2 seized engines, need help with jetting.

augustaf

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#23
83 mm bore and 35 cc domes = compression for race gas, especially since your application probably requires sustained high rpm. Consider checking squish and cranking pressure.
Is the above piston used in the 83mm bore mentioned in post #1?
 
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#24
83 mm bore and 35 cc domes = compression for race gas, especially since your application probably requires sustained high rpm. Consider checking squish and cranking pressure.
Compression reads 170 in each cylinder. Not sure about squish or cranking pressure. Riva assured me that 35cc domes was good for pump gas.?

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#25
83 mm bore and 35 cc domes = compression for race gas, especially since your application probably requires sustained high rpm. Consider checking squish and cranking pressure.
Is the above piston used in the 83mm bore mentioned in post #1?
No from original cylinder that was 82.75. The wash looks the same on this cylinder.

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smoofers

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#29
That piston has virtually no wash and looks super lean. Either your carb jets, internal carb filter or something is restricting fuel or putting air in your fuel lines. What are you using for fuel line? Are you running a fuel selector (On/off/reserve)? Are you running a check valve on your fuel tank vent (valve should let pressure in but not out)?
 
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#30
That piston has virtually no wash and looks super lean. Either your carb jets, internal carb filter or something is restricting fuel or putting air in your fuel lines. What are you using for fuel line? Are you running a fuel selector (On/off/reserve)? Are you running a check valve on your fuel tank vent (valve should let pressure in but not out)?
The jets are 145 pilot, 180 main. Just check filter it's good. Auto zone fuel lines, yes on the fuel selector.
Is there a better fuel line?

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smoofers

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#31
The jets are 145 pilot, 180 main. Just check filter it's good. Auto zone fuel lines, yes on the fuel selector.
Is there a better fuel line?

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Auto zone line should be fine. Fuel selectors can be notorious for letting air into the fuel system, until you figure out your issue, you may try a section of clear line just before the carb to see if any air bubbles are present. Also, are you running a check valve on your fuel tank vent? The check valve keeps the fuel tank pressurized and helps with consistent fuel delivery. If none is present you could possibly starve your carb under high demand situations. If it is backwards you will definitely starve the carb.
 
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#32
The jets are 145 pilot, 180 main. Just check filter it's good. Auto zone fuel lines, yes on the fuel selector.
Is there a better fuel line?

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Auto zone line should be fine. Fuel selectors can be notorious for letting air into the fuel system, until you figure out your issue, you may try a section of clear line just before the carb to see if any air bubbles are present. Also, are you running a check valve on your fuel tank vent? The check valve keeps the fuel tank pressurized and helps with consistent fuel delivery. If none is present you could possibly starve your carb under high demand situations. If it is backwards you will definitely starve the carb.
Yes running a fuel tank check valve. Let's pressure in correct? So if I can blow in it, them it's good?

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#34
The jets are 145 pilot, 180 main. Just check filter it's good. Auto zone fuel lines, yes on the fuel selector.
Is there a better fuel line?

Sent from my SM-G930V using Tapatalk
Auto zone line should be fine. Fuel selectors can be notorious for letting air into the fuel system, until you figure out your issue, you may try a section of clear line just before the carb to see if any air bubbles are present. Also, are you running a check valve on your fuel tank vent? The check valve keeps the fuel tank pressurized and helps with consistent fuel delivery. If none is present you could possibly starve your carb under high demand situations. If it is backwards you will definitely starve the carb.
Its pretty hard to blow in. Seems it should be easier?

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smoofers

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#35
Its pretty hard to blow in. Seems it should be easier?

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If the tank cap is off, you should be able to easily blow through the check valve... Pull it off and try blowing through in different directions. One should be nearly impossible, the other should be like blowing through a straw. Is it a new or used check valve?
 
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#36
Its pretty hard to blow in. Seems it should be easier?

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If the tank cap is off, you should be able to easily blow through the check valve... Pull it off and try blowing through in different directions. One should be nearly impossible, the other should be like blowing through a straw. Is it a new or used check valve?
used, the one from the ski. I reached in and felt that the hose was vacuumed shut. Increase stock hose diameter?

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#37
I've seized a few engines while racing and the piston wash never looked like that. So you probably do have a fuel issue but there may be more to it. The underlying problem is most likely excess heat in the cylinder around the sleeves. Some things to think about...i never liked how the typical bpipe set up only allows one cooling outlet from the head. That slows down water flow thru the motor. Also if you are under propped that increases the piston speed drastically when you accelerate which builds up heat. A light flywheel makes that problem even worse...and finally the b pipe exhaust manifold Imo is a bit restrictive (it's what maybe 44-46mm diameter?) for running wide open again creating more heat. You can bore it out but that may or may not help.
Just my 2ct