Author Topic: 75 cb750f SS Reverse choke problem (Read 2232 times)

scw1984 · « **on:** June 13, 2011, 04:38:34 PM »

Hi everyone, I'm new to the forum and the world of bikes, I usually work on my own vehicles so thought I would try my hand at a bit of a restoration project. Picked up a 75 cb750 ss with 3300 miles on it, from a friend who has had it in his garage for the past 18 years sitting. As far as I can tell everything is OEM. He didn't do any of the normal storing procedures but I got it running, replaced all fluids, spark plugs and filters. Took the floats bowls off and cleaned the idle jet with a small wire and used car fluid to clean the other jets as best I could through the ports. It does have the original airbox on. It starts right up without a hitch and idles around 11 or 1200 rpms with the choke all the way on but the problem I am having is when I try to disengage the choke the rpms jump up to around 4500 with just a 1/4 turn of the choke lever. I haven't checked the boots for leaks(which I found searching the forum for other choke issues) but I plan to when I get home tonight or in the morning. Is there another issue I need to look at?
Also when I started taking things down to the carbs I noticed that there was an inline filter, passed the T and to the second to carbs only, is this stock?. I redid the lines with the filter just on the otherside of the carbs right after the petcock valve, is this ok?
Sorry for the long winded story

just new to bikes and am stumped at this time $:-\$

Shawn (It will look shiny soon lol)

scw1984 · « **Reply #1 on:** June 13, 2011, 04:50:15 PM »

Forgot the Pic...

BeSeeingYou · « **Reply #2 on:** June 13, 2011, 06:33:24 PM »

Well first off since you are new to bikes and old bikes in particular are you sure you are operating the choke correctly. Not implying you are a doofus but it has happened before. The lever in the down position is no choke and up and sticking out to the side is full choke. A leak in the carb boots could also be part of the problem so you are on the right track there but because of the history of the bike I think you may have multiple issues. Did you clean the main jet and emulsion tube along with the idle jet? How about the needle valve and seat? Did you thoroughly clean the tank and while doing so pull the petcock so you can replace the tank filter that is most likely deteriorated? I would get rid of the inline filter it is not needed with the proper tank filter. It is probably junk at this point anyway. If the float bowls were really gunked up with varnish from evaporating gas a disassembly and cleaning may be called for. How about the airfilter? While with the low miles in theory it would not be too clogged up who knows if any creatures used it as a nest over the years. It's great that you got it running but know it will take a bit more to get it running properly.

You will need to rebuild the brake system calipers and master cylinders before you take it out on the road. That is pretty much a given when they sit that long. And by the way nice find. Its really cool when one of these show up after a long slumber with such low miles. I found my 76 F in a similar way.

scw1984 · « **Reply #3 on:** June 13, 2011, 07:42:38 PM »

Yeah I'm pretty excited about it. Couldn't have gotten luckier with a first bike

.
I haven't completely broken the carbs down yet as I am a bit nervous about it but kinda getting tired of trying to run around it so it will most likely be started on by the end of the month. I am mechanically inclined for the most part, I understand the need to ask for the choke. To answer that yes the choke was turned down (opened) about a 1/4 turn for it rise in rpms. I replaced the old fuel filter (was thinking it didnt look like it was meant to be there will probably just remove mine), disassembled the brake calipers and cleaned and lubed in the proper place and both work great still no issues with them, I replaced the air filter and cleaned the housing out, although the boots from the housing to the carbs do not seal as well as I like in the housing, just figured this would not make a significant impact on the performance or at least enough to cause the rise in rpms from the choke.
I did clean the tank, line it with kreme liner so far no problem and checked the petcock valve for proper function and the outside filter on it, everything is in working order with no tears and proper flow through it. I did clean the idle jet out with a small piece of wire and carb fluid to the point that I could not see any dirt or build up inside. I will have to check the main jet later when I order the rebuild kit and not sure what the emulsion tube is?
I replaced the front fork seals and fluids according to the klymers manual. Checked the wiring system for any aging issues (thank goodness he kept it in his garage the whole time), chain is still within tension guidelines and cleaned and lubed it up accordingly. Rear shocks make a sucking noise when I sit on the bike probably seals that are worn out?
It has good compression thankfully also. I might try to have the carbs vacuum synced if I can get to a buddy's house a few miles away. Might help with the rpm trouble I am thinking.

