Backfire on decel...

[ti2ibal1]

Hey y'all, got a question for ya. After installing my HMF slip on, Uni filter and re-jetting to a 165 main and 42 pilot, I'm getting a lot of backfire when I'm deceling.

I tried fattening up the main to 170, but that didn't help. I've got a 155 main laying around, but I think that may be to lean with my mods.

Could it be the pilot? Is this something that aftermarket exhaust just does? It's not that it bothers me, I just don't want to harm the engine.

[dariusld]

It could be more than one thing. One it could be your jetting. Two it could be your header pipe. I f the exhaust isn't sealing at the head then you will get popping. Did you just put the slip-on on or did you mess with header pipe also?

When you jetted it, did you mess with the pilot screw? And what is it set at?

No, backfire isn't normal. Did you use a jet kit?

[ti2ibal1]

Originally posted by dariusld
It could be more than one thing. One it could be your jetting. Two it could be your header pipe. I f the exhaust isn't sealing at the head then you will get popping. Did you just put the slip-on on or did you mess with header pipe also?

When you jetted it, did you mess with the pilot screw? And what is it set at?

No, backfire isn't normal. Did you use a jet kit?

It's just a slip on. I was gentle with removal and installation. I made it a point not to tweak the header.

I have not touched the pilot screw. All I've done is install the new jets. I did not use a jet kit. I just purchased a new main.

It's not so much of a backfire, as it is popping and snapping. I haven't really had a chance to get out on it for any period of time since the install. I haven't had it fully warmed up. Could that pose such an issue?

[dariusld]

I'm no jetting expert, but your pilot sounds a little rich to me. Some will say your rich all over. But its better to be on the rich side then the lean side. If your bike pulls hard I wouldn't worry about it. But that popping is annoying. I would screw the pilot screw in a little at time and see if that helps with the popping, then adjust from there. First know where its set at initially, so you can get back there if have to. Is this the year with the D adjusting screw? Maybe someone else will chime in also.

[440challenger]

Try w/o the lid.
Did it b/f before the exhaust/jetting?

[leasureryan]

lol^^^...do a search....every and I mean EVERYONE will tell you that a backfire/pop/snap crackle, etc...means you are lean on your pilot circuit. Bump the pilot up 1 size, and turn your screw out to 2 1/2 turns out from seated. Guarantee fix!

[440challenger]

If it did it before ,your air cut valve could be bad.

[ti2ibal1]

Originally posted by leasureryan
lol^^^...do a search....every and I mean EVERYONE will tell you that a backfire/pop/snap crackle, etc...means you are lean on your pilot circuit. Bump the pilot up 1 size, and turn your screw out to 2 1/2 turns out from seated. Guarantee fix!

I'm running a 42 pilot and that is to lean? I understand there is a pilot screw, where is it located? I don't want to go adjusting the wrong thing. Is it the one on the side of the carb?

Thanks for your help.

[leasureryan]

I tried every possible jetting combo with my stock carb and full HMF....only thing that cured my backfire on decel was getting the 450R carb. Running the 48 pilot, and 175 main. Sounds beautiful now...perfect.

The air screw in on bottom of carb, front, by the edge of the float bowl motor side intake. You will have to use a 90 angle driver to adjust it, or turn carb 90 degrees or take it off. Pain in the rear

[drillteamleader]

what you need to do is put a 40 pilot in and adjust your idle mixture screw. It is on the bottom of the carb and is a d shaped head, so you need to get the tool to adjust it. That popping is from being lean on your idle circut, but even with all the stuff done to my quad I still don't need a 42. the screw you are talking about is to adjust the rpm's at idle, so you need to look a little closer to the bottom of the carb, there is a place that sticks down and has a little screw in it.

[Eviltanker]

You might want to think about changing your needle also. 06 did not have an adjustible needle. when I did mine I put a new needle in and set it in the middle. along with a 40, and a 160

[400ex28]

Throw in that 155 main.

[dang400ex]

A 165 or even 160 is way to rich if you only have a slip-on and stock motor. I run a 155 main and 42 pilot at 1000 ft above sea level. No popping. I have a hmf slip-on and uni filter...

[ti2ibal1]

Thanks you all for your input. I'll install the 155 main and adjust the screw out two and one half turns to get a baseline. If that fails, I will purchase a 40 pilot, as all I currently have is the stock one and the 42.

Thank you again.

[dariusld]

Originally posted by ti2ibal1
as all I currently have is the stock one and the 42.



