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Discussion Starter #1
Just finished restoring an ‘04 TRX450R, bought it stock from original owner. Project took several months, waiting on various suspension parts. Ran good prior to tearing it apart and modding. Having an issue now with mid-high throttle range that I cannot figure out.

Bike starts easily, idles smooth. Quick snappy throttle pick up to about mid throttle, with a load on engine or without, then it cuts out and sputters. I tried several different jetting combinations and/or fuel screw settings and no real changes to problem. It runs awesome down low, will not pull to the top. Pops very little on decel, not thinking it is lean at all. Riding at 1000-2000’ elevation, 50-60 degrees. Stock carb other than jetting, no ignition changes, brand new spark plug.

Here’s what went into the bike performance-wise...

Pro Circuit full exhaust
Velocity intake, K&N w/ prefilter
Hot Cams Stage-2
Dynojet needle

Jetting:
50 pilot (did not try changing this)
Tried 180, 185, 190, 195, and 200 mains.
Tried needle on 3rd, 4th, 5th clip positions.
Tried screw all the way from 4 turns to all the way in.

Weird part is that if you stop it, let it sit for just a few minutes, then start and go right away, it pulls hard all they way to the top, but within just a minute or so it starts losing the top end again, and it seems to be at lower and lower RPM that it stumbles until it levels off at like 1/4 throttle. Ride all day at this level, but try to rev and it cuts out almost like a rev limiter. To me feels like it is not getting fuel, like the float bowl is getting emptied out faster than it can refill, or the flow from the tank is restricted. I removed the inline fuel filter thinking this was the smoking gun, no dice. Just feels like it is running out of fuel.

Only other thing to note is that the fan never comes on. When first starting it up the red overheat light comes on for about 2-3 seconds then goes out. Could it be overheating anyway? How often should fan run? Not smoking or losing coolant or and milky oil.

Any help much appreciated!
 

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Discussion Starter #2
Also, I adjusted the valve lash during the cam install, was very careful not to let the cam chain move on the sprocket, triple checked TDC alignment of cam and crank.
 

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Discussion Starter #4 (Edited)
Check the vent in the gas cap.
Good idea. I had also installed a IMS tank as part of the build, with an Alba stubby gas cap vent, thought for SURE this was going to be the easy fix. Took the Alba vent off and found it difficult to blow air through, so I swapped it back to the stock vent hose. Rode it up and down the street after warming it up, pulls hard to about 1/2-3/4 throttle and starts cutting out. So problem did not go away. Ugh

Still looking for ideas. Took carb apart and didn't see any problem with the floats, will also triple check the valves and timing again. Bad spark plug or ignition maybe...? TPS sensor ohm readings were slightly off so I adjusted that to within spec. Nothing is making sense here. Problem feels more like 'surging' than 'blubbering', so gonna go richer and go to the 5th clip down on the needle, even though that seems crazy rich to me with the 200 main in it. Looking through other people's jetting specs with cams and intakes and that doesn't seem right, but will try anyway. Thanks
 

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Making HP ain’t free. . .
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I would go the other way on jetting, you are way too fat. Might not be your main issue, but it’s definitely not helping. being rich will cause a false rev limiter well below the actual limiter. Since your problem isn’t until it’s warmed up it may not be related to the main jet size, but it could be part of the issue.
 

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Discussion Starter #8 (Edited)
I would go the other way on jetting, you are way too fat. Might not be your main issue, but it’s definitely not helping. being rich will cause a false rev limiter well below the actual limiter. Since your problem isn’t until it’s warmed up it may not be related to the main jet size, but it could be part of the issue.
I hear ya, I thought the jetting was way too high as well, but as I went lower it just didn't seem to make any noticeable difference. And it always felt like it was starving on top, not overfed. But what you are saying makes sense, when it does start cutting out it kinda feels like a rev limiter scenario to me too. It's not so much a cold/warm issue as it is I noticed if it sits, off, for a couple minutes it seemed to run better initially (still warm), right upon start-up when I just took off and ran it up high in the rpm, then the problem returns very quick, progressively worse until, after riding for few minutes, you cannot get above about 1/3 throttle or so without it cutting out. That's why I was leaning toward a fuel delivery issue, but fuel seems to be flowing good, and the floats and float valve look to be unhindered.

