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strange running problem. help needed

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New here to the forum, and not really a DRZ owner. I have a couple of older Hondas, but I have my nephews DRZ400 in my garage currently trying to fix it.

To start with, we pulled it in the garage to give the carb a cleaning and fix the radiator fan shroud, which was bent into the fan. We pulled the carburetor, gave a good cleaning and re-assembled. We also flushed the old fuel from the tank and cleaned the petcock and put in fresh gas. All buttoned back up, we fired it up. It started fine, but would not run past idle. I'm am at my wits end now and will do my best to continue with what I have tested.

I have since had the carburetor back off the bike 4 or 5 times, being sure that each passage is thoroughly clean and flows carb cleaner through each passage as intended, including the idle air circuit. (Yes, I turned the idle air screw in gently to verify the correct number of turns before removing, and set it back to the same number of turns when reinstalling.) The diaphrams also appear to be in good working condition with no holes or cracks.

I have tested with and without the air filter, verified that fuel is flowing into the carburetor by opening the drain screw and setting the petcock to prime, but still get the same results. The vacuum line going to the petcock has no holes and is connected properly. The only other item to note is that sometimes I can get it past midrange to the upper rpm's and get it to run there as long as I hold the throttle open. After releasing the throttle, the bike will typically die.

This past weekend, I pulled the valve cover and verified that the cam chain is indeed tensioned properly and saw no obvious issues. I also tested the compression with no luck. I would see the gage jump to 100-120 (hard to tell) and fall immediately back to zero. I realized today that the schrader valve was not installed in the compression tester hose as it should be, so I will be re-testing the compression when I get time as well as performing somewhat of a leak down test.

I'm not familiar with a dry sump oil pump, so maybe someone can enlighten me, but with the valve cover off and turning the engine over, I expected to see oil being pumped into the top end, but did not. Possible problem, I'm unsure?

This bike only has around 2000 miles, but has set up for quite a while. The last time it was running there were no apparent issues. What have I done wrong or missed? Any help will be greatly appreciated.

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Its gotta be the carb or intake boot - I'd double check that the intake boot is installed right and sealed on both ends, or some tiny bit of crud got blown into the wrong passage while you were cleaning it. If you have some compressed air try blowing through the passages, making sure the air is moving through the passages freely. I'm a real amatuer when it comes to carbs but you gotta go back to the thing you last screwed with..I know its frustrating taking the carb off a dozen times. Good luck and a bump for some more opinions....

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auto-decompressor makes doing a compression test just about impossible. As for running: gotta be a carb problem. Check to be sure you have the right jets in the right places (main, air, pilot, secondary...whatever they are all called-there's a couple of very similar size and can be confused)-there's also an accelerator pump that can be messed up if taken apart carelessly, as well, there is the throttle position sensor, which actually doesn't do anything on north american bikes, and can be unplugged at the harness.

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Is the little oring in place under the slide diaphram cover, the oring is next to the slide diaphram & is the needle in tight?

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Thanks for the suggestions so far. Was hoping you wouldn't all point me back to the carb...:smashpc: but I really have been thinking that could still very well be the problem.

I have verified the accelerator pump is assembled correctly, the oring is installed in the correct spot with the diaphragm, and I have shot carb cleaner and compressed air through passages. Not saying you guys aren't on the right path...thanks for the feedback. I'm thinking maybe I need to order a rebuild kit just to make sure everything is still sealing properly.

Funny thing, as I start the "simple" project, I'm thinking this is only one cylinder...too easy. I have rebuilt several old 4 cylinder bikes, including tearing down, rebuilding, syncing and tuning carbs, but it just shows there's alway more to learn.

_________________________________________________________________

Dee

Portland, TN

1977 Honda CB400F

1985 Honda CB700SC Nighthawk

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what year and model (S, SM, E) is this bike?

If it has a CV carb with a diaphragm it doesn't have an accelerator pump.

If it has a FCR carb with an accelerator pump it doesn't have a slide-lift-diaphragm with the small o-ring.

On 4-strokes it is a fuel screw, not air screw. Turning out the screw allows more fuel to richen the idle mixture. Typical setting is between 1 and 3 turns. It does not noticeably affect mid or high speed, only idle.

Does it start with/without choke? On these bikes the choke is separate from the other circuits and when engaged adds fuel even if the throttle opens. After 10 seconds the choke should not be needed and after about 45 seconds should probably make the engine stall too rich. If it won't run without choke when warm possible plugged idle jet/circuit (still). Most suggest if it needed cleaning the idle jet is best replaced as tolerances don't allow for a wire cleaning job.

Have you removed the emulsion tube and cleaned it?

Here is another thread with basic carb info:

https://thumpertalk.com/forum/showthread.php?t=978287&highlight=carb

Edited by slowriding
"without choke when warm"

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on the side of the mikuni is a diaphram operated mechanism under a small cover: at high intake manifold vaccuum it changes floatbowl pressure to enrichen the fuel ratio-I call it an accelerator pump, but it can also be called a coast enrichener.

