Need photo of connected GSX250 carb - Mikuni BS30SS?

[wired00]

Hi all I'm new here and in need of some help with carby setup :) Im also new to bikes so its been really interesting working on this GSX

Im in the process of restoring a 1984 GSX250. I got the bike for nothin from a guy. It was missing plenty of parts including wiring, accelerator, entire carby, battery, clutch lever etc...

Anyway... finally its back together but we're really struggling to start the thing. Its ALMOST kicking over when we spray aerostart into the carb. I'm thinking its a problem with either: carby setup, ignition timing or cam timing.

My question: Is it possible for someone with this bike/carby to take a photo showing all the connectors to make absolutely sure i have it setup correctly? All the diagrams i've seen just don't show exactly whats connected where. The two im most concerned with are the Vacuum and bleeder hose and fuel hose.

Is it correct that the Vacuum hose connects to the carb and just sits up under the seat? I assume this just allows the float bowl to stay at atmospheric pressure so the vacuum sucks fuel through into the venturi? When i got the bike there were two hoses ~ 1/2 foot long just sitting under the seat not connected to anything. Im assuming these are the vacuum hoses.

Anyway any images or clarification would be a huge help... I should really just go find a dealer selling the same bike to checkout how its setup

[wickle]

Try here
http://www.alpha-sports.com/choose_the_year_suzuki_you_have.htm

[wired00]

Cheers i just tried that and couldn't find my model but found a GS550 with what looks like a similar carby... but its a similar diagram from the haynes manual i have. It just says "Hose" for both party 59 and 60. Doesn't show where they're meant to connect to ... ie which one goes up under the seat.

http://www.alpha-sports.com/spst/1984%20GS550ES/06.htm

Hopefully the thing will be started tonight

[motorbyclist]

can you give us a photo?

vacuum hoses are generally needed to open/close things, like raising the slides in the CV type carbs or open the diaphragm in the fuel tap ;)

vacuum hoses very rarely go nowhere. if they do they are referred to as breathers or intakes:innocent:


simple process with bikes (and any motor in general):

spark? - does it and at the right time?
fuel? - getting it to the plug? even getting through the carby or out of the tank?
air? - remove filter, any difference?


if you've got those you look more closely at timing, compression, and fuel/air mix

[wired00]

:2thumbsup Sure I'll take a bunch of photos tonight. I still have the carb detached from the bike after cleaning and "tuning" last night.

Few things we found:

- left intake manifold is badly worn/brittle and leaking air. I'll get a new set from suzuki. It was leaking air so badly that if I sprayed aerostart across the leak it made the engine chug over just as much as if I sprayed directly into the carby's left air intake! o.O If spraying directly into a leak in the intake manifold produces just the same result as spraying via the carby intake then something must be fairly wrong with the carby setup right...?

- checked the ohm's across both coils and they match...think it was 4 ohm. So coils seem fine

- Ignition timing was spot on, so thats not an issue. We also rotated the crank to check the ATU lined up perfectly for spark right when the piston was at top. As crudely as the check was, it *seemed* the piston was dead top as the spark should be produced.

- float bowls are full of fuel

-when adjusting the carby's A) left and right thottle butterflys were out of sync by at least a few mm, it was obvious to the eye. These are now spot on. B) The Throttle stop screw was set very open... i adjusted to what I thought was right. Now the throttle butterfly's are only open enough for 1 of 3 innermost bypass orifices to show. Not sure if this is correct I'll take a photo tonight...

- The airbox isn't connected at the moment because I'm waiting for new inlet hoses to arrive to join the carby air intake and the airbox. I've heard from a bunch of people this really effects idling performance especially CV carbys but surely it should still start ok yeh?

