Help needed :( Cylinder 1 & 2 not firing CB400SF

[VocalNeal]

 

I think this is you? 

 

So you say definitely no spark on 1 and 2? 

 

Swap leads 1 and 4 and 2 and 3 if there is enough cable and see if it runs on 1 and 2 this way? Should but not on 3 and 4. This will eliminate the carb. as well.  

 

Unusual for two coils to fail at the same time?

[Pepper9187]

17 hours ago, Isaanbiker said:

OP, just had an enlightenment, my thoughts went back to a time where I had the same problem. 

 

   I had something very similar in 1977 when I'd bought a Honda CB 500 F from a guy for almost nothing, with the same problem(s). They'd taken the half bike apart, but didn't check on the easy things. 

 

   It took only 20 minutes to find the culprit. One screen inside the tank was so full of dirt that there's no more fuel flow getting to two cylinders. I'd assume that you've got two outlets as well, haven't you? 

 

   Please do following: Take the tubes that go to the carbs/fuel injectors? off, then open and see. The two cylinders not working could be on one particular tube.

 

   Please report back. 

 

 

 

  

   

Interesting.

 

Ok : im a <deleted>, i forgot i had to make contact with the chassis when trying the spark plugs.

I feel like 14 years old again trying to fix my MBK41. The good Honda god was very kind with me so far i never had to get my hands dirty on my honda's or any bigbike, it's payback time now !

 

I checked and basically, 1 fuel out from the tank, splitting in 2 lines, it could be that because these 2 lines handle the carbs 1&2 / 3&4, but

 

I'm just wondering, i always have gas in the carbs, every-time i emptied them with the screw, there's some gas, so ... could it be like half stuck, it can deliver but just not enough ?

My kingdom for a decent toolbox ! that fuel line is held by a kind of "inverted" clamp  in a very twisted location aaaaaaaaaaaaah

 

 

[VocalNeal]

Tap each carburettor with a small hammer. 

 

Stuck float?

[Pepper9187]

Just now, VocalNeal said:

Tap each carburettor with a small hammer. 

 

Stuck float?

Ok, NOW you're talking.

 

THAT is something i can do, WHERE IS MY HAMMER ????

 

Yaaaaaaaaaaaah

[Isaanbiker]

57 minutes ago, Pepper9187 said:

Ok, NOW you're talking.

 

THAT is something i can do, WHERE IS MY HAMMER ????

 

Yaaaaaaaaaaaah

A great idea. Once the bowls are totally empty they can easily hang and stay fully open, which can overflow the gasoline into the cylinder. Using the plastic part of a screw driver would be safer for your carb bowls.

 

  So, you've got a spark on all? 

 

P.S. Is there a vacuum line at the petcock? Have you checked for vacuum leaks, yet? 

 

Edited July 12, 2019 by Isaanbiker

[Pepper9187]

Gotta put this on hold, heading to kanchanaburi, will continue sunday / monday but thanks everyone

[thaiguzzi]

Master technician here.

My recommendations;

1. There are a couple of Honda 400/4 bikes on the B&S website, running, one is even legit with a book.

Buy them both.

Build one good one out of the 3 and you have useful spares.

 

or;

2. Make sure your bike has insurance.

Set fire to it.

 

Thank me later.

[Isaanbiker]

On 7/12/2019 at 3:46 PM, thaiguzzi said:

Master technician here.

My recommendations;

1. There are a couple of Honda 400/4 bikes on the B&S website, running, one is even legit with a book.

Buy them both.

Build one good one out of the 3 and you have useful spares.

 

or;

2. Make sure your bike has insurance.

Set fire to it.

 

Thank me later.

Or buy a real classic Yamaha Virago 1100 that runs well and looks even much better. Only 220,000 baht. 

[Rolanddrums]

Hi, as it is 2 adjacent cylinders sounds like head gasket gone ( Often burnt/eroded away on the land between the 2). Comp test would confirm. Previous continuous detonation (Pre-ignition) is a favourite cause. Top speed runs, ie high load with long duration  combined with low octane fuel or over advanced ignition is a common cause of this. Applys to a high percentage of car or bike engines. 9/10 people  can never hear the warning ' crackle  or  tank tank' sounds.

[VocalNeal]

^ I believe the OP has bought a compression tester so we will soon find out.

[alacrity]

You don't give the age. So, distributor or rotor arm. Could be crankcase bearing also.

[Pepper9187]

said, 2006 - about 40K km on the clock.

 

I have very limited time / day to work on it, and i dont have a roof above my bike (well just a tiny one) so i'm either burning at 70degres under the sun or sinking under the rain, hard to get the proper combination no rain + free time + daytime + not 70 degres under sun.

 

I ordered a compression test kit but yah ... it's ebay China, you never know when it's gona come, somewhere between tomorrow and summer 2020 i guess.

[Pepper9187]

On 7/14/2019 at 6:46 PM, Rolanddrums said:

Hi, as it is 2 adjacent cylinders sounds like head gasket gone ( Often burnt/eroded away on the land between the 2). Comp test would confirm. Previous continuous detonation (Pre-ignition) is a favourite cause. Top speed runs, ie high load with long duration  combined with low octane fuel or over advanced ignition is a common cause of this. Applys to a high percentage of car or bike engines. 9/10 people  can never hear the warning ' crackle  or  tank tank' sounds.

Interesting, that could be it.

 

I wish i had more tools to check everything, it's really complicated right now i only have few cheap tools.

But that makes sense, even if i dont really do long high RPMs runs and i always use benzim 95, it's a strong possibility.

 

Hope ill receive my comp kit test someday and i'll check

[Rolanddrums]

Another way to test if has compression or no compression is remove all the plugs then get someone to crank engine whist you stick your finger or thumb ( If accessible) in the top of the plug holes one at a time. If no comp you will feel big difference between the 2 good and 2 bad cylinders easily . Mind the plug leads etc for electric shocks etc.

I assume you've tried all new plugs and rested the body of plug on outside of head to earth it and cranked the engine already ? Easy test ...do it at night to see spark or no spark. Cleaning an oiled up plug often isn't sufficient to get it sparking again btw.

Edited July 18, 2019 by Rolanddrums

[Pepper9187]

Guys, just wanted to apologize for not keeping you updated, especially to all the fellas who gave me advices and tried to help me, and i never updated, anyway long story short i left thailand for EU in late July and i just dropped that topic as soon as i was in the cab for the airport, coming back soon now.

 

I'll be back home in 3 weeks and HOPEFULLY i will fix that thing or have it fixed.

 

I'll update the results here, finger crossed. But still thinks it stinks reaaaaal bad.

[shchemelevev]

I had somewhat similar problem with my cb400sf. One of the carburettors was not blocking the petrol flow even after it was full + i didn't close petrol flow each time, so petrol was flowing right to the engine. As result I got too reach air\gas mixtures and carbon oxide all over the combustion chamber, spark plugs, valves and piston rings... That lead to low compression ratio.
When I was disassembling the engine one of the cylinder was filled with petrol, so I think you can try to look inside the cylinders or stick something there to check for petrol there. Btw, don't try to start the engine before you check this, it might be unsafe and cause a lot of troubles.