Fuel & Carburetor

[Dannyralph86]

Hi everyone, thanks for accepting my account.

Ok so I have an SV 650 s 1999.

After relatively long rides my bike will bog down and backfire allot, if you open the throttle it's fine just below 5k and it plays up...

I've now balanced the carbs, cleaned them, set the mixtures as best I can but it's almost like the carbs empty of fuel which a pin it, once I've cruised for a short time it seems all good again.

I've also changed the spark plugs, oil, fuel lines etc.

The bike is completely standard except and exhaust which was on it when I got it, the issue didnt appear to be present when I bought the bike but since I hadnt ridden it far I'm guessing it's been an issue the whole time I just didnt know until my first proper ride

Any ideas or input grateful.

I dont know a huge amount about v-twins so im at a loss.

Regards

Dan

[R1ffR4ff]

As you have done work on the Carbs make sure you put the Cap back on the Front cylinder Vacuum spigot that you used as part of the Carb balancing,


https://cx500.000webhostapp.com/SV650Carb_Balance.html

https://cx500.000webhostapp.com/frontube.jpg


If it's not that look to checking the Fuel filler and under the Tank to make sure the Fuel cap breather system is not kinked or blocked.Use the Forum search as there are posts over the years about these being blocked.

[Seeker]

If the carbs were emptying of fuel it would be worse on large throttle openings. The curvy does have a fuel pump, it's vacuum operated.

When you said you "set the mixtures as best you can" - the air screws should be about 2.5 turns out. You could try a plug check (for mixture), although with modern fuels I don't know how accurate they are.

Are the carb vac covers (nipples) in place? This is the front one:

http://www.bluepoof.com/motorcycles/howto/svs_carb_sync/nipple_from_outside_lbl.JPG

A v twin is like any engine, a pain in the neck when it goes wrong.

One perennial problem on carb'd SV (curvys) are the choke plungers. They frequently stick on and generally make the bike run badly.

[Dannyralph86]

Thanks guys.
The cap is over the front cylinder balance nipple, I added a pipe for next time..
I had the screws 2.5 turns out as per the manual but it wouldn't run.

Now I have the front cylinder at 3 turns out and the rear at 2 3/4 turns.

The fuel filter (inline filter) had rust in it so tried to replace but the filter was too big to fit under the tank so cleaning the old one was the only option.

I went for a long ride this afternoon think I've fixed it now except the top end is a bit noisy so need to search for a thread about how to do that on this thing.

I did check the choke plunges were sliding etc as I thought that could be an issue but they were fine, I had to replace a fuel line that snapped and the cap for the balancing nipple was split so I think a mix of air leaking through that cap, a dirty fuel filter and dirty unbalanced carbs all played a role.

Thanks again for the comments.

[johnnyrod]

Set the mixture screws back to 2.5 turns. Even if you had a different filter, exhaust etc. there is pretty much no need to adjust these. If it won't run like that then you've got a problem of some sort such as an air leak, but it sounds like you're working your way through some stuff just now. When you say noisy top end, do you mean tapping or the camchain rattle? If it's the latter then it could be because the original tensioners are clapped. They're a bit crap anyway, the 2003 ones go straight in and are a much better design. If you wind the engine backwards with a socket a turn or two and next time it runs it's quieter until you thrash it, then yeah they're toast. You can also put it in 3rd and bump it backwards a couple of times, works just as well. If it's appy then you can check the valve clearances but they tend not to go anywhere. Has it got a lot of miles on it?

[Dannyralph86]

It's got just under 24k on it.
Sounds more like valve clearances to me but as I say I'm a total newbie to bigger bikes and engines.
It wont run at 2.5 turns out, it did have an air leak from the nipple you balance it from on the front carb but I sorted that out when I balanced them.

I'll give it a a turn backwards and see how I get on with that.

I was tempted to just out it in a garage but I cant really afford it at the moment and I'm good with doing my own work just not familiar with V-Twins

[Dannyralph86]

Would the timing chain tensioners cause the spluttering?

When you full throttle it the bike is fine but if you try and partially hold it open it feels like it drops down to 1 cylinder and then picks up again.

In corners its causing nose dive and acceleration before I'm even round the bend, its normally only when hot and if I turn it off for 10 minutes it most of the time sorts it out, sometimes it doesnt sort it but after thrashing down the road a bit it seems to sort itself out, intermittent issues like that cant be caused by an air leak as it would always be doing it.

[Dannyralph86]

Is it not possible that the Regulator Rectifier is the issue?

Once it warms up that's the biggest problem with it not running properly, how do you check it with a multimeter does anyone know?

I'll definitely look into the cam tensioners and probably get new gaskets and do the valve clearances just to rule everything out as a possible rattle.

