Exhaust coming from intake

Today I did a 2nd test run of my charcoal gasifier.Its a simple fire made from a 16 gallon drum with a 1 inch inlet and outlet. It ran my 7250 watt predator well for 15 minutes before I shut it down.

One thing i cant understand is how i am having what feels like constant positive pressure coming from my intake ball valve with occasional exhaust fumes, instead of suction. My cloth filter going into the intake was even slighlty burned.

The 1st test ended after 2 minutes with a small part of my foam filter coming apart and blocking the intake. I removed the blockage from the intake today but wonder if there could be another piece wedged farther in? Seems unlikey.

Basically i am wondering how my engine can run so well with exhaust coming from the intake? Is this a problem, what is the cause? and how should it be fixed?

Its almost like the intake is pulling air in and pushing exhaust at the same. Or alternating between vacume and positive pressure within each cycle of the engine. Doesnt make alot of sense but i have slight vacume at the intake of the gasifier and its running so it has to be.

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Hi Taylor.

Pulsation is normal on a intake manifold but smoke is not. If it was a leaking valve l dubt it wuld run so good. Does the engine maybe have a crankcase vent in the manifold? It may be piston blowby thats showing as smoke.


Thank you for the response. I was not aware that pulsation was normal just knowing that makes all the difference.

The engine has 2 vents. If I am thinking right one is a tank vent. The other vent is most likely a crankcase vent they are both currently unhooked from the carb.

The exhaust that i saw could have been small amounts of char gas being pushed out the intake as well. That would make more sense now that i think about it. I will have to do some more test to see if my gas was to hot and if that was the cause of the filter burn or if it really was hot exhaust.

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Taylor can you take a photo of how you have your filter set up?


What Cody sayd. Good chargas shuld have no colour whatsoever. If its visible it either means your charcoal is wet (bad) or tary(wery bad)


You have just entered into the 75% woodgassers talk about—25% time building and 75% learning to run it. TomC



The last picture with the red cloth is inserted into the into the intake in the first picture.

I have 2 set of ball valves so the engine can be run on gasoline while the gasifier is running without stalling the engine. The reason i have done this is because i transition to chargas by shutting off the fuel shut off vavle .It takes about a minute to start running low on gasoline. If the gasifer is making alot of gas already it will stall the engine if i dont wait for it to start running low on gas. I realize i could start the gasifer through the suction of the engine but so far i have let my unit get warmed up before trying.


The picture with the junction box has a foam filter in it that is posistioned before the ball valves.

Disregard the second picture it was a mistake.

Also i will admit my charcoal was wet on this run. A rain storm caught me off gaurd and it got in a open storage barrel. The gas was much hotter then usual from the moisture in the chargas. Alot of times the chargas is invisible.


Hi Taylor sometimes its very hard to understand systems from photo’s it would have been nice to have seen the gasifier and downstream system set up , so i will just mention what i can see from the photo i did understand , the red cloth on the end of the pipe that you push into the air intake of the carb , is no good at all , for a few reasons one is that the area you are filtering out is very very small and will soot up very fast , do you have a filter box before it with finer material in it ? if so then just use that , also if soot and small particles get into your engine it will foul up your valves and they will not seal as they are meant too and yes you will get back fires and that cloth will maybe singe or worse still get sucked into the engine .
I love the simple way a simple fire can be used just remember to not over complicate yours too much keep it nice and simple .
All the best Dave


I’m not the biggest fan of a foam filter. I’ve tried using them and they just clog up and the soot creeps around it.

Check out Matt’s sawdust filter. You don’t need to weld just use pipe floor flanges and red RTV to seal it. Use window screen to keep the sawdust from going into the engine. Simple 50 cal ammo box design.


Hi Dave thanks for your input.

Is the cloth filter still bad if that is a secondary filter that cannot get sucked in? I have a foam filter before it. Or does it just need to go all together?

I will try to get some pictures up of the whole system.

Also I would be curoius to know anyones input on the wet charcoal. How dangerous is this as far as corrosion goes? I know sometimes people run stuff so dirty it gets filled with tar and they have to disamble and clean the engine before it will run again but corrision is usually not mentioned.

Would running gasoline after using wet fuel be good to try and clean things up or atleast evaportate the moisture to prevent rust/corrosion?

I have seen his and actually bought some ammo boxes. I will make one thanks.

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The problem with that cloth filter is the surface area is too small.

If you wanted to make a cloth filter sew up a bag from towel material or cotton canvas. For that engine I think a bag about as big as those reusable grocery bags would be a good size. It would need to be inside a box.

Also yes running gasoline will help clean up your valves and prevent soot from clogging your jets as badly. Maybe just when shutting down, fill up the float bowl and let it run dry again.

Here’s what my ammo box sack filter looks like for the Mazda B2000. I welded these pipes in but had to seal with RTV back when I had my crappier welder. I just hose clamp the bag to the pipe coming from the lid. The lid pipe is where the filtered gas leaves.

That way all the excess soot will fall off and settle in the box. You could also use sawdust with this box if you hose clamped some window screen over the exit pipe.

Here’s what foam did in this same filter box. Clogged and then slipped past. Lots of carb cleaner was necessary to unclog my jets.


Hi Taylor , the no 1 best choice for a quick and cheap filter material goes too Wool , yes those old jumpers knitted for Christmas many years ago that shrunk in the wash are perfect so are old socks blankets well you get the picture they also wash out pretty good as well .

The wet charcoal can cause a few problems for you , apart from maybe making it hard to get going you will hear a few pops and crackles from your nozzle to start with , then as it gets going you will start getting far too much water /condensation in your gas line , filters and engine , that will if left for any length of time will seize up the throttle butterfly in the carb , running the engine on petrol after the charcoal run will help but you will need to run it for at least 10 mins to help dry out and clean up the intake and cylinder valves , i also used to give the intake a quick spray of WD40 just as the engine stops as i have servo motors on my carb that got stuck with the smallest amount of dust on the butterfly , but i only did that if the charcoal i was running was wet , Oh and you will also get that a very strong smell of Ammonia on your filter material .


Thank you. My charcoal is always a little damp because of high ambient humidity.

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Edit: moved this to Marks topic to not clutter this one

Thank you. I am gonna jump this thought over to my S.E.M.F.S. thread so as to be polite and not hijack BH’s thread.

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