- Carby was quite clean inside especially the pilot fuel jet, pilot air jet and pilot screw...which I suspected might be badly gunked up to prevent the thing starting :weep:

So:


vacuum hoses are generally needed to open/close things, like raising the slides in the CV type carbs or open the diaphragm in the fuel tap
Yep I'm worried about the vacuum hose too. I think your right about the fuel tank, the bottom of the tank has 3 hose connections. 1 fuel, 1 vacuum, 1 breather i guess. But we're not using a tank at the moment we just have a funnel and hose connected to the fuel intake. I assume then the fuel tap diaphram prevents fuel running if there's no vacuum from the carb. Hence the PRIme setting which allows free flow



spark? - does it and at the right time?

Yep Ignition timing seems to be fine, coils seem ok and new spark plugs. We checked the old spark plugs fire outside the engine and they sparked fine.



fuel? - getting it to the plug? even getting through the carby or out of the tank?

Not sure how to check if the fuel is getting to the "plug"? But we checked the float bowls are full. We removed the plug screw at the bottom of each bowl and an equally large amount of fuel pissed out everywhere...so seems fine!



air? - remove filter, any difference?

No air filter is attached. waiting on inlet hose from suzuki

Cheers for that i'll get some photos up later aswell as the diagrams i have from my Haynes manual. Sry my response was so long

[wired00]

Actually regarding how far the butterfly should be opened, after reading this thread:
http://newsgroups.derkeiler.com/Archive/Rec/rec.motorcycles.tech/2007-03/msg00422.html

I'm pretty sure I shouldn't have any of the 3 "transition" ports visable. I guess only the single pilot port should be used at idle. Then as the thottle opens up the transition ports start to kick in. When enough vacuum is created for the diaphragm to activate the slide raises and the main needle jet starts working...

[motorbyclist]

:
Not sure how to check if the fuel is getting to the "plug"? But we checked the float bowls are full. We removed the plug screw at the bottom of each bowl and an equally large amount of fuel pissed out everywhere...so seems fine!



fuel on, full choke, flood the bastard. if the sparkplug becomes wet/reeks of petrol you've got fuel:woohoo:

now there are better tests, but it basically comes down to getting fuel into the combustion chamber.

just because it's getting into the bowls doesn't mean it's getting though a blocked jet or even has enough vacuum to draw it through the needle to begin with

that big air leak is going to be a major problem. fix it, even if only with some silicone sealant

[wired00]

fuel on, full choke, flood the bastard. if the sparkplug becomes wet/reeks of petrol you've got fuel:woohoo:

now there are better tests, but it basically comes down to getting fuel into the combustion chamber.

just because it's getting into the bowls doesn't mean it's getting though a blocked jet or even has enough vacuum to draw it through the needle to begin with

that big air leak is going to be a major problem. fix it, even if only with some silicone sealant

righto I'll see if i can flood it

yeah would be good to know there's enough vacuum for the pilot jet to even work. I'll be picking up a new intake manifold early next week which will help things.

Bloody batteries flat in the camera will those pics tomorrow

cheers again

[FJRider]

set fuel tap to reserve, if you can. this bypasses the vaccum...usally..

there should be two lines off the tank. one fuel line, one vaccum. with vaccum line attached to tank and fuel line attached at tap. but if left off the carbs... sucking on the vaccum hose... fuel should come through fuel line.

[wired00]

set fuel tap to reserve, if you can. this bypasses the vaccum...useally..

i think PRI (prime) does that on the tank i have but actually we're just using a funnel connected to a pipe to get it started atm :)

[FJRider]

i think PRI (prime) does that on the tank i have but actually we're just using a funnel connected to a pipe to get it started atm :)

it does... but vaccum hose is connected at a different point, on or near tap. fuel line is usually smaller...
check fuel flows on "prime" from tank...maybe tap problem...not uncommon...

