Choke Circuit Diagram?

Hi all, further to a couple of threads on here, I think my cold start (ie NO start) problems might be related to the choke circuit.

Carbs have (once again) been stripped/cleaned. Valve clearances are spot-on (re-shimmed recently) and fuel levels appear there or there abouts.

The bike was running two days ago, when I synched the carbs with dial guages. All plugs and plug caps are brand new. I set the idle at a steady 1000rpm with a hot engine.

Now it won't start, and the plugs are bone dry!

Anyone got a diagram of the choke circuit, or can identify the relevant parts/drillings in the carbs?

Any other suggestions appreciated.

Thanls,
Nige

 

Even the "Drawing" in the Factory Manual does not fully illustrate the Circuit with enough detail to "Picture" it.

Beginning in the Fuel Bowl.
There is a separate Reservoir, ... a "Well" ... which fills to the Level of the Gas in the Bowl when the Bowl is full.

Two Metering Ports at the Bottom of the Fuel Bowl ... 1 within the Well ... control the Volume of Fuel and the Time required to Replenish the filled Well.

A Brass "Siphon Tube" ie guided into the Well when the Fuel Bowl is attached to the Carb Body.
The Siphon Tube has several very tiny Metering Holes drilled in it to regulate the Fuel.
One at its Bottom.
Another, ... across the Outside Diameter near the point where the Siphon Tube protrudes from the Carb Body.**
(** Not all tubes have cross drilling)

The Siphon Tube runs straight up the side of the Carb Body, it's open end at the point where the Enrichment Plunger's Seat and Plunger regulate how the Fuel from the Well will be drawn-up into an Opening which allows the Fuel to Enter the Combustion Chamber with the Throttles Closed.

Vacuum draws the Fuel to the Engine.
The Small amounts of Fuel is easily pulled into the Head.
Flooding is regulated by Fuel Bowl Bottom "Jets" replenishing the Enrichment Circuit Supply very slowly.

KEY to the Cold Start Enrichment Circuit working to start a Cold Bike is the
FLOW of Fuel to Fill and replenish the volume in the WELL.

If those Posts are Blocked ... the Cold Start System is disabled.

 

OK, thanks for that.

It looks like those carbs are coming off again!

Nige

 

Some time ago one of the members here did a cross section drawing of the Hitachi fuel bowl. The tiny orifice in the bottom of that well Rick spoke of is clogged often enough that I circled it and keep it handy for threads like this.

I forgot long ago who did the original drawing or I'd give credit.

 

If you can find a #79 drill bit, it is the correct size to clean out the orifice that is shown in the diagram above. It's a small drill bit. so you have to be very carfull with it. After cleaning, a strong flashlight aimed in the bowl, you should see a small pin of light down in the orifice. Chacol sells the correct bit.

Kenneth

 

Clean the Well and its Bowl-connecting Orifice so that when you shoot Carb Cleaner into the opening in the Bowl ... It will SHOOT >> OUT from the Well.
Be careful.
Those Zany Yamaha Engineers have the angle worked-out to give you an Eye-full of Carb Cleaner if you have the Bowl at the right angle.

Don't mess around.
If the Bowl Bottom Metering Ports are clogged ... Drill-out the Clog.

A Guitar String will Clean and Probe the Siphon Tube.

Shrink Wrap that fits over the Siphon Tube snugly ... can be Shrinked on to the END of a Carb Cleaner Tube ... then, fitted-over the Siphon Tube for a Power Flush.

Hold OPEN the Enrichment Valve if they are not removed.

MEASURE the DRILL Depth.
Don't drill through the Bottom of the Bowl.

 

Thanks for all the info guys (and the diagram). I will check these things out.

Nige

 

Right, carbs now off.

Have removed the float bowls - everything looks ok (in the little "well" etc) but I'll try the old guitar string method to make sure there's no gunk in there.

I've removed the cold-start plungers and everything is clear on the top, however, I'll deploy the guitar string up the brass tubes which extend down into the float chamber and then blow carb cleaner through.

