carb cleaning

[rwh]

I've got a 1993 Suzuki GSX750F, which according to the Clymer manual has Mikuni BST36SS carbs.

Recently it started running on only 3 cylinders - after a somewhat more spirited than usual blat through the Wairarapa, including the former site of the sprints ...

In my efforts to find something wrong, I've started dismantling the carbs. This may have been a mistake, but never mind.

I've been following the instructions in the Clymer manual, but got stuck on removing the jet block - plastic thing that the piston slides through, and forms part of the main tube the air goes through, with the jet at the bottom. The manual says I should withdraw that after removing the pilot and main jets (I'm slightly confused there; I've removed what the pics show as the main jet, but there's still something left in the jet block. Pity the manual gives very little description of how the damn thing works, and what the bits are for). I'm wondering if the bits sticking out the sides of the top of the jet block are clips that hold it in, but the manual doesn't say anything about that.

In terms of gunk that I'm cleaning out, I'm a little worried by the brown sludge around the top of the piston - if I can successfully attach the pics I've taken, I've shown two pistons, one cleaned and the other not. Is that normal?

I'm going to have to assemble them without replacing all the o-rings the manual tells me I should replace - and in fact, without some of them altogether, since they weren't there. I intend to use Loctite 518 Master Gasket there instead (this is around the little tube that comes up through the top cover, and is then capped on top), as suggested by the mechanic I spoke to this morning, and what appears to have been done by the last person to service it.

Any more suggestions?

Thanks

Richard

[offrd]

Go easy on the locktite or it may get into little places you really do not want it to be and block god knows what up. Little on the finger and light smear
Better i guess than silicone which some when in contact with petrol can swell like you would not believe...

[rwh]

Go easy on the locktite or it may get into little places you really do not want it to be and block god knows what up. Little on the finger and light smear
Better i guess than silicone which some when in contact with petrol can swell like you would not believe...

The only place I'm using it is around the tube that goes through the top cover - you can see the red remains of the previous lot in the 3rd pic. Since that tube is then sealed off with a cap fixed to the top cover, I'm assuming that it doesn't matter if I block it - that it's there for a slightly different application (there's a hose coming off there on one of the carbs on the GSXR750 covered by the same manual). Is that a reasonable assumption?

Richard

[Paul in NZ]

My strong advice would be NOT to use any gasket goo on carbs but its your bike.... Try to find some O rings - you would be amazed what turns up at supercheap or repco... That 'tube' is kinda vital to the carbs function.

I assume you did identify the dead cylinder before diving into the carbs?? If so - did you find anything in that carb?

Paul N

(pricks of things getting the jet blocks out of those things - leave em be I reckon...)

[rwh]

My strong advice would be NOT to use any gasket goo on carbs but its your bike.... Try to find some O rings - you would be amazed what turns up at supercheap or repco... That 'tube' is kinda vital to the carbs function.

Despite being blanked off? Is it a tuned length or something? Hmm, perhaps I should redo the first one ... I think the others were better. And I'll try and get some o-rings next time - which will hopefully be at a better time of year (not that I didn't see some o-rings that looked 'about right' at Schrodoco this morning ...)

I assume you did identify the dead cylinder before diving into the carbs?? If so - did you find anything in that carb?

Well ... not really. At one stage, I fired it up briefly, and found that #4 header was stone cold while the rest were hot, so I figured that was it. Then later, I did the same thing and they were all hot - but maybe I'd run it a bit too long and the heat had transferred. Anyway - didn't find anything particularly bad in #4 carb. I did find differences that looked like they're intentional, though.

In the float bowl, there's a pilot jet that's screwed in down a deep hole in the casting, off centre. In carbs #2 and #4, there's a rubber bung in that hole, that isn't mentioned in the manual - I can't see how any fuel (or anything else) gets to that jet. #3 doesn't have one, and I haven't opened #1 yet (next task)

Thanks for all the help (whether I'm following it or not ...)

(pricks of things getting the jet blocks out of those things - leave em be I reckon...)

Ah ... well, you're probably going to be horrified at this ... but I screwed the main jet back in, then backed it off about half a turn at a time, and tapped it (gently) with a screwdriver handle ... hopefully not hard enough to distort anything

Richard

[Paul in NZ]

Tappings probably fine...

Personally - I would not have worried too much about removing them unless the bike was running rich etc Sounds like you are having fun - If you get stuck, I have a book here someplace that covers carb basics but it does not go as late as those mikunis.

[The Pastor]

carbs are very simple things, you cant go too wrong with them. just take them apart (one at a time) and check that all the jet holes arnt blocked up. wack em back together and then balance the carbs (i get the shop to do mine as i cant do it / dont have the equipment).

