went riding at a large ride area on saturday and my new honda 400ex was running like crap.I put 93 octane gas in it in the morning.Almost a full tank.And this is what i have ran from the start in it.After about a hour it started being boggy in second and third gear untill you kicked in the powerband and it cleared out.I have only had the quad for about 3 months and put about 12 hours or so on it.I just did my first oil change on it last tuesday and this was the first ride after the oil change.Checked the plug and it was perfect.I know the quad was running hot but i have also heard this could be a sign to get the valves adjusted.What do you guys think.Bad gas or does it need a valve adjustment already?

 

drain the gas and put fresh in.

 

I don't think it's either.

 

What do you think it is then.

 

Nothing personal,just my opinion, but first of all, you are wasting your money on premium gas,that motor was designed to run just fine on 87 octane regular. Premium does not mean more power, it burns slower to prevent predetonation in higher compression motors. While it may run fine, over time it can cause unburnt fuel deposites or other problems. As far as your bogging problem,is it on the low end,as you are taking off? could be a bad or plugged accelerator pump passage,or the pump diaphram is bad (I think that carb has a little acc.pump diaphram,I could be wrong). If it seems to run ok when you get the revs up, it kinda points to that, once you are rolling, the acc. pump is out of the circuit, and you are running on the main jet. May be time for a carb cleaning/rebuild.

 

I don't know where this kind of misinformation comes from (maybe from folks who don't own one and don't know what they are talking about?), but my owner's manual specs "92 octane or higher"! This engine is air cooled, so it will run hot at times. For this reason you need to keep the octane up there to avoid any possibility of detonation.

Good suggestion to drain and refill the tank. Also, be sure your tank vent is not blocked!

Normally, one does not do a valve adjustment until the engine is completely broken-in at 20 hours, but yours could have been off from the factory.

In any case, it should still be on warranty, so make it the dealer's problem!!!

 

I'm not starting a fight, just stating a fact, it may say that in your manual, but a standard Honda motor is about 8.2 or 9:1, well below the need for premium. I own a 300ex that has never had premium and been run hard for years,I do have a 440ex with 11:1,that runs premium. My 95 Wolverine with a 446 big bore and 10.25:1 piston has run quite well on pump gas for the last year and a half, the only time I filled it with premium was during the ATV parade record in Silver Bay,MN in June, I spent most of the day idling and moving very slow,so it got VERY hot,and I used 92 octane to battle preignition from lack of cooling. I have never heard so much as a ping on trail rides or working around the woods. The only quads I know of so far that spec 92 or better from the factory are the new 450 sport quads, the Suzukis run 11 or 12:1 in stock form,I don't know about some of the others.

 

Well i took it out for a little bit today and it is still running like crap, even cold.It is basically spitting and sputtering but only when you are on the gas.And it does it in every gear.If you get on it hard it seems to clear a little like a carbon build up but goes right back to it again.It does not do it at idol.And it does not stall out.I guess i am going to drain the gas out and see if that makes a difference first.

PS.It ran great 2 weekends ago.And all i did was change the oil on a tuesday and add gass on saturday morning.Then went riding and about a hour after i started riding it started running bad.

 

This is a classic case of simplistic thinking! Just because some other engine of whatever compression needs a certain octane....doesn't transfer to any other engine out there!!!

Again, the EX is air cooled and will run hot at times! Besides, lots of other things come into play, like valve overlap, etc., etc. The engineers who designed your EX knew this, and therefore speced 92 or greater. Get real.....you going to believe them, or some Wolverine owner?????


And....don't mess around here! If it is new and on warranty, get it back to the dealer quick......

 

Sounds like one of the jets may be stopped up and the carb may need to be cleaned but I agree with RR, if it's under warranty, don't let any time go by unnecessarily... get that thing back to the dealer quick!!!