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Discussion Starter #1
I have a 1992 Honda Nighthawk 750 project. I'm trying to run straight through exhaust and pod filters. So I put in 125 mains, 40 pilots and 2 shims. After putting everything back together on the bike, it turns over, but backfires through the exhaust and the carbs. It does not start. Fuel is new. Any advice...besides the typical 'put the airbox back on'?

It definitely flooded the first time I tried to start it. I cleared it and dried the (new) spark plugs and... same result.

What am I missing here?
 

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What am I missing here?
Common sense, a scientific approach, thinking like a mechanic.

Here is what you do. Put everything back to the way it was stock. Perform tune up procedure including carb sync and valve adjustment. Start bike and verify everything works as it should. Then remove mufflers. Run the bike and do a plug chop to see if the bike needs more fuel or not. Then walk over to your neighbors and ask him if the noise is tolerable. If he punches you in the face put the mufflers back on. If not then jet accordingly by going up size by size until the bike is no longer lean/rich. Then remove airbox. Take pod filter in hand. Ask yourself "did I buy shitty cheap used pod because I am not smart enough to google pod filter before hand?". Look at box, does it say EMGO, Dixie, or tucker rockey on it? Does it say anything other than Uni or k&n? If so throw in trash. Look inside pod and see if there is an internal ledge that actually shrinks the opening down? If so throw in trash. Buy new filters from k&n or Uni, spend more than $8 on them. Spend real money. Learn lesson about parts selection. Install new better filters. Start plug chop. Keep increasing in size until lean/rich condition goes away. Realize a month later that you are not smarter than a Honda engineer and you don't like people hating you and put mufflers and airbox back on.

any schmuck can buy a kit and be a parts changer. Being a real mechanic requires you to think and diagnose. Your carbs are actually weather measuring devices and as such are sensitive to the atmospheric conditions dspicific to your locale. Sometimes jet "kits" work and sometimes they do not, it all depends on how lucky you are. Advice on what sizes to use over the Internet is useless and not a substitute for actual carb tuning skills.
 

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Don't forget to put a screwdriver (preferably JIS) into a butane flame long enough to get it red hot, then jam it directly in your eye.

That will give you an idea of how painful it will be to get your motor to run well by throwing parts at it.

-Deek
 

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Change one thing at a time homie. Even if you want to go against everything these guys tell you, don't do it all at once, or you'll have no idea what's causing your problem. The best advice is usually the stuff you don't like hearing, and this thread is a great example of that.

A word about running straight pipes: I'm going to assume you're in your early 20's, maybe even late teens. There was a time in my life when I thought I could get away with anything, when it came to the way I treat my body, so I get it. Never mind the fact that your neighbors will hate you. Never mind the fact that you'll be missing valuable sonic information both from the environment and your bike (Like how your motor is running or if a wheel bearing is about to fail), and never mind that you're making riders in general look like assholes who don't care about anyone else. Think about your ears man!
 

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When I hear and read about people modifying intakes,carbs,exhausts,etc. it makes me wonder if and/or how much scientific research is done by aftermarket companies. An example of this, is Vance and Hines. Terry and Byron actually bench flow tested their products,and were one of the first to do this and the results showed in their work. They took the early gs Suzuki's to a status that we still see today. That is only one example and I'm sure there are many. There have been a few times when I've been given the pipes at a stoplight by some hacks that do not realize the difference between symbolism and substance. I will continue to reach down and disconnect the#1 spark plug wire just before the light turns green , and leave them sitting there with wide eyes and slack jaw as I launch when the light turns green and I'm gone. Most of those fools turn off somewhere and won't even speak to you at the next light.
 

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Discussion Starter #9
Hahaha you guys are harsh! I'm going to get it running well, don't you fret. I'm going to mess with the carbs tonight. If the exhaust is too loud, I'll change it. Maybe it will be, but I don't see a lot of difference between that and drag pipes. Neighbors are not that close anyway. I'm not a kid, just a guy with a garage and a dream. Thanks for the constructive feedback!
 

