Leaking carburetor boot/holder

[shauno]

Hi all,

Have a KDX that I have rebuilt slowly and had issues with. After doing topend and revamping bike it had issues starting and was chasing a few things. Replaced the coil and that got spark back but couldn't get it to fire until spraying some "Start ya Bastard" starting fluid. It got it going but won't use it again.
Explored the possibility of a leak and found the ''packing'' seal on the right KIPS shaft was leaking. Went back in and replaced that which sealed up the top end and then did the leak down test again which showed that it was holding pressure in a leak down test. Unfortunately while I was in there I noticed the bore looked a bit rough and seemed to have a small crack and got that welded and a new coating to bring it back to new.

So have just put it all back together and did another leak down test to see how it is and now there is a leak from the carburettor holder. New gasket was installed against the engine intake then reed block and then carb holder. Pressure leaks straight away on the left upper side through one of the release areas built into the carb holder. (Circled on the photo). It wasn't doing that before when i checked it prior to this replating and reassembly. Nothing has changed.

I believe when i first pulled it down there was some kind of silicon sealant in there and the previous owner was trying to jet the bike to get it to run right. Certainly if this is the issue I'll be happy as that is probably why the thing wasn't starting the way it should. Everything else being new (Lectron carb, gaskets, good new piston, rings and reeds and clean air filter, new spark plug and fuel).

After finding the leak from between the reed block and the carb holder on upper left side I reassembled and made sure all bolts were tight. Still leaking. The white insert in the reed block that channels the air seems a bit loose but it looks like that is how it should be. The raised circular seal that sits against that on the carb holder feels good but the rectangular one doesn't seem particularly high compared to the flat carb holder surrounding that. All surfaces have been cleaned.

Is the whole area supposed to be black rubberised but the bronze area shows where that has been worn away? The fact that it leaks from the small lower release channel indicates that it is leaking from both the circular seal and the rectangular one. Do i just replace 160651298 Carb Holder (not cheap) or does perhaps the fact that the white internal built of the reed block also need replacing (which only can be done by replacing the valve assembly reed - 120211067)?

Seems a bit drastic. The weird thing was that there didn't seem to be a leak there before. Although that would explain the hard to start issue. Making a gasket would lift the circular seal even further away from the white part of the valve assembly reed and create messy air intake. Silicon sealant? Seems like it would also be a problem.

Has anyone else had this or have any suggestions? The air pours out in a loud hiss so it is not small.

leaking carb holder.jpg (729.84 KiB) Viewed 2135 times

[KDXGarage]

cylinder, gasket, reed cage, boot is the order

Are you tightening in a star pattern? Using a torque wrench?

The o-ring looking part must be the seal. I don't think the indention matters, as it has them all around.

Which model KDX??

[shauno]

Yes to all. H series.

Very strange that it suddenly doesn't seal.

[kdxdazz]

I've been through the exact sane issue. The problem is definitely the oring becomes flat over time. First off trying sealing it with threebond, 1104 I believe but my memory is a little hazy. Mine was so bad that it didn't work so I bought the thinnest gasket material I could and made a gasket, only thing is that holds the boot off of the plastic insert so it would rattle about, I ended up putting an oring between the insert and the carb boot. Tighten the bolts to 10n/m. all up it was a huge pain and if funds allow just buy a new carb boot or possibly a Boyesen rad valve

[kdxsully]

Reed valve/cage/boot leaks seem common in a lot of bikes. I just use a tiddly bit of sealant. But that’s just me, I’m a bit on the frugal side. I wouldn’t use non drying sealant, I’ve seen a (vforce) reed cage ruined from it

[ericr]

I had the same problem which showed up during a leak down test. I just put a bead of ultra copper over that molded o-ring area and then lightly tightened things up. After a few hours, I came back and torqued to spec - no leaks at all.

[shauno]

Okay, I was toying with the idea of another gasket but as kdxdazz mentioned that would hold the o ring bit off the plastic insert and would surely mess up the airflow more. Looking at it closely the bottom part of the circular o ring is slightly flattened compared to the rest which must where the air leak from but then it also leaks from the rectangular o ring also. A new carb holder would be at least 10 - 12 weeks away and I am bit worried that Ultra Copper sealant isn't gasoline proof and might get sucked into the engine so was thinking perhaps a thin gasket cut to shape around outside of o ring and inside rectangular o ring....just sick of spending money and chasing leaks and issues. Just want to ride.

[kdxdazz]

Threebond is gasoline proof

[shauno]

So managed to seal it up. Got some gasket material and created one that went over the whole inside surface with a hole cut for the intake. Then used JB Weld Grey Gasket maker and sealed it up around edges. Pressure tested it again and then saw that it was also leaking from base gasket. Took the jug off again and used the grey gasket maker to seal that. Job done. Held 6 psi for 15 minutes without any loss.
Now the bike starts but seems to have an electrical short somewhere because it started first kick and ran perfectly until i touch the front brake. The bike died instantly so the front brake switch is obviously shorting somewhere. Quite strange though as that is not really connected to the start circuit on normal bikes. ON the Australian models though it is all linked. So might have to hunt through the loom to check all the wiring.