1971 CB175: PROJECT FELIX

[diesel450]

hey as far as your timing stuff goes don't worry about the oil spilling out with the cover off. Just ignore it, there is still enough oil in the case. Just remember to top it off when you are done. if you use a timing light just follow the combined instructions from the bike manual and the lights manual. Its funny, I don't know much but I have dealt with these same issues on my CL450.

 

[magnang]

So last night I ran into the same problems as the weekend. I don't think it's a vacuum leak because I tested it at warm up and nothing happened when the boots were sprayed with starting fluid. Both of them were running and idling fine.

Steps to repeat problem:
1. Start bike
2. Idles fine around 1,200 rpm
3. Once warmed up (3-4 minutes), revs down, has problems idling
4. Once taken on the road, it pulls through all the gears
5. After about a mile, the backfiring starts
6. Then misfiring
7. Then only runs on both cylinders every 3 seconds with a 'pop' from the second, then back to one
8. Once at a stop, the idle creeps itself to 6,000 then down to 1,200, then back up, then down, etc. without throttle play
9. Plug reading shows the right cylinder good/little lean, and the left cylinder tan/white (lean)

What I've done:
- Rebuilt both carbs (no floats) and throttle needles
- Filed/cleaned points
- Cleaned tank and petcock 3 times
- Cleaned carbs 10,498,109 times
- Greased and rerouted throttle cable

What I need to do:
- Check timing (how do I do this with a light?)
- Set static timing (how do i do this when oil spills out of the left crankcase when the cover is removed?)
- Set points gap
- Check voltage from battery (new) and at coils
- Charge battery (it died after leaving the ignition on. Oops. I charged it for about an hour just enough to crank the starter.)

It could be the close to dead battery not providing enough voltage at high RPM, but once the bike is running, shouldn't there be enough power from the generator to supply a continuous circuit, enough for spark? I'm not even running a running headlight or brakelight during the day, with no turn signals.

I'm going to replace the floats and set the float height next, then check the timing (i don't know how to do this :-\) and if that doesn't fix it I'm REALLY throwing in the towel. ARGHHHHHHHHH

Timing on a CB175 is easy, even without a light.

Open up the points and clean them with contact cleaner. Open and close them manually and make sure they close evenly to make a good contact. Set the gap (I believe it's .012 - .016)

To set the timing, remove the alternator cover on the left side of the engine. Take off one sparkplug, plug it in the wire and ground the base of the sparkplug against the engine. Turn the engine over manually with a 14mm wrench and watch the spark go. It should fire when the F mark lines up to the line. Loosen the two screws on the outside of the points backing plate, and rotate the points assembly to advance / retard timing untill it lines up with F perfectly.

The backfiring to me sounds like you are running rich. Could be your float height on that one cylinder is off and there is too much gas in the bowl. When it's cold, the fuel doesn't atomize properly, which is why you need more of it. You should also set the air screw only when the engine is at operating temp, so it runs well once warmed up. This means it will be lean when cold. Sounds to me like you set up the carbs when cold so the mixture is good when the fuel isn't atomizing propely, but once it warms up there is too much fuel.

How is your compression? One cyclinder could be leaking.

 

[rafanomenon]

Whew what a long day of diagnostics and wrenching in the garage. I'm a little hesitant to say I fixed it, but I'll take the instant gratification - whether temporary or not.

I fixed it.

Things I did:
- Filed points
- Set gap to .014
- Checked and adjusted float height
- New plugs

Going back to the previous symptoms, one of the plugs was reading a bit rich. I can now blame one of the float tangs being bent off spec - about 4mm-5mm off from where it should be. The spec says to adjust the bottom of the float to the gasket surface, but this was WAY too high. As soon as I put the carbs back on and turned the petcock on, fuel started pouring out of every crevice that the carb bodies had. Turned it off, took the carbs back off, and reassessed my float heights. I used the stock spec (19.5mm = ~.75") and measured using a micrometer to the outer carb body lip, as opposed to the gasket this time around. This seemed to work. Who knows - it could also be off a little do to the new float needles in the carb rebuild kit. Whatever it is, it's now working for me. No leaking fuel, and they seem 'balanced'.

I then changed the spark plugs, and cleaned and set the points gap. I also blame a fouled plug for the inconsistent firing, which could be the result of one of cylinders running too rich.

I didn't check the timing, but this is something that I still want to do before the final road-ready checklist, along with checking volts at the coil, condenser (if possible?), rejetting and tuning and finally - carb synchronizing.

Whew. Thanks for the help guys. Here's a sound bite I took from today. Idle still sounds a little off, and that will be fixed once I get the main jets in, and move the needles up one clip. Fingers crossed...

http://www.youtube.com/watch?v=7E0whnHQKM4&feature=player_embedded

 

[rafanomenon]

Oh, and I put the new bellypan on. This is originally made for the Ducati singles, so I had to make some tweaks to get it to fit on my 175. I want to keep the sidestand, and I didn't chop off the stock footpeg mount on the right side. :-\

The green zip ties are only temporary. That's all I had laying around...