BeSeeingYou · « **Reply #4 on:** June 13, 2011, 09:18:15 PM »

Sounds like you have things well in hand.

The emulsion tube is the tube with the holes in it that the main jet is screwed into. It unscrews and may even come out when you remove the main jet. Be wary of the rebuild kits unless they are OEM Honda. The tolerances for the jet needles, jets, and needle valves in some of these kits are suspect at best and these parts seldom wear out anyway so use your original parts . The gaskets are probably the only real usable parts in some of those kits.

It could be that it is a combination of things adding up so eliminate them one at a time and while I too think a small leak on the airbox side should not cause this it may be a contributing factor. Make sure it is firing on all cylinders too, just touch each exhaust header after start up to tell. You can check the fuel level in the carbs by using a piece of clear tubing of a size that will "screw" into the drain fitting . Hold it up to the side of the carb and it should be around 4mm below the gasket area. The sync should be the last thing after all the issues and adjustments are made. Valve clearance and check the cam chain adjustment to name a few. Your ignition points should be fine but run a points file across them to clean them up

The rear shocks were not that great to begin with so they may need to be replaced.

That bike looks like it may polish up nicely and you may have a real nice looking survivor on your hands. Be nice to keep it that way.

On my bike I have to start it with full choke but almost immediately after it fires I have to open it just a bit. It will not run long on full choke.

There are Honda manuals here to download and many consider the Klymers to be not very good. Here is a wiring diagram for you in two parts.

scw1984 · « **Reply #5 on:** June 14, 2011, 05:47:29 AM »

Those diagrams look familiar lol been using them and the manuals on the website here more than the clymers when I have a computer to sit down at

. I'll take note on the carb kits, half way thought about just getting some gasket material and cutting them out myself save $50. Do you know if the Keyster kits are any good or heard anything about them?
I have checked that all cyclinders have been by that very same method although I waited a little too long to check it haha. I'll check the float levels on Thursday, thanks for the method to do so. I'll look up the way to check the valve clearance and cam chain adjustment.
On the shock adjustments I am thinking the tighter you compress the spring the more load you can put on the bike or for better cornering?
Well thats all the time for now, time to make some chocolate chip pancakes for the family...

Shawn

david 750f · « **Reply #6 on:** June 14, 2011, 06:01:01 AM »

If you dont have vacuum leaks make sure the throttle cables are not binding. Turn the handle bars from side to side when the bike is idling. If the bike has been sitting for years the cables may be sticking.

scw1984 · « **Reply #7 on:** June 14, 2011, 07:03:23 AM »

They don't bind as far as I could tell, you think I should spray some wd-40 down there?

david 750f · « **Reply #8 on:** June 14, 2011, 07:28:54 AM »

While you have the WD-40 out, spray some around the carb boots. If the idle changes you have a vacuum leak.

ekpent · « **Reply #9 on:** June 14, 2011, 07:56:26 AM »

Nice find on your new bike,looks like a nice one. If the bike has been sitting that long though you really need to take those carbs off the bike and really give them a good cleaning.High idle may be a slide or two sticking,just a very little bit will dramatically change the idle.Stick with all the stock brass items in the carbs if you can,better than Keyster etc.Did you mention how many miles are on the machine.?? Also do a quick tune-up like clean points,set valves and timing,new plugs and maybe air filter and you should be real good to go. Welcome and enjoy. Eric

scw1984 · « **Reply #10 on:** June 14, 2011, 08:13:19 AM »

Davind,
Yeah thats a good idea I might as well do that while its out and maybe put some electrical tape around boots in the filter housing as a quick fix to see if there is any difference at least untill I find some replacements.
Ekpent,
It has 3300 miles on it so far. I still need to clean the points but I havent read yet about how to set the valves and timing. I have install new plugs, oil filter and an air filter along with the appropriate fluids. Ive read the wars on the type of oil to use lol many of them, and since I live in Texas I decided to try some castrol 10w40 synthetic blend to start with and will probably do another oil change a couple hundred miles after I start riding it to get rid of the residue left over from sitting.

