No low end power

Hi,

I bought my '82 CSR last year and the carbs were in pieces. This was a totally stock bike with the exception of a sissy bar, as far as I could tell. It has 20K miles on it. I’m going into some of the history, just in case it helps in diagnosing the problem. Also keep in mind I’m not a mechanic (in other words, don’t forget to point out the apparent obvious).

The previous owner was trying to fix a problem where gas was leaking out of the carbs he said. Once I started looking at them, the problem was obvious. Apparently he had done some type of tank liner and pieces of it were blocking the fuel inlet valve. I cleaned and rebuild the carbs and put on an inline filter. I also put in a new set of stock coils, wires and plugs. I ran the bike that way for a month or so with no problems. At one point, during a hard acceleration, it developed a bad exhaust leak. I found that cross-over pipe had been replaced with some flex tube that was too bid and sealed with what looked like furnace grout. A large piece of this grout had blown out. Since it was the end of the season, I pulled the pipes, cleaned and painted them, bought a new crossover, gaskets and clamps and eventually put everything back together. I also chemically and mechanically cleaned all the crap out of the tank, put on a new fuel filter and adjusted the float level using the external tube method. I also checked the valve clearances. Two of the exhaust clearances were close, but still in spec. I also cleaned, checked and lubed the mechanical advance. I haven’t done a compression test yet, but it is on the list.

Ever since then, I don’t have any low end power. It tends surge, wallow and run rough until about 2.5-3K rpms at which point it takes off and runs great. Just reving without a load seems fine. I’ve disassembled the carbs several times and blew everything out, re-adjusted the float levels lower and then back. Constantly tweaking the mixture screws, etc. The pilots are 37.5 and the mains are 122.

There are a few questions I have. The manual shows in a diagram that the fuel level should be X amount below the shoulder where the bowl screw seats, which is about 3/16 or so below the top of the bowl. The text of the manual says in two different places that it should be measured from the top of the bowl. From the top of the bowl is what I’ve been using. Is that correct?

The next item is the fuel mixture screws. From what I’ve read, if you close one of the screws, you should hear or see a difference in the idle. I’ve used an external tach and do not see any real difference. Even when I close or open two of these at the same time. Changes to these do seem to make a little difference when riding, but I haven’t found any setting that even seems close to right.

This weekend, I synced the carbs with a manometer I borrowed. At idle it was next to impossible to adjust, but at 3K, it was easy. I don’t know if this is an acceptable method or not, but the engine does seem to be slightly smoother now, but still no low end to speak of.

Sorry for such a long post, but I figured maybe something in it might give some clues.

Wes

have you checked the advancer to make sure it is not froze up, and also check the timing

The pilot circuit must be cleaned... includes internal passageways and pilot jets. In fact, I would replace the pilot jets as it is difficult to clean them without doing damage. Set the mixture screws out 1.5 turns from lightly seated. When you sync the carbs, you sync 1 to 2 and the 3 to 4 and then 1 and 2 to 3 and 4 using the center adjuster. The BS carbs are fairly sensitive to fuel level in the bowl. With the carbs LEVEL, put a 1/4" ID hose on the drain nipple, open the drain screw and make sure the bowls are full of gas by turning the petcock to PRI. Gas will fill the hose which should be held steady next to the bowl. Blow or tap out any air bubbles. The gas should settle 1/8" below the gasket mating line. If it is higher or lower, the bike will not run right so adjust by turning off the gas, draining the bowl and bending the tang on the float up to lessen the amount of gas in the bowl or down to increase, as necessary. The tang is the part that contacts the float needle; don't bend the float itself. A small bend will make a fairly significant amount of difference so be patient to get the service fuel level right. Don't use the "float level" adjustment method as someone has surely already ruined the orientation of the floats in the past by bending the floats themselves.

Oh yeah... do check the advance and ignition timing as well, as suggested. The timing shouldn't be adjustable on your bike BUT if it is off significantly, it WILL produce idle problems exactly as you described. If the advance is frozen, this is the same issue.

Post edited by: wiredgeorge, at: 2007/08/06 11:21

Yes. This was one of the items I listed as done. I checked the timing at the time, but I have not checked the timing recently. I did re-verify that the advancer was not froze up, but because the timing can't be changed anyway, I didn't check it with a light.

Ok, thanks guys. I'm betting on the pilot jet or pilot circuit. I will go through each of these items and let you know how it goes.

Wes

I just wanted to update you on this problem. As it turned out, it was a stupid mistake that I wish I could say was someone else's, but it was mine.

I followed all the recommended procedures; separated the carbs which I hadn't done before, cleaned everything, blew out everything, replaced the idle jets, verified the bowl levels, the timing, the advance and synced the carbs. None of which seemed to help.

While I was syncing the carbs, I noticed that the air tube from the emission control valve to the air box was hot and thought, that's strange. Of course by now you guys have probably guessed what was wrong.

I had put the reed valves in upside down when I had the top end pulled apart to correct an oil leak and check the valve clearences.

Now everything is great! The bike runs better than it ever has!

Thanks much for the help,

Wes