Topic: 1973 CB350F top speed?

[scottly]

Please just post pictures of the plugs that are in the bike now. The condition may give clues as to why the bike isn't running properly, instead of just making Wild Assed Guesses.

[Tracksnblades1]

3 more pieces of intel re- my top speed stutter:
1- there is a quarter-sized hole at the end of the header right before it connects to muf
2- it pissed fuel all over garage floor 2 nights ago. It was dripping from the #2 carb (from kick starter side), or at least thats where it was condensing into drops & falling. I had firgotten to turn the petcock off after last ride- but still- it shouldnt have done that. I gave it a few taps w brass hammer and it stopped
3- it has an upgraded ignition: no points

Today I will pull & inspect plugs. Yesterday I changed oil to Rotella T4 15w40 and no more slippage on test ride. Unfortunately I couldnt get the bolt off to change the filter. I read on here thats a common problem

I’m more worried about #2. “It pissed fuel all over the garage floor”..
Did it do that before you changed the oil or after..?

To run through the intake valve fill the cylinder enough to run out the exhaust valve is a long way to the hole in the exhaust..
Wonder how much gas ended up in the sump instead of on the floor..? 🤔

[grcamna2]

3 more pieces of intel re- my top speed stutter:
1- there is a quarter-sized hole at the end of the header right before it connects to muf
2- it pissed fuel all over garage floor 2 nights ago. It was dripping from the #2 carb (from kick starter side), or at least thats where it was condensing into drops & falling. I had firgotten to turn the petcock off after last ride- but still- it shouldnt have done that. I gave it a few taps w brass hammer and it stopped
3- it has an upgraded ignition: no points

Today I will pull & inspect plugs. Yesterday I changed oil to Rotella T4 15w40 and no more slippage on test ride. Unfortunately I couldnt get the bolt off to change the filter. I read on here thats a common problem

I’m more worried about #2. “It pissed fuel all over the garage floor”..
Did it do that before you changed the oil or after..?

To run through the intake valve fill the cylinder enough to run out the exhaust valve is a long way to the hole in the exhaust..
Wonder how much gas ended up in the sump instead of on the floor..? 🤔

carb issues.

[Tracksnblades1]

3 more pieces of intel re- my top speed stutter:
1- there is a quarter-sized hole at the end of the header right before it connects to muf
2- it pissed fuel all over garage floor 2 nights ago. It was dripping from the #2 carb (from kick starter side), or at least thats where it was condensing into drops & falling. I had firgotten to turn the petcock off after last ride- but still- it shouldnt have done that. I gave it a few taps w brass hammer and it stopped
3- it has an upgraded ignition: no points

Today I will pull & inspect plugs. Yesterday I changed oil to Rotella T4 15w40 and no more slippage on test ride. Unfortunately I couldnt get the bolt off to change the filter. I read on here thats a common problem

I’m more worried about #2. “It pissed fuel all over the garage floor”..
Did it do that before you changed the oil or after..?

To run through the intake valve fill the cylinder enough to run out the exhaust valve is a long way to the hole in the exhaust..
Wonder how much gas ended up in the sump instead of on the floor..? 🤔

carb issues.

It’ll be a lot bigger issue if the sump is full gas and he’s still running it trying to figure out the obvious. “Carb issues”..

[grcamna2]

3 more pieces of intel re- my top speed stutter:
1- there is a quarter-sized hole at the end of the header right before it connects to muf
2- it pissed fuel all over garage floor 2 nights ago. It was dripping from the #2 carb (from kick starter side), or at least thats where it was condensing into drops & falling. I had firgotten to turn the petcock off after last ride- but still- it shouldnt have done that. I gave it a few taps w brass hammer and it stopped
3- it has an upgraded ignition: no points

Today I will pull & inspect plugs. Yesterday I changed oil to Rotella T4 15w40 and no more slippage on test ride. Unfortunately I couldnt get the bolt off to change the filter. I read on here thats a common problem

I’m more worried about #2. “It pissed fuel all over the garage floor”..
Did it do that before you changed the oil or after..?

