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barfy

Idlling ideas

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I read the recent post from @barfbrianreed62 about his Scorpa not idlling properly and I'm going to have a closer look at the bike tonight, but I thought I'd ask about possible areas to look at first.

At the weekend my lads 125 Twenty started to not idle became inconstant when closing the throttle. It's done it a couple of times before and I've given the carb a good clean which has made it better. I'm beginning to wonder if it is hiding another problem, because this is becoming almost every trial. The air filter is washed every trial, including for this weekend. I've not changed the jetting and the mixture screw is at about 3/4 of a turn from being fully in. Are the 125s very susceptible to crap in the carb?

Tonight I was going to clean out the carb, clean and reseat the inlet manifold. Pull off the flywheel to look for any signs of oil seepage in the crank case seal. Look up the exhaust outlet for any signs of something iffy in the piston, well make sure it looks shiny.

If there anything else that I might want to check?

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@2stroke4stroke I did give that a bit of a try during the trial, about 1 1/2 turn out and all the way in on the mixture screw, but it made it worse rather than better. I think there must be a slight leak somewhere.

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@pauls320 It has a Keihin 28mm carb.

I just whipped off the fly wheel cover and there is no signs of any oil, it's git a slight covering of dust but no oil. Also there is no movement on the flywheel; obviously it goes around both ways but there is no in / out, front / back, up / down movement. So unless someone can tell me why I should take the flywheel off, I think that the crank case seal is ok. It wasn't excessively smoking on, I assume that the other crank case seal must be ok.

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The pwk is a great carb, but problems can be had if contaminants get into the very small orifices beneath the ''never remove'' jet block (has two tamper proof screws) can often purge out from slide side and mixture adjust screw hole. Sometimes the jetblock gasket (special multi piece oring) leaks due to bad fuel damage or being dismantled too many times and not making a perfect seal any more, which  causes MAJOR tuning problems. Hope you can get her sorted soon:)  

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Thank you @pauls320. Next time I disassemble the carb I’ll take out the never tamper block. I have some tamper proof torque keys. Also I’ll order some new gaskets because they seem quite cheap.

I’ve just put it all back together, resealing the inlet and it seemed to be running fine. I also put in a fresh plug to pull it out to see what it looked like for mixture. I thought I’d give it a quick blast up the road where it stopped on me after about 1/2 mile. Then restarted second kick. When I got back I stopped the bike and pulled out the plug.

Hopefully I’ve attached a photo to show that it’s running very weak and blown the electrode. It was about 1/2 to 3/4 throttle when it stopped so might indicate I need a bigger main jet but I’ve never seen a plug with a blown electrode. 

5A9D0F48-8745-4845-ADCB-896814CAE636.jpeg

Edited by barfy

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Barfy, I do not recommend removing the jet block...only as a last resort after finding you have a leakage problem with it. It can be a pain to seal...and Keihin do not sell the seals/gaskets individually, they tell you to buy a whole new carb:wall:   . Looks like a little detonation there, air leak, jetting, fuel. how much oil in fuel...too much and it gets lean...fuel displaced by oil....Good luck

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@pauls320 Thanks for the advise about the jet block. I’ll see if I can blow it out best I can with the airline, if there is any contamination. 

There is a dealer in Chesterfield, Derbyshire, England that does all of the gaskets for the PWK and they’re only a few ££. I’ve ordered them this evening. 

I run the oil at about 90:1 on 98 octane pump fuel, normally BP. I’ve ordered some new plugs at the same time as the gaskets. 

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Chatting to someone today about why a plug would burn out the electrode and he said he’d only seen it before when the timing was far too advanced. The timing is fixed by the flywheel pickup and CDI isn’t it?

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 By the way you can order the seal for the jet tower from OKO carbs. Slightly larger and seals better. And yes when the passages are bad the ildle will search. Pull it apart.

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Been waiting a few weeks to reply until I was confident in my findings. 

I bought all new seals for the carburettor and inlets, but it didn’t make much difference. Was going to get the crank seals changed because that was about all that was left to do but before I did that I thought there was nothing to lose by taking out the “tamper proof” block to give it a clean.

Under the tamper proof block on the idle jet circuit there was some fluff so I blew it out with the air line. Since then it’s been running great. 

I’d normally have taken off the carb every trial to give it a clean. Then I’d hope it would run ok for the whole trial. I’ve not taken off for the past 3 trials. I think the action of blowing out the jet holes mush have blown through a less restricted path through the fluff for a sort while.

Hopefully sorted, but put this in the thread if someone has a similar problem in the future. 

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On 19/08/2018 at 10:36 PM, barfy said:

Been waiting a few weeks to reply until I was confident in my findings. 

I bought all new seals for the carburettor and inlets, but it didn’t make much difference. Was going to get the crank seals changed because that was about all that was left to do but before I did that I thought there was nothing to lose by taking out the “tamper proof” block to give it a clean.

Under the tamper proof block on the idle jet circuit there was some fluff so I blew it out with the air line. Since then it’s been running great. 

I’d normally have taken off the carb every trial to give it a clean. Then I’d hope it would run ok for the whole trial. I’ve not taken off for the past 3 trials. I think the action of blowing out the jet holes mush have blown through a less restricted path through the fluff for a sort while.

Hopefully sorted, but put this in the thread if someone has a similar problem in the future. 

That tamper proof block was intended to be a problem so that when the owner had running issues and returned the bike to the dealer, they just cleaned out the tamper proof block curing the problem and looking amazing so you would keep returning to the dealer for the smallest thing. A profit generator I call it!🙂

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