1974 ct70 carb troubleshooting

N

nanaimogreg

Member
Im new to this forum and to fixing bikes. I am fixing up a 74 ct70 for my son that was given to us by my father in law. It has sat for many years inside his shop without being run. So far I have changed the oil, restored the fuel tank, replaced wheel bearings, brakes, exhaust, rear tire tube, air filter, fuel lines, two new fuel filters, cleaned oil spinner, spark plug, battery, cleaned and Lubed throttle cable. I also adjusted valve clearance. There seems to be good strong spark.

I'm having trouble with the carb. I've taken it apart and cleaned it thoroughly. Installed a $30 rebuild kit from chp motor sports which seemed to have pretty much everything in there. Also new gaskets and heat stop were installed.

While rebuilding the carb, I had the peacock apart to replace the rubber metering device and I'm not 100% confident that I reinstalled it right.

Here is my problem:

i am getting fuel to the bowl of the carb but not into the cylinder therefore no start.

1. can someone give me an idea what could be causing this and how to troubleshoot the cause.
2. also could someone post a picture of their installed carb showing the petcock installed and what position it is in in the on position.
 
If you've got fuel in the bowl there's no problem with the petcock. Assuming the pilot and main jet passages are clear - adjust the screws. Idle screw is centered with the throttle valve - don't worry about that one yet so you can drop the idle to nothing if need be. Make sure the throttle cylinder is installed right - tapered cut away is on the screw side of the carb. Set your mix screw to 1 1/2 turns out and see what you get. Crack the throttle open a touch when you kick it. You may need a little choke too.
 
Took a quick look at the carb slide. As far as I can tell it will only fit in one way with the slot on the slide lined up with the pin on the inside of the carb. Not sure what you mean by tapered side on screw side. The slide is flat on the top near the cap and has two slight tapers on The bottom. There is a shallow slot on one side of the bottom of the slide and a small gap on the other side of the slide.

Does that sound right
 
Yes, sounds like you have it right. If it's turned 180 it will not drop all the way in but you could still get the cap on. It's a common mistake.
 
Assuming that the fuel level inside the bowl is correct, then the problem is that it's not flowing through carburetor's metering circuits. The pilot jet orifice is minuscule, far smaller than the main, and thus doesn't take much to clog. Try an eyedropper worth of gas, down the carb throat or the sparkplug hole, then kick it over. The engine should fire. If you can keep it going with the throttle but it won't idle then the problem is a lean pilot circuit.

First step there is to set the pilot airbleed screw richer...i.e. turning it clockwise. As a diagnostic tool, I like to start with it 1/2 turn out from seated. If that doesn't cause a pig-rich idle, then it's time to pull the pilot jet (along with the airbleed adjusting screw) for an inspection...along with the passage in the carb body.

An inconsistent idle/inconsistent starting usually means there's a vacuum leak at the intake flange(s)

If the engine will start, idle more or less normally (once warm), but won't take throttle normally, then I'd pull the main jet holder - which is also the main fuel circuit emulsion tube. Those tiny little holes need to be clean and frequently aren't. A small wire, such as a bristle from a wire brush, can be used to gently "rod them out". If any of them were clogged, the difference can be like night & day.
 
Still troubleshooting

Thanks for the advice everyone. I took the carb back off and noticed that I had he valve under the float on upside down. Put it back together and kicked it about 50 times and gas was making its way to the cylinder. Bike started and ran. It ran good until I tried adjusting the mixture screw and idle then stalled. Then no amount of kicking would restart it.

Off came the carb again. It smells like its flooding so I'm guessing that the float level is out. Rechecked all the jets for cleanliness and noted the long one with the holes I the bottom was slightly plugged. Cleaned that and now putting it back on. Anyway is there a proper procedure for setting the float level? I have read that it's supposed to be 20mm as measured from the gasket surface to the top of the float when the carb is held upside down.

Also what procedure do you recommend for setting the carb air mixture and idle.

Also which notch should the needle in the slider be set to?
 
Here's a tip for you. Remove the float and shake it. Often times old floats develop pin holes and take on gas. I hope your problem is that simple. Good luck!
 
Reinstalled carb

Put recleaned carb back on and kicked until my leg hurt with no fire. Checked for spark multiethnic times with nice blue spark each time. Gas is getting into cylinder. Can smell it on plug which gets a bit black and can after kicking with wide open throttle smell smoke. I know there is fuel to the cylinder because it lights on fire when a BBQ lighter is placed near the spark plug hole. I have. Feeling that its flooding.

I'll recheck to see if the float has a pinhole in it but I do think it does cause I did a close inspection when I had it out last.

This is weird. The bike did fire up earlier with no backfiring and actually ran good at high idle but did bog a bit when reved up. Anyone know how to post pictures on here? I'd like to show how I installed the float to make sure it looks right.
 
Try a different spark plug. I wish I knew more about the CT70 engine but are you sure it is firing at the correct time? Could it have jumped time?

And what about the valve gap?

What about the compression?

It is hard to chase all of these little things unless a basic, per the shop manual tuneup has been accomplished beforehand.

Rick

Rick
 
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I'm with Rick. If you are getting fuel to the plug but it still wont run, #1 culprit is points in my experience . You might try cleaning them up and set to .16 before starting a complete tune up. Also, just because the plug sparks does not necessarily mean it's good.
 
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Anything obviously wrong with these photos?

IMG_0252.jpgIMG_0254.jpgIMG_0256.jpgIMG_0261.jpgIMG_0262.jpgIMG_0263.jpgIMG_0264.jpgIMG_0265.jpgIMG_0266.jpgIMG_0267.jpgIMG_0270.jpg
 
I don't notice anything wrong but follow the advice in post #9. Also when using the "on" position on the petcock make sure you have plenty of gas in the tank. The shape of the tank makes it deceiving.
 
