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DRZ400SM - FCR 39 Problem

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I normally dispise cross posting, but I haven't been getting much response in the drz forum, and this is more of a carb expert question anyways. Mods, feel free to delete if I'm being an ass.

 

So, the good news! I just bought a 2005 DRZ400SM. It has stage 1 hotcams, pro circuit t4 exhaust, holes drilled in the side of the filter cover (instead of 3x3 mod? don't ask me) and a FCR 39 carb. And it was professionally installed and tuned! I absolutely love riding the thing, it's the most fun I've had on 2 wheels. It seemed like it rode really well when I test rode it, but after a week of riding it around, I can tell the carb isn't quite adjusted right. So, to figure out my baseline and see what jets and such were in it, I took it out.

 

So, the bad news! It's the wrong fricking carb. It's a FCR 39 alright, but it's got the fixed bell, the throttle hookups are all messed up (I'm not honestly sure how they installed the cable on the push side). So this also means that the main and slow air jets will never be right. It was kinda jerry rigged in there with radiator hose. Here are pics, I think its from a yzf450. (I don't know why some are sideways... thanks photobucket)

 

IMG_2569_zps88baea63.jpgIMG_2568_zps38c20366.jpg
IMG_2567_zps29656448.jpgIMG_2566_zps10ee730b.jpg

 

I do have the stock carb, but... well... no. So what are my options? Buy the correct carb i guess. Does the TT FCR 39 MX kit have the hot start and air cutoff valve? Is there any reason I wouldn't want both of those things? Can that kit be adjusted properly for 4500 ft with above mods (replacing holey side cover with proper 3x3 mod)

 

Can I mill off the intake bell to take a removable (proper) bell? Does anyone have pictures of the proper fcr with and without intake bell attached? Pics of intake bell?

 

Thanks!

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ACV valve is not needed. You are better off without it.

Hot start is probably not needed: if you learn the dropped when hot restart procedure, you will never use it

All FCR 39 CR/MX carbs will jet identically. 

The real issue is the bell. You need to make a smooth transition, without making it too much shorter or longer then the DRZ kit carb has it set up.

 

Other wise, it's great.

 

http://www.dirtrider.com/features/protips/141_0707_keihin_fcr_carb_rebuild/

 

There are plenty of on line pics of the kit carb

Edited by TheKoolAidMadeMeSick

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Sadly, it will never run as well as it can with the correct carb. As Krannie, says, the transition into the carb bell will not be smooth enough and will never jet quite right. Even with machined 'adaptors', it will never be right.

Also, holes in the airbox is not the same as a 3X3. Even nit the square inches match, all the holes have turbulence from all the edges and problems that can come from your pants covering them and wind.

 

No way was it 'professionally jetted'. A real pro would not try to or claim he properly set up a jury rigged bike.

 

Get the correct carb.

 

No, TT carb does not have a hot start or ACV. Most aftermarket kits do not. People do not want to spend the money and many disable that stuff anyways.

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Sadly, it will never run as well as it can with the correct carb. As Krannie, says, the transition into the carb bell will not be smooth enough and will never jet quite right. Even with machined 'adaptors', it will never be right.

Also, holes in the airbox is not the same as a 3X3. Even nit the square inches match, all the holes have turbulence from all the edges and problems that can come from your pants covering them and wind.

 

No way was it 'professionally jetted'. A real pro would not try to or claim he properly set up a jury rigged bike.

 

Get the correct carb.

 

No, TT carb does not have a hot start or ACV. Most aftermarket kits do not. People do not want to spend the money and many disable that stuff anyways.

 

I agree, no way it was set up by a pro (especially read below). Although, I'd rather have self installed than pro anyways, because I don't cut corners. Either way, I cracked open the carb and this is what I found:

 

158 main jet

OCEMN needle, clip 3

45 pilot jet

O ring mod (but fell off)

1/4 turn out (!!!!) fuel screw (red, aluminum, assembled incorrectly... screw, washer, spring, oring)

100 pilot air jet

72 some other jet (starter jet? slow jet?)

 

Do I want hot start or ACV? If I'm spending $600 on a carb, I want to do it right. It's on a supermoto ridden mostly on the street if that makes a difference. I will be replacing that air panel and doing the 3x3. I think the holes look dumb and it's an unkown.

 

That said, I'm kind of leaning towards making the carb work, assuming my boss lets me use the cnc lathe to make my bellhousing adapter. I'm both a mechanical engineer and a machinist, so I'm pretty sure I could make a sweet adapter. I dunno, $600 is $600

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Jetting is pretty much standard for a FCR 39.

The 72 is the starter jet.

 

A hot start is not needed on the DRZ unless you were a single track rider and speeds real low. Never a issue on a street bike.

ACV, while nice (reduces decl pops) is not a big deal and if not maintained, can be a issue (which is why a lot of guys disable them. I like them)

To get a ACV, all the FCR's I have seen also have a TPS, which is not needed on a DRZ. You will spend a premium to get a ACV and it is simply not worth it.

 

Get a non-aloy fuel screw. Adjust it for a perfect idle, hot engine.

 

Any adapter you make will not it perfect. Better possibly. Fixing the holes may make a valid difference.

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Looks like the acv/hot start is another $73. What maintenence do they require? Do you think it's worth $73? Either way, that alloy fuel screw is going to get replaced with a R&D flex jet, whether I buy a new carb or not.

 

Since I've got the ear of someone who knows stuff, what exactly does the TPS do? My gut feeling says that it was there stock for a reason, but nobody seems to think it makes any difference

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Every FCR I have seen with a ACV and/or a hot start also has a TPS. TPS are expensive.

 

What happens to the ACV is the diapghram go bad, the springs weaking and debris gets in the passage way. Many people simply are unable to properly service the carb. So they end up with a carb they are unable to get a good idle/fuel screw setting. So they disable the ACV and remove it from the equation. I've run tests with it disabled/enabled and find if I have it, I keep it. Anotyher thing to think about is the addition of an ACV costs money. If the value was not there, a OEM would not use it. One reason why any modification must be considered realisitcally. When I was a kid, I took a cheapo Japanese transitor radio and began to remove components. I took a bunch out before I noticed degredation. I am sure it happened with the first cap I removed, I just did not notice it. I knew the board was not packed for the fun of it, that every part was there for a reason.

 

TPS tells the CDI where the throttle is. The CDI also reads rpm. On many bikes, it then accesses two or more ignition maps that advance or retard ignition. On a DRZ, the CDI is very simply and it only has a advance above idle and when in gear. No TPS connection, the CDI defaults into advance mode. The result is slightly more powerful idle and slightly worse emissions.

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