Idling issues / carb identification

[daz_j]

Hi all, I'm struggling to solve erratic idle issues, been round the houses a few times, now trying to get a deeper level of understanding of my CV carbs using the diagram attached which explains the idle system.  It's labelled 850GT but I believed the principle was the same for my GS550 BS32 carbs.  
However I've discovered my carbs have a mystery additional hole drilled from above the pilot jet through into the main bore, I've added it in red on the diagram, and see also the carb photo.  I queried this on one of the Facebook groups - only had two responses but both said it was a correct part of the idle system.  To me it seems to be at odds with the mixture screw.
Now the plot thickens.....I've just taken delivery of a spare set of carbs, they appear to be identical in every way apart from they don't have the mystery holes above the pilot jets. They are like the diagram shows, so there is definitely some inconsistency here. 

So my first question please - is there a way to identify which model / ID carbs I have?  There doesn't appear to be any numbering on the carbs themselves.

 

[TonyGee]

I assume they have had a proper clean and they have been balanced ? 

[daz_j]

35 minutes ago, TonyGee said:

I assume they have had a proper clean and they have been balanced ? 

Yes thanks Tony; any thoughts on the mystery holes or ID’ing the carb bodies?

[TonyGee]

1 hour ago, daz_j said:

Yes thanks Tony; any thoughts on the mystery holes or ID’ing the carb bodies?

that small hole is part of the idle circuit, can't I/D your carbs though. 

[daz_j]

3 hours ago, TonyGee said:

that small hole is part of the idle circuit

Then I’d like to understand what it’s doing, it appears to be putting unmetered mixture into the system?And why isn’t it present on the carb manual diagram, or in my spare carbs?

[TonyGee]

37 minutes ago, daz_j said:

Then I’d like to understand what it’s doing, it appears to be putting unmetered mixture into the system?And why isn’t it present on the carb manual diagram, or in my spare carbs?

it is metered,  by the pilot jet.  

Edited September 5 by TonyGee

[daz_j]

Yes I see that, but can’t really see why we pay so much attention to setting of the mixture screw when ‘the mystery hole’ is letting mixture straight into the main bore?

[TonyGee]

50 minutes ago, daz_j said:

Yes I see that, but can’t really see why we pay so much attention to setting of the mixture screw when ‘the mystery hole’ is letting mixture straight into the main bore?

it only lets a certain amount through, the rest is metered and adjusted by the mixture (fuel) screw.  

[daz_j]

Ok thanks for your advice Tony, much appreciated. It seems that leaves me with a set of spare carbs that aren’t correct for my GS550, which brings me right back to my original question - how do we identify carbs? 

[daz_j]

One more go!  I'm still a bit foxed by the inconsistency in my 2 sets of 32mm carbs (~1mm hole above pilot jet vs. no hole there).  What I'm fishing for is a way to ID the carbs as there doesn't seem to be any number marked on them, unless it's very cunningly hidden! 

It was the Haynes manual that got me thinking about this as it lists 4 possible ID numbers for the 550E (see photo).  And then there's the possibility that carbs from other models/manufacturers would also fit?  I have no history for the bike, so no idea what a previous owner may have sourced and fitted; the bike came with the idling issues. 

I expected this would be a common question covered previously but it seems not - feel like I'm missing something! 

Any insight gratefully received.

[TonyGee]

if the carbs have had a good clean and all jets and drillings are clear i would be looking at the engine, do you know its history/mileage ?  before doing any ignition or carb work the engine has to be healthy or you are just pissing against the wind !!!!!!   do a compression test just to rule it out. 

[Toecutter]

As above, but in addition, you said the carbs have been cleaned. Have you checked all the passageways in the float bowls are clear? Just double check the orifices are clear in each bowl. Have chased issues with rough running at idle before only to find the float bowl vent spigot was partially blocked( and the hole in the bottom of the bowl this leads to), resulting in fluffy idle. This was on my own gsx 750 and a customer's Kat 1100. Similar float bowls. 

[daz_j]

Ok cheers chaps, I'll park my carb ID obsession and get back into the garage!

No I don't know any history of the bike. It's an early model but fitted with a later non-kickstart CV carb engine; it came with 2 spare kick-start engines in various stages of dis-assembly, and many other spares.  Reading between the lines I think the PO had struggled to get it running properly.  It was set-up with an airbox, but in the spares were a set of crappy pod filters.  On investigation the carbs were in nice condition but had been re-jetted, I'm thinking to try and use the pods.

So a summary of what I've done so far:

• Carbs u/s cleaned, all passageways appeared to be clear.  Refitted with standard size jets and new O ring seals.  Float heights set, fuel levels checked.  Balanced.
• I discovered 2 of the airbox->carb rubbers weren't correct - used ones sourced and fitted.
• I wasn't 100% confident of the carb->head rubber boots - new aftermarket ones bought and fitted. 
• Compression checked and all seemed acceptable.
• Valve clearances checked and re-shimmed where necessary.
• I haven't yet delved into the ignition/electrics.

