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Discussion Starter #1
I have an 05 750

It sat most of the winter without being ridden, I had some dickhead "tune it up" for me while I was gone due to being unable to do it myself and I know for a fact he screwed something up,

Now when riding it backfires hard pretty much anywhere in the 20-100% throttle range only time it's not doing it is like first 10%, doesn't matter if engine is cold or warm. I have it completely stripped down to frame right now all plastics off

Both plugs are very black, I need to pick up new ones

I need a new belt, one red indicator light on dash but it's been on before this issue started.

I pulled the fuel pump and checked the sock it's spotless, but it seems rich so I don't think flow is the issue, it's been bone dry under the quad so no fuel overflowing

Carbs are both pulled off, I haven't opened them yet, should I get a new carb kit or try cleaning it without? (covid is making things hard to get atm where I am)

This is one the most over complicated piece of equipment I've disassembled in a long time, atleast the 05 year anyway. Pretty annoying
 

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If you think the 05 is complicated to pull down, wait till you have to do a new one.

Check that the fuel is all new, no old stuff in it, drain the bowls to assure there is no water in them. Check the head-side carb boots for cracks. Usually under the clamp. Most important-check that the choke plungers are shutting. That the cables are not twisted, rusted or have any pinches. Second most important-it's an 05-that means it has the buss connection issue. ALL of them have corroded wheather they were ever in water or not. There are videos on this and we have then in out Brute Technical section. Also check the valve lash.

What red light is ON? It may be in limp mode.
 

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Discussion Starter #3
Stripped it down
Front carb was extremely green and gross looking I'm guessing from ethanol fuel, but the back looked pristine it was really odd, forsure tho my front carb jets and tubes were very plugged up, I'm gonna say that most likely why it was running bad but why only one of the carbs?

I checked the fuel pickup that was totally clean, started putting it all back together tonight but now I have no spark, quickly reading I'm thinking maybe a rollover switch? I pulled the entire electrical box out so maybe I installed the switch upside down, it's late so I packed it in, didn't have time to print the service manual last week I'll do it on Monday, but I know it's something I did putting it back together, also I tried it without the belt, belt guard and the sensors for the belt guard box on, would that also affect it?
 

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Discussion Starter #4
Also forgot to add, new plugs, fuel was drained, no water, buss connection has been done already
 

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Discussion Starter #5
Tilt switch was upside down 🙃

Fires starts, doesn't backfire and idle poorly anymore. But it is in limp mode because I have no belt on, I'll replace it this week and report back. Already sounds better then it did last week so I have high hopes
 

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Did you adjust your valve clearances yet? Having such drastic symptoms in one carb kinda makes me wonder if your backfiring may have been seeping into the carb. For some reason the front piston valves always get really sloppy, at least more than the rear piston.
If you already have the fenders off what is another 10 min on those bad boys? 😉 I just did a "plastic off" overhaul on my '06 650i which included adjusting the valves as they were getting the chatter at all revs with some backfiring at steady throttle and deceleration. Dying when you engine brake to a stop etc.

WOW, what a difference! Sounds like the day I bought her! And she fires right up when cold. Be sure to use the alignment port just left of the eng oil dipstick. Even a half degree off TDC throws the clearance off noticably.
 

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Discussion Starter #7
I got a new belt, new plugs, cleaned carbs new gas, reset the limp mode belt light and it's still backfiring both in the exhaust and the airbox. Doesn't sound right idling

The rear plug is pretty black compared to the front.

I picked it up and drove it home from this moron that "went through it for me" a few months ago and it didn't backfire at all on the way home, so I don't think it's valves. I've never done them before but I will try it tomorrow.

Any other suggestions, no fuel coming from the overflows, no boots ripped or cracked,
 

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Discussion Starter #8
Also what should the stock fuel screws be set to, I counted 5 half turns out on each before I took it apart to clean. Aka 2.5
 

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What mods are done to the exhaust, engine, and is there snorkels installed ? If snorkels installed - What size intake snorkel ?
What brand of jets do you have in each carb, and what are the sizes stamped on the jets, what needles are in the slides ?
Have you checked timing, and have you checked / adjusted valves ?
 

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Discussion Starter #10
I have owned this quad for years and never had a problem before so it's nothing to do with jetting, and it's all stock no mods
 

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Discussion Starter #11
Lmao.

So I adjusted the valves for rear intake and exhaust with timing mark set in line with TR. And same for front with TF.

.005 for intake and 008 for exhaust. Now it's ticking, still back firing and running like ****.

What am I doing wrong here


Also the backfiring doesn't change with choke applied or not, the plungers aren't sticking. Nothing is ripped inside the carbs
 

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Discussion Starter #12
So the manual says you line it up basically so the T is at the same mark as the notch on the inspection port.. But there is a line above the T, is it supposed to be lined up with that instead?
 

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So the manual says you line it up basically so the T is at the same mark as the notch on the inspection port.. But there is a line above the T, is it supposed to be lined up with that instead?
You line the marks up at the ( T ) of the TR - rear / TF - Front marks.
Just out of curiosity, what is the running battery voltage.
 

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Discussion Starter #15
this is pretty much exactly how i set the valves except i used the TF/TR marks right on the T line, i went and rechecked with my feeler gauge the the clearances are still where i set them... but this thing is ticking so loud now, i will check what the output voltage is in the morning when its running, im starting to think this is an electrical issue, because it came out of nowhere, and i did have to use a jump pack to start it once in the winter, and thats when i noticed the backfiring, the ride before that was fine
 

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Discussion Starter #16
Ok update

I found the carb vent line past the white plastic 2 to 1 fitting was completely blocked with ****, so I cleaned that out, I re did the valves again and they are much quieter but still a bit noisier then they were before I touched it, I used 005 for intake and 007 for exhaust, it seems as if the intake popping has completely disappeared, it idles now without popping, on the gas it still pops around 20%of the time instead of 80% so im getting closer to solving this.


With the intake off it can give it solid 1/4 throttle with no backfiring, at idle the carb slides fluttering with the motor rpm is that normal?

I went from 2.5 turns out in each float bowl to 2 5/8 that didn't seem to make a difference, I've sprayed started fluid all around the boots while running and no change in idle so I'm not leaking air

Any more ideas what to try next?
 

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Discussion Starter #17
I just made a video and it started backfiring out the carb again...im kinda glad though you can see what's happening.


Watching this now it just sounds to me like it's not inhaling air smoothly? If that makes sense, sounds like it's chugging maybe, let me know what you think

 

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I feel your pain....... had the same issues on my 05, ended up being clogged carb passages. Also got improvement from the tiny adjustment screw at the bottom of the carb
( pilot jet screw ? ) Still has a little backfiring when cold but goes away after 5 minutes so i live with it.
 
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