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I have a Honda CB400 Super-Four.

My bike starts and rides but I can't get more than 5000rpm out of her. If I do then she floods and cuts out. Two of her exhaust pipes are cold and two are warm.

What could be the problem?

Please help thanks

  • 3
    Well, the two cool pipes indicate those cylinders are not firing. Have you checked the spark going to those two? Are those two getting fuel? When you're sitting on or looking at the bike, which two are warm, and which are cool? – JPhi1618 Dec 9 '15 at 18:53
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    What two pipes are cold and what are hot? Does the condition only surface once the bike get's to operating temperature? – DucatiKiller Dec 9 '15 at 20:50
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    Also, do you have the original ignition system with points or have you swapped it out for an aftermarket with an electronic ignition? – DucatiKiller Dec 9 '15 at 20:57
  • Thanks guys if I sit on the bike the to that is cold is one on my outer left n second one from my right. When I start the bike it smells flooded – Ricardo Dec 10 '15 at 18:57
  • I'm not sure if the ignition was changed the bike did have a service about 2 months ago – Ricardo Dec 10 '15 at 19:02
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Background

You have two coils on that motorcycle. One coil is for cylinder 2 and 3 the other is for cylinder 1 and 4. It utilizes what is known as a wasted spark system, the spark is fired off on TDC compression and TDC exhaust strokes.

You apparently have an issue with one of your two systems. Each system, as you probably know, is comprised of two spark plugs, one coil and one point with condenser.

Any one of these could be the source of your issues.

Motorcycle Coil Test

You can test your coil with a multimeter. Set the multimeter to ohms and test between the low voltage primary wire and the ground wire. Resistance should be 1 to 1.5 ohms. Next, test the secondary high tension wire (attaches to spark plug) and the grounding bar that would touch your frame when it is mounted to the bike. It should be somewhere between 5500 to 13000 ohms. If you are outside of that you may want to consider replacement. If the bike seems ok when it is cold and then loses spark once it's heated up, you could have an open inside the coil where the gap in the open is expanded due to the heat and is actually created when the coil get's hot. You can test the coil when it's hot and then put it in your freezer for a bit and test it again to see if your results vary. If they do, it's bad and you will need to replace.

You can also do a voltage test on your hot lead, of course it should be 12.6 volts.

Errata

Your points are so cheap that they aren't worth testing and frankly, due to the cost, I have never researched or even attempted to test points and condenser on any of my old bikes. Just R&R and move on regarding that one.

You indicated that the bike 'floods out'. Do you have any evidence that the bike is actually flooding or is this just a feeling you have? If it is flooding on your cold cylinders then it could be fouling those plugs which would explain why those cylinders are cold. Initially, you can take a screwdriver handle, and vigorously tap the associated carburetors to free up the needle and seat in your float bowls. If fuel is flowing through the system, be careful, it can leak into your cylinders and fill them with gas. When you go to try and start the bike you would get a hydro-lock condition and bend your connecting rods. I've seen it happen to A LOT of people on older bikes with petcocks and carburetors.

If you fear fluid has filled up your cylinders remove your spark plugs and turn over your engine by hand. Any liquid will squirt out of your cylinders so place rag accordingly and have a fire extinguisher handy, just in case. Once you've turned it over by hand, turn it over with the starter to eject any remaining fuel. Allow the any remaining fuel to evaporate, if you have an air compressor shoot some compressed air around the area and into the cylinders to deal with the last of the fuel before you insert your spark plugs and attempt to start the bike.

  • Wouldn't the coils fire just before TDC on both of those? Semantics, I'm sure, but every good running engine I've ever dealt with has advance in the ignition system to get the best performance. :D Good answer, BTW - +1. – Pᴀᴜʟsᴛᴇʀ2 Dec 10 '15 at 0:46
  • yes, I just been really wordy and was trying to apply brevity. I typically fail there. Attempting to remediate. You are correct though. TY – DucatiKiller Dec 10 '15 at 0:49
1

Loss of high end performance can be due to several issues.

Old gas. Old gas doesn't burn as quickly. My bike is always sluggish running through the gas that's been sitting in the tank over the winter.

Not enough gas. Check the filter on your petcock. It might be clogged with rust and only letting through enough gas for lower speeds. Disconnect one of the hoses from the carbs, open the petcock and let the gas run into an appropriate container. You should get a good stream.

If the petcock tests ok, maybe your carbs need to be cleaned. The float pivots or float valve might be sticky with varnish so it can't react quickly or move freely enough to keep the bowls filled during high demand.

Out of tune. How long has it been since you performed a tune-up? Get a Haynes manual and do a basic tune-up. Adjust your valves, points/ignition timing.

Weak or failing ignition. @ducatikiller covered most of this but I'll add that your points could be arcing at high RPM due to a bad condenser. Take the points cover off and rev the engine and see if you can see arcing.

  • Good point regarding the arcing and a more comprehensive response +1 – DucatiKiller Mar 1 '16 at 21:40
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cb 400 has limiter after replacing the display panel with an after market digital or analog the limiter supply is cut off so you nee to go to the ecu igniter just connet the 2 wire orange with blue stripe to the black with white stripe the you can notice that the limits revs in the 5000 rpm will disappear good luck

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