[Fourtrax 400]

So I have this 2004 Honda Rancher TRX 400 FA which has performance issues at low rpm, I picked up a carb kit for it, thinking something might have gotten plugged up as it sat awhile, and a compression tester as well as I had noticed air coming out of the oil dipstick w/ the engine running.

I measured 73PSI on an cold engine. I dumped a bit of seafoam down the spark plug hole to maybe get the rings unseized as it is a 14 year old machine and only has 300 hours.

I will also try adjusting the valves tomorrow. I would like to get around a top end rebuild if possible because a seal kit (not including valves) runs me around 320$CAD at my Honda dealer.

Any suggestions what I might try??

Thank you!!

 

[wheelsquad]

So I have this 2004 Honda Rancher TRX 400 FA which has performance issues at low rpm, I picked up a carb kit for it, thinking something might have gotten plugged up as it sat awhile, and a compression tester as well as I had noticed air coming out of the oil dipstick w/ the engine running.

I measured 73PSI on an cold engine. I dumped a bit of seafoam down the spark plug hole to maybe get the rings unseized as it is a 14 year old machine and only has 300 hours.

I will also try adjusting the valves tomorrow. I would like to get around a top end rebuild if possible because a seal kit (not including valves) runs me around 320$CAD at my Honda dealer.

Any suggestions what I might try??

Thank you!!

If you do go the path of a top end rebuild, I would consider these guys:
Honda TRX 400 Rancher Engine Motor Top End Rebuild Kit and Cylinder Machining Service - G&H Discount ATV Supply

 

[mrbb]

I doubt any oil down a cylinder will fix low compression
but ??

 

[retro]

I would not be the least bit concerned about that 73 PSI reading unless there is other supporting evidence that the topend is worn out. The reason being, there is an automatic decompression mechanism on the end of the camshaft... those tend to behave very inconsistently at starter cranking speeds.

Also, since the spec is only 107 PSI @450 RPMs if your compression tester requires that you attach an adapter to fit the spark plug hole, you'll always get a reading well below the spec, simply because the low-pressure schrader valve is not installed in the end of the adapter. You're effectively adding volume above the piston when you use an adapter. And most of them are too short, which adds ever more volume.

So nevermind your 73 PSI reading at this point. And nevermind air exchange while the dipstick is out... thats perfectly normal behavior. Adjust valves, clean the air filter and make sure the crankcase vent is connected up right, change motor oil & filter, clean the fuel tank & carb and run it for a while. If the topend is worn out it will let you know through other, more obvious signs.

Follow the service manual word-for-word as you work and let us know how it goes if you can.

 

[retro]

I dumped a bit of seafoam down the spark plug hole to maybe get the rings unseized as it is a 14 year old machine and only has 300 hours.

Before you crank that motor over again oil the cylinder down with an ounce of motor oil poured into the spark plug hole, or flush the cylinder with 2-cycle premix at 24-1 ratio to replace lubricating oil that the solvent washed away.

300 hours is nothing... I imagine your motor will be found to be in excellent condition once you get the fuel system & carb back in tip-top shape.

 

[mrbb]

I dumped a bit of seafoam down the spark plug hole to maybe get the rings unseized as it is a 14 year old machine and only has 300 hours.

300 hours is nothing... I imagine your motor will be found to be in excellent condition once you get the fuel system & carb back in tip-top shape.

300 hours can be LOT pending HOW Them 300 hours were added ??
I have seen treads and known of folks ruining a brand new ATV in a few minutes of owning them, NOT even an hour on motors and in need of motor work

so, hours are only PART of the picture to things

lots of folks take atv's swimming these days LOL
some one maybe needs to come out with a life jacket for them ! HAHA!

 

[retro]

Yeah thats true! I saw a guy break an anvil once... some folks are just real good at ruining stuff!

 

[Fourtrax 400]

I just started working on the atv and saw this when I removed the crankcase breather from the air box. What is it? Is it normal? Thanks!

