backfiring issue.

Hi guys im doing my first ever bobber build and i'm having a problem . As soon as the bike warms up it starts to backfire . It only takes about 5 minutes when i start up the bike then it starts to backifre and run rough . Any suggestions of what i might wanna check first ? I dont know alot about bikes because it is my first attempt at a build but i would appreciate any feed back you guys might have . Thanks

 

When is the last time valve clearances were checked?
You have pod filters on it?

My understanding is that backfiring / popping (are they the same?) is a reaction to the carbs running too lean.

If you are new to bikes what makes you think doing a 'bobber build' will be an easy task?
An easy task is to get an old (yet gently used) XJ, come here and refurbish it to factory condition with proper safety upgrades. You can be guided through it by this community. A bobber (to me means; must have pod filters) is a project that has you throwing darts in the dark to get the jetting of the carbs correct. . . . It can and has been done but every project is unique, the science behind it does not compare to the finally designed and engineered stock setup.

 

yes i do have pods on it .

 

I agree with Stumplifter. You are taking on a difficult project for being new to bikes. If you can replace the pods with the standard breather box and get the carbs set up with the stock jets and have a stock exhaust system it will make life a lot easier for you.

 

+1 Aribox is best.

You are running lean, maybe dangerously lean. If you insist on pods you must rejet, start with two sizes larger for both the pilot and the main jets. That will get you better, but not good, fueling. You'll have to play around with jetting from there.

Also, bobbers don't have pods.

 

I knew it would not be an easy task when i started it . I was only coming on here to ask for some advice. I thought that is what these forums were for , to help fellow riders with problems they encounter not to condemn them for their choices of setups they want to run on their bike . I m sorry if i took your comments the wrong way , but not everyone wants to ride a completely stock bike and so far i think my xj is turning out pretty good . Just having a few problems along the way and i expected to have some, nothing ever goes right the first time around . Well thanks for your feed back .

 

We are giving advice, not condemnation.

If you want to ride and not be frustrated with an engine that has fueling problems (midrange bog) then run the stock airbox. CV carbs don't play well with pods.
If you are building for looks and don't mind having fueling issues then do pods and start with the rejet that I reccomended.

What I can guarantee is that if you keep running the engine as it is now you will burn a hole in at least one piston before long.

Which XJ do you have?

 

thanks for your advice k-moe . I have an 82 xj 650 maxim

 

Keep the pics coming while you are building it.
I would start with airbox and get it running right. If you still want to move to pods, at least you start from a good base.

I run stock airbox on my somewhat customized bike and it runs great. I couldn't imagine having the work, which I am proud of, messed up by a poor performance/behavior of engine.

 

Hey, I have a great idea. Triumph created fuel injection bodies that look exactly like carbs. Why doesn't someone create air intakes that look like pods!!

 

Oh right? I saw them for the first time the other day. Didn't know how to take it though..

 

This is a pic of what it looks like right at the moment .

 

Nice. I like white walls.
See, with the battery box still in there, you might as well put the airbox back in.
Looks good, hope you get her running right soon.

 

Thanks Saftie , i'm still trying to decide what i'm gonna do . I might stick the airbox back in to see if that fixes the problem , if it doesnt then i'll just have to start back at square one again and send carbs out to be rebuilt i guess .

 

Please do not take it wrong ... pods may look cool but can be a bear to tune just right and can damage your engine if ran too lean . My seca 750 runs great with stock airbox I have not had to touch carbs since I rebuilt 2 month a go ... make your bike run well is what our aim is your bike looks good ... I just hope you take advise from some of the good folks here on the forum cheers

 

Good choice. If the airbox is back in, it will be easier to trouble shoot too.
The guys on the forum helped me and many others through some difficult carb times.
And trust me, you will love the bike even more once it purrs like a kitten.
I am working on another bike at the moment that backfires and leaks fuel and stuff. It is a bit annoying but I learned so much on here that I know once carbs are synced, it will go away. And if not, I can count on the guys...

