Starting trouble

[IBO]

I just picked up a nice cb750F2.  It has 16,961 miles on it.  It's been improperly stored (garaged) since 1998.  I stuck a new battery in it; doused (sprayed) the carb throats  w/ starting fluid and Vroooomm!!!  The initial start was smooth running until it stalled out.  It will not idle.  Each restart was progressively worse until breaking up and backfiring became common.  The following is what I have done to date:

1. I cleaned the airbox.

2. I attempted to clean the carbs but I must be honest I only cleaned what I could without tearing down the carbs to the itty bitty piece level.  

3. I removed and cleaned the threaded main jets. I cleaned the pressed in main jet seats.

4. I attemted to clean the slow jet as best I could with a thin wire and compressed air because they are pressed in.

5. I cleaned the floats and pivots to ensurre smooth operation.

6. I installed new needle valves in all floats

7. I cleaned the accelerator pump assembly.

8. I blew compressed air through every hole in the rioof of the float bowls and the carb throats.

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The following is what I did not do:

I Separate the carbs.

2. Remove or adjust the air mixture screw.  However from cyl 1 - 4 , the number of turns to bottom out each screw was 3 - 2.75 - 3 - 2.75.

3. Remove or adjust the sycro screws.

4. Anything else.  

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I re-assembled and re-installed the carbs.  I doused (sprayed) the carb throats w/ starting fluid and Vroooomm!!!  The initial start was smooth running until it stalled out.  It will not idle.  Each restart was progressively worse until breaking up and backfiring became common.

As you can see, the end result was absolutely no change...except the float bowls properly fill with gas but carbs are no longer leaking gas to the garage floor.  This is the only bright spot.


Help  -- what do I do now?














 seats and what I could see such as the main jets and installed  float bowls and main jet,  spark plugs, and installed new float valves, fresh gas and V-r-o-o-o-o-m-m-!!!!!  The start was not smooth and the motor will not idle at all.

Next I want to install this new tune-up kit I have (points and condenser). but the ignition cover is more stuck than GW on Iraq.  A closer look reveals the trans cover and the road surface have had contact.  The prior owner confirmed he took a tumble into a ditch.  Now I can't get that infernal ignition cover to budge.

Help!!
 
 

[Rod_Knockin]

carbs!!!! rebuild

[79810k]

Get new Plugs

[IBO]

Plugs only have 16,961 and still look new and fire great.
 

[IBO]

Yes I think so but I must admit I'm more than a little intimidated by the task.

I've taken the rack out again.  It's now sitting on my work bench

I've drained out all the gas.  By the way, each bowl had exactly the same amount of gas in them (about half-full once lowered away the floats.

I have removed all the float bowl goodies (except the pressed-in slow jet).  Another forum indicated the pressed in slow jet can also be removed by wrapping it in leather and twisting it oput with pliers.  After cleaning, reinstall w/ a rubber mallet.  Anyone ever try this or have an opinion?



These parts have already been cleaned and blow well under pressure.  The carb body ithough was cleaned well also. But the proof is in the pudding.  The thing won't idle.

Now I'm lost what I should do next.  I know enough to be dangerous.

Please help -- I'm a basket case . . .

[IBO]

Heres' some more angle shots:
The inside of the carbs look brand new.  The round slides are gleaming.

[Rod_Knockin]

does it run at a higher rpm? I had to clean my carbs 3 times. I guess that stuff shakes loose / works free. Mine ran good for a day and then got progressively worse. That being said your carbs are way different than mine.

[IBO]

Yes it runs at high rpm when  you goose it.  But it will not run smooth at steady high RPM of 1000 to 3000.

Yes the carbs are very different from one model year to the next.  The Japanese never seem to repeat designs much.  I noticed this with many different type of Japanese products - home stereos, hand held devicies and such.  Its' a nightmare.. To my knowledge carbs from other model years will work but you have to make silly little modifications and adjustments.  Oh well . .

So how to you throughly clean these things?

 

[Rod_Knockin]

Ive been assuming its running lean. if its a lean condition it has to be in the low speed circuit. carb cleaner and air hose and safety glasses are the way to go. If its rich and flooded then its the float settings bleeding up into the carb throats. Is the situation better choked or un choked?

[pena750f]

I ran into the same trouble and it was in the tank. Cleaning the carbs every day is a waste if they keep pulling crud from the tank. The petcock screen will keep out big stuff but if it is rusty the gas will break some up and the carbs will suck it in and it will clog your jets every time it runs. It doesn't take much to do this either. If was stored poorly for so long the tank is probably a mess inside.

[IBO]

Regardless of choke setting -- No change  - still will not idle or run smooth.

No bleeding to throats - no carbon buildup

Yesterday I cleaned them again and seem to break through a clog in the slow circuit of Carb #1 (left stand side).  This is another bright spot.  

[IBO]

Sounds good;  I'll do it . . . .

Crap!!  the carb fell off the work bench and broke off the bowl overflow nipple.  Anybody got a #34 bowl they can part with?

I also need one o ring for the air mixture screw hole.