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The Vintage Japanese Motorcycle Owners Group: Discussion Forums

Vintage Japanese Motorcycle Owners Group :: View topic - Suzuki T250II poor performance


Suzuki T250II poor performance
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dorT500
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Location: Galveston County, Texas

PostPosted: Tue Oct 31, 2017 9:45 am    Post subject: Reply with quote

MartinR wrote:
Battery is showing 12.7V after 12hrs, so looks like it's Ok

Is there a way to test the coils...........


Hey Martin,

It's been my experience that these ignition coils rarely go bad but I suppose a little abuse from previous owners like leaving the ignition on and the kill switch in the run position while parked too many times or too long could be one of a few reasons they might fail.

Your service manual will have the instructions on testing the ignition coils as well as the charging system on your bike but find below a couple of vids on testing ignition coils.

You might as well switch the spark plugs around or better yet install a new plug. It is very rare but a spark plug can be bad right out of the box........not to mention the rash of blackmarket NGK knockoffs years back.

What have both spark plugs been looking like? http://midasrandburg.co.za/all-things-spark-plug-related/

As you will see in your manual, your multimeter should read 3 to 6 ohms of resistance on the primary side and 10K to 25K on the secondary side.


https://www.youtube.com/watch?v=rRQ45lT2d3c

https://www.youtube.com/watch?v=S6hnL0Jn6w8

What all did you do to the carburetors? If you replaced any parts, were they genuine Mikuni parts? Did you replace the jet needle? As you probably know the jet needle and the needle jet controls mixture at medium speeds up to around 3/4 throttle. The main jet controls the mixture at full throttle but also a little at lesser throttle openings.

What have both spark plugs been looking like? http://midasrandburg.co.za/all-things-spark-plug-related/

I would also check the ignition points gap again and of course time it again if you have to make an adjustment.

Hopefully, we can help you get this sorted out but if you can't get it sorted out in short order, you might run it by the guru's over at the Suzuki specific site.....Sundial Message Board. I see you were lucky enough to find them and are registered over there also.

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MartinR
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PostPosted: Tue Oct 31, 2017 3:38 pm    Post subject: Reply with quote

Thanks again for all your advice and links, very helpful.

The Haynes manual merely says to get the coils tested at an authorised Suzuki dealer - the average person not being in possession of a multimeter back in the day. But it looks pretty straight forward having watched the youtube video.

I've put two new plugs in and it's made no difference. The colours of the plugs are normal after adjusting the mixture.

I've not replaced any parts in the carburettors as all looked fine, but they may bear another examination. I'm slightly dreading doing this as the rubber hose between the carbs and air box is so difficult to fit, took me about 2hrs last time. It's a replacement part (the original had badly split) and I don't think it is quite the right shape.

I'm wondering if the lack of pulse/heat/smoke from the right exhaust at tickover is caused by the same problem that is causing the lack of power.

One strange thing is that when I first got the bike the timing setting was at the extreme end of the adjustment slots for both cylinders. I replaced the points with new ones and the adjustment is still at the extreme end. I can only think that this is caused by a worn cam.
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spurlock
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PostPosted: Tue Oct 31, 2017 4:39 pm    Post subject: Reply with quote

MartinR wrote:
...........I'm wondering if the lack of pulse/heat/smoke from the right exhaust at tickover is caused by the same problem that is causing the lack of power.

One strange thing is that when I first got the bike the timing setting was at the extreme end of the adjustment slots for both cylinders. I replaced the points with new ones and the adjustment is still at the extreme end. I can only think that this is caused by a worn cam.


On the weaker right exhaust, have you checked to see if the two throttle slides are synched? If there is a problem with one of the cables at the Y junction or where they attach to the slides so one slide is opening way ahead of the other, that might explain the difference in exhaust pulses and to some extent the uneven running at low throttle openings.

And on the timing needing to be at the extreme of the range, that sounds like points gap could be off i.e. if the gap is too small the timing would need to be advanced to compensate, and vice-versa.

