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Thanks for the info about the effect of the different filters and airbox mods on the CFM. Great stuff! Glad I found this forum!

If the UNI filter provides an additional 9CFM, should I expect any carb issues like backfires, running lean, hard to start, ...?
So that I can always have a clean filter on hand I have a stock foam air filter and a UNI filter.

When one filter gets dirty, I pull it and install the clean one. Notably, whenever I switch between the two filters there are no changes in carburetion behavior, suggesting that the air flow capability is similar between the two filters.

Jason
 

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Thanks for the info about the effect of the different filters and airbox mods on the CFM. Great stuff! Glad I found this forum!

If the UNI filter provides an additional 9CFM, should I expect any carb issues like backfires, running lean, hard to start, ...?
The Uni flows 9 CFM better than the K&N, not 9CFM better than stock. I would suspect the stock filter's performance is closer to the Uni than the K&N; you should be fine.

Dave
 

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Regarding the screen, I pulled off my Uni filter to check inside. I couldn’t get inside the clean side of the air box because the screen was in the way. I didn’t know that was a “feature.” Mine was about 50% blocked by some kind of waxy deposits, presumably from oil deposits from the filter. About 15 minutes of scrubbing with a parts brush and kerosene, then more with carb cleaner, got it off. I’m thinking of cutting it out completely. Any pros or cons?

People have done it though it's a safety measure as Paul said. Myself, for the loss of backfire protection, relatively small flow gains and the gigantic PITA to remove the screen, I don't bother. I've heard some people say they've "popped out" the screen, but when I tried I had to cut it out and then I was left with little bits of wire around the edges that I thought could end up where they shouldn't. Pulling the snorkle and the L mod should really get you all the flow you need unless you have a ported and cammed 719.

Dave
 

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That was my thinking too. It looks like it is molded into the plastic of the air box, so to get it out would require removing the airbox and working on it on the bench to cut it out. I’ll leave well enough alone. But as for the safety factor, I have a hard time seeing how a backfire could get out past the air cleaner assembly anyway.
 

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That was my thinking too. It looks like it is molded into the plastic of the air box, so to get it out would require removing the airbox and working on it on the bench to cut it out. I’ll leave well enough alone. But as for the safety factor, I have a hard time seeing how a backfire could get out past the air cleaner assembly anyway.
Though rare, what happens is a backfire toasts the air filter....sometimes to the point of a hole.

Dave
 

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But as for the safety factor, I have a hard time seeing how a backfire could get out past the air cleaner assembly anyway.
When people clean only in a highly flammable fluid in the field or in their own garages and do not follow up with warm soapy water, 2 rinses & allow to thoroughly dry before re-oiling, but rather just slop some oil on the still gaseous foam filter and stuffem' back in the air box, is when they are susceptible to a back-fire caused filter fire.

Luckily, the KLF and KVF atv's have a replaceable plastic filter mounting triangle, rather than the permanently molded in triangle like the KLR. As I have replaced numerous atv mounts & foam filters.
Many of the atvs use a plastic throttle slide rather than aluminum. I've seen the lower rear edges singed, so the engine had to still be running or at least Cranking continuously. Wow!
 

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When people clean only in a highly flammable fluid in the field or in their own garages and do not follow up with warm soapy water, 2 rinses & allow to thoroughly dry before re-oiling, but rather just slop some oil on the still gaseous foam filter and stuffem' back in the air box, is when they are susceptible to a back-fire caused filter fire.
That sounds a lot like what I do! LOL.......well, as I've mentioned, I'm pretty lazy. I do wash my filters in gasoline but I try to let them dry out before the "slopping"! ;-)

Dave
 

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The 'back-fire' flame arrestor screen is there for a good reason on 4 stroke engines. Do as you wish.
Did you drain the cleaner from the clean side Air Box drain hose? Hopefully, the clean side drain hose still has a cap?
Lol my hose cap and bottle was so brittle first time I saw it underneath it broke completely off. At the time, didn’t even know what it was (when I first got my KLR).

As for the 1” filter vents: they’re not “safer” than the L mod, then? I was thinking of lining up several instead of the wide open L mod before your advice of air boxes.

But are they equally useless on the sides or door to gain air without completely removing 1/3 of the door?

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Lol my hose cap and bottle was so brittle first time I saw it underneath it broke completely off. At the time, didn’t even know what it was (when I first got my KLR).

As for the 1” filter vents: they’re not “safer” than the L mod, then? I was thinking of lining up several instead of the wide open L mod before your advice of air boxes.

But are they equally useless on the sides or door to gain air without completely removing 1/3 of the door?

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Yes, the little filter vents are 100% useless wherever you put them; all they do is reverse the flow increases that you made by making the holes in the first place and you have zero need for additonal filtration - your main filter does the filtering regardless of where the air is coming from. With those little filters, all you are doing is forcing the flow to come from the stock filter location as air always takes the path of least resistance......once they get dirty, I suspect they wouldn't flow much at all.

....and I don't recommend messing with the door; there is no need - you can get all the flow you can handle by doing the L mod.......if you really wanted more than that then you can enlarge the snorkle opening too but unless you are heavily modified, that isn't going to make any difference.

Dave
 

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Gotcha. Saw the door mod tested in diff ways from a guy pushing 50-60hp it was amazing...but I’m not chasing that. If I can get closer to 40 than stock without wrecking the engine or MPG I’m good. Not chasing power, just looking for it where it comes easily (KLX kit will be first upgrade, then L-mod w/ a Big Gun exhaust eventually).

It’s more important to me my engine lasts so I don’t need a new one for many years. I’m at 20k miles so it’s not too far along.

Not trying to let it sit outside taken apart nor do a 685 since I don’t have a garage. Much less the cost...trying to save for suspension.


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