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2008 DRZ400SM Power Loss

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Hey all, I'm really in need of some help with this bike. I just purchased a used 2008 DR-Z400SM, and it has a problem with losing power. When I am in neutral I can rev the bike as much as I want and it gives me no problems. When I put the bike in gear and start going I can only give the bike about 1/4 throttle before I completely lose power. Any more than that 1/4 throttle and the bike drops power completely. If I stay in lower RPM's I can get to about 60MPH, but once the bike hits 5th gear it barely stays alive. If I try to go any faster than 60 I get the same power loss. The only way I could stay above 60 when riding it home is if I was going down a hill. 

The bike has a full Yoshi exhaust, as well as the 3x3 airbox mod, but does not have any aftermarket carburetor parts. I have done a ton of diagnosing over the past few days, so there will be a lot of info ahead. Any help is appreciated, I'm willing to do whatever I need to get this bike running how it should be!

So the first thing I did was get some help from reddit, but I could only get so far on there. I replaced the petcock with a raptor petcock to make sure that it wasn't a fuel problem. I have pulled the carburetor and cleaned everything out. Everything looked totally fine, but I went ahead and pulled all jets out and cleaned them anyways. After that, the bike seemed to idle a little better but it would still lose power while riding. While I was inside the carburetor I did notice that it was drilled to where I could access the (air / fuel mix? I'm still a newb...) screw, but it did not have any aftermarket jets or an aftermarket needle.

I then pulled the spark plug and it was very dirty, so I went ahead and replaced it. The bike seemed to run just barely better, but again still the same issue. After that I followed the thumpertalk guide for charging system diagnosis, here are the results:

Engine off / key off - 12V | Engine off / key on / lights on / 11.9v | Engine idle - 13.4v | High idle - 13.3v

Stator side Y1/Y2/Y3 to ground - no continuity

Y1 to Y2 - 1.3 Ohms | Y2 to Y3 - 1.3 Ohms | Y1 to Y3 - 1.3 Ohms | Continuity on all 3 tests as well

Engine on, stator side test (3k-ish RPM's) | Y1 to Y2 - 66V | Y2 to Y3 - 56V | Y1 to Y3 - 69V (all AC)

Diode check for RR | Y1 - 560 | Y2 - 560 | Y3 - 560 | This is with the black test lead to the red wire, and the red test lead to the yellow wires. Flipped the other way I get no reading. My multimeter doesn't have a diode test so I used the continuity setting and this is the number that it read.

My battery voltage seems lower than it should be, but everything else tested fine as far as I could tell. I do have a light bar and a phone charger hooked up to the battery as well, but neither pull power unless they're being used, and both are currently off. I'm going to get my battery tested anyways to make sure it's good.

After going through that guide I tested my ignition coil. The coil in my bike looks like it's already been replaced, as the coil that's in there is a Yamaha coil. The number on the side of the coil is F6T535, I couldn't find any sort of data or spec sheet for this so I have no clue what readings I should be getting. I tested both of the coils and got 1Ohm and 15.4KOhms.

At this point I'm pretty much stuck, I'm not sure where to go from here. Any help is appreciated, thanks guys!

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Posted (edited)
1 hour ago, bumtarder said:

Did you mix up the main jet and the pilot jet?This has happened more than once around here.

I took them out and put them back in one by one so it definitely wasn't done by me if they are switched. I'll attach a picture of the inside, I don't think they're switched around but I could be wrong.

 

https://imgur.com/a/Pmj6hxl

Edited by Tricker12345

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Carb looks to be in rough shape.Anyway,if it's bone stock with the 3x3 airbox mod and a full Yosh exhaust it's probably running pretty lean in the mid-upper rpm range with it set up like that.You'll need a decent jet kit to help sort it out and get it running right.The stock needle is non-adjustable and it's already jetted pretty lean from the factory to satisfy the EPA.I'd look at the JDS005 jet kit and get a Kientech extended fuel screw to make tuning the pilot circuit easier.

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Just now, bumtarder said:

Carb looks to be in rough shape.Anyway,if it's bone stock with the 3x3 airbox mod and a full Yosh exhaust it's probably running pretty lean in the mid-upper rpm range with it set up like that.You'll need a decent jet kit to help sort it out and get it running right.The stock needle is non-adjustable and it's already jetted pretty lean from the factory to satisfy the EPA.I'd look at the JDS005 jet kit and get a Kientech extended fuel screw to make tuning the pilot circuit easier.

That's what I was thinking as well, I was literally just about to buy the JDS005 haha. I'll make sure to get that extended fuel screw as well. I'll get that installed and report back once it's done, I'm hoping that fixes my problem!

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That lack of power is definitely improper jetting, I bet if you covered up that 3x3, itll run better. Still not great since you have a full exhaust, but better than now. Get the JD jet kit and follow the directions as per the sheet they supply. You'll have it running in no time.

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On 4/20/2019 at 6:11 PM, D1rtyPelican said:

That lack of power is definitely improper jetting, I bet if you covered up that 3x3, itll run better. Still not great since you have a full exhaust, but better than now. Get the JD jet kit and follow the directions as per the sheet they supply. You'll have it running in no time.

 

On 4/20/2019 at 2:38 PM, bumtarder said:

Well, I installed the jet kit and it's now even worse lol. I can't even get to 1/4 throttle now without all the power dropping.

 Red needle, third slot, 160 Main Jet, 25 Pilot Jet. I'm at about 4500 feet, I'll be riding between 4000 and 8000, along with the full yoshi exhaust that's what the paper recommended. I messed around with the (extended) mixing needle and it didn't help at all.

Any ideas as to what else the problem could be?

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Since it's a CV type carb the vacuum diaphram under the top cover should be closely examined for a leak,like a pin hole or a small tear,a fold etc. Also make sure the small o -ring under the top cap is not missing and the vacuum line to the petcock is connected to the vacuum port at the top front of the carb.

 

 

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1 minute ago, bumtarder said:

Since it's a CV type carb the vacuum diaphram in should be closely examined for a leak,like a pin hole or a small tear,a fold etc. Also make sure the small o -ring under the top cap is not missing and the vacuum line to the petcock is connected to the vacuum port at the top front of the carb.

I didn't see anything when it was open, but I'll take it all apart and make sure that there isn't any damage to the carb at all. The o -ring is there, I made sure that it stayed in place when I was working on it. I did replace the petcock with a raptor petcock, I thought mine was having problems but it ended up being something else. The raptor petcock works fine, and I've put a rubber nipple onto where the vacuum line goes into the carburetor. I was having this same problem before I swapped out the petcock so I don't believe that's causing any problems.

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Looking back the battery voltage appears weak and charging voltage are low. Probably due to some voltage loss between the regulator/rectifier and the multiple connectors and the fuse by the battery.

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10 hours ago, bumtarder said:

Looking back the battery voltage appears weak and charging voltage are low. Probably due to some voltage loss between the regulator/rectifier and the multiple connectors and the fuse by the battery.

I had just installed a phone charger on the bike and I left it plugged in overnight, I believe that was my problem. I'm going to test the voltage again today after letting the battery charge on a charger. If it still isn't correct then I'll take a look into the electrical again.

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