To run through the intake valve fill the cylinder enough to run out the exhaust valve is a long way to the hole in the exhaust..
Wonder how much gas ended up in the sump instead of on the floor..? 🤔

carb issues.

It’ll be a lot bigger issue if the sump is full gas and he’s still running it trying to figure out the obvious. “Carb issues”..

Agreed.

[Vfrman]

3 more pieces of intel re- my top speed stutter:
1- there is a quarter-sized hole at the end of the header right before it connects to muf
2- it pissed fuel all over garage floor 2 nights ago. It was dripping from the #2 carb (from kick starter side), or at least thats where it was condensing into drops & falling. I had firgotten to turn the petcock off after last ride- but still- it shouldnt have done that. I gave it a few taps w brass hammer and it stopped
3- it has an upgraded ignition: no points

Today I will pull & inspect plugs. Yesterday I changed oil to Rotella T4 15w40 and no more slippage on test ride. Unfortunately I couldnt get the bolt off to change the filter. I read on here thats a common problem

I’m more worried about #2. “It pissed fuel all over the garage floor”..
Did it do that before you changed the oil or after..?

To run through the intake valve fill the cylinder enough to run out the exhaust valve is a long way to the hole in the exhaust..
Wonder how much gas ended up in the sump instead of on the floor..? 🤔

carb issues.

It’ll be a lot bigger issue if the sump is full gas and he’s still running it trying to figure out the obvious. “Carb issues”..

Agreed.

The fuel was leaking From the bowl area and dripping straight down onto the case, not into the engine, filling up a cylinder. To my knowledge, there’s no way for gas to permeate the case and mix with the oil just sitting on top.  But I changed the oil after that issue was fixed with the mallet tap. And the old oil that came out did not have any discernible mixed in gas, assuming it would be floating on top of the oil.

[HondaMan]

3 more pieces of intel re- my top speed stutter:
1- there is a quarter-sized hole at the end of the header right before it connects to muf
2- it pissed fuel all over garage floor 2 nights ago. It was dripping from the #2 carb (from kick starter side), or at least thats where it was condensing into drops & falling. I had firgotten to turn the petcock off after last ride- but still- it shouldnt have done that. I gave it a few taps w brass hammer and it stopped
3- it has an upgraded ignition: no points

Today I will pull & inspect plugs. Yesterday I changed oil to Rotella T4 15w40 and no more slippage on test ride. Unfortunately I couldnt get the bolt off to change the filter. I read on here thats a common problem

Just for consistency's sake: the carbs are numbered from the left side (shifter side), as 1-4.
It's not uncommon for these bikes to 'piddle' when parked, particularly after they were sitting a long time. That's why you'll need to get used to the 'startup/shutdown drill', which always includes switching the petcock in addition to the keyswitch.

Part of the issue with the dripping float bowls is due to modern fuels being lighter specific viscosity than 1970s fuels: the floats were designed to be used in a more dense fluid, which was [real?] gasoline instead of a gas/ethanol/lube mixture like we have today. Also, the modern fuels expand about 3% to 6% more with heat (as in, parked with hot engine under them) than the old-time fuels. After the float bowl gaskets get soaked a little longer in the modern fuels, they will also re-expand to [more than] their original sealing size, which will actually help stop the weeps. The ethanol in today's fuels make the O-ring seals on the float bowls expand about 5%-7% (difference being how much ethanol % is in your fuels) when they get wetted, and shrink below their original size by around 4%-7% when they get dried out after the exposure.

One way to minimize all this expanding/shrinking/hardening of the O-rings is to add a bit of oil to your gas: this neutralizes the ethanol's attacks on the rubber substantially. I use a capful (1-2 ounces) in every tankful when I fill up. It doesn't seem to matter WHICH oil, so I use synthetic 2-stroke oil so it doesn't smoke.

