1972 Honda CB175 Super Sport restoration

[911hillclimber]

Some shots of the copy carbs:
Amazing value at £22 a pair, delivered.

[911hillclimber]

Still have the strange starter situation, the engine turns over well and fast until you open the throttle with the twist grip and then the starter stops working! WHY?

Anyway, got it started (by luck) on these new copy carbs.
Got the tick over to a rather lumpy 1800 and screwed the pilot screw in until the revs maxed, which it actually did, and appreciably too, so adjusted the engine down to 1800 again on the one carb.
Repeated with the other, the pilot screw had NO EFFECT.
Messed about for 15 mins tweaking the screws up and down, in and out until I have an engine equally hot on each side and both exhausts slightly smokey.

Cant seem to get it all better.

There is considerable lag if you snap open the twist grip to max open, which I think indicates too rich as the revs when up drop quickly to the twist grip position.

could do with some learned input please.

Too late in the afternoon to be blipping motorcycle throttles, so decided to resume battle tomorrow,
At least it runs!

[911hillclimber]

Decided to give the carbs a rest until I resolve the awful noise from the starter system.

I think I've found the culprit, a very worn white metal bearing/bush in the starter main gear that allows a lot of movement so disengaging (I think) the 3 locking rollers.

No bearing replacements are available, infact the bearing is not even listed. It is made from the soft bearing material used in vintage bearings, so I have 2 repair choices.
First is to machine the soft metal out of the gear and turn up a brass sleeve to suit the crank journal, done this but not too happy with the baras as a bearing material. The crank can run at 9000 rpm with the gear stationary, and lubrication is by splash only.
Second direction is to machine a custom made oilite sintered bearing (20mm ID x 27 mm OD x 15 long), and a blank is now on order.
Being sintered the bearing will saturate in engine oil and I think is the best solution maybe...

Outside runner is to get a simple lump of white metal from a bearing specialist and machine that up to size. Asked the question to a specialist over the weekend.

All part of the fun of fighting old things.
And winning.

[911hillclimber]

After the world's longest wait for a simple bearing to arrive, it did and with some lathe work all back together. Bloody thing still rattles, so ordered a new Chinese replacement for £23 delivered, a last gasp to fix the starter.

Bike fired up awkwardly and ran very rich.

Back to basics tomorrow, valve clearances, ign timing and start again. If this fails, swopping the jets from the original carbs to the copies, and try, try, try , again.

[coomo]

I wouldnt use any copy carburettor.especially a Chinese one.One of my mates who runs a well respected mainly Japanese restoration business,will only use genuine
factory kits for servicing carbs.With good reason.
The tolerances with replacement jets have questionable accuracy,if what ive been told is correct.Id rebuild the original carbs myself.
Or do as Ive done on both twins and single cylinders, fit a single Mikuni.They even come jetted correctly to spec, if you purchase from Allens.Ive fitted 4/5 never had to touch one.

[911hillclimber]

Thank you, these were an experiment simply because the primary air mix on the originals were not responding to adjustment.

There are no new carbs available that I can find, and 5 years ago those available were north of £500 a pair.
Getting the engine to run right is one thing, but fitting the awkward air cleaners is another.

Just had a quick look, nothing on Allens for the Honda cb175, carbs or parts.

The stock carbs are Keilin 644.

[coomo]

Thank you, these were an experiment simply because the primary air mix on the originals were not responding to adjustment.

There are no new carbs available that I can find, and 5 years ago those available were north of £500 a pair.
Getting the engine to run right is one thing, but fitting the awkward air cleaners is another.

Just had a quick look, nothing on Allens for the Honda cb175, carbs or parts.

The stock carbs are Keilin 644.

Id give Allens a call.They are REALLY good at recommending carbs.Or rebuild the originals.Get a kit from David Silver.

[911hillclimber]

All my jets are absolutely clear, and I'm 95% sure all the drillings are too, but the air fuel needle does nothing even when the engine is down to near stall rpm, about 1600.
Screwing them in or out from 1.25 turns out does nothing to the engine speed.
I'll contact Allens and see what they say.

