06 brute force 750 stumble and backfire - MudInMyBlood Forums
User Tag List

Reply
 
LinkBack Thread Tools Display Modes
post #1 of 19 Old 05-09-2017, 01:48 PM Thread Starter
Newbie
 
Join Date: May 2017
Posts: 10
 
06 brute force 750 stumble and backfire

Don't mean to sound short but there is a lot of info and I'm going to try and keep this short. Bought an 06 BF 750 that had a stubble and backfire on hard take offs. Only way it would run decent was with the a/f screws 4.5 turns out. Installed mimb snorkel, dynatek cdi and a stage 1 dynojet kit. The dj needles fixed it, it ran like a scalded dog.

Took it down a creek one day and after being stuck running in the water for a little while it started to want to bog down when I gave it the gas. Took it home cleaned the carbs and decided to try and turn the a/f screws back in a little since the dj needles fixed the stumble. Put screws at 2.5 reassembled and tested it, ran great snatching wheelies and all. Noticed fuel leaking where the line connects to carbs. Went to auto parts store got a fuel line and replaced the line and clamps, tested it, all good, put plastics on asks fueled it up. As soon as I took it for a ride it was stumbling again, no big deal, I'll just turn the screws back to 4.5 and go up in pilot jet size right. No, put it all back to the way it was and it's still stumbling and backfiring. Idles fine, runs wot fine, stubble on hard acceleration and if I rev the engine it doesn't want to come back down all the way to idle sometimes. Carb setting are dj 144 front 150 rear (around sea level) pilots are 40, dj needles 4th notch with one washer that came with the kit on them. I am lost, any suggestions are appreciated, I feel like changing stuff in the carbs might not be the answer because it ran well before on these settings. Isn't 40 pilots usually the fix for stumbling, do I need to go higher?
fightermatt is offline  
Sponsored Links
Advertisement
 
post #2 of 19 Old 05-09-2017, 07:02 PM
Moderator
 
NMKawierider's Avatar
 
Join Date: Apr 2009
Location: NM
Posts: 6,913
           
Not always is the #40s the fix for stumbling but it's a common need with the Dynatek CDIs. I would look at a couple of other things like..float levels, cracks on a carb boot under the head-side clamps, tight valves, low fuel volume or pressure, stuck tank vent check valve, low coil voltage.

06 BF 750 (Silver)
EZ-Steer EPS | Elka Stage-3s | 26" Grim Reapers on 14" SS112s | Dynatek CDI | Twin Air Filter | TPI Adjustable Airbox Valves | YFZ Catch Can Mod | Perma-Cool Oil Cooler | Diamond "G" Tie Rods w/Moose Ends | EPI Pink Primary W/ Almond Secondary | PowerMadd Handguards & Mirrors | Energy Swaybar Bushings | OMI Stem Bushing | 2013 a-arms & bushings | 2012 Seat | Ricochet Armor | HL Front Bumper | Direction2 Overfenders | Moose Dual Gasser Throttle

15 ZForce 800

NMKawierider is online now  
post #3 of 19 Old 05-09-2017, 08:11 PM Thread Starter
Newbie
 
Join Date: May 2017
Posts: 10
 
Thanks for the response. I know the boots are good, and I just adjusted valves. I replaced fuel line but it is a tiny tiny tiny bit smaller than factory, the bike runs great up top so I didn't think it was lacking fuel from that, could that be the problem? Where is the tank check valve? I don't know how to check the regulator or check or adjust float levels but I might could find a YouTube video. 42 pilots?
fightermatt is offline  
Sponsored Links
Advertisement
 
post #4 of 19 Old 05-10-2017, 07:22 AM
Forum Admin.
 
Polaris425's Avatar
 
Join Date: Dec 2004
Location: Tuscaloosa, Al
Posts: 15,122
Images: 77
         
Tank check valve will be above the tank, tucked into the frame rail. Most have pulled it out, and put a longer tube on it, and run it up with their other vent lines.

If it wasn't a returning issue, I'd say something electrical just got wet under the seat. My 07 had a similar issue when coming out of water, it would stumble and spit for the next few minutes until everything dried out. A little DE grease on all electrical connections under the seat and problem solved...

But since your's didnt just happen after being stuck in the water, I don't know that that's the problem.


MIMB - The REAL "Brute Central"


www.MudInMyBlood.com We Have a Thread for That...
Polaris425 is offline  
post #5 of 19 Old 05-10-2017, 07:48 AM Thread Starter
Newbie
 
Join Date: May 2017
Posts: 10
 
The only thing different on the bike is the fuel line, like I said, it's a touch smaller in diameter than oem. Even though it still runs hard on top I guess that could be the problem, I'll try a bigger one, and see if that helps. I've had for delivery problems on my motorcycle before and it presented when I tried to go fast. I'll look into the check valve as well. Thanks guys I'll keep you posted.
fightermatt is offline  
post #6 of 19 Old 05-10-2017, 12:38 PM
Moderator
 
NMKawierider's Avatar
 
Join Date: Apr 2009
Location: NM
Posts: 6,913
           
Grab the service manual and go for it.