[Seeker]

It wont run at 2.5 turns out

this is probably a clue to your problem, by running it with the airscrews further out you may be covering up the problem. You are giving it a richer mixture which implies you may have an air leak. This is where I'd be focusing my troubleshooting, it's very unusual for a curvy not to run with its airscrews set at 2.5 turns.

Would the timing chain tensioners cause the spluttering?

No, it's highly unlikely. The tensioners might be a source of noise if one or both have stuck which does happen on rare (ish) occasions. There are youtube vids showing the noise.

Is it not possible that the Regulator Rectifier is the issue?

Wow, you are firing shots in all directions. The reg/rec is unlikely to be causing this problem unless the charge voltage was very low in which case you'd get a flat battery. Put your meter (set to DC voltage) across the battery with the engine running you should see about 14.4 V DC(above idle speed) if it's working well. It will be slightly less at idle.

[johnnyrod]

Check the carb diaphragms for holes, it sounds like it's running lean. The bogging-surging when opening the throttle is classic. Is the airbox seated properly? As Seeker says, richening the idle mix is just masking the problem.

[Dannyralph86]

Ok seeker thanks.
I'll look at timing chain noise on youtube.

All the diaphragms were ok when I had the carbs apart but I will buy a seal kit and take them apart again.

I've literally run out of places to check for air leaks, also just wondering here, if it is an air leak why is the issue only when it's hot and ridden for more that 20 miles?

The mixture screws were set at 3 and 2.5 but the front carb had a leak before which I've now fixed, I'm almost certain it still wouldn't run at 2.5 turns so I had to put them back out to 3 and 2 3/4 when I changed the spark plugs the colour was perfect as they should be I'll get on it at the weekend and check everything again, I'll test the R/R, spark plugs, every single pipe hose diaphragm in the bike then
I'll set mixtures back to 2.5 turns and try to ride it.

If I find any issues I'll reply here for future reference.

Thanks again ��

[Seeker]

...digs out book entitled: "How I did things when I was a lad".

If you spray WD40 or carb cleaner on the inlet boots with the engine running it will change speed if there's an air leak from there. It isn't a totally reliable method admittedly but it's a starting point. 20 year old rubber components tend to get brittle and not seal as well with age. There was an old trick of spraying them with furniture polish (original Pledge) to soften them but that was when they were definitely rubber.

Is the tick over smooth or uneven?

Assuming you do have an air leak, I suppose you could try giving it a little choke when the engine is hot and see how it runs then. Beyond that, you might want to do a compression test.
What mpg are you getting, over the years I've had 2 curvys and would typically get mid 60s mpg (I'm a slow rider though).

[Biker Biggles]

You mentioned rust in the fuel filter. Could there be crud in the fuel tank that is intermittantly getting stirred up and blocking the line? Or------water in the fuel that is causing erratic running? A bit of a long shot with your symptoms but it is a common problem with old curvys as water gets into the fuel tank and settles to the bottom.

[Dannyralph86]

Thanks Seeker, I'll try WD40 on the intake boots, I had tried to remove them before but the bolts are well in there.

Idle is perfect, lovely and smooth, the ride itself has good power delivery as expected, nice and smooth all the way up to 100+ mph.

It really is faultless and then suddenly the symptoms appear, riding to and from work daily is no issue 10 miles each way, it's only when I ride further afield, originally I said about the lack of fuel because it almost seems like when you really pin the throttle the symptoms come on quickly upon slowing down.

Sure feels like it goes down to 1 cylinder intermittently and I had read on another forum the R/R caused these issues, perhaps I've got more than 1 problem as you have already said like an air leak on top of something else.

I was getting around 155 miles per tank, I'm not sure what that translates to in mpg but I accelerate hard to the national speed limit.

[Dannyralph86]

Hi Biker Biggles.

Yeah there was rust in the filter, I've tried to replace but the filter I bought is too big and sits on top of the engine whilst not letting the tank sit down.

I did run it down to the light and then some, drained the tank and refilled but I feel like it wouldn't hurt to take the tap off the tank and the fuel pump apart to ensure them diaphragms are intact and clean.

I will get a seal kit for the carbs and just strip them right down this time and replace everything.

The choke o rings are worn this could be causing the issue but the new ones are yet to turn up.

I sort of wanted as much info as possible from you lovely lot here before going crazy with buying parts I dont need.

[Dannyralph86]

Also I think there is 4.4 litres in a gallon so my tank is under 3 gallons, 155 miles per tank that's 4 miles with the light on works out at about 50 mpg

[Seeker]

Don't forget the screw heads are JIS not Philips, you'll need JIS screwdrivers. You don't need Suzuki o rings:
https://forums.sv650.org/showthread.php?t=230784
Bikes of that era were already being tuned for weak mixtures for pollution regulations, any air leak will make the bike run badly.