After performing a bench-sync, I'll re-fit the carbs and try again.

Nige

 

Note at the top of the brass tubes there is a small hole that needs to be clear. Look right where the tube goes into the carb body.

MN

 

Thanks, will do.

Through a cursory spray of carb cleaner it would appear there is a blockage in one of the "well" passageways in the float bowl, and in two of the brass tubes or further up the passageways.

Will investigate further tomorrow.

 

OK I've made sure all the brass tubes are clear, and the little holes near the top.

I still have one float bowl blockage - I think its the actual pilot jet which lives way down in the tunnel...

Is there any way of removing these, as it doesn't appear to be slotted for a screwdriver - are the a push-fit, if so how do you get 'em out?

Nige

 

Press fit, drill or soak compressed air ultrasonic clean very tiny hole guitar string

 

Hello Nige...at this point all I have to say is get th carbs done right and you're well on th way to having th bike running sweet, take your time and follow th process ..

 

Phew!!!

After trying all sorts of bits of wire in the hidden-away cold-start jet, finally an Ernie Ball 9 gauge string came to the rescue... an 11 is too big.

I don't know what was in there, but I guess its been there all the time, as carb cleaner wouldn't shift it.

I will now double check everything before re-assembly.

I now wish I had kept hold of my two spare sets of carbs, as they would have been a good source of bits.

Thank you all for the shared knowledge and advice.

Nige

 

Everything now thoroughly cleaned and reassembled. Will fit to bike tomorrow.

Regarding butterfly position at cold start setting - should these be fully shut for cold-stating or (as I would think) should they be open a chink - if so, is there a datum opening measurement?

Nige

 

The butterflys are open just a 'chink' of light, that is the idle setting not affected by the 'choke' enrichment.

 

OK+,I'll set them up like that and take it from there.

 

At this point, you're supposed to "bench sync".
I use 2 strips of regular printer paper, which is 0.010 (inch)
This just happens to leave a good idle setting.

I keep tweaking the sync screws until the "drag feel" is the same on all 4.

 

Thanks, will try that.

Nige

 

Right, done that...

Looking through from intake side, just a small chink of light in each one.

Put carbs back on and.... NOTHING!

So:
Carbs thoroughly cleaned (again)
Cold-start passageways and jets all clear
All other jets clear
Floats are right way up
Float levels are good (checked)
Bench-synch done
Sparks are present - all new plugs and caps

LAST WEEK IT RAN PERFECTLY - STEADY IDLE, PERFECT PICK-UP ON THROTTLE etc.

I'm going to look again tomorrow - the only thing I can think of is that last time it was running I had the vacuum gauges and a slave tank on it and I now wonder if the caps on the vacuum take-off stubs are leaking (they've gone pretty hard). I suppose leaks here would be the path of least resistance for the intake airflow and therefore stop fuel being drawn up from the carb bowls.

As I really can't think of anything else that has changed since it last ran I am going to go with this as the potential cause and shall try and find something to give a good tight seal on the stubs and see if it solves this (now extremely frustrating) problem.

Nige

 

In the states you can pick up those vacuum caps at any auto parts store. Replacing them will be a cheap way to eliminate extra headaches.

Since it ran with a slave tank you might also check and make sure the petcock lets fuel flow, fuel lines not kinked etc.

 

Will try and pick some caps up, or make something up.

The fuel line is new, as is the in-line filter which also shows/proves fuel supply - as does the float chamber level-check.

thanks,

Nige

 

When you have had the carbs off to clean, after reinstating it can be a problem to get started the first time, I have commented on this before, you might need some starter fluid just to get the whole system flowing, I jump from a car battery as well (car not running) just to get that extra oomph, you need the best rotation speed & a good spark, it'll run.

 

Yeah. I've put the battery on charger overnight (proper charger, not the Optimiser). Fingers crossed can get it sorted soon.

 

On charge all night, but still won't run.