06 BF 750 (Silver)
EZ-Steer EPS | Elka Stage-3s | 26" Grim Reapers on 14" SS112s | Dynatek CDI | Twin Air Filter | TPI Adjustable Airbox Valves | YFZ Catch Can Mod | Perma-Cool Oil Cooler | Diamond "G" Tie Rods w/Moose Ends | EPI Pink Primary W/ Almond Secondary | PowerMadd Handguards & Mirrors | Energy Swaybar Bushings | OMI Stem Bushing | 2013 a-arms & bushings | 2012 Seat | Ricochet Armor | HL Front Bumper | Direction2 Overfenders | Moose Dual Gasser Throttle

15 ZForce 800

NMKawierider is online now  
post #7 of 19 Old 05-12-2017, 11:26 AM Thread Starter
Newbie
 
Join Date: May 2017
Posts: 10
 
Ok, I read through the mimb jetting guide and it seems I'm lean on the slow circuit (hesitation stumble and a little rolling idle). I don't think it's the check valve because the bike runs the same with the fuel cap off. Even when it ran good it still had a little stumble and pop at a slow pace and I was 4.5 turns out on the a/f screws, so I ordered 42 pilots. However, my plugs are jet black, I think I'm rich on top. I've heard you shouldn't change more than one thing at a time but I can change the mains down a size when I install the 42 pilots right, I fell like the 2 circuits are doing opposite things, and I don't want to have to take the carbs off again if I don't have to, I've done it 5 times now and it's getting old?
fightermatt is offline  
post #8 of 19 Old 05-12-2017, 03:05 PM
Professional Mudder
 
dman66's Avatar
 
Join Date: Feb 2011
Location: Oley, Pa.
Posts: 1,163
Images: 18
 
Actually, if you dug deeper into the MIMB snorkel thread, you would have noticed that dialing in the 2" intake snorkel sucks ***. A lot of us went to a 3" intake snorkel which can allow for easier carb tuning. I personally did the 3" intake and installed a restriction on the intake so I could jet the carbs closer to stock jetting rather than installing bigger jets. I think if you are at sea level, then the 2" intake is OK, but once you get higher in elevation - you will struggle to properly tune those carbs with the 2" intake. The belt intake and exhaust are good with the 2" pipe. If you have a newer quad with fuel injection, then there are fuel programmers that seem to allow people to successfully tune the fuel system with the 2" intake.

05 750,Stock Engine,Muzzy Pro Exhaust, Uni Air Filter,
14" Vision Bruiser wheels, 26" Kenda Bear Claw HTR,
3" PVC Intake w/restriction - 2" ABS CVT, center snorkels,Carbs Keihin-#40 pilots 2 1/2 turns out A/F ,#158/#158 mains w/30 thous. washers under stock NFKL needles, 2012 front suspension,
Mr. Gasket 42s Fuel Pump Mod
10" Hayden s-type Electric Rad Fan Mod - mod fan mount
Aftermarket ebay radiator
dman66 is offline  
post #9 of 19 Old 05-12-2017, 07:21 PM Thread Starter
Newbie
 
Join Date: May 2017
Posts: 10
 
I think mine is 2.5 with 3 at the air box.
fightermatt is offline  
post #10 of 19 Old 05-13-2017, 06:41 AM
Professional Mudder
 
dman66's Avatar
 
Join Date: Feb 2011
Location: Oley, Pa.
Posts: 1,163
Images: 18
 
Sounds like ur pilot jets need to be cleaned.Ore the carbs need re cleaning.

05 750,Stock Engine,Muzzy Pro Exhaust, Uni Air Filter,
14" Vision Bruiser wheels, 26" Kenda Bear Claw HTR,
3" PVC Intake w/restriction - 2" ABS CVT, center snorkels,Carbs Keihin-#40 pilots 2 1/2 turns out A/F ,#158/#158 mains w/30 thous. washers under stock NFKL needles, 2012 front suspension,
Mr. Gasket 42s Fuel Pump Mod
10" Hayden s-type Electric Rad Fan Mod - mod fan mount
Aftermarket ebay radiator
dman66 is offline  
post #11 of 19 Old 05-19-2017, 07:03 PM Thread Starter
Newbie
 
Join Date: May 2017
Posts: 10
 
I installed keihin 42 pilots in and turned the a/f screws down to 2.25 out. No change, a/f to 3 turns out, got a little better; so I moved the needles to the 5th notch to richen up the mix, it is much better now but it will still stumble every once in awhile. Because the plugs were so black I put in 142 and 148 mains. I do think the float levels should be adjusted but I don't have a manual or special tools, so that will have to wait. Should I turn the a/f screw out to 3.5 to clean up the hesitation and backfire that happens every once in awhile on hard take offs, or take the needle to the 6th notch and go in on the screw? Maybe leave it alone until I can get to the floats.
fightermatt is offline  
post #12 of 19 Old 05-21-2017, 06:18 AM
Professional Mudder
 
dman66's Avatar
 
Join Date: Feb 2011
Location: Oley, Pa.
Posts: 1,163
Images: 18
 
It sounds like your carbs pilots need cleaning to me. You should not be adjusting pilot screws out past 3 turns. I don't know of anyone with a stock 750 engine - with snorkels running # 42 pilots - too rich in fuel. Lets see a pic of that snorkel set up.

