Carb rebuild recommendation

[Crass]

Once I've got them off I'll assess the state of them. I may well still go for a good clean up through one of the people recommended on here as they definitely need it externally and they might be less than shiny inside.

Edited August 30 by Crass
Spelling

[Crass]

So an update on this as the bike is now off the road for winter and I had a fun morning removing the carbs.  The first revelation is that it appears that someone has been in there before me, which fits with the bike having an aftermarket full exhaust and a K&N. I'm pretty sure that a Dynojet kit is fitted as the needles seem to have a step part way down the taper and a magnet isn't interested in them, so they're not steel. I'll know more once I start dismantling. This may alter what is actually worn depending what I find, as it may not be the tubes I guess.

[Upshotknothole]

18 minutes ago, Crass said:

So an update on this as the bike is now off the road for winter and I had a fun morning removing the carbs.  The first revelation is that it appears that someone has been in there before me, which fits with the bike having an aftermarket full exhaust and a K&N. I'm pretty sure that a Dynojet kit is fitted as the needles seem to have a step part way down the taper and a magnet isn't interested in them, so they're not steel. I'll know more once I start dismantling. This may alter what is actually worn depending what I find, as it may not be the tubes I guess.

DJ needles are usually Ti, so that would check out. When you get to the jets, you can compare the sizes they have on them with what DJ has in the instructions for the jet kit for this bike.

[Crass]

Can someone confirm these are DJ needles, now removed. 

Seem to me to be the issue as there is a lot of wear towards the top of the needle as you can hopefully see from the photo. It is not uniform around the circumference, more like a flat on one side and the metal is noticeably rough/pitted.

Note that the needle clip is on the 3rd groove, whereas according to the installation instructions the 2nd groove is standard so this would make it richer, no?

I do have a dyno run from an OSS day which I'll post up in due course.

 

Edited November 6 by Crass
Forgot photo

[Crass]

One of the slide lift holes has been tapped larger as per the DJ instructions but the corrector has been left out, which is optional of course. 

[Crass]

I shall pack in for today after this and await any comments from knowledgeable OSS peeps before stumbling blindly on. So, main jets removed and I assume they are DJ as the only marking is a number 120. Again this doesn't exactly tally with the DJ instructions which recommended 124 with an aftermarket exhaust and can.

The emulsion tubes look fine. Would I be correct in assuming that if they are not visibly worn / oval they are probably not significantly worn? Presumably they are DJ tubes.

I don't seem to be able to get the emulsion tubes out of the plastic slide mount thingy by gentle tapping and as plastic is involved I'm reluctant to go nuclear. This may be academic as if the tubes are fine I'll leave well alone.

Edited November 6 by Crass

[Upshotknothole]

DJ needles only work with DJ emulsion tubes, so all the parts will be matched. Personal experience has been people often don't follow the instructions on these kits and just toss whatever into the carbs if they think it runs half way decently according to their butt dyno. I pulled a DJ jet kit out of a set of running carbs that were absolute crap. Horrible fuel mileage, none of the sizes matched up with the setup on the bike, etc. You can order spares from DJ, though the last time I talked to them, if you want replacement needles, you have to send your old ones back.

The emulsion tubes will come out of the plastic guides. I usually hit the tube on the work bench, or hold it upside down and tap it with a screwdriver or whatever tool I happen to have handy, rarely a hammer. They're just press fit, they'll come out.

Typically, if you have a Ti needle and a brass emulsion tube, the tube is going to be the part that wears. Of course if the needle is aluminum, and I'm not convinced that DJ needles have always been Ti, the needle will wear. It really doesn't take much for the emulsion tubes to get worn. Once you get them out, it helps if you can find an appropriately sized drill bit or rod that you can slide into the tube and look at the gap around it for roundness.

As it sounds like you're not in any rush at the moment to get these back on the bike, I'd methodically take all of the jets, needles, and emulsion tubes out of the carbs, keep everything organized as far as what came out of which carbs, check all the parts as well as the gaskets, and make a list of all the parts that you'll need to rebuild them. A basic rebuild kit with new o-rings and gaskets will probably be a good idea depending on how old they are. As you've currently got a DJ kit in there, you'll be stuck with DJ unless you can find a NOS set of OEM emulsion tubes.

I'm also curious what jet you have in your power jets. They're the jet in the float bowl that feeds the tube that runs up the outside of each carb. DJ usually blanks them, Factory Pro uses them, but they're primarily there to help with fine tuning of the top end when used with an air box. Lastly, there's a good write up in the archives about the BST38 carbs, it'll help with setting them back up after you have them rebuilt. They're good carbs, and not nearly as finicky to setup as the BST40s, and they do like running with pods as opposed to an air box if you should ever decide to go that route.

