Idle and Starting Set Up

[mgy66]

Hi,

Following on previous post to get better understanding on the right carb set up. I have a K1, big bore 830cc. Pilot #40, Main 110, air screw at 2.0.

I went through a carb balancing procedure (using 4 gages) and setting the readings at 150 Hg/mm.

I ended up with adjuster screws fully turned to lowest position, while in the Haynes it recommends to keep 1.8mm between the stopper nut and the tip of the adjuster screw. The idle is holding up for few secs but I need to rev up at red light or it would fade and stall.

Also, for my understanding does anyone know if the adjuster screw move only the throttle valve or is it both the throttle valve and the needle together?

Another question on my settings is the 26mm floater position. Can I get confirmation it is 26mm when the floater is up (floating valve closed)? Would a higher position overflow the carb or would foul the plug (assuming it is not high enough to reach the top of the carb to prevent closing of the valve nor the bowl gasket as I would notice leakage at the gasket).

Many thanks,
Marc

[hairygit]

The adjuster moves both. Are you running standard pipes ( 4 into 4)?  I seem to recall that K1 with std pipes should be 120 mains, but I'm sure someone will tell me if that's wrong. Raising the float height may well cause the carbs to flood, better to lift the needles by 1 notch will give more fuel for any given throttle opening.

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[mgy66]

Hi,

I am running 4 in 4 standard but I think I have no bafle at the end of the pipe. I also have velocity stacks but I tried as well standard air box without being able to get a steady idle between 1000 rpm to 2000 rpm.

If I go with moving the needle up via the pin, has anyone tried to change the pin set up in situe, I.e carbs on the engine? Is there an easy access from the top of the carbs?

It seems that my starting problems come from gas not accessing the chambers despite new slow jets. Few supporting symptoms are:

- I usually.need to open up the idle screw at cold start taking the risk to foul the plugs. I can run a battery load without any succes otherwise. No need to say the choke is totally useless;
- My starter is actually a can of carb cleaner that I spray like a full on the velocity stacks.

Rather than changing the needle height pin, do you thing using a bigger slow jets, say #42 instead of #40 could help?

Thanks...

[Spitfire]

120 mains rings a bell from my CH750K1 days, it had a 900cc conversion, a standard airbox with no filter inside, and at various times 4 into 4 and 4 into 1 exhausts, the carb was standard settings apart from the needle which was up one notch if I remember correctly.
Here's a chart


Cheers

Dennis

[mgy66]

Thanks for these inputs.

From my reading, I thought the main jets were not so critical for start up and idle. Once in run, it may not be the most performing set up but it does run.

The issue is really the start up and idle. wrt to the start up, spraying carb cleaner into the inlets is a great solution until I get to understand how I should set my carbs. The idle is more tricky and other than running at 2000rpm or setting the idle screw lower and keep rev'ing at redlight I have not any solution.

I think I need to go a step beyond and dismantle all the carbs for a good and long ultrasonic bath... I think despite having brand new slow jets somehow not enough fuel reach the cylinders at low/start rev.

Any suggestion on what ultrasonic bath and product I should be considering? How long I should leave the carbs into the bath? Wrt to my former question on the 26mm floating position, can you confirm it is 26mm when the valve is in close position (i.e. floaters are up in their bowls)?
Thanks,
Marc

[Chris400F]

Came across this article (referenced from elsewhere on these forums, I searched for 'float height') on setting float height which may be of use:
http://www.salocal.com/sohc/tech/carb/asmpg_mgs/flthgt.htm

[mgy66]

Thanks Chris,

This is actually the post that triggered my question initially... The post clearly debates about whether the measurement should be from the lip or from the gasket surface but the below text between the pictures seems to indicate the measurement should be from the valve in open position ''so the valve pin tip is just barely touching the float tang''. Doing the work on the spot with the carb mounted is not easy as you would not see when the tip is barely touching the float tang and contrary to the description, in my carbs it does not seem that I have any spring on the valve (it looks like it is gravity). I would be interested to know if the 750K1 should have a spring in the float valve. That may explain why it looses rev as I wait at red light.

Wrt the approach I have taken and which I am sharing with the forum to get some feedback, I am now pushing the float at the highest point so when the valve is in close position I make sure I still have some little gap between the float and the top of the carb (i.e. the float does not bang onto the top of the carb which of course would prevent full closure of the valve). I may have a level a bit higher but I think as long as it is not over the gasket (which I will notice as it will leak from here). The assumption I am making is that high level (but no leak) is not affecting the carburation as what is moving the full up into the jets is the suction pressure and the diameter of the jets (i.e. it does not depend on how much of the jets are immerged into the fuel)... Any further experience to share on that one?

Wrt to Dennis post and table, do you know what means 4 for the needle jet? Is it a length, diameter or just the level where the pin should be attached at the top?

