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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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MartinR
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Joined: Oct 19, 2017
Posts: 15
Location: Nottingham, UK

PostPosted: Fri Oct 27, 2017 11:35 am    Post subject: Suzuki T250II poor performance Reply with quote

I've completely restored a T250, including replacing the crank seals. The bike will start and tick over fine and above 5000rpm it pulls away nicely. But below 5000rpm it lacks power and stutters a bit.
I've checked the timing several times, put new plugs and points in and set the carburettors up as per the Haynes manual, but it is still under powered at low revs.
I've run out of ideas now. Anyone have any suggestions?
Thanks.
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Billybobbigbear
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Joined: Aug 25, 2017
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Location: New Zealand

PostPosted: Fri Oct 27, 2017 9:32 pm    Post subject: Reply with quote

Maybe coil is bad they can do sum weird stuff sometimes.

Double check spark plug gap for good luck.

Air filter may be restricted somehow if oiled maybe to much oil

Timing advance could do it ?? maybe try adjusting points gap to smallest specified gap to retard it.

engines are noted for there lack of power below 5000rpm see below link

The link

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1-Suzuki FA50
2- Suzuki TS250ER
3 - Suzuki AC50
4 - Yamaha RD250 dressed as RZ
5 - Suzuki GSXR250R 1991
6 - Suzuki 1985 gsxr750
7 - Suzuki 1984 GSX-R400
8 - Suzuki1984 RG250
9 - 1987 Nsr 250 mc-16
10 - Honda vfr400r 1991
11 - Suzuki rm250 1996
12 - Suzuki gsxr 750t 1996
13 - Triumph Daytona 955i 2002
14 - Suzuki ac50ll 1973(current bike)
15 - Yamaha R1 2013
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Russell
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Location: New Zealand

PostPosted: Sat Oct 28, 2017 3:46 am    Post subject: Reply with quote

Had you ridden a T250 Hustler(?) in good condition previously? My memory of a couple I rode when my own machine was a T350(315cc version of same engine as yours) is that the 250 did need to be kept 'on the boil'. My contemporaries riding T250's would often run a different grade of plug in town to counteract plug fouling and would put the colder plugs in when going to do open road running. It just may be that your bike is actually pretty close to normal?
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MartinR
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Location: Nottingham, UK

PostPosted: Sat Oct 28, 2017 4:24 am    Post subject: Reply with quote

Thanks for your replies. The article certainly confirms that the engine is flat below 5k. I have ridden one before, but it was 40 years ago and so memories are a bit vague! But I don't remember it being quite as poor at low revs as this one is.
I'll double check on some of your suggestions and see if I can coax anything more out of.
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fodder
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Location: Near Harlow, England

PostPosted: Sat Oct 28, 2017 8:57 am    Post subject: Reply with quote

I have a T20 which is essentially the same engine. I am currently sorting the engine on mine as it wasn't pulling too well.

Like you I have experience of this model dating back some years. Mine was when I had one as a student in 1981. The engine had been rebuilt, with new seals, and it had better performance than my latest acquisition which is why I knew this one wasn't running properly.
Back then my girlfriend regularly rode pillion so between us we had about 21stone (294 lbs) on the bike and it went fine, even at lower revs - 3,000 to 5,000, say. They are definitely not built for pootling along at 2,000 rpm, though.

Yours shouldn't be stuttering/stumbling so something is not right.

Things I would do/check:
- compression check - see my thread on "cold compression values:
- leakdown test. Even though the seals are new they might have moved during assembly, or not be doing their job too well for other reasons?
- make sure the carb faces are flat and sealing well on the cylinders - they are known to warp and be hard to seal properly.
- exhausts - did you clean these out? They could be blocked up.
- are the carbs worn? I have put new needle jets and needles in mine. The old needles were pretty loose in the old jets so the fuel mixture at mid-throttle range would have been a bit random.
- if your needles and jets are not worn, have you checked that the needles are in the right position? I think you have the same carbs as me and the needle retaining circlip should be in the middle groove of the needle. You could try moving the needles up and down to see if it makes any difference.
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MartinR
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PostPosted: Sun Oct 29, 2017 1:06 pm    Post subject: Reply with quote

Thanks Fodder
Yes I used to ride mine back in 1977 with my then girlfriend on the back and don't remember it being so lacking at lower revs.
Some good suggestions, particularly with regard to the carburettor, which I suspect maybe the culprit since some of the other areas would also affect the performance at higher revs - but it seems good at that end of the rev range.
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dorT500
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Joined: Jul 10, 2008
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Location: Galveston County, Texas

PostPosted: Sun Oct 29, 2017 1:16 pm    Post subject: Reply with quote

Would you go far as to say it may be running/partially running on one cylinder in the problem range? With the bike on the center stand at idle and just at operating temperature, cup your hand close to the end of each muffler one at a time. Feel any significant difference in the strength of the pulses and temperatures of the exhaust?
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MartinR
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PostPosted: Mon Oct 30, 2017 9:42 am    Post subject: Reply with quote

It could certainly be misfiring on one cylinder, but probably not cutting out altogether.

