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Old 10-25-2009, 09:58 AM   #1
scarysharkface OP
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DR350 w/pumper bogs and backfires

My new-to-me 98 DR350 offroad has the pumper carb. It has an uneven idle (alternating 5-10 seconds high rpm, 5-10 seconds low rpm, not consistent), bogs on acceleration or open throttle 95% of the time and backfires on deceleration. I strong suspect that this bike has only seen idle or slightly off-idle for several months, so a little junk in the carb is what I'm hoping this is.

Bike was jetted with a .45 if memory serves, but the fellow I bought it from was going to set it back to stock before I picked it up. I'm not certain whether he did that or not, or if that's the problem.

I saw in another thread the suggestion to verify that the cap is venting, which I shall do as soon as I finish typing this.

Where do I look first?

Thanks in advance.

John
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Old 10-25-2009, 03:34 PM   #2
mudmantra
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Quote:
Originally Posted by scarysharkface
My new-to-me 98 DR350 offroad has the pumper carb. It has an uneven idle (alternating 5-10 seconds high rpm, 5-10 seconds low rpm, not consistent), bogs on acceleration or open throttle 95% of the time and backfires on deceleration. I strong suspect that this bike has only seen idle or slightly off-idle for several months, so a little junk in the carb is what I'm hoping this is.

Bike was jetted with a .45 if memory serves, but the fellow I bought it from was going to set it back to stock before I picked it up. I'm not certain whether he did that or not, or if that's the problem.

I saw in another thread the suggestion to verify that the cap is venting, which I shall do as soon as I finish typing this.

Where do I look first?

Thanks in advance.

John
Did you drain the old fuel and gunk out of your carburetor? Is your bike stock, stock exhaust, stock airbox filter? If it is the pilot should be a 37.5 and the main jet should be 127.5 or 137.5 depending on year TM33SS pumper. Some California carbs 122.5 ??? Anyway I have a pumper with #40 pilot 140 main jet.. opened airbox and aftermarket exhaust. Just right. Check your pumper operation. remove carburetor and pump the throttle with some gas still in the bowl. should have a good spray. sometime's they get plugged up. also be careful and don't spray yourself in the face. don't ask me how i know this..
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Old 10-25-2009, 03:44 PM   #3
scarysharkface OP
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Quote:
Originally Posted by mudmantra
Did you drain the old fuel and gunk out of your carburetor? Is your bike stock, stock exhaust, stock airbox filter? If it is the pilot should be a 37.5 and the main jet should be 127.5 or 137.5 depending on year TM33SS pumper. Some California carbs 122.5 ??? Anyway I have a pumper with #40 pilot 140 main jet.. opened airbox and aftermarket exhaust. Just right. Check your pumper operation. remove carburetor and pump the throttle with some gas still in the bowl. should have a good spray. sometime's they get plugged up. also be careful and don't spray yourself in the face. don't ask me how i know this..
This is a new bike to me. Bought it from Yoshi in the flea market and brought it home yesterday. He's done a bunch of work on it and it's spectacularly clean, but I don't think he's ridden in at all this Fall. I put a little over 40 miles on it today.

It's this bike:
http://www.advrider.com/forums/showthread.php?t=491732

If memory serves (and I suck at remembering the technicals of anything), it had a 45 pilot (I think) and he was going to put the stock pilot back in. The airbox has been opened, and it looks like an aftermarket pipe. I haven't had an opportunity to ask him if he had a chance to swap the pilot back to stock or if it still has the 45.

I ran some carburetor cleaner fuel additive through it a little while ago and will see if it helps tomorrow. If it does, then great. If not, then I'll pull it and clean it.

Even with the carb issue, I love this bike!

John
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Old 10-25-2009, 03:47 PM   #4
duxrneet
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May want to double check timing while you're at it. Was my problem.
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Old 10-25-2009, 03:59 PM   #5
scarysharkface OP
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Quote:
Originally Posted by duxrneet
May want to double check timing while you're at it. Was my problem.
Oh my god how do I do that (without taking it all apart)!?

Bike sometimes runs incredibly well, so I doubt it's a timing issue as that would be more of a persistent issue. When it runs well, it runs really well.

John
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Old 10-25-2009, 04:35 PM   #6
GordMounce
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Quote:
Originally Posted by scarysharkface
Oh my god how do I do that (without taking it all apart)!?

Bike sometimes runs incredibly well, so I doubt it's a timing issue as that would be more of a persistent issue. When it runs well, it runs really well.

John
Definitely check the float height before any other carb tweaks. You need to make sure you have that baseline right, or nothing else will work right.
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Old 10-25-2009, 04:36 PM   #7
mudmantra
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Quote:
Originally Posted by scarysharkface
Oh my god how do I do that (without taking it all apart)!?

Bike sometimes runs incredibly well, so I doubt it's a timing issue as that would be more of a persistent issue. When it runs well, it runs really well.

John
If you haven't done this already, do this.. drain the carburetor into a carburetor and see if any gunk comes out. water, dirt, old fuel stabilizer, etc. A fuel cleaner may work but it may eat rubber parts in your carburetor too. If you take your carburetor apart write down the jet size. I tried a 145 main jet and it lost power above 7500rpm. with a 140 it rips past Red line no problem. I think a 40 pilot jet is as big as you need to go also. Set the needle at 4th from the top groove. With it set up right that bike should rip the front wheel in the air every time you blip the throttle in 1st gear.
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Old 10-25-2009, 06:04 PM   #8
BikePilot
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There's nothing to check re ignition timing and cam timing can't change without something breaking/chain skipping or a bonehead putting it together wrong.

Your issues could be any number of things. I'd start by giving the carb a good cleaning, check jet sizes to make sure they are reasonable and check float level. Re-fill with fresh, clean fuel and take it from there.

good luck and post up when you get it figured out!
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Old 10-26-2009, 05:10 PM   #9
scarysharkface OP
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Took the carb apart and it is clean, clean, clean, clean, clean and clean. So varnish isn't the problem.. Fiddled with the air screw (I think) under the bottom front and it's now significantly happier. I'll need to do more fiddling though, and read up on what I've done. It was 2 turns out. Bike runs like crap at 2.5 turns, and runs much better at 1.5 turns. My hand will heal and I'll use some aloe vera to take away some of the burn...

I love this bike.

John
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Old 10-26-2009, 06:38 PM   #10
duxrneet
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My bike was re-assembled by a bonehead so the chain skipped a few teeth.

Quote:
Originally Posted by BikePilot
There's nothing to check re ignition timing and cam timing can't change without something breaking/chain skipping or a bonehead putting it together wrong.

Your issues could be any number of things. I'd start by giving the carb a good cleaning, check jet sizes to make sure they are reasonable and check float level. Re-fill with fresh, clean fuel and take it from there.

good luck and post up when you get it figured out!
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Old 10-26-2009, 06:53 PM   #11
scarysharkface OP
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Quote:
Originally Posted by duxrneet
My bike was re-assembled by a bonehead so the chain skipped a few teeth.
I AM a bonehead, but I've got all my teeth and can't skip worth a damn.

John
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