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Discussion Starter · #1 ·
Hi, I have a '69 CL350. Starts and runs great, hot or cold. The ONLY problem is that after running a while and coming to a stop, the idle will sometimes be lower than before, maybe down to 800 from the initial 1100. A blip of throttle brings it up momentarily but otherwise it will just go lower and almost die. Only seems to do this after it is pretty hot. Don't notice it so much on a long night ride for example. I have seen many questions about this problem but never a definite cause. Compression is around 160 both sides. Timing and point gap correct. Valves set accurately to .002 and .004. Carbs clean and rebuilt a few hundred miles ago with stock jetting and new diaphragms. Carbs synced by setting both idle screws just at the stops, then turning each in equally to 1100 RPM. Cables adjusted so both butterflies start opening simultaneously. No vacuum leaks. Advancer working smoothly. Spark plugs read clean and almost white with a nice black ring around the base of the insulator. Bike never needs choke hot or cold, but always starts right away. If I use the choke at all the bike dies. I think that's everything. Like I said, the bike starts and runs perfect, just the hot idle thing has got me stumped. Any ideas I might have missed?
 

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Sensei
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From your discription, some possibilities I can come up with are:
A... White plug color indicates too lean..... It might just be starving at idle... Plugs should be a medium tan color, with no black ring.....(re-clean idle jet, check float level)
B... Weak or borderline battery (fine at revs when the alt is adding to the available electrical supply,) not quite enough at idle....OR, surface charged battery "runs down" by the time you get it to the "hot" state...(check battery fluid levels, charge state)
C... Improper heat range plugs..... Run 8's....
D... Carbs not correctly synched... What are the air/mixture screws set at? Did you adjust them (individually) to the highest idle and then back off the idle screws to achieve the correct idle speed? (1100 is just low enough to cause the "fall-off" on a low comp. engine)
E... How "close" to 160 PSI is the compression?... 155 is minimum spec....170 is normal.

Numerical corrections edited in....
 

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Discussion Starter · #3 ·
Thanks for the reply. Compression was maybe 158 or so left and maybe 163 or so right. Battery is good and kept on a tender. Plugs are 8's. The book gives three different float levels by engine number range. Mine is the later and calls for 26mm which is certainly lower (leaner) than the earlier 19mm. To set the idle mixtures I first set the RPM to about 1100, then turned the left mixture screw in and out for the highest RPM, which was just about 1 turn out, where it started so RPM was still at 1100. Did the same for the right and it also peaked just about 1 turn out. You mentioned 1100 causing "fall off". What does that mean, is it possible I need to run the idle up slightly above 1100? And how accurate is the stock mechanical tach on these bikes by the way? My guess was that I wasn't lean because if I add any choke at all the bike stumbles rather than picking up. Thanks again.
 

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go_hercules said:
My guess was that I wasn't lean because if I add any choke at all the bike stumbles rather than picking up. Thanks again.
I have the idle on my CL350 set for about 1000 rpm. I just bought a tach/dwell meter the other day and I'm going to hook it up to see how accurate it is. I'm willing to be the idle on the bike tach is reading high.

I'll post up my findings.
 

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Discussion Starter · #5 ·
Hey Mike, does your 350 do what I described - drop down in idle after running awhile? Or does it keep a steady idle? By the way, will you be coming out this way?
 

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Specified idle speed is 1100 RPM..... While you can get/run a lower idle on a fresh engine, as the compression is reduced (age, wear, etc...) the vacuum drawing the fuel into the idle circuit is also reduced and a low idle can "not quite" draw enough fuel to keep it running.....This is what i meant by "fall-off"... Try setting the idle up to 1200 or so.... I might also try "raising the float level" to 21mm (3-C carb)... Your bike could have replacement carbs from a different engine number sequence......Also, your choke should not "kill the engine" when cold starting... If it does, there is something wrong (usually with the carb set-up), but we HAVE experienced a member who had the operation of the choke backwards... He pulled the lever up (thinking that was off) to get the bike to run (I'm NOT saying that you are doing that, just pointing out things that have occurred)

I'm basing "lean" on the white color of the plugs.... They actually show what is going on, regardless of anything else....
It could be a fleck of rust that got through, plugging the idle jet intermittantly.....
 

