Home › Forum › Ask A Member › Compression check question › Re: Compression check question
Regarding my views on the matter, here’s some background – one of those godforsaken anecdotes – for what it’s worth.
A number of years ago on a popular moped enthusiast’s site, this same topic was hotly debated. I was on the "carb WOT" side of the debate, which should come as no surprise. But there were a number of dissenting opinions, so several members agreed to test their compression with the throttle both at WOT and fully closed. I also tested one of my ‘peds, which I believe was a Motobecane 50V.
Now bear in mind that virtually all mopeds are 2-stroke engines, and +most+ of them are simple 3-port (aka loop scavenge) designs lacking reed or rotary valving. The results of the test were interesting. In this case, all engines tested were in fact 2-stroke.
One member reported no significant difference between WOT and closed, while a couple other members (including myself) reported a non-trivial difference in the two figures. It was agreed that while it’s not always a necessity, holding the throttle WOT is simply good, workmanlike practice when testing compression.
It certainly cannot harm anything to do so, and it eliminates any questions about the measured figures. And again, that’s just good shop practice.