Devil Bike: CL350K2 with limited power - Out of ideas, need help

Hey guys,

I decided to make a new post for my ’70 Honda CL350 K2 Scrambler, as the other thread was months old and over 10 pages long.

After putting in ~6 months of blood, sweat, and tears into this thing, I dropped it off with a mechanic. I haven't been able to get the bike running for more than 1 week at a time since I've owned it. I hoping that the mechanic would be able to fix the bike, but he just called me to say he has no idea of what is going on with it and wants to know if I should pick it up. (Currently they're tearing into the mechanical advance because I shortened the spring by 1 loop on each side)

I'm at my wits end, I love the bike and want to fix it, not sell it for a huge loss (of $$$, but also time and ego). I have to decide whether to pick it up or let the mechanic continue, but he says he's not sure what he should do next. :'(

Symptoms:

Bike idles and revs fine. Has very little power under load and is basically unridable.

Summary of knowledge:

• Has compression (~150psi in both cylinders)
• Carbs have been rebuilt 3 times (twice by me, once by the shop), and rejetted by shop. Carbs have diaphragms from JBM industries.
• There aren’t any air leaks (shop fixed one that was there, says it’s good now)
• All the electrical components are new (battery, condenser, coils, points, plugs) and timed (with strobe)
• Shop says bike has spark
• Rebuilt Advance plate (chopped off 1 coil of the spring because it was stretched)
• Fuel flow isn’t an issue (cleaned the petcock, have fuel filters, new fuel lines), running with cap off does not help

Old Thread: http://www.dotheton.com/forum/index.php?topic=53402.0

Compression - 150psi on both cyl's

Fuel
Carbs rebuilt and rejetted
Fixed Carb Air leak
New JBM Industries diaphragms (didn't glue, should they glue?)
New carb boots
New Fuel Line
Petcock cleaned (no water inside)
Fuel Filters added (don't see any rust collecting)

Electrical
New Points
New Coils - Need to check them with heat method
New Condensor - never tested
New Battery
Rebuilt, cleaned, and shortened springs for Advance Plate
New Spark Plugs
New plug caps

I could use any advice you guys have. I work long hours these days and don't have time to tinker like I did before. Is there more that I should have the shop look into, or should I pull the bike from the shop asap?

Mike

Bike has had a lot of history with no diagnosis, so it would seem it's best to start over from the beginning.

First up, that compression is a bit low. You want at least 165 PSI on a warm engine. 150 PSI is OK if the measurement is taken cold, but double check your value after the bike warms up.

Next check spark with the strobe light again. Check timing for both cylinders at idle and at 4000 RPM.

Once you'd checked those previous two items, the very only issue you could be facing is carb trouble.

Seeing as the compression numbers are a little low, I would start by adjusting the valves and then on to verifying the timing chain is tensioned properly. Any idea of the condition of the timing chain rollers? None of these were mentioned in your previous thread.
See if the compression comes up a bit.

Is anything binding? How are the wheel bearings?

where are you located?

Have you had the cam out / checked the cam timing? Having the cam a tooth out can give you these syptoms.

And the bit about cutting the advance spring has me wondering if the advancer is working properly - double check the ignition timing like Sonreir suggested.

Warm, the bike has compression of 165-170psi. I adjusted the valves this winter, they should still be in spec.

The timing is on at idle, but the bike will not rev to 4k RPM.

The shop just went through both carbs. Replaced both bodies, I used all new brass internals, which were transferred over. They still don't like the thicker JBM diaphragms.

I am located in Chicago.

Nothing is binding as far as I know. Wheels are recently replaced and spin freely.

Cam chain tensioner has not been adjusted by the shop but they say they "don't hear anything to suggest it's loose". No idea about the cam/guides, I have not opened the engine and was hoping that I will not have to. They're currently going to check the advancer.

Suggestions?

The brass you used to replace the internals: Did you use a kit or buy the brass yourself?

Have you had the bike on a wideband sensor yet?

