M600 carb problems

tridentperu · 09-09-2020, 02:17 PM

Hi,

This is an ongoing saga, and I thought I was near a solution... When I got the bike it was in a poor state, with one carb flooding and generally running badly. I farted about setting float heights that were miles off, all to no avail. It turned out in part, to be a knackered fuel pump. Sorted that out with a rebuild kit. Finally, being unable to stop the flooding I invested in a couple of carb seal kits and a pair of float valve kits from Allens - problem solved - no more flooding. Great.

Now, the problem is the bike starts and idles but as soon as you give it any throttle it just won't go - like it is starved of air. Revs ok with no load, but on the road, terrible.

Further inspection reveals that the diaphragm slides do not move when I rev the bike - I suspect this is the root of the new problem? Can anyone confirm before I pull the airbox off to have a look at the diaphragm sealing area? I am ok with slide carbs but these CV carbs are new to me.

I am getting really good at taking the carbs on and off now though - so it hasn't all been a waste of effort!!

Thanks for any suggestions,

Jim

slob · 09-09-2020, 02:56 PM

Usually a split diaphragm, although you'd only expect that to only affect one carb, unless both are split or failing to seal.
There's usually a hole in the bottom of the slide which connects the venturi in the carb body to the space above the diaphragm, although it may be a drilling elsewhere in the carb body.
This means the area above the diaphragm is at the same pressure as the venturi, while under the diaphragm atmospheric pressure is maintained.
When the throttle butterfly opens and air rusehes through the venturi, the pressure drops below atmospheric and the slide lifts against the spring.

Nasher · 09-09-2020, 03:14 PM

Worth whipping the carb tops off, inspecting the diaphragms, but also seeing if the slides do indeed move in the bores smoothly.

A set of carbs I had arrive with a bike that hadn't been used for a couple of years looked OK but the slides had sticky oil/fuel residue on them which stopped the slides moving properly.
A quick clean had them working fine.

It's also worth noting that the springs might have been mucked about with.
For example the Dynojet ones are a little less powerful than the standard ones, which would give you the opposite issue, but there could be some spacers or something in there.
I've found some odd mods on old bikes.

A quick google will reveal the visual difference between Dynojet and standard springs so you can see exactly what you've got.
And whilst you are about it look at the different shape of Dynojet and standard needles.

So many of these bikes have been fitted with Dynojet kits it's possibly rare to find one which hasn't.

tridentperu · 09-09-2020, 04:31 PM

Thx, update ...

Neither diaphragm was seated properly - a bit of gentle stretching and all seems ok. Slides now lifting with a twist of the throttle...BUT...

On the road it is now just as bad, if not worse...It is running so rich that it is choking. Literally. So rich it was only running on one cylinder in the end and popping and banging in the exhausts.. Looking in the a/box there is fuel spraying about when I twist the throttle!

Chokes are not stuck

Needles seem to be seated ok -

Def Dynojet springs and needles fitted .. Any idea what groove the needles should be in?

Air screws are 4 turns out

Thx

J

slob · 09-09-2020, 05:44 PM

You'd need to identify which Dynojet kit you have, but 4 turns sounds like a lot to me.
Lots of info on Dynojet's website but both Stage1 and Stage 2 kits say groove #4 (counting from the top) and start at 2.5 turns out.
https://dynojet.co.uk/media/attachme.../e7204.001.pdf

However, the air screws only affect ~ less than 1/4 throttle
1/4 -3/4 throttle is usually needle position, although this will be affected slightly by the main jets too.
Time to take the float bowls off and see if one of the main jets has come unscrewed? Although if you've recently had the carbs apart you;d hope not.

I assume running it with no air filter makes little or no difference?
Also what kind of exhaust are you running?

350TSS · 09-09-2020, 06:18 PM

My guess would be the float height is incorrect. Measuring and setting the right float height is quite tricky but you can check it with a clear pipe connected to the bowl drain pipe and if you lift the clear pipe alongside the float bowl the petrol meniscus should be in the middle of the boss on the side of the body of the carburettor. I am sure if you google it there is a video/guide/document there somewhere.

tridentperu · 09-09-2020, 06:45 PM

I thought of float height too, as I didn't check it with the new floats - thought they may come pre adjusted
(or at least not this far off!)

I doubt it is a jet unscrewed, I just put them all in...And not on both carbs

Hey ho, carbs off again tomorrow. Check I didn't do anything silly..and check float height and needle positions ....

Thx

J

tridentperu · 09-09-2020, 06:53 PM

Thx v useful dynojet info.

tridentperu · 11-09-2020, 12:20 PM

Update...

All sorted - it turns out I had fitted two jets (the ones under the little clips) upside down..Doh. Odd that they actually fit the wrong way round. My error.

And I checked the float heights while I was in there and gave them a little tweak to 14mm. Also checked needle pos and mixture screw settings against the recommendation on dynojet sheet - all put to their settings.