I really want to paint the pan gray, but there will be an ugly black 'gap' because of the side stand and footpeg mount on the opposite side. I could do a two-tone? Black on top, pinstripe black line, then gray on the bottom? I'm undecided...

 

[diesel450]

Sounds like a chainsaw!! Looks great! Nice perseverence!

 

[monteboy84]

Cool! I love that little bike, the stance, exhaust, it all works great together. Nicely done!

-matt

 

[diesel450]

Bike looks great and I like the two tone belly pan idea. You realize of course that with all this nice work that old chain is sticking out like a sore thumb. :

 

[rafanomenon]

Bike looks great and I like the two tone belly pan idea. You realize of course that with all this nice work that old chain is sticking out like a sore thumb. :

touche'! that'll come eventually...

in other news, i stripped a spark plug hole, so i swapped the top end with a spare motor i had lying around. bummer. then i forgot to align the cam sprocket with the T-mark on the crankshaft, so i had to fix again. luckily, there was enough clearance to get the top cover off and redo the chain adjustments without having to remove the motor again.

previous problems i've had with these carbs are them running too rich. i swapped the stock jets in (#98) and now it shows lean. The aftermarket carb rebuild kit came with #90's. Obviously WAYYYYYY off. I'll be moving up to #100 mains, then test ride, plug reading, repeating - if necessary. the joys of rejetting...

Would anyone recommend moving up the idle jets? or should I keep them stock and adjust the idle/low throttle with the air/fuel screws and the needle clips? eeesh.. so many ways to adjust one thing : The way the bike runs now is that it's kind of boggy/poor acceleration from 1,000-3,000RPM... has great mid-range, and lags at wide open throttle not wanting to go any higher than 7,000rpm. i assume the latter will be fixed with the #100 mains.

glad to finally have this one running, more or less.

... and i'm looking for a new light and chain as we speak

 

[diesel450]

I'm learning a lot from this as far as jetting is concerned. I've got similar problems with my 450. Lags a bit to 3k then goes like stink! Let us know what jetting resolves it.

on another note I blew a rear tire at 40mph couple weeks back. That'll put a spot on the seat let me tell you. kept it upright though. Brand new tire is okay the tube or stem went. lesson learned? ALways use new tubes with new tires.

 

[rafanomenon]

Alright, I must've messed with the carbs enough to where I could be called a CB175 carb specialist... But this one's got me stumped.

Yesterday, I had stock idle jets, #105 main jets, center needle clips and both float heights set to 21mm. Ran fine, up until about 6,000-7,000 RPM then it sounded like it was starving for gas. It did this at #102 mains, and #100 mains.

Today, I swapped in #110 mains and it ran WAY too rich. I moved the needles down to slightly restrict the amount of gas towards the high power band, but still - sputtering at 6,000-7,000. I even tried moving the needles UP when i had #100 and #102s, and still the same thing happens.

Anybody have an idea of what else it could be? Timing? Bad coil? Ignition points? I've set the static timing, filed and set the points gap. Battery is new showing 13+ volts. I guess i could also post on the F-160 forums?!

With the exception of these forthecoming carb tweaks, I'm comfortable in saying this one is FINISHED

 

[1974 cb200]

Buy you some Mikuni VM-20's and all of your problems will be solved!!! Have them on my 200 with a 115 main, 3rd groove on clip and a 17.5 pilot! Much bigger opening so the bigger main gets more air as well. HUUUUUUUUUUUGE improvement especially midrange!
NATE

 

[magnang]

You are still too rich... As reference, jet #100 came stock on CB360s that have almost twice the displacement / HP than the 175... 105 and 110 are definitely too much gas. Sputtering means you are rich. Try to put the choke on a bit while you are driving, I'd bet it will give you the same thing.

100 is probably as big as you'll ever need to go. Depending on altitude, the range you are looking at is #95 to #100. Points and timing make all the difference too. Make sure you have a full 12v at the coil as well, you could be losing current somewhere in another circuit... I had the exact same thing when my starter relay stuck, it was robbing juice from everything else. Another thing to check is that your timing advancer is working. Sometimes it will seize up due to rust ect and cause bad high RPM performance. It's worth taking the points plate off, cleaning the mechanism, lubing it and setting the ignition timing again.

On mine w/ #100s, shorty exhausts and the snorkel removed around the stock air filter, I have no issues getting up to 80MPH, and I can rev smoothly to 11000RPM +. I found it runs better with this setup than pods, especially at startup / idle.

Cheers,

Guy

Alright, I must've messed with the carbs enough to where I could be called a CB175 carb specialist... But this one's got me stumped.

Yesterday, I had stock idle jets, #105 main jets, center needle clips and both float heights set to 21mm. Ran fine, up until about 6,000-7,000 RPM then it sounded like it was starving for gas. It did this at #102 mains, and #100 mains.

