CB650 Help, Turns over, not starting

tron97

tron97

Been Around the Block
Hey all,

Im working on a 79 cb650 and am having some issues with getting it to run.

Its got the stock keihin slide carbs, and I removed them, cleaned them, installed 120 main jets, left the stock pilots in, and stock float height, and threw them back on with pods (dont hate!)

I left the stock pilots in so I could hear it run, before fine tuning to get the mixture right. Apparently ill need around 42 sized pilots.

I am getting spark on all 4, have gapped the plugs properly, and they are brand new. I have also removed them, and re-cleaned them after trying to get it start. They are coming out quite clean, smelling slightly like gas.
The battery is fully charged, BUT, one cell is dry due to the P.O. losing the cap.

When I try and start it, it turns over strong, but puffs smoke out the left exhaust, a but out the right, and coughs and puffs smoke from the carbs. I will also get a good sized backfire every couple of seconds as it turns over. What gets me is it will not start even with a bit of starter fluid. I have tried choke on, half on, off with throttle on, etc. Still nothing

Does this sound like a issue with the pilot jets, and running to lean, enough to not even start the bike?
Or could the one dry cell in the 6 cell battery be not providing quite enough juice? (although it turns over very strong)
Or perhaps timing or something else?

I will be replacing the battery but would like to eliminate all other possible issues now..

Help!
I can post a video if it helps with diagnosing.
 
did it ever run right for you or did you buy it as a non running, changed things and are now trying to start it for the first time?

If the coils are not getting the right amount of voltage they will not produce enough spark to start
Pods and the wrong jets make the bike hard to start.

Do you have a factory manual?
read the section on how to tune and adjust things.
Make sure that the ignition is clean and timed 100%
were all the float heights set to factory specs?
intake air leaks?
 
The bike apparantly ran, on 3 cylinders, and the guy gave up. It had a flat battery, old gas, and missing airbox.

When I tore into the carbs, one of the main jets was completely clogged, hence running on 3 cylinders.

I have a factory manual, yes. All the floats were set to factory yes. It doesnt seem like a fuel problem because it wont start with starter fluid either.

I think timing is the next step..

Ill re-check the intakes for air leaks as well. I think I will have to pick up a voltmeter to check voltage from the coils.
Can I get the ignition timing close without a light?
 
go thought the manual for the correct way to time.
starter fluid is not always a great indication of if it is a fuel related issue or not.

Since you have more then a few variables added to your bike it might be a good idea if you can find a stock air box. Get it running as honda intended before trying to mod it.

Have you checked the compression or done a leak down test?
 
Wires are definitely connected to the correct cylinders.

Today I played with the timing, advanced, retarded, etc. It was static timing only.

I also pulled the pilot jets, 2 seemed a bit clogged, cleaned them out, and re-installed, as well as re set the mixture screws to 1.75 turns out.

I hooked my battery to a car battery for a little extra juice,

But STILL nothing!

Any other ideas? Tomorrow ill get the compression numbers and go from there.

So again, bike cranks, but just farts, coughs, and backfires.
Today, i also saw a few flames shoot from the carbs...
 
Just did a dry compression test, one cylinders low. Keep in mind the bike hasn't been run for a while, so hopefully the numbers will rise with a good run of the motor.

Numbers are 119, 118, 123, 80

Anyone else?
 
while the compression may or may not rise after the motor gets hot you still need compression to start.

Flames out the carbs is normally a sign of timing being off.
Did you do everything exactly like the factory manual said?

Personally i think that you have to many bad variables to get this thing running right now
-CV carbs HATE pods and make things hard to start
-Timing still sounds like its off, maybe the advancer is messed up?
-You sure that you have a HOT spark on all cylinders? and clean plugs?
-Compression should be within 10-15% of each cylinder. you are way off of that. Low compression is bad and not something to be over looked. With the number that low and uneven the CV carbs will not really work all that well and cause it to be hard to start.


MAYBE if you soak the motor in MMO or something you can get the rings to free up, that is if it is the rings.
The only compression test that really matters is a leak down, that way you can tell if its the valves or the rings.
Just spraying some oil into the cylinders should boost the compression numbers if its the rings, but this is really false hope that there is not a big issue.

If i had to guess this is what i would assume
-The cylinder will low compression was open for the last million years and stuff "grew" on the valve face. This caused the valves not to seat and leading to the low compression. Since the bike sat it is a good chance that the rings are also not the happiest either.

There is no easy fix
 
I definitely get what your saying about the pods. Though, the bike SHOULD in theory still run, even if it runs like complete shit.

It doesn't seem to want to do anything, but crank.

Just a side note: Cv carbs were on the 81-82s, 79 has slide carbs..though, they hate pods as well.
 
Did not know that the early 650s were slides.
But still, yeah they would run....not well.....but thats on an engine that was in good shape
Yours is not in good shape. those are really bad compression numbers

basically you need to solve that problem before you can fix the other problems.
You sure that the carbs are giving the motor the correct amount of fuel?
maybe you can get everything else fixed and the motor will start, and if that many stars aline then maybe the compression will come back.

but you know what they say about wishing and hopping....

I hate to be negative but some times this happens in the hobby
 
Something I ran into that took me FOREVER to track down was a broken kill switch wire. So the circuit was always open. So the bike just wouldn't turn over. Might not be anything like what you are seeing, but might be something to check.

Cheers,
Balek
 
OK So,

Surfffly,


Just triple checked the compression on #4, and I got a 120.

Must have had a poor seat on the guage...twice in a row. Haha


So now whats my next step, compression is within 5% on each cylinder..
 
All dry. I was just checking it one more time before a wet test, but it passed..
 
Back firing and blue flames out the carb? Id be double checking timing and plug leads, meter open close across all cylinders in relation to top dead centre?
Timing chain? (not sure what this bike has)
I agree, it should fire with pods
 
Can someone run by the static timing without a light with me?

I have read the shop manual and done it as per the instructions, but it still seems off..
 
Are you sure you have the coils hooked up right? Sounds like you might have them the wrong way round if you're getting backfires.
 
The spark plug wires are definitely right, but what just occurred to me is, I did re-wire it, and maybe I got the wires going TO the coils mixed up...

Ill check tomorrow.
 
WOW!

I think i got it.

So as everyones telling me, make sure your spark plug wires are on correct, and im thinking ya,ya,ya thats the first thing i looked at.

WELL, stupid little me, I wired the COILS backwards, yellow on left instead of right, and vice versa.

So I haven't fired it up yet because its 11pm, BUT im 90% sure it will fire tomorrow. I cant fuggin wait.

Wish me luck!
 
You must log in or register to reply here.

DTT Light or Dark

  • DTT Light
    • www.jadusmotorcycleparts.com
    www.lostapostle.ca/
    www.sparckmoto.com

    Spread the Love

    Back
    Top Bottom