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Discussion Starter · #1 ·
I have an 03’ Suzuki Ltz 400 and I’m doing a lil project on it slowly but surely and adding more parts on it here and there but I decided to install an HMF Competition Series Slip-On. Look I know and would do all the work myself but I don’t necessarily have the time so I take it to a very good and trusted lil shop around my town and it’s just a solo mechanic doing all the work and I’ve known him for a very long time and he’s done work on my bike for the longest and has always left my bike minty as possible and running as strong as possible, so about a month ago I took him the HMF pipe and he installed it and he even rejetted it and even put a new kit on the carb and it absolutely sounds mean and sounds nice at idle and I ride it a little bit around my neighborhood and it seems to be running fine with absolutely no flaws. But not until today till my uncle tried it out he said that it’d bog when he wanted to run up on the gears he said it wasn’t pulling the power to it’s potential mind you this my uncle has been riding quads way longer than me until this point and he’s worked on bikes and quads also at a point and my dad tried it out and he said the same thing and in my head I’m trynna think how come all of a sudden they’re noticing this? Because I rode it before them and it was running fine in my opinion, then my uncle suggested to remove the air box lid because he said the bike wasn’t getting enough airflow and it needed to breathe and he said to run it like that and to romp up on the gears to see for myself how itd run now so I ride it without the air box lid and as I’m going up through the gears I noticed a heavy increase in power like drastically, in second gear it literally had so much snap now that I thought I was throttling it down in 3rd the bike felt happier if that makes sense because before I removed the air box lid I wasn’t getting that much as response in the throttle but initially I didn’t see nothing wrong with it at the time personally in my opinion I thought it was normal the power was like that because the more open I got on the throttle the power felt normal but I guess it wasn’t because now it feels so much better and more responsive and I guess you can say runs more better without the air box lid. Anyways I had some questions due to these circumstances what do you guys request I should do? Cause currently Im running just your normal standard foam filter but a week back I ordered a UNI foam filter that I still have yet to install myself and the HMF website requests that is a recommended filter for the quad so you think I should install that one or look into a k&n one with an outerwear sleeve? You think I won’t experience any engine damage in the future because I see removing the air box lid does increase and open up power but I hear people damaging their engines in the long run? Will running the bike without the air box lid make the bike ever run rich or lean? Any other mod suggestions that’ll make the bike run good and strong in the long run in the state that it’s in at the moment? I am eventually planning to take it out to the dirt this season coming up and I know the lid prevents dust, sand, dirt and clutter make its way into the filter and I obviously don’t want the bike running bad out there so what would be the best idea for that? Is it also normal that the bike runs properly now without the air box lid and should I be on the lookout for negatives cause of it?
 

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If I recall correctly typically with a slip on rejetting is not required. Only until you add the head pipe does it really make much of a difference. That being said your mechanic could have jetted it rich therefor removing the air box lid leaned it back closer to correct jetting by allowing more airflow. I have been running my quad without the lid since 2003. The engine damage comes from people removing it and not jetting for it. And as far as the UNI vs K&N filter most here will probably tell you to stick with the UNI. I would suggest keeping an eye on your spark plug to see if it showing signs of lean even though it can be difficult at times to diagnose.
 
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Discussion Starter · #3 ·
If I recall correctly typically with a slip on rejetting is not required. Only until you add the head pipe does it really make much of a difference. That being said your mechanic could have jetted it rich therefor removing the air box lid leaned it back closer to correct jetting by allowing more airflow. I have been running my quad without the lid since 2003. The engine damage comes from people removing it and not jetting for it. And as far as the UNI vs K&N filter most here will probably tell you to stick with the UNI. I would suggest keeping an eye on your spark plug to see if it showing signs of lean even though it can be difficult at times to diagnose.
Thank you for responding and taking time to read my thread bobsz! But how checking the spark plug will show signs of lean? And you think my bike is fine overall and normal then?
 

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You wont tell much with unleaded fuel looking at the plug., unless its actually melting the electrode or has melted piston stuck to it.
bobz is right on about the jetting. Either put the lid on and jet it back down, or enjoy it with the lid off. Be careful around water though.
 
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Discussion Starter · #5 ·
I appreciate the reply! Yeah ima just run it without the lid I called my mechanic the other day and he said he jetted it to the number as the instructions said he said as well to run it w the UNI filter because it’s thicker material and has more restriction letting dust and other gunk in. I don’t ride in the water at all where I’m from it’s very very dry.
 
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