-Bill

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dorT500
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PostPosted: Tue Oct 31, 2017 5:13 pm    Post subject: Reply with quote

good points bill and when fighting those rubber air box boots and jostling around the carbs just about anything can happen.
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MartinR
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PostPosted: Wed Nov 01, 2017 2:49 am    Post subject: Reply with quote

Thanks for your further comments.

I did check the throttle sliders were synchronised when I put the bike together again, but as you say, something could have disturbed that, so definitely worth re-checking. Will probably have a look this weekend.

With regard to the points, the gaps are definitely set correctly so the extreme adjustment isn't caused by this. They open at the very late end of the adjustment, ie as if the cam lobe is worn down. I can still set the timing Ok, but would have expected them to be around the middle of the adjustment after fitting new points.

Martin
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spurlock
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PostPosted: Wed Nov 01, 2017 6:17 am    Post subject: Reply with quote

MartinR wrote:
Thanks for your further comments.

I did check the throttle sliders were synchronised when I put the bike together again, but as you say, something could have disturbed that, so definitely worth re-checking. Will probably have a look this weekend.
Martin


An easy way to synch twin throttles is by sound. Back out the idle speed screws, then open/close/open/close the throttle (opening just slightly) and listen as the slides knock against the bottom of the carb bores. If you hear two knocks instead of one, dial in the adjusters on top of the carbs until you hear a single knock. Once the cables are synched, reset the idle speed screws so the bike will idle. Then turn off and do the knock test to synchronize the idle speed screws. Finally fine tune idle speed.

-Bill

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1989 Honda NX250
1989 Honda GB500tt
1989 Honda CB-1
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dorT500
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PostPosted: Wed Nov 01, 2017 10:41 am    Post subject: Reply with quote

MartinR wrote:
..........I'm slightly dreading doing this as the rubber hose between the carbs and air box is so difficult to fit, took me about 2hrs last time. It's a replacement part (the original had badly split) and I don't think it is quite the right shape..........


One strange thing is that when I first got the bike the timing setting was at the extreme end of the adjustment slots for both cylinders. I replaced the points with new ones and the adjustment is still at the extreme end. I can only think that this is caused by a worn cam.
You are one of many who have wrestled with air box boots fitting on carbs. I use to buy a new OEM one every now and then but I quit doing that. I ride almost everyday of the year and between the ethanol fuel and that new but old rubber ....the boots get hard, shrink.. out of shape. I wasn't going to spend the $50.00 or $60.00 every 18 months or so. Lately, I have just been bridging any gap with high quality black duct tape. I'll probably keep doing that until Clauss Studios http://claussstudios.com/id39.html starts making one for my '75T500. They already are reproducing the one for early models but they say they won't reproduce the later version until Suzuki stops supplying them. I don't no for sure if the rubber they are using will be adequate for this application, but I'll research it and it's got to be better than an old NOS part. I need to double check to see if that 'won't make it until it't discontinued from the OEM' policy is still in effect.

On my T500, it is easier in the long run to go ahead and remove the battery box first and then a couple of bolts on the air box to take off/fit it to the carbs. If I were you, I would go ahead and take it off again Crying or Very sad Wink while your sorting out the current problem. Good time to check and see if all is as it should be in the carbs. Once re-mounted, if you need to, you can use a small mirror to see if the throttle valves(sliders) are entering the carbs at the exact same time.

What brand ignition points did you buy....I know you may have gotten them from Suzuki but what was the brand on the boxes themselves? I remember an issue with some brand.

Stand by...

After entering keywords 'timing points plate' into Sundial Message Board search engine.............



Well here.......Sundial will save me some time and typing Smile ...... http://www.suzuki2strokes.com/forum/viewtopic.php?f=9&t=11983&hilit=timing+plate

This is probably just one of several related threads....you might go back and forward and check for other related threads by entering the same keywords.

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MartinR
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PostPosted: Wed Nov 01, 2017 4:22 pm    Post subject: Reply with quote

Both your comments are so helpful, thank you for taking the time share your knowledge.

