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Discussion Starter #1
Never used a forum so this is new to me but hopefully someone has some good input because I’ve never been stumped this bad. Just rebuilt my 2003 Honda 400ex with a 440 big bore kit and hot rods crank. New valves and seals which were lapped and readjusted to spec. getting spark,fuel,and compression is at 110-115psi, which to me seems a little low.bike will not start only backfires occasionally. Checked timing over and over and it is correct.timing chain was stretched and really loose when I got the bike but I put a manual tensioner on and it’s tight again. piston is highest at tdc so I don’t think the flywheel key sheared.it’s the stock cam, the plunger and spring were missing and I put them back in ,still nothing.looks like someone before me cut the longer tab off of the rocker that controls the decompressor but from what I could tell that only affects the reverse decompressor.I’m at a loss and really don’t wanna sell it.Any input would be appreciated, thanks.
 

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First, welcome to the forum.

Engines are like baking - get the ingredients right and it turns out perfect every time.

If you have compression, spark, spark at the right time, air, the right amount of fuel mixed with the air, it will run.

Now the spark timing is set by the crankshaft and as long as the flywheel key is good, then spark will be at the right time - so you say you have spark and compression - we don't know about fuel and air yet and when you say you have checked the timing, I presume you mean cam timing?

The only thing that concerns me is the manual tensioner - why a manual tensioner? Most people tent to over tighten the cam chain and that can prevent starting or make starting very difficult. The manual tensioner cannot be properly set without the engine running.

Here's my suggestion - back the tensioner off and run it in by finger just to the point you can feel it pushing on the chain, then back it off 1/4 turn - remove the carb and check the compression - should be at least 120 psi - if the compression is good, spray some starting fluid in the intake while cranking the engine - it should start and try to rev uncontrollably, but it will only run as long as you give it a shot of starting fluid - once you know the engine will run, you are down to fuel and air - service the carb and it should be good to go - if it won't run with starting fluid with the carb off, then it's mechanical (spark, spark timing, cam timing, valves, piston rings, piston to cylinder clearance............), but something perhaps off a little.

If someone cut the decompressor tab off the rocker arm, you might as well remove the spring and plunger from the head that activates the decompressor ans it will do nothing other than possibly cause noise at idle - if you want the decompressor to work, you will need to replace the rocker arm.

Let me know where you get with this.

Sorry for the late reply, but I run a motorcycle/ATV repair shop and have been busy with inventory and end of year accounting routines. I have an 05 TRX400EX and built a 460 (440 with a stroker crank) for a friend who races flat track.
 

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Never used a forum so this is new to me but hopefully someone has some good input because I’ve never been stumped this bad. Just rebuilt my 2003 Honda 400ex with a 440 big bore kit and hot rods crank. New valves and seals which were lapped and readjusted to spec. getting spark,fuel,and compression is at 110-115psi, which to me seems a little low.bike will not start only backfires occasionally. Checked timing over and over and it is correct.timing chain was stretched and really loose when I got the bike but I put a manual tensioner on and it’s tight again. piston is highest at tdc so I don’t think the flywheel key sheared.it’s the stock cam, the plunger and spring were missing and I put them back in ,still nothing.looks like someone before me cut the longer tab off of the rocker that controls the decompressor but from what I could tell that only affects the reverse decompressor.I’m at a loss and really don’t wanna sell it.Any input would be appreciated, thanks.
Just opened this but ya think you might want to check valve adj? Also sounds like it’s flooding. Mine done this an mine done this bad a few weeks ago an don’t know why but took hooking jumper cables up to my truck to get it to finally start!
 

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Just opened this but ya think you might want to check valve adj? Also sounds like it’s flooding.
Mine done this an mine done this bad a few weeks ago an don’t know why but took hooking jumper cables up to my truck to get it to finally start!
Sorry for jacking up your post btw

No problem - I fixed it
Here 2 help
 

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Discussion Starter #5 (Edited)
I put a manual tensioner because with the original one the chain had a lot of slop and I plan on replacing the chain soon but wanted to get the motor running first.checked compression again and only got 75 psi valves were all seated perfect so I assume it’s because I reused the head gasket I thought was still good because I never ran the engine.new gasket comes today. I had the jetting extremely rich ( piston was soaked when I took head off) so I swapped them back out to what was previously in there when I got it, which I thought was a bit lean for the big bore(38 pilot and 148 main). I also replaced the cut rocker arm to eliminate the decompression as an issue. I figured it was something to do with the battery not having enough cranking power so I’m gonna try hooking it up to my car and give it a good jump and see how that goes. Thanks for the replies , ill keep you guys updated
 