Once its all done nicely go to trademe, list the bike and buy one with FI

[rwh]

Well, they're all back together, and the bike is running no worse than before ... in fact I thought it was running better to start with, then it deteriorated again during my test ride. I've got a feeling it's somehow related to heat.

Sounds like you are having fun - If you get stuck, I have a book here someplace that covers carb basics but it does not go as late as those mikunis.

The fun part is a bit mixed - it would be better if a) there were more shops open to buy bits from when I need them (though then I probably wouldn't be doing it at all), and b) I hadn't planned to be heading to Auckland on it yesterday (though again, if there wasn't the hurry I'd be leaving it to the shop).

I could be keen to borrow that book at some point - or just get enough info so I can find it in the library or something.

Once its all done nicely go to trademe, list the bike and buy one with FI

LOL - tempting, though I don't have the dosh at the moment. And the more I've played with it, the easier it gets. I could now dismantle the carbs, starting from a fully faired bike, without looking at the manual every step, so that probably saves about 90% of my time

Richard

[awayatc]

Well, they're all back together, and the bike is running no worse than before ... in fact I thought it was running better to start with, then it deteriorated again during my test ride. I've got a feeling it's somehow related to heat.

Richard

Well done on the carbs, but if you think its related to heat....did you check/replace your sparkplugs....?

[rwh]

Well done on the carbs, but if you think its related to heat....did you check/replace your sparkplugs....?

That was my next step, though without real knowledge to correlate heat with plugs.

#4, which is the cleanest (best?) looking, is the one I thought was dead in the first place. #2 is the darkest, with #1 and #3 not that far behind (pic 1). However, when I pulled the lead for #2, that's all I got (pic 2) ... the cap (pic 3) was left behind. Does that mean it was probably faulty already, or is it just a bad move to pull on the leads rather than the caps? I assume I can't fix it, so I'm waiting till the shops open to get a replacement Pic 4 shows a coil - do I fit a new lead to that? I hope I'm not up for a new coil as well ...

Do those plugs give useful clues as to the source of my problem?

Sorry about my inability to focus properly ...

Thanks,

Richard

[Pixie]

I've seen the strainers on each individual carb become blocked with debris.This causes one or more carb to be starved of fuel
The strainers can be accessed with the bowls removed.Just follow the path of the fuel to each carb.
This was the cause of an RF 900 running on three cylinders.
The outer carbs are more susceptable than the inner ones.

[Paul in NZ]

If I pulled those 4 plugs out of any bike i owned I'd be concerned regarding the differences between them. Somethings not working at all.. In the unleaded era and given the carbs on your bike I'd expect em to be a bit dark so the super clean one would worry me most.

I can't help with the HT lead as I can't see how it connects - ie on my old bikes they are easy to replace from repco or shite I have laying about the shed... Many jap ones are not designed to come to bits and you need to replace it as a unit. I doubt the usual bandits will have one in stock either - not a good thing to break.

[offrd]

Swap the clean as plug with one of the others and see what the plugs do colour wise, the white plug would look to be either very new, like almost out of the box no km or running very lean, lean is not a good thing..The plug next to the super white one is not too bad, the others are too rich. Of course you will have to fix the plug lead sone how... It may screw back on, have a look if it has what looks like a screw up inside that cap that goes into the lead..
With the carbs check that the needle comes of the seat when the float drops in the bowl and that fuel can pass thru into the bowl. If the carbs are back in and a prick to get out it may have fuel drains on each bowl, see if fuel comes out.

Many other things to try like swapping coils between cylinders, not just the leads

Engine must have 3 basics to run... Air, Fuel and spark.

If nothing else you are learning your bike i guess....

Good luck

[rwh]

It may screw back on, have a look if it has what looks like a screw up inside that cap that goes into the lead..

Aha! Just had a nosy, and it does indeed appear to have a screw in there, so that gives me something to look forward to in the morning - I'm not stuck after all. Then I can have a look back over all the rest of these wonderful tips.

If nothing else you are learning your bike i guess....

Yes - I played with cars as a teenager, but never dared dismantle carbs ... though I'm guessing the Stromberg (I think) on my Hunter might have been simpler ... and of course there was only the one.

Thanks all

Richard

[Motig]

OK I'm not terribly mechanically minded but I'll have a try at most things. The very last thing I would have done is start pulling the carbs to pieces without first checking that the dead cylinder was getting a spark or fuel, it pays to try the easy things first and by the process of elmination find out whats causing the problem. If you've already done that my apologies but you dont mention anything else but the carbs in your post.