Std vega exhaust rather than expansion
Excessive spit back
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johnny650
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conservative port timings are all very well but it kinda depends on what piston has been fitted and if the skirt has been modified thickness of base gasket , how aggressively the edges of the ports were deburred etc too I'd imagine.
Like you say the only way to be sure is to remove the cylinder and do a port map and check the various dimensions of the piston, gasket and ports etc
Coasters suggestion of excessive backpressure or blockage in the exhaust is a good one too, I didn't think of that
Like you say the only way to be sure is to remove the cylinder and do a port map and check the various dimensions of the piston, gasket and ports etc
Coasters suggestion of excessive backpressure or blockage in the exhaust is a good one too, I didn't think of that
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Snails
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The exhaust idea is the most tricky to do anything about as options on Lunas is very very limited. Only 2 - 3 very expensive options even if you can find them.
Out of interest, what sort of port timings would be likely to start to cause problems in respect to spit back
Can the carb/jetting have any influence?
Out of interest, what sort of port timings would be likely to start to cause problems in respect to spit back
Can the carb/jetting have any influence?
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Snails
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So coming back to this subject, its been suggested to me that incorrect ignition timing could be a cause of spit back. Would anyone agree or disagree?
If its true, is it a sign that its too far advanced or retarded or could it be either way?
If its true, is it a sign that its too far advanced or retarded or could it be either way?
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johnny650
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do you not know how to check your ignition timing ?........ or what it is currently set at ?
As has previously been said the most likely cause of spitback through the carb is inlet /exhaust overlap due to poor porting , piston skirt mods ring blowby etc ........The only way you are going to know for sure is to remove the cylinder and do a port map. i have posted a couple of examples on here somewhere . Compare the results with the barrel supplier or post the map on here. Also check the piston is correct for your setup and the skirt hasn't been modified naturally check your gasket thicknesses and squish .