After re reading this thread, it sounds like the you are experiencing the common 2" snorkel intake problems.

05 750,Stock Engine,Muzzy Pro Exhaust, Uni Air Filter,
14" Vision Bruiser wheels, 26" Kenda Bear Claw HTR,
3" PVC Intake w/restriction - 2" ABS CVT, center snorkels,Carbs Keihin-#40 pilots 2 1/2 turns out A/F ,#158/#158 mains w/30 thous. washers under stock NFKL needles, 2012 front suspension,
Mr. Gasket 42s Fuel Pump Mod
10" Hayden s-type Electric Rad Fan Mod - mod fan mount
Aftermarket ebay radiator
dman66 is offline  
post #13 of 19 Old 05-21-2017, 09:13 AM
Moderator
 
NMKawierider's Avatar
 
Join Date: Apr 2009
Location: NM
Posts: 6,913
           
To me this indicates either a blockage or low float levels. No one goes to #42 pilots like Dman says..way to rich for any 750...and the extra A/F opening indicates a lean condition as well. Check the float levels per the manual and check for carb boot cracks under the head side clamps. Also check fuel supply and the tank vent check.

06 BF 750 (Silver)
EZ-Steer EPS | Elka Stage-3s | 26" Grim Reapers on 14" SS112s | Dynatek CDI | Twin Air Filter | TPI Adjustable Airbox Valves | YFZ Catch Can Mod | Perma-Cool Oil Cooler | Diamond "G" Tie Rods w/Moose Ends | EPI Pink Primary W/ Almond Secondary | PowerMadd Handguards & Mirrors | Energy Swaybar Bushings | OMI Stem Bushing | 2013 a-arms & bushings | 2012 Seat | Ricochet Armor | HL Front Bumper | Direction2 Overfenders | Moose Dual Gasser Throttle

15 ZForce 800

NMKawierider is online now  
post #14 of 19 Old 05-24-2017, 08:59 AM Thread Starter
Newbie
 
Join Date: May 2017
Posts: 10
 
First let me say thanks to you guys for your help thus far, I know it gets old hearing the same problems from newbies like me. As of right now it has 42 pilots, a/f 1 turn out 142 front and 148 rear dynojet, dj needles on 5th notch. It is much better than before but I think I should have left the 144 and 150s in, right when I get to 60 mph it starts backfiring and dying, then backfires on deceleration. After it gets back to idle it will stumble and hesitate if I give it any gas for a bit then it cleans back up and goes back to normal. Sorry for the misinformation, it is 2 inch snorkel with 3 inch into the air box. I'm moving right soon so haven't had a lot of time to dig into it too much. I don't know how it's so lean, I know no-one is running 42s especially with the needles on the 5th notch, I'm going to put the 144/150 mains back in when I get off work Friday, after than everything else will have to wait until I finish moving. Can I get a manual from mimb?
fightermatt is offline  
post #15 of 19 Old 05-25-2017, 05:23 PM
Professional Mudder
 
dman66's Avatar
 
Join Date: Feb 2011
Location: Oley, Pa.
Posts: 1,163
Images: 18
 
A Dynojet 142 in front and a 144 or 146 in the rear carb should be good. You stated she gets up and boogies at WOT. So I would doubt that the slides are a problem, or the float levels either. So, I recommended cleaning you pilot jets, because it sounds like they are blocked with crap. I don't think you went and did this yet, but tried other crap. While your in there cleaning the pilot jets, check you float levels - I think the MacGyver way is to measure the bottom of the float to the middle flat side of the carb body where the bowl meets the carb body - I think it is like 3 to 4mm - This is spelled out in the service manual which you can google search for a free brute force 750 service manual pdf. Reinstall the #40 Keihin pilot jets and set the pilot screws at 2 1/2 turns out. Reinstall the OEM needles if you have them, or set the Dynojet washers back to mid range on the needle - you can richen her up later if needed. Disconnect the 2" intake and your machine should flip over backwards as long as your battery is good, valves were set properly, timing is proper, and other stuff needs to be running properly as well - You claimed it runs great from mid to WOT.

05 750,Stock Engine,Muzzy Pro Exhaust, Uni Air Filter,
14" Vision Bruiser wheels, 26" Kenda Bear Claw HTR,
3" PVC Intake w/restriction - 2" ABS CVT, center snorkels,Carbs Keihin-#40 pilots 2 1/2 turns out A/F ,#158/#158 mains w/30 thous. washers under stock NFKL needles, 2012 front suspension,
Mr. Gasket 42s Fuel Pump Mod
10" Hayden s-type Electric Rad Fan Mod - mod fan mount
Aftermarket ebay radiator
dman66 is offline  
Reply

Bookmarks

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the MudInMyBlood Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome