Third Thursday

Ii have been invited to speak at a program KSU holds every third Thursday, called “The Third Thursday Thing”. I will be presenting the truck and giving a talk about woodgas. Here’s the presentation I pulled together. Some of the slides are from my earlier presentation with my old gasifier.

So I’ve been doing some much needed work to the wood truck, getting ready. One of the areas I really needed to fix was the ammo can under the hood, very leaky area, also not too pretty. So I solved that this morning:

Even without taping it up, the all-PVC solution is much tighter, meaning I can finally kill the engine with too rich gas. No more flex hose under the hood!

Further preperations all day…

Hi Chris, Last time I went to do a presentation at a school I blew a brake line on the way there in the middle of a thunderstorm … I was also pulling the trailer … I wish you MUCH better luck … Oh, it is good to know you can kill the engine with rich gas. Rarely happens here but when things get warmed up I can usually blend in quite a bit of air … Engine runs rough when too rich … ML

Hello Chris. Your engine compartment looks great…nice clean finished look to it. I saw it in Argos and this definitely looks better. Thank you for posting it. I will be duplicating your underhood work with my carbureted Ford and am glad I saw this post. By the way, what is the throttle body that you used from? Did you acquire it from a junk yard or is it something you had to buy new?

That looks really good. Can you explain about not having any butterfly adjustment on the wood gas. I know you have a throttle body just past the mixer for engine power, but is there not a need to regulate W/G ?? Also did you use 2" PVC??


Hello Chris,
Great presentation. I can’t see your new and improved engine compartment. The photo is just black. That particular photo is truly worth a thousand words. Any miles on the improvement yet?



I guess it just took a long time to load. I will go watch it now.

Richard Craig

Hi everyone,

Thanks for the compliments, it really was bugging me and I have it fixed pretty well. The throttle body is out of the junkyard, just a nice large bore throttle body. All secondary or idle passages must be closed, this one didn’t have any.

Carl, all the plumbing is dual 2" PVC, they do join to a single 2" right into the carb riser but that’s a necessary compromise.

There are different schools of thought on the valves, how many and where. For a dual fule engine you must be able to regulate the fuel air mix for both, and shut off both when they aren’t being used. The throttle body also serves as a shutoff for the woodgas, and the regualr gasoline throttle also serves as a shutoff for the gasoline, although not a perfect one. The carb mixes air with the gasoline, while the single butterfly valve mixes air with the woodgas.

I just made a critical discovery which will be posted elewhere as well. My carburetor is getting considerable airflow through it when running woodgas. Yes it is! I can put my hand over the intake to the air cleaner and it richens considerably. The throttle is closed, but there are small idle passages built in, to allow closed-throttle idling, I must find and plug those! If I could block ALL the air from the carburetor I should see a considerable drop in gasoline consumption and be able to control the air fuel mix much closer! I just figured this out like 30 minutes ago. Still processing… But I think it means the rest of my system is very tight, and a bit less than half of the air is coming through the carb. It was more than half, which is why I couldn’t kill the engine. Now it’s slightly less than half. Once plugged I could have a big gain in performance.

I guess your find with the air passing through the carb is what Wayne and others refer to as part of “the other 75%”. Good catch. Do let us know how your performance changes once you eliminate this source of air.

OK, after further experimenting (and data I knew from earlier) I am getting a weird phenomenon, and will have to consult a carburetor whiz… When I close off the choke entirely with the throttle also closed I get a massive flow of gasoline, wildly changing the mixture. Enough gas comes out to run the engine, I can lean the air out all the way. it’s akin to opening the throttle a bit… But open the choke and gasoline flow stops. Again we didn’t touch the throttle, all the way closed but has idle passageways.

Any carb experts want to take a guess?

HA HA, Now you understand why I shy away from short warm up competitions. There is almost no way to fully turn off a carborator. It has to be run fully dry and I mean to the last drop. My 66 chevy got the best of me when the solenoid I used on it was leaking a bit through. I was so proud driving 65 mph until I fixed it. With fuel injection I believe when the fuel pump AND injectors are turned off there is little chance of a liquid dribble. I have yet to find time to add my dribble switch to the cavalier. It is going to take 1.65 ohms of nichrome to make it right. Maybe this weekend I’ll get it rigged up. Was 100 here today … Too hot for this fat old fkr … New cyclone is built and needs testing and filter is cleaned and ready to pass way more gas than it did last week … ML

Hi ChrisKY
No guessing - observable fact.
When you close a carburator choke flap up stream of the gasoline/emulsifier jets the purpose was not so much to choke off the air flow but to create a temporary low pressure zone to suck more blended/emulsified gasoline out of the float bowl through any jet/orifice possible for cold cranking engine enrichment.
Old British SU and German side draft Solex gasoline carburators used a cable pulled dropping main needle nozzle sheath to allow greater fuel flow for cold starting versus a choke plate. Worked poorly for cold cranking enrichment in comparison.

Now IF you modify for better carburetor throttle plate sealing while operating on woodgas it would have to be from the cab running reversable to be able to allow enough air again to idle on gasoline.

Carburetors really do suck man.

Steve Unruh

Hi Steve,

Just had a long chat with a long time carb guy who basically told me the same thing… So my plan now is to try and seal the throttle plate better, and plug up any idle bypasses allowing air in. This should allow a perfect vacuum under the throttle plate. I can hopefully idle it by opening the throttle a crack. Going now to shut off the idle mix screws. I will also try running the carb dry to see what effect it has.

looks great, the under the hood stuff, is not my strong point.

Chris, There is one thing you can try that I used to do with propane conversions and that is to hook a tube to the vent on your carborator and apply a vacuum to it and it will usually virtually turn off the flow through it. I’m guessing you have a 2 barrel on that with a one hole inlet and one vent tube. That system worked perfect on my old ford truck at any rate. I just had a valve in the cab with some extra rubber tubing out to it … ML

Hey Guy’s, I havn’t posted before. But I just had a thought. What if You mounted a throttle body or butterfly valve under the carb. That way You could shut off the carb altogether when running on woodgas.

That would work Sheldon, but it would have to be airtight. Even the machined throttle plates aren’t airtight. Any leak will allow vacuum to build up and pull gasoline out.

The real solution is to drain the carb. I’ve been avoiding this but I think it’s time to try it. Looking at fuel shutoff solenoids now.

adding a spacer under the carb can also change how you have to jet the carb… or atleast that is something i heard back when i was in autoparts

OK, I shut off the idle screws and it did exactly as you’d expect - it won’t idle but you can rev it on gasoline. This measn it’s not getting any gasoline at closed throttle. Now there is still some air getting past the carb, due I think to the idle air passageways. I will plug those up at my next opportunity. For now all this means is I run the mixer nearly closed and accept the air coming through the carb as part of my secondary air supply.

On the vehicles I have used with a carb I also had an electric fuel pump on them.

On some of the older VW motors they had a solenoid on the carb, And when you kill the switch the fuel shut off. I have had a dune buggy or two that I learned this from. This might be a good carb to use on a wood gas ride.