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Need some engine advice. What to do next?

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DonnellyShard
Two Stroke Sniffer



Joined: 11 Jun 2016
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PostPosted: 17:13 - 19 May 2019    Post subject: Need some engine advice. What to do next? Reply with quote
Hi guys. As title says I'm having some engine issues. Its a K157FMI 125cc engine. Its got good compression, have put 2 different carbs on it to no luck. It was running poorly so I changed out the plug, coil and CDI from a running bike to rule those out. Still no luck. So I changed the stator, made sure timing was all good. The bike sort of stutters and only runs on choke when its hot. Sort of revs and holds idle for 1 or 2 minutes before it dies. Pops and bangs then dies. Don't think I've ever had a bike this troublesome. I have put another carb on it and still has the exact same issues so I'm ruling fuel out as fuel is fresh and is getting to the 2 carbs I've tried. Also just going to add the valves are correctly adjusted and in good condition, did check those too when I took the head off to check timing. Whats my next move here guys? Any help would be greatly appreciated. As most of you know its frustrating when issues like this come up.
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jaffa90
World Chat Champion



Joined: 06 Apr 2016
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PostPosted: 17:26 - 19 May 2019    Post subject: Reply with quote
You are concentrating on the input side of the engine, what about the output?
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DonnellyShard
Two Stroke Sniffer



Joined: 11 Jun 2016
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PostPosted: 17:35 - 19 May 2019    Post subject: Reply with quote
jaffa90 wrote:
You are concentrating on the input side of the engine, what about the output?


Thanks for the reply jaffa. Not too sure where to look with that one. The exhaust valve is all good and adjusted correctly to spec and can hear feel air from the muffler on turn over
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Pete.
Super Spammer



Joined: 22 Aug 2006
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PostPosted: 18:47 - 19 May 2019    Post subject: Reply with quote
If you're sure the carbs are ok check the valve timing again. As a quick visual check the inlet and exhaust should be at about 10 and 2 o'clock at TDC every other turn. Check the timing mark on the exhaust cam sprocket and then the mark or pin count on the inlet.

Does the exhaust glow red when it's idling?
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DonnellyShard
Two Stroke Sniffer



Joined: 11 Jun 2016
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PostPosted: 19:31 - 19 May 2019    Post subject: Reply with quote
Pete. wrote:
If you're sure the carbs are ok check the valve timing again. As a quick visual check the inlet and exhaust should be at about 10 and 2 o'clock at TDC every other turn. Check the timing mark on the exhaust cam sprocket and then the mark or pin count on the inlet.

Does the exhaust glow red when it's idling?


Thanks for the reply. The timing is spot on, when I rotate the engine to the TDC mark the lines on the cam sprocket line up and cams are operating as they should. This is what confuses me, I thought I have gone through everything on the bike and have gone over things twice to make sure of not missed anything but there must be something somewhere. Currently swapping loom over to rule out any electric issues. Handy thing with spares lying around I guess.

The exhaust doesn't glow or do anything unusual. I'm stumped!
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mentalboy
World Chat Champion



Joined: 05 May 2012
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PostPosted: 19:34 - 19 May 2019    Post subject: Reply with quote
Would we be correct in thinking that before you started everything you double checked the carb rubbers and the airbox filter?
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DonnellyShard
Two Stroke Sniffer



Joined: 11 Jun 2016
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PostPosted: 20:20 - 19 May 2019    Post subject: Reply with quote
mentalboy wrote:
Would we be correct in thinking that before you started everything you double checked the carb rubbers and the airbox filter?

Yep that would be sensible, when I swapped carbs over off running bike I took the carb rubber with it and the other bike uses a pod filter. Both engines are the same model and same tuning, even down to the same exhaust. Other bike runs with the carb of the bad running bike. Bad running bike still runs bad with the other carb. I've got fuel, spark and compression and am no stranger to bikes so honestly I am stumped. Wiring loom is good, carb good, CDI is good, stator good, coil good, plug is good. Bike is getting fuel, valves are good and adjusted properly, timing is good. What am I missing?
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Oldie
Brolly Dolly



Joined: 05 Dec 2010
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PostPosted: 20:27 - 19 May 2019    Post subject: Reply with quote
Vacuum in the fuel supply? See if it runs with the filler cap open.
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DonnellyShard
Two Stroke Sniffer



Joined: 11 Jun 2016
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PostPosted: 20:29 - 19 May 2019    Post subject: Reply with quote
Heres the bike in question. As you can see I even swapped over a spare head and cylinder I had that I took off a working 125 before it was swapped over for a bore kit. Again off a K157FMI motor. Still the same. Could this be something in the bottom end? No rattles or anything and no excessive play in the rod. Just fortunate that I've more than one of these here at the moment.

https://i.ibb.co/37Y0wbg/IMG-0022.jpg
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DonnellyShard
Two Stroke Sniffer



Joined: 11 Jun 2016
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PostPosted: 20:32 - 19 May 2019    Post subject: Reply with quote
Oldie wrote:
Vacuum in the fuel supply? See if it runs with the filler cap open.


I'll give that go, I know fuel is getting to the carb and the bowls are full as I run a clear fuel line and did crack open the bottom to check if fuel came out. My little Honda gets me about a mile home before dying when I realize I left the fuel tap off Laughing
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Old Thread Alert!

The last post was made 4 years, 334 days ago. Instead of replying here, would creating a new thread be more useful?
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