GP100 not starting - UPDATE - Rebuild completed

[FretGrinder]

OK guys, here's an interesting one for you...

The lad that bought my GP100 from me is having problems with it.

He went and put fuel in the bike and it wouldn't start after. He left it at the petrol station and picked it up after work.

He replaced the spark plug, tried to start it and there was a bang from the "front end of the bike"

I went down today to have a look and I did the following -

- Checked spark and there is a strong spark and the gap is correct. Spark plug is also the correct type.
- Checked the piston to see of it had any holes, piston is fine.
- Stripped the carb down, blew all the jets with compressed air, float is correct and fuel is getting through
- Compression is good, correct amount for the bike
- checked the exhaust, bit of carbon in there, but nothing major that would cause a blockage.
- fuel filter is fine
- Won't fire on a bump start

The only things left that I can think of are -

- The ignition timing is retarded
- Not getting enough voltage for the spark

Any advice would be greatly appreciated.

Cheers
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Yamaha MT-09

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[hazza]

Sounds like a timing issue to me. have you tried a different plug? could be breaking down...
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3 Honda NC50's(Sold)-->'72 Puch Maxi S (Sold, want it back!)--> '90 Yamaha RXS 100 (Stolen)--> '87 Honda Cub 90(Sold) --> '95 Kawasaki Eliminator (Sold) --> '98 Bandit 600 (Sold) -->'07 SV650S (Current)

[FretGrinder]

[N cee thirty]

ain't the gp on points ?

could be them thats fannied
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'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

Jewlio Iglesias wrote: I actually did vote BNP once

[hazza]

chopped a bit of the HT and refitted cap? new Cap?

I had a similar popping/Bugger to start issue on my RXS which turned out to be the pickup coil (?) under the flywheel breaking down. I know what i mean, but im having a mental mind-block at the minute and doubting if that's the correct term!
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3 Honda NC50's(Sold)-->'72 Puch Maxi S (Sold, want it back!)--> '90 Yamaha RXS 100 (Stolen)--> '87 Honda Cub 90(Sold) --> '95 Kawasaki Eliminator (Sold) --> '98 Bandit 600 (Sold) -->'07 SV650S (Current)

[hazza]

[FretGrinder]

Yep, it seems the points seem to be the last thing that I need to check is the points.

The lad won't be available till friday, so I'll have a look then and then report back with what I find.
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Yamaha MT-09

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[N cee thirty]

[temeluchus]

One of the boyer electronic ignition boxes that uses the points as the trigger is a good investment for points bikes.

Stops the points burning and makes them last ten times as long.

Fairly cheap too.
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Some shite cruiser. Now with guns and FREEDOM!

[N cee thirty]

[temeluchus]

No, this is still handled by the existing timing gear-the points set up runs as it was. The box simply switches the earth to the coil, so the points are no longer carrying the current.

You provide 6 or 12v from the loom to the box, connect the wires from the points to the box, and connect the coil directly to the box.

Had a box on my r80 motor and it made life much easier as the points don't seem to wear so don't go out of adjustment.

I don't think it will be much of an issue on the gp I think those things run fixed timing.
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Some shite cruiser. Now with guns and FREEDOM!

[cb1rocket]

as an owner of the gp100 here's the following.

Its quite likely the timing is naff or the points are knackered.

Fixed timing, no advance. Although this can be adjusted by moving the stator plate so the timing of the spark fires at the right time. Should be 22° BTDC if i remember rightly.

Its probably just needs a simple adjustment on the contact breaker assembly that contains the points. This adjusts the gap so that its set correctly - they do wear out

[Wyldkat]

I'm glad that someone has already asked this because I'm having a similar problem with my GP.

Basically - last time I rode it (probably about 4 months ago now, has been charged since) I started having electrical problems which are now sorted. Now there is no spark.

I've checked the following -
new plug/checked gap;
New plug cap;
Replaced condensor (soldered, good joint);
Replaced the points;
Stator plate put back in same position as it came off (marked position for accuracy)

Was going to replace ignition coil but have been advised that they are not normally the thing that buggers up!?
Connections to/from the battery/rectifier/stator plate (inc. coils etc) ignition coil and plug etc are all good.

The next thing I'm trying is the timing/adjustment of points.

Stumped now and getting p***ed off!

Any ideas?
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Oldie - 1987 Suzuki GP100 SOLD!
Current (as of 12/7/12) 2001 Honda Varadero 125

[Nope.]

[Wyldkat]

computid - my apologies for 'resurrecting' old posts but there also seems to be a dislike to starting a topic that has already been somewhat covered....no win?!!

No I can't borrow one but I will try testing the battery, forgot about that actually thanks.
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Oldie - 1987 Suzuki GP100 SOLD!
Current (as of 12/7/12) 2001 Honda Varadero 125

[FretGrinder]

ok, so an update -

Got the bike back to my place and made sure that the timing was correct, using a feeler gauge I made sure it was fine.

I cleaned the carb one more time to make sure it was getting fuel.

After to or so kicks I found that the spark plug was completely dry but fuel was getting in to the bike as it was coming back through main air hole in the carb.

