1972 Honda CB175 Super Sport restoration

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911hillclimber
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Re: 1972 Honda CB175 Super Sport restoration

Post by 911hillclimber »

No filters on the bike, have tried to tune with them on a few weeks back, still the same issue.

At 1900 rpm the main jet is coming into play (I've read) and explains why the air screw mixture jet does nothing, BUT they do nothing on both carbs.
To get to the air mix circuit you need about 1200 rpm, this bike will never go that low (assuming the tacho is reading accurately), so where I am I cant get to the idle position to set the tick over mixture and around I go yet again on this roundabout.

Tomorrow I will check the main jet side, carb to carb again.
I almost feel like fitting just one cab on the bike and run the engine on 1/2 capacity and gwetting it right.
Do the same if I can on the other carb and then fit the engine with both and see.

Getting to be a silly situation this.
Thank you for reading it all and helping, I think at times I'm talking to myself.
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Cortina
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Re: 1972 Honda CB175 Super Sport restoration

Post by Cortina »

Something is not right when you can't get the revs down. Think it through - (I'm talking to myself now) . What causes revs ? , answer - fuel and air. --- so ? Why is the engine getting too much of one , or other , or both ........ answer that question , and get the revs down , then other bits of the system may start to "work properly" ..... and you'll take a big leap forwards.
In my head , you should be able to get the revs so low , that the engine will actually stall ................. so why can't you do that. Where are the throttle slides when they are fully closed ? What do they rest against ? - a screw , a spud , ?? ... are they where they should be ? If open - there is your excess air , which in turn will draw excess fuel .... etc etc
over to you (it SHOULD be easy !! ??)
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Re: 1972 Honda CB175 Super Sport restoration

Post by Cortina »

PS - are slides handed ? If so (and I suspect they MAY be??) , are they in the correct carbs ? Look very closely - I am guessing there is a groove in them (vertical) which means they can't go in wrong way round ..... but check the other

AC
Royal Enfield .. still in India
GL 1800 Tour DCT, for pleasure / Fantic 240 Professional - play
Rally 911 (1966) build parked for a while
Rally 928 (work started again - inc serious weight loss programe !)
.... and now another VW Up GTI owner.
911hillclimber
Nurse, I think I need some assistance
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Joined: Mon Mar 10, 2008 6:26 pm
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Re: 1972 Honda CB175 Super Sport restoration

Post by 911hillclimber »

Good clarity, thanks.Starts to get that you can't see the tree for the wood.
Will check the slide height tomorrow.

The slides are handed as the carbs are.
There is a crescent shaped cut out at their base that must face the filter, they can be placed wrong way round, but they are correct, that I do know.
There is 1mm of play in the throttle cable outer to the top of the carb.

Should add that the engine will not hold a tick over below about 1900rpm, it will stall any lower.
These engines are known to reliably run at 1200, maybe 1000rpm.
My only measurement of engine speed is the tachometer.
Also, above 1400 rpm the carb moves to main jet circuit.
The sooty side I think is drawing main jet mixture at near tick over speed.
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Re: 1972 Honda CB175 Super Sport restoration

Post by Cortina »

I think they are "capable" of ticking over at 950rpm.
Should not need rev counter to "tell you" tick over is too high or too low - it should sound "right" ?
Find another way to measure rpm , if you are unsure a) modern electronic tacho (you may need to put a factor on the figure due to no of cylinders !!) , b) some strobs have the facitity , c) osilcascope (spelling ??) , d) mechanically driven meter (rubber cone drive jobbie) ... spring to mind !
Main jet circuit should be out of the equation ............ ??

have fun
Royal Enfield .. still in India
GL 1800 Tour DCT, for pleasure / Fantic 240 Professional - play
Rally 911 (1966) build parked for a while
Rally 928 (work started again - inc serious weight loss programe !)
.... and now another VW Up GTI owner.
911hillclimber
Nurse, I think I need some assistance
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Re: 1972 Honda CB175 Super Sport restoration

Post by 911hillclimber »

Yes, 1000 rpm on a parallel twin would feel very slow and at the indicated 1800 that feels a tad fast, but not by much.
The air mix jet does nothing at this speed, you can close it tight or open it 3 turns, engine speed just sits still.
Fun?
Yes, when I've cracked it!! :)
73T 911 Coupe, road/hillclimber 3.2L
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Cortina
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Re: 1972 Honda CB175 Super Sport restoration

Post by Cortina »

https://www.ebay.co.uk/itm/Rev-counter- ... SwQ3Ffw91X

this was the only one I could find at quick glance - lovely "tools" to have !
Royal Enfield .. still in India
GL 1800 Tour DCT, for pleasure / Fantic 240 Professional - play
Rally 911 (1966) build parked for a while
Rally 928 (work started again - inc serious weight loss programe !)
.... and now another VW Up GTI owner.
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Re: 1972 Honda CB175 Super Sport restoration

Post by coomo »

911hillclimber wrote:Yes, 1000 rpm on a parallel twin would feel very slow and at the indicated 1800 that feels a tad fast, but not by much.
The air mix jet does nothing at this speed, you can close it tight or open it 3 turns, engine speed just sits still.
Fun?
Yes, when I've cracked it!! :)
1000 rpm is right for my Commando, a parallel twin.Im not au fait with Jap bikes really.However I cant see why tickover should be much higher.
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KS
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Re: 1972 Honda CB175 Super Sport restoration

Post by KS »

OK, so you've checked the timing very accurately when static - what advances the ignition when the engine is running? Bob weights? Advancing the ignition will cause the engine revs to increase. On a VW mechanical advance distributor if you remove the springs that control the bob weights, you can still statically set the ignition but the moment you start the engine, the ignition will advance, causing the engine to increase in speed. No amount of adjusting the carb(s) will have any effect. Is there any way you can monitor the rate of ignition advance? Just a thought...
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911hillclimber
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Re: 1972 Honda CB175 Super Sport restoration

Post by 911hillclimber »

Yes, all done by classic bob weights, checked and freed-off etc when I did the engine, but at this stage, anything is worth a check!

