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Discussion Starter · #1 ·
Hi guys! I’ve mostly been lurking here over the past year or so, soaking up the wisdom. But I have a serious problem that I need help with. Forgive the long post but I’m going to try to provide as much info as possible.

My bike is a ’70 CL450. Bought it last year. Low miles, good solid bike. It ran great when I got it, and for a few months I had no problems at all. Then, one beautiful day in the fall I went for a ride in the country, and it’s never run right since. I mention this because that was the first time I really rode the bike “hard” at all, meaning at sustained speeds of 50-60 mph. Before that day I was mostly taking short trips cruising around town. This is the first bike I’ve owned in about 10 years, so I was taking some time to get my feel for riding again.

Now to the problem. When the bike is cold, provided it has a good charge in the battery it starts up very easily. Never more than 5 or 6 kicks. Idles well, runs well, no problems. But once the bike gets heated up, it starts to run like crap. On a hot day, it can be as little as 10 or 15 minutes before I have trouble. On a mild day, it may be 30 or 45 minutes. The problem is that the bike begins surging, meaning the throttle revs up uncontrollably and won’t come back down. I can touch the throttle gently, and the bike will rev up and stay there. Sometimes I sit at a stoplight with my hands off the bars, the bike in neutral and it’s raging at 4K RPM or higher. I can look down and see that both throttles are clearly all the way down, and if I rev it up, it will go even higher and then come back down to where it was, but NOT back down to idle. Sometimes I can use the choke to bring it down, but it has to be done very gently or I usually just stall the bike. Once this starts happening, the bike is unpleasant and - frankly - a bit dangerous to ride.

Now last year I had some issues with the spark advancer sticking, opening and not closing, and the bike hanging at around 3500-3600 RPM. A friend showed me how to use the clutch to bring it back down, and that worked fine. We cleaned and lubed the spark advancer and it didn’t happen as much. I eventually replaced the spark advancer with a NOS unit, so I don’t think the issue is there. Besides, when the bike revs up and stays now, using the clutch method does nothing to bring the revs down. That’s why I have to use the choke, or just turn the bike off. Nothing else will bring the revs down once it sticks.

So I thought the problem may be inside one of the carbs, something sticking once they got hot. So over the past couple of weeks both carbs have been rebuilt, not completely and totally but using the typical rebuild kit. The problem is still there. Once the bike gets good and hot, it starts giving me trouble. I will add that once the bike is hot, if I turn it off it’s often very difficult to restart, and once it does it doesn’t idle well. I think that’s a clue but I have no idea what it means.

Now my questions:

1) Could it be something related to the spark advancer, but not the unit itself?

2) Could it be something in one of the carbs not covered by a basic rebuild?

3) Assuming the carbs had NOT been rebuilt, any likely parts of the carb that could be causing this?

4) Anything completely and totally unrelated to anything I’ve mentioned that might cause this?

I tried to provide all the info I could but I’m sure I’ve missed some important details. Ask and I’ll help fill in the blanks as best I can. I greatly appreciate any help that anyone can provide. Frankly, I and everyone I know are pretty stumped on this one. Thanks in advance.

Derek
 

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It could ba an advancer but I think it is carbs that are out of synch. Start from scratch on setting them up and synchronizing them first would be what I would do.
Don
 

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dlslick said:
It could ba an advancer but I think it is carbs that are out of synch. Start from scratch on setting them up and synchronizing them first would be what I would do.
Don
It is either that or it could be a vacuum leak (hence the choke working to bring rpm down.)
 

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Discussion Starter · #4 ·
I just looked over the carb setup thread. Never synched carbs before but it looks straightforward enough. I'll try it out as soon as possible.

Would the most likely place for a vacuum leak be at one of the intake boots? Someplace else? Any preferred method to check for a vacuum leak?

Keep the info coming. I really appreciate it! :)

Derek
 

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I have heard that you can spray something close to the boots that will increase the engine speed if there is a path that shouldnt be there. I just cant remember what they were spraying. WD40 maybe, starting fluid? Get someones opinion that has done it first so you dont get blown up. :eek:
Don
 

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Discussion Starter · #6 ·
Someone else suggested WD-40 for that, so I think that may be the way to go.

Derek
 

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dlslick said:
I have heard that you can spray something close to the boots that will increase the engine speed if there is a path that shouldnt be there. I just cant remember what they were spraying. WD40 maybe, starting fluid? Get someones opinion that has done it first so you dont get blown up. :eek:
Don

I generally use a propane torch - unlit of course.
Spray a little gas around suspected areas-if there's a leak, you'll know it.....
 

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Discussion Starter · #8 ·
tbpmusic said:
I generally use a propane torch - unlit of course.
Spray a little gas around suspected areas-if there's a leak, you'll know it.....
That's a great idea. I have a small butane torch I could try. Seems better (meaning more precise) than spraying WD-40 everywhere.

