Time to go from updraft to downdraft charcoal gasifier?

Hi Martin.
Please check my English manual DRIVEONWASTE. You can download it for free. Is an updraft system very simple. One long lasting metal nozzle. Speed 72 miles per hour or 115 km/h. I have just drive 3000 miles or 4800 km with no gasoline. The cyclone design holds 95% of the eventual moisture in the load. Download from my Facebook DRIVEONWASTE or my website WWW.AUTOABASURA.COM.
Also lots of videos in my Youtube channel AUTOABASUR.


Well, s@*t happens. I fixed the starter and got the generator going for about 30 seconds until this:

Bent a push rod too. Now starts the saga to get the right repair parts. I got an older Honda GX340 engine. Honda in its infinite wisdom went from an 82mm bore to 88 (same bore and stroke as their GX390), but kept the same model number. I’m not sure they changed the head, but I think they did.

Since I’m ordering from overseas, I have to confirm every dimension. Then wait…wait…wait. :confused: Maybe I’ll finally get to test the gasifier in July? Oh well, just hope there are no long power outages.


I’m sorry to see that, Marty. Maybe you could go ahead and swap the heads and not worry about parts interchange later on?


I did a quick search and it seems they pair the 340 and 390 now, but they still have different designations. Maybe try to look for an older parts catalogue to find the specific ones needed?

Or you may want to drop the hammer on a similar sized Chinese made engine. I’ve yet to have a catastrophic failure on a Predator/Lifan engine.


Thanks Cody. I did see the parts on some US sites. However, the shipping charges were exorbitant. I do most of my shopping on eBay and AliExpress simply because of the shipping charges. I can get free to minimal shipping charges from Asia. For example, I needed a power transmission belt for a sander. The cost of the belt from China was a few bucks with free shipping. It was a similar price from the US but shipping was about $24. Often times the stuff from the US is the same Chinese stuff.

I have been doing a lot of research on this engine this evening, and there seems to be two different sized intake valves for a GX340. I did discover that there are Chinese knockoffs of the Honda engine and they have at least named them 182F and 188F for the 82mm and 88mm bores. This has allowed me to narrow down the choices. And some sellers have given dimensions on the valve that match what I have. I think I can get the correct valve and head gasket now. I’m still working on the push rod.

To save money I prefer to fix if possible. But I admit a new engine would be tempting. :thinking:


Hi Marty , a few years back i had problems not being able to get a 100%seal on my valves , and the tappets kept coming loose so i looked on ebay , and found a complete head for my clone GX390 for less than $50 AU inc delivery including delivery quick change over and back up and running , that was about 4 years back so i guess prices have risen by now .



Hi Dave,
Thanks for the suggestion. I did see a head for a GX390/GX340 for about $60 USD. But this is I think for the 88mm bore. I can’t find one for a 82mm bore. I think my engine is so old there isn’t much available for it.


Well, the parts are coming in for the repair. I got most from AliExpress. The shipping times were real good. However, the one part I got a few years ago locally is a problem. I was running the generator pretty hard for a year and a half and anticipated needing some renovation at some time, so I ordered a piston and some rings.

So of course when I disassembled the engine I found that the pistons are not exactly the same. Good diameter and geometry regarding the ring lands and rod end bore, but there is no depression in the top and the weight is about 4% heavier (.4 oz). I figured the extra compression wouldn’t be too bad (as long as the valves cleared), but I think the extra weight is a deal breaker.

I was contemplating getting out the dremel and hollowing out the top, but measurements showed that the top of the piston is no thicker than the old one:

I can’t figure out where the weight difference is. It looks like the old piston should be heavier. I will probably just reuse the old one. :face_with_diagonal_mouth:


What issues would you think that 4 percent weight differential would cause, Marty? I have seen so many different piston configurations for small block chevy engines that I’m sure they must have different weights.


Tom, I guess I was thinking of performance engines where they like to get down to 1/2 gram difference or so between pistons. But, those engines are revving at high rpm’s so my 3000 rpm generator would probably be ok. It shakes a lot now, so I was worried it would get worse or put undue strain on it.

I might be premature with the weight thing though. I am also replacing the connecting rod which is arriving next week. Might be that the specs have changed and the connecting rod is lighter. We’ll see.


I think with a new connecting rod, piston, and the bearing surfaces involved with those you should be fine. Definitely run the engine by hand to make sure those valves don’t hit the piston.

