its diagnosis time! (carbs..maybe)

[that_impulse_guy]

friends! I have a problem I want to fix, and will dive deep into fixing it, and will fix it.

but before that happens, lets see if I can get any clues.

bicycle: suzuki gsx400x inline4
stood for many years.
stuff I have done
tappet clearances, ultrasonic'd carbs, rebuilt carbs with pretty much new anything I could lay my hands on
new spark plugs, coil packs, cdi
airbox, air filter, inlet orings.

Lets move onto what happens: (bear in mind I'm still in the process of doing my license, so lots of the last years have been me, starting the bike up, going through a warmup cycle, noticing nothing has changed, and moving on to next problem)

dead cold: use choke, bike starts, wait a minute, remove choke, idle is real bad...sound like it is running on only two cylinders, but all 4 exhaust downpipes warm up evenly. Try to blip throttle, bike will immediately die (in the first minute, I can fix this by leaving choke on a bit...i.e. it is defo lean and needs choke when totally cold).

...restart bike (no choke needed, its already a bit warm)...slowly start coaxing some revs out of it, you can hear it moaning out the exhaust like it is running overly rich or lean or something..yet doesnt want to rev up.....let it idle.

after 5 minutes, can do anything you want, rev the tits off it, everything sounds clean as a whistle, idles like a champ.

So the problem is:
takes a bloody long time to warmup. Cant do anything while it is warming up but wait for it to warm up.

As above, a load of parts have been thrown at it for mostly refreshing reasons as the bike is old and has been stood, but of course I tested prior and after fitting things like the coil packs, cdi etc to note if any change.

This weekend I decided to recheck valve clearances and theyre still ok, and decided to pull the new spart plugs out and see

1 and 4, defo rich (probably to be expected with all the sit idle and choke use)...3 and 4...clean and shiny!!!!

OK, so like me youre probably going!!!! yay!!! its the choke for cyl 2 and 3 not working. You get a medal, and you get a medal and everybody gets a medal...UNTIL...I point out that this bike has these weird twin siamiese carbs which have only two choke cables and two choke plungers...one for cyl 1 and 2 carb...and one for cyl3 and 4 carb....so "if" there is something carbs related, it should pair with cyl 1 and 2....OR cyl 3 and 4...and NOT the middle , (or..outer) two...(two carbs, each carb does two cylinders...)

So...who wants to take a stab at whats going on:? the only individual items the carbs has for the 4 cylinders and pilot and main jets and slides...the rest is shared between the cylinders (one diagphram, one float bowl per 2 cylinders)

Aisan as27vw carbs if youre into googling stuff...

so, I'm wondering...pilot jets? but then, why when it is warm is it sooooooo good and perfect.
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Gone: Yamaha DT50lc, Suzuki DR500, Suzuki A100, Kawasaki z250ltd, RD350YPVS, Suzuki DR Big, Kawasaki AR125, Kawasaki KMX200, Suzuki GS1000S, Katana 1100, GS550M, Suzuki RGV250
Now: Suzuki GSX400X, Suzuki RF900R, NS400R

[Nobby the Bastard]

Does it have a thermostat in the cooling system? If it's missing or has failed it will cause the engine to take longer to warm up.
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[that_impulse_guy]

good call.
it doesnt have a thermostat. Not just this one...all of them didnt have one. There is a housing, but it was always empty from the factory. The parts manual also doesnt show a listing for one.

Unfortunately my frame of reference for this bike was..."africa"...where it was always hot, so didnt notice anything weird to do with warming up.

I have thus spied the first minute or so of this video as my "what does normal seem like"
https://www.youtube.com/watch?v=PI7Qvahibtc
and i can 100% attest that mine does not behave like that.
____________________
Gone: Yamaha DT50lc, Suzuki DR500, Suzuki A100, Kawasaki z250ltd, RD350YPVS, Suzuki DR Big, Kawasaki AR125, Kawasaki KMX200, Suzuki GS1000S, Katana 1100, GS550M, Suzuki RGV250
Now: Suzuki GSX400X, Suzuki RF900R, NS400R

[Nobby the Bastard]

If you are used to using it in africa the jetting could be wholly wrong for temperate zones.