Tried to start it again and ther was an almighty BANG! from the carb area.

I took off the exhaust and low and behold there was bits of piston ring in there.

Damn! I'm gonna start stripping down the engine tomorrow. The weird thing is that this happened to the guy right after he filled it with petrol and the same thing has just happened to me - what caused the explosion?
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Yamaha MT-09

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[N cee thirty]

[FretGrinder]

[cb1rocket]

timing is off as per usual. Feeler guage is for checking gap on points/contact breaker assembly. Doesn't have much to do with timing although its tricky to get perfect. Its a rotor/flywheel pull off job to adjust the timing and check it.

timing is 22 degress or 1.87mm BTDC

[FretGrinder]

Well after taking the exhaust off to check for a blockage there was a "clink, clink" inside the exhaust..... not good

Turns out there was bits of piston ring in there.

Me and my dad took the engine out today, whipped off the head and checked out the barrel state and what state the piston was in.

The barrel -

https://i49.photobucket.com/albums/f292/d0xicle/Gp100%20engine%20overhaul/barreltwo1.jpg

https://i49.photobucket.com/albums/f292/d0xicle/Gp100%20engine%20overhaul/barrelone1.jpg

The piston -

https://i49.photobucket.com/albums/f292/d0xicle/Gp100%20engine%20overhaul/pistonside1.jpg

https://i49.photobucket.com/albums/f292/d0xicle/Gp100%20engine%20overhaul/pistontop1.jpg

It looks like the explosion took some of the piston out.

Will this require a rebore and an oversize piston? I can't really see any scoring, but if the barrel gets polished will this require an oversized piston anyway?

I can get some more pics if needed.
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Yamaha MT-09

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[FretGrinder]

After I cleaned off the piston I noticed that it had "0.50" on it. Does this mean that the barrel has already had a rebore? Does this also mean that I have to get an identical piston?

https://i49.photobucket.com/albums/f292/d0xicle/Gp100%20engine%20overhaul/oversizepiston.jpg

As there is no scoring that I can see, would I be safe just dropping in the same size of piston with suitable rings?
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Yamaha MT-09

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[27cows]

Yep, that's .50mm oversize. Think you can get at least 1mm oversize for the GP100, maybe even 2mm. So you should be able to have another rebore on that barrel. You might get away with just a new .50 piston...but I doubt it. Probably do the same again.

GP motors tend to be pretty fragile. It'll be the main bearings next, trust me
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The RXS100: vehicle of choice for Chuck Norris

[cb1rocket]

yes its been rebored before, which is a 1st stage rebore ie its only been rebored once before. There does appear to be some light scoring to the barrell but you could get away with using the same piston size and new rings. It doesn't look as bad as when my gp100 decided to shatter itself to pieces.

I would go for a new rebore and new next size up piston rather than waste time trying to make use of just a new piston and rings. Your know its been done properly rather than trying to bodge it, and your also know it will last another 15 - 20k miles then.

Check there is no debris in the crank case and give it a thorough wash out with petrol/parafin mix or a hose pipe with water and then rinse and fill with oil and drain several times. Repeat if necessary.

Also check the big end bearings are good that there is no vertical movement. Side to side movement is ok but no vertical.

see my thread on what happend to mine:


https://www.bikechatforums.com/viewtopic.php?t=204850&highlight=gp100

[FretGrinder]

Another update on the gp100 -

One of my dads friends had a look at the cylinder barrel and suggested that I would get away with just honing it.

I borrowed a honing tool and now the barrel looks a lot smoother.

I sourced a new piston - Potenza (made in japan) with subsequent rings, gudgeon pin and circlips.

I set about rebuilding the engine today. I put back both the crankcase halves, used new gaskets and some gasket sealant as there was a few chips in the crankcase where someone had chipped away some of the surface when levering it off.

I then fitted the new piston, smeared some 2 stroke oil on it and reinserted the barrel and fitted the new gaskets.

I then set about sorting out the timing. I set the piston to 1.87mm BTDC with the aid of a vernier caliper and then set the stator accordingly. Followed by setting the points gap.

I reattached the oil pump, the carb, put on the flywheel. I bled the oil pump and primed the carb.

I then did a compression test which gave a reading of around 150 PSI, I'm guessing this pretty good?

Then it came to the pivotal moment - will it start.

Believe it or not it started after 2 kicks, once I realised that the kill switch was on.

Everything then started heading south. The bike stopped, I tried to start it again and it kicked back with quite a bit of force. After careful inspection it seemed that I forgot to tighten the flywheel up and the bike had sheared the bloody woodruff key!

Now-

Are woodruff keys fairly generic items?

I have scoured teh internet without any sign of one for this bike, but they seem to pop up all over the internet, without any specific reference to any car or bike.

Luckily everything else is tickety-boo.

- I can select 1st and 2nd gears as normal, and then return to neutral
- No backfiring
- No oil leaks
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Yamaha MT-09

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[Nexus Icon]

You can usually buy a sized-ish Woodruff key to suit but, worst case scenario, you'll have to buy a set of various sizes just to get the one you want. You can get hard and soft keys, straight ones, half moons, all sorts so they're not completely generic, no.
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