20 H.P. GX 620 Honda coil problem

highpockets · December 09, 2005, 06:44:59 PM

I have a 20. h.p. Honda on a saw. The engine seems to miss on one cylinder on ocassion. I notice that it may clean up and run right then start missing and blowing smoke. I have had the engine down, checked pistons, valves, carb is great, etc. This engine has less than 40 hours operating but has set up for a long time. I am leaning toward a bad coil. Has anyone had coil problems with this engine?

Wife · December 09, 2005, 09:18:26 PM

Chris here, if it is the one side not firing and it has been sitting for awhile I would check the ignition coil, (you have a left and right) they are adjustable as well. It may just need a clean up.
Sorry can't be more helpful. :(

highpockets · December 10, 2005, 05:22:28 AM

Yes I am thinking coil. The engine was left sitting in the weather for some 5 years. I have had it apart and the flywheel magnet was pretty rusted up which I cleaned and check the clearance on the coils. My first thought was that water had run down the sparkplug wire and invaded the coil but in looking there is a drip loop in the wire. It has definitely been exposed to the elements.

D._Frederick · December 10, 2005, 03:24:45 PM

Could you have a valve sticking open?

ohsoloco · December 10, 2005, 05:35:50 PM

Don't know a whole heck of a lot about engines, but the Honda GX620 that came with my mill had a bad coil pretty much from the get-go.

highpockets · December 11, 2005, 07:00:58 AM

ohsoloco

Thanks for the information. I have three Kohler, 2 ea. 18 h.p. and 1 ea. 20 h.p and they run ok. I have not had much experience with Honda engines other than this one.

Did you coil just not fire or was it irratic? I put one of these little Harbor Freight igition things in the plug wire yesterday and it show to be firing but that is not a true test. Tomorrow I'm going to see if I can swap positions with the two coils and see what happens. I am hoping that both are the same and I can simple exchange places with them.

ohsoloco · December 11, 2005, 02:26:33 PM

I only had a few hours on my mill when I heard all kinds of clatter coming from the engine. Shut it down and tried it again...it happened a few more times, but then quit, so I just kept sawing :

It was at least a year later that the engine would die after every cut when I would take my hand off of the throttle. Took it to the Honda repair place since it was still under warranty, and he said the coil was just barely hanging on (don't know anything about these engines or coils, so I'm just tellin' ya what I was told). Runs like a champ now ;D

This reminds me...I think it's time to put the cold air kit on the engine :P

D._Frederick · December 11, 2005, 06:01:32 PM

highpockets,

If your Honda engine had been sitting around for a long time, my bet would be that you have a rusty valve stem on a exhaust valve that is not letting the valve close every time.

highpockets · December 11, 2005, 07:41:34 PM

When I started on the mill some three weeks ago I did a pretty good once over. I had just bought an old pressure washer with an 18 h.p. Kohler and found the carb had some kind of stuff in that looked like cotton candy. So I took the carb off the Honda and took my time cleaning it. Actually the only thing that was needing some attention was the solenoid fuel shutoff. It has a little trash and cleaned up ok.

When I first started the Honda, it ran reasonable well. I have noticed that these V twins sometimes will miss on a cylinder for a few minutes. Anyway we started sawing and after about an hour, the engine started blowing smoke. I had heard it start to miss some but thought it'd clean up. After I got through the cut, I idled the engine down. When I throttled it up the smoke started again. Immediately I shut it down thinking I had a broken ring or piston.

I removed the engine and took it in the shop. I pulled the heads and pistons. Everything looked perfect. I mean it looked like it had never run. Of course this engine has only about 40 hours since new. I reassembled it and set the valves. I put in new plugs and reinstalled it on the saw. It ran perfect for maybe two hours. Then it started backfiring and missing again. I swapped the plugs from side to side. The plug that was cold started firing.

When I first looked at the engine, I had noticed that there was rust on the flywheel magnet. I polished this and the armature on the coils. I did not reset the gap on the coils but they seemed to be tight. I am going to remove the flywheel cover and see if the coils are the same. If so, I plan swapping the coils and see if the other cylinder will then fail to fire. If so, I think I can assume that the coil is faulty.

