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Messages - K2-K6

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CB750 / Re: 1976 CB 750 Clutch upgrade
« on: July 23, 2024, 09:30:01 PM »
Hi we have a customer with a 1976 CB750 the clutch pressure plate the one with 4 springs has a crack in it can we use a clutch from a new Honda CB750 that will fit straight in with more springs.

Many Thanks Sheps

Unless you've got something there, available and definitely fits, then I dont know of something with that replacement potential.

The early CB 750 is fairly unique in tbat design, with not much in the way of compatability from later type designs.

As noted above, the cracked spring plate on these comes from incorrectly assembled components, ultimately tightened down on springs with some internal misalignment.  Durability when correctly assembled isn't usually a problem with them.

CB500/550 / Re: Your thoughts on this peculiar vid.
« on: July 23, 2024, 09:24:08 PM »
What's it the product of ? Chat gpt or similar, whole bike (new) looks ai generated, absolute shite  :(

CB500/550 / Re: Carb sync question
« on: July 23, 2024, 01:08:35 PM »
So if I get 5-10 miles on it then hit the kill switch and get the plugs out

The miles should clean out combustion, allow it to reach full running temperature, and clean any fouling from the plug surfaces to avoid giving false perception after cold start etc.

Kill switch routine is ordinarily when you are checking fully loaded running at big throttle opening and hard on torque demand. That entails pulling it hard with substantial throttle, running up fully on main jet at maximum demand conditions to asses the mixture under those circumstances. Valid for those reasons as you want to suspend running right at that maximum demand to get the most accurate picture of the prevailing combustion conditions.

  It's not for this scenario of general setup and checking if the very low speed system of jetting is accurate.  A simple run out to get it fully warmed etc is just fine to build a picture.

I don't routinely replace plug washers, always use a light smear of copper type lubrication on threads, and lightly tighten. Never have any leaks or compromised threads in practice.

CB500/550 / Re: Carb sync question
« on: July 23, 2024, 09:07:46 AM »
The picture of plug shows the tip oddly hot, in contrast to the running rich observation.

I'd doubt of there's any problem with plug and it's manufacturing if they all start and run reliablly.

Likely the short run wouldn't give a valid and more comprehensive view initially though. If it's all together and seems to be running without error generally., then more miles 5~10 run to then look at the plugs again would give more insight.

CB500/550 / Re: Carb sync question
« on: July 22, 2024, 08:13:02 AM »
All back on and set to 1.5 turns out, no more hanging idle but smells very rich.  Could it just be that I need to get out on it and get some miles on it now?

Aside from it smelling rich are there other signs such as an overly cold exhaust - I assume you have tried opening up the air screws a tad.

I found a decent run often helps as you get the whole system up to temperature plus when riding you will burn up the fuel through the rev range moving onto the main needle jets.

Agree with this.

Would go further in this direction to evaluate what range you're actually operating in. Turn the airscrews out to 2 3/4 for a functionality check in establishing IF there's enough range of adjustment to correct what exists currently.

If they get to 3 turns out, and without correcting mixture adequately, likey that the idle jets themselves are flowing too much fuel. This is effectively what an "engine check light" on fuel injection is doing, telling you it's reached the maximum allowed in programmed adjustment but not successful in fully corrected output.

MOST of these carburettor would have the adjustment range of screw within 1 ~ 3 turns out, past those positions would indicate the fuel jet is too large or too small for application.  That could be partly blocked, enlarged through cleaning, or the wrong size simply installed.

Going for maximum outwards is not to run it like that but to answer the question of IF it can be corrected within design parameters.  Try it to find out. It could be that one size smaller jet is suitable in this case.

Before this though, are you confident of the air filter fitted ? That could also significantly skew results here.

APPARENTLY  :) it wasn't a reshell, as noted in the catch-up show.