There’s actually something similar with the old carbureted Mazda B2000 and B2200 engines. I believe if you put B2000 flat pistons and the B2000 cylinder head into a B2200 engine block you get an increase in compression. Granted those are both Non-Interference SOHC engines.


I just realized that the aluminum alloy used in the pistons could be different. There is about a 6% difference in weight between the lightest and heaviest alloys. The engine is pretty old, probably about 25 years, so that is a very likely occurrence. Originally manufactured in Japan and then later in China where anything is possible. I remember when China first started manufacturing for the world and the scandal with substandard bolts used in aircraft. Maybe they copied the piston geometry fairly accurately, but skimped on a more expensive lighter alloy? I guess I could copy Archimedes’ procedure and see if that is the case.


The connecting rod came and it was lighter than the old one. The complete assembly is less than 3 grams heavier than the old one (only 1/2%). So that issue is moot. :slightly_smiling_face:

I installed the piston and the head temporarily. I didn’t use a head gasket and there was no valve lash.
Under this worst case scenario there was no interference between the piston and valves. :slightly_smiling_face: :slightly_smiling_face:

Next rainy day, I should have the generator rebuilt. Then comes the test of the gasifier which got aborted over a month ago. At least I get a practically “new” generator out of the deal or should I say ordeal.


Just being nosy Marty, but when you moved to Chile were you already versed in the language and did you have to jump through many hoops for employment? Must have taken a major set of balls.


Tom, when my wife and I moved here, we knew very little Spanish, oh let’s just admit it - practically none. We set up a real estate company to cater to expats wanting to move to Chile, so we controlled our own employment. Yes, that was quite ballsy and it was very challenging, but we don’t regret it. I could not have done it without my amazing wife - actually she was the one that wanted to move here most!


Boy, I thought I would be much further along at this time. The generator rebuild took much longer than I expected. To be fair, a lot of time was spent on other projects that had to happen before the building season begins here.

The internal build of the engine went quickly, but once completed the engine ran poorly. The old carburetor was a mess. Both the throttle and choke were stuck. The fuel shut off solenoid was also stuck. In trying to free the throttle, I accidently broke the throttle plate.

So I bought a new carb. When it came I saw that the inlet and outlet were larger than on the old carb. I installed it anyways. I had to crank the engine forever with the electric starter to get it going, but once running it ran smoother than it ever had. But the starting issue was a problem. It would never do on the gasifier.

So I went back and resurrected the old carb. I freed up the throttle and choke spindles and fashioned a new throttle plate from some flattened copper pipe.

The new carb came in handy as it suppled a new shutoff solenoid and throttle nozzle which had also been stuck in the old carb and damaged. So the generator now starts and runs fine.

I do wonder though if the gasifier was responsible for the carb issues. I am thinking that water in the gas may have caused the sticking issues of the choke, throttle and nozzle. I wouldn’t have thought the solenoid would be affected, but I suppose water could have leaked down the throttle nozzle into the float bowl and around the solenoid shaft. The generator began to be hard starting when I was getting a large amount of water in the gas.

Going forward I wonder if I have to run the generator on gasoline after a run on the gasifier, or maybe now that I got the water issue solved with the new nozzle it is a moot point. Has anyone else had this problem? I would hate to have to rebuild a carburetor every once in a while. :roll_eyes:


Nowdays l pour a shot of engine oil in the air inlet just before shuting off the engine. Specialy if l know its not gonna run for a while. Its amazing what difference it makes at next startup


Kristijan, great advice, thanks. How much oil constitutes a shot?


I think it’s two squirts. :thinking:
I have had the throttle plate stick several times on my generac generator after running wood gas Marty. Doesn’t appear sooty and not hard to get working again. I think there is some merit to running a little gasoline through it before shut down. Unfortunately my alternate fuel is propane. That doesn’t help.


Hey MartyS.
A “shot”, “two squirts” could/would be from an oiler can. You know the old style you’d press the bottoms; or any style with a pump trigger.

Removing the spark plug and a teaspoon of engine oil down the hole, then pulling the engine over to distribute is standard advice putting an engine into long term storage.

Some small engines folks runout their four stroke carburetors of gasoline. Pull a line and fill the bowl with straight un-mixed 2-cycle oil.
I’d have try a few ways to see if that could be done from running on gasoline to a change over to woodgas.
Separate small gravity reservoir for the carb-oil. A three way manual valve. Fish tank supplies have all different kind of tubing valves.