Topic: 1973 CB350F: top speed stutter=header hole?

[Vfrman]

Still getting to know my 1973 CB 350 F. I’ve got a couple of hours riding it now and I have noticed it tops out at 70 miles an hour and at that point starts stuttering a bit. I just realized there is a nickel sized hole at the end of the header right where it narrows down to the one pipe outlet to the muffler. Could this be the reason?

[denward17]

I don't think so.....

Did you check any of the suggestions in your earlier thread?
http://forums.sohc4.net/index.php/topic,194908.0.html

[Vfrman]

Yes, certainly, and still intend to employ some of those suggestions. Just didnt know about the hole in the pipe when I posted that. My previous experience with higher displacement sportbikes made me think this might be relevant

[Vfrman]

Delkelvic sells 2 complete systems for this bike, a straight muffler and a megaphone. Is one better than the other or does it come down to personal taste?

[willbird]

Delkelvic sells 2 complete systems for this bike, a straight muffler and a megaphone. Is one better than the other or does it come down to personal taste?

I waffled on which for my CB750K2 and settled on the straight. I think IMHO one could buy the other muffler and swap them. I have not installed mine yet, had some carb issues to sort out before getting too many changes heaped on top of each other while I was not happy with how it was running.

Bill

[bender01]

Does it hit redline in the first 4 with you on it? Ive used permatex gas tank repair kit on many things. Patched a gas tank after i blew a hole trying the electrolysis method. My fault. It worked for 2 years and i sold it. Plugged a spot farther back underside on my 450 muffler and its been soild 6-7 years. Does sound like a carb /fuel issue though. Pull those emulsifier tubes and check float height. First run it with gas cap off . Might be air getting locked up there.

[Vfrman]

My plugs. All gapped to .024, within spec. I see 1 & 4 look about right. The #3 carb bowl is the one that dripped gas out of it all night a few nights back.

What think?

[newday777]

My plugs. All gapped to .024, within spec. I see 1 & 4 look about right. The #3 carb bowl is the one that dripped gas out of it all night a few nights back.

What think?

Poke them into cardboard so you can picture the inside of the porcelain

[scottly]

Your #3 spark plug is fouled. The bike is only running on three cylinders, which explains why it can't go faster than 70 MPH! You've been flogging the team with a dead horse.

[Tracksnblades1]

Your #3 spark plug is fouled. The bike is only running on three cylinders, which explains why it can't go faster than 70 MPH! You've been flogging the team with a dead horse.

+1

3 for sure…2&3 needs to look like 1&4..

[newday777]

Here is how you inspect plugs and read them.

[Vfrman]

Your #3 spark plug is fouled. The bike is only running on three cylinders, which explains why it can't go faster than 70 MPH! You've been flogging the team with a dead horse.

+1

3 for sure…2&3 needs to look like 1&4..

Fouled as in not sparking at all?  It idles smooth…it must be firing. But the fact its the same cylinder as the carb that was dripping gas has to be related/cause. I’m going to try taking fuel line off petcock, draining carbs, and spraying carb cleaner thru fuel line to flush all 4 bowls/floats. Heard it might even be good to close screws & try to fill the bowls w carb cleaner & let set for 15 min then drain.  Anyone ever have success doing that?  I REALLY dont want to take the carbs off for a full rebuild if I can avoid it

[carnivorous chicken]

I don't think you'd make 70 on 3 cylinders, but three is definitely fouled and 2 doesn't look great either. 3 looks like it could be oil fouled -- does it smoke at higher revs?

[Vfrman]

I don't think you'd make 70 on 3 cylinders, but three is definitely fouled and 2 doesn't look great either. 3 looks like it could be oil fouled -- does it smoke at higher revs?

No smoke at any rev. It runs smooth all the way up to its 65ish ceiling where it starts cutting out a bit and if I WFO at that point it just gets worse & starts bogging

[newday777]

I don't think you'd make 70 on 3 cylinders, but three is definitely fouled and 2 doesn't look great either. 3 looks like it could be oil fouled -- does it smoke at higher revs?

No smoke at any rev. It runs smooth all the way up to its 65ish ceiling where it starts cutting out a bit and if I WFO at that point it just gets worse & starts bogging

Do you have an added inline fuel filter hanging lower than the float onlrts?

[Vfrman]

I don't think you'd make 70 on 3 cylinders, but three is definitely fouled and 2 doesn't look great either. 3 looks like it could be oil fouled -- does it smoke at higher revs?

No smoke at any rev. It runs smooth all the way up to its 65ish ceiling where it starts cutting out a bit and if I WFO at that point it just gets worse & starts bogging

Do you have an added inline fuel filter hanging lower than the float onlrts?

Nope. Just had drain screws out & blew carb cleaner thru the main fuel line removed from petcock. I def had some junk/rust come out. Hope that, new plugs, and patched hole in the header all add up to a fix

[grcamna2]

I don't think you'd make 70 on 3 cylinders, but three is definitely fouled and 2 doesn't look great either. 3 looks like it could be oil fouled -- does it smoke at higher revs?

No smoke at any rev. It runs smooth all the way up to its 65ish ceiling where it starts cutting out a bit and if I WFO at that point it just gets worse & starts bogging

Do you have an added inline fuel filter hanging lower than the float onlrts?