Today, I swapped in #110 mains and it ran WAY too rich. I moved the needles down to slightly restrict the amount of gas towards the high power band, but still - sputtering at 6,000-7,000. I even tried moving the needles UP when i had #100 and #102s, and still the same thing happens.

Anybody have an idea of what else it could be? Timing? Bad coil? Ignition points? I've set the static timing, filed and set the points gap. Battery is new showing 13+ volts. I guess i could also post on the F-160 forums?!

With the exception of these forthecoming carb tweaks, I'm comfortable in saying this one is FINISHED

 

[rafanomenon]

Buy you some Mikuni VM-20's and all of your problems will be solved!!! Have them on my 200 with a 115 main, 3rd groove on clip and a 17.5 pilot! Much bigger opening so the bigger main gets more air as well. HUUUUUUUUUUUGE improvement especially midrange!
NATE

I plan on making this upgrade, along with an electronic ignition and new coils in the next couple months... until then, my goal is to get it running right, or close to right, with what i've got now.

i'm almost positive it's got to be something other than the carbs. the cb175 came stock with #98 mains, which showed lean conditions. #102 also showed a bit lean, and #105 was almost perfect. I'd rather run a tad rich than lean. every time i rejetted, the engine stuttered towards the high power band... not a 'too-rich' kind of stutter, but one where it wasn't getting all the power it could. i'll check the timing again, with a light this time, and try to clean up the spark advancer as well. i tested the coils and those are fine. we'll see ??? ??? ???

 

[Swagger]

You may want to (if you haven't already) check your petcock strainer screen. It may be partially plugged and flow enough for lower RPMs but not once you get cranking along at higher.....

 

[rafanomenon]

You may want to (if you haven't already) check your petcock strainer screen. It may be partially plugged and flow enough for lower RPMs but not once you get cranking along at higher.....

Checked that too.. about 4-times over. Fuel is definitely flowing... I'm going to troubleshoot this week and let you all know what I come up with. It's a damn hoot to ride around town, but with how it's running right now, I'd get eaten up REAL quick on the freeway

 

[magnang]

I plan on making this upgrade, along with an electronic ignition and new coils in the next couple months... until then, my goal is to get it running right, or close to right, with what i've got now.

i'm almost positive it's got to be something other than the carbs. the cb175 came stock with #98 mains, which showed lean conditions. #102 also showed a bit lean, and #105 was almost perfect. I'd rather run a tad rich than lean. every time i rejetted, the engine stuttered towards the high power band... not a 'too-rich' kind of stutter, but one where it wasn't getting all the power it could. i'll check the timing again, with a light this time, and try to clean up the spark advancer as well. i tested the coils and those are fine. we'll see ??? ??? ???

Yes, but you have CL pipes which are considerably more restrictive. I believe the CLs came stock with #95. The bottleneck in your system is the CL downpipe, and they still have the same amount of back-pressure as stock. It's not unreasonable to say with all your mods you may not be flowing any more air than a stock CB175.

 

[rafanomenon]

Yes, but you have CL pipes which are considerably more restrictive. I believe the CLs came stock with #95. The bottleneck in your system is the CL downpipe, and they still have the same amount of back-pressure as stock. It's not unreasonable to say with all your mods you may not be flowing any more air than a stock CB175.

True, but there's a considerable amount of air moving through this system compared to the stock filter boxes and exhaust. I even had to put mini-baffles in the exhaust ends to create some backpressure, but even that didn't help a whole lot.

I did plug readings at both idle and high-band at #98, #100 and #102... all showed fine at idle and lean condition at open throttle. It could also be that the stock CB carbs and their specs just don't work with the CL pipes, but I find that hard to believe with others running similar setups just fine.

 

[miss alliekat]

Just a thought have you tried running it without the filters they do look very restrictive and a bit small. With the filters that have the metal end you get a reflected pulse from the carbs and this can upset the airflow, also the length of the spacer between the carb and the filter will do the same. The ram air foam filters tend to provide more consitant air flow and do not cause a reflected pulse but soak up the pulse hence better carburation and airflow. Just a thought

 

[Curbcast]

Great bike. I like the fat tank with the flared seat. Keep talking CL pipes so I can learn about them. haha.

 

[rafanomenon]

Just a thought have you tried running it without the filters they do look very restrictive and a bit small. With the filters that have the metal end you get a reflected pulse from the carbs and this can upset the airflow, also the length of the spacer between the carb and the filter will do the same. The ram air foam filters tend to provide more consitant air flow and do not cause a reflected pulse but soak up the pulse hence better carburation and airflow. Just a thought

Hmmm I guess I never thought of this. There's also a pipe on the inside where the filter clamps on to, and this could also very well be restricting air flow when the throttle is wide open, not to mention the 29mm pods. Might be time to try it with the filters off.. maybe run velocity stacks? I've also seen a lot of 160/175 racers with CL pipes that run the ram air foam filters. you recommend a good place to buy em?

thanks!