[scottly]

I'm reserving my opinion until I see the spark plugs.

[grcamna2]

3 more pieces of intel re- my top speed stutter:
1- there is a quarter-sized hole at the end of the header right before it connects to muf
2- it pissed fuel all over garage floor 2 nights ago. It was dripping from the #2 carb (from kick starter side), or at least thats where it was condensing into drops & falling. I had firgotten to turn the petcock off after last ride- but still- it shouldnt have done that. I gave it a few taps w brass hammer and it stopped
3- it has an upgraded ignition: no points

Today I will pull & inspect plugs. Yesterday I changed oil to Rotella T4 15w40 and no more slippage on test ride. Unfortunately I couldnt get the bolt off to change the filter. I read on here thats a common problem

Just for consistency's sake: the carbs are numbered from the left side (shifter side), as 1-4.
It's not uncommon for these bikes to 'piddle' when parked, particularly after they were sitting a long time. That's why you'll need to get used to the 'startup/shutdown drill', which always includes switching the petcock in addition to the keyswitch.

Part of the issue with the dripping float bowls is due to modern fuels being lighter specific viscosity than 1970s fuels: the floats were designed to be used in a more dense fluid, which was [real?] gasoline instead of a gas/ethanol/lube mixture like we have today. Also, the modern fuels expand about 3% to 6% more with heat (as in, parked with hot engine under them) than the old-time fuels. After the float bowl gaskets get soaked a little longer in the modern fuels, they will also re-expand to [more than] their original sealing size, which will actually help stop the weeps. The ethanol in today's fuels make the O-ring seals on the float bowls expand about 5%-7% (difference being how much ethanol % is in your fuels) when they get wetted, and shrink below their original size by around 4%-7% when they get dried out after the exposure.

One way to minimize all this expanding/shrinking/hardening of the O-rings is to add a bit of oil to your gas: this neutralizes the ethanol's attacks on the rubber substantially. I use a capful (1-2 ounces) in every tankful when I fill up. It doesn't seem to matter WHICH oil, so I use synthetic 2-stroke oil so it doesn't smoke.

Thanks for that tip on a 'spot of oil' for preventive maintenance.
I think that will also help the valve stems,etc.

[Tracksnblades1]

3 more pieces of intel re- my top speed stutter:
1- there is a quarter-sized hole at the end of the header right before it connects to muf
2- it pissed fuel all over garage floor 2 nights ago. It was dripping from the #2 carb (from kick starter side), or at least thats where it was condensing into drops & falling. I had firgotten to turn the petcock off after last ride- but still- it shouldnt have done that. I gave it a few taps w brass hammer and it stopped
3- it has an upgraded ignition: no points

Today I will pull & inspect plugs. Yesterday I changed oil to Rotella T4 15w40 and no more slippage on test ride. Unfortunately I couldnt get the bolt off to change the filter. I read on here thats a common problem

Just for consistency's sake: the carbs are numbered from the left side (shifter side), as 1-4.
It's not uncommon for these bikes to 'piddle' when parked, particularly after they were sitting a long time. That's why you'll need to get used to the 'startup/shutdown drill', which always includes switching the petcock in addition to the keyswitch.

Part of the issue with the dripping float bowls is due to modern fuels being lighter specific viscosity than 1970s fuels: the floats were designed to be used in a more dense fluid, which was [real?] gasoline instead of a gas/ethanol/lube mixture like we have today. Also, the modern fuels expand about 3% to 6% more with heat (as in, parked with hot engine under them) than the old-time fuels. After the float bowl gaskets get soaked a little longer in the modern fuels, they will also re-expand to [more than] their original sealing size, which will actually help stop the weeps. The ethanol in today's fuels make the O-ring seals on the float bowls expand about 5%-7% (difference being how much ethanol % is in your fuels) when they get wetted, and shrink below their original size by around 4%-7% when they get dried out after the exposure.

