Post by: DomP on October 09, 2025, 07:48:02 PM
Standard 069a carbs fully cleaned with the correct jets/needles and in the correct clip position.
Airbox is standard but I have used a Honda 500 air filter as I am missing all the breather hose parts, as a result ive blanked the breather hose port off.
Fuel is new, tank has been flushed and new tap and filter. The cam chain tensioner has been adjusted as has valves and timing.
Now if I really am running rich could it be because of the slight airlifted modification? I can't get smooth acceleration but instead a big flat spot until I hit 4k at which point is snatches horribly, this is the same when in neutral, I can't slowly raise the revs as it sticks at 2-2500 then races away past 4k.
Long shot but is there anyone near Herefordshire that is up for a tinkering session with coffee or beers? 🤞
Post by: Johnwebley on October 09, 2025, 08:12:24 PM
Have you had the head off?
I live in Hereford,
I could help, have you got vacuum gauges?
Are you available during the week?
Send me a PM in a couple of weeks, as I am in Italy
John
Sent from my SM-A546E using Tapatalk
Post by: DomP on October 09, 2025, 08:17:13 PM
I've got a Morgan carbtune
Post by: DomP on October 09, 2025, 08:37:42 PM
Post by: Johnwebley on October 09, 2025, 08:40:49 PM
Hi John, I've fully rebuilt the engine with a rebore by Bryan, are you thinking being a tooth out? I did it by the book so I'd like to think not but never rule things out, I'm not free in the week sadly. Italy, nice! We were in Brac, Croatia a few weeks ago which has some Italian influences. I've seen you are in Herefordshire, ironic with the surname WebleyGive me a message sometime after the 23rd,
I've got a Morgan carbtune
I can bring a 4 gauge carb tuner,
I also have a strobe,
Do you have a remote fuel tank?
We can have a play
Sent from my SM-A546E using Tapatalk
Post by: DomP on October 09, 2025, 09:19:31 PM
Post by: taysidedragon on October 10, 2025, 12:07:23 AM
Post by: DomP on October 10, 2025, 11:46:12 PM
Post by: taysidedragon on October 11, 2025, 12:15:50 AM
The springs have been trimmed byba preious owner, if anything one is too taught. The advancer itself has benn taken apart and greased so should be no free movement problems.
If you can't find any other cause of the problem it would be worth trying the advance unit with standard springs.
Post by: mickwinf on October 11, 2025, 08:56:48 AM
Post by: K2-K6 on October 11, 2025, 10:15:17 AM
Post by: DomP on October 11, 2025, 10:30:01 AM
Post by: McCabe-Thiele (Ted) on October 11, 2025, 11:40:02 AM
No cam cover removal just something to do with what the valves are doing at tdc?
IIRC Bryan or Ken posted it ages ago.
I've forgotten what you do, it might be in my 500 rebuild blog.
Post by: neat street on October 11, 2025, 12:37:29 PM
Quote
Airbox is standard but I have used a Honda 500 air filter as I am missing all the breather hose parts, as a result ive blanked the breather hose port off.
dont think the breather port should be blocked off... any thoughts?? this may cause some issues???
Post by: Bryanj on October 11, 2025, 01:09:48 PM
Post by: DomP on October 11, 2025, 05:35:22 PM
Post by: DomP on October 11, 2025, 05:36:40 PM
There is a simple test to check if the valve timing is a tooth out.
No cam cover removal just something to do with what the valves are doing at tdc?
IIRC Bryan or Ken posted it ages ago.
I've forgotten what you do, it might be in my 500 rebuild blog.
That's interesting Ted, be great to know what the method is to rule that out.
Post by: McCabe-Thiele (Ted) on October 11, 2025, 05:56:35 PM
I suspect I asked the question on the 400 section
Post by: K2-K6 on October 11, 2025, 06:05:35 PM
The springs have been trimmed byba preious owner, if anything one is too taught. The advancer itself has benn taken apart and greased so should be no free movement problems.
I'm suspicious of this as a modification generally, also the logic behind it.
Ignition is retarded to first start it .... without it trying to go backwards! .... secondly to make it tick over smoothly and to prevent it "hunting" around but stay calm when not needed.
Other than that, and say above 1500rpm, then advancing it quickly will usually increase torque from low into mid range output .... which is desirable. To delay that effect seeming pointless as you want it to get on and go a bit.
They are quite low compression for the output, and so will not usually be at risk for getting the advance going as early as possible. To mod them with tighter springs apppears to fly against optimal running
Post by: DomP on October 11, 2025, 08:52:30 PM
Post by: Bryanj on October 11, 2025, 09:45:23 PM
Post by: DomP on October 12, 2025, 09:50:58 AM
500 is same as 550
The advancer springs Bryan? What about the cam chain check Ted mentioned?
Post by: Bryanj on October 12, 2025, 10:58:29 AM
Post by: DomP on October 12, 2025, 12:59:01 PM
Post by: DomP on October 12, 2025, 01:57:49 PM
Do you think these advancer springs will fit, they appear to have the correct number of coils
Post by: K2-K6 on October 12, 2025, 02:32:53 PM
Verification is needed, given it's just been assembled, to definitively remove that from the scene.
Post by: McCabe-Thiele (Ted) on October 12, 2025, 03:36:11 PM
I don't know how to copy the text found it by searching valve timing item 7 iirc.
Post by: DomP on October 12, 2025, 08:42:31 PM
Post by: McCabe-Thiele (Ted) on October 12, 2025, 09:19:51 PM
Select Home its about the third item down.
Post by: DomP on October 12, 2025, 10:00:37 PM
Post by: McCabe-Thiele (Ted) on October 13, 2025, 07:24:35 AM
www.ebay.co.uk/itm/187506333851
Post by: DomP on October 13, 2025, 07:32:01 AM
Post by: McCabe-Thiele (Ted) on October 13, 2025, 07:34:09 AM
Ah ok, to turn the crank
I found that a T bar enabled one to rock the crank very slighty left or right with plugs removed.
Post by: deltarider on October 13, 2025, 08:11:15 AM
Post by: McCabe-Thiele (Ted) on October 13, 2025, 08:24:25 AM
I always use a T-handle and a 23 mm socket when cranking some millimeters a CB500 for timing. I estimate the risk of damage by removing the spark plugs far higher than cranking that WASHER, SPECIAL which, btw, is still the original... Things may be different with a CB750. I've seen more than once that problems that can occurr on CB750s, were bluntly transferred by experts to CB500550s.
Luckily in my case as it was an engine rebuild the plugs were still out from the head decoke.
I share your fears every time I take a plug out of an alloy head.
Post by: DomP on October 13, 2025, 04:56:50 PM
Post by: K2-K6 on October 13, 2025, 07:00:42 PM
I always use a T-handle and a 23 mm socket when cranking some millimeters a CB500 for timing. I estimate the risk of damage by removing the spark plugs far higher than cranking that WASHER, SPECIAL which, btw, is still the original... Things may be different with a CB750. I've seen more than once that problems that can occurr on CB750s, were bluntly transferred by experts to CB500550s.
Luckily in my case as it was an engine rebuild the plugs were still out from the head decoke.
I share your fears every time I take a plug out of an alloy head.
Take them out hot to avoid many problems ... makes a significant difference.
Recently in technical/advisor and oversight capacity :) (son bought his first car) a significantly complex all aluminium V8 with plugs right down the end of long tubes, they seemed too tight and felt risky to me when he tried to remove them to inspect, bringing it up to temp through running and they came undone easily.
Although against advice from many manufacturers, I use a smear of copper grease on thread when installing.
Post by: DomP on October 13, 2025, 08:59:03 PM
Post by: exvalvesetdabbler on October 13, 2025, 10:51:35 PM
On my 400 F I had rich running, tail pipe smelled a bit too much like the choke wasn't coming off.
After a lot of poking around and swapping carb internals it turned out that the emulsion tubes had worn a bit oval internally where the throttle slide needles go.
The other symptom was stumbling of and on the throttle at low revs and the adjustment of the pilot air screw made little sense. Plugs were a dark colour bordering on being sootey.
Put some new needles and emulsion tubes in and the problem disappeared.
Regards
Dave
The difference between old and new was visible if the needles were inserted into the emulsion tubes and rocked side to side.
Post by: deltarider on October 14, 2025, 08:17:11 AM
[...]This is in contrast to what I experienced the other day. For a silly reason - to be explained later - I had the carbs on the table. I closely examined needle jets and needles. On reassembly I accidently have mixed up jets and needles - so they were not the pairs they were before, and to my surprise bike runs nicely. The same accidental mix up happened to float needles and their valves and again: no negative effects. These parts have been in service over 140.000km. Makes me wonder what parts have been in your carbs: aftermarket or OEM and the same question to which parts you have put in now.