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Discussion Starter · #7 ·
That's some pretty interesting info for sure. I think maybe I will bump up the idle slightly just to see what happens. Like I mentioned, the tach is probably not that accurate anyway, maybe I'm idling lower than I think when I set it initially. As for the float levels, I wonder if Honda kept lowering the float level for tuning purposes or if it was for fuel economy/emmisions - that was about the era all that crap started. I will double check to see which carbs the bike has for sure. Thanks for the help.
 

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go_hercules said:
Hey Mike, does your 350 do what I described - drop down in idle after running awhile? Or does it keep a steady idle? By the way, will you be coming out this way?
I have the idle on my '68 set at 1000 rpm. I went out for a long ride on it today and had a similar problem to what you mentioned. I purposely took my hand off the throttle to see what would happen and on a couple of occassions it would die. I think subconsciously I problem keep it running at the stop lights and don't even realize I do it. This came to light the other day when I let my friend ride when we went out for a 100 mile ride while I was on the Gold Wing. It would die on him frequently at the stop lights.

I think my problem is partly because the carbs are not sync'd. Also, I think setting the idle up to 1100 like Steve suggests is probably a good idea.

We'll be coming out your way on Halloween weekend (2 weeks). I'll give you a call a few days before we leave.
 

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Will wonders never cease. This is exactly what I came here for this morning. My 68 CL350 does the same thing. I have a fresh top end on mine. My mechanic set the carbs but did suggest that I try enriching the mixture a touch. Same thing though. Idles great when cold but idles too low when hot.

Edy
 

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When crappy coils get hot they tend to become well crappy. Look into that?
 

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If your motor is running a rich mixture (the 450s commonly seem to do this), your idle will be faster with the motor cold. AND you may not need a choke to start. The rich mixture is good for the cold motor, since not all the fuel vapourizes - but is too rich for the hot motor. Incidentally, too high a float level will definitely flood the motor, but once you're at or a little below the correct setting, the float level won't affect your mixture very much. Try shutting the fuel cock off while you're riding and hold the throttle at a fixed position: you won't notice a difference in how the motor runs 'til your fuel level in the float bowls gets so low you start to suck air in with the fuel. One atmosphere will support a column of fuel over forty feet high - you can imagine what percentage of that a slight difference in float bowl fuel level represents. Of course, if the level's too high it gets sucked into the air passages and into the venturi as raw fuel.
 

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Discussion Starter · #12 ·
I think I finally figured it out!!!!!!!!!!!!!! Like I mentioned in my initial post, I set each mixture screw by turning it in and out to find the peak RPM. What I didn't mention was that after I did that, I turned each one in and counted the turns. Like I had said, they were each about 1 turn. In hindsight, and after thinking about it for awhile, one was actually a little over 3/4 turn and the other maybe a hair over 1 turn. At that point, I set both of them at 1 turn because I'm anal and like things to be equal. Bad move. I did the whole thing over and kept the mixtures at about 3/4 and 1 turn respectively. I've now done about 50 miles of various riding and the idle is excellent all conditions. I never would have thought less than 1/4 turn from optimum on one side would make it act like that, but I guess a little rich on one side caused it to idle down when warm. Still doesn't like the choke, but starts right up hot or cold with no choke and warms up quickly. Thanks for the suggestions, I always manage to learn something new.
 

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To add, I was thinking too lean and turned the screws out a bit...NG.. so I turned them in and sure enough, the idle went up a tad. That equates with the bike hardley needing choke to start so maybe we've got it, eh?

Edy

My mechanic says, "Ride it, get it out of your system and get a modern bike"
My response, " But they don't look like motorcycles anymore"
 

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solarae said:
........Edy

My mechanic says, "Ride it, get it out of your system and get a modern bike"
My response, " But they don't look like motorcycles anymore"
A Big +1 on that one !

Although.....a Triumph Bonnie would be nice.... :roll:
 
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