Bogging when stabbing the throttle

[adinocr7]

Just bought a used 2006 Honda TRX450R. The thing is like new and the only thing done was that the baffle (silencer) was removed. The problem I'm having is that when I stab the throttle from a start or very low RPM range it bogs for a second and then takes off. When it runs it runs very strong. It feels like an 04' - 05' TRX450 that is piped and jetted. My concern however is the bogging. You have to ease into it and then let it eat. When I took the air box lid of it really ran like crap. My friend said its not a low RPM machine. From the best of my knowlege the jetting is stock as well. I really don't feel that it should be bogging at all though when you punch the throttle. Should I find a stock baffle and put it back in? Is it running too rich and should I play around with the jetting? Any thoughts or advice would be appreciated.

[underpowered]

it is the FCR carb. that particular carb is best at or above 3000RPM. to solve this get the boysen accelerator pump cover. it is a common problem with the FCR carbs.

[GPracer2500]

Don't get the Boysen pump cover. Your FCR has a tunable accelerator pump. A ~50 leak jet (or smaller) should cure the lean bog you're experiencing (stock is a 70, HRC is 55--I believe). The AP timing is adjustable as well via a scew on the pump arm--prolly don't need to mess with that for now.

The earlier model FCRs didn't have these tuning features and those are the carbs in which a Boysen Quickshot AP cover might be applicable.

[adinocr7]

Appreciate the advice. I'll head down to my local dealership this evening and pick up a ~ 50 leak jet. I know the main jets are a piece of cake to swap out. Is there anything I should be aware of when replacing the leak jet?

[GPracer2500]

Just that you'll have to remove the float bowl. The leak jet is located in the bottom of the float bowl--literally screwed into the bowl itself.

[adinocr7]

You're the man. Thank you again, I'll be sure to post the results.

[300ex mxracer]

if it wasnt rejetted after the baffle was taken out, it is running lean and probably starves for gas when u punch it. try going up 1-2 main jets and see if that helps.

[wilkin250r]

Did they change the design on the acc. pumps themselves? Last I knew, the leak jet wasn't the issue. The fuel amount was fine, it was simply delayed due to air trapped under the acc. pump diaphram.

However, myself having never owned an FCR or ever hearing of any redesign, I would trust GPRacer over me at this point.

[440_Turtle]

My EX is at the local Honda Dealer getting jetted to fix that very problem, and a lean popping at WOT. Cant wait to get it back, they did a very impressive job on my Foreman.:eek2:

[2muchquad]

It could have been a simple fuel screw adjustment is all you need.;)

[adinocr7]

Went to my local dealership and the smallest leak jet they have is ~ 72 (the stock one is ~ 75). I was told to get a leak jet thats ~ 55 or in that same area, I would have to order a jet kit because the dealerships do not carry them. These are the times when its good to have a few reliable friends . . . who happen to own an identical machine.

It turns out after a few phone calls a friend who runs an HMF setup still had his stock exhaust from his 06'. Not only did he have the stock exhaust but he was even nice enough to pull the spark arrestor while I was on my way there. We had it installed within less then 5 minutes and I impatiently waited watching this thing idle for another 5 minutes so it was properly warmed up.

All I have to say is wow. Way better throttle response. There is no hesitation and it runs like I felt it should. It doesn't feel as though it winds out as fast but its much torquier and when you stab the throttle from almost an idle and just pulls the front end like there is no tomorrow.

It was concluded yesterday evening amongst some good friends and a few beers that if I had access to a ~ 55 leak jet the machine would have been every bit as responsive without the spark arrestor. For now though it looks like I'll be riding it fully corked . . . and to be honest its more then enough to handle seeing as though I've been running a KFX 400 for the past year.

[GPracer2500]

Your dealership is as clueless as most of them. I believe your stock leak jet is a 70, it's the starter jet that's a 75. Or did you actually look at the leak? Anyway....the Honda part number for a #55 leak jet is 99108-MEB-0550, a #45 is 99108-KRN-0450, and a #40 is 99108-KRN-0400.

Also, Yamaha part numbers for leak jets: 4JT-1494F-XX-00. Replace the XX in that number to get these various sizes (e.g. a 50 leak jet is 4JT-1494F-07-00):

#130 XX = 33
#120 XX = 31
#110 XX = 29
#100 XX = 27
#90 XX = 23
#80 XX = 19
#70 XX = 15
#60 XX = 11
#50 XX = 07
#40 XX = 03
#35 XX = 01

Another opition is to skip the dealerships altogether and just order through Sudco. They'll have all sizes of leak jets. There website isn't much to look at but their PDF catalog is comprehensive (almost to the point of being cumbersome to use).



One point worth noting if you're new to leak jets is they work "opposite" normal jets. In other words, the smaller the leak jet the richer the AP squirt.

[adinocr7]

GPRACER:

I must have just had a good or lucky day when I took my machine out with the spark arrestor installed because it seemed fine (for the 5 minutes I rode it). However the past few times it not only still bogged but it also ran slower verses having the baffle out. I took the baffle out and it felt much better through the mid range and top end but it still bogs whenever you stab the throttle.

I took your advice and ordered some leak jets ~55, ~50 and ~48 leak jet from magicracing.com. They had a really easy site to navigate through and I found exactly what I needed. I should be receiving my Dyno Jet Kit and Leak Jets no later then Friday.

I'm just going to drop in the ~50 leak jet and see how it runs. If it goes well and time allows I will throw in the Dyno Jet(s) / needle per their instructions and see how that works as well. My machine's engine is bone stock with the exception of having the baffle removed. I'm not looking for any significant power gains, just really crisp throttle response and solid power throughout the entire RPM range.

I'm riding Monday so I'll post the results come Tuesday morning.

