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Messages - garyjpaterson
1
« on: September 17, 2023, 03:56:13 PM »
The stutter/roughness I am speaking of occurs just above idle - 1500-1800 RPM. It is most apparent if holding a steady throttle in that range - say 1st or 2nd gear in slow-moving traffic or maneuvering in a parking lot.
I have it in both my CB350 twin and CB750, I've yet to be able to tune it out. Maybe a little faster, 30mph in 4th gear is the when its most noticeable, just when you crack the throttle it doesn't like staying there. Give it a fistful and away it goes
2
« on: August 25, 2023, 02:08:16 PM »
I got myself these for my CB750- https://www.suspension-store.com/YSS_RD222-335P-02-18- the Koni 76f-1302 ones that came on it were shorter than stock, so it was sitting too low on the rear plus made it much harder to get on the centre stand, as well as sitting near vertical on the side stand. They seem fine, they were the correct diameter for the top mount, but they were tight against the chain guard. The coil spring seems to be a looser coil than in the pics, but it doesn't bother me. It rides nice enough 
3
« on: August 21, 2023, 11:54:43 AM »
I've only registered twice, and both times I had a title but no dating certificate. No inspection for me so far, seems I've been lucky!
4
« on: August 21, 2023, 09:37:57 AM »
Speedo cable is new, since the bike didn't come with one. And it does oscillate a little, but not much, about what I'd expect for this age. My CB350 is really wild, at speed it can swing around to quite the extreme! But tbh I'm not overly concerned about the speedo, just knowing its off and by how much is good enough for me for now.
Interestingly, cyl 4 compression is fine, at 150psi. But cyl 1 is a bit lower, at 130psi, yet that plug is in line with 2 and 3. I'll be testing compression on them all again once ive got more miles on it.
I'll probably end up with the carbs off again just to absolutely make sure the idle circuit is totally clear, floats are definitely correct etc
5
« on: August 20, 2023, 07:22:45 PM »
Oh good shout Julie. I had was going to have a little look myself but couldn't even work out how to take the casing apart without breaking anything.
6
« on: August 20, 2023, 06:43:07 PM »
Turn 1 and 3 air screws in by about ½, giving more fuel, and 4 out by about 1 turn, giving more air. Clean plugs, go for a hard ride and re check plug colours after.
Hi,
"and 4 out by about 1 turn":
That's interesting. I have fouling on no.1 after about 100 miles on my K6, it comes on at low throttle openings, behind traffic and clears for a while once i give it some beans. It's dry soot and brushes off easy, not oily. No. 4 is good, so not timing / ignition. The workshop manual suggests a range for the air screw of 7/8, to 1 1/8 out. Going by the manual, I've been at 1 1/8 out with no difference. I've tried slightly more, but never a full turn further out. I'll try that. 👍
However, my suspicion is it is related to my leaking head, which I plan to do this autumn. But it's not a wet sootiness?
Mine seems very similar to yours, dry soot, cleans up easy. Haven't done a high speed chop, so not sure if it clears up, but it feels very healthy beyond the idle circuit. Some big (half and full) turns haven't done a whole lot for me, I think i'll revert and just try and tune it by ear. I dont like one being so different from the rest, and overall it feels quite lean still so I'd rather bring them all to the richer side for now. Was able to verify with GPS that the speedo is off quite a bit. Actually, that's a bit unfair, it can be quite accurate, but its slow to react, especially beyond 50-60mph. Its often 10-15mph behind on acceleration, but will catch up eventually. My guess is the needle pivot is sticky, maybe it'll free up with more use at those higher speeds  Rode it back to back with the CB350 twin, was really fun doing a direct comparison. I'm in love with the smoothness of the four cylinder, and it sounds just sublime to my ears. The drum front brake on the 350 is far far better at coping with its mass though. And of course overall the little one is a lot more agile. Struggles on bumps though, like a bucking bronco, the 750 is a lot more stable. Fun pair, looking forward to many miles on both.
7
« on: August 19, 2023, 04:58:13 PM »
First proper voyage complete, really good fun. Sounds and feels great, lovely smooth engine. I think (and yes this will have been contributing to my earlier problem) that the speed is reading significantly low. The bike feels every bit as punchy as I'd expect it to, yet the speedo seems to tell a different story. Went through a radar speed sign - it was telling me I was doing 49, and my speedo was saying 40! And I'm quite sure the discrepancy gets worse the faster I go. Usually cars/bikes will over-read, not under! Seems odd, as the odometer seemed to track roughly the right amount of miles, so I'm not sure what's happening. Otherwise, I still need to dial the carbs in more, still not always happy to return to idle. I'm wondering if this is a sync issue (not yet done). Bit concerned about the vast difference in plug fouling of cyl 4 compared to the rest. Overall very chuffed though. Still need to get the cosmetics sorted (I daren't show what it looks like atm), but despite it looking so rough I had a guy gleefully asking questions at the fuel station! Quick clip, uphill, starts in 2nd gear. Poor quality image but hopefully you can see (and hear) that it pulls well, but does the speedo seems quite lethargic? 7k rpm in 3rd gear must be about 80mph, speedo reads 70 https://streamable.com/qd19qj
8
« on: August 18, 2023, 04:55:18 PM »
Will do. Need to get it insured and put my reg plate on first  Been testing on "private ground" up until now...
9
« on: August 18, 2023, 04:34:42 PM »
the new plugs and caps seemed to make a huge difference, power seems to be much closer to what I would expect. Really chuffed with that!
Now i need to focus on getting the idle mix sorted. Its a bit slow to return to idle, so I checked the plugs and 1 to 3 look potentially a little lean, 4 is very fouled though. All were just 1 turn out
10
« on: August 16, 2023, 08:40:05 AM »
I took the lower half and filter out, left the top half on.
But as I said, i'm not overly concerned with the overall numbers, it seems quite normal to be down on brand new compression after 50 years.
Its just one cylinder being a bit down on the other that i something i'll need to keep an eye on.
11
« on: August 15, 2023, 09:37:13 PM »
Yeah throttle was wide open. I checked them in reverse order, so 4 first and 1 last, so the battery wasn't able to spin it quite as fast by the end, so that probably has a small effect
12
« on: August 15, 2023, 07:00:43 PM »
should be 175psi on a new or rebuilt engine. Looks like you have quite a few PSI missing across the cylinders, which could be anything from worn bores, worn rings, bent valve or not seating properly 
Yep, though given its not rebuilt, I'm happy enough with the overall compression. I'm only really concerned with the ~15% dip in cyl 1.
13
« on: August 15, 2023, 06:39:22 PM »
Plugs and caps are here, waiting for new clamps for the intake boots still as the old ones were very stretched, so hopefully that'll stop any leaks.
In the meantime, I did what I probably should've done ages ago - a compression test!
Would've liked a little more uniformity, but I think its just about acceptable. Engine wasn't properly hot, just slightly warm. I checked valve clearances before, they were just fine.
cyl 1: 130psi
cyl 2: 145psi
cyl 3: 145psi
cyl 4: 150psi
I'll certainly keep an eye on cylinder 1, and check in future once some miles are on it. Hoping that the rings are a little stuck or something
14
« on: August 12, 2023, 10:57:10 AM »
Checked resistance on the caps - i'm getting about 12-13k ohm on the two outer caps, and just under 9k ohm on the middle ones. They should all be roughly the same, no? Not different by that much.
And I'm using DR8ES plugs atm - should i be looking into non R plugs?
15
« on: August 09, 2023, 08:24:26 PM »
So over the past few months, when time permits, I've been going through my very scabby 750. But once getting it out on the open road, I quickly noticed it lacked a lot of power. Low and mid range seems decent enough, but there doesn't seem to be a lot happening beyond half throttle.
I have 657A carbs, but it came with 130 main jets. I replaced them with stock size 110s (i'm running a stock airbox now) as well as moved the needles to position 4, and that improved things significantly - its not completely stumbling at half throttle any more - it has a little more punch at the top but it still feels very weak. Can't really get over 60mph
Low end punch seems mostly fine - right now I know its not running perfect, i haven't balanced the carbs beyond the best i can do by eye, nor set the idle mixture beyond the stock 1 turn. But as far as i know, that shouldn't affect much once you are deep into the throttle?
I haven't done a compression check - perhaps a big mistake. I don't have a gauge yet, but maybe i should've thought about getting one before spending money on a bike! Though it doesn't seem to gallop, so I'm guessing if its down on compression, they are all roughly equal.
Since last putting the carbs on, the idle has been hunting quite badly, I think I have an intake leak, though the heavy throttle behaviour has been the same before and after this, so I'm not expecting that to be the solution - though of course I need to fix that asap.
I've been through the carbs fairly thoroughly I think, I'm quite sure everything is clear, emulsion tube holes etc.
Tank has been cleaned, and new filter sock over the petcock (I have the threaded on style petcock, took me a while to find the part)
Spark advance is free, so that should be fine. Static timing should be fine, though perhaps I should try and verify with a timing light
Could it simply be that, for whatever reason, stock main jets aren't close enough? Or can anyone think of anything else that might create this sort of behaviour?
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