Just how far the panel replacement went in getting it back to competent wasn't revealed in any significant way. There's been some notable repair jobs on these car show programs generally though, with shells welded with temporary significant internal frame + jigs etc to keep the original salvageable structure as much as possible. 

I think it's good to save cars like that, but open to interpretation as to just how much metal has to be replaced. After all a shell is literally a collection of pressings anyway.

Other Bikes / Re: Suzuki GT750J
« on: July 20, 2024, 04:08:51 PM »
I wouldn't worry too much about the smoke as they're doing quite a job down here when they set those there "electrical" buses on fire, 3 at least in public, more apparently in storage  :o

They make a heluva smoke screen, much worse than a herd of two strokes  ;D

Other Bikes / Re: Suzuki GT750J
« on: July 20, 2024, 03:07:31 PM »
A very good example Honda enthusiast, the Japanese paint colours of that era are particularly good to.

Looks really good with its original 4LS brake as well, also surprisingly torquey engines (in comparison to general perception of two stroke) a lovely bike.

CB750 / Re: Fuel restriction.
« on: July 20, 2024, 11:26:35 AM »
Some of the earlier taps look like they weren't bespoke, more off the shelf type arrangement tgat didn't take account of other items close by, not a huge amount of room around there anyway.

Original fuel pipes had quite thick wall, making them resistant to kicking like this too.

Wouldn't hurt to use length change in looping lower and back up again to ease pathway either.

K type 750 would usually run for about 3 miles with fuel off just on float bowls as I often turned mine off on way home to habitually leave the carbs more or less empty when not in use.

CB750 / Re: Intermittent noise when riding, could it be my chain?
« on: July 19, 2024, 10:09:59 AM »
Thanks Bryan, I’ll see what happens when I get it put back and ridden again. If I do the chain, I will probably do the sprockets for peace of mind.

The difference in the slack before I readjusted the chain and after, is there any logical explanation for that? There is definitely less variance and more uniform now for sure??? Could poor alignment do that?

Certainly odd that you've got a variable as the error would usually stay the same.

As a check though, put your fingers in behind the frame at left swingarm pivot, now squeeze one of the chain runs (top or bottom) to the arm itself. You'll be checking for movement in swingarm bushes when the chain loads and unloads tension.
Any shift there with arm bushes, and it'll give you problems.

For variation in chain like this (never taken one apart to look at links) comes down to some level of corrosion / wear along the run.

Suggestion to use GL5 oil initially will give results usually in this scenario. It will penetrate the links to the pins etc and highly effective in taking chain load. It's a low cost way to verify those links etc.

Failing that, definitely into chain replacement to deal with it.

CB750 / Re: Intermittent noise when riding, could it be my chain?
« on: July 17, 2024, 09:52:19 PM »
If you find anything significant, then also include rear sprocket for concentricity to eliminate that part.

Sometimes you can here quite clearly when someone pulls away from a bike meet or similar a pulsing noise as they rotate the wheel.

If the chain is definitely bad, then not much option but to replace.

If it did in any way appear to be corrosion linked (chain pins etc) then trying a EP gear oil application could be effective. GL5 rated is very good on chains and has not much smell like older oils of this type are characteristic in pong.

Hopefully detailed inspection will confirm if there's anything to be acted apon.

CB750 / Re: Intermittent noise when riding, could it be my chain?
« on: July 17, 2024, 08:18:54 PM »
Fairly normal to have those mark in the rubber, as you note, it's there to stop it rattling on the aluminium.

A thought though. Have you checked chain slack at multiple points ? If its uneven (sometimes when contemporary you'd get a chain that was significantly different in dimension along different parts) to make it flap up and down, hitting the guard variously.

Worthwhile checking to see if there's any inconsistency present.

CB500/550 / Re: Pistons
« on: July 16, 2024, 09:12:44 AM »
Obviously no options with std piston to change compression specifications.

It is though a consideration, in that a camshaft with extended overlap /duration will lower the effective compression ratio, all things being equal.