Derek
 

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Discussion Starter · #9 ·
As a follow up, so far I've been unable to find any evidence of a vacuum leak. Carbs are synched and seem fine. Replaced the battery yesterday. Bike is running better but still gets crazy once it's heated up.

When it revs up and hangs at 3 or 4 thousand RPM, if you pull either plug wire it comes back down to idle. This would seem to indicate the problem is not specific to one cylinder or one carb but somewhere central to the engine. Am I correct in thinking that? I still suspect there may be issues with the spark advancer, but it was replaced with a NOS unit. Is there something related to or connected to the spark advancer (but not the unit itself) that could be responsible?

Thanks.

Derek
 

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Discussion Starter · #11 ·
tbpmusic said:
Just shot-gunning here, but tight intake valves can cause high idling on a 450........
I do plan on checking the valves as soon as I can. It's too big a question mark to leave unexamined.

Derek
 

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I had problems a few years ago with my 450 running like crap after I ran it for longer than about a half an hour. It didn't rev high like you're having. Anyway, it turned out to be a bad coil. The way I discovered was by putting a timing light on the spark plug wires after a long ride when it started running poorly. One side gave a nice consistent flash, the other side was sporadic.

You could try that to see what it looks like.

-Nick
 

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Here's a stupid response. Have you checked that the throttle cable is not being acted upon by improper routing? Or that the clutch cable isn't bumping into your carb controls failing to let them return to idle?
 

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How about the vacuum slides sticking/ hanging up as the carbs get warm?
 

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Discussion Starter · #15 ·
mtnlvr said:
Here's a stupid response. Have you checked that the throttle cable is not being acted upon by improper routing? Or that the clutch cable isn't bumping into your carb controls failing to let them return to idle?
Yes, I've checked the cables. And it's not stupid. :)

Derek
 

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Discussion Starter · #16 ·
WOZERD said:
How about the vacuum slides sticking/ hanging up as the carbs get warm?
I suspected that too. Carbs were recently cleaned and largely rebuilt. Frankly I was really expecting that to fix this problem, but no luck.

Derek
 

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I've had a very similar problem in the past and it turned out to be vacuum leak after checking virtually everything I could think of. :D :D Suggest you remove carb rubbers to head clean gasket surfaces replace both gaskets and hylomar both sides of gasket well before refitting and tightening. Check rubbers carefully for cracks especially where the clips tighten them up.
I would then tend to start engine & rev up manually without any throttle cables attached to totally eliminate cable problems and if not cured you should be able to find out which side is causing the problem. Regards Chris.
 

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gamd5, nice response. i'm experiencing similar problems and plan to double check my "rubbers" tomorrow. i really hope that is the issue. and tight intake valves also seem like they MAY be a possibility, thanks. my exhaustive problem was posted earlier in project logs: "kitchen build" post...
 

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You may also find a few things to check in Honda black bomber -project 6 -page 2.Having now completed six bomber rebuilds my MAIN problems have ALWAYS been:-
1/Batteries not holding charge-bombers do lots of funny things if low on volts which I'm sure most of us have put down to other problems.( lots of us charge overnight run OK for a few miles and then have problems) answer ELIMINATE THAT PROBLEM FIRST- THROW THAT OLD RECTIFIER AWAY AND FIT A £5.00 SOLID STATE ONE AND CHECK CHARGING VOLTAGE.
2/Throttle cable adjustment ( You must leave more slack in front cable than you would normally think-another reason revs don't die down)(Cables must be adjusted and work totally freely-move handlebars side to side check & double check.
3/ carb to engine rubbers.-don't just check the rubbers for splits-them there gaskets that seal the dam things may be 40 years old,also the aluminium faces are sometimes not as flat as they should be :D(I always seal with plenty of hilomar but try to keep it thicker on the outside edge of the gasket-or remove the bead of excess from the inside when tightened to head before fitting carbs.
3/Make sure the clutch cable is not fouling on the LHS carb throttle cable.(think this mainly relates to KO's)
4/Things sparking in the wrong place.(points to cover,bare generator wires)Try things with covers off-look for small black marks on inside of covers.
5/Get the choke off as soon as possible when engine runs,they don't like running rich and I've had several bombers take new plugs out astoundingly quickly leading me totally in the wrong direction.
Follow the stickies in the forum and my final tip would be if charging OK try to find which side the problem seems to be coming from by swapping things side to side if you get my drift. Regards Chris.
 

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i've never used hylomar before. i did take my boots off today and cleaned both surfaces, boot and head. one boot had an OLD gasket totally glued to it the other was just funky. i had some replacement gaskets but just put everything back together. should i go back and apply some of this hylomar stuff? i actually did notice my left carb bouncing a little every now and again at idle, a little thud would knock it around. air spitting out i'm assuming? makes sense now. hylomar universal blue, thats the stuff i want?

and can you photograph your throttle cable routing for me? i'm sure i'm still not getting it right...
 
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