 

[retro]

That is water mixed with motor oil. You can get that two ways:

1) Condensation of water vapor inside the crankcase. This frequently happens to some degree each time the motor is started cold, used for a very short period of time, then shut off... before the motor reaches operating temperature. Repeat that scenario many times and condensation buildup inside the crankcase becomes a very serious problem.

2) Water entered the crankcase.

Did you just buy this bike? Was it ridden in deep water or sunk?

 

[Fourtrax 400]

Yes I just bought it. The seller claimed that it was never used for mudding but who knows... the engine oil on the dipstick hadn’t looked foamy at all.?

 

[Fourtrax 400]

But it is possible that it is from the frequent on off cycles. Supposedly it was used for laying temporary phone wires beside the highway

 

[retro]

Was the motor oil fresh and clean looking when you bought the bike? If so, the seller may have sunk the motor, changed oil a few times to flush it out.... you get the picture...

If not, but the old, used oil showed no other signs of water being in it, then its probably just condensate inside the breather hose. That hose does not ever reach normal oil temperature, so condensate inside the hose cannot get boiled off once it forms.

Have you adjusted the valves yet?

 

[Fourtrax 400]

This is the oil in it currently. I haven’t changed it yet. I did not notice any signs water being in the oil.

 

[Fourtrax 400]

No I haven’t done valves yet. Just tearing into the carb

 

[retro]

Oil looks used... its probably gonna be a fine motor. That carb doesn't look too bad either for having been stored for a long time. No corrosion that I can see anyway.

If you're still concerned about a compression test there is a trick you can do for working around those inconsistent automatic compression releases. This works on every Honda ATV that has an auto decomp cam on the camshaft.

Once you get the valves adjusted (and before you put the valve cover back on) run a compression test and write the max pressure down. Then loosen the locknut on the exhaust rocker arm and turn the adjuster screw out (increasing valve lash) 1.5 turns, hold the adjuster screw still and snug the locknut down temporarily. The exhaust valve gap will be very loose... Then run a compression test and write that max pressure down.

Once you've got both compression tests done, readjust that exhaust valve to the proper lash, tighten the locknut, recheck the lash, and put the valve cover back on. You're done.

Backing out the exhaust adjuster prevents the auto decomp cam from holding the exhaust valve open at cranking RPMs like it normally would. Your max pressure should be about 175 PSI (or higher) unless you used an adapter on your tester. If you used an adapter the pressure will be lower that 175, but likely at least 130 PSI or more... depending on the compression volume lost to the adapter.

Some gauges are very inaccurate too, so judgement is always in play when running compression tests.

Let us know what you find out...

 

[Fourtrax 400]

Thanks for letting me know about that trick. It’s not likely that I’m getting low compression due to carbon buildup on the valves, is it?

Carb is cleaned up, will start putting it together now if I can find out where all those little parts from the kit go lol

Picture of the intake valve:

 

[retro]

That intake looks fine... got photo of the exhaust valve/port?

A leaky valve seal on the exhaust valve (more common because the exhaust valve stem runs at a hotter temp than the intake valve stem, which leads to deteriorated exhaust seal quickest) will cause oil coking & caking on the seat and valve. They rarely leak because of that caking though.

Carbon buildup on the valve seats can cause them to leak slightly, but during a compression test you are likely to leak more pressure around the o-ring seal tightened against the spark plug hole, than you'd find leaking past a carboned valve seat. The valves & seats are self-cleaning due to their 44 & 45 degree seat angle design.

 

[retro]

Here ya go in case you don't have a manual handy.

 

[Fourtrax 400]

Thanks. I did print out part of the manual from this site.

My carb kit didn’t come with a main jet. Can I reuse this one or should I get a new one?

 

[retro]

You should reuse every OEM jet if each are in good condition, because OEM is more precisely matched to the application than any other aftermarket jets are. So if corrosion has not compromised a jet and you can get it clean inside and out, reuse it.

I generally use the gaskets and o-rings from aftermarket kits only, but I never use an aftermarket jet in a rebuilt carb. That practice pays big dividends!