You could just try the stock one and adjust your pilot screw. I had a 416 and stock pilot and it did fine.

[ti2ibal1]

Originally posted by dariusld
You could just try the stock one and adjust your pilot screw. I had a 416 and stock pilot and it did fine.

You're right. As long as I've got everything torn apart, I may as well try the stock pilot.

Thank you.

[leasureryan]

Originally posted by dang400ex
A 165 or even 160 is way to rich if you only have a slip-on and stock motor. I run a 155 main and 42 pilot at 1000 ft above sea level. No popping. I have a hmf slip-on and uni filter...
Dude...HMF sends a 165 with thier slip ons....and I don't think thats to rich for an HMF. Now...FMF powercore is more like a 155


Be careful running lean bro.....thats all I'm going to say.

Now...I'm out before someone gets upset with me for having an opinon

[dariusld]

Originally posted by leasureryan
Now...I'm out before someone gets upset with me for having an opinion

When it comes to jetting there is right and wrong. Now if it was "this is what it did" or "you can try this"or "this should get you close". Not "do this" or "this is the way to do it". You always come off the second way....to me. Thats my opinion;)

[dariusld]

The red circle. This is a older carb, yours won't be slot , it will look like the letter D.

[ti2ibal1]

Originally posted by leasureryan
Dude...HMF sends a 165 with thier slip ons....and I don't think thats to rich for an HMF. Now...FMF powercore is more like a 155


Be careful running lean bro.....thats all I'm going to say.

Now...I'm out before someone gets upset with me for having an opinon
I did not recieve any jets with my slip on.

Perhap I'll just concern myself with the pilot settings for now until I can pull the plug.

When turning the screw out, am I fattening the idle? In would be leaning it?

[dariusld]

Originally posted by ti2ibal1
I did not recieve any jets with my slip on.

Perhap I'll just concern myself with the pilot settings for now until I can pull the plug.

When turning the screw out, am I fattening the idle? In would be leaning it?

Yes:) But remember if you have the air leak at the header all this jetting won't get rid of the popping.

[the Z Man]

Probly an exhaust leak, could be at the head or the clamp for the slip on, seen both...
Put in new head pipe gaskets and tighten the clamp, bet it goes away..

[ti2ibal1]

Is a header leak something that's pretty obvious? I mean, is it something that I could diagnose by checking it? I'll go over everything with a fine tooth comb. It did not do this before the installation.

I'm still going to change the pilot out and adjust the screw. It hasn't been idling right since I've installed the pipe, intake and jetting.

[dariusld]

Check the header bolts to see if they are tight . But unless you removed the header I don't know why it would leak.

I think after you put the stock pilot jet back in and adjust the pilot screw you will have a nicer idle.

[ti2ibal1]

Originally posted by dariusld
Check the header bolts to see if they are tight . But unless you removed the header I don't know why it would leak.

I think after you put the stock pilot jet back in and adjust the pilot screw you will have a nicer idle.

I'll double check the bolts when I get home. I was extra gentle when I was removing the stock muffler and also when installing the new one. I honestly don't think that's the issue, but it won't hurt just to make sure.

I'm hoping the pilot work will help with idle. It for sure feels like it's getting to much fuel. When i give it a small 1/4 throttle rev, it stumbles and stalls while returning to idle. Like I mentioned before, this also may be due to it not being fully warmed up.

I truely appreciate everyones posts.

[leasureryan]

Originally posted by ti2ibal1
I did not recieve any jets with my slip on.

Perhap I'll just concern myself with the pilot settings for now until I can pull the plug.

When turning the screw out, am I fattening the idle? In would be leaning it?

All HMF's are supposed to come with a jet.

If you are turning the air screw out...that would be leaning the mixture

in would be less air meaning more fuel=rich

[440challenger]

Originally posted by leasureryan
All HMF's are supposed to come with a jet.

If you are turning the air screw out...that would be leaning the mixture

in would be less air meaning more fuel=rich

Were an HMF dealer direct, and through TR and never did an hmf come with the jets or JET,unless you bought it off ebay and the seller throws in a jet to try and sweeten the deal

[drillteamleader]

this is what is wrong with forum pages. there are people who want to be experts and tell you what they know, but they might confuse people who don't. The screw that is in the picture is what you need to adjust. It will fatten up only the idle if you unscrew it. You must adjust it while the bike is running to get it right. If the motor is not warmed up it will run lean unless it is over jetted to begin with, so before you go changing a bunch of stuff, let it warm up fully.

