Topic: 350F fires all 4 again, but...are my jets not stock?!?

[Jugghead]

 
Hi all, Thanks to your good info, (and a Clymers manual) I have a stock, 9/72, CB350F back on the road! Also has a Martek440 electronic ignition? NOT stock.
Only problem is now I have power problems...
1.  I cleaned the gas tank with molasses
2. Installed in-line filter.
3. Charged the battery,
4. Set valve clearances,
5. Checked spark and good spark on all four cylinders.
6. Checked cold compression and all were reading about 160 +/- psi.
7. Drained carb bowls and confirmed fuel flow to all four bowls.

 Went to start and YEAH!! there she goes! Although, cylinder number four does not fire reliably--the header pipe does not acheive the same temp as the other three.  Pulled the plug again to confirm spark, and it gave sparks, but was also dark, gas smelling and slightly wet. 
All the plugs are dark, and I have no good accelleration and under load it struggles to go past 5000 RPMs
Any tips as to what the next step should be?  Why would one cylinder not fire when it gets spark and fuel?  What do I need to check next?
Thanks!

[turtle]

I have no idea jugghead.
Its great to hear of another 350F going though. How about some pics? Also visit loonymoon's photogallery at http://gallery.loonymoon.org.uk/thumbnails.php?album=5.

[Jay B]

A few things I'd do right off the bat.


-If your tank was rusty, install an inline filter. The low speed jet is tiny, it will plug very easily.

-Pull the carbs and give them a good cleaning. This is one of the first things to do on any bike being brought back to life.

- Get some new boots and check the rubber manifolds very carefully. It doesn't take much of an air leak to throw a wrench in things.

-New spark plugs if you haven't done so.

Glad to hear about another 350f on the road. One of the funnest bikes I've ever owned!

[Jugghead]

-If your tank was rusty, install an inline filter. The low speed jet is tiny, it will plug very easily.

Did that, got a three dollar job and put it on the line. thanks

- Get some new boots and check the rubber manifolds very carefully. It doesn't take much of an air leak to throw a wrench in things.

Got a plenum? (plastic box with rubber boots) off ebay for 99cents! But so far the rubber cement i used is holding up fine.

-Pull the carbs and give them a good cleaning. This is one of the first things to do on any bike being brought back to life.

I tried Two Tired's recommendation to Fish that he try cleaning them while still on the bike first...I used the yamaha carb cleaner fluid mixed 3:1 with gas, poured directly into bowls via fuel line. Tapped the electric starter a couple times as per the instructions on the bottle, rocked bike back and forth. Let sit while I went to a movie.  Came home and drained the bowls of this stuff, rinsed with spray type carb cleaner, refilled bowls with fresh gas and tried to start it.   
Now it is worse than before! Before it ran on cyls 1 2 and 3 and idled at 1200 RPMs.  Now it does not start and I had two strange back fires. Like opening a vaccuum sealed container. First from exhaust 1 then number 2, both accompanited by light colored smoke issuing from the exhaust tubes. What could this be?

-New spark plugs if you haven't done so.

Ok will need to do this.  will double check compression and valves again upon replaceing my plugs.  i just want this baby to work again.  I was so close and then POOF! I am 10 steps back. 
Any help/advice for this nooB is greatly appreciated.
Thanks!
Jugghead
PS: how about a pic?!!?
http://www.sohc4.us/gallery/v/members/personal/jugghead/CB350F.jpg.html

[schneider419]

not shure if this will help, but my 350f started to back fire through the carb. i had just put gas in it and drove 10 miles, it ran fine started it back up and it started on what ended up being no. 3 cylinder. i thought bad gas, noooo. ended up it had a bad aftermarket set of points an condenser in her. put a good(i hope) set in and it's back. yaaaaa hoooo!
                                                                                                                                          mike

[Jugghead]

 ::)99% sure the backfire was due to the carb cleaner trying to ignite .
I took off the bowl to cylinder 4 (the non-firing cylinder) and removed the slow jet to find it......surprise! clogged!
Cleaned with carb cleaner to "see the light at the end of the tunnel" and put back together
Replaced the spark plugs like Jay B said to do and VROOOOM  on all 4! woo hoo!
Thanks Jay B, Thanks Two Tired!  your posts sure helped me get her firing on all four cylinders again!

Now the next question, if I may...I noticed the main jet in there is 75 and the slow jet is 35...
1.  What are the original jet sizes, aren't they 80 and 40?  
2.  What will this due to performance?
She still doesn't start cold while choked, but I throw the lever down to normal run position and she fired right up.  
3.  what gives?
I want to return this bike to as close to stock as I can, as it seem sthat will give the best all around performance.  Any advice to that end will be much appreciated.  Thanks!

[Bodi]

The stock 350-4 carbs have setting mark 656C, with #75 main and #35 slow jets.
Sounds like yours are correct.
Airscrew is specified as 7/8 ±3/8 turns out, float height should be 21mm.