boxxer 421 problem

**imagecarpetcleaning** · 11-07-2008, 01:16 AM

anyone own a boxxer 421 truckmount? i had this machine for about 5 years and now im having problems. it was working fine since early part of this year. while cleaning the engine starts making loud popping noise noise almost like muffler back fire noise but its coming from the carburetor. it stopped completely several times. i have kept it well maintained thru the years but this time the mechanic cant seem to find the problem. we checked the fuel line, changed oil,fuel filter, gaskets replaced, and today we replaced the carburetor. Help!

**Ara Klujian** · 11-07-2008, 02:49 AM

Sounds like it could be a timing problem. Also check to see if your distributer cap is not cracked.

**STEVE LOMBARDI** · 11-07-2008, 09:59 AM

do a compression test to the engine. I usually find that the right side head gasket or push rods are bent.

Steve

**Chris Sheldon** · 11-07-2008, 08:21 PM

Definitely have your mechanic do a leak-down test; it is more revealing than just a compression check. It's suprising that he hasnt done that already. I am with Steve, sounds like a head gasket to me.

You could also test the ignition coils.

**Ara Klujian** · 11-08-2008, 01:42 AM

Can you describe the popping sound a little better Mark? I know its not easy but try your best. Unless you figured it out already. Did you see flames come from carburetor?
Unrelated to flames shooting from the carb. A blocked or restricted exhaust can definately cause a loud roar to come out of the carburetor. This can happen when raising RPM quickly.

**ultracleaning** · 11-08-2008, 02:22 PM

I have a Boxxer 421 5 Years old I have had the popping noise too. it was the push rods on the right side. the exhaust push rod is aluminum, so is easily bent and hard to retrieve out of compartment, use some dum-dum on a screwdriver. after repairing I adjusted valves, has quit eating push rods.

**Ara Klujian** · 11-08-2008, 06:41 PM

Yeah sometimes a lean mixture or carbon buildup on the exhaust valve will cause it to overheat the valve and push rods can bend. Most bent push rods are on the exhaust valve(s).
That popping noise hes hearing could be from breathing problems. Or from the exhaust valve staying open because of carbon build-up. or some kind of restriction somewhere.
Whats a dum-dum on a screwdiver Robert?

**imagecarpetcleaning** · 11-08-2008, 10:59 PM

he did the compression test and said both are the same. the back fire sound comes from the carburetor. i can see the lid of the air filter moving up and down. the sound it makes its like a muffler back fire. if u can imagine the sound a of a old motorcycle engine similar to that.

**imagecarpetcleaning** · 11-08-2008, 11:01 PM

the back fire noise is coming from the carburetor. it sound like an old motorcycle engine when its in idle. put put put sound. geez i wish i could be more articulate!

**imagecarpetcleaning** · 11-08-2008, 11:03 PM

Originally Posted by Chris Sheldon

Definitely have your mechanic do a leak-down test; it is more revealing than just a compression check. It's suprising that he hasnt done that already. I am with Steve, sounds like a head gasket to me.

You could also test the ignition coils.

he replaced the head gasket

**imagecarpetcleaning** · 11-08-2008, 11:06 PM

Originally Posted by ultracleaning

I have a Boxxer 421 5 Years old I have had the popping noise too. it was the push rods on the right side. the exhaust push rod is aluminum, so is easily bent and hard to retrieve out of compartment, use some dum-dum on a screwdriver. after repairing I adjusted valves, has quit eating push rods.

did your machine stall on you?

**imagecarpetcleaning** · 11-08-2008, 11:13 PM

Originally Posted by ultracleaning

I have a Boxxer 421 5 Years old I have had the popping noise too. it was the push rods on the right side. the exhaust push rod is aluminum, so is easily bent and hard to retrieve out of compartment, use some dum-dum on a screwdriver. after repairing I adjusted valves, has quit eating push rods.

thanks i will let the technician know when i see him on monday. darn machine did again today at a job site. I wasted my entire day cleaning 2 couches and a chair. the darn machine just keeps acting up every few mins. so i had to stop and try to figure out what the problem is ..

**Certified Carpet** · 11-08-2008, 11:14 PM

Check the push rods, and the intake/exhaust valves. I'll bet one or more are bent.

**imagecarpetcleaning** · 11-08-2008, 11:16 PM

Originally Posted by ultracleaning

I have a Boxxer 421 5 Years old I have had the popping noise too. it was the push rods on the right side. the exhaust push rod is aluminum, so is easily bent and hard to retrieve out of compartment, use some dum-dum on a screwdriver. after repairing I adjusted valves, has quit eating push rods.

its weird, sometimes when i release the vaccum hose from the machine it starts normal. when replace the vaccum hose again it starts to make noise again ...this happens very often during a job.

**Certified Carpet** · 11-08-2008, 11:18 PM

Originally Posted by imagecarpetcleaning

its weird, sometimes when i release the vaccum hose from the machine it starts normal. when replace the vaccum hose again it starts to make noise again ...this happens very often during a job.

When you have the vac hooked up, your now putting the engine under a load. So if its not breathing right weather its intake or exhaust that load will drag the engine down more and thus giving you the grief your experiencing.

**Ara Klujian** · 11-09-2008, 01:31 AM

Shouldn't all of that been checked when he did the head gasket?

**Ara Klujian** · 11-09-2008, 01:34 AM

Maybe its valve lash.
A bent push rod sounds very specific. It sounds like a loud knocking sound that can be controled with varying RPM's.

**jbedoun** · 07-01-2009, 11:57 AM

Your heat exchanger is clogged. All of the blower exhaust is back pressuring the engine.

**ttkcollectibles** · 09-19-2009, 04:55 PM

Im also having a problem with my 421, the water wont pump into my Boxxer from the clean water tank.

**Jaeman** · 09-01-2010, 04:41 AM

My 421 is about the same age and I could be wrong but after $200 spent with a machanic checking it over and finding nothing, I found the top float in the waste tank need taking off but then tapping the inside rod to loosen the inside spring unit which fixed it. You can check by cuting out that switch altogether and see. Man it brassed me off too. Runswell ever since.....