Aces High Bulletin Board
General Forums => The O' Club => Topic started by: SFRT - Frenchy on August 06, 2008, 03:24:13 PM
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I bought my first bike ever, a 1975 CB750F from a guy that ran the bike to the ground and couldn't get her to go anymore. After cleaning her up for a couple of days, changing the coils, spark plugs, new A & B throttle wires, redoing entire electrical thanks to oldmanhonda.com, and cleaning the carbs thanks to SohcCBs, I finally got her to run.
Throttle response seems great, I do have some issues that maybe some comunity member can help with.
1/ When I rev up the engine, the RPM increase fast, but when I left the trottle snap back to idle the RPMs decrease very slowly. Takes about 5-8 secs to come back from 4K to 1.5K. I do see the slider cylinder rod push all the way back in, so I'm thinking the "butterflies" close.
2/ How can I adjust the tension of my cam chain? I ear a pretty loud rattle from my engine.
3/ My left side case was leacking oil from the bolts. I opened it to find what seems to be an alternator mechanisum. Is it supposed to be drenched in oil? Same with the clutch mechanisum? I attached some pictures.
(http://photos-e.ak.facebook.com/photos-ak-snc1/v263/150/40/790661307/n790661307_670444_1890.jpg)
(http://photos-f.ak.facebook.com/photos-ak-snc1/v263/150/40/790661307/n790661307_670445_2209.jpg)
Hopefully will daily ride the thing soon so I can learn how to ride. :uhoh
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I might ask you if that's an electric clutch, Frenchy, but I don't know enough about Bikes to say for sure.
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Clutches are usually 'wet' clutches.
There should be an tension adjustment roller for the cam chain.
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congrats on your first bike.
My first was a yamaha 450 man that thing had so much vibration at 55 that my feet were numbfor an hour after riding for only half an hour.Anyway Inow have a Yamaha V-star 1100 and love it.You will really love that thing after you get the hang of it.
As far as your questions go. I am no expert and I am sure someone here will be able to help more than I can.
My bike has a fairly loud vibrating noise coming from the engine as well (well maybe not loud but definitely noticeable). I have been told by several people that that noise is slop in the valves, that is put there on purpose. Since the engine is air-cooled they put the slop in there to allow for expansion and contraction. Not sure if that is the case with yours or not but maybe.
don't know about any of the other questions though.
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1/ When I rev up the engine, the RPM increase fast, but when I left the trottle snap back to idle the RPMs decrease very slowly. Takes about 5-8 secs to come back from 4K to 1.5K. I do see the slider cylinder rod push all the way back in, so I'm thinking the "butterflies" close.
Check for intake leaks and check that idle mixture screws are not broken. Screw them out and inspect them. Setting the idle speed as low as possible might help, but there certainly is a real cause somewhere. I had the same problem with my bike, but it's a single carb and so it's much easier to troubleshoot.
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The Hondas definitely had "wet" clutches. They are supposed to be in oil. I am not sure about the alternator however.
The slow responding throttle could be sticking cables, weak return spring, dirty butterfly mechanism but very doubtful to be air leaks unless it's spitting and backfiring too.
If you can find one I'd get a copy of the Clymers manual for your year and model bike. If not check the used book stores and maybe even the public library for a copy to look at for more info about the bike's internals.
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I did put the carb appart and cleaned/ dipped cleaned everything already. I set the fuel screew to 1.5 turn. Went to ride her, and the thing is screaming with great acceleration (as far as I know about acceleration and bikes as I don't know how to ride). But engine definitly sounds healthy accelerating.
(http://photos-d.ak.facebook.com/photos-ak-snc1/v263/150/40/790661307/n790661307_671107_4625.jpg)
(http://photos-e.ak.facebook.com/photos-ak-snc1/v263/150/40/790661307/n790661307_671108_4946.jpg)
They do look much better after cleaning:
(http://photos-f.ak.facebook.com/photos-ak-snc1/v263/150/40/790661307/n790661307_671109_5255.jpg)
(http://photos-g.ak.facebook.com/photos-ak-snc1/v263/150/40/790661307/n790661307_671110_5575.jpg)
I cosmetic side, I removed the high handle bar and replaced with clubmans. I removed the highway floorboards and replaced with regula pegs. I'm building the tail with fiberglass as a side project. She's going to look like, a 55FG inspired paint. And here's a squetch I did :
(http://photos-f.ak.facebook.com/photos-ak-snc1/v263/150/40/790661307/n790661307_671117_755.jpg)
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The Hondas definitely had "wet" clutches. They are supposed to be in oil. I am not sure about the alternator however.