[440_Turtle]

Well i got mine back the other day from teh honda shop and shes just as sick as when she got there. SUM IT UP: Under hard acceleration (drag racing) about half way through 2nd it woudl start to starve out and just didnt have any power. so i took it to teh honda shop and they said they went from a 155 to a 205 main jet, that it was starving out but needed an aftermarket rev box and more gears b/c it was bouncing off teh top. Well i rode it yesterday and i think they smoek too many rocks. now if feels like its too fat in teh middle where it was popping b4. Now when your accelerating hard it still pops but if you keep it pinned it pulls through and then accelerates again. Im at a loss. Ive ordered a sparks CDI and im going from a 14 to a 16T front sproket. but anyway i think they are way off on teh jetting and i find it hard to believe its the CDI that they say is causing the popping b/c they are saying thats the top of the revs but it pulls through and beyond if you just stay on it. Could it be that i may have to go to a programmable CDI. is there anyway to check the spark output. Also what plug would you recommend. they put a stock DRP8z back in. thanks to anyone who stuck around and read all my ramblings. any input woudl sure help:(

[BigFish]

440_turtle, u didn't take it to performance did u?

[440_Turtle]

Ricky hendrix in pineville

[BigFish]

Thats ur problem. streetbikes yea, but not quads or dirtbikes (even though they got a mx team). They've never impressed me when it comes to the offroad end of it

[bsjoe]

sorry to cut in, but what about my quad? Same problems, I was planning on buying the accel pump, but you say only older models? Mine is a 04' YFZ450, what should I buy?

as of right now, my 06 450r is stock as far as the carb and exhaust is concerned, except for a 55 leak jet, and an aftermarket air/fuel mixture screw...the leak jet made the bog go bye bye...these things come lean form the factory...real lean...

[GPracer2500]

Originally posted by bsjoe
sorry to cut in, but what about my quad? Same problems, I was planning on buying the accel pump, but you say only older models? Mine is a 04' YFZ450, what should I buy?

The AP is integrated into the carb--you already have an AP. A smaller leak jet is what you need.

Here's the deal: The leak jet is part of the Accelerator Pump circuit.

The "bog" that you get when whacking the throttle open from idle or low RPMs is (almost always) a temporary lean condition. When the carb's slide is suddenly raised, the engine takes a big gulp of air. But the carb isn't able to respond to that change in airflow instantaniously. It takes a moment for the vaccum signals within the carb to "normalize" and draw fuel up through the main-jet and jet-needle circuits as they normally would. The result of this delay is a temporarily lean condition.

It's the AP's job to correct this situation. The AP works by squirting a thin stream of raw (not atomized) fuel directly into the engine. There is a small brass "squirter" that's within the carb's throat just upstream of the carb's slide. A linkage system activated by the throttle cables pushes down on the AP diaphram. This creates pressure within the AP circuit and pushes fuel through the circuit. When the diaphram is compressed the fuel has two places to go: 1) out of the squirter and into the engine and/or 2) through the leak jet and back into the float bowl. The leak jet bleeds off (i.e. "leaks") a certain amount of fuel out of the AP circuit and that's how the duration of the AP squirt is controled.

The AP circuit is designed to only operate with reletively fast openings of the slide. There is an oulet check valve just below the squirter. If the slide is opened slowly then the AP diaphram doesn't create enough pressure to open the oulet check valve and no fuel makes it through the squirter--it all goes out the leak jet.

Leak jets work the opposite of the other jets we're use to. The smaller the leak jet the richer the AP jetting. The larger the leak jet the leaner the AP jetting. In other words, the bigger the leak jet the more fuel is bled out of the AP circuit causing less fuel to actually make it out of the squirter.

Hope that's clear enough to follow!

[GPracer2500]

Originally posted by 440_Turtle
Well i got mine back the other day from teh honda shop and shes just as sick as when she got there. SUM IT UP: Under hard acceleration (drag racing) about half way through 2nd it woudl start to starve out and just didnt have any power. so i took it to teh honda shop and they said they went from a 155 to a 205 main jet, that it was starving out but needed an aftermarket rev box and more gears b/c it was bouncing off teh top. Well i rode it yesterday and i think they smoek too many rocks. now if feels like its too fat in teh middle where it was popping b4. Now when your accelerating hard it still pops but if you keep it pinned it pulls through and then accelerates again. Im at a loss. Ive ordered a sparks CDI and im going from a 14 to a 16T front sproket. but anyway i think they are way off on teh jetting and i find it hard to believe its the CDI that they say is causing the popping b/c they are saying thats the top of the revs but it pulls through and beyond if you just stay on it. Could it be that i may have to go to a programmable CDI. is there anyway to check the spark output. Also what plug would you recommend. they put a stock DRP8z back in. thanks to anyone who stuck around and read all my ramblings. any input woudl sure help:(

205 sounds awfully big. I'd get yourself a handlful of jets and start testing. Keep backing down from the 205 until the performance improves. Do 4th gear WOT passes to test. Just roll-on the throttle slowly in getting to WOT to mitagate the affect of the AP. You don't want misfires caused by the AP to confuse your interpretations of the main jet.

The needle is harder to say. I'd just start with it in the middle clip position. Get the main close, then test one way and the other on the needle clip position. Remember the needle clip postion has it's affect in the 1/2 throttle range (give or take a 1/4 throttle). WOT passes won't tell you much (if anything) about what the needle is doing. Once you get the needle performing satisfactorily then go back and fine tune the main.

Remember, when tuning carbs it's all about throttle position NOT what gear you're in.

I highly doubt your CDI has anything to do with what your experienceing.

[suck my pipe]

Turn your idle up, so its on the gas a little. you wont stall as much eather like when your in tight woods or wherever.