BST38ss Carbs - emulsion tube o'ring

[blagle]

Does anyone know if there is an o'ring on both sides of the emulsion tube retainer for BST38ss carbs?  

Pulled carbs apart, changed emulsion tubes (new genuine part) and replaced o'ring outside of retainer (see pic - o'ring sits where red arrow is pointing).

New emulsion tube seems a looser fit than the old one so I'm wondering if originally there were also an o'ring on the other side of the emulsion tube too? Or is the tube just a press fit into the retainer and only sealed one side? Maybe it doesn't matter, just confirming as already had a bitch of a time with this carb so limiting new issues.

For info - bike is 1990 GSXR750L (UK spec) 

cheers

 

[Blue]

Any use https://alpha-sports.com/suzuki_parts.htm

[blagle]

thanks, looked at schematics before (same as these ones) and none of them show the emulsion tube retainer.  Pretty strange, only managed to find the bottom o'ring part number through "Litetek" who make seals in Thailand.  Nothing in the service manual either and Mikuni site couldn't help! 

Someone out there must have pulled these down so hopefully will get an answer. cheers mate

[Dezza]

All BST carbs I have ever pulled apart have only had a single o'ring in the position shown by the red arrow in the picture above. The last set I rebuilt were a set of 750L carbs and they had the same o'rings as other BST carbs. I replaced the o'rings with a set from Litetek and all was good. Have you mixed up the new o'rings and accidentally fitted the wrong one to where the plastic slide fitting meets the carb body as pictured? What was the source of the new o'rings? I noticed the new Litetek o'rings are a very tight fit initially. If the ring is not seated correctly the assembly could remain loose so maybe check everything is going back together as it should.

[Lachie04]

The. Slide guide itself may be worn I replaced a set in a bst36 set once. From memory they were a tight fit.

Check this site 

https://store.moto-lab.com/articles/bst33-slide-guide-wear-indicators

Although a different area may be related the guys that run this site very knowledgeable maybe have a chat with them for advice

 

 

[Simbec1863]

As @Dezza says o ring as per red arrow no o ring on the other side,I’ve rebuilt many sets of these BST carbs.

The emulsion tube should be a very firm push fit to seat in the guide they should also be oriented in the guide in order to align with the peg in the carb body when fitted in order to seat correctly before then fitting and tightening the main jet.

[blagle]

12 hours ago, Dezza said:

All BST carbs I have ever pulled apart have only had a single o'ring in the position shown by the red arrow in the picture above. The last set I rebuilt were a set of 750L carbs and they had the same o'rings as other BST carbs. I replaced the o'rings with a set from Litetek and all was good. Have you mixed up the new o'rings and accidentally fitted the wrong one to where the plastic slide fitting meets the carb body as pictured? What was the source of the new o'rings? I noticed the new Litetek o'rings are a very tight fit initially. If the ring is not seated correctly the assembly could remain loose so maybe check everything is going back together as it should.

Thanks for reply.  Sourced the o'rings from Megazip - genuine Suzuki part from Japan.  Did look at Litetek and decided to go genuine. The o'rings looked identical to the old ones I took off and fit, perhaps seemed a bit thin but so did the originals.  Major issue was that new emulsion tubes seems to have a slightly looser fit when pulled into the retainer by hand, old tubes where very tight.

Was considering using the old tubes with new needles to keep things tight but guessing that would be a mistake to pair new needles with old tubes. Yes/no?  New tubes are also genuine (stamped with Mikuni symbol like ones removed).  Perhaps tightness is from varnish build up on oldi ones and I'm just being anal! 

[blagle]

4 hours ago, Lachie04 said:

The. Slide guide itself may be worn I replaced a set in a bst36 set once. From memory they were a tight fit.

Check this site 

https://store.moto-lab.com/articles/bst33-slide-guide-wear-indicators

Although a different area may be related the guys that run this site very knowledgeable maybe have a chat with them for advice

 

 

thanks, good info. I'll definitely have a good look at the slide guide while things apart to check for wear.  Only 38,000k on the bike so hopefully all good.

[blagle]

update - just got out parts and noted every part I bought from Megazip was made in Japan apart from the emulsion tubes!  They are listed as made in China.  They have the Mikuni Stamp on them as shown in pic but now I'm wondering if I got fleeced. At $25USD a pop that's a good rogering!

 

 

[Dezza]

If the tubes do not fit correctly in the holder, then it appears to me that the problem is the tolerances of the tubes are incorrect. As Simon states, the tubes should be a very tight fit in the plastic holder when seated correctly so I'd be sending them back to the supplier and sourcing an alterative. I see the website given above, moto-lab, supplies both pattern and 'OEM' tubes so maybe contact them and ask their advice. The emulsion tubes do not move relative to the holder so I cannot see how wear can cause the problem. Can you measure the old and new tubes with a micrometer to confirm the new ones are slightly smaller than they should be? Personally, I would measure each old and new tube multiple times (4-5) both in the shed or after they have warmed up for a few ours indoors, then average out the measurements for each so you get a 'warm and cold' mean value for each tube but I understand this approach is a bit nerdy for most people.

[blagle]

12 hours ago, Dezza said:

If the tubes do not fit correctly in the holder, then it appears to me that the problem is the tolerances of the tubes are incorrect. As Simon states, the tubes should be a very tight fit in the plastic holder when seated correctly so I'd be sending them back to the supplier and sourcing an alterative. I see the website given above, moto-lab, supplies both pattern and 'OEM' tubes so maybe contact them and ask their advice. The emulsion tubes do not move relative to the holder so I cannot see how wear can cause the problem. Can you measure the old and new tubes with a micrometer to confirm the new ones are slightly smaller than they should be? Personally, I would measure each old and new tube multiple times (4-5) both in the shed or after they have warmed up for a few ours indoors, then average out the measurements for each so you get a 'warm and cold' mean value for each tube but I understand this approach is a bit nerdy for most people.

thanks mate, will do a measure and see how it goes.  Checked with the supplier and they provided evidence of parts being made in China now by Mikuni (that's some comfort).

[blagle]

On 1/25/2022 at 9:36 PM, Dezza said:

If the tubes do not fit correctly in the holder, then it appears to me that the problem is the tolerances of the tubes are incorrect. As Simon states, the tubes should be a very tight fit in the plastic holder when seated correctly so I'd be sending them back to the supplier and sourcing an alterative. I see the website given above, moto-lab, supplies both pattern and 'OEM' tubes so maybe contact them and ask their advice. The emulsion tubes do not move relative to the holder so I cannot see how wear can cause the problem. Can you measure the old and new tubes with a micrometer to confirm the new ones are slightly smaller than they should be? Personally, I would measure each old and new tube multiple times (4-5) both in the shed or after they have warmed up for a few ours indoors, then average out the measurements for each so you get a 'warm and cold' mean value for each tube but I understand this approach is a bit nerdy for most people.

Tubes measured up OK so back in carbs.  Started first crank and seems to be running OK.  Willl balance them up once I get a set of gauges and hopefully all good.  thanks again for advice