Best,
Marc

[Chris400F]

I was actually searching for a different thread when I came across that link, which I have now found.
http://www.sohc.co.uk/index.php/topic,7617.msg48072.html#msg48072
The thread relates to 350/400 models but methinks the principles should be the same.
I did my own float heights around that time so it was useful information.
From my experience I would think trying to set heights with the carbs in situ would be vey difficult; I wouldn't even attempt it.
Working with the carbs off the bike and the bank of carbs vertical (as suggested somewhere) seemed a good scheme to me.
I don't know enough about the operation of carburettors to know how crucial float height is or what effect it has but guess a value is specified for a reason.
On the 400, and other carbs I have come across, the float valves have an internal spring which I assume is to prevent excess pressure on and consequent damage to the valve seat.

[Spitfire]

Thanks Chris,

This is actually the post that triggered my question initially... The post clearly debates about whether the measurement should be from the lip or from the gasket surface but the below text between the pictures seems to indicate the measurement should be from the valve in open position ''so the valve pin tip is just barely touching the float tang''. Doing the work on the spot with the carb mounted is not easy as you would not see when the tip is barely touching the float tang and contrary to the description, in my carbs it does not seem that I have any spring on the valve (it looks like it is gravity). I would be interested to know if the 750K1 should have a spring in the float valve. That may explain why it looses rev as I wait at red light.

Wrt the approach I have taken and which I am sharing with the forum to get some feedback, I am now pushing the float at the highest point so when the valve is in close position I make sure I still have some little gap between the float and the top of the carb (i.e. the float does not bang onto the top of the carb which of course would prevent full closure of the valve). I may have a level a bit higher but I think as long as it is not over the gasket (which I will notice as it will leak from here). The assumption I am making is that high level (but no leak) is not affecting the carburation as what is moving the full up into the jets is the suction pressure and the diameter of the jets (i.e. it does not depend on how much of the jets are immerged into the fuel)... Any further experience to share on that one?

Wrt to Dennis post and table, do you know what means 4 for the needle jet? Is it a length, diameter or just the level where the pin should be attached at the top?

Best,
Marc

The JN related to the needle position 4 being the 4th from the top, if I remember correctly, have a read of the following for more details

http://forums.sohc4.net/index.php?topic=63177.msg687840#msg687840

Cheers

Dennis

[mgy66]

Thanks...

@Chris, it looks from the post that they are referring to a spring in the float valve (pin 'contacted but unloaded'). I am pretty sure I do not have any spring in the float valve. I am not sure this can be done with the carbs on the bike. Interestingly, there is also a sketch referring to the adjusting procedure (from Bodd). This should be done with the needle screw sufficiently engaged. I think that was my mistake when doing the sync.

@Spitfire, I will try to take out the carbs and do a full cleaning. The post you copied also refer to some white calcification on the main jet holes (from HondaMan). I don't think it is my case as I have cleaned them with a carb cleaning drills but I am pretty sure I have some calcification or some kind of deposit in the starting chamber or channel where the slow jets are connected. I see there is a small hole at 3 or 9 o'clock when you face the inlet.

Does anyone can recommend some product to use in a ultrasonic bath? Is it the same product sold in spray as 'carb cleaner'?

All good stuff which should take me to a much more usable bike.
Thanks,
Marc

[Bryanj]

There is a spring in the float valve and if it doesn't work you need new valves. Having done these foe years I would say the job for an inexperienced mechanic is impossible on the bike and few experienced ones will try it

[mgy66]

Humm, I guess you are suggesting riding the bike to a professional mechanic for a complete rebuild of carbs... I will check with my mechanic what would be the charge.
Thanks,
Marc

[hairygit]

I think what Bryan means is that trying to change the float valves with the carbs on the bike is impossible for the average home mechanic, with the carbs on the bench, it's straightforward and easy, so get the carbs off and sort it!

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[Bryanj]

I meant setting the float height but was tired when I wrote it, either way easy with carbs off, damn near impossible with them on

[mgy66]

Got it!

Carbs dismantled, 1.3L ultrasonic/heater cleaner on the way. Will probably use some dish hand washing detergent. Meanwhile, inventoring of spare parts I need, incl. trying to unscrew the damn needle to check size and pin position (I think it is 1 below the top one currently). I can tell you that I am not the first to unscrew these needles. Screw heads are worn...

Need to check whether it is also the right needle (it is a conic one). I have confirmation that no spring in the float valve. Would need to resupply the spring but I also want to check Haynes picture of the carbs to double check whether there is one. If I add a spring and OE do not have one by construction, then the 26mm may not be the right target as I would need more immersion to push the floats and close the valves.

Question around keeping some gaskets, seals and rings. Some are marked but overall they seem ok...

Main goal is to solve the start up/1000rpm idle, i.e. make sure I have good flow in the slow chambers of the carbs...
I am sure I will come back for further advices as I progress in the clean-up.

I am sure I will come back for more advices as I progress...
Thanks,
Marc