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Topics - blackeagles

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1
SOHC Singles & Twins / CB250T
« on: February 28, 2024, 10:19:37 AM »
I have not been on the site for a while (cancer) but after 3 odd months of 'nil by mouth' and an operation I have lost a lot of strength and as I cannot manage the 750/650 anymore I thought I try a 250t.

I know most will say they like to rev but it's a bit much to me so I was thinking of changing the gearing a bit.  The stock is 15/40 and 'Gear Commander' says going up to 17/40 will drop the revs by about 250 at 8k (60mph).

Anyone done this or similar??

It seems to me the options are :

1 - stay with 15/40 and put up with it;
2 - go to 17/40;
3 - try 18/40 (not sure it will fit in and I would have to change the chain) or
4 - go 17 but lower the wheel sprocket to say 35 ish (no idea what rev saving this is)


Any comments?

2
SOHC Singles & Twins / 1981 CM250T
« on: March 11, 2023, 07:17:22 PM »
Can anyone tell me if the original speedo fitted to a 1981 CM250T is a max of 80mph or the 100mph one; both of which I have seen advertised for sale for the CM250T, I'm just interested how come a bike which is supposed to have a top speed of 85 would have an 80mph speedo.

3
SOHC Singles & Twins / 1981 CM250T
« on: March 05, 2023, 11:03:27 AM »
I'm buying a 1981 CM250T with a bit of paint damage to tank.

Anyone know the paint name and/or paint code of the light red and dark red 'decal' with the Honda badge of the tank?

4
CB650 / 1981 cb650z - carbs
« on: July 23, 2022, 10:07:54 AM »
I suspect I know the answer to this but I thought I would post my problem as there may be something I’m missing.

I have never had much luck with 4 cylinder carbs (3 too many) but I spotted a tatty 1981 cb650z so against my better judgement I thought “how hard could this one be?” so I have spent the last few months cleaning it up and now I have got to the carbs.

OK, the problem, it ran and ticked over well without any smoke/hunting or choking so I was going to leave it but being a meddler I had to check it and the carb sync showed 1 and 4 twice the value of the base carb and 3 just a little high but the real thing I could not live with was the slow running screws were set between 3 ½ and 4 ½ turns out ( the correct setting is, I think, 1 ½ out).

So anyway I re-synchronised them with the screws at still out and it ran hwhen hot so I reset the screws to 1 ½ and big surprise it no longer runs. It starts on full choke but if I touch the throttle it stops even when hot.

I’m going to guess they will have to come off but before I do that any other suggestions or things to check?

5
CB750 / testing coil
« on: September 18, 2020, 10:59:00 AM »
i'm not sure if the coils are 'wrong' or not but having finished the bike i took it for a 'shakedown' and in the last few miles it went onto 3. it started straight away on all 4 and has been ok running in the garage since so i am assuming it only happens when hot so intermittent and maybe a sod to find.

prim - slight fluctuation prob. the gauge

coil 1/4 - 4.5 to 4.6 ohms
coil 2/3 - 4.7 to 4.8 ohms

sec.

1/4 - 14.70 ohms
2/3 - 14.60 ohms


plug caps

1 - 5.68 ohms
2 - 4.29 ohms
3 - 4.81 ohms
4 - 5.48 ohms

i have bought new caps.

these readings seem ok to me but electrics is a 'dark art' as far as i'm concerned so not sure. obviously the readings are for a cold engine and since the 'running on 3' was when hot i'm not sure if it makes a difference or if it can be checked hot.

only other thing to say, and i still feel a bit dumb mentioning it, was that just before the problem there was a odd noise like a demented bird tweeting - only way i can describe it - which i was thinking may be a plug cap resister giving up.....maybe?.

any suggestions?

