Topic: CB 350 F - fouling plugs, backfiring...

[NapraP]

All pasages are squirtable, float chambers vents are not blocked and overflow tubes is not blocked too...

[NapraP]

Jet towers were really full of dimples so i made special tool from very fine sanding paper (nail with glued strip of s. Paper So it was self centered when rotating ) for my dremel and polished towers inside. Carbs are ultrasonic cleaned again, jets and emulsion tubes too. Tommorow i try to find some o-ring which will properly fit.

I will send pics soon - i write from phone and i can't resize pics to 1024kB...

[harisuluv]

Jet towers were really full of dimples so i made special tool from very fine sanding paper (nail with glued strip of s. Paper So it was self centered when rotating ) for my dremel and polished towers inside

Ok, I personally would not have done that, but if you are sanding/smoothing out corroded emulsion "holder" then you are already missing material there.  Chances are the inside of your emulsion tube is also pitted. 

For example, I recently had a set of carbs sent to me for rebuild that was running rich, fouling plugs.  Upon inspection, I saw a lot of pitting both from corrosion and media blasting.  Turns out the carbs were sandblasted.  Passages no longer had as much material as they were supposed to, pressures changed, more fuel got here or there.  They ran rich.

A nail is typically also not straight, I don't think your surfacing method is as refined as you think it is/was.

[MoMo]

Is it possible one of the clips fell out of the needle slot?...Larry

[NapraP]

Jet towers were really full of dimples so i made special tool from very fine sanding paper (nail with glued strip of s. Paper So it was self centered when rotating ) for my dremel and polished towers inside

Ok, I personally would not have done that, but if you are sanding/smoothing out corroded emulsion "holder" then you are already missing material there.  Chances are the inside of your emulsion tube is also pitted. 

For example, I recently had a set of carbs sent to me for rebuild that was running rich, fouling plugs.  Upon inspection, I saw a lot of pitting both from corrosion and media blasting.  Turns out the carbs were sandblasted.  Passages no longer had as much material as they were supposed to, pressures changed, more fuel got here or there.  They ran rich.

A nail is typically also not straight, I don't think your surfacing method is as refined as you think it is/was.

I said nail because it was easier to translate. I use shaft from dremel cutting tool so i hope it was straight. My language skills do not  allow me to write it exactly, but in high rpm the sanding paper tail (about 400 grade and 30000rpm) only petted the tower inside surface. It takes about hour and half to smooth resurfate all carbs. Material is missing but main jet with standard o-rings fits quite tight but i want really tigtness. I will try many of o-rings to be sure it will be ok.

You make service of this carbs so you know how hard is buying this carbs in good condition...

[NapraP]

Is it possible one of the clips fell out of the needle slot?...Larry

Nope i inspect all of them.

[NapraP]

pics...

[flybox1]

whats up with that float post in the first picture, and how did you verify accurate fuel level?

[NapraP]

Float post repair isn't my work. At this carb i checked float setting with tube and it work good.

Edit: what you see is drilled screw so the holes for flat is in the same position. I think it is quite good idea how to fix broken "leg" from float holder.

[seanbarney41]

do you have access to a known good set of condensers?  If you do, try 'em.  They are not expensive to buy new here, but I do not know about in Czech Republic...

[NapraP]

I measured condensers capacity cold/hot and both are like new.

[seanbarney41]

I  would still try some known good capacitors.  Like I said, they are cheap and easy to change.

[NapraP]

I still have the another cb from i borrowed carbs so i can borrow capacitors too. I guess capacitors too but with my capacitors and another carbs it run like new. How you said - capacitors change is few minutes...i can try it...

[MoMo]

Is it possible one of the clips fell out of the needle slot?...Larry

Nope i inspect all of them.

Here is another problem I found once-someone had installed different size main jets-like 110, 120 in the same set of 750 carbs.  another problem I once incurred was one of  the main jets had been reamed out.  Keep plugging and I would disregard all advice not pertaining to the carbs as it seems that you have narrowed it down-unless you could possibly be disturbing the point connectors when you are taking the carbs on and off...Larry

[NapraP]

Is it possible one of the clips fell out of the needle slot?...Larry

Nope i inspect all of them.

Here is another problem I found once-someone had installed different size main jets-like 110, 120 in the same set of 750 carbs.  another problem I once incurred was one of  the main jets had been reamed out.  Keep plugging and I would disregard all advice not pertaining to the carbs as it seems that you have narrowed it down-unless you could possibly be disturbing the point connectors when you are taking the carbs on and off...Larry

I tried three sets of jets - new aftermarket, old (cleaned) from my carbs, old (also cleaned) from borrowed carbs so I think that the jets are ok. After second ultrasonic cleaning inside channels in carbs are like new - i saw clean grey surface in it. I really guess that my problem is in the jet towers. i hope my resurfacing will help. If not i have plan B. My plan B is to use different construction of main jet. Towers have very thin side so make sleeve into is not possible. I will make special brass screw which will be screwed into tower, hold emulsion tube and have screw thread inside for common jet with 5mm thread. I have to measure all and make design drawings for this. If i have to do my plan B and it will works i share my drawings here...

Boots for carbs at the engine are in good condition and yesterday i made test with start spray and all about carbs are tight.
 

[ttr400]

Check if the slides are not installed backwards.

Kevin

[NapraP]

Check if the slides are not installed backwards.

Kevin

I checked this and the slides is placed right.

[Psychonaut]

My 400 ran like this from the previous owner. He "rebuilt" the carbs. Side holes in tubes looked clean until a pushed a small needle in them and  twisted. Float height was too lean, I think he had them at 23mm. Could be too much plug gap but usually a miss from that  is a little rough at WOT.

[NapraP]

Thanks a lot for help!

I bought one size thicker o-rings than original to main jet and spent many hours with dremmel, paint polish (a little abrasive) and 600 grade sand paper on my polishing tool to make smooth surface and right inner diameter for new o-rings and main jets. Bike run awesome now, all spark plugs are the same little grey color...