One way to minimize all this expanding/shrinking/hardening of the O-rings is to add a bit of oil to your gas: this neutralizes the ethanol's attacks on the rubber substantially. I use a capful (1-2 ounces) in every tankful when I fill up. It doesn't seem to matter WHICH oil, so I use synthetic 2-stroke oil so it doesn't smoke.

Thanks for that tip on a 'spot of oil' for preventive maintenance.
I think that will also help the valve stems,etc.

Just wondering out loud 🤔 at 640:1 to 320:1 how much help is it for the stems..🤔

[grcamna2]

3 more pieces of intel re- my top speed stutter:
1- there is a quarter-sized hole at the end of the header right before it connects to muf
2- it pissed fuel all over garage floor 2 nights ago. It was dripping from the #2 carb (from kick starter side), or at least thats where it was condensing into drops & falling. I had firgotten to turn the petcock off after last ride- but still- it shouldnt have done that. I gave it a few taps w brass hammer and it stopped
3- it has an upgraded ignition: no points

Today I will pull & inspect plugs. Yesterday I changed oil to Rotella T4 15w40 and no more slippage on test ride. Unfortunately I couldnt get the bolt off to change the filter. I read on here thats a common problem

Just for consistency's sake: the carbs are numbered from the left side (shifter side), as 1-4.
It's not uncommon for these bikes to 'piddle' when parked, particularly after they were sitting a long time. That's why you'll need to get used to the 'startup/shutdown drill', which always includes switching the petcock in addition to the keyswitch.

Part of the issue with the dripping float bowls is due to modern fuels being lighter specific viscosity than 1970s fuels: the floats were designed to be used in a more dense fluid, which was [real?] gasoline instead of a gas/ethanol/lube mixture like we have today. Also, the modern fuels expand about 3% to 6% more with heat (as in, parked with hot engine under them) than the old-time fuels. After the float bowl gaskets get soaked a little longer in the modern fuels, they will also re-expand to [more than] their original sealing size, which will actually help stop the weeps. The ethanol in today's fuels make the O-ring seals on the float bowls expand about 5%-7% (difference being how much ethanol % is in your fuels) when they get wetted, and shrink below their original size by around 4%-7% when they get dried out after the exposure.

One way to minimize all this expanding/shrinking/hardening of the O-rings is to add a bit of oil to your gas: this neutralizes the ethanol's attacks on the rubber substantially. I use a capful (1-2 ounces) in every tankful when I fill up. It doesn't seem to matter WHICH oil, so I use synthetic 2-stroke oil so it doesn't smoke.

Thanks for that tip on a 'spot of oil' for preventive maintenance.
I think that will also help the valve stems,etc.

Just wondering out loud 🤔 at 640:1 to 320:1 how much help is it for the stems..🤔

Can't hurt 

[Vfrman]

3 more pieces of intel re- my top speed stutter:
1- there is a quarter-sized hole at the end of the header right before it connects to muf
2- it pissed fuel all over garage floor 2 nights ago. It was dripping from the #2 carb (from kick starter side), or at least thats where it was condensing into drops & falling. I had firgotten to turn the petcock off after last ride- but still- it shouldnt have done that. I gave it a few taps w brass hammer and it stopped
3- it has an upgraded ignition: no points

Today I will pull & inspect plugs. Yesterday I changed oil to Rotella T4 15w40 and no more slippage on test ride. Unfortunately I couldnt get the bolt off to change the filter. I read on here thats a common problem

Just for consistency's sake: the carbs are numbered from the left side (shifter side), as 1-4.
It's not uncommon for these bikes to 'piddle' when parked, particularly after they were sitting a long time. That's why you'll need to get used to the 'startup/shutdown drill', which always includes switching the petcock in addition to the keyswitch.

