No go after 3/4 throttle??

morningwood

morningwood

New Member
81 honda cm400e. Stock shorty straight pipes(muffs etc removed) and pod filters (air box gone). Carbs were just cleaned and am using fresh 93 octane fuel. Bike starts and idles fine and accelerates decent until 3/4 quarter throttle then starts sputtering and doesnt accelerate. Other problems noticed include: right cylinder backfiring and running noticeably cooler in temp. left cylinder running much hotter then right and firing much harder (exhuast gasses coming out with much greater pressure then right) and making loud popping noise, stuck intake valve? Mainly trying to figure out the problem with post 3/4 throttle (main jet problem?), but listed known problems incase they are contributing factors? any help welcome and thanks!
 
My vote is on a plugged main jet or maybe the needle was put back in at the wrong height. Sounds like a main jet problem tho if its only sputtering from 3/4 and up. If cool exhaust is coming out at idle then start checking electrical things. Not sure if that bike has points or not
 
Why no mufflers and airbox? To each their own, but that's the first red flag I saw.

The other problem is the firing on one side either you have an electrical issue (spark), fuel (clogged carb), or loss of compression.
 
appreciate the input. more help is welcome! will be working on it this week, if solved I will let ya know what did it! thanks
 
did you tune you carbs accordingly to your mods? youll need to do that if you didnt.
also sync them.
and from experience and other's experience, our old bikes prefer regular gasoline, no fancy stuff.
try all that first.
back firing and popping are all signs that your carbs need tuning.

and you didnt mess with the timing right?
 
Sooper dooper lean.
When you up-jet, it will run like shit mid-range
They don't like pods, carbs will need a lot of work to run close to stock.
I haven't done one so can't help with jetting or modifications
Easiest thing to do is re-fit stock airbox, you loose a lot of performance with pods on the Kei-Hin 3 jet piston CV carbs
It has a double ended coil so if one side is firing the other side has to.
Must be carbs or mechanical.
Don't know how far/long you've ridden it but you could have already damaged exhaust valves
 
adjusted valves. installed larger main jets and lifted the needles. Bike now screams mid and top end! low end is a little sluggish but ive been tuning it out and its getting better. couldnt be happier.
 
You can't "fix" an exhaust and filter problem with jetting. You can make it feel less bad, but you will still have less performance than stock.

First problem is short pipes without mufflers. They screw up any bike, and are way noisy, so you get worse performance and too much noise. Pods screw up the jetting on those carbs that can't be fixed with just main jet changes.

It may sound good to you but it's a good bet that it's making much less power than stock. Unfortunately thems the facts.

There's a great video on Youtube by S&S about the problems of so called drag pipes. It's well worth watching.
 
dam bud, hate on. Please let me know where i said i fixed your listed problems. I simply did the adjustments i stated and then shared my results. Im not guna argue with you. you win! and clearly you know everything about my bike from your desk! Thanks for your contribution to this thread.
 
You are kidding yes?

Don't get your knickers in a knot. I'm not a hater. Just because people don't agree with you or they offer advice or insight doesn't make them haters. I'm just trying to add a reality check to your results. Correct. I don't know your bike, but I do know a little bit about carbs and pipes.

I don't know everything though. I'm still learning. I used to know everything, but the more I learned, the more I realized that I didn't know.

Your post said you had short pipes sans mufflers - at least that's how I interpreted what you said - and we know form experience the issues that they create. Here's that link

http://www.youtube.com/watch?v=KjKUKhHQLHg

As you can see from that video, it is possible to change jets to smooth out and reduce some of the problems, but you still end up with a bike that makes less power than stock (as a rule).
 
He is right. No performance Out of straight pipes unless you "need" them because of heavy engine modifications.
But if the straight Pipes fit the look and style you like then tune the best you can for your app, that way you don't burn your valves.
 
Hurley,
The issue with straight pipes is that they only work over a very small powerband and at all over engine speeds they send a pressure wave that arrives at the "wrong" time and makes things worse than stock. Agree totally that if you fit straight pipes, changes in jetting can make it less obnoxious.

Not sure that you ever "need" drag pipes - unless of course you run a bike that stays within that narrow band like a drag bike and usually there are better alternatives. I have a race bike with straight pipes and it's fine as long as I keep the revs where they need to be. On our small twins we usually fit 2 into 1 because that works slightly better at most revs than straight pipes, but on the street most decent mufflers will work better than open pipes - an of course they are obnoxiously loud.

There are tracks where we can't run straight pipes and have to fit rudimentary mufflers to take the edge off the noise, and race track noise limits are fairly lenient, so I can't imagine running open pipes on the street.
 
Totally agree with everything you have said you are absolutely correct.
by saying "need" I meant pretty much a drag setup.
And yup totally annoying on the street.
And +1 on the muffler.
 
I think 4 other peeps already mentioned mufflers and pods as a problem before I stumbled across the thread. I was really just trying to let Mr wood understand that he can make it less bad, but it isn't optimal. Sometimes that comes across slightly bluntly.
 
I didn't think you came off bad at all, I just took it as helpfull advice.
Besides, the Internet always messes up things and makes things sound different.
I feel sometimes people add pods and modded exhaust for looks, but don't realize that sometimes it can be harmful instead of good.

Mr.wood, don't take all this the wrong way, I assure you the tone in which all this is being written is not rude at all. We like to make motorcycles not war. Lol
 
teazer, again your contributions to this thread are useless. You dont understand I never said I fixed "some problem" or complained about the problems associated with my straight pipes, which is clearly evident have your panties in a bunch, that is the way my bike is set up not yours. I posted to share my results after the listed changes I made and what there effect was, never anything about my bike running better than stock and making more power. Some people mod in a similar way as I and will experience similar effects so i posted what i had done to help bring back some power and ride-ability for those. As i found numerous threads about pods and exhaust mods performance complaints but none with people sharing changes they had made after to help. That is why I posted, to hopefully help some people. I could give a shit what anyone thinks about my bike.
 
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