I like the carb synch method by sound, since it doesn't involve taking the dreaded air box boot off. I can certainly give this a try before committing to a wresting match with the boot. My original plan for fitting the boot (after realising how difficult it was going to be) was to have the air box and carbs loose, connect the boot and fit the clamps, then bolt the air box and carbs in to position. Sounds good in theory, but didn't really work out in practice.

Looking at the points posting on Sundial, it seems the same problem but the opposite way round. i.e the points opening too early. I don't recall the make of the points I bought, but it wasn't Suzuki.

I have some time on Friday and will carry out the checks you've suggested and let you know the results.
Thanks
Martin
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dorT500
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PostPosted: Wed Nov 01, 2017 5:44 pm    Post subject: Reply with quote

MartinR wrote:
.............I like the carb synch method by sound, since it doesn't involve taking the dreaded air box boot off......



Laughing I'd fuss at you and call you lazy............if I hadn't chosen that method myself a few times over the years. Smile

Damn boot. Rant

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MartinR
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PostPosted: Fri Nov 03, 2017 7:10 am    Post subject: Reply with quote

So, I've checked the coils and they are both within spec on primary and secondary windings.

I checked the carb synchronisation and it was slightly out, so I have corrected this. On taking it out for a ride I noticed a definite improvement in that it now pulls better between 4-5k rpm and it sounds smoother too. But it still lacks power below 4k and still sounds a bit rough. I'm going to recheck the points gaps, timing and mixture again, but assuming all is as it should be there, any ideas on what else to check would be gratefully received.

Thanks
Martin
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ConnerVT
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PostPosted: Fri Nov 03, 2017 8:44 am    Post subject: Reply with quote

Ah... Tuning Mikuni carbs on a 2-stroke.

"But it still lacks power below 4k and still sounds a bit rough" is hard to translate to what to suggest next. Mikuni carbs have several systems that feed fuel to the engine, that overlap, and are affected by how open you have the throttle.

HERE is one of the best explanations of the setup and tuning I have found.

The first thing to do is be sure you are only using Mikuni genuine parts in the carb. They have the Mikuni square stamped on them. I have found that the aftermarket kits (ie. Keyster) rarely, if ever, have the correct dimensions, and dimensions are exactly what make a Mukini carb work.



My gut feeling is that, at this point (assuming the correct parts are installed), you may need to try some different settings of the jet needle. Today's gasoline (especially if you run E10) acts a little different, or you needle jet/jet needle is a bit less than pristine. If it feels just flat (not developing power), move the clip down a notch, lifting the needle higher, and making things more rich. If it is "4-stroking" (rough/gurgling), then move the clip up one notch, lowering the needle and making it more lean.

I have found that you can even find a noticeably better tune if you move the needle a half notch (my T500 is like this). You can purchase a shim kit that allows you to adjust the clip position 1/4 notch at a time.
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dorT500
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PostPosted: Fri Nov 03, 2017 11:29 am    Post subject: Reply with quote

^ It's time to get serious......have a look at the carbs. From an earlier reply...........it does sound like you may have overlooked giving enough attention to the carbs including how well they were cleaned. What is the condition of the inside of the fuel tank?


but first, have you checked the charging system at different rpm's as per your service manual? As I hinted at before. Wink

What is the voltage reading of the battery right now?

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MartinR
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PostPosted: Sat Nov 04, 2017 3:46 am    Post subject: Reply with quote

Thanks Connor for all the info about tuning Mikuni carburettors, that article makes interesting reading, hadn't realised how complicated it can be. I can certainly experiment with adjusting the needle position. I assume the carburettors consist of completely genuine Mikuni parts, I haven't replaced any part of them, but that is something I should positively verify now. It's true I didn't spend a lot of time on the carbs when I did the restoration, so I think you are right dor, I need to do that now.

The fuel tank is clean and I did check the charging system, but easy enough to check again.

