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Steve_W |
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Steve_W Two Stroke Sniffer
Joined: 14 May 2019 Karma :
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Posted: 19:42 - 14 May 2019 Post subject: Suzuki GP100 bogging at Full Throttle |
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Evening everyone, new member here.
Having a bit of a mid life crisis ( ) so decided to buy an old 1984 Suzuki GP100 because I had one 30 years ago when I was 17!
I have a bit of an issue with it though and wondered if anyone has any ideas or is able to maybe back up what I am thinking could be the problem.
Bike ticks over fine, pulls fine up to half throttle and rides great in 30 - 40 mph limits when you don't need to give it more than half throttle, but when I open it up to full throttle it dies, until I move throttle back to half throttle and then it runs fine again.
Initially thought it was carb related, bike has been looked after by previous owner but has been stood around for some time, covered 2 miles in the last two years according to MOT history (so I guess just ridden to get MOT and back again!). So I booked it into local bike shop to get carb cleaned. After clean it was still doing it so bike shop then suggested it could be electrical. He did check the timing and has confirmed it's now spot on and the points are in a decent enough condition with no pitting
I have also checked the oil pump settings and adjusted according to Haynes Manual so I know that's correct.
So, since then I have replaced the following so far:-
Spark plug - goes without saying on a 2 stroke really I guess.
Condenser - there was a fair bit of arcing across the points before and now there is hardly any, as you'd expect I think.
Ignition coil and plug cap - after drilling out the seized screws!
So before I get to changing the stator plate (bought a second hand one from ebay as almost impossible to find new) as it's a bit of a ball ache and I've already soldered the new condenser onto the original stator, I decided to run it in the garage on the stand and get it to die, as before it's always been out on the road and I've not been able to check the plug til I've got back home.
it kicks over and starts beautifully now since I've replaced all of the above, comes off choke after a few seconds and idles just fine, revved to 7k with no issue with throttle below half open. But the minute I open the throttle wide open it dies and stops.
Took the plug out and it was drenched.
So, decided to take another look at the carb and the main jet size as that's what controls the throttle range I'm having problems with right? The size that's in there is 105. According to Haynes it should be 97.5 (or 105 for the "D" model).
I've ordered a 97.5 main jet and just waiting for it to arrive to see if it fixes my issue.
I suppose my questions are:-
does anyone on here know what the difference is between the "C, N, X and D" models of the GP100U and how I tell which one I have?
And do you think my thoughts are correct that it may be that the main jet is too big and it's flooding the engine at full throttle?
Sorry for the essay, but I've searched and searched the web for a while over this and thought I'd finally ask rather than just looking at other posts! |
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Nobby the Bastard |
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Nobby the Bastard Harley Gaydar
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Steve_W |
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Steve_W Two Stroke Sniffer
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Posted: 20:43 - 14 May 2019 Post subject: |
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Nobby the Bastard |
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Nobby the Bastard Harley Gaydar
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Steve_W |
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Steve_W Two Stroke Sniffer
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Nobby the Bastard |
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Nobby the Bastard Harley Gaydar
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Steve_W |
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Steve_W Two Stroke Sniffer
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Nobby the Bastard |
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Nobby the Bastard Harley Gaydar
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Steve_W |
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Steve_W Two Stroke Sniffer
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Posted: 21:19 - 14 May 2019 Post subject: |
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Yeah good point, I've got a 97.5 jet on order anyway but could try that at the weekend first (I don't get much in the way of spare time in the week unfortunately ) |
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jaffa90 |
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jaffa90 World Chat Champion
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Steve_W |
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Steve_W Two Stroke Sniffer
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Steve_W |
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Steve_W Two Stroke Sniffer
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Steve_W Two Stroke Sniffer
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Easy-X |
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Easy-X Super Spammer
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Steve_W |
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Steve_W Two Stroke Sniffer
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Posted: 09:00 - 16 May 2019 Post subject: |
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Thanks all for your replies, it's much appreciated.
I'm quite good with my engine theory, I'm just not the most practical person in the world, hence why I decided to go into IT after failing my BTEC Engineering 30 years ago
I have always thought this was fuel related rather than electrical, it's just that the bike shop has sent me down the electrical route, so I've been replacing bits and cleaning earths etc but so far although it starts much better now, my problem is still there and the only thing left to change really is the stator plate - and because that's quite involved I thought I'd take a look inside the carb and see what's what.
That's when I discovered the 105 main jet, which according to Haynes IS the correct size for my model (GP100UD - finally worked out which model I have after much googling!).
The thing is, every other GP100 lists a 97.5 main jet size, in the same model carburettor, with the same needle and pilot jet.
It's all a bit confusing (but weirdly I am enjoying trying to fix it!).
I get that with 2 strokes it's always better to run a bit rich rather than too lean, so if I do change the main jet and it seems to fix it while running it on the stand, I would only take it for a very short run on the road before bringing it back and inspecting the spark plug, to avoid prolonged running if it's then too lean
How can you tell if the needle is worn? Or is it just a case of "replace and see if it fixes it"? |
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Easy-X |
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Easy-X Super Spammer
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Posted: 09:52 - 16 May 2019 Post subject: |
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ofc the other arrangement for having a rich A/F is the choke. Double check that's okay when you need a distraction ____________________ Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter |
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Steve_W |
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Steve_W Two Stroke Sniffer
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Posted: 10:02 - 16 May 2019 Post subject: |
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I think the choke is OK.
