Topic: wont start up, CB750K4 (update, with new issues)

[nightpoison]

Ok, so I'm having some issues getting it to start up. here's what I've done and what I've checked.

new oil
cam chain tension adjusted
valve tappet checked and adjusted
new wiring harness
dyna S ignition
3 ohm coils

at this point the bike started up, but it was leaking fuel out of the carb T fuel line, so I added the following to my to do list.

hondaman resister pack
new spark plug wires with resister caps
carb clean and rebuild

so that was all completed and today I went to start the bike up, so I could sync the carbs and take it out for a ride.  but no go. put the battery in, after getting it juiced up on a tender over night, and I started to crank the engine. I got a really loud single pop after about 2 min of trying to get it to start.  I tried to kick start and use the starter no go. So I went through the following check.

checked fuses
checked that all electrical was working properly
lights check
turn signals check
horn check
brake light check
then I pulled the fuel lines from the tank to make sure fuel flowed out of the tank.
checked the carb bowls for fuel
checked the choke on the carbs
pulled each of the spark plugs one at a time to check for spark


did the check above and then went to start it again. after about 5-10 min of trying the battery wasn't strong enough, so I had to pull it and throw it back on the charger (should the battery drain this fast, about 20 min total of trying to start it)

so everything looks and works correctly that I can see. Any suggestions on getting the engine to actually start?

[Bodi]

Confirm the coils are wired correctly. It sounds like you swapped them while installing the resistor pack them so the 1-4 output is firing the 2-3 plugs.

[brandEn]

Did it start and run before all the maintenance was done?

If yes I kinda suspect its an ignition problem. Re-check that dyna install. Thats where I would start. Especially if you verified its got fuel.

[nightpoison]

Left coil is set up for 1 & 4, right coil is set up for 2 & 3. Other than that what should i check for?

[nightpoison]

thank you guys, it seems I must have swapped the wires as you suggested. After swapping the wires again, the bike started right up. Wow, such a simply thing can really rack the brain.

so I got her started up, but really couldn't get her to idle and it was rough. I had to give it some gas in order to get her to keep from cutting out. after about a minute started to see some smoke coming off the header wrap. normal baking of the wrap, no big deal. but then the bike cuts out completely. well I figured it was the spark plugs. they are old and didn't really want to change them out till i got everything else up and running. so i changed them out and it came alive when i went to start it up again. still won't idle. it starts up and sits just under 1k rpms for about 4 seconds and then dies. so i give it a little gas to get it going and about 1500rpm its sounding real nice. warming up let off the gas still won't idol will just cut out.

heres a question for you. when i bench synced the carbs I used a 1/8th allen wrench for spacing. Which side of the carb are you suppose to use the spacer on for bench syncing? from the air intake side or the back engine side?

Here is where I am really concerned so i mentioned earlier I noticed some smoke coming off the header wrap. Well i noticed it again after 5 min. this time I looked a little closer and it was only coming off cylinder 4 pipe. So i taped the wrap and it was HOT. I touched the 1st, 2nd, and 3rd pipe and they were warm, but no where near as hot. did the same thing and touched the cylinder head and wow that was scalding hot, compared to the cylinder 1 which was warm to the touch. I shut everything down and here I am.

I don't even know where to start with this issue. When I got the bike the engine was running fine. I didn't touch the engine, other than cam chain tension, and valve adjustments. I started school tomorrow, I'm not going to have a ton of time to work on her and I don't have the funds to hand her over to a shop for work. What do you guys think?

[martin99]

I don't think you're too far off.

Bench sync from intake side. Only gets you in the ballpark IMO, needs to be followed up with proper vacuum sync. Raising the tickover will allow you to do that. You say it is fine around 1500, that's a little high but not too much. Personally I aim for around 1100 - 1200.

Before you do that though, I'd be inclined to check your valve clearances again. Sounds like #4 may be out. Not easy to get them right first time, takes experience and feel.

Good luck

[ekpent]

Have you tried using the idle adjustment knob and are familiar with it. These bikes do not really like to idle well till they are fully warmed due to their primitive choke circuit. If the bike had been running for 5 minutes you should not be able to touch or hold your finger etc on any of the pipes. The #4 pipe may be normal and your other 3 not.

[nightpoison]

ekpent,

didn't think of it that way. I just got really concerned with it being so hot. my only comparison really has been working on liquid cooled car engines. this is my first jump into motorcycles, so when #4 got crazy hot and the other three were just warm. I thought there was an issue with one, and not the three.

didn't think about the idle adjustment, I'll play with that, get it up to around 1100 to 1200 and see how that runs. Before that I'll take a look at the valve clearance again like oldskoolnuts suggested. Double check to make sure that's good.

here's a question, what should I have the pilot screws set too? What is a full turn? is it 180% or 360%?

Thank you everyone for the help.

[ekpent]

A full turn would be one hole turn with the screwdriver or the hash mark of the screw slot going by twice while backing out from a light seat. As for the pipes getting hot they will do that very quickly up by the head, that is fire coming out of there. As for the difference you may have in the temp you need to make that judgement and compare but it is a simple starting point to the health of each cylinder be it fuel flow, spark etc. . On a 750 1 turn out is the base or starting point on the air screw.

[nightpoison]

Its been about a week and i finally got some time to work on the bike.

First you guys rock. Thank you for the suggestions and help. I took another look at the valve clearance and wow were they way off. I re-read up on the proper way to do it and i re-did them. Turned the bike over and adjusteded the idle screw. Its up and running. Engine is even temp at all four cylinders and pipe.

That exhaust wrap is baking like crazy.

I had to glue the grips down on the bike, so waiting on them to dry. Will be taking her out in the a.m.

Thanks again for the help

[Spanner 1]

NP... please don't run your bike on it's mainstand while doing adjustments etc. without a good fan blowing across the motor. these bikes are designed to be air cooled and will quickly overheat to a dangerous level IMO without airflow across the cylinders....