Once again, thanks for taking the time to give helpful advice. It maybe a week or two before I have time to spend on the bike, but I will report back when I've had a go.

Martin
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ConnerVT
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PostPosted: Sat Nov 04, 2017 7:29 am    Post subject: Reply with quote

The old Suzuki 2-stroke engines are true simplicity - There are only 9 moving parts when it runs. Two pistons, 2 connecting rods, a crankshaft, 2 ignition points, and 2 carb slides. No mechanical or vacuum ignition advance, no valves to time correctly, and the spark timing is fixed to a single point in the cycle. The carb controls basically everything on how the engine performs at every throttle opening and engine load.

Reviving my T500 for the road, I have spent at over 50% of my time addressing issues with the carbs. Some of that was due to my having a mix of model years ('73 motor with early model carbs/intake), some of it due to bad choices (using aftermarket carb kits).

My bike arrived with the carbs so gummed up, that I needed to cut the throttle cables to get them off the bike. Old gasoline, sitting for decades, turns into a hard varnish that an aerosol can of Gumout isn't going to do much at all. To clean the carbs, you really need to take them completely apart. Disassembly can be a bit intimidating the first time ("Is that supposed to come apart?"), but it is necessary. There are a number of tutorials (written and video) on the internet.

Pick up a bucket of carb chem-dip and some chemical gloves (eye goggles are a good idea, too). The task is soak, clean, repeat. Remember that brass is soft, so don't use hard metal (such as steel) to clean out holes in the brass, you may scratch/enlarge the openings (which meter the correct amount of fuel to the engine). Cleaning the openings in the carb body, it is OK to use wire (an appropriately sized guitar string works well). I flush everything with my garden hose sprayer. This allows me to see how well the openings in the carb body are clear, and are equal in both carb bodies. Air dry (nothing to rust in there) or use compressed air if available.

Before reassembly, check the condition of the parts:

Are they all true Mikuni parts? (square in square stamped logo). If not, Main and Idle Jets are available at retailers, and are not expensive. Same for the float needle/seat. The Jet Needle/Needle Jet are more problematic, as they are made specifically for Suzuki, and are NLA.

Is everything clean, and in good condition? Check that the small holes at the base of the Needle Jet and Idle Jet are clean (these are the hardest spots to clean, and can greatly affect performance). Is the Jet Needle smooth? Is the interior of the Needle jet smooth and clean? (This controls mid-range throttle, and turbulence from dirt/corrosion can affect performance). Is the enricher plunger (choke) rubber in good enough condition to seal when closed? (These always seem to get hard, looking worse than they really are. Not likely your problem, but good to note before reassembly).

The first time doing this is a bit intimidating, but once you do it once, you'll find it isn't that difficult. Tools are simple enough: A proper cross head screwdriver, a small flat screwdriver (to remove the Pilot Jet), a large flat blade screwdriver for the Main Jet, some small wrenches to remove the float needle seat and enricher plunger. You may need a wooden dowel and a small hammer to gently tap out the Needle Jet (the first time it can be varnished in, you may need to soak the carb before it decides to come out. If so, it really needs to come out and be cleaned!).

When you reassemble, remember that the carb slides are not interchangeable. The curved cutout faces the air box. Just about everyone makes this mistake at least once. Embarassed
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MartinR
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PostPosted: Mon Nov 06, 2017 1:47 pm    Post subject: Reply with quote

I've taken the carbs off and dismantled them. The interiors are clean. The jet needles are Mikuni set at the middle notch. Haven't taken the needle jets out but they look clean. The float arrangement is different to what I've seen before and what is in the manual. There are two independent floats per carb which slide vertically on a spindle. They each have a small projection that operates a lever and hence the inlet needle valve. A couple of the floats did seem to stick a bit sometimes when I filled the bowl with fluid, but given no fuel overflows from the carbs when the fuel tap is on 'prime', I don't think there is a problem there.

All in all they look perfectly Ok, so I may try lifting the needles up a notch to see what effect that has - as suggested.
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