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Hesitation with quick acceleration

By myetman23,
in DRZ400/E/S/SM

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myetman23

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I've got an 03 DRZ400 which was stock when I bought it and have since installed the FCR39MX carb, did the 3x3 air box mod, E-model header, holesawed the end cap, and MCCT. Before this past winter, the bike ran great with these mods, the jetting as recommended on this site worked out pretty much perfect. I had a hanging idle for a little while, but corrected it with the remote fuel screw. Anyway, after taking the bike out of storage this year, I've been getting an intermittent hesitation on acceleration and quick shots of throttle. It's like I'm losing fuel for a split second and then it picks back up, or I'm getting too much fuel for a split second. And if you slowly roll on the throttle, then it'll accelerate fine. At first it would act up for maybe 5 min, and then it'd go away and everything would be normal. Then it became more frequent, and now it's there constantly. It never happened at all last fall when I did the mods. So I'm wondering if maybe I have a dirty carb after all winter? Or do I have an issue with my accelerator pump? Or do I need more carb adjustment? I've adjust the fuel screw in and out 0.25 of a turn (I didn't want to go too far with it) with no results. I'd like to get some feedback before I pull the carb off the bike - which I hate dearly!   

 

Anybody else here have this problem? Or have any insight?

 

Thanks,

 

Mike

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myetman23

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I was sorta thinking the same thing, I was just trying to prevent pulling the carb. The o-ring mod is done on the carb, but it's wired instead of using an o-ring, however, I didn't check to see if it was broken.

I believe it's recommended that the fuel screw be at 2 turns out, and I think I had to go a little more than that to get rid of the hanging idle, so I'm at 2.25-2.5 turns out.

Do you think there'd be an issue with the accelerator pump? Or should I check my pilot circuit first? A bad pilot circuit seems to be most logical since the issue wasn't there before storage.

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myetman23

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I'll pull the carb when I get a chance, see what it looks like inside.

I checked the AP squirt when the carb wasn't on the bike, everything seemed to be normal, it was squirting just as the slide moved up and wasn't hitting the slide, so I cant see how it would come out of adjustment?

In any case, I'll post my findings when I pull the carb.

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myetman23

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Just wanted to give you guys an update, I pulled my carb last night for inspection, everything was as clean as a whistle! I took the jets out, blew through them, there didn't appear to be any restrictions. I checked my fuel screw position, it was about 2.5 turns out, so I set it at 2 turns out for now, I'll adjust it once I get the bike running. The accelerator pump is pumping strong and the fuel spray is not hitting the slide. The "wire mod" on the carb isn't broken, so that's all good. I haven't found anything out of the normal, so I'm going to install the carb again and see if I still have my issue.

 

The last thing I installed on the bike was the MCCT, I followed the procedure and set the motor to TDC as recommended before I pulled the ACCT out. Is it possible that even at TDC the chain slipped on a sprocket?? I may pull the head and see what's up, just for peace of mind.

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Mike in Fresno

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I know it ran well before, but I will explain another way the AP squirt can affect the bog.

The duration of the squirt.

The different makers will use different squirt lengths.  First way to affect squirt is the diaphram button which is internal and 2nd we put on the  the o-ring mod.

For instance on a KTM 525 I changed to a Honda 450 diaphram and did the o-ring mod to quicken the squirt. A long squirt is useful for on road riding  in a high traction situation. Off-road the short squirt works due to the slip of the rear tire in the dirt.

So, could it be the short squirt is just too much fuel all at once? Were you on dirt before and now on asphalt? Did you change tires?

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  • 2 weeks later...
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myetman23

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Here's another update..

I had a look at my cam sprockets after, everything was lined up as it should be, so no issues there! I went for a couple long rides, and had no bog on acceleration, everything ran perfect. You can get on the throttle as hard as you want and it picks it up perfectly. So I thought I had my problem solved by cleaning a bit of dirt or something out of the pilot. However! I went for a ride yesterday, only to find out that the low end bog is back! I guess its possible I got something in my pilot again, but looking back on it now, the rides that the bike ran well were very warm days, say about 20-25 celcius, abd the day that it acted up again was a colder day, around 10 degrees celcius. So im curious if I have a cold/lean bog. The next warm day, im going to try it again and see what happens.

In the meantime, I'm going to go from a 45 pilot to a 48 pilot and adjust the fuel screw accordingly, since im at 2.5 turns out now and its not recommended to go out anymore than that.

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Stuwy123

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Adjust your fuel screw.

The change in temps/ air pressure will affect the carb.

I don't know about the extended fuel screws but the stock one can be adjust way far out (5 turns or so).

Record your settings that work and then adjust.

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  • 2 weeks later...
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myetman23

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Yesterday was 26 degrees celcius, so I figured it would be a good day to test my theory, however, I was proved wrong. The bog is still there and just as bad as ever. I took the carb off again, and again I cant see anything that was out of the norm. The AP pumps consistently, I squirted out whatever was left in the float bowl just to check and see if it'll screw up, but it never. All the jets were clear. I'm still waiting for my 48 pilot to come in. I'm running out of options!

Edited by myetman23
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boatxr

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Since it was put away running well and now it's not what could have changed in storage?

I'd run some fresh gas and fuel cleaner and run her hard again.

I use Lucas fuel additive all the time in all my gas fill ups.

Keeps gas from going funk even when the bike sits for a few weeks.

http://www.amazon.com/Lucas-10013-Fuel-Treatment-Gallon/dp/B000FW7V50/ref=cm_cr_pr_product_top

 

Did you seal the airbox and exhaust? Maybe a mouse built a home in there?

There is also a filter inside the carb too i think? It is on the slant FCR.

Is that clean? Do you have an inline fuel filter?

Edited by boatxr
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Spud786

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Here's another update..

In the meantime, I'm going to go from a 45 pilot to a 48 pilot and adjust the fuel screw accordingly, since im at 2.5 turns out now and its not recommended to go out anymore than that.

Its not going to hurt to turn it out for a test. a fuel screw will have a effect all the way to 4 turns out. One reason with those kientech heavy fuel screws, tend to fall out if you turn them out father than 2.5 turns

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