 

Trust us when we say, running pod filters is a terrible decision unless you actually value aesthetics over a bike that runs well. CV carbs need a very specific intake air volume and velocity to function properly.

 

Thanks for all the advice guys . I'll let you know how it turns out .

 

i don't care about your pods but those mufflers need some support, there's too much leverage with a muffler that long just to be clamped on. your passenger peg mounts can be cut and trimmed to do a good job and not look too bad

 

Thanks for noticing Polock , i'm not done the bike yet . That is on the list of things to do still . I just got the pipes welded on that day that i took the pic.

 

I don't know but, aren't your mufflers mounted on the wrong side? I see something like a bracket or support under the RH side muffler that could be helpful to hang the same muffler on the LH side, just saying.

 

Great looking bike, - i can understand why you felt inclined to take the big ugly airbox off even though it's not been recommended. I nearly went the same route after taking my carbs on and off at least twenty or so times trying to get bike to run right, the worst part being the reattachment of the rubber boots to the air box every time. Anyway there was so much conflicting information about what jets needed changing etc, I gave up on the idea but will be interested to see how you get on with yours.

 

I like the look of your bike, but still would ditch the pods. Also, you better be careful not to slip off the seat or you'll sing several octaves higher--that is, if you survive.

 

Hi,

First of all: I agree with the rest, if you don't need to remove it, use the stock airfilter..

However, if you are like me, you listen to people, acknowledge their advice, bet get determined on making it work regardless. I got Pod filters my self now, and I ordered a 6sigma jet kit for them. I will tell you how that works when I recieve the kit.

Good luck with your build!

 

thanks for all the positive comments guys . I'm just in the middle of putting the air box back in now to see if it clears up some of my issues i'm having. Andnil please let me know how the carbs turn out for you i'm very interested to see if they work . I will post some more pics when i get more done on my bike .

 

Too easy, I will let you know.

I received the kit today, but the bike is in to get tires changes. When I get the kit, I talked to an old mechanic who will let me use his synchronise gauges and gas analyser, so should hopefully get a good normal mix which is not too lean.

The kit included Pilot jets size 45, Main jets sized 120 and 130 so I have options there, spacers for the needles and a drill for the shim.

I will put up pictures from installation when I get so far, will give it a go next weekend when bike is back.

 

Ok thanks Andil look forward to hearing back from you .

 

First off nice looking bike I hope the project goes well for you.
second I would also like to know how that jet kit works out because I also bought one but I'm a little skeptical (that's how I am about everything) but I have 2 sets of carbs so I'm going to put one set to stock settings and the other I will put the kit in, so if I do have to get rid of the pods I will have other carbs ready to go I will just have to find an air box.

I also saw a post a wile back that had pod filters but made I guess what you would call a breather tube that basically conects 1 pod to 2 carbs so I'm going to try and make something like that up but with a little more restrictions to the air flow through the pods

 

Well i put the airbox back in and put it all back together and im still getting the backfiring when it warms up . So i guess my carbs must be messed up . Don't know much about rebuilding carbs so i guess i'm going to have to send them out to get rebuilt .

 

Learn to do it yourself. It's not difficult, and they will come out better than paying a shop (unless you send them to Hogfiddles).

IN THE CHURCH OF CLEAN


But before you do that pull the plugs and post up pics. number them by which cylinder they come from and take the photos over a white background. Also count how many turns it takes to bring the idle mixture screws to a soft seat. They should be between 2.5 and 3 turns out.

 

This is what my plugs looked like when i pulled them out of the bike .

 

It's a bit hard to see with those. We really need to be looking at the insuator, base ring, and ground strap.
I think see incomplete combustion, but can't tell if the soot is dry or wet, or oily.

 

I think my problem is that when i was putting the engine back in it had got hung up on a couple of the spark plug wires and had pulled the boot off of 1 . Unless those boots are removeable which i dont think they are .

 

I tried pushing it back on but i think it is getting an intermiten spark and that might be my problem . ?

 

They screw on. Righty tighty.

 

Thanks K-moe .