complicated carb problem

[gallant_pilot]

i recently built a b4 out of scratches, and did the engine,gearbox and etc..the problem started with idling,i replace the pilot jets (standard32.5)and rejeted the mains with 95.cleaned the carbs more than 10 times,synchronized them,replaced the o rings,checked out the needle and seats and it was just fine,floaters are great..my buddy is a bike technician and he helped me on that.bike used to flood first and then after adjusting the float height to very low,the flooding went away.but recently i faced new problems,still it smells too rich and any time if i start it the first try will work,otherwise if i dont keep the revs up by first crank,it wont start,specially in cold.even after riding for while and shuting down the engine,it wont start and it needs to settle down for while(10 to 30 min).then again it runs well and after  getting warm,by stop signs,it tends to shut down with rough idle.so i have to keep the revs up or adjust the idle screw  high.the bike struggles in low down and doesnt move properly,after a point it just guns up and rides nicely.then again when even the idle is fine when i pull the clutch the revs r not coming low easily and it slows down gradually.idle works fine just when bike is cold.but again sometimes if start it in cold,i feel like the engine is flooded as i have to open the throttle fully and it sounds like its working on 3 cylinders.recently the dude said that he doesnt understand the problem anymore.also the float level is too low( workshop manual says 14.6mm more or less and its now around 12.5 mm) .still i smell fuel on the bike and it also gets hot quickly.he also did some air screw adjustment on carbs while engine was running,but actually it made it worse even,specially on idling.please if u guys had the same problem and sorted it out,help me in this case.she is like my babe and i wanna enjoy riding it.this babe runs like a rocket and can beat any 600 while its on the high way.

[Squishy]

First off, I would suggest you work a bit on your writing skills because it's very hard to follow the story in my opinion. No punctuation and many different problems summed up after each other. 

Anyway...
I would suggest putting the carbs on their stock setup and going from there.
Why did you rejet the mains? did you re-jet the pilot jets also? If so why? (based on what?)
Unless you have a different airbox/filter the bike should run fine with stock carb settings.
This means 14.6mm bowl and 1.5 turns out on the pilot jets with needle in the middle. You can then work from there.

You says it sounds like its working on 3 cylinders.. you can easily check this by touching the exhaust header pipes.
You need to remove all other problems before fiddling with the carbs.

Other things to check:
Does choke mechanism work properly? Does it return?
How is the throttle valve on all carbs?
Do all the needles go up if you throttle without airbox?
Vacuum hose from left carb connected/not torn?
Small little o-rings under vacuum cap?

Not returning to idle quickly is usually a sign of bad carb sync or too lean mixture.
Don't forget you need to sync after change valve clearance.

Or you could do a dyno run for A/F readout and see what the problem is.

[andrewsw]

What Squishy said!

Get everything back to stock settings and start over. Your float setting is way off and at least part of your problem. Even a heavily modified bike won't need more than 1 or 2 mm of float adjustment.

A

[gallant_pilot]

first i have to apologize for my writing,i am not English and tried my best.
second thing is that the main jets were #102.5 standard and it was heavy on fuel.also i dont have problem with them,the last owner replaced the exhaust pipe and made it smaller without rejeting  it. the pilot jets are also standard #32.5 according the workshop manual.i just put new ones. the throttle valves open properly without airbox.spark plugs are tested and they are brand new.bike has no electrical problem.but in idle by touching the exhaust pipes, i can see one of them is cold and its not one specific one,it shifts from 1 to 3 or 2 or 4.but at high revs they all get hot.i actually did the stock setting at the beginning and it was flooding.and the needles and seat are 100%,then we started the lower the float levels.choke mechanism works perfectly ,throttle valves open nicely and all needles go up with no hesitation,vacuum house also works 100% and the vacuum orings are in position,even i put some silicon around them to make sure that there is no leak.
to me it seems to be very lean at the moment,bcs last time the dude adjusted the air mixture screws,he made it lean i guess and the high revs problem started from that day.
now i am gonna set everything back to stock setting, and get back to you guys.
if u have any other suggestion,plz let me know before i strip the carbs,
by the way,i am from South Africa and the climate here is not same as the US,currently its spring time and weather is a bit chilli.
tx

[Squishy]

I'm not talking about your English. English isn't my native language either.
I'm talking about general punctuation/writing. You don't use spaces, paragraphs or capital letters.. you just write one wall of text. It's very hard to read.