These simple Jap carbs have 2 stages, idle to 1400 and then transition to the main jet/slide needle. The main jet and emusion tube have a lot of progression drillings and all are clear and stock sizes, both carbs checked and are the same.
I have a set of fine drills from 1.5mm dia down to 0.3 dia I use as size comparators, so know all are the same.

So, with these carbs on, the RH one runs well and the LH is very rich.

Could be the LH rich one is drawing fuel from the main jet but at 1800 rpm, above the idle circuit, the RH carb is still just in the idle circuit at the same rpm.

On either, the air fule needle that sets the mixture at tick-over to main jet rpm has no effect on either.

The tuning method is, warm the engine up.
Get both carbs to about 2000 rpm such that moving either has an effect on engine speed, call synchronising the carbs. The ait ration needles at 1.25 turns out from tight, factory setting.

Drop the engine rpm to low as possible, ie below 1400 to bring the idle into play.
Screw the ait ration needle in/out to raise the rpm to a max.
Wind the slide screw out to bring the rpm down to below 1400.
Repeat on the other carb.
Bring the engine down evenly using the slide screws to about 1000 or there abouts and the engine is in tune low down.

I cant get to sub 1400 without the engine stopping like it has been switch off.
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911hillclimber
Nurse, I think I need some assistance
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Re: 1972 Honda CB175 Super Sport restoration

Post by 911hillclimber »

After some discussion on the excellent USA site, Vintage Honda Twins, KS may well have the problem highlighted!

The mech advance weight are free to move about 10 degs from fully retracted before the 2 small springs come into tension.
If the advance so allowed stays there then tickover may well be never achieved.

I think the bike's advance assy is very very tired, another piece of gold dust to find...

might lock the weights to the fully retracted position for now and see if this makes things better.
73T 911 Coupe, road/hillclimber 3.2L
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KS
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Re: 1972 Honda CB175 Super Sport restoration

Post by KS »

I (may) have my uses... Fingers crossed that it turns out to be something as simple as this!
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911hillclimber
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Re: 1972 Honda CB175 Super Sport restoration

Post by 911hillclimber »

Well....

Locked the one bob weight to secure the advance. Did all the timing again etc and ran the engine. Not much different, engine will not hold less than 1500 rpm, which is the lowest I've seen ever on this engine.

Had the usual hot one side, cool the other, smoke on one side then the other etc.

On the LHS that went 'out' had a good spark, so assumed no compression, (ie tappets too tight holding a valve open when hot). Did a compression test which was not that good, 100 psi with throttle wide open, hot and cranked for 5 secs. Other side was 120psi. Just about in the green sector.

So, why was the LHS not working. Found out.
Embarrassingly, the fuel container I am using instead of the tank had slipped down the pole it is mounted on and the petcock was below the LHS carb's inlet, so the bowl was empty....
Now you have all stopped laughing.

That fixed, ran the engine again and had even exhaust temperatures BUT the RHS exhaust smoke has an even 'pulse' in it, the LHS does not, it is the RHS that had a chuffing tone to it, so I suspect the tappet(s) are too tight and a valve is held open.
2 thou is a very tight clearance cold, so might go to 3 for now to see if things change.

Not sure if I've stepped Advanced, Stayed Static, or Retarded today for all my hours of toil.

Anyway, one thing to rejoice, the UK has an approved vaccine for Covid, Father Xmas has indeed come early.
73T 911 Coupe, road/hillclimber 3.2L
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911hillclimber
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Re: 1972 Honda CB175 Super Sport restoration

Post by 911hillclimber »

Still at it, and reaching for a rope to hang myself.

Thing still won't run correctly.
Decided to go right back on the engine.
The second hand mech advance unit came and is much tighter than the original one, the 2 bob weights are tight to the centre shaft. Good going.
Pondered if all this cr"p is due to the OHcam being timed wrong, so removed the cam cover, set TDC and the faint mark should be at 12.00 noon at TDC. It is. Good going.
Put it all back together, torqued the head etc etc etc, did all the timing checked all the tappets, and started it.

Horrid, started on both cylinders, and after a few mins dropped onto one. Messed about, but really did not want to run. The full choke nearly strangles the engine to death in a few seconds so a fast re-set to 1/2 choke and it just about kept going.

Whilst it was running and looking down the RHside carb the bloody thing spat back with a short flame in the carb and I decided to switch off.

Battery now almost flat, so, swore copiously at it in fluent Brummie, attached the charger, and pushed it into it's dark corner.

I really do not know what to do now except put the copy carbs on and try them.

What a depressing position.
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Re: 1972 Honda CB175 Super Sport restoration

Post by Nine One One »

Condenser??????????/
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