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i think you're ignoring the sage wisdom in this thread.

the question really is what is your goal, if your goal is to get it running well, and I'm assuming, fast, then yeah, put everything back the way it was and do a proper tune up, ride it until you're familiar with how fast it goes and where it makes power and doesn't. change one thing, if it improves, continue to tweak until it stops improving. move on to the next part, keep doing that until you run out of things to do to make it faster (you never do really, that's the fun). believe me, you're about the 20,000'th person to log on here and ask for jet sizes for open exhaust and pods, and it always begs the question, why do you think honda built the bike with an airbox and muffler? because the engineers there were knuckledragging cro-magnon? nope, it was cause it worked very well, and trust me, no shitty pods are going to work better than a large cavity of air and properly designed intake stacks. how many motogp bikes do you see with pods and open exhaust? do you think rossi would be just a bit faster if he hacksawed his exhaust and threw some pods on that bike? don't you think most of the people on here have tried the open exhaust and pods before? we're not coming down on them because we're grumpy. well, we are, but that's not the reason. anyway, maybe you'll take the advice, maybe you won't, just hope you don't get dusted by a 400f with airbox and muffler, that would just be plain embarassing
 

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Mr.Bill, some are harsh because we've been there and done that. We know what works and what doesn't. Those that have a long history and have built competitive bikes for racing or competitive use, already know what works and what does not. You can experiment all you want, but I doubt very much that you know more than the Honda engineers that designed your bike. I know nothing about you or your motorcycling knowledge, and I won't speak for others, but I won't do your homework for you, when it comes to experiment time. You need to give specifics regarding stock carb size,jet sizes, etc. The fact that you are running pods on an inline 4 speaks volumes about your ignorance about airflow. Take a course in small engine repair, then automotive courses in performance and then you may grasp what the grumpy old codgers (like me )are telling you. BTW, don't give me the pipes with your whippoorwill, for someone will surely piss in your pickles .
 

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Discussion Starter #12
Yes, I get it. It's difficult to do and affords marginal improvements. The goal here is to get it running. I've seen it done before, so I know it's possible.
I'm not questioning the wisdom of Honda engineers, at all. By your logic, no one would ever modify anything.

I'm not asking for jet sizes. I tried to hedge this whole jet size trial and error ordeal by using a jet calculator, which gave me the sizes I installed based on the criteria of this setup. Even if it's not running as well as it should, it ought to at least start. I'm simply asking for advice on how to get it running.

There's so much unwarranted negativity here. It seems like there are plenty of knowledgeable people around, but no one can offer any tips.

I'm just some guy in his garage building a bike in his spare time. I've resorted to forums because it's getting warmer and I want to finish this thing up. There's no need for condescension. There is, however, need for tips on how one might get a bike started which (currently) has no filters, larger jets, and an open exhaust. Has no one rebuilt a machine and had starting problems?
 

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The problem here is that we have no idea if your bike ran fine before the mufflers and air filters were removed or if there is a huge issue such as holes in pistons or timing chain skipped a tooth or so on.

Th eother issue that others are alluding to is that you want help with a very poorly defined probelm and you appear to expect to get that help even though you don't appear to listen to what is being said. I get that you don't appreciate the way it might have been delivered, but there's some wisdom among those words in most cases.

Think of it this way, some dud walks into your local bar/club/backyard/whatever and says my car won't start and he tells them as much as you told us, you might feel inclined to help or you might just think that the guy needs to re-think his approach. All I'm saying is that it would be helpful if you better defined the problem and were maybe a little more open to listening to what was said and to reflect on those replies.

If you want to be helped, then help us to help you. :)
 

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You guys all suck and are meanies. I am going to help this guy.
1. you need fuel, spark and compression, which one is missing?
2. If you have all 3, is the spark arriving at the right time?
3. If it is, then are you getting enough fuel or too much at idle?

There, answer those questions and it should run.

BTW, it will never run well with open pipes and pods. It might run ok at some RPM, but it will always have a miss or stumble somewhere, especially if you whack open the throttle. With careful jetting, you can move the miss around the rev range but never make it go away.
 

