Slow/idle jets for CL77 at higher elevation

[RetroBiker]

Hi everyone,

I've been having idling issues with my newly rebuilt engine, so I checked the slow/idle jets and the right hand cylinder (which was not running properly) had a blockage in the slow jet! After some work I cleaned it out, and while the bike runs now it still is not idling great no matter what I do with the air or throttle stop screws. I'm in Denver at over 5,000 feet of elevation, and some info I've found online suggests I try smaller jets (i.e. #38 or #40). Currently I've got #42's for idle jets.

Does anyone have experience with higher elevations and does this suggestion of using smaller jets make sense to you? If so, does anyone have a pair of good OEM idle jets in these sizes I might be able to purchase? Ebay is filled with options, but I'm leery of buying foreign aftermarket parts. I have enough challenges already. :-)

Thanks Guys.

[Tim Allman]

I was just looking at the Honda Common Maintenance Repair Service Manual (section 8) and see that they recommend adjusting the idle screw for high altitude and installing a smaller main jet. Keep in mind that the main jet will have little, if any, effect on the idle so it won't help your problem.

[mike horvath]

Retro-
Late post I know, but adjusting either carb air fuel mixture screw has no effect? Maybe timing is off.

[RetroBiker]

Here's my latest update. I have not gotten my scrambler running properly yet; still chasing carb gremlins I think. I found that I also had some gas feed problems as I noticed no gas in the filters. So I drained and removed the gas tank and rebuilt the petcock (again). I also blew out the gas cap thinking there may be a vapor lock issue, so I believe that will take care of the fuel feed problem. Having said this I had already tried to get the carbs working properly by bypassing the tank/petcock altogether by using an external tank set-up. Still no luck getting the bike running right.

When initially starting the bike it now seems to run/idle well, but as it warms up the RPM's continue to climb to ~3,000-5,000. If I open close the choke quickly, that sometimes calms it down for ~15 seconds, but then it starts to rev back up. Quickly accelerating and releasing the throttle appears to have no positive impact either. So I assume there's something going on with the jets, jet needle or more likely the throttle bodies or the throttle cable. I don't think its a air leak, but not sure yet. I believe something in those darn carbs isn't right as one cylinder seems to idle and run much better than the other. I'm currently using #38 idle jets and have the jet needle clip on the 2nd notch setting. I live in Denver and would be curious what factory specs would be for the size of idle jet and clip placement on my jet needles?

I haven't verified float levels yet, nor have I checked all the ignition possibilities, so these go on my "to-do" list. After removing the tank I noticed that the throttle cable had moved such that the casing where it splits was caught on the mounting bracket for my new coils. This may have caused the throttle cable to flex thereby increasing drag on the cable and slowing the return of the throttle bodies(?). Just guessing at the moment based on what I'm seeing. Not sure how this would translate into higher revs from idle, but I imagine the throttle bodies could vibrate up and not return properly.

It's cold here in Denver now so I probably will be delayed until spring to get back working on the bike as I hate working in a cold garage. :) I know this is a lot of info to absorb, but please keep your suggestions coming as I continue to search for solutions to get this machine running like a top.

Thanks guys and Happy Holidays!

[Michael Stoic]

You mentioned one cylinder running hotter... I would be getting an infrared thermometer into the diagnostics mix to get this documented and logged. Another thing to check is whether the carb mounting nuts are on just right or too tight. The carb bodies deform easily - lot's of threads about it on the forum.

Back to one side hotter - you are getting either too much air in that carb or too little in the other. The vector is either the internal carb circuit (mixture) or an external air leak - in which case we're back to the carb mounting issue. If this is a cable binding issue, that should be easy enough to check/fix and you've eliminated the fuel supply as a potential source. So what's left?

As everyone knows, fuel problems are really ignition, and also the opposite. I'd want to get all the ignition variables beyond reproach, as a baseline, and then work on fuel - one adjustment at a time.

--
Mike Stoic


PS Get both needles on the bench together for a close inspection (clip, taper, length, condition) and then swap left to right to observe whether the cyl performance travels with the needle.