The slow responding throttle could be sticking cables, weak return spring, dirty butterfly mechanism but very doubtful to be air leaks unless it's spitting and backfiring too.
The throttle has new cables (both A & B), when I accelerate and let go, they snap right back to idle, I can see the htrottle assembly attached to the carb snap back to idle, I can see the butterflies closing also. Acceleration is immediate, deceleration of the RPM is very very slow back to idle despite evrything "moving right". I was thinking a timing issue, but I would think that would affect both deceleration and acceleration.
thx 4 for the brainstorming :aok
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Mine does the same thing... idles 3k + if I let the clutch out a bit with the brake on I can bring the RPM's down to normal idle, and it will stay there.
really odd.
I do know my throttle return cable is stretched out, and I have a replacement, but the throttle arm does go all the way back and it is still doing this.
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Nice looking paint scheme.
Google CB750 groups for help with your troubles.
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The slow responding throttle could be sticking cables, weak return spring, dirty butterfly mechanism but very doubtful to be air leaks unless it's spitting and backfiring too.
He told that he had checked that the throttle returns. This is a common problem and unlikely to be caused by slow return, as the slowing down period is so long and apparently the idle speed is at a correct level. Little spitting and backfiring goes pretty much unnoticed in an old bike like this. It's not a bad idea to check for them anyway as there more than likely is some. Obviously the problem is caused by fuel mixture entering the engine uncommanded, and it can't be caused by many things.
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Mine does the same thing... idles 3k + if I let the clutch out a bit with the brake on I can bring the RPM's down to normal idle, and it will stay there.
really odd.
I do know my throttle return cable is stretched out, and I have a replacement, but the throttle arm does go all the way back and it is still doing this.
As I wrote earlier, check your idle mixture screw(s). If broken you'll need to fish out the broken tip somehow. Very common with Mikuni's. Then check the fuel level in the float chamber and check for intake leaks.
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Oh and congrat's for the purchase! I love old Jap bikes, but I won't get one as they reguire far too much work for every mile driven.
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As I wrote earlier, check your idle mixture screw(s). If broken you'll need to fish out the broken tip somehow. Very common with Mikuni's. Then check the fuel level in the float chamber and check for intake leaks.
Yeah I have been reading in the Clymer about doing all the carb set up, tools I don't have, don't know, and don't have anyone I know to borrow them from :(
I plan on trying to tackle it this winter when I have time, now I have to ride it just to survive, otherwise I can't afford food.
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Frenchy,
1st congrats! Welcome to the fraternity.
The "slow return to idle" issue means the bike is running rich, adjust your carbs and turn down your fuel / air mixture a little.
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Yeah I have been reading in the Clymer about doing all the carb set up, tools I don't have, don't know, and don't have anyone I know to borrow them from :(
I plan on trying to tackle it this winter when I have time, now I have to ride it just to survive, otherwise I can't afford food.
Float level checking is easy. There is a plug at the bottom of the side of the float chamber. Unscrew it and attach a transparent gas line or similar to it(you need to seal it somehow). Hold it next to the chamber and check the fuel level per the instructions in the manual.
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I was thinking the slow return to idle could be a mixture issue too. 1.5 turns might be a bit rich. Did you check each of the mixture screws for equal length when you had the carbs apart? Did you replace the Jets?
Have you balanced the carbs yet? This could also be part of your problem. You will need a balancing set (4 vacuum gauges) and you hook them up to the vacuum ports in front of the carbs. Some models have srcews and some have blocked off vacuum take offs, you will have to check to see what you have. You hook up the balance set and adjust the throttle bodies on each carb individually until they read the same, then you adjust the master to get the correct idle speed.
I'm sorry I cannot remember if the old Hondas have an automatic tensioner or a manual one, your best bet is to refer to a manual.
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Congrats on your new bike. A Honda CB750 was the second bike I ever purchased. Of course that was back in the 70's. I started touring on the 750 and put close to 80,000 miles on it before I had to sell it. Having had numerous bikes since, and still own a couple and regularly tour on them, you see the world with new eyes while riding.