The geometric ratio of combustion chamber volume to swept volume remains the same, but with valve opening moved then the active ratio will usually be reduced (assuming longer opening etc) which will reduce the torque at lower rpm.

The changes effectively push the torque peak upward to occur a raised rpm point but looses combustion effectiveness at the lower speeds.
It gives something of a " false" gain, in that the brake horse power is a calculation involving rpm as a factor in projecting work rate.

Net effect is that you have to rev it to get to torque peak by using lowered gearing, seems more dramatic peak as the reduced torque in low rpm range has greater contrast to the high rev performance.

Itll be faster by the effect of fitting in more power stroke to a measured distance that before (lower gearing, higher revs) but at the same low range rpm it will be correspondingly slower from less real torque. In other words, you've always got to ride it at revs to see an increase in power.

Lifting the static compression ratio is a way of compensation to avoid some of this.

You'd probably need a dry build though to assess piston clearance to head and that to valves at the cam duration specification used.

Project Board / Re: Doms CB550F1 project
« on: July 15, 2024, 01:32:30 PM »
The absolute airscrew setting has always been part of adjustment scheme in reality, rather than solid set and forget.

With variation likely on component now in comparison to production line original, then highly likely that set point is going to be different.

Bore of jet, bleed holes, airflow passages, air filter performance, piston ring sealing, fuel burn characteristic, ethanol inclusion (contains oxygen over and above no e types) will all contribute to a setting that may be different to "book" value originally given.

The cleaning  of the jets and air passages are also a scource of variance too.

Establishment of a set for what you've now got in place should effectively accommodate these.

Fuel injection system do exactly this now, with more or less the same methodology as Honda originally published in their manuals, just automatic in itself via ecu programming, built in sensors etc.

Like these carbs though, if the sensible adjustment fails to yeald a competent combustion before reaching the end of logical steps available, then it'll usually throw emissions/check engine code and warning to request further work in establishing what is the real cause of going out of range.

Project Board / Re: Doms CB550F1 project
« on: July 15, 2024, 11:35:10 AM »
Yes, Nigel is correct.

Probably worthwhile looking through them again. Youjust gain more experience in doing this, a very pedantic/ critical eye in evaluation of them will often turn up something that may be causing an issue.

They are just plain fiddly to get right if there's any impairment etc, that's carburettor in general, even for experienced practitioners of the art. Can go round and round until finally sorting them. A friend runs a garden machinery business and hates the run around that inevitably comes with sorting out simple problems.

The bench sync is absolutely fine to run the engine without problem from tbat aspect. It has the major advantage of knowing they are mechanically in synchronization and helps in diagnosis of other faults if you don't try and sync them after installation.

The carb rack should allow for adjustment of the major rpm stop screw to fully lower the slides after setting them (if you use the drill method on here) which ensures that the slides have the capability of full restriction once set to parity.

You can then connect them to cables, without installing on engine, to ensure the cables definitely don't conflict with that function.  Emphattge slides should sit at rest on that master tickover screw stop, and nothing else should impede that operation.

Adjustment of the airscrew idle function when running is then where the attention should be. The suggested opening point 1 1/2etc should be seen as competent start point, from which you need to test what exactly is needed.  That method is in the Honda manual officially to instruct you.

Effectively, it gets you to adjust leaner until that cylinder falters, this  is the air fuel mixture just going past its technical ideal of 14.7 to one ratio. Thats pertinent to the hardware in place AND the fuel in use at the elevation you are working.
Then it requires you to make it richer by adjustment to bring a 100 rpm drop (multimeter with frequency will register this if you've got one) to bring that carburettor and cylinder to ideal operating point.
Later Honda manual detail recording that absolute setting in service notes as baseline for the operation. It can be different for each of the for cylinders. If you don't get something competently in range at that point, this suggests something else maybe wrong, or some impairment is still there withing that idle circuit.

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