firechicken93

1999 DR350-X won't rev under load! please help! (w/pic)

16 posts in this topic

Let me start by stating that I have done quite a bit of research and trouble shooting on this problem already, which is why I am seeking advise. I recently purchased a 99 DR350X (pumper carb dirt model). It ran like crap when I bought it but I thought it was a jetting issue. 

Mods: pro-circuit slip-on and airbox mod+backfire screen removal. 

Symptoms: Bike starts right up and idles clean, revs are pretty crisp all the way through in neutral, when in gear under load it will not rev past 4 or 5k rpms, it just bucks, sputters, and misses. It smokes when it hits these RPMs but not at idle, smoke is blue. The plug, which is new and correct, is black, dry, and sooty, the inside of the muffler is the same. sounds super rich, right? I'm not convinced. The carb is squeaky clean and jetting is at least close. The flat slide housing is a little worn, but I've read that the symptom of an overly worn slide is leaking air which causes inconsistent idle and decreased throttle response. I don't know if it would cause an issue this dramatic. 

Trouble shooting so far: New plug, adjusted the valves (they were pretty close to spec already), new and oiled air filter, compression test (80psi), adjusted compression release, rebuilt the carb, new plug and plug boot and slightly trimmed plug wire (to ensure good connection). The wiring harness is in pretty good shape but I cleaned every connection and ground, dialectic greased all connections, made sure all male/female connections were tight. Repacked the muffler and ensured that it is not clogged. Rebuilt the carb meticulously, including cleaning the float valve screen and checking float height, and thoroughly cleaning and inspecting the accelerator pump and can visually witness it operate correctly with a strong consistent "squirt". Current jetting is stock pilot, 3rd (middle) needle position, and 140 main. I have tried the following jetting combinations as well, all with properly adjusted air screw.

(all w/stock pilot)

4th clip needle 145 main

5th clip needle 145 main

3rd clip needle 127.5 main (stock)

and 3rd clip needle 135 main

 

none of these jetting changes made a noticeable difference in the way the bike runs, it still falls on its ass under load. It has great throttle response and power in low rpms but as soon as it hits the midrange it sputters, misses, and jolts. And it revs much higher in neutral, I think this is important. I'm starting to suspect an electrical fault, I've seen stators and internal coils go bad but they usually fail completely or will cause a miss throughout the rpm range. I'm pretty baffled. I've read 4 other posts with this DR350X condition and noone reached a conclusion. One guy rebuilt his top end because he thought that was the problem but of course that didn't fix it. I just sunk a bunch of money into this bike and i'm running out of time in my favorite riding season. Please help!

 

Thank you, 

-Calvin

 

 

 

 

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In those carb rebuilds, did you ever check the choke circuit? make sure the plunger isn't stuck. It would cause those problems and the re-jetting wouldn't cure it. Also, for smoking issue, how much oil do you put on your air filter? some people tend to saturate it and that can suck oil into the motor. It should be very, very light amounts.

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When you look at the choke/fuel enrichment circuit make sure that the o-ring at the tip of the plunger is good and will seal off the circuit.  The other thing is the o-ring/gasket that seals the assembly to the carb.

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Low compression + blue smoke sounds like toasted rings, but maybe there's something else going on.. can you roll/push in 2nd gear without a lot of resistance? Bad clutch/binding gears or something might cause it to stall when applying load if things won't move. Possibly a weak spark or bad timing, might not hurt to pop the valve cover and check for wear/damage to the cam/lobes/journals and make sure the cam timing is set correctly.

I've read that you can add a teaspoon of oil through the spark plug hole and test compression again - if it goes up significantly you almost def have bad rings/scored cylinder. (I haven't actually tried this but it makes sense!) Have also read that a badly worn piston wrist pin can cause piston play that can create binding/damage rings (no firsthand experience here either luckily!)

It seems unlikely to me that you would have this big of a problem from jetting/clip positions alone. In my experience, even going from a 127.5 main to a 145 just results in a richer mix, not falling on its face. If you've ruled out air leaks, fuel flow and 95% certain the carb is clean and working time to look elsewhere...

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18 hours ago, Tekime said:

Low compression + blue smoke sounds like toasted rings, but maybe there's something else going on.. can you roll/push in 2nd gear without a lot of resistance? Bad clutch/binding gears or something might cause it to stall when applying load if things won't move. Possibly a weak spark or bad timing, might not hurt to pop the valve cover and check for wear/damage to the cam/lobes/journals and make sure the cam timing is set correctly.

I've read that you can add a teaspoon of oil through the spark plug hole and test compression again - if it goes up significantly you almost def have bad rings/scored cylinder. (I haven't actually tried this but it makes sense!) Have also read that a badly worn piston wrist pin can cause piston play that can create binding/damage rings (no firsthand experience here either luckily!)

It seems unlikely to me that you would have this big of a problem from jetting/clip positions alone. In my experience, even going from a 127.5 main to a 145 just results in a richer mix, not falling on its face. If you've ruled out air leaks, fuel flow and 95% certain the carb is clean and working time to look elsewhere...

I did the "dump a teaspoon of oil down the spark plug hole" on my 1968 Chevy pickup.  The cylinder in question went from 45lbs to 110lbs.  Guess what we found when we tore the engine down?  Broken piston rings in that cylinder.

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I just saw a post from a DR-250 owner who felt like his bike was running out of gas under accelleration. It was suggested that the vacuum petcock diaphram might have a leak and that the owner should take the bike out and ride it with the petcock in the prime position.  He did and low and behold, the problem went away!