When I test the battery it shows 12.6 volts, but when starter button is pressed it turns over but reading drops down to 10.5 volts.

Is this normal or does it indicate a bad cell or something?

Thanks,

Nige

 

Hmmmm...There is a substantial voltage drop when you load the system with the starter motor but I don't have a clue about how much is normal. Have you had your battery load tested? It won't hurt it to test it and most shops will do this for free. I'll have to monkey with measuring my bike when the rain stops (next year). Have you checked for spark perchance? Mayhap you might have jarred something loose with all the poking around you did putting the carbs back in (coil ground or some such item). Best of luck to you!

 

Hi. I asked at the bike shop today and the guy reckoned the voltage could even halve under load. Mine only seemed to drop a couple of volts.

That aside, I will take that look at the vacuum take-off points as I still think these may have a part to play.

Plugs still appear to be dry, so fuel not drawing up from bowls me-thinks.
As I have checked all jets/passageways then it has to be something pretty basic.

Nige

 

This is fine. As long as you are getting more than 9.5V during cranking, your battery has the capacity to power the ignition system and fire the coils, which is all that is needed.

 

I've read this entire thread and other then thinking that you were going down the wrong path to begin with, I read with anticipation and hope that your bike would start after all your hard work(pulling carbs is just one of these pita jobs to me).

I'm not saying that the work you did was in vain and I'm certianly not knocking anyone here. After all, I'm the "new guy" who has NEVER worked on a four stroke yamaha before.

But, I tend to look at problems from where they originate and nothing else. I just don't want to come off as a azzh**e so please don't take it that way.

Ok, the bike ran and now it doesn't....since the plugs were dry did you pull a drain screw or three to see if fuel is getting to the carbs? I didn't see which model you have so I don't know if the check valve is applicable to your bike or not. If you are getting gas to the carbs yet it still won't start, I would spray some WD40 into a couple of cylinders and see if it tries to run. WD 40 will fire and will provide lubrication, personally, I never use "starting fluid" as it will not and repeated use will score the crap out of your cylinder walls as well as stripping the oil so when it does first start, then they REALLY get scratched....then loss of compression follows blah, blah...so if it runs on WD40 and you've checked for any intake leaks from the carbs to the engine, then I would check the plungers to be sure they are moving far enough. From what I've read, these bikes are very leanly tuned and the starting circuit isn't exactly going to pour a whole heck of a lot of extra fuel in there so the need to capture all of it is important, again, from what the manuals have told me.

Finally, before diving any futher into carbs....make sure that fuel is leaving the tank and getting to the carbs....sometimes, it's the simplist things.....

good luck,

jeff

 

Thanks for the input Jeff - and everyone else.

OK, I'm certain that fuel is getting into the float bowls. For some reason it's not going to the cylinders (to any of them). I have sparks.

As it was running fine before, and I can't really think of anything that's changed since, I'm at a bit of a loss.

I've tried it again with the synch gauges on (to rule out air leaks at the vacuum take-offs) and no joy.
I think I'll remove the intake snorkels so I can get at the intake side of the carbs with some WD40 and see what happens. Also I can gauge the "suck" on each carb by doing this.

INCIDENTALLY... the bike fired a number of times at the first touch of the button today, then refused thereafter. It did fire a couple of times (literally just two or three firings) last night after standing all day.

Nothing else to report for now.

Nige

 

It is possible to get the 2 jets in the float bowl reversed.

 

Hi, jets are in right place - however...

COULD IT BE CONTAMINATED FUEL???

THE REASON I've just thought of this is that I (have just remembered that I) had a similar problem with my car just a few weeks ago. It just wouldn't fire up (after running fine). I tried it at various intervals for a whole Sunday - it just wouldn't catch at all.
I thought the symptoms suggested fuel starvation.
I ended up having it towed to my local garage (who know their stuff) and it started for him straight away! He checked everything out and couldn't find a fault, and it's been fine since. (Though it cost me £47 to have it towed there - about a mile).

