OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Honda Engines HRM215 has me stumped

I have a Honda Harmony HRM215. I previously had a problem where the engine was very hard to start, requiring a dozen pulls or so to get it running. Once it started, it ran fine, but even when it was warmed up, it still would not start unless I set the choke.

Late last summer I got tired of the problem and bought a brand new carburetor for it. However, the problem remains. I checked for a partially sheared woodruff key on the flywheel, and checked the overhead valves for decent lash. Compression seems ok, although I haven't been able to measure it. Valve seats seem ok. They were a little carboned up, but I can see where they were seating and there's a good seal pattern in the valve seats. Not sure how to check for a possibly weak spark, though. I'm not really a novice with small engines, but this one really has me going in circles.

Let's try to work through this a step at a time. First, to test the spark, take an old spark plug that has been used in a 4 stroke engine (2 strokes ruin spark plugs; in general 4 strokes don't, or at least not quickly), open the gap to 3 mm, connect it to the spark plug lead, clamp the spark plug body to the cylinder head so it makes contact, remove the "real" spark plug from the plug hole, put the controls in the starting position (so the spark won't be disabled), pull the start cord, and watch the enlarged spark plug gap. Expect to see a blue spark every second revolution of the engine. If the spark is red or orange, or irregular, you have ignition trouble. A consistent blue spark means ignition intensity is not the source of your starting problem.

The next thing to check is the valve clearance: 0.1 mm intake, 0.15 mm exhaust.

If you have access to a compression pressure gauge, it should read about 10 kg/square cm, or 140 psi, pulling it over briskly with the throttle open (600 rpm). It would take several pulls to show maximum pressure. If the compression feels normal this test is not essential, but is nevertheless useful.

If it passes all the tests so far, you should check whether the problem is fuel feed. The simple, crude way to test this is to remove the air cleaner and squirt a few cc of fuel into the carburetor air intake (or at a pinch, into the cylinder through the spark plug hole) then use the standard Honda starting procedure. Stand clear of the carburetor air intake, in case it spits burning fuel. If it starts when primed in this way, the starting problem is getting fuel into and through the carburetor jet; we can talk about what might be wrong if that turns out to be the problem.

hate to jump in on grumpy because he is doing such a good job but i have had problems with the choke not activating fully on my Honda and that led to hard starting. it needs to be fully closed to work. also the main jets have a tendency to get varnished up more so than others and cause predominantly hard starting but OK running.
try what grumpy says first but keep that in the back of your mind
regards jay

Jay, one of the symptoms (needing choke to hot-restart) matches lean mixture when starting better than it does anything else, but to sort these things out reliably it is often best to eliminate other basic faults; sometimes you get a mixture of causes combining to give a specific fault. Hard starting is also sometimes caused by one of the valves having negative clearance, or weak spark (at higher speeds the magneto usually does better than it does at starting speed). I think jet obstruction is fairly unlikely in this case because the carburetor has been replaced recently. I haven't checked yet whether the fuel filter was replaced as part of the carburetor change; the fuel filter is sometimes the culprit on this engine. The choke not closing, a clogged fuel filter, or an intake pipe air leak are the best guesses I could make at this point - but I'd rather not start chasing guesses until we know we have a sound base engine.

One of the objectives here is to end up with an archive case on this problem that will be helpful to others. If we follow a fairly standard diagnostic process (without going overboard and ignoring major symptoms, the way manufacturers' process charts usually do) we will probably get the best archive outcome, and matts156 will probably get an orderly progression toward a solution - which may be useful for him in future situations.

Grumpy, well said mate, a good archive data base could be an invaluable resource in the future of this forum.

i agree that an archived type thing is best as i often search old posts and find a new solution as you say. i was just adding my recent experiences on my Honda, but now you mention it it seems your right about a lean mixture. ill keep it in mind next time.
thanks
regards jay

Jay, I set out that explanation so that you'd give some thought to the archive aspect. I did that in recognition of the value you give this forum with your input - you are an important contributor to the archives.

Well, fellas, you're going to love this one...

I set up the valve clearances and rotated the engine a couple of times to verify it. I was puzzled to see the exhaust valve opening slightly during the compression stroke. I put an indicator on it and the valve stem is being opened .050", which is 1.27 mm. In my experience, that's more than enough to lose compression. The valve begins to open just after bottom dead center and doesn't close until the piston is about 1 cm from top dead center. Of course, on the next cycle the exhaust valve opens it full stroke for the exhaust cycle.

I talked to the original owner when he gave it to me (free, thank God) and he said that it never really ran very well. I think I see why. I think this engine had a manufacturer's defect and the bottom side of the cam lobe wasn't ground properly. Short of replacing the camshaft, I don't think there's anything I can do to fix this.

I can't imagine that this would be a normal characteristic of the camshaft. Compression would be shot to hell on any engine that had a .050" deflection in the exhaust valve during the compression stroke, whether it's a lawnmower engine or a car engine.

