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Bad Backfire coasting downhill

16K views 24 replies 10 participants last post by  1stRhino 
#1 ·
I have 450 with the intake snorkeled out under the hood. It was running fine. I did a header wrap on it last week. Now when I am coasting downhill it backfires alot everytime. If I give it just the slightest little bit of gas on the downhill it does not backfire. Is this an issue with the idle screw adjustment? To lean or to rich?

Thanks in advance
 
#3 ·
It's probably an exhaust leak. I Had a ALBA head pipe crack just inside the flange area on both pipes where they bolt up. I think it was due to using the header wrap. It gets the pipe too hot and under stress it is weaker and subject to failure. The header wrap also is not good if you are going to be getting it wet alot. My stainless pipe had rust on it from the header wrap getting wet alot which could have also led to the cracking. I had to buy a new headpipe because ALBA wouldn't warranty the cracked one. good luck and keep us posted on the outcome.
 
#7 ·
Thanks for the input. I checked the exhaust for leaks/cracks and didn't notice any when I reinstalled the pipe after the wrap. I will try turnig out the idle screw a little and see if that helps. Probably will not get a chance to try it again until next weekend. I will let you know what happens.

Thanks again for the input.
 
#10 ·
Donut is back in. I checked the exhaust for leaks after the re-install. I put my hand as close to the pipe as I could feeling for escaping exhaust. Is there any other way to check for exhaust leaks. I find it hard to believe the pipe would crystalize and crack in the first 5 miles after the install. The first hill I coasted down it was backfiring. I'm thinking that the extra heat may becausing it to detonate and backfire. I am going to try working with the idle mixture screw first and see if that will fix it. That will be this coming weekends project.
 
#9 ·
Absolutely adjust the idle screw for backfiring and popping...

Actually you need to tune the carb from top to bottom...

All those kinds of problems go away with a well tuned carb and consistent fuel delivery...

Assuming you don't have a cracked header...

Even still...the tuning is woth it...

Also...snorkels totally dork the operation of the stock carb...tuning is much more difficult...and can be impossible to get to fully work depending on HOW the snorkle is done...
 
#12 ·
Absolutely adjust the idle screw for backfiring and popping...

Actually you need to tune the carb from top to bottom...

All those kinds of problems go away with a well tuned carb and consistent fuel delivery...

Assuming you don't have a cracked header...

Even still...the tuning is woth it...

Also...snorkels totally dork the operation of the stock carb...tuning is much more difficult...and can be impossible to get to fully work depending on HOW the snorkle is done...
Agree!!
 
#13 ·
I was only kidding about the get what you deserve part...

But... it's true... :lol:

Actually...

It takes more time and effort to try to fix it w/o doing it right and with piss poor results...

In the end...it pays to get what you need and learn to optimize every element of the fuel delivery system...but especially the carb it's self...

And, believe it or not... A restrictive air intake is your worst enemy when in high temps, high elevation, hill climb/decent and throttle response in general...especially with the stock carb...
 
#14 ·
Believe this or not, most snorkels make the engine run lean and it is because the opening in the end of the snorkel is larger than the stock opening and you lose some of your vacuum needed to operate the slides correctly and meter fuel correctly.

If this is your case you can start taping off the opening a little bit at a time until it runs right.
 
#15 ·
I agree that the snorkles...including the factory one causes leaner operation...but, worst of all...it causes lean stumble when you stomp the throttle from a dead stop...and kills throttle response...the slide doesn't lift as it should but opening the throttle let's in a huge amount of air w/ no gas to go with it...

But it's not the opening size...and the stock snorkle opening is smaller than the airbox opening...so just tossing the factory snorkle is a huge improvement...running 04 style with proper tuning helps tremendously...and that is basically what WW did with his raise tube...which works better than stock but not nearly good enough for me and puts noise more noise in the cab...

Taping off the opening is like putting a turniquette on your leg for a scraped knee... :)

People say backfiring....to describe the symptom...

However I have seen it many times in two forms...

1. Any time you let off the throttle and it starts "popping" like a .22 rifle...that is lean idle a/f and typically the pilot jet in the stock carb is way too small...making it somewhat difficult to tune out with a/f screw alone...if the vehicle is bone stock...try removing the snorkle and see if helps...then try removing the airbox lid...that will almost certainly help....careful not to let the filter come loose...

2. At warm/hot operating temps...when the motor is settling down towards idle...especially after a hard wot run...you may get a loud KA-BOOM...one time...more like a 12ga shotgun blast...that is usually the result of a combination of high idle rpms, needle postition too high, rich idle a/f...if the vehicle is bone stock...again opening the air box will help with immeadiate relief as will lowering the idle rpms...lowering the needle postion is quick and easy and done from the top of the carb...

IN ALL CASES...your best performance will come from completely tuning the carb...and in all cases...your best throttle response will come with the highest possible flowing air intake....which is a big-ass k&n with no airbox...

It's not always practical to run no air box and there is no debating w/ me that the k&n let's in super fine dust where a well oiled (spray-on is best) 2 stg foam filter will keep the air intake charge absolutely clean as a whistle...
 
