I've had these 35's on the 727 for awhile now and have tried to adjust, adjusted some more and more and more and more and more. I'm going nuts here and my frustration level is OFF THE CHARTS!!!

My problem is if at high idle (still relitively low R's) with no load or even at low RPM's with load, if I hit the throttle (twist) quick to 1/4-1/2 it bogs real bad. It clears up after a second or two bog, but this can't be right!

Now, if I hit the throttle more then 1/2 off of idle or low RPM's it will die out.

At high R's it's fine (so it seems). Probably killing me somewhere, but since I have not been able to get them right from the start, I'm really not sure!

I have spoken with Harry over at Trinity (where I bought them from), spoke with Paul at SUDCO (where they came from) and have recently spoken to another builder (hoping somebody knows something more then I do about these things). I have tried and tried and tried with no "good" results yet. WTF?

Anybody with any relative experience with using a pair of FCR's on either a Rap or DS with any info, I would really appreciate it. I'm willing to try anything at this point!!!

I waited for several weeks to get these DAM carbs, went through other issues to get them to fit correctly and still can't get any benefit from them as they are! At this point, I may as well be using the stock CV carbs and send these back to Trinity where they came from![img]i/expressions/face-icon-small-mad.gif[/img] I've about had it!!!

 

Welcome to the wonderful world of " I can't believe that i spend 1000 dollars on these carbs" Sudco has a couple of 100 page carb tuning books. My thought is you have more carb than you need. Not knowing how the FCR's tune i am of not a whole lot of help. I guess you have checked and rechecked the obivios. Have you tried putting the stockers back in???? Just to see?? Have you cranked the air screws down??

 

If it was me tuning it, I would only do one circuit at a time. Once you have that circuit done, then move to the next.

From what you have described, It sounds like you are too rich when the acc. pump is activated. To remedy this, you will have to lean out your pilot jets or lean out your needles. The acc. pump on the FCR's that I have played with, are not adjustable.

One other thing that you might try is to take off the acc. pump arm and see if you still have a big stumble. You most likely will, but it is something that can be done real quick. If you take them off and the stumble is not as bad, then you are to rich in one of the two circuits mentioned above.

James

 

It sounds just the oppisite to me. Lean on the accel pumps.
I had a simalar prob on a hot rod VW with Webers. Bumping up the accel pump jet remied it.

 

Well, I tried to put a piece of hose over the accell arm to make it come on sooner and it made oit worse. But, there is not enough adjustment to make it coma on much later, so that is why I am so stumped.


And Dune, I have been dooing 1 circuit at a time. Doing more then one get's ya in trouble. LOL

 

I know my carbs are different, the whole motor for that matter, but I had the same problem with the stockers until I switched to the clamp-ons. This may have been because of my earlier carb tuning, or non tuning, but the two clamp-ons cured it. This would make me think that you are rich on the idle circut as well. Check your PMs

 

Swytak, how does it run if you ease through the throttle? Does it studder at 1/4 to 1/2 throttle if you ease through it? Remember, you have two air jets under the removeable bell. Some FCR's have an air screw there too. I have heard you can buy new accel pump cams to adjust the rate and amount of pump travel, but I am not sure. I am guessing this is on gas? If it is alky, you MUST remove the large air jet, and modify the other jet behind the bell. It has been months since I tweaked on my FCR, and 2 years since I changed it over to alky, so my mind is drawing a blank on all I had to do for tuning.

Also, how far around will your twist throttle go to go from idle to full throttle? 1/3 round, 1/4 round, 1/2 round? You might actually be opening the throttle farther than you think when you punch it. This still shouldn't have an effect.

Just remembered, try this. Take the raptor out on the road. In third/forth gear at barely above idle, open it wide open and hold it. It will take approx 3-5 seconds to use all of the fuel the accel pump provides. If it is studdering, wait the 3-5 seconds, if it then opens up and runs fine, the problem is in the accel pump. If not look somewhere else. I filed the top of the accel pump push rod to shorten it and modified the cam to bring the fuel on slower.

If I can think of anything else, I will let you know.

 

swytak- I find this very interesting. I wish you could find the time to tell us what Harry and paul at Sudco have suggested doing to solve the problem. I have a pair of stockers being tweaked now just to avoid that problem you are having. Letsa try to solve the fcr problem for the rappy's. All the ds guys do not seem to have the problems raptors do.

 

Nope, not using a disc system, so that is ruled out. And even if I was, I still don't think that's the answer, it's definitely the carbs themselves. Thanks anyway.


how does it run if you ease through the throttle?
- Seems fine.
- No stuble or hesistation, but my expectation here is that it is a racing carb and I want to use for racing. Which means going slow is not gonna work for me.
- Also, under the bell, there is the main air jet and the air adjustment.
- Yea, it is being run on gas and the twist throttle is full at about a 1/2 turn. It is your basic motion pro twist throttle with push/pull cables.


Take the raptor out on the road. In third/forth gear at barely above idle, open it wide open and hold it. It will take approx 3-5 seconds to use all of the fuel the accel pump provides. If it is studdering, wait the 3-5 seconds, if it then opens up and runs fine, the problem is in the accel pump. If not look somewhere else. I filed the top of the accel pump push rod to shorten it and modified the cam to bring the fuel on slower.

It bogs for a couple of seconds then clears up and goes!


What I think and what I have found that could the culprit.

Reading through the info I have from SUDCO, everythings points to the accell pumps. But, I have done the adjustment to them going faster and slower, both without correcting this bog.

So, last night while e-mailing Harry again. I look at their website to confirm "baseline" jetting for sea level. I know this is baseline and will not be perfect for me at 600' over and it being 40 degrees outside, but I wanted to confirm I was starting from the "baseline" they recommended.

Well, to my suprise, all the specs have changed AGAIN (well most, not all). What is on the left of this chart is what I was told to start from and to the right is what the site now suggests, which has changed atleast 2 times I know of.

This is what I found:

Main fuel jet: 142's (site now shows 143's)
Main air: 170's (your site now shows 130's)
Needle type: OCGMR (your site now says BCGMR)
Clip position (from top): 3rd
Air adj: 1-1/8 out (unspecified on your site)
Air/fuel adj: 2 (now your site says 2-1/2)
Pilot jets: 52's (same as site)

So...... what I am now thinking is the culprit is a couple of things.
1-Definitely the Main air jet is WAY off. (170 vs. 130)
2-The needle type has changed (OCGMR vs. BCGMR)
The air/fuel mixture has changed some, but probably not any real affect to my problem. Only 1/2 a turn out more then what they told me before.

Makes sense hu? Needle is different, which makes sense to my problem and the main air jet is way off too, compounding the issue.

Any thoughts on this?

I asked Harry to send me the correct componentry (needle and main air) so that I could try to see if this is the problem.
The alternative is sending them to him and waiting weeksn (2+) to get them back, which I am not real keen about, considering I was delayed a month just getting these carbs to begin with. Sending them back is a last resort in my mind and at that point I may as well just go to the stockers.

Thanks for any and all help!

Swy

 

i have a yz426f and had the same problem with my fcr. it is your accelerator pump. you have to drill and tap a holl in the side of your carb so that there is an adjuster screw this alows you to make less gas squirt every time you hit the gas. this mod is called the bk mod. go on the dirt bike furoms and they can give you pics of how to do this mod. it will fix your problem.