Then, looking good - it wouldn't start!! Grrr. Just weak popping ad farting. Checked spark with another plug to head, all good. Then tried the plugs from the motor to the head - dead as a dodo.

Two fresh plugs and fired right up. Now running the best it has ever done since I got it, a few tweaks to mixture / balance settings to clear up low pickup hesitation and all should be good.

thx for the tips

J

slob · 11-09-2020, 12:56 PM

probably just fouled the plugs when it was running super rich

350TSS · 11-09-2020, 01:30 PM

Its good feeling when dogged persistence triumphs over a recalcitrant bit of machinery

Darren69 · 11-09-2020, 01:57 PM

I went through several sets of plugs when I was setting up the carbs on my rebuilt Lav triple. Once they are fouled they never seemed to be any good after, even if dried and cleaned up. I'm not sure why?

slob · 11-09-2020, 02:12 PM

strange, they should be ok once cleaned properly, a good coating of carbon will short out the electrodes, so no spark

Darren69 · 11-09-2020, 02:45 PM

I was told they were probably 'fuel poisoned' but have never investigated any further.

tridentperu · 12-09-2020, 08:28 PM

I tried cleaning them, gapped them, no good. Dead. Almost certainly got toasted when it was running super rich (and hot). I used to get this occasionally on one cylinder on my trident - Iridium plugs sorted that out.

Been out again today, it still isn't quite right, still running a bit rich but a lot better than it was. I need to get it MoT'd so I can try a proper road test - until now it hasn't really mattered because half the time I ended up pushing it home! So not going far was for the best.

09-09-2020, 02:17 PM	#1
tridentperu Registered User Join Date: May 2019 Location: Gloucester Bike: M600 Posts: 32	M600 carb problems Hi, This is an ongoing saga, and I thought I was near a solution... When I got the bike it was in a poor state, with one carb flooding and generally running badly. I farted about setting float heights that were miles off, all to no avail. It turned out in part, to be a knackered fuel pump. Sorted that out with a rebuild kit. Finally, being unable to stop the flooding I invested in a couple of carb seal kits and a pair of float valve kits from Allens - problem solved - no more flooding. Great. Now, the problem is the bike starts and idles but as soon as you give it any throttle it just won't go - like it is starved of air. Revs ok with no load, but on the road, terrible. Further inspection reveals that the diaphragm slides do not move when I rev the bike - I suspect this is the root of the new problem? Can anyone confirm before I pull the airbox off to have a look at the diaphragm sealing area? I am ok with slide carbs but these CV carbs are new to me. I am getting really good at taking the carbs on and off now though - so it hasn't all been a waste of effort!! Thanks for any suggestions, Jim

09-09-2020, 02:56 PM	#2
slob . Join Date: Jul 2003 Location: East London Bike: Multiple Monsters Posts: 9,708	Usually a split diaphragm, although you'd only expect that to only affect one carb, unless both are split or failing to seal. There's usually a hole in the bottom of the slide which connects the venturi in the carb body to the space above the diaphragm, although it may be a drilling elsewhere in the carb body. This means the area above the diaphragm is at the same pressure as the venturi, while under the diaphragm atmospheric pressure is maintained. When the throttle butterfly opens and air rusehes through the venturi, the pressure drops below atmospheric and the slide lifts against the spring. Last edited by slob; 09-09-2020 at 02:58 PM.. Reason: linked image

09-09-2020, 03:14 PM	#3
Nasher Registered User Join Date: Jul 2014 Location: Portsmouth Bike: M900 Posts: 1,510	Worth whipping the carb tops off, inspecting the diaphragms, but also seeing if the slides do indeed move in the bores smoothly. A set of carbs I had arrive with a bike that hadn't been used for a couple of years looked OK but the slides had sticky oil/fuel residue on them which stopped the slides moving properly. A quick clean had them working fine. It's also worth noting that the springs might have been mucked about with. For example the Dynojet ones are a little less powerful than the standard ones, which would give you the opposite issue, but there could be some spacers or something in there. I've found some odd mods on old bikes. A quick google will reveal the visual difference between Dynojet and standard springs so you can see exactly what you've got. And whilst you are about it look at the different shape of Dynojet and standard needles. So many of these bikes have been fitted with Dynojet kits it's possibly rare to find one which hasn't. __________________ Heaven doesn't want me, and Hell is afraid I'll take over.

09-09-2020, 05:44 PM	#5
slob . Join Date: Jul 2003 Location: East London Bike: Multiple Monsters Posts: 9,708	You'd need to identify which Dynojet kit you have, but 4 turns sounds like a lot to me. Lots of info on Dynojet's website but both Stage1 and Stage 2 kits say groove #4 (counting from the top) and start at 2.5 turns out. https://dynojet.co.uk/media/attachme.../e7204.001.pdf However, the air screws only affect ~ less than 1/4 throttle 1/4 -3/4 throttle is usually needle position, although this will be affected slightly by the main jets too. Time to take the float bowls off and see if one of the main jets has come unscrewed? Although if you've recently had the carbs apart you;d hope not. I assume running it with no air filter makes little or no difference? Also what kind of exhaust are you running? Last edited by slob; 09-09-2020 at 05:52 PM..

