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S7 has no more than 4 or 5 gallons on it. Always ran fine at around 240 degrees. Was running fine for 3 practice laps and then started running rich and boggy. Too much smoke and temps were about 140 degrees. Air filter was replaced, no inline fuel filter, but disassembled carb and cleaned. Tried new plugs and checked for any driveline drag. Engine refuses to run hotter than 140 degrees. When needles are leaned out, engine really starts to run bad.
With clutch off, I pressurized the engine with an air compressor. Front bearing has some air leak, but how much is normal and would this cause my problem? Never heard of a engine running rich and cold.
Posts: 11 | From: Northern California | Registered: Nov 2006
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Impossible to quantify this and I do not think this is related to the engine running too rich and too cold. Normally if you lean out the HSN only the engine normally becomes hotter unless your not leaning out the engine but richen it up.
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I don't consider myself to be a newbie to tuning, but so far, this has me stumped. And no one locally has heard of an engine refusing to lean out. Yes, I did change plugs (4 times). There was a small split in the exhaust rubber, but no blockage. HSN and LSN CW should have raised the temps, but little effect. The engine would finally bog down too much to move the vehicle. I'll replace the bearings, assemble the engine and test for leaks. Onward. :-)
Posts: 11 | From: Northern California | Registered: Nov 2006
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I've been advised by some that an engine unable to run up to temperature is worn out. I've disassembed the engine and all looks fine. Pinch (with plug out) is present, but maybe not so much. Hard to tell what is normal. What's strange is that it died while on the track running fine. Air Filter has never fallen off and has always been clean. Engine acts like it swallowed dirt and destroyed itself. It's just strange for a engine with not more than 5 gallons on it. I'll test again in a few days, but I'm not hopeful.
Posts: 11 | From: Northern California | Registered: Nov 2006
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check that the tip of the main needle hasnt broken off..it only needs a mm broken off and you wont be able to lean the engine enough.
Posts: 5 | From: uk | Registered: Jun 2008
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Any chance you can install a known good carb and see if it runs? I know every motor tunes differently but in this case I think it's worth a try.
Any chance a bolt on the motor came loose and gave you an air leak?
Good call on the needle.....definately worth a look.
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HSN needle assembly was replaced, no help. Single chamber pipe was checked, no obstructions. I have a C6 engine. If the carb will fit, I will try it.
Posts: 11 | From: Northern California | Registered: Nov 2006
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S7 is history. Cold pinch is practically non existant.
Talked to driver using this engine. The theory is that massive dirt clogged the prefilter (no dirt entered engine). Continued running with restricted airflow caused low temps (140 or less) and destroyed the piston/sleeve pinch. RIP
Posts: 11 | From: Northern California | Registered: Nov 2006
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I'm running an S7 with no cold pinch (but reasonable compression) at the moment and it's a real screamer, on faster tacks I run it in preferance to my C6's as it just revs and revs...
Posts: 26 | From: Southampton, UK | Registered: Nov 2007
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Pinch is the piston blocking at TDC when the engine is cold and the glowplug removed.
Compression is when your piston travels to TDC(with the glowplug tightened) and after the exhaust port the air will compress and not leak around the piston area.
If your engine has lost its compression then or the engine has swallowed dirt or the glowplug is not tightened or leaking.
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Ok than mine has lost all of its pinch. I was told that this could have been caused by running way too rich? I didn't know that that could destroy your engine. Here's a pic, I can push the sleeve all the way through the piston
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How can you see that? There are no scratches on the sleeve? Also Rody, what is your opinion on doing a re-pinch of the sleeve? Or am I better off looking for a new one..
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If the piston has a universal matt color like this, then the dust(very fine of course) has wiped out the carbon which should normally be there and used in this way the piston.
We never suggest the pinch method, it is very bad for the conrod and the result sometimes is worse then it was before. If the bearings are still in good shape and the pin of the crankshaft is still at 5.02 then I would change the piston/liner/conrod.
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