Part of the issue with the dripping float bowls is due to modern fuels being lighter specific viscosity than 1970s fuels: the floats were designed to be used in a more dense fluid, which was [real?] gasoline instead of a gas/ethanol/lube mixture like we have today. Also, the modern fuels expand about 3% to 6% more with heat (as in, parked with hot engine under them) than the old-time fuels. After the float bowl gaskets get soaked a little longer in the modern fuels, they will also re-expand to [more than] their original sealing size, which will actually help stop the weeps. The ethanol in today's fuels make the O-ring seals on the float bowls expand about 5%-7% (difference being how much ethanol % is in your fuels) when they get wetted, and shrink below their original size by around 4%-7% when they get dried out after the exposure.

One way to minimize all this expanding/shrinking/hardening of the O-rings is to add a bit of oil to your gas: this neutralizes the ethanol's attacks on the rubber substantially. I use a capful (1-2 ounces) in every tankful when I fill up. It doesn't seem to matter WHICH oil, so I use synthetic 2-stroke oil so it doesn't smoke.

Great intel, thanks very much!

[MauiK3]

I wonder if the previous owner set the jetting up for that exhaust system

[grcamna2]

I wonder if the previous owner set the jetting up for that exhaust system

Seal-up the holes in the exhaust;they always hurt performance.

[Vfrman]

I wonder if the previous owner set the jetting up for that exhaust system

Seal-up the holes in the exhaust;they always hurt performance.

I ordered some JB Weld High Temp that many ppl have used successfully. I will lay a small square of metal mesh over the hole and put the stuff all over it like patching a hole in drywall

[carnivorous chicken]

Looks like a 400F header -- might be able to find a replacement for not too much although I haven't really been looking lately.

[grcamna2]

Vfrman,remove all your spark plugs and bring them out in the sunlight(marked #1,#2,#3,#4)with the bottoms pointing straight up for a good view and take a picture so we can see the way they're burning.
This will give us a correct view of the way the engine may be struggling.

[Vfrman]

Vfrman,remove all your spark plugs and bring them out in the sunlight(marked #1,#2,#3,#4)with the bottoms pointing straight up for a good view and take a picture so we can see the way they're burning.
This will give us a correct view of the way the engine may be struggling.

I will definitely do that. Sick today tho…hope I can get to it tomorrow

[carnivorous chicken]

Looks like a 400F header -- might be able to find a replacement for not too much although I haven't really been looking lately.

I should also add: the way the exhaust sits on that bike is way off -- I've got a 350F with 400F exhaust, and you can compare with my photo. The exhaust should sit way tighter to the frame and not sag so much (no wonder there is a hole) so either it's been shimmed somehow or it's just not mounted correctly. 400F exhausts on 350F bike require changing the pegs (with shift linkage) and brake lever to 400F as well, and a 550F kickstarter otherwise the brake lever will hit the exhaust. this is probably why the exhaust is sitting so low in the photo, to clear the lever, but a compromise was made somewhere else to get it to mount like that.

[grcamna2]

Looks like a 400F header -- might be able to find a replacement for not too much although I haven't really been looking lately.

I should also add: the way the exhaust sits on that bike is way off -- I've got a 350F with 400F exhaust, and you can compare with my photo. The exhaust should sit way tighter to the frame and not sag so much (no wonder there is a hole) so either it's been shimmed somehow or it's just not mounted correctly. 400F exhausts on 350F bike require changing the pegs (with shift linkage) and brake lever to 400F as well, and a 550F kickstarter otherwise the brake lever will hit the exhaust. this is probably why the exhaust is sitting so low in the photo, to clear the lever, but a compromise was made somewhere else to get it to mount like that.

Yes,the exhaust is mounted way too low;is that an aftermarket 4 into 1 head pipe ?
The exhaust header is wrong for that application.. Way Too low.
I wouldn't be surprised if the carb. main jets don't match the flow requirements of that exhaust.

[carnivorous chicken]

Looks like a 400F header -- might be able to find a replacement for not too much although I haven't really been looking lately.