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"By your logic, no one would ever modify anything."

no, by my logic, the things that are modified will be fast as shit and have zero instagram appeal.

let me tell you a bit about my experience, years ago I got a cb750 and tried running pods and open exhaust and knew absolute jack shit about bikes, but I knew everything, so I ignored the advice of others and had a bike that ran like shit but in my mind was super awesome because it looked cool. then I met a friend who also had a cb750 that looked pretty plain but kicked the shit out of mine, had literally twice the acceleration, so it got my attention, I listened to his advice, and through that, learned just how little I knew, so I shut my mouth and opened my ears, my bike got faster bit by bit, I started buying the right tools, better understanding tuning, better understanding what makes a fast engine and what makes an engine suck, understanding the importance of tuning by ONE variable at a time, keeping tuning logs so I always know what settings the bike is at and the correlation with my experience and a/f readings. in the world of building fast bikes, I consider myself still knowing jack shit, but I can at least tell you that you're making the same mistakes I did and if you want to progress, you need to open your mind to some of the good input you're getting here
 

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If you feel like there's no place for condescension here, then it's your problem, not anyone else's. I'll tell you one thing though; the fact that you think there's a "need" for us to give you tips on how to start a bike at all means you're being pretty condescending yourself.

As to your question: "Has no one rebuilt a machine and had starting problems?" The answer of course is "yes." The difference is I don't know anyone here who would "rebuild a machine" and try to get it running with no filters, larger jets and an open exhaust UNLESS they had it running well in that state before the rebuild.

So give us some information: What do you mean by "rebuild?" Did you have the motor apart or just out of the frame? Did it run before the "rebuild?" What changed during the "rebuild" other than the things you've mentioned?

Start with the basics:

Air.
Fuel.
Spark.

Assuming compression and correct ignition timing, that's all you need for an Otto cycle motor to "run" so start there.

-Deek
 

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I've seen it done before, so I know it's possible.
I saw David Copperfield once ride a harley fatboy off a 10 foot platform into thin air, but I wouldn't want to try it without proper instruction, training, practice and knowing what the fuck I was doing. Also it probably would help to for me to know it was an illusion and not have me thinking that DC can actually bend time and space.

you've seen it done - ask yourself, are you saavy enough to know what a good running bike looks like? taking someone else's word for it has as much significance as a fart in a stiff breeze.

We are not saying your goal is impossible (actually ken is kinda saying that and he is 99.9% right), but we are saying your methods of getting that goal are not going to get you there. If you were a saavy mechanic who has done this 100 times you can kind of skip the learning curve stuff, but then again if you are that person you aren't asking these kind of questions on the internet - you are getting it right on the first or second try. For you the best thing is to make small changes one at a time and take readings. That is how you learn and also how you figure out how certain things have certain impacts on the running.

It sounds to me like you have a combination of problems stacked on top of each other and right now you don't know what caused these things. If you were making changes one at a time you would know because you would make a change and the thing changes for the worse. So go back to stock and now test the system by making changes one at a time to figure out what's causing your issue. This is us teaching you how to fish, we can't catch a fish for you because you can't catch fish on the internet.

I think your first big mistake was assuming that because you were running an open pipe and no aribox your carbs needed a rejet. While I do agree they will need some kind of adjustment I have no idea where you pulled that 125 main jet out of, or that you needed to shim the needle with 2 shims since you can't tell me if the bike was rich or lean after removing the airbox and mufflers.

Stop applying car logic. motorcycles are not cars. the airbox is not necessarily restrictive and motorcycles have way more gran prix racing tech than cars and usually the engineers that design this stuff know what they are doing. At very least they know more than you. respect the technology, be humble, and try to understand the function of every part. The airbox usually has velocity stacks built into it (most pods do not) and use the plenum effect and helmholtz resonance to help improve part throttle rideability. Pods do none of this crap.
 

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I'd listen to what everyone else has posted. Don't want to? atleast do this.

Make sure static timing is kosher.
Remove shims from the needle and put idle jet back to stock. Probably should put carb back to 100% stock. Then see if it will atleast idle. Work your way from there to get bike running right.
Still won't run? put the stock air box on, and keep on reversing what you did till it runs.
 

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There's so much unwarranted negativity here. It seems like there are plenty of knowledgeable people around, but no one can offer any tips.
I'm full of positive energy, been meditating, you should try it.

So you killed the plugs when you flooded it. How did you flood it? There's no accelerator pump right?(I don't think anyway) So you had to have had a needle and seat, a float or a spark issue. I can't tell from here. What did you find?
 
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