[400exrider707]

I agree with the above post...

This thread is full of wrong information.

Ok so you put an exhaust on and need to jet.

First off, if your HMF came with a jet, the HMF's notoriously come with way too rich of a main jet. The chances of a 400ex needing a 165 main with just a slip-on are extremely rare.

The size of your motor (400,416,426) doesn't dictate was size jets you need. I've seen large bore motors have to drop down main jet sizes. It's all relative to the vacuum pulse on the carb, that the motor creates. Some motors can pull more fuel through a given jet size than others, just because of how well the motor is pulling vacuum.




Ok so on to your problem: You say its popping on Decel. I think most are in agreement taht you are lean on the idle circuit, which is correct. Changing the pilot is not the best solution here, though it may be needed. Start with unscrewing that gold adjustment screw in the pic. You are supposed to do this with the quad running! WIth it warmed up and at idle, turn the idle up to a good fast idle. Now adjust that screw 1/4 -1/2 turn at a time. Let it sit for a few seconds after each ajustment because the motor needs to catch up to the adjustment. Once you get it to where it sounds like it is idling the best, then lower your idle back down to normal and ride on! If it still pops on decel, back the screw out another 1/4 turn.

HOWEVER.... if you have to back the screw out more than three (3) full turns from fully seated, you need to bump the pilot jet up one size and repeat the first steps of adjusting the idle screw. This should cure your problem.

If it's running fine everywhere else I wouldn't worry too much about the other circuits for now. Though your main does seem a touch high, and I would also invest in an adjustable needle.

[ti2ibal1]

Last night I adjusted the pilot screw and installed the stock pilot and the 155 main. It fired right up and purred like a kitten in the garage.

I let it run for 5 minutes or so and started to just lightly stab the gas. (No choke on.) It revs up great and doesn't seem like it's falling on it's face anymore when coming back down to idle.

I did give it a 1/2 throttle rev and during the motors decel, it popped and sputtered. Like you all have said, this is something I need to do when I've got it fully warmed up and running. I guess it was also help if I didn't work on it at 3am, and could take it for a spin and see how it's running.

I'll report back after I take it out tomorrow. Thanks again for your help everyone. I really do appreciate it.

[400exrider707]

Originally posted by ti2ibal1
Last night I adjusted the pilot screw and installed the stock pilot and the 155 main. It fired right up and purred like a kitten in the garage.

I let it run for 5 minutes or so and started to just lightly stab the gas. (No choke on.) It revs up great and doesn't seem like it's falling on it's face anymore when coming back down to idle.

I did give it a 1/2 throttle rev and during the motors decel, it popped and sputtered. Like you all have said, this is something I need to do when I've got it fully warmed up and running. I guess it was also help if I didn't work on it at 3am, and could take it for a spin and see how it's running.

I'll report back after I take it out tomorrow. Thanks again for your help everyone. I really do appreciate it.

Running it in the garage and riding it aruond the yard are two way different things. You need to have a load on the motor to see how the jetting is. I've heard quads that sounded awesome in neutral, click them into gear and try riding it and its stumbling and falling on its face cause the jetting is so far off. It really needs to be warm and have a load on it to check for proper jetting.

[ti2ibal1]

I couldn't agree more. Unfortunantly, I live in the city and my neighbors probably wouldn't be to happy with me buzzing up the street at 3am. (I work 2nd shift.)

I'm going out with a few friends tomorrow for a Thanksgiving ride. I'll take some tools and the jets with me in case I need to make some adjustments in the field.

[ti2ibal1]

Today I finally got a chance to get out and get some seat time on my bike since making the jetting changes.

Like I previously posted, it idles just fine now. I got out to the trails and just cruised around letting it warm up. Once it did, I started to hit it hard, and boy did it go!

I could tell right from the get-go that this set-up of slip on and air filter really uncorked this thing! We have a sand bowl that I used to hit in second, pop out, and then hit a big berm. Before, it really used to bog hard when I'd enter the berm after the jump. Now, I nail it and it pulls like a train right through it! I come out of it and it's pulling the front tires and begging for 3rd!

The backfiring issue is all but gone now that I've put the stock jet in and played with the pilot screw.

I would like to thank everyone for all their input and help with all my questions and concerns. I'm glad to be a part of this forum!

[dariusld]

:) :) :) Ask a question. Get responses. Apply the responses. Post results with a positive outcome. Perfect post. Way to go ti2ibal1. A little effort and a little help goes a long way
:D :D :D