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I put a manual tensioner because with the original one the chain had a lot of slop and I plan on replacing the chain soon but wanted to get the motor running first.checked compression again and only got 75 psi valves were all seated perfect so I assume it’s because I reused the head gasket I thought was still good because I never ran the engine.new gasket comes today. I had the jetting extremely rich ( piston was soaked when I took head off) so I swapped them back out to what was previously in there when I got it, which I thought was a bit lean for the big bore(38 pilot and 148 main). I also replaced the cut rocker arm to eliminate the decompression as an issue. I figured it was something to do with the battery not having enough cranking power so I’m gonna try hooking it up to my car and give it a good jump and see how that goes. Thanks for the replies , ill keep you guys updated
I put a manual tensioner because with the original one the chain had a lot of slop and I plan on replacing the chain soon but wanted to get the motor running first.checked compression again and only got 75 psi valves were all seated perfect so I assume it’s because I reused the head gasket I thought was still good because I never ran the engine.new gasket comes today. I had the jetting extremely rich ( piston was soaked when I took head off) so I swapped them back out to what was previously in there when I got it, which I thought was a bit lean for the big bore(38 pilot and 148 main). I also replaced the cut rocker arm to eliminate the decompression as an issue. I figured it was something to do with the battery not having enough cranking power so I’m gonna try hooking it up to my car and give it a good jump and see how that goes. Thanks for the replies , ill keep you guys updated
As far as jetting goes that does sound a little lean my stock bore new rebuild with stage1 full exhaust an no choke is 42/170
 

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Jetting for a 440 is the same as for a 400 - it's not the size of the engine that determines jetting, it's the size of the carb.

If no changes are made to the intake and exhaust, then the jetting is the same with minor changes for idle and top end.

If the exhaust is changed, then changes for top end is required RPM.

If the intake is changed, then it affects idle, mid-range and top end.

There is no way to know what the final jetting will be without a dyno or many runs using the seat of the pants dyno.

First jet for idle (if needed) - usually only one size larger jet is required - no more than two and it's rare for an engine to need the idle to be richened up two sizes over stock - stock is a 38 so a 40 might be in order if the air box is opened up and a K&N filter installed. even with a K&N if the lid is on the air box the only adjustment to idle is the fuel screw to get the smoothest idle possible.

Until you are over 3/4 throttle, the main jet is not even needed.

Start the engine ride moderately until fully warm (about 15 minutes) and make some mid-range straight line runs at various partial throttle settings in 4th or 5th gear - if it does not blubber (too rich) or surge (too lean) then the slide needle is fine and now go for top end.

It should rev linearly and smoothly from about 1/8 throttle until topped out - if it runs clean and then falls on its face like the choke is on - it's too rich - if it runs clean up to a point and just loses power and acts like it wants to to more, but can't - it's too lean.

There are no charts to say which jet to use if you have this header and that air filter or if your set-up is with or without the air box lid - it's up to you to adjust the jetting for your set-up.
 

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Discussion Starter #8
I have tried all of your suggestions and still nothing just a loud backfire from the exhaust and no start.put a brand new battery coil and spark plug cleaned carb for the 3rd time adjusted valves again and again. I have no clue what this could be.
 

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It's just a machine - if everything is right it will run. What is not right? Start with the basics; what's the compression? How did you time the camshaft? Please detail your procedure.
 

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Discussion Starter #10 (Edited)
Compression is 105-115 (keep in mind this bike has never ran with this full rebuild)timed it by lining the t up turning counter clockwise and then put cam in lobes down marks lines up with the head.it’s getting fuel and spark. Im going to check the flywheel key again to make sure it’s still in tact but other than that I have no clue. Everything is brand new and put together correctly, but still just a loud backfire after turning over for like 10-15 seconds. Could this be a ground issue? Cdi or stator? The frame was recently painted but I sanded all the ground areas.I adjusted the valves at tdc to .004 for intake and .005 for the exhaust.
 

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Discussion Starter #11
Tore the motor down yesterday and rebuild it from the ground up again put a new timing chain while it was apart.everything inside the motor is all good and brand new. Got the compression up to 125psi. Still no start with a flaming backfire. it’s got to be carb related or electrical somehow
 
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