Nope. Just had drain screws out & blew carb cleaner thru the main fuel line removed from petcock. I def had some junk/rust come out. Hope that, new plugs, and patched hole in the header all add up to a fix

Check the full operation of your ignition system including advance mechanism,then remove the carbs and clean them/check all jets,floats,etc.

[Vfrman]

I don't think you'd make 70 on 3 cylinders, but three is definitely fouled and 2 doesn't look great either. 3 looks like it could be oil fouled -- does it smoke at higher revs?

No smoke at any rev. It runs smooth all the way up to its 65ish ceiling where it starts cutting out a bit and if I WFO at that point it just gets worse & starts bogging

Do you have an added inline fuel filter hanging lower than the float onlrts?

Nope. Just had drain screws out & blew carb cleaner thru the main fuel line removed from petcock. I def had some junk/rust come out. Hope that, new plugs, and patched hole in the header all add up to a fix

Check the full operation of your ignition system including advance mechanism,then remove the carbs and clean them/check all jets,floats,etc.

No idea how to check ignition system. But I just took a 5 min test ride and it ran smooth and sounded alot better with the header hole patched. Didnt want to run hard cause 2nd coat of hitemp goo could use a longer cure before running max temp exhaust. I am hoping hard the girl runs up to 90mph tomorrow. I really dont want to do a full carb rebuild. I will if necessary tho

[Don R]

 Usually, they don't need carb rebuilds with kits, they just need the jets and passages cleaned out. The smaller fours have the smallest passages and are especially prone to anything that gets into the bowls plugging the pilot circuit.

[grcamna2]

Usually, they don't need carb rebuilds with kits, they just need the jets and passages cleaned out. The smaller fours have the smallest passages and are especially prone to anything that gets into the bowls plugging the pilot circuit.

Vfrman,what he said here, #1.

[Vfrman]

My attempt at a high speed test was total fail: bike running rough from the start, put on side stand and fuel pouring out of #3 overflow tube. Came home, tapped w hammer, no change. I guess I have no alternative than yo take the carbs off. Might as well do a full rebuild while its off. I’ve torn up & reassembled carbs from thumpers….and watches & double-action revolvers— so I can do this if I take my time.
Is there a good “kit” for all the wear items?  Good parts list of what I need if I need to get parts individually?

[grcamna2]

My attempt at a high speed test was total fail: bike running rough from the start, put on side stand and fuel pouring out of #3 overflow tube. Came home, tapped w hammer, no change. I guess I have no alternative than yo take the carbs off. Might as well do a full rebuild while its off. I’ve torn up & reassembled carbs from thumpers….and watches & double-action revolvers— so I can do this if I take my time.
Is there a good “kit” for all the wear items?  Good parts list of what I need if I need to get parts individually?

Remove your airbox mounting bolts and shoot a little wd40 around the rubbers so you can slide the air filter box all the way back;it will aid in removing the carbs back towards the rear and save your rubber manifolds from getting torn.
Open up the carbs and see/i.d. the jets(OEM brass is Best)and other parts in there.
I highly recommend sticking with stock Honda parts,especially new rubber seal kits.

The inside of the fuel tank may need to be rust-cleaned;I like to use a container of BB's and shake that tank up and down like a huge rattle. The BB's can get into every angle and surface(don't forget how rusty the inside top of the tanks get!)and when your done shaking it for an hour(over the course of a day,lots of exersize),you can slowly roll all the BB's out the petcock opening;a thin telescoping magnet will get the last one.
Rinse it over and over with some 'wash gas' into a white 5gal. bucket until it comes up clean.

[scottly]

Is the new #3 plug fouled again? I would remove the #3 float bowl and see if you can find out the problem, before removing the whole rack of carbs.

[Vfrman]

My attempt at a high speed test was total fail: bike running rough from the start, put on side stand and fuel pouring out of #3 overflow tube. Came home, tapped w hammer, no change. I guess I have no alternative than yo take the carbs off. Might as well do a full rebuild while its off. I’ve torn up & reassembled carbs from thumpers….and watches & double-action revolvers— so I can do this if I take my time.
Is there a good “kit” for all the wear items?  Good parts list of what I need if I need to get parts individually?

Remove your airbox mounting bolts and shoot a little wd40 around the rubbers so you can slide the air filter box all the way back;it will aid in removing the carbs back towards the rear and save your rubber manifolds from getting torn.
Open up the carbs and see/i.d. the jets(OEM brass is Best)and other parts in there.
I highly recommend sticking with stock Honda parts,especially new rubber seal kits.

The inside of the fuel tank may need to be rust-cleaned;I like to use a container of BB's and shake that tank up and down like a huge rattle. The BB's can get into every angle and surface(don't forget how rusty the inside top of the tanks get!)and when your done shaking it for an hour(over the course of a day,lots of exersize),you can slowly roll all the BB's out the petcock opening;a thin telescoping magnet will get the last one.
Rinse it over and over with some 'wash gas' into a white 5gal. bucket until it comes up clean.

Good tip on the airbox...I was wondering what was best way to attack the removal.  Plan on watching some Youtube vids this eve.  Ordering an ultrasonic cleaner! 

If I get an ultrasonic big enough to put the entire carb bank into, is there any reason NOT to do that?

My tank has previously been sealed/treated with something.  It appears to be in good shape as the gas I drained from the tank had NO rust/crud in it at all.