After a lot of poking around and swapping carb internals it turned out that the emulsion tubes had worn a bit oval internally where the throttle slide needles go.
[...]
Put some new needles and emulsion tubes in and the problem disappeared.
[...]
Post by: exvalvesetdabbler on October 14, 2025, 09:18:44 AM
Regards
Dave.
Post by: DomP on October 14, 2025, 10:18:19 AM
Post by: florence on October 14, 2025, 11:59:46 AM
I'm assuming you have had the carbs set up and balanced.
Are the chokes opening fully?
Is it flooding, are the float heights correct?
Post by: DomP on October 14, 2025, 01:18:06 PM
Post by: taysidedragon on October 15, 2025, 11:37:50 AM
With this in mind might it be worth trying my needle clip one lower, which on an F will be the last position.? All of my parts are genuine Keihin and correct for carbs/bike
If you put the clip one groove lower that will raise the needle and make it run richer.
Try going the other way, put the clip one groove higher to lower the needle.
Post by: DomP on October 15, 2025, 04:31:15 PM
With this in mind might it be worth trying my needle clip one lower, which on an F will be the last position.? All of my parts are genuine Keihin and correct for carbs/bike
If you put the clip one groove lower that will raise the needle and make it run richer.
Try going the other way, put the clip one groove higher to lower the needle.
Sorry Gareth thats what I meant to say, its the last clip position so im not going to get any lower than that, im hoping ill have enough range to play with the air screw in this position
Post by: K2-K6 on October 15, 2025, 05:09:15 PM
In effect, you'd be moving the two parts further alway from each other as it'll not change (much) the lowest point metering. Low would stay rich and mid would move toward lean.
If it's definitely rich at low slide opening, then it's usually the idle jets (assuming the others aren't nuts in volume) and so you'd correct with them by going smaller idles.
Of interest, what absolute vacuum reading is shown on the sync gauges if you use them ?
This complexity is why I'd be absolutely sure of cam timing before you begin diagnostics of carbs. If wrong, it'll run you ragged trying to think what you can adjust or the permutations of error ... all in vain too.
Post by: McCabe-Thiele (Ted) on October 15, 2025, 05:40:39 PM
Post by: DomP on October 15, 2025, 06:47:52 PM
Post by: DomP on October 19, 2025, 10:53:31 AM
Post by: deltarider on October 19, 2025, 11:53:11 AM
Leaking O-rings on the main jets have to be excluded, as well as accidently reamed slow jets.
Aftermarket air intake can make a difference, aftermarket exhaust hardly at all.
The correct fuel level in the floatbowls can easily be checked by applying this method: http://forums.sohc4.net/index.php/topic,185754.msg2151647.html#msg2151647.
Without having read all the above, make sure air intake is unobstructed, the airfilter element is good, meaning not moist or fouled by crankcase fumes.
Post by: DomP on October 19, 2025, 12:57:14 PM
*Little update, I did this today by extracting the needles through the top of the carbs while still fitted which is a whole lot easier. It then wouldn't start off choke which is encouraging as before it would start with no intervention at all. I made the battery a bit weak while trying so stuck it on charge chopine listening to the football. That's as far as I got, can't rush these things!
Post by: ozzybud on October 20, 2025, 03:11:12 AM
Standard for an F is 2nd slot from top so I'm proposing using the very last slot
*Little update, I did this today by extracting the needles through the top of the carbs while still fitted which is a whole lot easier. It then wouldn't start off choke which is encouraging as before it would start with no intervention at all. I made the battery a bit weak while trying so stuck it on charge chopine listening to the football. That's as far as I got, can't rush these things!
Please remember after you change the needle positions in place or on the bench you will need to start the bike and get it warmed a bit and do a vacuum sync before test riding.
You will.never get the arm positioned in the same place. On the shaft it was before and your synchronization will be all.over the place.
If not synchronized it will mimic lean and rich conditions on the plugs after a ride.
I believe it is the most important step when tuning.
Post by: DomP on October 20, 2025, 07:24:55 PM
Post by: DomP on October 24, 2025, 08:35:55 PM