The carbs have been US cleaned twice, soaked in thinners before hand and pokes through with wires.
Carb cleaner aerosol squirts through every drilling.

My previous cb175 was exactly the same....

[coomo]

Float height checked/sticking float?

[911hillclimber]

Yes, floats sound and set at factory 21mm though some confusion as to how to actually measure the 21mm.
I have them set to 21 by allowing the float to hang vertically and tilt the body until I can see the float tab and the needle valve just touching.
Seems that is correct, doubt the Keilin factory were that fussy or had a far quicker method of checking the manufacturing of the tab in the totally brass float construction.

Carb don't flood and the valve works well against me blowing down the feed tube and the carb inverted.

All parts are to factory spec, no rouge jets or diy drilling.

[Hugo 356]

Screwing them in or out from 1.25 turns out does nothing to the engine speed.

Could air be getting in somewhere eg join between carb & inlet manifold? Are the mating surfacing flat with good gaskets?

[coomo]

Screwing them in or out from 1.25 turns out does nothing to the engine speed.

Could air be getting in somewhere eg join between carb & inlet manifold? Are the mating surfacing flat with good gaskets?

This was my next question.My mate has a 450cl scrambler from 1968.He did a carb refresh, and couldnt get it running right.The original air filters were NLA, and he tried a cheap fix.I tried to ride the bike.It was horrid.Lacking power terribly.He then sent the airboxes off to a guy who fitted correct paper filters.Issues solved.

[911hillclimber]

The carbs are sealed to the manifolds and the manifolds to the thermal break surface and the lot to the head via fresh O rings and (mani tohead) by fresh paper gaskets.

I have before now sprayed the joints with carb cleaner while the engine ran with no change in note etc.

All tuning so far without air filters.
Today spent some time on it.

Checked the points gap, 0.35mm with the heel on one of the 2 lobes, other lobe also gave 0.35mm. This engine is a parallel twin, ie two single together, so both pistons come to tdc together.
Checked the timing which was odd.
The timing check I use is a separate battery, lead with a bulb in line from +'ve to the screw that holds the points together. The screw insulation is good and new. Condenser lead off the screw disconnected.
Earth wire from the points back plate to the battery -'ve.
Rotate the engine anticlockwise and noted the bright bulb dulled noticeably when the contacts just broke open at the right 'F' timing mark on the alternator magnet on the crankshaft.
The bulb did not go out even when the points were wide open, some current flow somehow.?

Rotate the crank a further 360 and the same happens, this partial dimming of the bulb is repeatable.

The timing was out a little, so adjusted the plate by around 1mm on the 60mm dia plate and the dimming is now on F for both cylinders.
The F mark is the static advance and is 4mm before tdc on the 60mm dia alternator.

Decided to put the stock carbs back on, did that and had had enough in the damp cold.

Here is a picture of the set-up on my old 'Gold' cb175 I did 5 years ago which gave me very similar problems.


Will get on it tomorrow morning.

[911hillclimber]

I decided to simply start the engine first and see what I have.

It started, now with the original carbs on, and ran. The LH carb side ran rich, smokey fume exhaust, the RH side ran 'clean', and cooler to the touch (about 600mm downstream of the head)
This is with the air mix screw at the lowest tick-over I could get (about 1900).

No amount of tweeking to the LH side would delete or even change the richness, so after about 30 mins, engine hot and having run at tick over most of that time, killed the engine and removed the plugs, see picture.
The sooty one is the LH 'rich' side.

So, the bike restarts from cold well, re starts from stinking hot with one quick press of the starter and I have one side very rich and can do nothing externally to change it.

The RH engine side looks ok to me considering lots of time at tick-over.

The LH carb is now off, totally stripped in sitting in clean cellulose thinners for the night.
Will go though the carb passages and jets yet again tomorrow once I've bought and planted a Maple leaf tree!

[coomo]

the air filters have a pronounced effect on mixture.They need to be fitted whilst adjusting.If you have any rubber seals,the thinners will destroy them.it also softens plastic.Just sayin...