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1971 CL 175 refusing to start or even cough after rebuild!!!

3K views 29 replies 7 participants last post by  Bikenutmart 
#1 ·
Hi, I have just finished a complete rebuild of my 1971 K5 CL 175, it looks beautiful and I am really pleased with the look of it, but am tearing out what hair I have trying to get it running, firstly I consider myself to be a reasonable mechanic, having restored quite a few classic bikes and a couple of old MGs, I have a nicely equipped workshop and work cleanly and methodically(or so I thought!!) the engine was running reasonably well before the stripdown.
The kickstart pinion was u/s this being replaced and now working fine, I also replaced the clutch along with all gaskets and seals. the bores were excellent only needing a light hone, I cleaned up the pistons and reused the rings as they were within spec. I cleaned up the head and lightly lapped the valves in, fitting a couple of new stem seals, all the parts were put back in their original locations. I have double checked the valve clearances set to 3thou with T mark aligned then 360 degrees and other cylinder checked and both correct. I have a lovely fat spark at both plugs which are new Denso X24FS-U. Points gap is 15 thou, and timing correct on both cylinders, points breaking at F mark on both cylinders. I haven't got a compression tester but putting thumb over plug hole and cranking there is a fair bit of pressure which seems fairly equal. Also with the air filters off there is a fair suck on the carbs when cranking. The only thing I will say is that there doesn't seem to be a great deal of fuel on the plugs after cranking with the throttle open, I did rebuild the carbs with rebuild kits from Vietnam I think, I did this carefully, are these kits deemed ok? I did keep all the old parts from the carbs. Cant think what else to say really, except that after 2 afternoons in the garage I had to walk away and have a beer (or two) !! Please any suggestions really appreciated. Ride Safe Mart.
 
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#2 ·
Well, walking away for a beer or two isn't a bad thing, especially if it keep the hammer away from the bike. The first thing I always think of is the breaker cam on the advancer - if it somehow came off, it might be 180° out. I haven't worked on a 360° crankshaft ignition is a very long time so I'm not sure you could get the timing correct with the breaker cam lobe 180° off, but it would be worth checking
 
#3 ·
Hi Ancientdad, Many thanks for the reply, I did remove the advance retard mechanisim, but im sure its back on correctly, I will check tomorrow,i am thinking now about valve timing, I made sure that the O mark was at 12 oclock on the cam sprocket and the T mark was in line with the pointer, someone said about the pin being at 12 oclock also, which pin is this? could this be a carb problem? im dying to get on the road with this bike, hopefully with help from you guys I will!! Keep the ideas coming Mart.
 
#4 ·
It's not the points breaker cam, there's a wasted spark system on the 175.

I'm betting it's the float valves in the carbs. Check that there is actually any / enough fuel in the float chambers.

Also, try squirting some Easystart down the intakes whilst cranking the engine, if it fires and runs carbs are the problem.
 
#7 ·
Correct, you can swap plug wires side to side........
Some bikes must be "choked" for initial start-up.....
Are the mixture screws 1 1/4 turns out?.....
Slides in the correct carbs?......
 
#8 ·
From your background with motors and such, you already have a grasp on the whole “internal combustion” motor, so im sure it’s only a matter of you locating that “gremlin”...
Are you getting any kind of fuel ignition???
 
#9 ·
Right, both float bowls were full of fuel,mixture screws 1 and 1/4 out from fully closed,slides in correct carbs, and no im getting no fuel ignition whatsoever, even with easy start!!, checked the valve timing again and its spot on, T mark aligned, pin on cam at 12 oclock, valves on 1 cylinder rocking and set to 3 thou, turned crank one turn pin now at 6 oclock and valves rocking on the other cylinder and set to 3 thou. I m taking the carbs off tomorrow to put back the original jets, that I had changed for the Vietnam pattern set. if that doesn't sort it i think the top will have to come off for further investigation (Gutted) what do you guys think. Anyone want a lovely looking CL 175 for decoration only !!!! Mart.
 
#10 ·
If u are getting “spark” at the correct time (piston position)..AND you are introducing a fuel (spray or other) and NOT getting any “ignition”..,
I would say check ur valve timing and adjustment..,I think u may be lacking compression .
I have had old triumph 650s on my workbench running with no carbs and only a can of starter fluid..
 
