'72 CL175 engine trouble?

[echo]

Hi all, I have a CL175 I am working on and I have a problem with getting it to go fast ;D. I should say I am the mechanic's equivalent of a tenderfoot - not a novice but not highly experienced by any means.

The bike revs up nice in first, 2nd and 3rd gears on the flat straighaways, but after I am shifting up to 4th, going maybe 35-40 mph, the engine just seems to bog down and won't rev higher no matter how much throttle I give it. It just makes a hollow sound and won't give me any more power. In fact I can go faster in 3rd than in 4th. 5th is even worse. And even in low gear the bike can barely drag me up the hills.

I tested the compression and it seems pretty low - Left was 114 psi, Right was 129 psi. After adding a little oil to each cylinder through the spark plug holes, the Left was 126 psi and the right was 150 psi. But I don't see how the low compression would not allow the engine to rev in high gear, I would think it would just reduce the power of each rev.

I have checked valve tappet clearance and made adjustments (no change in compression). I have checked the main jets and they are clean. The carbs look in great shape upon inspection. No obvious leaks. I adjusted the air screw and idle screw per the manual.

What do you guys think is going on? Oh I should mention I am a big guy for this bike (230 lbs) but I would think that's a minor contributing factor.

 

[cxman]

what rpm are you up shifting

have you set the valves points and timing

have you cleaned the carbs and made sure the tank filter/petcock is cleaned out

 

[echo]

CXman thanks for your suggestions. It has an electronic ignition upgrade (from previous owner). Don't know much about those ... are they maintenance free? I did adjust tappets and cam chain tension. I may double check the tappets. I agree, next step is check the petcock. Also I am gonna look at the plugs and will post a photo if I have trouble reading them. Other folks mentioned jet needle height could possibly help. I guess my remaining question is- For folks familiar with this bike, with the compression test results I posted and my rider weight, are those factors the "obvious" culprit? Or should I sniff around at some other things before a full-on top end job? Thank you

 

[teazer]

Those bikes only make about 12hp at the rear wheel despite what they say in the sales brochures. So they don't have a lot of power to begin with and are not well equipped to carry a larger rider.

That said, it should do better than that. CXMan asked already about shift points, because those little motors like to rev to around 9,500 or so. Electronic ignition is typically "fit and forget" but check the timing anyway and fit new plugs and plug caps and snip 1/4" off each plug lead. Compression is a little low and suggests the rings may be leaking a bit.

Check that the baffles are reasonably clean and that the air filter is also clean. You might also check the gearing. What are the front and rear sprockets?

You should also make sure the wheels turn easily and that brakes are not dragging and tires are pumped up. It's also possible that the chain may be old and adding resistance, so you should see how easily it rolls by spinning the wheels or push it up and down the drive. It will be heavier than a pedal bike but should be easy to push. Flat tires also create a lot of rolling resistance.

 

[echo]

Thanks for the advice. I was not expecting to rev that high. I have always had larger bikes before. I'm not expecting to set any speed records on the 175, just hoping to do around 50 mph on the back roads, so if I can just get a bit more out of it...

 

[themotoworks]

clean the carbs, make sure the battery is charged fully, and is relatively new. those bikes are quite sensitive to dirty pilot jets in my experience.

 

[teazer]

They can be and cleaning the carbs is always a good idea if the bike has sat for any significant time. Pilot jets make little difference above 1/4 throttle but they should be cleaned anyway, and timing set and so on.

The think with small, low powered engines is that they need to be ridden fairly hard. At low revs they can't get out of their own way and will just bog under load.

 

[trek97]

Just for baseline information...
My 72 CL100 w me at 175lbs will cruise along at 57mph (top speed) in 5th on a level road all day. It makes 180 on compression test.

 

[cxman]

if the bike has been sitting it could take a bit of running for the compression to come back up

 

[echo]

Here's what the plugs look like. The left is looking nice and brown. That's the cylinder with the lower compression. The right looks a little oil fouled to me.

 

[teazer]

Plugs look close enough for government work. FOcus on the other items such as carbs, timing, exhaust etc and let it rev. I don't remember the red line on that bike but somewhere closer to 9500 would work for shift points.

 

[cxman]

how long has it been sitting?

 

[echo]

I'm not sure how long it was sitting but obviously a 45 year old bike with 5000 miles did an awful lot of sitting . When I drained the oil it was black and smelly. I have heard that bikes which sit too long tend to develop pits in the cylinder at the spot where the rings come to rest. I wonder if it sat on the side stand a long time and maybe that's why the left cylinder has lower compression. All speculation of course.

Is there a good thead out there on checking timing on an electronic ignition? I've been willfully ignorant on that subject to now.

If everything else checks out I'm going to run it hard for a while and see if I can bring the compression up a little.

Ultimately I would like to rebuild the motor anyways if for no other reason than as a "fun project"

Thanks guys

 

[cxman]

dont fix what is not broken

check teh valves in fact set them 2 thou loose in case you have some carbon or crud build up

reset the valves to stock setting after 100 miles

run it for a bit ride it in town so you are changing rpm a lot by shifting

up and done in the rpm is what you want to re seat the rings

2-3 oz of marvel mystery oil in the tank may help as well

dont run it full bore yet

check every 50 if compression is increasing

change oil and check oil screen at 200 miles

 

[echo]

Great I'll give it a try and let you know how it goes.

 

[echo]

Last night I checked timing, valve clearance and the petcock.

Timing was a couple degrees early. I rotated the plate very slightly so the test light comes on just as the F mark lines up with the index mark on the case.

The valve tappets had moved a bit since I set them before. No clearance. Perhaps the valves were not even closing fully. I set them a little loose for now as cxman suggested.

The petcock screen wasn't clogged, but there were some nasties in there that needed to come out. When I put it back together it leaked, so I need to see what the issue is tonight. Maybe a pinched o ring or something.

 

[echo]

Got my bottle of magical marvel mystery oil at Wally Mart tonight.

What do y'all think I should do with it?

a) put it in the gas
b) put it in the oil
c) put a little in the spark plug hole and let it soak in
d) all 3
e) drink some
f) go away ;D

 

[teazer]

Yes...

CXman suggested adding some to the fuel. I prefer to use Seafoam to clean things out. How does it run now? Any better since you set valves and timing?

 

[cxman]

i suggested it in the fuel to clean and crap in teh top end and rings area

 

[echo]

I read on some other forum some guys suggested putting some in the cylinder to soak in. On the bottle it says add to fuel (4oz per 10 gallons) or replace up to 20 percent of your oil with MMO. To me that sounds excessive. I'm just gonna try it in the fuel for now.

It's been cold as hell here in NC, so no chance to ride yet. We have snow on the ground tonight.