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Post by bing on Oct 15, 2011 7:43:42 GMT -6
My Piaggio x8 125 LC loses power at max throttle! At first when it was at max throttle (60 mph) it would break down power and felt it was runing short of petrol or choked up. Now it only runs at 1/2 throttle (40 mph) before losing power continuously if the throttle is kept open. Until I shut the throttle right off it will recover when opening my throttle slowly and the motor has slowed down sufficently to low revs. (consider its a twist and go). The work done to try and rectify = Air Filter, Fuel Filters in lines and tank, vacume fuel pump, Vac lines and pipes inspected, Inlet Hose collapse, Carb cleaned blown out and diafram cheqed for as much as visual for leaks. (CV Carb)
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Post by raford3 on Oct 15, 2011 8:23:58 GMT -6
Try blocking the filter about 1/2 with a piece of carboard from a shoebox over the element.
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Post by bing on Oct 15, 2011 10:18:50 GMT -6
Try blocking the filter about 1/2 with a piece of carboard from a shoebox over the element. Hi raford3, I have blocked the inlet orifice by 1/2 and now I am able to attain full throttle ? The inlet comprises of a 40mm Dia tube (11/2") from the carb into an airbox. The airbox has a 3/4" thk foam as a filter, the inlet into the airbox from outside is only 1" Dia hole of which I half blocked.
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Post by royldoc on Oct 15, 2011 10:54:52 GMT -6
Have You checked the valve lash?
Roy
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Post by bing on Oct 15, 2011 13:18:26 GMT -6
Have You checked the valve lash? Roy Roy when you say valve lash? is that another word for valve clearance, bounce or seating! as it happens I have reset the tappet clearance, `they were all tight due to valve seating and would require the removal of the heads to inspect seating surfaces. A compression test was 90 to 100 lb
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Post by sprocket on Oct 15, 2011 13:27:37 GMT -6
Yeah same thing.. lash, gap...there are no tappets.. just valves and rocker arms...
The valves in these engine regress into the aluminum heads, so you need to check the gaps every 1500 miles or so... it eventually starts to slow down after about 3000 miles...
90 to 100 psi is low.. it should be 140 -150 in a hot compression test
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Post by royldoc on Oct 15, 2011 15:01:18 GMT -6
Sorry, valve lash is the same as clearance. I don't have first hand experience with piaggio's. What did you set them at? Compression seems low. It should be checked hot with throttle at wide open.
Roy
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Post by bing on Oct 15, 2011 17:15:43 GMT -6
My pressure test was done before the setting of the tappets of which were all tight, (4 valve head) inlet 0.010" exhaust 0.015" set cold. I have not tested the compression since the reset of tappets as I assumed this was not the problem.
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Post by jct842 on Oct 15, 2011 23:25:12 GMT -6
if you can get full throttle by blocking the air in you are changing the fuel/air mix. you are effectively choking it and adding more fuel showing it is starved. john
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Post by bing on Oct 16, 2011 2:34:50 GMT -6
if you can get full throttle by blocking the air in you are changing the fuel/air mix. you are effectively choking it and adding more fuel showing it is starved. john Yes John, I do not know the reason for this as I have no experience in KEIHIN CVEK Carburettor. My friend has gave me some new main jets to try: 120/130/140. `the standard is 105` but why the reason to change the mixture ? maybe raford3 will know as he first as he first pointed this out ? I will rejet and let you know the answer.
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Post by bing on Oct 16, 2011 6:13:03 GMT -6
I have tried 120 jet and a bit improvement then the 150 jet of which it gives me full throttle without the engine revs breaking down! although it has not solved the reason why evolved. I am open to comments or suggestions.
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Post by sprocket on Oct 16, 2011 10:41:27 GMT -6
Your valve gaps are HUGE.. on the GY6 they are set to .004 INCH (.010mm) intake and .005 inch (.012mm) exhaust...mind you your engine could be different but not that different...
Looks like the numbers you have are metric in millimeters...common error...you have used the metric numbers and set them in inches...
But your compression is marginal for the engine to even run...
Don't start messing with the carb... until you get the engine sorted out or you will have two things wrong and be chasing the problem for months...
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Post by bing on Oct 16, 2011 12:04:17 GMT -6
Your valve gaps are HUGE.. on the GY6 they are set to .004 INCH (.010mm) intake and .005 inch (.012mm) exhaust...mind you your engine could be different but not that different... Looks like the numbers you have are metric in millimeters...common error...you have used the metric numbers and set them in inches... But your compression is marginal for the engine to even run... Don't start messing with the carb... until you get the engine sorted out or you will have two things wrong and be chasing the problem for months... sprocket you are right; on checking with the equipment that I used was imperial instead of metric and they should be gapped at 0.10mm and 0.15mm also will get a compression test tomorrow. I am changing the jet back to standard.
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Post by raford3 on Oct 16, 2011 20:07:38 GMT -6
I don't get your meaning when you say evolved. Somehow the air/fuel mix got screwed up. It got lean. It may have another path for air to enter the engine. Some engineer decided it would run good with a certain setup (OEM). Many people mess up the air box when they fool around with the carburetor by not removing it properly to do service. They just loosen the clamp and pull it out of the way creating a hole, if you have a hole you need to fix it cause it's getting unfiltered air which will screw with your rings, cylinder walls, valves and make the engine not last long.
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Post by raford3 on Oct 16, 2011 20:10:06 GMT -6
I don't get your meaning when you say evolved. Somehow the air/fuel mix got screwed up. It got lean. It may have another path for air to enter the engine. Some engineer decided it would run good with a certain setup (OEM). Many people mess up the air box when they fool around with the carburetor by not removing it properly to do service. They just loosen the clamp and pull it out of the way creating a hole, if you have a hole you need to fix it cause it's getting unfiltered air which will screw with your rings, cylinder walls, valves and make the engine not last long.
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