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Have you also considered the 5606 that is under $90 and seems to get better reviews. I have neither one so cannot say which is better.

Fred- I did consider the 5606, but ruled it out because you have to use an 12mm adapter with the 14mm hose. This results in an air gap, which can reduce the compression reading. Also, it isn't advertised as Motorcycle gauge kit. I don't fully understand the differences between a motorcycle version, but I am convinced there are some differences in the design for small engines. The Schrader valve at the spark plug end, without the use of an adapter, is one difference, but I think there are others too. Thanks for your suggestions.

Good point, if the 5604 has a 12mm end then that is the one I would get. I did see the 5606 has to use an adapter.

I've had a cheap Equus compression gauge for years and have had good results with it.
The 79 has 150 psi across all 4 which was a big difference from the 78 before. (85 to 135)

I built a 12mm adaptor out of an old spark plug with a rubber O-ring.

My 79 never had embarrassing smoke upon startup. As mentioned, Honda musta changed something.

Got the new water pump installed and this morning I started testing for smoke. Over the years, I have found that they smoke badly after filling the oil to the top line, getting it hot and parking it on the side stand for an hour or two. So, the engine has been filled to the top line, it is hot and I have tilted the engine to the proper angle. We shall soon see if all my time and money made any difference.

I've said this before:
If you add the exact amount of oil recommended in the manual it will come to almost exactly to the middle of the sight glass (right where that useless wiper is). The upper mark is not a "full" mark but rather the maximum permissible level (think of it like the maximum pressure number on the side of the tire - you could under extreme conditions but it is not what you should normally do).
When the oil level is too high more oil is splashed up by the moving parts so that it can be carried out of the engine through the breather until the oil level is reduced to the correct level, at which point there will be less splash and less oil will be lost through the breather.
Note also that the breather is connected to the air cleaner so that unburned gasses expelled through it can be sucked back into the cylinders to be burned. Some of the oil that is in those gasses will be separated and end up in the collector but the rest will go to the cylinders. I don't imagine that contributes a lot to the startup smoke but it wouldn't decrease it.

:-

I have a new CB750 piston and it also has these holes. I know nothing about piston designs, but I am hoping the new aftermarket pistons I installed will stop or reduce the smoking of the GL1000. Ok, now for the results of the first test...drum roll...NO SMOKE. I even started the engine while it was tilted and it did not smoke at all, none. If I do this five times in a row and it does not smoke, the problem may be solved. Still not optimistic, but who knows.

I turned it off and will go back out later for test 2.

I appreciate the comments from Bob regarding the oil level. I always thought that the full mark (maximum level) was the upper mark and the lower mark was the minimum level.

Most people that have owned a GL1000 will agree that when you fill one up to the upper mark, they smoke worse than one filled to the lower mark. I filled this one up to the upper level because I am intentionally trying to make it smoke . Now for the test 2 results...drum roll...

NO SMOKE

I will leave it tilted over night.

FWIW, CX/GL500 engines are the same regarding oil consumption (the amount specified fills to halfway up the dipstick's hatched area and they don't use much unless you fill higher) but they aren't known to smoke.

cfairweather wrote: ↑Sat May 17, 2025 10:33 pm I will take a few pictures tomorrow. It isn't fancy, but it works. I leave the intakes mounted to the engine and the vacuum gauges stay attached too. I will explain this tomorrow if I have time. Today, I noticed oil is dripping out of the water pump weep hole, so I ordered a new water pump.

Cedric, see the thread on the water pump seal!

Test 3 Results:
NO SMOKE

I hate to admit it, but the oil coming out of the weep hole was my fault. I forgot an o-ring. I decided to replace the pump anyway because it was one of the cheap ones. I am actually glad I screwed up because now there is a genuine Honda pump in place now. I know you needed a laugh .

Now if someone could only figure out a way to stop the smoke without taking the engine apart.......

That would be great, but nothing is easy with these old bikes. This project has been a lot of work, but I am glad I did it. At this point, I think I can safely say, I have at least improved the engine because I have never seen a GL1000 stay tilted for over a day and not smoke when started, three times in a row. I was using this engine on my test stand, but it actually was originally mated to the BOY GL1000. After I finish all testing and have some time, I will put it back in the BOY bike where it belongs. This is my only GL1000 and probably my last.

If this solves the problem, I will attribute it to the Ridge Reamer machine shop and the aftermarket pistons. To review, I had them bore the cylinders out for the .50 over sized pistons with .03mm (.0011") of clearance. This is the minimum clearance according to the manual.