My suggestion, since you stated you are not a experienced rider, is to take a safety course like the MSF. You will learn a lot from it. Having the battle scars from some mishaps, believe me you don't want to see my X-Rays, wear the proper gear and start slowly.
I'm not a safety guru, just someone that learned the hard way.
Fred
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Since the bike has been sitting up for a while, the slow response to idle might be as simple as sticky cables. The cables can be dragging on return. I have had it happen a couple of times.
unhook the accelerator cable from the grip, make a funnel around the cable shroud, then use MML or WD-40 . Stand it in place upright and give it time for the lubricant to work it`s way though the cables.
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My suggestion while building up the CB, buy a cheap small bike to learn on first and take a few lessons after six months on that and your still around try out the CB and do some more advanced courses. After a year you'll be enjoying the bike a lot more.
<S>...-Gixer
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As I wrote earlier, check your idle mixture screw(s). If broken you'll need to fish out the broken tip somehow. Very common with Mikuni's. Then check the fuel level in the float chamber and check for intake leaks.
I'll bet it's something like this... obviously too rich, getting lower MPG's than I should and sluggish some times (flooding my guess)
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1/ When I rev up the engine, the RPM increase fast, but when I left the trottle snap back to idle the RPMs decrease very slowly. Takes about 5-8 secs to come back from 4K to 1.5K. I do see the slider cylinder rod push all the way back in, so I'm thinking the "butterflies" close.
PLEASE MP's this isn't a "punt"
Frenchy, with all the work did you get this problem solved? I am still struggling with it on my bike, and was looking for insight on to what caused it / what fixes were involved?
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Oh boy ... I don't recall what fixed it. I did adjust the valve clearance and the timing. The timing was a off mainly because of my point gap. I used a dwell meter to adjust them, and a light gun to adjust the timing. It seems I'm doing ok now, still a bit slow to decrease, but not nearly as extreme as it used to, seems definitly "acceptable".
My problem now is my idle not wanting to stay put. I have to blip the throttle ot maintain it, or it just jump 1.5K by itself. I did put new intake manifold rubber boots suspecting an air leack but it still does it. I still have to synch my carbs, I have still to pay some bills first.
If u can get your hand on a timing gun, a dwell meter and a feeler guage set, I definitly you adjust all that. It doesn't take a rocket scientist to do and it's quick. As mention earlier, adjust ur mixture screews per manual. What year of bike/type are u driving?
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NM .... 1977 KZ650 :D search function is a beautifull thing.
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I found my first bike... in San Antonio... in the basement of some old ruined mission.
(http://www.jonco48.com/blog/bike1_small.jpg)
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:cool:
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Oh boy ... I don't recall what fixed it. I did adjust the valve clearance and the timing. The timing was a off mainly because of my point gap. I used a dwell meter to adjust them, and a light gun to adjust the timing. It seems I'm doing ok now, still a bit slow to decrease, but not nearly as extreme as it used to, seems definitly "acceptable".
My problem now is my idle not wanting to stay put. I have to blip the throttle ot maintain it, or it just jump 1.5K by itself. I did put new intake manifold rubber boots suspecting an air leack but it still does it. I still have to synch my carbs, I have still to pay some bills first.
If u can get your hand on a timing gun, a dwell meter and a feeler guage set, I definitly you adjust all that. It doesn't take a rocket scientist to do and it's quick. As mention earlier, adjust ur mixture screews per manual. What year of bike/type are u driving?
hmmm
I don'e even know what a "Dwell meter" is of where I'd find one. I did read in the Clymer book that it was the best tool to use. I did just put on new points a month and 1/2 ago, used feeler gauges to set it.
My problem has steadily gotten worse, I have no money, and need to keep riding it to save the gas money LOL. What it's doing is listed above, it will race at 4K RPM and just sit there. I can engage the clutch a bit and force it down to normal idle (1K) but it will not go down on it's own if I rev it. Lately it has also given me a ton of trouble starting. I can't help but think it is all related to the carb adjustment, and syncing. best price I can get to sync them is $350 (no one will touch them and just sync them, they will only sync carbs they have cleaned / rebuilt fully because they don't know what might be mis-set).
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Have you checked to see if the cables are letting it return to idle without sticking?
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Have you checked to see if the cables are letting it return to idle without sticking?
yup, the throttle arm on the carbs does return to idle, and I have replaced the throttle return cable (it was stretched). I do have about 1/4 inch too much play right now in the cable I need to adjust, but the arm does go to the correct idle position.