Edit, if it's an African edition, does the Euro version have a thermostat?
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[that_impulse_guy]

sorry nobby..pls dont freak out coz this is going the way of most "i have a 125 and have this problem..." type thread.

I realise i thought I gave enough info in the OP but sounds like I didnt....it was not my intention.

I last rode one of these in africa 30 yrs ago. The one I have now has lived in the uk since 2000 onwards. Its not the same, individual bike, just another one identical to it.

I'd love to focus in on how plugs 2+3 are clean as a whistle....yet 1 and 4 arent. The crankcase breather isnt outputting much, if anything...else I'd say "ah, stuck rings" or similar, as a starter for 10.

The way the choke works, is fuel enrichment..and from understanding how the carb works, if you so much as touch the throttle while the choke is on, the pressure difference caused would cause the choke not to work at all. (I hope I explained that right..)

Hmm...I wonder if idle is set too high (when it is warm its about 1200-1400rpm or thereabouts).....and all you'd need is for the butterflies to be slightly worn for some cyl to not get any enrichment due to too much air decreasing pressure on the choke side.....so they take much longer to warm up.

hmmmmmmm
but then, all 4 downpipes seem to get warm equally.

arggh.
____________________
Gone: Yamaha DT50lc, Suzuki DR500, Suzuki A100, Kawasaki z250ltd, RD350YPVS, Suzuki DR Big, Kawasaki AR125, Kawasaki KMX200, Suzuki GS1000S, Katana 1100, GS550M, Suzuki RGV250
Now: Suzuki GSX400X, Suzuki RF900R, NS400R

[stinkwheel]

If the issue is on 1 and 4, it's probably not the ignition timing anyway.

My diagnosis is it needs the fuel draining out of it, battery taking out and to be left alone somewhere dry until it can be taken out on the road and given a proper run to see how it runs under load. Sort out the rest of it, leave the engine be. Repeated cold starting and fannying with it probably isn't helping.

If I leave my VFR to sit for over a month, it fires up poorly and on only one cylinder initially, then idles badly for the next few minutes as the other cylinders kick in one at a time then idles rough for a bit until it's off the choke. Then I pile it up with luggage and go and thrash the tits off it for 500 miles over a weekend and it runs fine the whole way, fires up off the button from cold and does everything I'd expect of it and will continue to do so unless I leave it sitting for over a month..
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[that_impulse_guy]

i think i'll make a video of the behaviour...

cheers stinkwheel! Yeah, I've been doing this every week on a sunday, while I fix other things, to make sure battery (new) stays charged up.

Tank was drained and I used bill hamling (or whatever its called) to do some rust removal, and put new fuel tap on today while fiddling with everything else.

I'm at the stage where (next month) I "could" be riding, so its mostly through the recommisionning phase so to speak already.

and as you said, thing is 100% fine once warmed up. I'm confident the motor is fine and strong...but dont want to leave the house 10minutes early just to sit at the side of the road letting it warm up...I think that should not be like that.
____________________
Gone: Yamaha DT50lc, Suzuki DR500, Suzuki A100, Kawasaki z250ltd, RD350YPVS, Suzuki DR Big, Kawasaki AR125, Kawasaki KMX200, Suzuki GS1000S, Katana 1100, GS550M, Suzuki RGV250
Now: Suzuki GSX400X, Suzuki RF900R, NS400R

[stinkwheel]

Idling your engine is a piss poor way of keeping the battery charged. If you want to keep the battery charged, charge it, take it off the bike and keep it in the house or connect it to a trickle charger.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[jeffyjeff]

[Nobby the Bastard]

I have difficultly seeing how carb balancing would make much difference when it runs properly when warm.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[jeffyjeff]

fair enough
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History shows again and again how nature points out the folly of men - BOC

[that_impulse_guy]

those of you on tenderhooks waiting for a thrilling update, here it is.

(apologies for missing yesterdays update, I had to go work and wasnt near mr internet)

Started bike up again on Sunday, exact same as everytime before. As expected. (p.s. yes I have a trickle charger and all that stuff..anyway)

I did mention i replaced the air filter...I didnt mention the part is no-longer-available, so had to order generic air filter foam of the same thickness...but the density of the oem one was unknown so we went with what felt right.
I thus, had a look in that direction, and all was well. The airbox has two snorkels intakes, so while bike was busy warming up and throttle was unresponsive etc I though to stick my hand into one intake and block if off, and it did in fact make a difference (p.p.s yes new airfilter foam has oil applied and squished out etc as you;d do yourself)

So with one snorkel blocked off, bike would respond to throttle much cleaner than with both snorkels open (while warming up...in fact..it was almost perfect)..

