Suzuki SV650 coughing and spluttering

[mealexme]

Hi guys,

 

I picked up a 2002 SV650 a few months ago. The bike has carburettors and a previous owner installed an aftermarket slip on exhaust, with the removable baffle still in.

 

What I'm finding is that its hard to start in the mornings (even on full choke) and it coughs/splutters on idle. It start's ok in the evenings, but still coughs and splutters on idle. My worry is that if it's struggling now, whilst we have unseasonably warm weather, it may fail to start at all when the winter hits. 

 

It does also feel underpowered and lumpy when I'm riding, but I'm not sure if that's in my head as I've not ridden in 2 years and my last bike had a lot more power with a smoother 4 cylinder engine, so it may be underpowered and lumpy or it could be what a normal 2 cylinder SV650 from that year feels like to ride.

 

I did a service when I first got the bike, changing the spark plugs with genuine NGK platinum's,  the oil with compatible Castrol and the air filter with an OEM filter. I also installed a new battery as I had one lying around, but the old one still felt like it had plenty of charge.

I've cleaned the carbs but couldn't see any dirt or grime in there, and re-adjusted the pilot screw to OEM specs at the same time, which seemed to have tamed the pops and bangs that were happening.

 

As part of the service and general looking over the bike, I checked the valve clearances, which are within tolerance and the chain looks good, with no wear on the chain or guides and good tension

 

I've also balanced the carbs using a generic tool, which indicates that there could be an air leak at the intake manifold or heat riser (whatever that is?)

 

 

I sprayed a butt load of carb cleaner all around the carbs/airbox area, but couldn't see any obvious leaks, but there were a couple of cracks. 

Firstly a perished rubber on the airbox, which I'll get replaced as soon as I can find somewhere that doesn't want to charge me £15 for a tiny rubber cap.

Although it looks like it's done for, a squirt of carb cleaner would suggest that it's still doing it's job, and sealing off the pipe

 

Also, whatever this is (between the carbs and engine), looks as though it's starting to crack. But again, a squirt of carb cleaner would suggest it is not letting air past.

 

I've had a look over the HT leads and can't see anything obvious. I took them off and stuck a multimeter on them (on settings Ω @200k, because that's what YouTube told me to do haha) recording a resistance of 26.0 and 26.7. I have no idea if that's good, but it's consistent.

 

Spark plugs have been in for a few hundred miles now, mainly doing short rides of about 10 mins of commute. They look OK to me, aren't wet, don't smell like fuel or oil or anything really. I thought I'd include some pictures though as someone may be able to look at them and see if the fuel/air mixture is wrong just by looking at them.

 

 

My current thoughts are that I need to replace the rubber cap in the airbox even though it is still sealing it (for now)

The carburettors may need adjusting, to make it run smoothly with the slip on exhaust, although I would have thought it would work ok as it's just a slip on and has the baffle in

The carb internals may benefit from just being replaced with a new carb kit

 

I've been living the last year on under minimum wage, whilst still paying for a mortgage etc (first year apprentice), so I don't really have the money to just throw at it and hope for the best.

 

Does anyone with a bit more experience have any idea of where I should be looking?

Cheers in advance

Edited September 9, 2023 by mealexme

[rennie]

No idea about the bike!  But good to see you back! 

[mealexme]

6 hours ago, rennie said:

No idea about the bike!  But good to see you back! 

Cheers Rennie. Good to be back tbh, aswell as back into bikes in general

[Stu]

Hi @mealexme good to see you around again and back on a bike 

 

Looks like you have gone through a fair bit already 

 

I suspect its fuel related and more than likely the carbs 

[Bender]

I'm with stu on carbs/fuel, after a few yrs off a bike it should not feel underpowered and it shouldn't feel lumpy.

[mealexme]

13 hours ago, Stu said:

Hi @mealexme good to see you around again and back on a bike

Cheers Stu, it's nice to see some familiar people still on here.

 

Also, thanks @Bender, I'll order a carb kit, which includes new fuel filters and just replace the lot

[Tiggie]

Welcome back 

[megaross]

You got the original exhaust?

 

I'm willing to bet the most of your issues are the exhaust isn't helping matters and it wants to go up a jet size.

 

Since it sounds as is a dynojet kit is maybe off the table I'd suggest refitting the stock exhaust for now.

 

Can't really do a plug analysis without a look under the otoscope, you can say they're a bit light (lean).

 

I'd also be asking where you bought them from - there's lots of fake NGKs out there. If they were eBay specials I'd swap them for a set from a reputable suppliers.

 

Did you calibrate the carb balancers with each other prior to balancing?

[RideWithStyles]

Hi and welcome back.

Yes we like pictures. 
 

id agree with the others with special note to megaross.

 

the first pipe which will be on the right side of the bike is the drain pipe, it should be alot longer that just that but shouldnt be too much of a problem but all that will do is add more unfiltered air to the engine without The restriction.
The ones on the left side (mirror rhe airbox) are the crank breather and return pipes connecting to the tank oil return just below the airbox.

Which one? If you mean the one with the part rubber covering it and metal crimped sleeve on the left looks with the ribbs showing? looks like the choke cable.

if you mean the 90 degree rubber pipe connecting to joint going up and to the left in the near background is a return pipe sometimes shared between to two carbs.