[motorbyclist]

yeah would be good to know there's enough vacuum for the pilot jet to even work. I'll be picking up a new intake manifold early next week which will help things.

yeah

technically it's the velocity of air passing through the venturi that draws fuel, but if you're sucking in air though the manifold the mix will become WAY too lean


it does... but vaccum hose is connected at a different point, on or near tap. fuel line is usually smaller...
check fuel flows on "prime" from tank...maybe tap problem...not uncommon...

i doubt it's a tank problem if he's ditched the tank....

and fuel lines are usually much bigger than vacuum lines.

an easy test is to suck on the carby end of the vacuum line and see if fuel runs out the fuel line

[wired00]

thanks everyone for your advice. Ok so its been a couple weeks since I created this thread/question.

So today we finally got the thing started! Got new intake manifold, the left had a ~3mm gap/tear around 70% of it! Also, the valves were completely stuck open not sure what the previous owner was thinking... but yeah it was never starting like that. So with everything put back together it started first time but with full choke.

Which is now the problem. With full choke while cold it runs perfectly but if I lower the choke a little it starts racing and revs very high. If the choke is further lowered till about 1/3 or 1/2 it dies. The engine also dies if the choke is full and I turn the Throttle even a fraction. So yeah, reduce choke it dies, add any throttle it dies. Any idea what this could be?

Symptoms wise, to me it seems like the only thing running the bike is the choke and that the pilot jet is blocked. As soon as the thottle bodies open a fraction its getting far too much air and no fuel so it dies. BUT I've checked and rechecked the pilot circuit and it seems fine - perfectly clear. I've also checked both carbies transition holes and they are all clear too. I've checked the pilot screw and its wound out exactly as the manual says (1 1/2) and its using the correct jet sizes for the engine.

A question: There are 3 tiny transition holes (each the same size as the single pilot hole). Should the Idle speed be set so the throttle body closes just in front of these 3 holes or should 1 of the 3 be in front of the throttle body or anything? Currently, the pilot hole is visible, and when the thottle is pulled a fraction the butterflys expose 1, then the other 2 transition holes.

[wired00]

Here are the images of the carby pilot and transition ports. I have a bunch of questions below!

Heres a photo with the throttle open. Green arrow: choke/enrichment inlet, light blue arrow: idle port, red circle is all transition ports which are usually just covered by the butterfly. The orange arrow is the one I'm questioning as to whether it should be partly exposed or not. I'm fairly certain that none of the transition ports should be exposed at all.
http://www.washeretoo.com/images/IMG_0530.JPG

Picture showing when the throttle is closed. You can see a fraction of the transition port (orange arrow) is showing even when the thottle is closed. I think this is wrong
http://www.washeretoo.com/images/IMG_0529_closed.jpg

More Questions: what im still worried about are the hoses. Here are some diagrams from a haynes manual and pictures of my carby.

I'm concerned about a few things with pipes
1) here is a diagram for the GSX400 carby which i believe is a Mikuni BS34SS.
Red arrow- pointing to a outlet which should have 45 (Connecting pipe) connecting between each carby. I've checked on my carby and these outlets are open - i can squirt carby cleaner through them. But if you compare to the GSX250 diagram below it doesn't have a connecting pipe nor does it mention that outlet at all??! This is what i don't understand.
Green arrow- Breather pipe. I don't have this connected to anything. You can see in my carby photo.
Orange arrow- Vacuum pipe. I assume this connects to the vacuum port on the petrol tank? We haven't got this connected because we're just letting fuel run into the carby via a pipe&funnel at the moment.
http://www.washeretoo.com/images/carb400.jpg

Here's the diagram for what is supposed to be my carby on a GSX250- BS30SS. I've checked and all the jet sizes match so i assume this is the correct carby...
Red arrow- You can see the lack of a "connecting pipe" and if you compare the diagrams the actual outlet isn't very visible on the 250, but this might just be the way it was drawn. So, should i have these pipes connected??
http://www.washeretoo.com/images/carb250.jpg

Heres photos of my carby.

