Rejetted, and WORKS! now running rich in low revs??

[Saracen]

Following on from my adventures here (http://forums.sv650.org/viewtopic.php?t=33888), here (http://forums.sv650.org/viewtopic.php?t=34189) and here (http://forums.sv650.org/viewtopic.php?t=34410&highlight=):

I've put everything back togethere, with the new 145 Mikunis and moved the clip up one notch on the needle (so there are now two free notches below it, away from the point).

Fantastically, the bike started. I had to run it on the starter for about 30 secs, but I presume that's because there was no fuel in the carbs? Anyone confirm?

It runs fine now.

But at around 2-4k RPM, the revs don't back off normally when I close the throttle; there's a small delay. I resume this means it's running a bit rich? Everywhere else is fine.

This can;t be the jets can it, since the jets mainly affect the upper revs? Any ideas why this might be? I did readjust the mixture scres 2.5 turns from where it just seats. I've also made sure the idle ias around 1300 RPM.

Any tips (Northwind?) :D

[Scoobs]

Are all cables and linkages free and lubed?

[Saracen]

Bit naughty, ut I didn't actually lube anything. But it only happens at low revs, so that shouldn't be the cause. What's recommended for lubing the throttle cables and stuff anyway?

Thanks.

[NedSVS]

Yes it is normal normal to take a few seconds more cranking when the float bowls have been emptied (but perhaps not as much as 30 seconds). Your revs hovering at 2 - 4k is usually an indicator of the air pilot mixture being lean (the increase in main jet size will only have had a very small effect on the low speed running). First I'd try turning the pilot air screws out to 3 1/2 turns out and see if that helps. You may well find you need larger pilot jets with your de-baffled CCC. If you do, you can get them from Allens R&D in Nottingham (01949836733) part number N224.103 follwed by the number of the size you want (17.5 is standard, so you want 20.0 or 22.5). Hope this is of help.

[northwind]

I doubt that... 3.5's a lot, I'm running a full system, better filter, and tank spacers and I'm on 2 3/4. He's not changed the induction at all since before the rejet and it ran normally before.

There's a chance you have a problem with the choke cables- did you remove them at the carb end? They can stick there, and the cables can get stuck in teh wrong position at the ends and at the y-splitter (sleeve pulls out of the mounting sometimes.

[NedSVS]

Northwind wrote:

I doubt that... 3.5's a lot, I'm running a full system, better filter, and tank spacers and I'm on 2 3/4. He's not changed the induction at all since before the rejet and it ran normally before.

This just shows how much variation there is from exhaust system to system. I beleive you (Northwind) run a BMC RS filter like me, but with my micron/Quill hybrid I am running 22.5 pilots at 2 1/4 turns out. I could get it to run on standard pilots but always had a tiny flat spot just off closed throttle. I don't beleive I have any air leaks (I put everything back to my known stage one induction settings to check this).

[northwind]

What I mean is, I doubt it's his problem. Different systems call for differen thtings, you're right- the restrictive headers of the Micron systems fuel better low down while a more open system like mine gives more top end... But he's got a standard system.

[NedSVS]

Northwind wrote:

But he's got a standard system.

Not quite true, I'm sure the CCC will have some effect too, not just the headers. I'll be very interested to know the result of this one; so let us know how you get on :!:

[Stig]

Following on from Northwinds point on the choke cable. Mine has been running very rich. So rich that you can smell the stink of petrol coming out of the exhaust.

The choke cable was working fine. I have now stripped the the carbs off again and found that the front choke plunger had seized in the open position. This caused the front cylinder to run rich constantly, regardless of the choke position or indeed the operation of the choke cable itself.

When I finally got the crappy cheese bolt undone on the front plunger and pulled it out, it was actually rusted in position.

Having now sorted this problem the bike runs a lot smoother in the lower rev range.

I do however need to replace the choke cable, but seeing as I never use it anyway, it can wait.

[northwind]

Marginal though. Certainly not enough to have this huge impact on the idle circuit. And not when it wasn't an issue before he rejetted. This is something new that's happened as a result of the breakdown and/or rejet, and since everything else he's done is to richen things up, why would he now be dramatically lean at idle?

I bet you 10p ;)

[Stig]

I don't think it is running lean. You wanna raise that bet to... wait for it... 15p :lol:

[northwind]

Ah, I was responding to Ned, you just got inbetween us with a post ;)

[Saracen]

OK,

The choke plungers were a bit "powdery" inside; not rust but some residue, making them a little unlubricated. Should I get them out again and lubricate them? (Can this be done without taking the carbs out again? Cant be bothered!

To be honest, it ran much better today. But is there a surefire way of knowing whether it's runinng rich or lean without a dyno visit (which I will do at some point).

The reason I thought it was rich low down was because I would imagine if there was extra fuel left due to richness, it would burn before the revs decreased, hence keeping the revs up a little.

I just want to check I put the clips in the right place on the needles:


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I'll prob get it dynoed when I can, but before that, I'd rather be sure I'm not damaging the engine.

The bike pulls so much better al round now, which makes me feel a little reassured. If it was rich how would it behave?

[Mike1234]

The last time I jetted a set of carbs I didn't bother adjusting any pilot screws.

Just chucked a dynojet kit (JHS variant rather than off the shelf) in, BMC RS Race Filter and off it went.

Sounds like something was sticking or hadn't been adjusted properly after putting it all back together or you just got unlucky with the choke.

[northwind]

I just had a thought... Vacuum leak? Never ridden a bike with one but I do know if you (for example) stupidly pull the cap off your carb balancing hose the idle races up... Could a minor leak cause these symptoms withotu causing problems elsewhere?

You can get to the rear choke without removing the carbs, but the front one's way down inside the frame. Maybe you could get to it, I doubt i could. But you can check all the cables without removing the choke from the carbs at all, just not hte mechanism itself.

What seems to happen sometimes with the SV parts (and other Suzuk chokes) is that the cable sleeve pulls out of its housing. This can happen at the carb end, and at the splitter. It's not visibly obvious either, or at least it doesn't have to be. Basically, have a fiddle with the cables wherever they join to anything else, and see how well they're seated. Mine's pulled out of its housing at the rear choke mounting, and also at the y-splitter after the plastic there cracked.

I'm not saying that's your fault though, it's a possibility but I'm not sure I'd put another 10p on it ;)

[Robw#70]

Also check the diaphrams on the slides are not split or caught up and slides move freely (spring trapped etc)
Or needles porperly secured in slides
Or o-rings on chokes damaged
Or linkage bent putting carbs out of balance (holding one butterfly open)
Or carbs not sat fuly home in inlet rubbers

All possible airleaks