After some head-scratching we concurred on it being most likely caused by bad fuel (from a local supermarket), and mine was not an isolated case - he gets two or three cars a week who have similar symptoms with petrol from the same source.

I HAVE REALISED that last time I had the bike running it was on a slave supply with fuel from my Jerry can, which I sourced elsewhere. The fuel in the bike's tank is recently sourced from the same supermarket as that which caused the problem with my car.

So what do you think? The fuel is definitely something which has changed from the last time it ran.

Nige

(BTW - Thanks for your continued patience and suggestions on this one guys - it's much appreciated).

 

Keep the gas & dump the bike ;o)

 

I'm just curious I suppose, which is why all my friends always brought me their bikes when they didn't run. How are so so sure that you are getting fuel into the carbs? I'm sure you could have pulled a couple of screws and not posted it here but I'm going strictly by what I"m reading when i ask.....you would be amazed at the things I"ve seen when the owners were positive about one thing or another.
What it has taught me is that just becasue of X, don't assume that Y is happening.

I just keep getting this picture in my mind of a half filled fuel filter sightglass which isn't really flowing any fuel.....which is why I'm prodding you a bit.

Heck, i want your bike to run as badly as you do at this point<LOL>!! Also, try the WD trick yet? That proves/disproves a lot of things......


jeff

 

"COULD IT BE CONTAMINATED FUEL???"

Could be the problem. In the USA we are having constant problems with the mix of methanol and additives in our fuel. Leave it for a week or 2 and it turns to garbage. Had several problems like this in some other seasonal machines (lawn mowers).

Get your auxilliary tank, get some known good gas in it, hook it up to your carbs and see. If it runs fine, dump your current tankful and get a refill.
It's a quick test, but just so you know ahead of time - if the fuel were bad it should still wet your spark plugs.

Did you check the fuel level in the float bowls when you had the carbs off and were doing your bench sync (checks to see if you get fuel to each float bowl as well as proper fuel level)? Did you disconnect your filtered line from the carbs and see if you were getting adequate flow from your tank (checks petcock and fuel cap venting)?

 

Hi everyone...hope you had a good Christmas.

Briefly, bike has been stood for a few days without me trying it.
This morning I re-checked fuel levels in bowls - well, three of them, as one has a seized screw - and all OK. I'm having to presume the remaining one is OK too, as set up the same as the others.

On turning over, the bike definitely tried to fire. However, I know that I will have to re-set the idle screw as I've moved it around a bit - but I'll have to have it running to fine-tune this.

I'm beginning to have thoughts about the battery though (after all, it's been on the bike for two years and not used much). Though it's showing 12.6 volts on the meter, it is only lighting the first of the four lights on my optimiser. I will leave it on trickle charge 'till tomorrow and see if this improves. I think though that I will have to invest in a new battery to rule this out as a cause.

Nige

 

Tried it this morning, same as before - (tried to fire) - then a very loud bang from the exhaust.

Before stripping the carbs again, I'm going to check over the whole ignition system with a meter.

Nige

 

Did you change out the battery?

That last symptom sounds like a battery without enough juice to run the starter and ignition at the same time. When you let off the starter the motor is still spinning for a second and tries to fire because now the ignition has all the amps it needs.

 

Sometimes when I change something on my bike I have to turn it over for what seems like forever, but it eventually fires and starts. To do this I have to jump it of course, otherwise the battery would run down.

Can't explain why it does this, but once it starts it runs fine and starts fine after that.

It'll start firing on one cylinder, then the others will pick up eventually. Just remember to give your starter a break fairly often.

 

Yes, I can run with that thought.

I'm definitely suspecting the battery now (not producing enough amps to give a good spark!?)

After sitting, wired-up to the optimiser for 36 hours it ran for around three seconds today, before dying.

After leaving it another hour to recover it ran again (on half-choke) for around five seconds.

Even though it caught straight away, the lights on the optimiser dropped to three out of four lights.

I do recall the spark - although present - being a little pathetic.

Time to invest in a new battery??

Nige