Anyway with stock carb settings it should not flood.... why do you think it's flooding or running too rich? How do you know this?
You don't need to rejet after a new exhaust. At least not with the stock headers/pipes. My 400 runs fine with open exhaust.

Why not put it to stock settings and put it on the dyno for a A/F run? Saves you a lot of trouble.

[gallant_pilot]

good advise for writing !

1- first of all, at the beginning after riding it ,the bike used to die on the way and by opening throttle fully it used to come back alive sometimes.

2-nowadays after running it ,the moment i switch it off,it doesnt want to start again unless i leave it for while.

3- rejeting the main should affect on high rev,not the idle and i dont have any problem with the fast running or fuel.she doesnt struggle on high way at all.not loosing power even.

[gallant_pilot]

hey guys !

i set the carbs back to the stock setting and started it.(didnt struggle that much)
float level(14 mm) air mixture screw 1.75 turn.

without the airbox on,the idle is fluctuating and number 3 ( second from the left) doesnt get hot,its just a bit warm. also when i put my hand to check the suction on all,this one doesnt react and doesnt have any vacuum.

i stopped working on it  till i read yot comments.
please i am waiting for u guys to gimme ideas before i put everything back.

tx

[vintagemilano]

I would start off by checking valve clearances and then a compression check.

[gallant_pilot]

u think it can be kind of tight on that one?

[Squishy]

Unless the valve clearance and/or compression are WAY off, the cylinder should run and the pipes should get hot.
Normally, checking for compression is always a good thing to do because even when everything is perfectly working but you have bad compression, your engine will not run well.

However in this scenario I would remove the sparkplug from cylinder number 3 as you call it, and clean it. (since you say the carbs are clean)

My 400 works fine for 30000KM but in my experience it's very sensitive to a good spark.. especially when your spark plug drain hole is clogged up with dirt or when you haven't run it for a while.

Use a steel brush to clean the spark plug and check if the wiring is good.


If the carbs are clean and in stock settings.. it can't really be a fuel problem unless the carb doesn't get fuel at all. You can check this by opening the drain plug.

It can't really be an air problem either because the other 3 cylinders are firing and you say the carbs are clean.

What remains is a good spark, valve clearance and compression.

[ventYl]

Hi,
how many O-rings did you found and replaced in each carb? There are totally of five O-rings (each of different size) in each carb. One under top cap, one under pilot jet screw, two seals float assembly into carb body and one is burried deep inside carb and seals needle emulsion tube. You need to remove whole slide assembly to get to this one. If it is cracked (which usually is), carbs may leak even with float level set up properly.

Another little detail: GSF400 mikuni carbs should have rubber plugs covering hole of pilot jet fuel intake. This is due to relatively small vacuum on idle RPM. if these are missing, you'll get rough idle and there's nothing you can do about it except fitting the plugs back. It is possible that some of previous owners removed them because he thought he is smarter than manufacturer.

[gallant_pilot]

i replaced the orings and all 5 orings are fine.

i put one oring around the rubber plugs as well and it is seald properly.

problem is number 3 which doesnt have vaccum suction on idle. but at high revs it works nicely.

[gallant_pilot]

Squishy !

is it possible for the spark plug to just make sparks on high revs? bcs at high revs the number three comes back to the system and it works..

[ventYl]

yes, it is possible. it may be internally damaged. try to change spark plugs between cylinders.

[Squishy]

Squishy !

is it possible for the spark plug to just make sparks on high revs? bcs at high revs the number three comes back to the system and it works..

Yes it's possible.
When my spark plug drain hole was quite dirty and it had rained all day, 1 cylinder would stop working when it was idling.
When I got in high RPM it would start to work again.

This problem causes a lot of starting problems because you will try to start it on 3 cylinders basically.. if you haven't run it for a while it will hardly start..and may even cause the other cylinders to get flooded causing more problems.

I've also had it the other way around where it would work at idle but not when giving full throttle. Also caused by rain and dirt.

If you are 100% sure the carb's idle circuit is clean and all the mechanisms on the carb work (perhaps carb is so out of sync that on 3rd cylinder the throttle valve is closed while the others are open?), then it almost has to be spark(plug) related.