I did the test you suggested and there is a marked difference between the two exhausts. Starting from cold, on the left side there are pulses, smoke and the exhaust gets warm quite quickly, but on the right there are no pulses until you increase the revs significantly, less smoke and the exhaust takes longer to warm up. The right side has been problematic. Before restoration it would only ever start on the left cylinder.

Could this be a faulty coil as BBBB suggested?
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dorT500
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Location: Galveston County, Texas

PostPosted: Mon Oct 30, 2017 11:30 am    Post subject: Reply with quote

Well, people around here are going to start calling me 'Batt. Man' but it's been said for many years by Suzuki guru's a lot more knowledgible than me that if there is a battery issue in a T250, the T350 and the T500, it can cause the right cylinder to drop out. It is usually the right cylinder but it has been known to happen on the left. I just recently started having near the same problem as you are having on my T500.

How many times have I heard, "I have a brand new battery" or "The battery is only a few months old." I don't care. I have seen/known countermen at dealerships and auto supply stores charge and fill these little flooded type batteries wrong......so I've got to know that there are some bike enthusiasts not following the charging and FILLING instructions 'to the letter'. Not doing so can lead to premature failure of the battery.

The problem could be an ignition coil....easy enough to check with a multimeter or swapping out with a know good coil set. It could be something else....it could be the ignition points gap way wrong (might have changed, closed up on you, when you were setting it and timing) but why not eliminate the battery as the problem first? I just don't get it why posters in the past don't do that.

Charge the battery to about to 13.4 volts. Test with multimeter...not what your charger is indicating(if applicable) and let the battery sit for at least 12 hours not connected to anything. Then test the battery and see if it is holding at least 12.6 volts if this is a flooded type battery...up to 12.8 if an AGM battery (absorbed glass mat) A mini battery hydrometer could also be used along with the multimeter.

I'm just saying eliminate the battery as the problem first....before any further trouble shooting.

Good Luck



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GONE.......WITH A PUFF OF SMOKE AND A BLUR OF SPOKE
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:old: https://www.youtube.com/watch?v=C-F3vSrJIUQ
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dorT500
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PostPosted: Mon Oct 30, 2017 12:09 pm    Post subject: Reply with quote

Here is some service data I have handy. http://www.ozebook.com/compendium/suzi/suzidata1.htm The chart below is included in it.



Arrow http://www.ozebook.com/compendium/t500index.htm

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kbts250m
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PostPosted: Mon Oct 30, 2017 1:55 pm    Post subject: Reply with quote

If you have the black hard plastic spark plug caps they contain resistors and can sometimes go bad causing weak or no spark. If your battery is marginal, the condition will be worse at low rpm, better at higher as the battery voltage rises. Also, the black hard plastic caps screw on to the plug wire and that connection can degrade over time, resulting in the same problem as a bad cap. If you do have the hard plastic caps you could try unscrewing them, cutting about 1/4-3/8 inch off the coil wire and then screwing them back on. That will fix a degraded connection and very well may fix your low power issue.
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MartinR
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PostPosted: Mon Oct 30, 2017 1:59 pm    Post subject: Reply with quote

That's interesting, would never have thought a battery issue could cause an asymmetric problem like that.

As you say, it's easy enough to check, so I'll do that and report back.

Thanks for all the info.
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MartinR
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PostPosted: Mon Oct 30, 2017 2:04 pm    Post subject: Reply with quote

I replaced both plug caps as part of the resto, so they should be Ok, but I can certainly try cutting the HT lead and remaking the connections if the battery passes its test.
Thanks.
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dorT500
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PostPosted: Mon Oct 30, 2017 3:20 pm    Post subject: Reply with quote

MartinR wrote:
I replaced both plug caps as part of the resto,............
.............That's good. I also recently replaced the ones on my T500 and on a spare ignition coil set I have. The NGK's with a little more rubber on the plug end (designated with letter P on the part number). If and when you go to test your ignition coils, in case you did not know, if you leave the caps on while testing the coils, each resistor cap will account for 5000 ohms of resistance while measuring the secondary coil.


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GONE.......WITH A PUFF OF SMOKE AND A BLUR OF SPOKE
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:old: https://www.youtube.com/watch?v=C-F3vSrJIUQ
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MartinR
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Location: Nottingham, UK

PostPosted: Tue Oct 31, 2017 2:12 am    Post subject: Reply with quote

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

Is there a way to test the coils or can they be interchanged to see if the fault moves with the coil?
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