Another attempt to stop carb from overflowing

[torp]

Still waiting for mine - he says he shipped on 3rd August.

[Warwick]

here is what seller sent as 3XV gaskets:

Those look right - for the R & RS 28mm carbs in any case. Might be worth letting him know once you've confirmed they fit so that he can supply those in the kits in future. Thinking about it, the original gasket he sent looks like it might be a gasket for the back plate of the TPS? Perhaps you could check that too? If the supplier is provided with the right info, kits supplied in the future are more likely to be accurate and complete. 

[torp]

My kit has arrived. I got stung for £3.80 VAT and £8.00 Post Office "Handling Charge" so it was pretty expensive all in all.
Even more so as, like sfo423's kit, I have been sent the wrong float chamber gaskets....
The gaskets in the photo with the car key are the right ones however - did you get those separately?
I mailed the supplier to tell him he send the wrong ones.

[sfo423]

Even more so as, like sfo423's kit, I have been sent the wrong float chamber gaskets....

The gaskets in the photo with the car key are the right ones however - did you get those separately?

Yes. I emailed the seller a picture of the proper bowl gasket and asked for two. He promptly mailed me two at his expense. Nice guy considering it was air mail from Japan to US.

[sfo423]

OK, I pulled the carbs today to see what I had in terms of settings/jets and put in the new gaskets, seats, etc. The parts that came in the non-oem kit that DO NOT work are:

-Seat ring was too big
-Seats looked a bit off so I didn't swap them out  
-Float needle was a bit different so I didn't use it (although its likely fine, just adjust height as needed)
-Top gasket does not work on lower carb and may not seal upper (I need to double check it tomorrow).
-Wrong pilots

I swapped out parts (vs. putting in what manual said was stock); new mains (190, 260), new emulsion tubes (Q-0) and bowl gaskets. Other than that, air screws are both 1.5 out and pilots were both 15's.

Here is an "issue:" I pulled the heating circuit. Capped the system at the back of the cyl. head and at the thermo and pulled the tubes to the upper carb. Do I need to cap the upper carbs? I assume its a "closed circuit" so therefore, no need.  I ask because I fired the bike up and it idles fine for a few minutes then cuts out at low rpm. I need to choke it to start again. This is where I think the top gasket for the upper carb may not be properly seating (and giving me an air leak). My other potential culprits are vacuum issue (kink or crack in hose) or the heat circuit.

Any ideas appreciated. BTW: '91 3xv.

[Warwick]

Shame about the bits.

The circuits for the coolant around the carbs are seperate from all the fuel circuits so only need capping if you are concerned to keep the water channels clean.

Upper carb should be a P8 needle jet by the way - with a 5FN117 needle. Lower carb has the Q-0 and the 5FN118. Both needles on the middle clip is the oem setting.

You might need to adjust the tickover and pilot air screws a little to get a consistent idle. Just experiment with them a bit perhaps? You should be bable to get it to idle happily at about 1250 - 1500 rpm or so.

[ybk2]

Since we're talking carbs - I pulled mine the other day and found only one had the hard yellow plastic tube that goes into the pilot jet hole. I cant remember whether this was right or if both carbs get one?

[Warwick]

Yes, both should have them. The pilot jet will struggle to get fuel without it... If it's hard to source a replacement, you could probably make something from a piece of suitable scrap tubing that would do the job just as well Id think?

[sfo423]

You might need to adjust the tickover and pilot air screws a little to get a consistent idle. Just experiment with them a bit perhaps? You should be bable to get it to idle happily at about 1250 - 1500 rpm or so.

Would I need to adjust the idle IF I only pulled the heating circuit (assuming all else the same)?

[Warwick]

The heating circuit has no influence on carburettor functioning at all. But if it isn't ticking over well then it would be useful to fix whetever is causing that problem - usually just some blockage or other problem with the pilot circuit or inefficient air screw adjustment - or simply the slide set too low at rest. It's generally worth a few minutes spent on adjusting and optimising the tickover and pilot air screws to get a nice steady tickover again whenever you've been tinkering with the carbs.

