Setting up carbs to start

[Omegasteve]

So I'll give you the full story. Bought a 1994 GSX600F, not been started in 2 years. Managed to have her turning over the next day. Removed carbs to find the mixture screws on carbs 3 &4 had been drilled in an effort to remove. Bought a full carb set and trial fitted, couldn't fit the tank properly so I used a small container and she started and ran for a few secs but the carbs leaked like an old biddy. Happy with that.
Removed carbs, replaced seals and reset float heights to factory along with setting the mix screws to the owners manual settings of 2 turns out. Re fit the carbs and hooked up the fuel lines. Primed, this time no leaks (win). But now she won't start at all (no win). Is it a case of turning out the mix screws until she does? They were definitely set further out than 2 turns when I got them and tried them the first time around.
Thank you in advance.
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1994 SUZUKI GSX600F project - 1997 Honda VFR 750

[Bhud]

Original airbox?

How do your spark plugs look?

[Omegasteve]

Hi, yeah original airbox. Plugs look fine and are sparking.
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1994 SUZUKI GSX600F project - 1997 Honda VFR 750

[Bhud]

Does it run on choke/starting circuit?

[Omegasteve]

No, it doesn't at all
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1994 SUZUKI GSX600F project - 1997 Honda VFR 750

[Bhud]

What do you know about the replacement carbs? Are they clean? Were they from a working bike? Did you check the jets are clear and that they're the standard size?

As it worked before, that would suggest it's not getting enough fuel.
Could be float heights or obstruction of fuel to carbs or air leak or something else. You mentioned the carbs are all primed. I'd double check that by loosening the drain screws. Also the float heights - the manual is gospel but where there's orthodoxy there's also heresy...

If you can't get it to work by any means, then the problem must be the carbs. Sometimes a bank of old carbs might be gummed up and blocked with rubber or dirt in the main fuel line, even if they're individually clean. Or they might have some other problem. What did you do with them before installation?

[Omegasteve]

Hi so the replacement carbs are very clean, and she started on them and ran for a few moments (before the small container ran out of fuel) prior to me then replacing the seals due to the leak. Whilst I did that I then adjusted float heights to 15mm (14.6mm+/- 1mm) in the owners manual and set all the mix screws to 2 turns out as I wanted a baseline to start tuning them from.
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1994 SUZUKI GSX600F project - 1997 Honda VFR 750

[Bhud]

By seals do you mean just the float bowl seals, or any others?

If just float bowl seals, then as it seems those aren't down-draught carbs, and since the new carbs worked before adjustment although they were leaking, the float heights were (originally) probably a little too high. You dealt with this by replacing the float bowl seals and resetting the float heights. You mention the turns of the mixture screws, but as you say it doesn't work on choke either, I don't think it's that. Although it's an easy thing to check by simply taking them out 2.5 turns. If not that, then I think it's time to return to the float heights. I would try setting them a smidgen higher than what the manual says, to see if that makes a difference. Higher as in they close up the needle valve once the fuel in each bowl has reached a higher level than now.

[Omegasteve]

Yes the bowl and float seals are the ones I changed. I've even tried them 3 turns out but still no life and didn't want to carry on going. If I'm correct, would that mean when they are flipped upside down to set them a smidge lower? If that makes sense. Would you say like 13/14mm?
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1994 SUZUKI GSX600F project - 1997 Honda VFR 750

[Bhud]

Yes, when the carbs are turned upside down and you're measuring the float height of each one and bending the little tabs, adjust them so they activate the needle valve when the fuel reaches a very slightly higher level in the bowl.

Oh one other thing: when you've got the carbs off, check that the needle valves are moving up and down and not getting stuck. Corrosion and whatnot can cause them to get stuck in a closed position. If that happens, the fault might be on and off, and sometimes one will be stuck and sometimes another. If the needle valves aren't moving smoothly up and down, then it's time to replace them.