I am sure they'll be expensive. I am guessing it will tear up $100.00.

highpockets · December 14, 2005, 05:01:51 AM

Well you can't exchange positions on the coils on a Honda GX 620. They made the left side coil with a wire 3/4" longer spark plug wire so the won't interchange. I guess I'll chance that that is the problem and give them my $ 75.00 today.

D Martin · December 15, 2005, 04:47:03 AM

I recently had a coil prollem with my atv. It was firing erraticly. The exhaust ended up getting cherry red hot a couple times from fuel making it in there un burned then firing in the exhaust.If one plug looks fouled it may be it. Suppose that could do damage though it runs ok now.

highpockets · December 15, 2005, 04:51:31 AM

If it warms up I'll find out if it is coil problems. I found one in Shreveport yesterday.

Minnesota_boy · December 15, 2005, 07:23:33 AM

Until it warms up enough to replace the coil, you might waste a few minutes determining if it really is the coil. Pull the spark plug wire off the plug that isn't firing. Hold it 1/4 inch from the plug and crank the engine. If it has electronic ignition, there will be a faint spark jumping that gap. Increase the gap to 1/2 inch and try it again. If it will jump that gap, then the coil is fine and the plug is bad. If it won't jump a 1/4 inch gap, replace the coil for sure. You might have to waste a few more minutes while you check the other coil too. ;D

highpockets · December 16, 2005, 08:23:37 PM

I think I have it. I installed a new coil which I think was breaking down after the engine warmed up. I sawed for about two hours and the engine worked ok. It did try to missfire once and blew some smoke. Then it cleared up and ran. I am 60 years old and had a lawnmower shop at 12 years old but this engine has about run me crazy. I have worked on engines from 1 to 3,200 h.p. but sometimes there is one that just shows itself.

highpockets · January 07, 2006, 05:54:55 AM

I hate to keep beating the same mule but I am still having major problems with this GX620 engine and was hoping that someone has experienced the same problems. As I stated above, I think, this engine was bought in about 1999. It may have 40 hours on it. It has set up for most of that time and has not been covered. After getting it back in from my customer I checked the carb, cleaned it and checked the fuel solenoid. I check the diaphram in the fuel pump. I also sanded the flywheel magnet, and coils.

After getting the engine running it missed on the left cylinder (looking at the flywheel) I put in new plugs and finally got it to hit on both. After it ran for maybe an hour it started missing and blowing smoke out of the exhaust. I finally removed the engine, tore it down to check for broken rings, or piston. EVERYTHING looks like new. I set the valves and restarted it. Still had some problems.

The left cylinder seemed to be the problem. I finally broke down and paid $ 80.00 for a new coil. It did not seem to solve the problem at first. Then after some minutes the thing started running ok. We sawed for about an hour then it started doing the same thing again. This time it would miss for a while then run fine.

Yesterday I decided to saw. The mill has been sitting for about a week. I tried to get it started and finally sprayed a little starting fluid in it and got it going. Still it missed. I noticed that the right cylinder was not hitting. After swapping plugs the right cylinder started firing also. As I sawed I noticed that when the engine gets loaded it may start missing and blowing smoke. If I reduce the feed speed, it will normally clean up and the next cut may be ok. It is not overloaded as I have sawed heavyer stuff with this mill before and had no problem with h.p.

Someone mentioned the possibility of valves sticking. I have not rulled this out. I do notice that this engine is hard to start and normally requires some serious choke to make it start. I guess I am going to have to break down and buy a service manual.

If anyone has had this experience with a GX620, I'd like to hear from them.

Captain · January 07, 2006, 07:04:35 AM

I had a customer's engine doing something similar, it would cut normally, then when warmed up exiting the cut when the governor would normally self reduce, the engine would skip and blow blue/black smoke. It was the left cylinder. Once it started, it continued. I was able to catch it on a comression test immediately after I shut it down. He had a slightly bent valve that was sticking....I don't remeber if it was intake or exhaust. I would check the valves and cam.