[sfo423]

Thanks Warwick! One more thing; I've seen / read multiple accounts of what the stock needle jet on the upper is; P-8 and Q-0. I'm pretty sure I had a Q-0 and will double check what I pulled shortly.

Would a P8 have a noticeably different effect at idle?     

[Warwick]

Wont make any difference at idle as the circuit in operation is the pilot circuit - and it'd make virtually no difference anywhere else either to be honest - a P8 is only two sizes smaller than a Q0 - ie: .010mm. Twenty years worth of wear will probably make more difference in truth. I'm fairly confident that the stock upper carb needle jet is a P8 in the 91 set-up though? Perhaps someone who's currently running stock 28s can confirm?

The trouble often is they get stripped and rebuilt over the years with varying degrees of competence and understanding and you end up with all sorts of odd combinations when they get put back together... If you are running standard pipes and a -00 CDI it'd be worth checking all carb settings are as stock for that year as that will probably give you the best possible fuelling. In particular make sure that you have the right carbs on the right cylinders, and that they have the correct bowls fitted. A quick guide is that the upper carb should have no fuel baffle plates fitted at the top of the body (inside) and should have a bowl with only one overflow outlet. The lower carb should have the body with the baffles in it (tip the carb upside down with the bowl off - the fuel baffles are little stainless steel plates fitted above the floats) and the bowl should have two overflow outlet stubs. It's quite important to have the right bowls on the right carbs as the powerjet is integral to the bowls themselves.

Check with the appropriate manual to confirm jetting and settings if unsure.

[sfo423]

Wont make any difference at idle as the circuit in operation is the pilot circuit - and it'd make virtually no difference anywhere else either to be honest - a P8 is only two sizes smaller than a Q0 - ie: .010mm. Twenty years worth of wear will probably make more difference in truth. I'm fairly confident that the stock upper carb needle jet is a P8 in the 91 set-up though? Perhaps someone who's currently running stock 28s can confirm?

The trouble often is they get stripped and rebuilt over the years with varying degrees of competence and understanding and you end up with all sorts of odd combinations when they get put back together... If you are running standard pipes and a -00 CDI it'd be worth checking all carb settings are as stock for that year as that will probably give you the best possible fuelling. In particular make sure that you have the right carbs on the right cylinders, and that they have the correct bowls fitted. A quick guide is that the upper carb should have no fuel baffle plates fitted at the top of the body (inside) and should have a bowl with only one overflow outlet. The lower carb should have the body with the baffles in it (tip the carb upside down with the bowl off - the fuel baffles are little stainless steel plates fitted above the floats) and the bowl should have two overflow outlet stubs. It's quite important to have the right bowls on the right carbs as the powerjet is integral to the bowls themselves.

Check with the appropriate manual to confirm jetting and settings if unsure.

I pulled the carbs again to double check everything. Everything was good but the upper had a Q-0 jet so I put in a P-8. I still have the same issue; fires up nicely on choke, then eventually putters out when choke circuit is off.

Today I hope to adjust the slides, idle speed 7 air screw w/out the air boxes on. I also should check the lower airbox for complete seal as I had it apart and maybe didn't get it sealed tight. 

[sfo423]

wholly crap; those idle speed screws are touchy! I am used the VM series on air cooled RD's: much easier.

I started to adjust the idle speed; one carb at a time. Bike needed to be choked to fire and then I removed choke and tried adjust from there. I over-did it. I think I need help getting back to "base" on the idle adjustment. Screw in; slower, correct?

Any tips on a good start point? Like, three turns out on each, stock air screw settings, etc? Also, that lower carb screw is tough to access; need little Japanese hands.

 One more thing; for the pulled plug cap, does it need to touch the cylinder for the firing circuit to complete (or can it just hang down and not touch anything)?  

[ybk2]

I used to have a lot of issues with my 3xv8 carbs (starting and idling etc). I soaked them in the yamaha branded carb cleaner (quite nasty stuff) but it cleaned them right up - all the fuel deposits and passages got a good clean out. That sorted most of the carb issues. A new float needle, o-rings and float bowl seal cured the persistent overflowing.