Low compression
Thread Starter
Instructor
Joined: May 2009
Posts: 180
Likes: 1
From: Prairieville Louisiana
Low compression
When reving the engine (L-48) slowly depressing accelerator the engine gets to 2000 RPM and slows down to around 1200 even while still going down on gas pedal. It starts to pick up slowly about half throttle. I have new plugs, wires, hei module. Checked timing , seems to be ok. Checked compression, 70-80 lbs. with throttle open. Added couple shots of oil, no change. Pressure tested cylinders. Can hear some air going by rings but nothing too excessive. No sound in carb or tail pipe. 17in. vacuum. No engine blow by when running even with pcv pulled out. Anyone think it possible the engine may have jumped timing?
Drifting
Joined: Aug 2008
Posts: 1,381
Likes: 11
If you did the compression test correctly and really have 70 to 80 psi on all cylinders you have a big problem. Did you crank the engine over until you got the highest reading (usually takes 3 or 4 revs)? I have seen low compression across all cylinders on engines that were overheated. Any chanced that happened?
Race Director
Joined: Oct 2000
Posts: 15,013
Likes: 79
From: central FL, near the beach.
so after 2 months of your best effort, now it won't run at all?
did u adjust the valves?
what do the plugs look like?
does it have a real old cat. converter on it?
how many miles did u drive it recently?
yes, it might of jumped a tooth or 2.
did u adjust the valves?
what do the plugs look like?
does it have a real old cat. converter on it?
how many miles did u drive it recently?
yes, it might of jumped a tooth or 2.
Thread Starter
Instructor
Joined: May 2009
Posts: 180
Likes: 1
From: Prairieville Louisiana
It runs, no power. Checked timing chain and it was true. Plugs are leaf brown, no cat. Not sure about actual miles, someone has been into the engine before, it has a double roller chain. I wonder if they put the rings in upside down? Just trying to get by till next year and its comming out. Adjusted valves also.
Thread Starter
Instructor
Joined: May 2009
Posts: 180
Likes: 1
From: Prairieville Louisiana
yes, valves were tighter than i liked. I backed each one off running till it started clacking. Then, tightened till it stopped plus 1/4 turn more. Some i backed off a whole round before it made any noise.
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