Red arrows- The "connecting pipes" in question. You can also see in the other side.
Green arrow- Vacuum pipe
http://www.washeretoo.com/images/carbback.jpg

Red arrows- The "connecting pipes". They really look like they should be connected :angry:
blue arrow- Breather pipe. Again, its not connected atm to anything, should it be?? Or should it just have a pipe running up under the seat
orange arrow- Fuel
http://www.washeretoo.com/images/carbfront.jpg

Anyway, thats it for now! Any help on ANY of these issues is really appreciated

Cheers

[wired00]

no one can offer advice on whether i need a connecting pipe between the carbies or not? plz :D

[motorbyclist]

well in the apparent absence of someone who owns that bike and/or knows the answer to that question, I'd say to fit one and see what happens :)

[wired00]

well in the apparent absence of someone who owns that bike and/or knows the answer to that question, I'd say to fit one and see what happens :)

yeah gunna give it a try :)

Just waiting for some mufflers to arrive, the thing is *far* too loud for extended running carby tuning :P

[The Pastor]

its a little bit past my skill level im afraid!

but keep us updated, i like to learn.

[wired00]

will do :)

I since learnt that the breather hose coming from the carby breather port should connect to a T junction kinda piece of pipe up under the seat which then connects to the two breather pipes (which were indeed there) under the seat

The vacuum port should connect up to the fuel tank tap, uses vacuum instead of a fuel pump to suck fuel.

Might help someone in the future? :)

Still waiting on the mufflers so haven't been able to start the bike and test whether a connector pipe between the two carbies is neeeded or not

[motorbyclist]

The vacuum port should connect up to the fuel tank tap, uses vacuum instead of a fuel pump to suck fuel.


:slap:

uses vacuum to open a diaphragm to let fuel pass through the tap - the only thing driving the fuel is head pressure in the tank but a 250/400 uses so little anyway it doesn't matter

[wired00]

haha I actually read that... spose it should have sunk in by now :third:

[SuziGSX250boy]

I don't know when you posted your carbie problem but if you still need help you'll find the hose which goes from the fuel tap goes to the outlet on the carbie which is between the the carbie and the cylinder head. This is the vacuum hose to operate your fuel tap and it gets its vacuum from each intake cycle of the piston for that carbie. On my bike it goes from the fuel tap on the left to the right hand carbie.
The other hose is an atmospheric balance pipe which leaves the carbie closer to the airbox side down between the two carbies and it goes up under the right hand side of the fuel tank. Make sure the metal pipe under the tank it connects too is actually clean and clear as it tends to get blocked with road grim over the years and doesn't allow the carbies to find proper atmospheric pressure.
If you haven't already solved it I hope this helps. Happy biking....

[wired00]

I don't know when you posted your carbie problem but if you still need help you'll find the hose which goes from the fuel tap goes to the outlet on the carbie which is between the the carbie and the cylinder head. This is the vacuum hose to operate your fuel tap and it gets its vacuum from each intake cycle of the piston for that carbie. On my bike it goes from the fuel tap on the left to the right hand carbie.
The other hose is an atmospheric balance pipe which leaves the carbie closer to the airbox side down between the two carbies and it goes up under the right hand side of the fuel tank. Make sure the metal pipe under the tank it connects too is actually clean and clear as it tends to get blocked with road grim over the years and doesn't allow the carbies to find proper atmospheric pressure.
If you haven't already solved it I hope this helps. Happy biking....

Cheers mate yep this is exactly what i was after a while back. The bike is all sorted months back and on the road. Just riding till June 2010 till my P's expire and can upgrade

Yeah was having problems because when reving it the engive would stay reving then slowly go down. I stupidly had the vacuum venting and the vent connected to the petcock. Of course in hindsight it seems obvious because on the engine side of the carby when reved it would have just been sucking air straight past the carby and making the engine run lean > Rev. Doh.

Anyway, bike runs like a dream now except for the rear wheel bearings which i'm currently changing. Pretty good for a bike scrounged from a curb side cleanup :)