These bikes are sensitive to the exhaust as the std ones were very restrictive, the new exhaust while still being road legal and baffled will allow more air flow with less back pressure pulling the air out too quickly, also id be surprised if the length is the same which has a effect too So it will run more lean.

if the coils were goosed the plugs would be wet or aleast one worse than the other so the sparks are good.

 

As Motoross says, spark plugs seem a little on the lean side, if its snatchy especially at low revs when it is running by opening, closing and then opening the throttle again it will be too lean.

 

also dont put in E10 fuel.

the pops and bangs were just a little bit of vapour reaching the exhaust manifold when the throttle is suddenly switched off as a touch of unburnt just goes through when the motor is moving slightly slower than the wheel. Which is why these older engines feel so smoother in the fueling that injections to this day, more so than an injection and tightening eu regs. 
unless it's doing it a lot and stupidly loud isnt bad for the engine or exhaust, thats just what happens back in the 2000's.

 

it might be worth just setting the carbs to be atouch richer that what you've set them too now to offset the exhaust and if any unforeseen air leaks you cant find, run it for a bit and check the plugs again...

Edited September 11, 2023 by RideWithStyles

[mealexme]

Thanks guys, that gives me some stuff to look at over the weekend!

 

On 11/09/2023 at 07:55, megaross said:

Did you calibrate the carb balancers with each other prior to balancing?

Yes, I calibrated both separately and they were both accurate

 

On 11/09/2023 at 11:45, RideWithStyles said:

also dont put in E10 fuel.

the pops and bangs were just a little

it might be worth just setting the carbs to be atouch richer that what you've set them too now to offset the exhaust and if any unforeseen air leaks you cant find, run it for a bit and check the plugs again...

I normally just put premium in the tank tbh. I'll make sure I check when I fill up.

 

I'll also probably mess around with the settings after I replace the jets/filters etc, which I'll do over the weekend if I get a chance

[Fozzie]

My kwak did this with a new exhaust, was just running too lean. I increased the jet sizes to balance it out but it has a less used carb setup, as there's no dedicated pilot jet for the idle.

Not sure if there is one on the old SV, but if you've cleaned it out and it still has the problem, you could try to increase the size of this jet and see if it cures your start/idle issue. The jet sizes are usually in the manual. Jets are usually quite cheap, so if there's no improvement, at least it won't have cost you too much!

 

 

[RideWithStyles]

When its warm whats the bike idle speed? 

[Bianco2564]

The vacuum at idle should be much higher than that, as the dial indicates a min of 18 inches. Assume it was at idle, not a higher engine speed?

I'd be looking for an inlet leak. On the 3rd pic, that looks like a cracked inlet manifold stub. On my gt380, the inlet rubbers weren't perished but had gone rock hard and not clamping up properly. Check for other perished hoses around the carbs.

That perished cap on the airbox drain won't make any real difference. You are looking for something between the carb and inlet valve.

A carb heat riser, various methods used to prevent the carb from icing over or fuel dropping out of the air and pooling in the manifold. Can be something passive as on a MINI A series engine where the inlet and exhaust casting are one piece , to flappy valves on the exhaust which direct exh gas onto the bottom of the inlet manifold. As it warms up, the valve diverts the gas straight down the exhaust.

IIRC, some Kawasakis in the 90s had carb icing problems and they had to retro fit some pipework into the cooling system?

[JRH]

15 hours ago, Bianco2564 said:

 

IIRC, some Kawasakis in the 90s had carb icing problems and they had to retro fit some pipework into the cooling system?

GPX 750R was one.

[mealexme]

So, I changed the fuel mixture screws, found a small leak in the exhaust which is now patched up and changed out the rubber cap on the air filter box and it seems to run better once warmed up.

It was still having trouble starting though.

 

Then, whilst riding past a military base, the thing cut out completely. At first I thought I'd stalled it, then realised there was no power at all to the clocks or anything. So I had to push the thing to the side of the road, but struggled to find neutral for a second, before I realised that I was looking for a neutral light on a dash that has no power

 

Anyway, I got it to the side of the road, convinced the security at the military base that I was just broken down and not doing anything suspicious, as I left the bike right outside their entrance and found another way home.

 

I grabbed some tools and the car, then spent hours on the side of the road, in the rain going through fuses, taking the thing apart, checking ground wires, changing the battery and just looking at everything I could think of until I was about to give in and call a recovery firm. Then I spotted it, behind the headlights; a red wire which looked like it had been corroded for a long time, until it finally snapped.

 

I twisted it back together, and all of a sudden the bike sprung back into life. The headlights seem stronger and crucially, now it starts on the button first time, every time!

 

It is still a bit spluttery whilst it's warming up with the choke on, but fine once warm. I don't know if thats normal now, but its a lot better than it was, and I'm no longer concerned that it won't start every morning.

 

There are still a couple.of things concerning me, such as the vacuum measurements, but hopefully it will get me through winter as it is and I can have another look when the weather warms up.

 

I'll have a look out for the carbs icing up, but I don't think it's quite cold enough for that yet