I know, groundbreaking stuff this isnt it...who wouldve though a cold bike would work better running rich.
But, wait a bit...we have a manual choke...so why when applying the manual choke doesnt it respond correctly to throttle too?

well, for the same reasons plugs 2 and 3 are clean...we have an intake air leak for those cylinders... I havent seen it, but we've proven it exists, therefor it is. I just have to find it.

Yesterday was spent thinking in the land of theory while away from the bike. I have the following theory:
https://cdn.freewebstore.com/resize/244687/1575412740308_img_20191203_170222.jpg/350/350/0/SOLD%20OUT?bg=FFFFFF
this is the back of the carbs, airbox side.
the airbox has two rubber oval boots that slip over the carbs mouths. Once on, you cant see the fitment except for far left and far right...you really, really cannot see it the intake boot is nicely over the carb mouth for the inner two cylinders, IF you assemble it all on the bike...i.e. carbs to engine, airbox to carbs.

Its my theory that the airbox-to-carb rubbers arent correctly seated for those two cylinders...so the inner cylinders are more prone to sucking in extra air. Its the only thing that kinda explains everything...so thats item 7 and 9 in the airbox picture attachment...maybe the oval clamps are also "out of oval" so arent applying correct force where its needed.

So next time I get the bike out from under the covers etc, I'll stick a boroscope up under and between the carbs and take some photos.. It may well be the correct procedure is to assemble carbs to airbox off the bike, then skip both in as a unit to make sure all is good.

pp.s.s.pp.s.s.: yes, carb synced with the meter doodah that measures vacuum. Its easy as it is only "two" carbs from that point of view.
____________________
Gone: Yamaha DT50lc, Suzuki DR500, Suzuki A100, Kawasaki z250ltd, RD350YPVS, Suzuki DR Big, Kawasaki AR125, Kawasaki KMX200, Suzuki GS1000S, Katana 1100, GS550M, Suzuki RGV250
Now: Suzuki GSX400X, Suzuki RF900R, NS400R

[that_impulse_guy]

also, I have to ask...are you Stinkwheel from unit5 romford?
____________________
Gone: Yamaha DT50lc, Suzuki DR500, Suzuki A100, Kawasaki z250ltd, RD350YPVS, Suzuki DR Big, Kawasaki AR125, Kawasaki KMX200, Suzuki GS1000S, Katana 1100, GS550M, Suzuki RGV250
Now: Suzuki GSX400X, Suzuki RF900R, NS400R

[blurredman]

400cc 4 cylinders I have experienced seem to all require 'warm up'. And I don't mean just to annoy people like people who 'warm up' a modern vehicle - the 400cc 4 cylinders seem simply unable to move until some warmth is in them. Or am I being silly? Had a fzr400 it was exactly as described in OP.
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CBT: 12/06/10, Theory: 22/09/10, Module 1: 09/11/10, Module 2: 19/01/11
Past: 1991 Honda CG125BR-J, 1992 (1980) Honda XL125S, 1996 Kawasaki GPZ500S, 1979 MZ TS150.
Current: 1973 MZ ES250/2 - 18k, 1979 Suzuki TS185ER - 10k, 1981 Honda CX500B - 91k, 1987 MZ ETZ250 (295cc) - 40k, 1989 MZ ETZ251 - 51k.

[stinkwheel]

[that_impulse_guy]

my boroscope potato cam pictures showed the rubbers are seated.

this problem shall henceforth be ignored.
____________________
Gone: Yamaha DT50lc, Suzuki DR500, Suzuki A100, Kawasaki z250ltd, RD350YPVS, Suzuki DR Big, Kawasaki AR125, Kawasaki KMX200, Suzuki GS1000S, Katana 1100, GS550M, Suzuki RGV250
Now: Suzuki GSX400X, Suzuki RF900R, NS400R

[jeffyjeff]

[that_impulse_guy]

cheers, appreciate the input,
(manual choke implied: manually operated by turny thing on left hand grip section...not the old skool choke restrictor plates, apologies)
yes, the cables actuate two plungers, one in each carb. Each carb fuels two cylinders (paired 1 and 2...and paired 3 and 4). Its fuel enrichment, as are the carb mixture screws (on the fuel side, not air side).

the only way the above may be the cause of the weirdness on the spark plugs is if the choke enrichment passage for carb1 rhs is blocked, but not lhs.
and then the passage for carb2 lhs is blocked, but not rhs.

odds on this?
after ultrasonic cleaning...