#12 ·
Yes its new fresh fuel and I have checked the valve timing and adjustment, both spot on!! I have been lent a compression tester but none of the adapters fit the 175, I am thinking that way now unfortunately, I really cant think what I have done wrong, its not much of a test but it is quite easy to operate the kickstart with my hand,( plugs in of course). will try some oil in the bores tomorrow and see if that helps, although bores and rings/pistons were in good shape, im thinking more cylinder head, wish I had done a leak test on the valves before assembly, more haste less speed I think!! Any more ideas before I pull the top off? Mart (Depressed!!!)
 
#13 ·
Quick and dirty compression test: remove plugs and SEAL the hole (but lightly) with fingertip.......IF it does not "pop" your finger off when cranked you have bad compression......
 
#14 ·
66 sprint I tried the dirty test and it did pop but didn't push my finger off, so started a top end strip, now am I being thick, but I don't see any way the head will come off with the engine in the frame, it just wont clear the studs, do I have to remove the 8 studs? any advice appreciated. Think I will go to the pub for a lunchtime pint!! Mart.
 
#16 ·
That's a shame!! the Haynes book of lies!! says you can remove head and barrels in situ, hence why I call it the book of lies!! Should have had 2 pints at my local THE RED LION, exactly 3 mins walk from my house!! Will report back when head and barrels are off. Mart.
 
#19 ·
If the ignition timing and valve timing are correct, there's no point in taking the top end off. I would try spraying a small amount of fuel in each carb throat (or spark plug hole) to rule out a fuel delivery issue. "there doesn't seem to be a great deal of fuel on the plugs after cranking with the throttle open", in order to create enough vacuum to pull fuel through the jets the throttle slides need to be almost closed, idle position or just barely open. Are the idle speed stops adjusted so the slides are just barely off the bottom? Are the choke slides properly adjusted to close at the same time? Are the little air relief flapper plates still in place on the choke slides?
 
#20 ·
Thanks for the advice mike, but it seems I have bad compression, I tried the ancient dad method and the pressure was very low, even spraying starter fluid into the intake manifold it still didn't even try to fire, started the top end strip as I suspect valve problems, will post when its apart. Mart.
 
#21 ·
Top end now off, the bores arnt bad, but have a bit of black staining and a small sharp ridge at the top, I had completely forgot but I have a new +20 thou or 50mm piston kit so im getting a rebore, the head looked ok I removed the rockers and cam, and turned it upside down and filled each chamber with petrol, the right hand one emptied in less than 5 minutes!!, out of the exhaust port, the l/h one seems ok but I will check it in the morning. So low compression it was, im having all 4 valve seats recut, can I have the valves refaced? will they need a gentle lap in? would new springs be a good idea? Am I doing ths right as although I have restored cars and rebuilt british bikes this is my first Jap!! Don't be shy, tell me what you think. Mart.
 
#22 ·
I think you should not arbitrarily get the valve seats cut, a decent lapping might be enough. Cutting the seats on these engines can lead to lost clearance in valve adjustment later, and tipping the valves to recover it is risky if you go too far - there isn't much hardened surface to work with on both the tips and the valve faces.
 
#25 ·
ok so the r/h emptied in a couple of minutes and the l/h was half empty this morning, so having the seats cut, the honda manual says its ok to do so, cant feel any play in the guides and all 8 valve springs are within tolerance, so with a rebore I should have compression again!! Mart.
 
#26 ·
I'm surprised that you can't get a decent seal just by lapping the valves in, unless the seats are deeply pitted.

When I did one of my 175 engines, one exhaust seat was pitted to the point that I thought it needed to be recut, I was not able to grind the pit out lapping it in myself. So I took the head over to a bike shop in Stourport, recommended to me 911Hillclimber, who used to frequent this forum.

Shop has all the kit, including AFAIK a Serdi machine, but the workshop chap advised against cutting the seat, and he lapped the valves using some diamond paste. After that, combustion chambers held fuel without leaks. Engine runs well. I can't find a photo of the pitted seat, but here's the head after reassembly, valves sitting well, not pocketed by excessive grinding.

303662


Charged me 50 quid for doing all four seats and reassembling the head. He did say that in an ideal world, new valve guides would be fitted, then the Serdi machine could do its job accurately, along with new valves and a bill for 500 quid or more. In his view, not worth doing on a 50 year old bike that I would be pottering along the back roads on.
 
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