Thread: No Top End Power

A little history first. 79 CT70 with a little over 700 street only miles. Bike was stored indoors. The car was one of the least dirty carb I've ever cracked open on an older bike like this. Zero visible varnish or gum but there was a slight clog in the "slow" jet.

No top-end power from day one. Here's what I have done.

Cleaned carb (3 times) and once soaked carb body and parts in cleaning machine that agitates.

Cleaned out and flushed Fuel Tank and replaced fuel filter.

Replaced Spark-Plug with new C7HS

Replaced points and condenser. Set points to 014 and set timing. Was able to nail it dead on the F mark at the exact moment bulb began to dim.

Checked Valve clearance. Both were set at 002.

The bike runs "exactly" as it did after I brought it home and cleaned the carb for the first time. It's pretty obvious that I'v broken open a gem and performed a lot of unnecessary work on it for nothing. I don't have any ideas whatsoever at this point and I will for sure sale this bike or pay some Honda dealer out the a before I change out the coil only to find out that it too is okay.

Anyone?!?!?

First off, check for vacuum leaks at manifold and cylinder head.
Once there are no confirmed leaks, remove the air filter element and take it for a test drive, if nothing improves, remove the top of the carb, detach the throttle cable,remove the retaining clip holding the needle in and remove the needle.CAREFULLY lower the C-clip one or two notches down on the needle, reinstall the assy onto the carb, warm up the bike and see if there is any difference, it sounds like you are running lean on the high end, this will richen up the mixture a bit, if there is an improvement, you will have to increase your main jet size a number or two.

Horn, do not give up. The work you have done was not in vain because you have narrowed down the list of possible causes. It is a process of elimination and verification. Busman had good ideas and Clymer's also suggests ignition coil breakdown ( I bet someone on here would loan you one )....compression test....restricted exhaust....down to silly but often overlooked stuff like dragging brakes or funky chain or wheel bearings with weight on the bike.

bisman,

"First off, check for vacuum leaks at manifold and cylinder head."

This is actually my next plan of attack. Both manifold o-rings look pretty flat. In my first post, I faild to describe the loss of power in a better way. I'ts not just losing power. It's more of a "rapping out" sensation.

"if nothing improves, remove the top of the carb, detach the throttle cable,remove the retaining clip holding the needle in and remove the needle.CAREFULLY lower the C-clip one or two notches down on the needle,"

I've thought about about doing this but have balked because I cant get my mind over the fact that the bike only has 700 miles and carb and needle set look almost new. What do you think? What would be the value of changing this?

"it sounds like you are running lean on the high end, this will richen up the mixture a bit, if there is an improvement, you will have to increase your main jet size a number or two."

If it were on the "lean" side, wouldn't it be "bogging" down more than "rapping" out? I"ve actually thought about this, but once again, the condition of carb and the fact that it apparently ran fine for so many years is making me pause. What do you think? I'm in the exact same altitude and temperture zone that this bike was orriginaly purchased. Does it make sense to change jets?

Thanks a lot!

hoser,

"Clymer's also suggests ignition coil breakdown"

That would be my luck, as these things almost never go bad in terms of how many thousands of bikes are out there.

"compression test....restricted exhaust....down to silly but often overlooked stuff like dragging brakes or funky chain or wheel bearings with weight on the bike."

I've not ruled out compression completely, but only because I have not performed a compression test. I've owned all kinds of bikes from 2 to 4 stroke and the compression certainly feels strong for a 700 mile bike. I have completely ruled out brake,chain and wheel bearing drag.

I'll keep trying.

Thanks!

vwbusman suggested removing the ail filter (good call) but keep in mind that without the filter it will be running leaner, and if your carb is gummed up even a little it's probably already running lean, so that could mask the problem. While you're at it take a close look at the filter, . . . old ones start to disintegrate and will restrict air flow, so make sure that's not where your problem is. Based on what you've said, odds are that it's in the carb somewhere. Carbs tend to be the problem children on bikes that have sat up for a long time.

As a last resort (rather than selling it) it'll be a couple of weekends 'til I'm free, but if you feel like driving to Longview some Saturday (Yeah, I know, . . . it's a pretty good trip) I'd be glad to spend the day going over it with you. I'm sure we could sort it out and if not fix it, at the very least, figure out what it will take to get you going. I've also got the Friday after Thanksgiving off though I have to work the Saturday before. Reply or PM me if you're interested.

-kevin

Miniac,
that's very generous of you to offer your time and if I ever get the time I 'll take you up on that if still necessary.

Replacing the Air-Filter was one of the many first things that I did. As for the carb, it has been cleaned so many times and all the jets are pristine. Carb looks like new. If it is the carb, my only option would be to replace it with a new one.

Here's what I have today.

Removed (new) spark plug and it did indeed show signs of lean running. Very dry with excessive carbon considering age of plug. I then removed the needle assembly and noticed that it looked like the c-clip was at the highest position of needle. I decided to disassemble and change the setting. "Not so fast sucker!" My poorly designed 1979 needle has only "one" slot. I really am tempted to go out and buy a new carb but I'm sure it would just go ahead and be something else anyway. I don't know.


Thanks for the support!

Is the baffle in the muffler if so take it out and try a larger main, I put a free flow air filter and took the baffle out went up to a 65 main ,and It will go over forty (Not much over) I'm runing a 14-38 gears now so it slowed it down some but it pulls better.

Originally Posted by CT70Longhorn

. . . . My poorly designed 1979 needle has only "one" slot. . . .

Aaaahhhh, listen grasshopper and mastah po will teach you new and wondrous things. The trick with your one slot needle is this - take your needle down to your favorite hardware store and buy 2 or 3 little teeny flat washers that will just slide onto the needle down (up?) to the clip. Each washer you install will raise the needle by it's thickness, which will richen things up. Cool trick, huh?

Now, snatch the pebble from my hand, . . .

-kevin

That was funny (Awesome Ideal)