Trouble starting...

[MSTRS:Me]

Yep. That's what you have with CV type carbs. They may not move when twisting the throttle. On the engine side of the slides, there will be a butterfly in each carb. Those will move. But the engine has to be going to create the vacuum that lifts those slides. The greater the vacuum, the higher the slides go. Which lift the needles further out of the jets, allowing more fuel to get where it's needed.

[magicmonkey]

thats the one, i figure if they move properly, and air is flowing through the carbs, must be a problem with the fuel in the bowl.

sweet, that's a job for the morning when I'm not quite so under the influence then

[magicmonkey]

Yep. That's what you have with CV type carbs. They may not move when twisting the throttle. On the engine side of the slides, there will be a butterfly in each carb. Those will move. But the engine has to be going to create the vacuum that lifts those slides. The greater the vacuum, the higher the slides go. Which lift the needles further out of the jets, allowing more fuel to get where it's needed.

well that's reassuring as that's what I thought they were doing and I was starting to get a bit worried that they might be screwed! I'll have a double check tomorrow though, just to be certain ...

[magicmonkey]

well, I checked the floats and they all seemed fine, then I took out the pilot screws and checked them, cleaned them and put them back in (I blew down the hole and covered a few openings with my finger so I knew there wasn't a blockage in the tubes as well). Then I popped the carbs back on and turned the engine over, no joy, surprise surprise!

When I was turning the engine over I noticed that there was oil coming from the engine cover seal which alarmed me, especially as there was quite a bit of oil coming out. So, off comes the engine cover and it turns out that the seal is perishing in quite a few places, it also looks like someone was once aware of this and tried to remedy the situation with a load of silicone sealant. So I'm not wondering, could I be losing compression through this seal and therefore be having problems starting? seems quite likely to me. Either way, it needs replacing with a new one but I'm not 100% sure that would have caused the problem in the first place or if it's just something incidental which happened to go at the same time ...

[bogan]

no, there is a breather from the engine casing to the airbox (usualy) anyway, so no compression down there. Just checking that when you put the pilot screws back in you turned them back the required number of turns? And how did the looking in the carbs from airbox go?

[MSTRS:Me]

When I was turning the engine over I noticed that there was oil coming from the engine cover seal which alarmed me, especially as there was quite a bit of oil coming out. So, off comes the engine cover and it turns out that the seal is perishing in quite a few places, it also looks like someone was once aware of this and tried to remedy the situation with a load of silicone sealant. So I'm not wondering, could I be losing compression through this seal and therefore be having problems starting?

You mean the topmost part of the engine? Above the plugs?
If so, then it is merely the cam cover. Nothing to do with the cylinders part, so no compression loss there. Do replace the gasket tho...gotta keep that oil contained within for the whirly bits.

[bogan]

You mean the topmost part of the engine? Above the plugs?
If so, then it is merely the cam cover. Nothing to do with the cylinders part, so no compression loss there. Do replace the gasket tho...gotta keep that oil contained within for the whirly bits.

i thort he meant a side cover, but good advice either way!

[magicmonkey]

You mean the topmost part of the engine? Above the plugs?
If so, then it is merely the cam cover. Nothing to do with the cylinders part, so no compression loss there. Do replace the gasket tho...gotta keep that oil contained within for the whirly bits.

Yup, that's the cover I mean, got the gasket on order now and I'll pop it on once I get it. It's almost a shame that it wasn't the problem as it would have been a nice easy fix! It has made me wonder if there are other gaskets which could be in the same state (even though all the rest of the rubber looks pretty much fine) I suppose it's time to think about compression testing the thing as I know the spark is fine, I can smell petrol from the exhaust and I've been over the carbs to the point of complete boredom ...

[MSTRS:Me]

Sure, get the compressions checked. But I'm betting that's not your problem. It ran before, yet you haven't touched the head or the valve clearances, so it must be as it was.
You've eliminated the weak spark, and you say the firing order and timing is right, which only leaves...fuel.
Your problem is fuel-related...ergo, something about the carbs is not right.

[bogan]

Sure, get the compressions checked. But I'm betting that's not your problem. It ran before, yet you haven't touched the head or the valve clearances, so it must be as it was.
Your problem is fuel-related...ergo, something about the carbs is not right.

i agree, maybe if the bike was running really poorly last time it could be compression, but it generally doesn't go from good compression to shit that quickly, not without grenading the engine that is, and you'd know if that happend! Have you adjusted any air mix screws and not put them back? pinched a choke cable? anything like that, dunno how familiar with carbs you are, but small changes can greatly affect how/if the engine runs

[magicmonkey]

yup, I pretty much agree with you guys, I'm just getting to a point where I've pretty much gone over everything to do with these carbs and can't find the problem. It's not helped by me not being able to find any diagrams of the carbs either as I'm running a bit blind :s

[kwaka_crasher]

I'm sticking with the problem being fuel related and think you're just overlooking some fundamental problem.

Dare I say it... and I say this very rarely... but perhaps you'd be best to take it to a shop. I don't think you have the patience, understanding & know-how to deal with carburettors at the moment. Getting them looked over properly by someone who knows exactly what they're looking for would be a worthwhile investment.

[magicmonkey]

i agree, maybe if the bike was running really poorly last time it could be compression, but it generally doesn't go from good compression to shit that quickly, not without grenading the engine that is, and you'd know if that happend! Have you adjusted any air mix screws and not put them back? pinched a choke cable? anything like that, dunno how familiar with carbs you are, but small changes can greatly affect how/if the engine runs

I checked the choke cable and it's operating ok. The air screws were turned out 3 turns rather than the 1.5 - 2 which most sites seem to recommend as a starting point so I've tried with both and left them on 1.5 turns for now.

As for the grenading, there was a backfire quite some time ago, I can't remember if that was before or after the problems but I'm pretty sure before. I'm assuming that grenading the engine would be a bit more violent than a backfire though!

[magicmonkey]

I'm sticking with the problem being fuel related and think you're just overlooking some fundamental problem.

Dare I say it... and I say this very rarely... but perhaps you'd be best to take it to a shop. I don't think you have the patience, understanding & know-how to deal with carburettors at the moment. Getting them looked over properly by someone who knows exactly what they're looking for would be a worthwhile investment.

I;m tempted to agree with you at the moment, I've found some carbs for $200 though which would probably be easier and might be cheaper than taking it to a mechanic. Still, I'll leave it until then end of the week before I start spending money I should be saving!

[bogan]

I;m tempted to agree with you at the moment, I've found some carbs for $200 though which would probably be easier and might be cheaper than taking it to a mechanic. Still, I'll leave it until then end of the week before I start spending money I should be saving!

best bet could be to offer a doz or two to a fellow kb'r to come have a look, second opinion could be very useful