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Carb behavior question

Posted: Thu Jun 15, 2017 10:26 pm
by Nobody
Carb is FCR39 slant on 2007 DRZ400E.
When I rev it up and close the throtlle it revs higher than idle for some 3-4 sec. and then returns to idle revs. Don't have a tacho, but I would say it revs about 2000-2200 and then returns to 1200-1300

What are possible causes to that? Air leak? wrong jets? wrong fuel mix?

My current setup:
Main 160, Pilot 45, Pilot air 100, EMM needle from JetsRUs

Fuel mix screw unknown, tried to turn it with homemade tool and now I really don't know where I am :D Probably on the rich side.
But the symptoms chased me from beginning to the end.

Re: Carb behavior question

Posted: Thu Jun 15, 2017 10:32 pm
by Wingfixer
If it's something that just started, with out any recent changes, I'd say dirty idle jet. I have had a little luck running some Marvel Mystery oil in the fuel to cure that.

Re: Carb behavior question

Posted: Thu Jun 15, 2017 11:17 pm
by Nobody
I had a non working AP because of stuck ball valve. So I took it off, carb clean + compressor. Can't say for sure that everything is tidy, but I think dirt is not the case now. Now the AP works and it is much better than before, just can't get it idle normally.
And I didn't really believe all those posts about bad gas until I saw my new jet after 1 ride and about a month after installation - it's covered with some green residue. Bought a bottle of seafom, will try to use it between rides :D.

At Mountain ridge I had non working AP and high idle or stalling.
At Granville's I had wrong jets and bike dying on full throttle in neutral :D. High idle or stalling.
So it's been chasing me from the start, but I hope that I can fix this without changing my current jet set as otherwise it's good enough for me. At least for now.

Re: Carb behavior question

Posted: Thu Jun 15, 2017 11:48 pm
by Bucho
Ha ha. Last minute fix/repairs just before a big trip. Me too!

Re: Carb behavior question

Posted: Fri Jun 16, 2017 5:33 am
by beejaytee
Is there any popping on deceleration? If you rev up in third gear let's say and chop the throttle, does it pop as you decel down? Could be an air leak if it does.

Double check the air boots around the carb and the oring at the op of the fcr. Also check the seating surface at the head pipe.

Idle is typically set around 1800 rpm +/- 100 according to the manuals for many bikes I've owned.

Fuel mixture screw shouldn't be turned more than 2.5 turns from fully closed. That is used to get the best throttle response from idle. So it's not likely it's the issue unless the oring and spacer were not installed properly.

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Re: Carb behavior question

Posted: Fri Jun 16, 2017 6:36 am
by anotherguy
Lean condition. Clean pilot jet and carb well. I'd use a JD Jetting kit and follow the directions for best results. He's got the FCR jetting down pat.

Re: Carb behavior question

Posted: Fri Jun 16, 2017 7:16 am
by Marylander
Good luck with it! I've got another R&T club member's klx300 in my garage. He left gas in it so long the gas wasn't liquid at all any more. It's the first time I've seen green residue (have seen brown and yellow before but not green). JT didn't even have jets for it in stock (just a common CV carb). He bought a new FI ktm so hopefully that solves this issue for him in the longer term. :)

Re: Carb behavior question

Posted: Fri Jun 16, 2017 8:12 am
by Boom Boom ... t-setting/

Sounds like good advise here.
Does the bike bog off the bottom or pull strong? A lean (or plugged) pilot jet will make your low end bog and idle go high from being lean in that part of the fuel range (0 - 1/4 throttle).
Remember your adjusting a fuel screw and not an air screw so turn out to supply more fuel / less lean. If outside the suggested range go up or down in jet size. Jets-r-us is good at fast turn around on jets. Ethanol is just evil shit as to what damage it can do to carbs. The trials bikes I run have tiny jets and will not tolerate any of the corn slop plugging a pilot jet. Startron has a marine ethanol treatment...since odds are you run pump gas I would advise treating the gas you run. Damage is done not from the gas passing thru the carb but rather the bike sitting and damp air can pass into the carb via the vent / drain tubes and the ethanol absorbs the moisture. Watch where your carb drain tubes run as that is a good way to suck water and dirt into the carb also. Just replace the pilot and while at it go bigger one size. Easier to ride a bike that is a little rich on the bottom than one lean plus a lean bike runs hot. Best advise was listed above....if owning a 4 stroke then make it a fuel injected one.

Re: Carb behavior question

Posted: Fri Jun 16, 2017 8:45 pm
by J&J
You just went up in displacement right, probably need some more fuel. Did you go up any on your jetting? Don't you have a JD kit? Probably came with a selection of jets. Like Mike said try 1 up on the pilot & see if it gets any better.

Edit: Sorry Nobody, I reread this post & realize I had you mixed up with another DAMN rider. Probably gummed up like others have said if you haven't changed anything.