6
CB750 / CB750 F2
« on: July 12, 2020, 01:24:10 PM »
following on from my earlier post about drive chain noise and syncing the carb to help....i have been having a little trouble setting them up and i just noticed, looking at an illustration of the pd42 carb, that the 3 pipes that connect the acc. pump to each carb seem to have a restrictor in each (is it part number 16026-393-004 or maybe that is what joins the carbs fuel supply together).  no surprise when i took the old pipes off they didn't have such a restrictor so i have not used one....is that likely to cause an issue with setting the sync or the slow running????

bearing in mind they cannot be obtained (as far as i know)

7
CB750 / primary drive train rattle - CB750F2
« on: July 10, 2020, 12:42:39 PM »
reading on this site and elsewhere i know that the annoying rattle these bikes have tend to be associated with the carbs being out of sync. and the primary drive chain thrashing about at tickover.

i had this with the cb400f2 i have but most of the (worst of the) rattle has gone after i crudely synced them using a cheap set of gauges from ebay (but they are not very accurate and i suspect th carbs are not spot on or even that near if i am truthful !!).

having set the 750 up - tappets, ignition etc i am still having trouble getting it right and the rattle tis more than i can put up with. the main problem is that the engine 'hunts' so its prob. a mixture of sync and pilot (which is out 2 turns)

anyway, does anyone know of a mechanic or someone who specialises in the older bikes (plenty in my area who do the new stuff) in the n/w kent and se london areas- i'm in orpington so the nearer the better.

thanks
 

8
CB750 / oil additives
« on: May 24, 2020, 11:12:12 AM »
anyone use oil additives in their engines?  from what I can understand they cannot be used in wet clutch engines  so I guess no but I thought I would ask.

9
CB750 / 1977 cb750f2
« on: April 03, 2020, 03:23:07 PM »
anyone know where I can get the carb air box seal between the top and bottom parts of the cleaner - it usually sold fitted to the 'separator' plate (17230-405-305) but since mine is usable I only want the seal - or any suggestions what substitute I can use.

10
CB750 / keihin pd41b
« on: January 05, 2020, 01:41:51 PM »
Anyone taken these apart?

 Its not fair to say that I have to do this but as its now got a sticking float im toying with the idea of taking the whole thing off yet again and replacing (with second hand)  the throttle link bit – the plate where the cable nipple fits into and opens the throttle – as half of one of the tangs is missing and maybe replace the choke cam as well since it seems a bit worn.

Watching a demo on the internet it seems rather complicated for me, especially as I have never worked on one of these before other than to take the float bowls off!!

11
CB750 / 1978 CB750f2 - air box
« on: December 13, 2019, 12:16:39 PM »
anyone know if its possible to get the rubber gasket which fits between the two halves of the air cleaner box.

from what I can see it only comes with the top - 17230-405-305 - mine is a bit perished but i'm ever hopeful of finding one without the top of the box.

12
CB750 / 1978 CB750F2 - Poor Starting
« on: December 04, 2019, 11:47:07 AM »
ok, almost finished this rather easy 'restore' but not been at it for some time - too cold and too old.... well mainly the latter.

still seem to have a problem, when its hot the bike ticks over at 1200 and revs up without hesitation to settle back to 1200 again BUT getting it to start is something of an art form.  I checked the jets and sprayed them with cleaner and even the pilots were clear! (in fact they all look new), they are the correct size, pilot screw is now 2 3/4 out and all the pump jets fire a jet of petrol into the venture.  press the button and it fires up after a few tries (twisting the throttle to get the pumps to jet petrol into the venture helps) with the choke on and revs at about 4k (I know I have set the grub screw a bit too high at the moment) and I can rev it as much as I like but as soon as I let go of the throttle the revs start to die and the bike stalls.

any suggestions?

13
CB750 / 1978 CB750 F2
« on: October 24, 2019, 11:21:58 AM »
Most carbs usually have the pilot air screw setting as 'x' turns out +- 'n' but the 'H' Manual and a couple of bits I have seen on the net say the pilot air screw should be 1 3/4 turns out without any +- so is this correct?

I also hate to ask this but is it in for less air and out for more  :-[

14
CB350/400 / 1978 cb400f2
« on: September 20, 2019, 11:21:30 AM »
I was doing a partial restoration of a cb400f2 but I have got a bit side tracked with a 750 f2, anyway I have taken the 400 out and it seems to 'go' ok but it does not want to rev above 6k. it has all stock size jets and the air screw is 2 turns out.

I am not keen on revving an old bike to high levels but am just interest what, if anything, I have screwed up!

any suggestions?

15
CB750 / 1978 CB750 F2 throttle cables
« on: September 17, 2019, 02:51:23 PM »
anyone know if there is any difference - length wise -between a push cable 17920-341-000 (which is fitted to the 750f and k1 to k6 and which is on my bike but seems to be sooo tight it is almost without any adjustment) and the correct one for a 1977/78 f2 - 17920-405-610

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