 

One last thing, when looking at the jets and emulsion tubes. Mikuni parts all have the Mikuni square logo with a number. DJ parts won't have the logo and their emulsion tubes aren't marked, just the sizes on the jets. Makes it easy to tell them apart.

Edited November 6 by Upshotknothole
more info

[Upshotknothole]

5 hours ago, Crass said:

Can someone confirm these are DJ needles, now removed. 

Seem to me to be the issue as there is a lot of wear towards the top of the needle as you can hopefully see from the photo. It is not uniform around the circumference, more like a flat on one side and the metal is noticeably rough/pitted.

Note that the needle clip is on the 3rd groove, whereas according to the installation instructions the 2nd groove is standard so this would make it richer, no?

I do have a dyno run from an OSS day which I'll post up in due course.

 

I don't have any DJ needles handy to compare to, but I've never seen wear like that on a needle. That would only happen at or just above idle to get the wear that far up the needle. The clip placement is merely a starting point when tuning the carbs, sometimes the bike prefers richer or leaner.

[Crass]

Thanks very much for your advice, much appreciated. There's a good chance that this DJ kit has been in the bike for quite some time, possibly before they started using Ti needles. I have my doubts that these are Ti as they are a bright, silver, shiny colour whereas Ti is usually a duller grey. The way the surface is pitted doesn't look right either. I'll do what you suggest with the emulsion tubes to see if I can see any ovality. There are no Mikuni marks on any jets and tubes, so it looks like it's all DJ.

The power jet in the float bowl is a plug. You can't blow through the plastic hose connector on the outside, it's blocked. The jet in the bellmouth is also a plug. I only have the external hoses connecting the two on carb 1, the rest are missing and one of the plastic connectors on one of the float bowls is broken off too. I wasn't intending commissioning the power jet circuit so it's not an issue.

I have a feeling that the wrong main jet has been put in and being too small they have compensated by raising the needle. The pilot fuel screw is 1 1/4 turns out rather than 2 1/2 as DJ recommend and my dyno run shows the pilot is still too rich, so I guess they've tried to further compensate with this. Result is the bike runs ok but not as it should. My plan will be to buy the correct 124 main jets, send the needles to DJ for exchange, then set everything up as recommended and go from there. I'll strip everything tomorrow and list what I need.

Edited November 6 by Crass

[Upshotknothole]

When ordering the jets and needles, might as well replace the emulsion tubes too. I think I paid about $20 for all four of them early last year. Mine was the same way, jets were too small, needles were lowered really far to make up for the emulsion tubes, and I think there were some non DJ parts in mine as the bike wouldn't even run when I started swapping in new DJ parts. I had a spare set of carbs, an old Factory Pro stage 3 kit, and new emulsion tubes, so I swapped everything over to the Factory Pro specs, and it runs great again.

It's really common for the plastic connectors for the power jet needles on the float bowls to break off. If you go back a few pages in this section, I have a thread on rebuilding these carbs.

[Crass]

Got everything stripped this morning. The extreme wear on the needles is on the section which sits in the slide, not in the emulsion tube. The slide holes all seem round so it looks like the plastic has worn the needles and they now rattle about in the hole. There is wear on the needles near the top where they sit in the emulsion tube but not bad enough to be clearly visible. You can feel a lip, not all the way round, with a fingernail and it's just about visible. I guess as fueling is so precise that would be enough to affect it.

Regarding the power jets, the air jet in the bellmouth is not plugged like I said above but the one in the floatbowl is. I did wonder about this some years ago when I noticed the linking hoses were missing and I plugged the open end of the connecting pipe stubs with a dab of silicone as I wondered whether this would allow unfiltered air to be pulled through these pipes- looks like I was right. As part of the rebuild I'll make a tidier job with some rubber caps.

Checked the emulsion tubes by putting a drill bit inside. I can't see any ovality but I'm just going to get a new set for what it will cost and be sure. I'll ring DJ and see how I get on with exchanging the needles.

Edited November 7 by Crass

[Jaydee]

18 hours ago, Upshotknothole said:

DJ needles only work with DJ emulsion tubes

Thats only with the kits that provide the emulsion tubes. Many dj kits don't  come with emulsion tubes (bandit 12 for example) so you have to use stock emulsion tubes.

[Upshotknothole]

3 hours ago, Jaydee said:

Thats only with the kits that provide the emulsion tubes. Many dj kits don't  come with emulsion tubes (bandit 12 for example) so you have to use stock emulsion tubes.

The only kits for the BST38s from DJ use their emulsion tubes, which is a good thing. OEM emulsion tubes for the BST38s are getting really rare now. Occasionally a set of NOS ones will pop up on Eblag when an old dealership is clearing out their inventory, but Suzuki hasn't made them for years. Factory Pro kits do need OEM emulsion tubes for these carbs.

