Jet Block O-ring.
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Post by lemmy »

I called Chad at Sudco. He said that Carbparts.com was probably thinking of the FCR o-ring that is no longer available. He said he had 5 of the PWK jet block o-rings. He said he didn't know if it was still being made or not. So I just ordered of couple of those and an extra float valve and two vent tubes and that put me up to $25. Sent priority mail it should be here in 2-3 days!
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Post by canyncarvr »

Are the A-B-C in jetblock 1 o-rings? Or fiber?

The seal around the jetblock looks to have been 'glued' to the jetblock?Or, that's just grease?

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Post by lemmy »

It is a one piece o-ring that seals the perimeter of the jet block and also fits around the A,B,C holes. I haven't tried taking it out yet, but I tugged on it a little bit and it was in there good. It doesn't feel like there is any grease on it at all though. It could be stuck in by the brown dried fuel/oil gunk. It is fairly dry even though it doesn't look that way in the picture.
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