Its worth a check, of course it is....in the realm of theory its a bit of a long shot though, luckily, I'm running out of obvious things so this may well be checked next time.
(p.p.s.s.s. as mentioned above, I have put a bunch of parts towards carb refreshment, this included the little tiny rubber orings seals on the end of the choke plungers in case they were worn).
____________________
Gone: Yamaha DT50lc, Suzuki DR500, Suzuki A100, Kawasaki z250ltd, RD350YPVS, Suzuki DR Big, Kawasaki AR125, Kawasaki KMX200, Suzuki GS1000S, Katana 1100, GS550M, Suzuki RGV250
Now: Suzuki GSX400X, Suzuki RF900R, NS400R

[that_impulse_guy]

putting this here for reference:
https://teamghettoracing.com/mechanical/carb-efi-work/suzuki-across-gsx250f-carb-overhaul/

this is a bloke overhauling carbs on a suzuki gsx250f (Across...also JDM special bike). Theyre not the same carbs, but they are...mine are brand "Aisan" these are Mikunis...I believe Mikuni took over Aisan at some stage.

Anyway, theres pictures and stuff of how the internals work.

One thing not mentioned anywhere much, is the choke pulls fuel from the float bowl into a little tube that is part of the float bowl that has a wee little ball bearing in it acting as a one-way valve which you will never see or be able to remove..but if it is stuck then you'll have no choke anywhere in that specific carb.
____________________
Gone: Yamaha DT50lc, Suzuki DR500, Suzuki A100, Kawasaki z250ltd, RD350YPVS, Suzuki DR Big, Kawasaki AR125, Kawasaki KMX200, Suzuki GS1000S, Katana 1100, GS550M, Suzuki RGV250
Now: Suzuki GSX400X, Suzuki RF900R, NS400R

[jeffyjeff]

[that_impulse_guy]

1 and 4 share(d) the same coil yes.
This particular model has a weakpoint with coils overheating...so..
Coils were removed and put in a bin, and replaced with coilpacks (coil on stick? stick coil? "the modern things") from a cbr600 by me. (problem existed prior to this mod, and post this mod, it was part of my elimination thoughts) (primary ohm-age is identical to stock)

CDI has also been replaced with one from a similar enough bike (same thing, same pinout, same ignition advance curve, just doesnt contain the japanese hp restricted self-imposed rev limiter and is 1 year old instead of 36 years old)
____________________
Gone: Yamaha DT50lc, Suzuki DR500, Suzuki A100, Kawasaki z250ltd, RD350YPVS, Suzuki DR Big, Kawasaki AR125, Kawasaki KMX200, Suzuki GS1000S, Katana 1100, GS550M, Suzuki RGV250
Now: Suzuki GSX400X, Suzuki RF900R, NS400R

[redeem ouzzer]

Those carbs are also used on the Daihatsu Charade GT and are horrendous things. I’d fit a cylinder head off a K707 engine (Bandit 400 / GK73A) and convert it to four functioning carbs.
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Be a REAL MAN!

[that_impulse_guy]

yes....sigh..

of all the K70x engines...with bits that interchange.....this particular one fits into a frame that narrows so much post-engine that they used the 2 carb setup instead of 4 in a line for space issues.

so I have K706, ,and must make it work again.

gk71b, gk71e and gk71f used this setup.
and the gsx400fws, and the USA gs550e/4
____________________
Gone: Yamaha DT50lc, Suzuki DR500, Suzuki A100, Kawasaki z250ltd, RD350YPVS, Suzuki DR Big, Kawasaki AR125, Kawasaki KMX200, Suzuki GS1000S, Katana 1100, GS550M, Suzuki RGV250
Now: Suzuki GSX400X, Suzuki RF900R, NS400R