[Crass]

Wemoto seem to have a good reputation for carb parts so has anyone used their carburettor gasket and float bowl kit succesfully? There is a considerable saving over NRP, especially as x4 required, although TBF the NRP kit does come with float valve brass seat (not required, I just need to replace the o-ring on the existing one).  However, I don't want to buy cheap and pay twice if the quality isn't there with the Wemoto product.

Edited November 7 by Crass

[Crass]

Well I have to say I can't fault the customer service from Dynojet. Called them last week concerning the worn needles which I needed to replace and the lady on the phone was super helpful. Explained they don't sell needles separately but exchange them on receipt of old ones free of charge under lifetime warranty, which is what I was expecting from posts here. I also ordered new emulsion tubes and the 124 jets the Stage 1 instructions suggest should have been fitted. Sent my needles in and got a call this morning confirming receipt and that they will be exchanged and paid for the rest of my order so it can all be sent out. I'm not even the original purchaser of the Dynojet kit fitted. Outstanding. 

Slide guides are worn out by reference to the wear indicators so ordered a set of new ones from NRP, along with a pilot fuel screw which has seen better days having needed some persuading to leave home.

I'll give the Wemoto gasket kits a try, having never had any crap from them so I expect good quality.

Also like to say how invaluable all the info has been on here so far through doing a search of old posts and getting guidance on what to be looking for when assessing what needs to be done when rebuilding these. Thanks to everyone who takes time to share their knowledge. 

Edited November 11 by Crass

[Crass]

I know you like pictures so here are some of the carbs as they came off the bike. They were filthy. The bike as it came to me seemed to have been sprayed up with a sticky preservative oil film. It had done its job but it was a right mess to clean off and as I never had the carbs off the bike I couldn't get those properly clean in situ. First job on removal was to get them degreased and scrubbed with a small bottle brush. Two bowls of filthy water later they were fit to be worked on.

 

[Crass]

And after given a good scrub.

[Crass]

After stripping down I dropped them off at Doncaster Motorcycles for a session in their ultrasonic bath. And the result -

 

 

[Crass]

This is the pre-rebuild dyno run from a few years ago. I'm hoping after all this work I can get a better result. Not absolutely awful fueling but far from ideal either.

 

[Crass]

And finally I was reading the thread from some years ago about the plastic ring which fits on the needles and tends to wear. I see the modded versions are no longer available but the info was still useful. Mine seem to be a variety of thicknesses so have obviously worn, another issue affecting the fuelling no doubt. No point sticking those back in so I've sourced a set of NOS ones at half the price. When they arrive I will take accurate measurements and post them here so we all have a reference point in future as to what unworn ones should be.

[nickmac]

Nice work 

[Crass]

The needle washers have arrived and I've posted up the dimensions in the sticky thread devoted to that subject. 

I got these NOS from Legend Motorcycles on the internet. They seem to specialise in buying up NOS, it's good prices and there's currently a lot of Suzook stuff that may interest members. 10% discount until 31 Jan with site10. They're not an OSS trader so I'll leave it at that.

[Crass]

There's another issue which I haven't seen mentioned elsewhere is that as well as the plastic needle washers wearing the rotation can also cause corresponding wear on the stepped area of the slide. Two of my slides have a significant dip in the plastic where this wear has occurred which is rough. Just replacing the washers is only a partial fix as the needle is still not going to be at the correct height. It's not an easy location to work with being down the centre of the slide. I'm going to try a small fill of chemical metal which I should be able to blob on then smooth flush with the end of metal rod as it starts to set.

[Crass]

So to give you some idea of the scale of the wear in the slide caused by the plastic needle washer,I measured it with a depth gauge. The wear amounts to 0.2 - 0.5mm across the 4 slides. Clearly that amount of wear affecting needle height will also affect the fuelling. We are looking at multiple issues here from carbs manufactured out of cheese.

So, this morning I filled in the wear depressions. I decided against my original intention of a little chemical metal filler and used Plastex repair. The worn area is very rough so should provide a good key after a squirt and clean with brake cleaner. First,I put a small roll of plasticine in the slide and poked it against the step to form a dam against the area of depression. Then sprinkled a small amount of the powder down the slide and tapped it into place, followed by the liquid setting chemical. After an hour I remeasured. 2 were ok or very slightly proud so they were smoothed right with a small piece of very fine emery stuck to a t-bar rod with Blutac. The other two needed a bit more filler to get right. Gentlemen we can rebuild him, we have the technology....

[Upshotknothole]

Nice work, I have a large box of spare carbs that I dig through and pull parts off of as needed. I'm hoping to convert all of my bikes to flat slides before I run out of spare parts.