I would definitely check the floats for a leak. In pic #4, one side of the float is dry, the other has what appears to be a wet spot with black around it. I also noticed the same float has a dent in it. IMO, I would replace the float. The main jet still looks pretty cruddy, even with the new jet.
 
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The only omission in your photo series is the main jet holder itself, can't see the portion with the emulsion holes while it's in-situ. However, before dealing with that, top priority is getting the motor to fire, can't proceed any further otherwise. Considering that, previously, it started easily and idled...along with the fact that it's now flooded...pretty well crosses pilot circuit fuel flow and vacuum leak(s) off the list.

A nice, fat, blue-white spark is unlikely with fouled breaker points. It's easy enough to clean them. A scrap of white paper towel moistened with cleaning solvent will remove any traces of oil. If that was a problem, you'll easily see the traces. A few light passes with 600-grit paper, followed by another swipe with solvent ought to be more than enough to ensure clean contacts. IMO, that's not what's giving you the no-start; time to try a new plug.
 
Changed the points and condensor and checked that I have spark again. The old points looked a little worn and the centre of the condenser was loose in the middle. Still will not start. I was able to jump start it and it ran for about 50 feet before stalling during which time was quite boggy and did not want to rev up. Would not kick start after running either. Also noticed that I had oil coming out from what looked like either the round cam chain cover or head gasket. I guess the seals are old and dried out after siting for 20 years.

When changing the points I noticed that when they were opening that it didnt line up perfectly with either the 'T' or 'F' on the flywheel. Does this mean it could be out of time?

Does this sound like I need to tear the engine apart to see whats going on?IMG_0272.jpgIMG_0273.jpgIMG_0274.jpgIMG_0275.jpgIMG_0276.jpgIMG_0277.jpgIMG_0278.jpgIMG_0279.jpgIMG_0280.jpgIMG_0282.jpg
 
Going by your last set of pix, this bike spent most of its life in climate-controlled storage. Your stator asm. is about as clean & free of rust as they get. I mention this because it improves the odds of finding the upper end (cylinder walls & valves) in decent condition...in which case you could very well have acceptable compression. That's not a guarantee, not even close, but when diagnosing problems from afar every bit helps.

If there was no oil smoke/smell and the motor seems to have decent compression, then carburetion and cam timing are the only logical possibilities left to verify.

It's possible that the cam chain has jumped one tooth, just not the most likely source of your headaches. You should find that easy enough to check. Pull the round cam cover, line-up the "T" mark on the flywheel and even a single tooth misalignment will be easy to see.

At this point, my money is on carburetion. Pull the float bowl, check the floats for leakage, as Bill recommended; then pull the main jet holder and carefully clean every hole in the emulsion tube. while it's out, check the passage into which it fits; at the very least, blow it out using solvent, then compressed air. Lastly, reset the pilot airbleed screw to the 1-1/2 turn setting recommended in the shop manual, install a new plug and see what happens. Sounds like your idle fuel mixture is pig-rich and the main is clogged at the emulsion tube, giving you a terminally-lean mixture as soon as you roll-on the throttle and bring the main fuel circuit into play.

As for the oil leakage, probably a combination of rubber seals gone crunchy and possibly excessive blow-by. At this stage of the project, I'd not be ready to split the cases. Even if cam timing has jumped, splitting the cases may be unecessary...if compression is still good. Get it running, once again, before worrying about secondary issues. The rot problem(s) are going to be simple, finding them...not so much. Sequencing your work is sometimes the only way to save yourself wasted time & money.
 
Thanks for all the great information. I think the bike was kept inside most of its life and I dont think the points has ever been changed until now. Not much rust or dust for its age. Even the oil spinner was clean with only a small amount of black sludge on the bottom of the case that wiped off. All case bolts on the right side were easy to crack.

I did clean the emulsion tube with very small wire twist tie, engine cleaner and then carb cleaner. It is not pretty looking but could not find where to source a new one. I will order a new float and see if that helps as well. One question though. I did not take the seat that the needle in the slider sits in out. Would the seat wear and cause issues?

I have to put this project on hold for a few days or so (got to work, spend time with the wife and kids). Hope to get back to it soon maybe later in the week. I'll post more pictures then. I have a feeling that it may have jumped time. Should the points be just opening when it lines up with the t on the flywheel.
 
Got a clymer manual and new float today. When I took the old float back off upon closer inspection I noticed a pinhole in one of the floats which I did not see before (good call Hornetgod). One problem taken care of. I adjusted the float height to 20mm as per the Clymer, However, the manual doesnt indicate if you measure with or without the float bowl gasket in place. Anyone know what is the correct method? My new float gasket is probably 1-2 mm in width so it could make a difference if the float level needs to be exact.

Rechecked and recleaned everything and changed the gas in case it was dirty. I also double checked the valve clearance and point gap, cleaned spark plug. I noticed that the valve clearance was a little tight (maybe 1mm out) but the tapet had some slack in it and depending on whether it was pulled up or pushed down the measurement was different. Should the measurement be taken with the tappet pulled up or pushed down?

Kicked a bunch of times and still wont start. The only noise I got was two separate backfire/pop sounds out of the muffler. I have fuel getting to the cylinder. I tried a few drops of gas right in the cylinder and gave it a few kicks. It didnt even fire.

I have spark, but with nothing to compare it to so I dont know if its good spark. Is it possible that a spark plug wire could short somewhere on the frame/engined and still see spark at the plug? The spark plug wire is really stiff.

Any ideas of what I should be looking at next? Is it worth rigging up a light to check the timing? Do you have to remove the air cleaner to get to the wiring harness?
 
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