Captain

highpockets · January 07, 2006, 05:58:47 PM

Captain you have some interesting things to say here and I appreciate it. This morning I went out to try to saw. It was some 38 degrees. Before I started I had decided to remove the two leads (one off each coil) that kills the engine. I had made up my mind that maybe the diodes in the circuit were breaking down and doing something to the fire. After I did this, I removed both plug wires. I had two phillips head screwdrivers and inserted one in each plug cap. I had a friend to hit the start button while I held the screwdrivers near the block. I had a little yellow streak of fire on a 1/8 gap. More than that and I had nothing. The thing that amazes me is that I just paid $ 80.00 for the left coil last week.

I looked at the magnet on the flywheel and even put a screwdriver on it. Why, I am not sure. Later I was sitting with my friend and talking. He made a remark about the (two ) magnets. It made me think that I didn't remember seeing but one magnet. There is a gap in the flywheel (about magnet size) right behind where the magnet is. I am now curious and wondering if some way there is a magnet missing. Would you know if there were two on the engine. It seems there would need to be two, one passing each side of a given coil.

I am about to decide that I may have a dual problem and the second may be a valve sticking. The strange thing is that yeaterday the right bank started missing. It has always been the left bank until now. I simply changed the plugs around and got the hot plug in the missig cylinder and both finally hit.

I plan to see if there is a Honda manufacturing representative somewhere this side of the water. One would think that they have someone that can shed some light on this. I went on the net to see about getting a service manual and I found that I must go to a Honda service shop and ge them to order it. Boy they screw you every way.

ohsoloco · January 07, 2006, 09:08:36 PM

Highpockets, when I got in touch with another Norwood owner before buying mine he also had the GX620 on his mill. I remember him saying that there could be some problems with the engine if it was overfilled with oil. Apparently it was a common problem, but I can't remember if it was b/c the fill line on the dipstick was off or not :-\ I don't know if this could cause the problem you are describing, but I thought I would at least mention it.

highpockets · January 07, 2006, 09:28:13 PM

I am about ready to fill it with dynamite

Coon · January 07, 2006, 10:56:08 PM

highpockets before you blow the thing sky high you had better try this....
Go to the shop and get an aerosol can of WD40 or ether or anything that is flammable. Make sure that you have the little extension straw on the can because it'll help you out. Take this can of stuff over to the engine and start it and let it idle. Spray a little towards the end of the crank shaft that is coming out of the engine. If the engine seems to level out. Then you have crankseal problems. I had the same thing happen to me on a snowmobile one time and the coil changeovers did not help. Finally someone came along and showed me this. Yup the crank seals were leaking the tiniest bit of air and it would cause it to misfire just like an irregular heartbeat.

This may not be your problem but it's DanG well worth a try.
Brad.

WH_Conley · January 07, 2006, 11:09:27 PM

I never thought about it, but on my Onan, if the O-ring on the oil dipstick gets wore down to where the cap doesn't fit tight you get erratic running to.

D._Frederick · January 08, 2006, 01:09:16 AM

WH.,
The Onan is a opposed twin, they use the inpulse produced by the pistons to to run a fuel pump.

The oil level has to do with the low oil detector, it short out the ignition.

H.

If your engine has a mag for igniton, it would need something to direct firing since the pistons are 90 degrees apart. Did it run smooth when you got both banks to fire?

highpockets · January 08, 2006, 08:23:13 AM

Thanks guys,

I hadn't thought about a leak on the crankcase. I can see where this could definately effect the fuel pump. I hate those little pumps. I have one 20 h.p. Kohler and 2 18 h.p. Kohlers and they all have to be wound on before they start. Has anyone ever added an electric fuel pump to these types of engines?

Monday, I'm going to see if there is a Honda Service Rep in these United States. Each coil will spark about 1/8" and it is yellow. Something ain't right. Even the new coil is weak.

ohsoloco · January 08, 2006, 02:15:56 PM

Hope ya get that thing running good, highpockets

Good luck finding a rep. It took me quite a bit of detective work to finally find out who the service rep was in my area. Searched and searched on Honda's website, and I think I finally had to call someone (which took even more work to find a phone number :

). I honestly can't remember exactly how I got the info., but it turns out my local rep is an amish place over in the next valley :-\

highpockets · January 08, 2006, 10:42:38 PM

I'm expecting to have to call The F.B.I. or the K.G.B. to locate them. I get bad vibes when I go to their webpage and they advise me to contact a local service rep and he will order a service manual. Sure ain't like Wisconsin Engines. They will even call you back.