11-09-2020, 01:57 PM	#12
Darren69 Transmaniacon MOC Join Date: Sep 2013 Location: Sutton In Ashfield Bike: Multiple Monsters Posts: 6,022	I went through several sets of plugs when I was setting up the carbs on my rebuilt Lav triple. Once they are fouled they never seemed to be any good after, even if dried and cleaned up. I'm not sure why? __________________ Roast Beef Monster! Termignoni and Bucci - Italian for pipe and slippers! S4 Fogarty, S4R 07T, 748, Series 1 Mirage

09-09-2020, 04:31 PM	#4
tridentperu Registered User Join Date: May 2019 Location: Gloucester Bike: M600 Posts: 32	Thx, update ... Neither diaphragm was seated properly - a bit of gentle stretching and all seems ok. Slides now lifting with a twist of the throttle...BUT... On the road it is now just as bad, if not worse...It is running so rich that it is choking. Literally. So rich it was only running on one cylinder in the end and popping and banging in the exhausts.. Looking in the a/box there is fuel spraying about when I twist the throttle! Chokes are not stuck Needles seem to be seated ok - Def Dynojet springs and needles fitted .. Any idea what groove the needles should be in? Air screws are 4 turns out Thx J Last edited by tridentperu; 09-09-2020 at 04:53 PM..

09-09-2020, 06:18 PM	#6
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,419	My guess would be the float height is incorrect. Measuring and setting the right float height is quite tricky but you can check it with a clear pipe connected to the bowl drain pipe and if you lift the clear pipe alongside the float bowl the petrol meniscus should be in the middle of the boss on the side of the body of the carburettor. I am sure if you google it there is a video/guide/document there somewhere.

09-09-2020, 06:45 PM	#7
tridentperu Registered User Join Date: May 2019 Location: Gloucester Bike: M600 Posts: 32	I thought of float height too, as I didn't check it with the new floats - thought they may come pre adjusted (or at least not this far off!) I doubt it is a jet unscrewed, I just put them all in...And not on both carbs Hey ho, carbs off again tomorrow. Check I didn't do anything silly..and check float height and needle positions .... Thx J

09-09-2020, 06:53 PM	#8
tridentperu Registered User Join Date: May 2019 Location: Gloucester Bike: M600 Posts: 32	Thx v useful dynojet info.

11-09-2020, 12:20 PM	#9
tridentperu Registered User Join Date: May 2019 Location: Gloucester Bike: M600 Posts: 32	Update... All sorted - it turns out I had fitted two jets (the ones under the little clips) upside down..Doh. Odd that they actually fit the wrong way round. My error. And I checked the float heights while I was in there and gave them a little tweak to 14mm. Also checked needle pos and mixture screw settings against the recommendation on dynojet sheet - all put to their settings. Then, looking good - it wouldn't start!! Grrr. Just weak popping ad farting. Checked spark with another plug to head, all good. Then tried the plugs from the motor to the head - dead as a dodo. Two fresh plugs and fired right up. Now running the best it has ever done since I got it, a few tweaks to mixture / balance settings to clear up low pickup hesitation and all should be good. thx for the tips J

11-09-2020, 12:56 PM	#10
slob . Join Date: Jul 2003 Location: East London Bike: Multiple Monsters Posts: 9,708	probably just fouled the plugs when it was running super rich

11-09-2020, 01:30 PM	#11
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,419	Its good feeling when dogged persistence triumphs over a recalcitrant bit of machinery

11-09-2020, 02:12 PM	#13
slob . Join Date: Jul 2003 Location: East London Bike: Multiple Monsters Posts: 9,708	strange, they should be ok once cleaned properly, a good coating of carbon will short out the electrodes, so no spark

11-09-2020, 02:45 PM	#14
Darren69 Transmaniacon MOC Join Date: Sep 2013 Location: Sutton In Ashfield Bike: Multiple Monsters Posts: 6,022	I was told they were probably 'fuel poisoned' but have never investigated any further. __________________ Roast Beef Monster! Termignoni and Bucci - Italian for pipe and slippers! S4 Fogarty, S4R 07T, 748, Series 1 Mirage

12-09-2020, 08:28 PM	#15
tridentperu Registered User Join Date: May 2019 Location: Gloucester Bike: M600 Posts: 32	I tried cleaning them, gapped them, no good. Dead. Almost certainly got toasted when it was running super rich (and hot). I used to get this occasionally on one cylinder on my trident - Iridium plugs sorted that out. Been out again today, it still isn't quite right, still running a bit rich but a lot better than it was. I need to get it MoT'd so I can try a proper road test - until now it hasn't really mattered because half the time I ended up pushing it home! So not going far was for the best.