#16 ·
Tyrap I appreciate all the good advice. I consider you the most knowledgeable person on this forum when it comes to carb tuning. The whole reason I snorkeled the 450 was to get the noise out of the cab. I have photos on how it was done here:
http://www.rhinoforums.net/how/17639-quest-quieter-ride.html
It did a lot to reduce the noise. In a 450 you are going at a higher rpm most of the time to get any speed so it tends to be louder than a 660.
It actually did run the same as stock until I did the header wrap. The only thing not stock is a HW CDI and HW 1.5 exhaust tip. I was really surprised that it did all the backfiring due to the wrap. Like I said I will try tuning it out this weekend. If it does not work I guess I will be removing the wrap. Again thanks for the input. I was hoping you would chime in on this.
 
#17 ·
Thanks for the compliments...my BEST advice is to always consider EVERYONE's inputs... :)

I must also apologize my rants are always geared at the 660 which is the only rhino(s) I have had...

I do have lot's of time with lot's of snorkels/quiet intakes as well as super high flow ones...

IMO...

The best thing you could do to have best of both...quiet and high flow...is to remove the snorkle...block off the scoop...and just use the airbox "04-style"...that assumes you run in enough water and mud to need an airbox...

You give up cleaner air and have to clean the filter more often....that is nowhere near as bad as having the snorkle hamper performance or having the insane noise in your ear...and is made easier if you have 3 air filter elements....one on the vehicle...one soaking in zep orange bio juice...and one clean/dry/oiled in a ziplock bag ready to pop in/on...been there...done that...for a couple thousand miles...works great...

Or do what I do now...get a big-ass k&n and an aluminum adapter...stick it on the end of the intake tube where the airbox goes...it will make more noise than foam w/ airbox...but run better w/ far less maintenance...

I am not saying you can't make it work w/ snorkle...just saying you will always be after it with tuning and never get the full performance you surely desire...

Everything is trade-off...

A guy recently told me regarding marriage (his not mine...)...you are either going to be miserable or lonely... pick one.. :)
 
#18 · (Edited)
I went 04 style on my 05 660 - took the OEM snorkle that stretched from airbox to scoop, taped over the hole inside the scoop. Just to be sure, I took some wire mesh (from an old screen door) and wrapped it over the opening on the airbox, to keep any big clumps of dirt/mud from getting into airbox. Clamped it down with a hose clamp. So far it has worked like a champ. here's a pic:
 

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#19 ·
I did exactly what is in the picture above minus the screen door. I tuned the carb today, rejetting, and adjusting the a/f screw as stated. Replaced the fuel filter, air filter, lowered the idle rpms. Took it down the road and let off the gas and kaboom. Every single time you let off the gas after getting the rpms up on a run it will pop. I replaced the factory exhaust that was rusted out with a new factory exhaust. Saw no cracks at the header. Any suggestions now?
 
#20 ·
What pilot jet, mainjet, needle setting and idle a/f screw setting do you have it at now...???

Clear tubing from the Y to the carb inlet...????

What cdi... If you have an aftermarket cdi put the stock cdi in...

What does the plug look like...???
 
#21 ·
Well after trying several jet combinations, I think I finally have the snorkeled 450 running great. I went from a 20 to a 25 pilot jet with a 135 main and that was way to rich couldn't get over 34mph on a flat road before it started to sputter. Dropped the pilot jet to a 22.5 and put in a 130 main. It ran great last weekend. Much better acceleration and runs right up to 38-39 like before the snorkel. The 130 may be a little lean for the desert around Phoenix (stock main was a 133.8) but I will be taking it to the place in Heber (6,500 ft) next week for the summer. I will see if it is still good with the 130 main. If it is rich I will put in the 127.5 that I was using last summer in the mountains.
 
#22 ·
ok I've got the exact same problem[shotgun on the down hill]read the thread and and thinking about these steps .but heres what I got '08 450 ,2inch exhaust cap and the 9foot 2.5 inch underhood snorkle .stock air cleaner
so first do I raise or lower the Idle speed[it might be a shade low']
and if do rejet what #should I go to,I play mostly from sea level to about 3ooo feet
last time I checked the plug it looked gray and clean.
there is about 4750 miles on Brother Rhino,one of my buddies sugested I should start by checking the valves
any thoughts
 
#23 ·
I recommend going to the next size up on the pilot jet. That is what cured my problem. The pilot jet has a lot to do with fuel mixture for the 1st 1/4 of throttle then the main takes over. If you are popping when coasting downhill your main is not involved. It is your pilot and idle adjustment screw. On mine it had a 20 pilot and I went to a 22.5 and it fixed the problem and runs great. Make sure you get the same pilot jet. There are 2 types one is a little fatter. Take it with you when you go to purchase to be sure.

Hope this helps.
 
#25 ·
Faceman,

You should be able to change the pilot and or main jet. Just remove the float bowl from the bottom of the carb and the jets are exposed. Do a search on here for How to Jet a Carb (it is a sticky in the engine section) post # 41 has a detailed photo showing the different jets. The hardest part of the whole thing is getting out the soft screws that hold the float bowl. You will probably strip the head of at least one. You will want to replace them with stainless steel socket head screws if you are going to take this apart more than once. (Note these are metric screws)

good luck and let me know if this solves your problem.
 
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