A couple other details I can throw out there that may spark more input...

I bought a Moose DynoJet Stage 1/2 jetting kit off eBay (because I could not find the HRC needle that I wanted available ANYWHERE), but the only part from the kit I am using is the needle. The main jets I am using are Keihin, not the goofy, adapter-required ones that come from DynoJet. Not sure if the taper of their proprietary needle could be an issue here? Another thing, just remembered, the DynoJunk kit came with a tiny brass plug for the "main air jet" on the intake side of the carb throat, which I installed, you tap it into place with a small tool, seems unlikely but could blocking this main air jet be part my problem? Dyno also wants you to use a small washer above your needle clip, below the needle plate. I put it in but seems to me like it would have no effect on actual jetting.

The bike was torn down pretty far during the restoration, didn't remove the motor or pull off the main wiring harness but did unplug/plug a lot of stuff. Could it be something ignition related? If there was a busted wire or bad connector in the ignition system which one might cause this?

I still have the stock airbox on hand, could try reinstalling that. Same with the stock cam. Really prefer not to go that far backwards if at all possible.

I've owned several dirtbikes and quads over the years, including two early model 450x dirtbikes which I modded fairly heavily as well, never had an issue like this. I'm so confused at this point. But I'm not the kind of person who takes my bike to the shop for anything, so figure this out on my own I must...

Thanks again for any thoughts or help along the way!
 

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Making HP ain’t free. . .
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Personally, I would try going leaner. The fat false rev limiter does kinda feel like it’s fuel starved, but it’s the opposite.

I remember sticking a piston (I think 12:1), cam, exhaust, and no airbox lid on a 450 and started at 180 main, it ran like junk. Ended up at like a 162 IIRC and that’s where it was happy and made power. Can’t remember what it made on the dyno, but it ran well.

I wouldn’t try pulling parts, just keep moving forward with what you got. It’s pretty unlikely that any electrical connection would cause your issue, usually it either works or doesn’t. The only electrical related thing I would try is a new plug if it’s an old one.

back in like ‘05 I installed a DJ needle and jets and the plug. Needless to say, I removed it ALL and never touched DJ anything again. I would start with pulling that plug, should help with how it runs on the top end. And maybe even go back to the stock needle.
 

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The issue you are describing is not mechanical (they very rarely fix themselves and I've never seen one fix themselves for a minute and the f-off again). That leaves the fuel system or the ignition system. I don't see that you downgraded the CDI box to a double throwdown, worth 25hp, chinesum CDI box. So I would start with the fuel system easier and cheaper. Pull the fuel line off the carb and turn on the petcock and check out the flow if good put the fuel line back on and drain the float bowl leave the drain screw open and turn on the petcock and check out the flow (new gas tanks sometimes have shit floating around in them).
 

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Discussion Starter #11
Good copy on all counts. Yes, no CDI box changes were made. I will dump the DynoJet needle and try the stock needle again. As far as the jets, looking at jetting threads it seems like the '04/'05 models like mine are completely different then the '06-on models, much larger both pilot and main jets. Guessing that it was because the carb was smaller? What year was that 162 main in? I already checked the tank flow after changing the vent, took carb apart cleaned and checked for debris, but will double check bowl flow out the drain to be double sure. Will also pull the plug, and put a new one in just to rule it out.

Thanks!
 

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162 is for the 06+

So its cutting out above mid throttle? checked the stator out yet?
 

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Discussion Starter #14 (Edited)
Update...
Verified that I have plenty adequate fuel delivery all the way to the float bowl.
Changed back to the stock needle, 3rd (middle) clip.
Removed the tiny brass plug from the air jet port, the one that came in the DynoJunk kit.
Double checked the new cam orientation to TDC, and the valve lash.
Removed and replaced the spark plug, looked like a good medium brownish color, not oily and not chalky.
Changed to a 165 main jet.
Blew air through the whole carb and double checked pilot was clean.
Put the stock fuel screw back in (did notice the aftermarket one I had in there wasn't exactly the same length, where it seats), 2.5 turns.