When the jets were put back in the new carb bodies, did they go back in the right locations. I have seen swapped main and slow jets cause this kind of symptom. Also if the advancer is stuck you would have the reving issues, shop is checking that so after that if they still can't figure it out I would take it back home and systematically go over it to make sure everything is right. Is one of the coils hooked up wrong, or is there a buggered ground on the condesor causing weak spark etc. is frame ground ok? is choke hooked up correctly, are your slides smooth and clean and do they move up when you push on them. I had a real bugger of a time with my CX stumbling and not reving and was driving me nuts. I was pulling the carbs to check and clean them again when I hit the slide with my finger and it wouldn;t easily rise, took carb apart and found a small nick in the slide the slide would only open about 1/3 of the way up. I smoothed the nick and the slide went all the way up, the bike wheelied the first time I whacked the throttle.

The brass is pieced together from 2 kits (Sirius and DCC). As far as I know, the main and slow jets are in the right spot, I doubt the shop would have messed that up, this isn't their first CB/CL. The slides are definitely fine, I have lubed them and checked for smoothness (before and after installing new diaphragms)

No on the wideband. I'd install one if my pipes were 2-to-1, but I'm keeping the scrambler pipes. I can't get the bike far enough out of town to a dyno shop that might have a hookup.

I'll let the shop look at the advancer. But I'm thinking that the issue is electrical, because it seems the carbs have been reviewed so extensively.

Strobe lights are cheap and easy to use. No need to take it to a shop for that.

Also... a wideband kit is pretty cheap when compared with shop time. Usually under $200. And even if things were bad on one cylinder, you'd still be able to ride. I had an SL350 with a cylinder out that I rode 60 miles at 50mph.

Has the shop checked the cam timing? Not just the tensioner, the timing.

Sorry for the delay, here's an update:

The spark advancer seems to have improved the issue, but not fixed it.

Current major issue is that the throttle 'hangs' aka the RPM's don't drop when you let off the gas. It's an issue I've had since I've had it, but not one I've considered to be the most problematic. They say that they can't properly time the bike and that they think it is cam-timing related. (Well, that or the JBM diaphragms).

Is there a way to 'test' the cam timing without ripping off the head? The tensioner has not been checked either.

so2002 said:

Sorry for the delay, here's an update:

The spark advancer seems to have improved the issue, but not fixed it.

Current major issue is that the throttle 'hangs' aka the RPM's don't drop when you let off the gas. It's an issue I've had since I've had it, but not one I've considered to be the most problematic. They say that they can't properly time the bike and that they think it is cam-timing related. (Well, that or the JBM diaphragms).

Is there a way to 'test' the cam timing without ripping off the head? The tensioner has not been checked either.

Click to expand...

You only need to remove the valve cover to check the cam timing.

When at TDC the little pin that locates the advancer on the camshaft will either be straight up or down
You have good compression #'s so i am inclined to think the cam timing is not off but yeah for sure check it
As far as the tensioner while you have the advancer off watch the camshaft as you rotate the crank with a wrench, there are spots where the engine wants to lope over because the cam is trying to keep rotating the engine
when you get to a spot where the crank will stay relaxed gently rotate the crank forwards and back a few degrees while watching the cam
What you are looking for is any lag in rotation between the crank and cam
A properly adjusted tensioner will make it so basically there is zero lag
A loose cam chain only leads to somewhat eratic timing, rough running it wont retard timing or anything like that
A worn or stretched timing chain will retard timing a bit, more the worse it is worn

so2002 said:

Current major issue is that the throttle 'hangs' aka the RPM's don't drop when you let off the gas.

Click to expand...

Classic symptom of a carb sync issue.

Sonreir said:

Classic symptom of a carb sync issue.

Click to expand...

Is it possible that the thicker JBM diaphragms are responsible?

Seems pretty likely I'm going to be pulling it from the shop. They don't know what's up, and wouldn't want to open the engine till November. Apparently the loss of power issue is still very real, and I would have to tow it from the shop =(

I have the option of buying a used motor with 150psi compression. I'm thinking this is my play. Thoughts?

150 PSI is below spec on these motors. Fresh engine should be 165 PSI.
Reading will be lower on a cold enough though.

I've had it with MGBs using the Zenith Stromberg carbs (which are very similar in function to the Keihin carbs) that if there isn't a good seal around the diaphragm, or if there is a pinhole anywhere that allows air to move through it, the piston just won't rise because it won't have enough vacuum to suck it to the top. This results in a very laggy, low-power feeling. No matter how hard you stomp on the gas the car will barely accelerate.

I have a sneaking suspicion the diaphragms are at least part of the issue - they may not be seated right and not sealing.