Did you set the valve clearance with the crankshaft just past top dead center, at the end of the compression stroke? People sometimes have trouble adjusting valve clearance with Briggs & Stratton engines due to the Ezyspin feature, which deliberately holds the intake valve open .010" during a large part of the compression stroke. B&S do that on the principle that it eases the job of pulling the starter cord, and there isn't all that much leakage from just .010" valve lift once the engine is up to running speed. It sounds as if your Honda might perhaps have something similar, though .050" sounds rather a lot.

There is of course a possibility that the engine has a camshaft problem, either due to a manufacturing defect or through wear. I once saw a little Honda 4-stroke generator engine that stopped running, and the reason was that it no longer had any cam lobes. It doesn't sound like a highly probable explanation of your engine's problem though; it would be an odd kind of cam wear to create a bump rather than remove one.

If the compression feels OK, compared with similar Hondas, I doubt the camshaft is your problem. Bear in mind that your engine has a substantially higher compression ratio than a side valve B&S engine, so you should feel a fairly solid compression load on the starter cord. You can find out for sure by borrowing a compression gauge that fits the spark plug hole. In my experience an engine that is supposed to have 140 psi compression pressure will probably start fairly normally down to about 90 psi, but below that there may be a problem starting it. Remember that Honda specifies the 140 psi figure at 600 rpm, which is pulling fairly briskly on the cord. At lower speed, an Ezyspin-type feature might give you a much lower pressure.

No, that can be pretty normal, as it acts as a compression release to aid starting, similar to what briggs used for their "easy spin" starting.

Oh, that's a good point, I didn't think about the easy spin start. Is that something that's centrifugal and stops once the engine starts? If that's the case, I wonder if it's sticking or otherwise not operating.

If it was a cam problem, I don't think it would be caused by wear. It would almost have to be a manufacturer defect. The lobes have plenty of lift, more than my dial indicator can measure. A worn cam wouldn't have a high spot on the bottom of the lobe.

Some of the bigger B&S engines have decompressors, which relieve the compression for starting but stop operating as soon as the engine gets up to idle speed, but Ezyspin is not like that. It holds the valve slightly open during the compression stroke regardless of whether the engine is starting or running at maximum speed. B&S say they can do this because when the engine is running faster than a few hundred RPM, not enough gas has time to leak through the slightly open valve to have much effect on anything. Of course the valve is fully closed for the expansion stroke. The idea seems a bit weird but B&S is the world's largest manufacturer of small engines AFAIK: they must know something about what they are doing. It is not all that different from the "half compression" feature that some very old cars had, to make it possible to start them with a crank handle - but you disabled the half compression as soon as the engine started, unlike the B&S version which operates all the time.

I haven't worked on a Honda engine and I don't personally know whether it has a feature similar to Ezyspin, or just uses a conventional centrifugal decompressor. Someone on this forum will know the answer. Whether your engine has a decompressor or Ezyspin, the feature will operate while starting - so you would get the result you have described when you pull it over by hand and watch the valves. Since your engine works properly once started, whatever feature it uses for reducing compression while starting seems to be working.

The chances of Honda (a very reputable engine manufacturer) having made a complete shambles of making a camshaft, years ago before they moved mower engine production to China, are fairly low. I think it is more likely that the camshaft is not the cause of your problem. Nevertheless it is theoretically possible on a worn camshaft for the base circle to erode, while part of the lobe is still present (though perhaps horribly deformed). Such things are not usually worth investigating though, until you have eliminated all of the more common problems.
Post-Edit: This engine, like all of the small OHV Hondas, has a decompressor to make it easier to pull the pull start. The decompressor bumps the exhaust valve open during part of the compression stroke. It is deactivated by a centrifugal device mounted on the camshaft timing gear, at any engine speed above about 600 rpm.
matts156 described the decompressor's operation accurately in his post #17633, above in this thread.

G'day,
i now see what you were saying grumpy, misunderstanding on my part (probably due to the time of night i decide to read posts)
thanks
regards jay

Well, fellas, I got her running good and proper. The primary problem was that the intake rocker arm was too tight. I couldn't get the feeler gage in there at all. So I set the clearances again and put it back together.

I had a coincidental problem of a contaminated tank of fuel, which was gelling up in the carburetor so once I got that flushed out, she fired right up on the first pull. Also, when I shut down to empty the bag, it fired up again without the need for the choke.

Thanks for your help, your input was key in getting this thing running again. We're celebrating Memorial Day weekend up here in the states. I'm not sure if you have a similar holiday this weekend, but from a US Navy veteran I'd like to convey my thanks to our great Australian allies who fought so well by our side in WWII and continue to fight with us in Iraq. Happy Memorial Day!

I had a very small single cylinder Honda motor cycle once that was a bit hard to start. It turned out the problem was a tight intake valve clearance, the same as your lawnmower. I suspect your fuel jelling may have been a bigger part of your problem, though. The additives in US fuel have a bad effect on its shelf-life, unless you add even more additives (fuel stabilizer).

Our equivalent of Memorial Day is in April (ANZAC Day), but the memories and sentiments it celebrates are similar to yours. Thank you and all Americans for bailing us out in the Pacific war; we had no chance on our own. Happy Memorial Day to you and yours.