[Omegasteve]

Fantastic, I'll lower them and see what happens. Should I leave the mix screws at 2 turns for now? The float needles did all move freely, that is something I checked before putting the bowls back on.
This may be a bad idea but is it worth me changing the jets out of the original carbs that where on the bike? In case the ones in the replacement carbs aren't original? If no idea how I'd tell if they were.
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1994 SUZUKI GSX600F project - 1997 Honda VFR 750

[Nobby the Bastard]

If they were working before (abet with leaks) and aren't working after you messed with them, then the jets are not the problem. It was something you did.
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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."
Sprint ST 1050

[Omegasteve]

Oh I fully agree the jets aren't the problem, I just wondered if it was worth doing whilst I was taking them apart again anyway.
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1994 SUZUKI GSX600F project - 1997 Honda VFR 750

[virus]

So long as the jets are clean and the correct size they wont be a problem. I suspect youve set the float height too high resulting in not enough fuel in the bowls.


2 things I would do next:

After an attempt at starting pull all the spark plugs and see if they are damp with fuel.

with the bike on centrestand/ as close to vertical as you can have it, prime the carbs then turn the fuel supply off. Then using the drain screws drain off all 4 bowls into separate containers and confirm they are all holding the same volume of fuel.
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own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.

[jeffyjeff]

[Omegasteve]

[Omegasteve]

[Robby]

Crack open a float bowl drain plug to make sure you have fuel in bowls.

If it's running off the fuel tank, particularly if it's running off reserve, you may just have carbs full of rusty water.

[Omegasteve]

[Omegasteve]

Update:
I've set all the float heights to 13mm, higher than they were previously and we definitely have fuel in the bowls. When attempting to start I can see the vacuum pulling at the slides. Still no start though. She is cranking fine, I have checked the plugs and they are all sparking and I can also they are wet with fuel after a start attempt (not soaked). Ive even attempted easy start with no joy either and there's not even a cough of life. It just cranks and cranks. Any ideas?
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1994 SUZUKI GSX600F project - 1997 Honda VFR 750

[Bhud]

It's a working engine, it's got fuel and it sparks. Therefore, it should be working.

Are the plugs wet with fresh fuel? Have you checked whether you might have one or more vacuum leaks, around the carb-to-intake rubbers, or around the vacuum hose going to the fuel tap?

Tank was flushed, right? Do you think the fuel sitting at the bottom might be mixed with some of the flushing solution, water or anything else? Maybe try filling the carbs directly with fresh fuel from your container, instead of using what's in the tank.

[Omegasteve]

Yeah the fuel is fresh and the tank was dry before I then put the fuel in. The fuel in the carbs is clean too. Although you may have mentioned something there that I've not done. What vacuum pipe runs from the carbs to the tap? I've not seen any?
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1994 SUZUKI GSX600F project - 1997 Honda VFR 750

[Robby]

To be honest, after a completely dry fuel system and a bike that hasn't run in years, it can just take a load of cranking to get anywhere.

A fully charged battery is a good starting point. No throttle, no choke, and just crank it til it catches. Maybe a little bit of throttle now and then, but certainly no choke.

Your aim is to get it popping and farting a few times before properly catching, not straight into perfect even running. Choke will just flood it.

[A100man]

Here's my punt..

Choke circuit is blocked. Unless you squirt yourself in the eye with carb cleaner while checking to prove otherwise I'm going to assume this. Mix screws were then tampered with to compensate for blocked choke. you corrected this and no-starty.

Also make certain that the battery is tip-top or you're jumping it. TCIs on UJMs need good volts.
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Now: A100, GT250A, XJ598, FZ750

Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600

[Pete.]

Strange, I thought I replied to this yesterday but I guessI didn't hit submit.

A100man is on the money IMO this is the same engine as in the Bandit and I had to strip and service the cabrs on ine at least once, sometimes twice a year to keep t starting reliably.

In the end I did a bit of a write-up:

https://www.banditforum.co.uk/forum/index.php?topic=69488.0
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good