The fact that it idles, but won't take throttle points me to the carb, but it could be other things-don't know what though. I'd look carefully at the 2 jets that look almost the same, to be sure the right one is in the right spot. Main jet should be a 142.5 or 140 (stock exhaust), the other one is (I believe) an air jet of some sort.

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New here to the forum, and not really a DRZ owner. I have a couple of older Hondas, but I have my nephews DRZ400 in my garage currently trying to fix it.

To start with, we pulled it in the garage to give the carb a cleaning and fix the radiator fan shroud, which was bent into the fan. We pulled the carburetor, gave a good cleaning and re-assembled. We also flushed the old fuel from the tank and cleaned the petcock and put in fresh gas. All buttoned back up, we fired it up. It started fine, but would not run past idle. I'm am at my wits end now and will do my best to continue with what I have tested.

I have since had the carburetor back off the bike 4 or 5 times, being sure that each passage is thoroughly clean and flows carb cleaner through each passage as intended, including the idle air circuit. (Yes, I turned the idle air screw in gently to verify the correct number of turns before removing, and set it back to the same number of turns when reinstalling.) The diaphrams also appear to be in good working condition with no holes or cracks.

I have tested with and without the air filter, verified that fuel is flowing into the carburetor by opening the drain screw and setting the petcock to prime, but still get the same results. The vacuum line going to the petcock has no holes and is connected properly. The only other item to note is that sometimes I can get it past midrange to the upper rpm's and get it to run there as long as I hold the throttle open. After releasing the throttle, the bike will typically die. NOTE 1

This past weekend, I pulled the valve cover and verified that the cam chain is indeed tensioned properly and saw no obvious issues. I also tested the compression with no luck. I would see the gage jump to 100-120 (hard to tell) and fall immediately back to zero. I realized today that the schrader valve was not installed in the compression tester hose NOTE 2 as it should be, so I will be re-testing the compression when I get time as well as performing somewhat of a leak down test.

I'm not familiar with a dry sump oil pump, so maybe someone can enlighten me, but with the valve cover off and turning the engine over, I expected to see oil being pumped into the top end, but did not. Possible problem, I'm unsure? NOTE 3

This bike only has around 2000 miles, but has set up for quite a while. The last time it was running there were no apparent issues. What have I done wrong or missed? Any help will be greatly appreciated.

NOTE 1 : because it will rev up if you play with the throttle I say there is something plugged in the carb. If it would never ever rev up it could be stator.

NOTE 2 : it must be a special schraeder with a very soft spring or you will not get a reading on compression testing (any engine). As drzrobbcanuck noted with the auto decompression it is about impossible to get a meaningful compression test on a drz. For the leakdown test the schraeder must be taken out which is probably why it is missing. At least that is how I lost mine.

NOTE 3: dry sump isn't all that hard to understand. There are 2 parts to the oil pump. The scavenge part pumps any oil that enters it from the pickup in the case and pumps it into the tank in the frame. From the tank in the frame the oil feeds the pressure pump which pumps it like any other engine would to all the required places INCLUDING THE HEAD. You should definitely be seeing oil in the head. It might not be squirting but it should ooze from various places and everything should get wet. If you do not get flow it could mean a plugged pickup which would also mean no oil getting into the tank. Or it could be a stripped drive gear on the oil pump. See manual for flow path and pressure test if so inclined. The advantage of dry sump is ability to have more oil in the system without the gears running in the pool of it as much when the bike is going up steep hills or down. Also, a more steady supply if you catwalk or something that would normally starve the pump pick-up.

A unique thing about the dry sump is that you cannot check the oil dipstick unless the engine has been running for several minutes at least for the oil to collect in the frame tank. A sight glass might have been nice but when running and for hours afterwards it would appear to have no oil. It can take as long as overnight for the oil to slowly ooze through the pump and drain from the frame tank back to the crankcase. If you really need to check without running the bike you would have to drain the crankcase and the frame tank into a marked container. Chances are you would get the oil dirty doing so and have to replace it, but if you remove the bash plate and are careful to clean away any dirt you can keep it clean.

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Original intent was to clean carb since it had been sitting for several months to a year. Before parked there were no running issues.

Checked compression last night...130 psi. Seems ok.

Choke affects cold starting as it should and can be turned off after a few seconds. Bike still idles fine with choke off.

There is no gas in the oil, but I do believe the oil level was high before I drained some off, though this did not fix my issue. I will recheck oil level properly knowing what I know now.

This is a CV carb, so no accelerator pump, but coast enricher as mentioned. Could this enricher device cause any issues like what I'm talking about? It is a 2004 year model, but not sure what letter. Sorry, not too familiar with these bikes. I will try to remember and look at that this evening.

As I mentioned, I have soaked the carb in cleaner, blown through passages with spray cleaner and compressed air, but I could still be missing something.

Thanks again for all response and feedback.

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a 2004 with electric start is either an S or E model

S is street, full lights with turn signals, hi/lo beam <---with a CV carb this is probably what it is.

E is the dirt edition with electric start rather than K which is kickstart only. The E have only the basic headlight and taillight on USA models.

SM is supermoto with street tires and inverted forks, but these didn't exist in 2004

Edited by slowriding

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