I should also add: the way the exhaust sits on that bike is way off -- I've got a 350F with 400F exhaust, and you can compare with my photo. The exhaust should sit way tighter to the frame and not sag so much (no wonder there is a hole) so either it's been shimmed somehow or it's just not mounted correctly. 400F exhausts on 350F bike require changing the pegs (with shift linkage) and brake lever to 400F as well, and a 550F kickstarter otherwise the brake lever will hit the exhaust. this is probably why the exhaust is sitting so low in the photo, to clear the lever, but a compromise was made somewhere else to get it to mount like that.

Yes,the exhaust is mounted way too low;is that an aftermarket 4 into 1 head pipe ?
I wouldn't be surprised if the carb. main jets don't match the flow requirements of that exhaust.

If it's a 400F 4-1 with stock muffler, I've found that you don't have to mess with the jetting (although I may not be getting the maximum out of it, it seems to work just fine for me). But that's not a 400F muffler so all bets are off.

[Vfrman]

Looks like a 400F header -- might be able to find a replacement for not too much although I haven't really been looking lately.

I should also add: the way the exhaust sits on that bike is way off -- I've got a 350F with 400F exhaust, and you can compare with my photo. The exhaust should sit way tighter to the frame and not sag so much (no wonder there is a hole) so either it's been shimmed somehow or it's just not mounted correctly. 400F exhausts on 350F bike require changing the pegs (with shift linkage) and brake lever to 400F as well, and a 550F kickstarter otherwise the brake lever will hit the exhaust. this is probably why the exhaust is sitting so low in the photo, to clear the lever, but a compromise was made somewhere else to get it to mount like that.

There is a fabricated piece to re-angle the muffler from the direction it would have naturally hooked up with the header

[grcamna2]

Looks like a 400F header -- might be able to find a replacement for not too much although I haven't really been looking lately.

I should also add: the way the exhaust sits on that bike is way off -- I've got a 350F with 400F exhaust, and you can compare with my photo. The exhaust should sit way tighter to the frame and not sag so much (no wonder there is a hole) so either it's been shimmed somehow or it's just not mounted correctly. 400F exhausts on 350F bike require changing the pegs (with shift linkage) and brake lever to 400F as well, and a 550F kickstarter otherwise the brake lever will hit the exhaust. this is probably why the exhaust is sitting so low in the photo, to clear the lever, but a compromise was made somewhere else to get it to mount like that.

Yes,the exhaust is mounted way too low;is that an aftermarket 4 into 1 head pipe ?
I wouldn't be surprised if the carb. main jets don't match the flow requirements of that exhaust.

If it's a 400F 4-1 with stock muffler, I've found that you don't have to mess with the jetting (although I may not be getting the maximum out of it, it seems to work just fine for me). But that's not a 400F muffler so all bets are off.

I remember the CB400F I was running was happy with #75 main jets.

[carnivorous chicken]

There is a fabricated piece to re-angle the muffler from the direction it would have naturally hooked up with the header

I'm talking about where it mounts to the engine, and how the exhaust should hug closer to the engine and closer to the frame at the bottom. Look at the photo of my bike in my avatar and compare it to how your header sits.

[grcamna2]

There is a fabricated piece to re-angle the muffler from the direction it would have naturally hooked up with the header

I'm talking about where it mounts to the engine, and how the exhaust should hug closer to the engine and closer to the frame at the bottom. Look at the photo of my bike in my avatar and compare it to how your header sits.

Yes,I was questioning if that header is an OEM Honda part.. and if so,is it mounted properly to all 4 head ports? 
The 400F always has the exhaust collector outlet tight to the frame and hugging close to the underside of the engine.
I think it's possible that those 4 'head pipes' are sitting askew on the 4 cylinder head exhaust ports and leaking exhaust out the bottoms of them before the exhaust even makes it's way back toward the muffler;that would cause a bad exhaust leak and severely 'lean out' your mixture on all 4 cylinders. Do you have a picture of the color of the spark plugs firing tips;how are they burning lately ?  I suspect very white hot.