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11 hours ago, GlennRay said:

I just saw a post from a DR-250 owner who felt like his bike was running out of gas under accelleration. It was suggested that the vacuum petcock diaphram might have a leak and that the owner should take the bike out and ride it with the petcock in the prime position.  He did and low and behold, the problem went away!

great thought, I have had that scenario play out with old 70s 4-cylinder street bikes, but remember this is a dirt model DR with flat side carb, with a non-vacuum assisted petcock ;) though of course I checked the petcock for proper flow in the on and reserve positions.

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On 10/6/2017 at 9:56 AM, Todd157k said:

In those carb rebuilds, did you ever check the choke circuit? make sure the plunger isn't stuck. It would cause those problems and the re-jetting wouldn't cure it. Also, for smoking issue, how much oil do you put on your air filter? some people tend to saturate it and that can suck oil into the motor. It should be very, very light amounts.

I did check the choke and it is functioning properly, I did not replace the o-rings but they were still in good condition. and the choke works when running, I use it to start the bike, and the bike responds appropriately when disengaged. I was careful not to over saturate the air filter, I used proper oil and have a pretty good technique down.

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On 10/9/2017 at 2:40 AM, Tekime said:

Low compression + blue smoke sounds like toasted rings, but maybe there's something else going on.. can you roll/push in 2nd gear without a lot of resistance? Bad clutch/binding gears or something might cause it to stall when applying load if things won't move. Possibly a weak spark or bad timing, might not hurt to pop the valve cover and check for wear/damage to the cam/lobes/journals and make sure the cam timing is set correctly.

I've read that you can add a teaspoon of oil through the spark plug hole and test compression again - if it goes up significantly you almost def have bad rings/scored cylinder. (I haven't actually tried this but it makes sense!) Have also read that a badly worn piston wrist pin can cause piston play that can create binding/damage rings (no firsthand experience here either luckily!)

It seems unlikely to me that you would have this big of a problem from jetting/clip positions alone. In my experience, even going from a 127.5 main to a 145 just results in a richer mix, not falling on its face. If you've ruled out air leaks, fuel flow and 95% certain the carb is clean and working time to look elsewhere...

The plot thickens. I wanted to make sure timing was correct so I pulled the valve cover and guess what I found! Well the timing was correct, but also I found an Auto-Decompression cam sitting on top of my dirt model DR350! So that is why I have low compression readings! The auto decomp cam cannot be disabled for proper readings as far as I can tell. This also means I adjusted my exhaust valves too loose (as I adjusted them for the manual decomp 99 head), which wouldn't cause my running issue but it is strange. Can anyone tell me what my valve specs SHOULD be? lets assume it is a 99 dirt model head with an SE auto-decompresion e-start cam.

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I will also add that I checked the pick up and source coils and their ohm readings were right on the money. The ignition coil read 1.6ohms primary and should be 0.1-1.0 so I may be faulty but i'm not convinced, secondary ohms were proper.

 

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31 minutes ago, firechicken93 said:

The plot thickens. I wanted to make sure timing was correct so I pulled the valve cover and guess what I found! Well the timing was correct, but also I found an Auto-Decompression cam sitting on top of my dirt model DR350! So that is why I have low compression readings! The auto decomp cam cannot be disabled for proper readings as far as I can tell. This also means I adjusted my exhaust valves too loose (as I adjusted them for the manual decomp 99 head), which wouldn't cause my running issue but it is strange. Can anyone tell me what my valve specs SHOULD be? lets assume it is a 99 dirt model head with an SE auto-decompresion e-start cam.

i answered your post in advr, but your head is ok & stock.

all 94-99 DR350 have auto CR, the dirt 94-99 also have manual CR.

havent found a good way to check compression yet. .002-.004 intake  .007-.009 exhaust

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22 minutes ago, plugeye said:

i answered your post in advr, but your head is ok & stock.

all 94-99 DR350 have auto CR, the dirt 94-99 also have manual CR.

havent found a good way to check compression yet. .002-.004 intake  .007-.009 exhaust

oh alright, looks like a jumped the gun a little bit. I wish i would have checked that my cam is stamped "5" and not "6" while I was in there, but i'll assume it is correct for now. Thank you! i'm learning something new every day. 

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1 minute ago, firechicken93 said:

oh alright, looks like a jumped the gun a little bit. I wish i would have checked that my cam is stamped "5" and not "6" while I was in there, but i'll assume it is correct for now. Thank you! i'm learning something new every day. 

if it was a 6, you'd know it.

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Solved! As is tradition the fix was simple and I spent two weeks chasing ghosts. At least through my testing I know that my bike is good order. I was MISSING 2 parts in my carburetor, the previous owner must have lost them during a rebuild, I didn't notice them missing because the carburetor looked complete without them, I was missing the collar between the emulsion tube and the plastic cap that snaps onto that collar number 23 and 24 below. I've also attached some after and before pictures to show how far the bike has come in 1 month. new chain and sprockets, new air filter, full tune-up, new fenders, and new headlight, plus multiple little fixes here and there, and lots of paint removal. The carb still needs to be dialed in (running 4th needle position and 140 main, its a little rich in the midrange, need to drop back to position 3) but at least now I have a good starting point.:thumbsup:59dd45e2d332a_image11.thumb.JPG.a68584881be65c5de9ad810b5c3a82e5.JPG59dd46bb4c689_image21.thumb.JPG.9c76cf2b330c7f2fa7bee2ccbb64075f.JPG59dd46bf5ff31_image31.JPG.f866d172f647624e5644342a00132659.JPG59dd46c28e5a0_image41.JPG.a522e5b5e90a27adefbcfedf60547176.JPG59dd46c5b4ce8_image51.JPG.ee5ab5adb273f9a7e51332f5e7a5a30b.JPG59dd46c8f1a3b_image61.JPG.e6555d079409f351808b58fc0f0af97c.JPG

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