Suzuki 2 Strokes

Hi, my T500M has had a full engine rebuild, starts 1st kick, will idle all day, runs great up to 3000rpm and then bogs down, as if being starved of fuel. New main jet, slides with cutouts to the rear, stripped and cleaned numerous times. New plugs, colour ok.
Help!! Any ideas please?

I think you have your carb slides installed backwards, the cut out should face to the carb intake side. Yes, I have done this myself

Cheers Geoff

Hi Geoff, the cutouts are to the rear, airbox side.

rider wrote:Hi Geoff, the cutouts are to the rear, airbox side.

Hello rider,

A difference on how we view an engine I see that as the front of the carb. No other thoughts except where it bogs down you are probably transiting to needle/needle jet so try moving the clip on the needle (richer & leaner) and see if there is any improvement. It should give a guide on which way to go. If you can remove the needle jet to really see if all the small jet holes are clear.

Cheers Geoff

There is another current thread similar to this somewhere. Here are a few questions for you to ask yourself, which may help steer you into the finding or eradicating the problem:-
Have you checked the float levels?
Do you have the standard air filter fitted and is it oiled? (pod filters are notoriously difficult to set up right and usually worsen your power delivery as there is no airbox to smooth out the intake pulses and you may have a lot of trial and error trying to match jets to them. Which is why I recommend a standard or larger than standard airbox)
Have you got a good flow of fuel from the tank?
Do you have a fuel filter fitted? Is it clogged?
Are your exhaust baffles clogged?
Do you have a good quality spark on both cylinders?
If you have original points ignition.....
Have you checked the dwell angle/gap on points? (wrong gap will cause poor quality sparking)
Is the points cam greased? (it should be lightly greased and put a drop of oil onto the felt pad. Just a teeny bit, not a lot. This prevents points bounce and premature wear on the heel)
Are the points pitted and worn? (another cause of poor sparking)
Is the timing set correctly?
Are there any cracks in porcelain of plugs?
Are the plugs correctly gapped?
Have they been previously badly-sooted or oiled up? (once this happens they will often give poor performance as it can form a glaze on the insulator which can allow the spark to "track out" and cause misfiring, even after the soot has been seemingly burnt off. And as a useful side-point, if your plugs ever do get dirty, never use a wire brush to clean them (it can damage the insulator and leaves scratches which allow a faster build-up of carbon and shortens the performance and life of your plug))
Are the plug caps ok? (check they fit tightly, have no cracks and there are no signs of corrosion or arcing where they screw onto plug leads)
Do you have any inlet leaks? (Whilst running, check by spraying "Easy Start" around where the carbs connect to the inlet side of the engine and around any inlet gasket areas. If the engine note changes, you have found a leak. Don't spray around the air filter side of the carb as this may give you a false positive!)
If you have a vacuum pipe going to the fuel pump... does it have any splits or holes in it? (As a test, I suggest unplugging this from the inlet and plugging the pipe and running the engine with the fuel tap in the "prime" setting. If this solves your problem, you most likely have either a porous fuel pipe or a fuel tap in need of reconditioning due to a leaky diaphragm).

This is by no means an exhaustive list of things to check, but may help you with finding or eliminating the cause of poor running.
Good luck

Thanks for all the advise, really appreciated.
I'll have another go this weekend.

I have a DT400 yamaha that acted similarly, and one of the problems was the plug cap had really high resistance (100K!). So at low RPM it was OK, but trying to rev it would start missing. Just another thought for you.



Lane

i've had a similar problem - twice. started easy and you could rev them up to the redline, and everything was fine. drop it in gear and pull off, blurrrrr they died. it was the coil both times. changed the coil and ran sweet as a nut just another thought!
cheers, dd.

Are the pistons reversed Left/Right?

I would like to think that with L & R and arrows that I got the pistons on correctly, but I will lift a head and check. I have gone about as far as I can with it and it’s nearly time to leave it with a mechanic.

Are you using the stock airbox?

You say that it has had a full engine rebuild. Is there any probability that you may not have got a perfect seal when you reconnected the crankcase halves? A crankcase leak can give you a lot of unfathomable gyp. Has it got all new crankshaft seals?
Did you use the right type of sealant on the crankcase halves (not silicone based)?

tintruder wrote:re the pistons reversed Left/Right?

+1

Tintruder,

You have quite stable of bikes!

tintruder wrote:Are the pistons reversed Left/Right?

+1

rider wrote:I would like to think that with L & R and arrows that I got the pistons on correctly, but I will lift a head and check. I have gone about as far as I can with it and it’s nearly time to leave it with a mechanic.

No need to lift the head.just look through the ports.
You will see at T.D.C. if the piston skirt matches the ports.