16hp Duromax running lean

[justinduke]

I have a new 16hp duromax that is running lean. Is there any way to adjust the fuel mixture on the carb? The only thing I can find is the idle screw. Might have to rejet I guess? If so, where can I buy jets for this engine?

And just to double check my method for reading the plug I ran the motor at 1400rpm for 20 min with a medium load on it before pulling the plug. Is this ok or is there a certain method for this? Thanks

 

[matman55]

I have a new 16hp duromax that is running lean. Is there any way to adjust the fuel mixture on the carb? The only thing I can find is the idle screw. Might have to rejet I guess? If so, where can I buy jets for this engine?

And just to double check my method for reading the plug I ran the motor at 1400rpm for 20 min with a medium load on it before pulling the plug. Is this ok or is there a certain method for this? Thanks

if you have one of those retarded epa carburators(carbs without mixture screws) then theres no way to fix it unless u get a new carb

 

[anderkart]

When i wanna take a plug reading, I run the engine for a few minutes just to warm it up first. Then shut it off and instal a brand new spark plug. Then restart and immediately go out and ride the kart wide open for 15 or 20 seconds, then let off the gas pedal, hit the kill switch and stop the kart. Then I remove the plug and take a reading.

 

[anderkart]

if you have one of those retarded epa carburators(carbs without mixture screws) then theres no way to fix it unless u get a new carb

Yeah but he can simply drill the main jet slightly larger if its running lean.

 

[justinduke]

I will redo the plug reading and run it closer to full throttle. Somebody I was recently talking to said the plug won't show an accurate reading unless you add octane booster. This didn't sound right to me. Anybody heard this before?

Are there any similar motors that use the same jet as this one so that I could just swap one of those jets in?

I would like to have a spare set of jets on hand before drilling just in case I ruin the stock ones.

 

[devino246]

I will redo the plug reading and run it closer to full throttle. Somebody I was recently talking to said the plug won't show an accurate reading unless you add octane booster. This didn't sound right to me. Anybody heard this before?

Are there any similar motors that use the same jet as this one so that I could just swap one of those jets in?

I would like to have a spare set of jets on hand before drilling just in case I ruin the stock ones.

Whoever you talked to is an idiot.

The Duromax is a Honda clone so Honda jets will fit.

 

[Doc Sprocket]

When i wanna take a plug reading, I run the engine for a few minutes just to warm it up first. Then shut it off and instal a brand new spark plug. Then restart and immediately go out and ride the kart wide open for 15 or 20 seconds, then let off the gas pedal, hit the kill switch and stop the kart. Then I remove the plug and take a reading.

This is exactly how I do it. Running at 1400 RPM uses the carb's idle circuit and will not give you an appropriate plug reading.

 

[spyder1968]

I would run the engine for a while, pref under a load (5 - 10 minutes) to get it up to operating temperature. Switch the plug and take it for a blast (5 minutes of HARD driving) after which, DO NOT let it idle for more than 20-30 seconds before shutting it off ... THEN check your plug. Just my 2cents. I don't know if this works for everybody because I run a Tillotson carb (on a 420cc Clone), but I would think it should work for you as well.

 

[justinduke]

Thanks guys. I will redo the plug read tomorrow.

If the plug still shows it's running lean how would I determine what size jet I would need to go to?

I found some honda GX390 jets on boats.net. Are these interchangeable on the duromax?

 

[r_chez_08]

Yeah the 390 jets interchange.
IMO get a numbered drill set and go up by one size at a time until you get the right reading.

 

[justinduke]

Just checked the plug again. Warmed it up for a few min under medium load then gave it full throttle for 30 seconds straight and the plug still looks clean and lean.

I would like to buy new jets so that I have a backup set in case I decide I want to drill them out. What sizes should I try? I'm at sea level by the way so I have plenty of oxygen.

 

[Doc Sprocket]

Just to be certain- did you have it under load for the duration of the test?

Start by determining the size of your existing jet. examine it, with any luck, it's stamped. You might be able to find it on a spec sheet somewhere. Go up a size or two from there.

 

[justinduke]

Just to be certain- did you have it under load for the duration of the test?

Yeah I put it under a heavy load for the full 30 seconds.

 

[anderkart]

Are there any similar motors that use the same jet as this one so that I could just swap one of those jets in?

I would like to have a spare set of jets on hand before drilling just in case I ruin the stock ones.

You could order the "100-size" main jet here:--> http://www.affordablegokarts.com/mm...Code=A&Product_Code=HON***&Category_Code=AFC2

And then If you dont wanna buy a full set of number drill bits, I just brought my old main jet along to my local Ace hardware store. I asked and they brought out all their number bits (sold individually) so I could find the size that very-snugly fit through my old main jet, then I bought the next 5 larger sizes for under $10.

Don't use an electric drill, just clamp the drill bit in a vice (or vice grips), then carefully turn the jet by hand to drill it. I'd suggest you drill only one larger bit-size at a time, then re-install and take another plug reading.
Then if necessary, repeat using the next larger drill bit until your plugs insulator is burning a nice tan color.

If your not sure where your main jet is located, you'll find some pics and a diagram here in
this thread:--> http://www.diygokarts.com/vb/showthread.php?t=10957

 

[Doc Sprocket]

You could order the "100-size" main jet here:--> http://www.affordablegokarts.com/mm...Code=A&Product_Code=HON***&Category_Code=AFC2

And then If you dont wanna buy a full set of number drill bits, I just brought my old main jet along to my local Ace hardware store. I asked and they brought out all their number bits (sold individually) so I could find the size that very-snugly fit through my old main jet, then I bought the next 5 larger sizes for under $10.

Don't use an electric drill, just clamp the drill bit in a vice (or vice grips), then carefully turn the jet by hand to drill it. I'd suggest you drill only one larger bit-size at a time, then re-install and take another plug reading.
Then if necessary, repeat using the next larger drill bit until your plugs insulator is burning a nice tan color.

If your not sure where your main jet is located, you'll find some pics and a diagram here in
this thread:--> http://www.diygokarts.com/vb/showthread.php?t=10957

Good advice! Also- I just hold the jet in my fingers while I drill, but Bighead gave us a good one- clamp the jet into the bar assembly of a flaring tool!

DO drill just one size at a time. When I recently drilled my Doodlebug jet, I really thought I had more wiggle room than I actually did. I skipped a size, did a test pull- too rich! It's not a big deal to solder the jet and redrill smaller, but if you can avoid the extra work, go for it!

 

[justinduke]

Thanks for the help guys. I drilled it out one size at a time until I got it to 110 and I believe it's not running lean anymore. Been cleaning the plug each time but I'm just going to put a new plug in and run it again just to make sure.

Problem is that it is still low on power. It has less power than the 9hp briggs that it replaced. The briggs is around 290cc and the duromax is 420cc so I can't figure out what's up. Guess I will check compression and timing next. Any other ideas?

 

[spyder1968]

I am curious to see what you find out. In my experience, the 420cc motors have gobbs of torque! It should pull way harder than the 290cc Briggs. How old is the 420cc? Maybe check the valve lash?