I've experienced a variety of idling issues, most recently the bike dies at idle or if I adjust the tickover screw in it surges.  Plugs indicates rich running and I've experimented with the mixture screw to no avail.  I believe I've covered the basics pretty well hence trying to go to the next level of understanding.

The carbs are currently off the bike, clutching at straws I put everything back through my u/s cleaner and re-checked everything - I'll refit them and report back.
 

[prutser]

For what it's worth:

Have you verified the cam timing is correct?

Once i bought a re-assembled engine. It started with a fair amount of choke, revved, but ran rather rough and wouldnt idle below 2k orso. Turned out the cams were installed one tooth out of time (cant recall which direction).

[gs7_11]

18 hours ago, daz_j said:

... I'm thinking to try and use the pods....

Just don't.

You've a far better chance of getting it running correctly if you keep it standard.

Regarding carb i.d., sometimes there's a VERY faint number on one of the carb bodies. Otherwise, you're down to checking any other clues such as jets fitted. But, even if your spare carbs are off a different bike, theres a good chance they would run ok enough if they were clean and in good order.

Check that a PO hasn't fitted air corrector jets and left them in.

Besides checking all the drillings, including the float bowl one as mentioned, check that the o ring on the float valve is sealing, check the condition of the pilot screw o ring.

Obviously check for flooding, i.e. that the float valve is working correctly. You can buy or make a little tool to actually see the fuel level in the float bowl.

When checking drillings, it's essential to confirm they're clear, not just ultrasonic them and assume. Squirt WD40 through each one and makes sure it fires out everywhere it should.

Check your HT leads and plug caps are in good nick. Trim ¼" off the HT lead end and rescrew the cap on.

Check your carb balance isn't way out. Vacuum gauges will give you further clues, even if you've set your butterflies up with a drill bit or suchlike.

Finally, sometimes a bike that hasn't run for a while will benefit from a good long run. If the only problem is not idling, you can ignore that and ride it.

[daz_j]

5 hours ago, gs7_11 said:

Check that a PO hasn't fitted air corrector jets and left them in.

Thank you for your suggestions gs7_11, but apologies 'air corrector jets' is a new one on me - where would I find them if they were fitted please?

I have previously done all the other carb checks you mention.  Haven't yet investigated the HT leads other than a quick look, they're NGK and appear to be pretty new.  Also haven't checked the timing yet (thank you prutser).  I've convinced myself it's a carb problem but might need to take a step back.

I tried a test ride but struggled to be honest, didn't feel comfortable doing it.

And finally I didn't mean I'm thinking of re-using the pods, they went in the bin; I meant I thought the PO had tried them and rejetted to suit.  I'm aiming for standard, though the pods would no doubt have made it easier getting the f***ing carbs in and out!

 

Edited September 11 by daz_j

[gs7_11]

If you look on the airbox side of the carbs, there are air passages in the side which take inlet air to various places. Some are for the diaphragm that lifts the slide, 2 I think head for the float bowl.

(You'll know this because you've checked all the drillings are clear).

One of them houses the 'main air jet' and to get pods working right, its necessary to make that smaller, done by tapping a thread in the air jet's bore and fitting a small brass corrector jet.

Just check you haven't got an extra threaded jet, with a screwdriver slot, in  there. The original main air jet will be recessed.

[daz_j]

Thanks, I've taken a photo just to be sure - pilot air jet on the left of the air intake, main air jet on the right.  The main air jet has a brass insert which doesn't appear to be removable, the hole through it measures about 1.55mm diameter.  I'm assuming this is standard?

[gs7_11]

Yes, that looks correct.

[Dezza]

The air corrector jet is an M5 threaded brass insert with a smaller hole in it than the stock air jet. To fit means the blank hole needs to be tapped using a blind tap. NOS air corrector kits often crop up on eb@y. They used to form the basis of a LeDAR induction kit, one of the greatest inventions known to humanity .

[daz_j]

Thanks again for the previous advice - carbs now recleaned, checked and refitted.  I found a small split in the carb>petcock vacuum pipe - replaced.  Checked timing statically and found it to be very slightly retarded - reset.  Result was that the engine now idles better (good enough for a short test ride) but still not right, so I'm working through a few other checks. 

The bike has had electronic ignition fitted by a previous owner - at first glance I thought DynaTek but I can see now that it's a cheap knock-off as sold on Amazon (see photos).  I'm a bit suspicious - has anyone any experience of using these please?

[Jonjon]

No ,but how did it turn out?

[daz_j]

All good now thanks, after working through the other issues I was able to check the timing dynamically with a strobe and balance the carbs better, fresh fuel and a decent test ride.  Thanks again for all the previous advice.

[baldrick]

On 9/6/2024 at 6:53 PM, daz_j said:

Ok thanks for your advice Tony, much appreciated. It seems that leaves me with a set of spare carbs that aren’t correct for my GS550, which brings me right back to my original question - how do we identify carbs? 

they usually have a code on the sides just above the float bowl on  mikunis anyway.

it might be feint as its etched on rather than stamped.

give it a good clean and see if there is anything there.

those cheap dynatek ignitions arent all that great, lad on the z forum got stranded when one of the magnets fell off it.

Edited October 15 by baldrick