Started first kick with choke, then idled great, snappy throttle response (right off idle to about 1/4 throttle, I don't like to hit it too hard when in neutral).
Warmed it up. Rode it up the street (sea level at home here), opened it up, falls right on its face about 1/2 throttle. Almost seems worse than before now.

Changed to a 185 main, nothing else, rode it again...no real changes, same problem. Popping a lot on decel now, obviously lean. When it "falls on its face" it's almost like the motor just quits for a second, like a brief stall. And if you hold the throttle at that point, or push it even further, after about a second it comes back and surges hard briefly, then falls off again, etc. It's enough to send you sliding forward on the seat when it happens. It's crazy that it pulls so HARD up to that point and then it's like somebody starts moving the kill switch back and forth, but slowly.

Since I really do think I am in the general vicinity in terms of jetting, and I know I have fuel and air, I'm really thinking it is something with the ignition, like CJM said maybe the stator. I'm perfectly capable of throwing parts at it on my own, but would really appreciate some insight from others into where to start. The shop manual, under TROUBLESHOOTING, lists "faulty ICM" and "faulty ignition pulse generator" under the "ENGINE LACKS POWER" section. Looked them both up but do not see a good way to test either. Replace one? Both? Thinking a stock ignition control module would be the best choice, but as far as a stator maybe I should upgrade with a TrailTech or a rewind since I am there. Does a new or rewound stator usually come with the ignition pulse generator as well?

Thanks
 

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Discussion Starter #15
No replies so I went ahead and ordered a high output RM stator, and a Dynatek DSF1-13 CDI (non-programmable). We'll see how that affects things.

Is a regulator/rectifier and/or coil worth going after in my scenario if the above do not fix the problem?
 

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Making HP ain’t free. . .
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Sorry man, I got to thinking about it and was going to say I could send you some parts so you could try swapping them to see if it helped, wish I would’ve replied sooner! Again, sorry. I would start with the stator first. I had a bike I was working on, it would like nda start, ran ok for a bit then when warm ran like crap. Replaced the stator with a “good” used one and same issue, I chased the problem for quite awhile, finally bought a new RM stator and its ran perfectly and starts perfectly ever since. Hopefully that’s what your issue is.
 

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Discussion Starter #17
Sorry man, I got to thinking about it and was going to say I could send you some parts so you could try swapping them to see if it helped, wish I would’ve replied sooner! Again, sorry. I would start with the stator first. I had a bike I was working on, it would like nda start, ran ok for a bit then when warm ran like crap. Replaced the stator with a “good” used one and same issue, I chased the problem for quite awhile, finally bought a new RM stator and its ran perfectly and starts perfectly ever since. Hopefully that’s what your issue is.
No problem at all, and I do appreciate the offer. Didn’t mean to seem overly impatient, just wanted to get some parts coming since everything is so hard to get lately, decided a new stator and cdi on a 16 year old machine couldn’t hurt even if it’s not the problem.

Today I took the carb off, removed and cleaned everything, all the jets, accelerator pump, floats, just to be sure. Once the stator and cdi arrive I’ll install them and give it another test.
 

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Discussion Starter #18
Posting a quick update, since I do appreciate all the thought and input, although I still don't have a smoking gun as to the actual cause...

Installed a new CDI (Vortex), new stator (RM Stator, terrible customer service BTW), new coil and plug wire/boot (Honda) plus a new spark plug, new regulator/rectifier (Honda), and an entirely new carburetor (Honda) with 178 main, 50 pilot, stock needle on 3rd (middle) clip, 2 turns on the stock fuel screw. Triple checked the valve lash and timing, no adjustment needed there. Test rode it at 3000', 65 degree day, and it ran AMAZING. Pulls strong all the way to WOT in every gear, no stumble or surge or blubbering. No idea what the actual culprit was but it is gone now and that's all I really care about. Mostly ride high desert and mountains, but if I go down to sea level or somewhere like Glamis it may be a bit lean at 178, maybe throw in a 180 or 185 if that happens. It did dribble up a tiny bit of coolant out of the overflow tank hose, but they may have been slosh from the tank being too full and hammering it through whoops, will def keep an eye on it for possible head gasket issue but so far no smoke and no milky oil. Going to replace the thermostat and ECT sensor just to be sure, since that was overlooked during the build.
 
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