What I mean by that is I only really use the choke for a few seconds when it starts from cold and it idles faster as you'd expect it to, then idle drops down when it comes off choke and I rev it gently a bit to warm it up rather than keeping it on choke.
I'll take a proper look at it when I have it all apart over the weekend though |
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Steve_W |
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Steve_W Two Stroke Sniffer
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Posted: 14:04 - 16 May 2019 Post subject: |
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So I sent an email to a different bike shop in my home town because they run an online parts website (I didn't realise it was run by this specific company until I looked into it) to see if they could get hold of a new needle.....
I explained my symptoms and that I was looking for a Jet needle to fit my bike (using the part number on their website even though it was listed as "contact us" - a lot of other sites have already said it's unavailable but thought I'd try).
Their response has made me question whether they have a clue about what they're talking about to be honest (or whether they have bothered to read my email at all) -
one of their technicians has said it could be a blocked main jet and if I bring it in to them they will have a look through their box of jets to see if they have one that fits - no doubt at an extortionate amount of money!
Nah, think I'll just carry on myself and learn something in the process. The carb was cleaned by another (one man band "enthusiast") bike shop that I trust a WHOLE lot more than this particular dealer anyway. AND, if it was blocked surely that would give starvation symptoms, not flooding, right?? |
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- Super Spammer
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Posted: 15:54 - 16 May 2019 Post subject: |
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Steve_W wrote: | So I sent an email to a different bike shop in my home town because they run an online parts website (I didn't realise it was run by this specific company until I looked into it) to see if they could get hold of a new needle.....
I explained my symptoms and that I was looking for a Jet needle to fit my bike (using the part number on their website even though it was listed as "contact us" - a lot of other sites have already said it's unavailable but thought I'd try).
Their response has made me question whether they have a clue about what they're talking about to be honest (or whether they have bothered to read my email at all) -
one of their technicians has said it could be a blocked main jet and if I bring it in to them they will have a look through their box of jets to see if they have one that fits - no doubt at an extortionate amount of money!
Nah, think I'll just carry on myself and learn something in the process. The carb was cleaned by another (one man band "enthusiast") bike shop that I trust a WHOLE lot more than this particular dealer anyway. AND, if it was blocked surely that would give starvation symptoms, not flooding, right?? |
I've bought 2T bikes which were running like crap and found carb parts missing, such as emulsion tubes.
If you want spares, what carb is fitted? Is it correct? Allens Performance will probably sell parts for it.
You could try another carb and cable for £40 and clean it yourself. It;s not hard once the float bowl screws are off.
https://www.ebay.co.uk/itm/113640737602?ul_noapp=true ____________________ TZR250 2MA road, TZR250 1KT road, TZR250 2MA race, TDR250, YZF-750R Boost colours.
Jaguar S Type 3.0 V6 Sport R, VW Transporter T5 GP LWB Shuttle 140ps DSG. |
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A100man |
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A100man World Chat Champion
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Easy-X |
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Steve_W |
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Steve_W Two Stroke Sniffer
Joined: 14 May 2019 Karma :
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Posted: 10:25 - 17 May 2019 Post subject: |
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The Carb fitted is a Mikuni 39240, which is the correct one listed on CMSNL, Fowlers and all other places I've found that list them.
I can't see that model listed on Allens, but I have found a carburettor repair kit on wemoto for £25 incl delivery
https://www.wemoto.com/bikes/suzuki/gp_100_ud_ul_drum_brake_model/79-92/picture/carburettor_complete_repair_kit
That's about the only way I can see that I can get a new needle, although I guess I could call Allens, which I may do later if I get chance (I'm at work and supposed to be working now, but have spent a bit too much time over the last few days trawling the web searching for clues! )
I agree with you both about specialists and "specialists"
I didn't hold out much hope of the second bike shop being able to help me to be honest, they're main dealers for most makes, but I don't think they're in the same league as my first guy (the one man band guy that services, MOTs, restores and custom builds stuff) when it comes to older bikes like mine - but it was worth a try to see if they had anything in stock. I certainly wouldn't take my bike to the second one to be worked on anyway.
I'm going to work my way through a few more things at the weekend. It's a slow process with me as I never seem to get enough spare time, driving the kids about all over the place etc etc.
Check needle and float height
Check air/idle screw (can't remember if that's it's proper name) adjustment
Change to a smaller main jet (I have 3 different sizes I've ordered) and see if it helps (if not revert back to original). Bearing in mind I will only run it on the stand to see if it runs better than before and if it does will take for very short run and check plug, as I don't want to run too far if too lean!
Check exhaust to see if any blockages
After that if it doesn't fix it, I may have to buy the carb kit linked above and then it's back to changing the stator plate I guess, as suggested initially by first bike shop guy.
Incidentally, in my trawling that I mentioned earlier, I have found a lot of threads on dirt bike forums that show that a bad stator can cause similar symptons to the ones I am having.
I'll get there, eventually |
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- Super Spammer
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Old Thread Alert!
The last post was made 4 years, 338 days ago. Instead of replying here, would creating a new thread be more useful? |
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