BeSeeingYou · « **Reply #11 on:** June 14, 2011, 12:30:04 PM »

The Keysters are suspect with complaints about the main jet needle. To tell the truth I don't see any need for a carb kit at least in my experience, with the possible exception of gaskets. Mine still have the original gaskets and all the other parts and they don't leak and have not given me any trouble so far. My bike sat indoors for 25 years before I got it but the carbs were almost spotless inside when opened up so your experience may vary.

as far as the shocks, yes the tighter the spring the more load. Something you may need after too many pancakes.

JDWells · « **Reply #12 on:** June 14, 2011, 01:02:33 PM »

If you cleaned the idle jet with a wire you bored it out. Now it's way bigger than it should be and that's why you're revving when you take off the choke. It's a common thing, but you'll have to replace the idle jets. They're on bikebandit.com for cheap. To clean out jets you never want to put stuff in there, especially the idle jets since they're so small. Just spray a heavy dose of carb cleaner, then use compressed air and blow straight through and repeat. That doesn't always work but since they're so cheap it's usually ok to replace them. You could also try to soaking them for a few hours in carb cleaner or the like. Sometimes that works.

scw1984 · « **Reply #13 on:** June 14, 2011, 03:17:36 PM »

Srust58,
I'll keep that in mind for if I end up tearing the carbs down bc I was wondering this as well, I mean with only 3300 miles on the bike the gaskets should be ok still.

JDWells,
I would have originally thought that also but it was doing this before I even took the carbs off. When I did run the wire through I did the best I could to only clean off the gunk without scraping the sidewalls to the point that I didn't see any gouges when holding it to a light as I was looking through it.

BeSeeingYou · « **Reply #14 on:** June 14, 2011, 11:01:22 PM »

With the gaskets it's not really the miles but the age as they can tend to harden. I am a bit surprised mine are still ok. The level of fuel should normally be below the gasket but when the bike is on the side stand is when they could leak if they were bad. I would not worry to much about reaming out the idle jet as long as you are careful with a light touch and are not ramming a drill bit or needle through there. You're not the kind of guy who thinks a hammer is the first tool to reach for when you have a problem are you?

How long have you been able to run the bike? Pull a plug out and see what color the electrode is. It seems doubtful with such low miles that valves or cam chain could be far out of spec to cause problems but is is good to know how to check these items as you will have to do it evetually.

scw1984 · « **Reply #15 on:** June 15, 2011, 12:20:12 PM »

Haha no household hammer will do but maybe a sledge hammer

jk. I'm not that guy, usually go workout or go for a run when I get frustrated with something and it helps me to think through the problem lol works wonder for self therapy

.
Mine were leaking fuel from the dumps after I sprayed the float bowls through with cleaner before I actually took things apart but it did stop on its own which tells me that the floats were probably gummed up a bit, not anymore though. Yeah I agree I will probably see how much time I have in the morning and grab me a feeler gauge when I am getting some gaskets for my petcock valve. I will have more updates on it tomorrow with any luck !!

scw1984 · « **Reply #16 on:** June 25, 2011, 12:27:19 PM »

Well just an update, did not have nearly as much time as I had hoped over the last ten days.
However, I did procure a set of carb gaskets and rebuilt my carbs which I had a few questions with, new to rebuilding carbs so bare with me please.

The spark plugs were pretty sooty when I checked them out before I pulled the carbs does this mean I need to change the setting on the jet needle or is there an easier way to do this without breaking the carbs back down?

I benched synched the carbs using the 1/8 bit method but just checking that you measure on the air box side of the carbs?

I adjusted the choke valves to where they were all closing except on carb 1 there is a 1/8 or 3/16 gap which I am not sure how to adjust?

david 750f · « **Reply #17 on:** June 25, 2011, 02:04:12 PM »

Here is a great tutorial with lots of photo's for bench syncing the carbs.

http://www.salocal.com/sohc/tech/carb/asmpg3/syncprep.htm

scw1984 · « **Reply #18 on:** June 25, 2011, 02:19:49 PM »

Ok, check on that one bc it looks about the same clearance on that side!

Haven't put them on the bike yet so maybe ill pick up some of that silicon, anyone know what brand it is or prefer one over another?

BeSeeingYou · « **Reply #19 on:** June 25, 2011, 10:46:06 PM »

I would leave the jet needle alone at this point as you have the stock airbox and muffler. It seems doubtful with the low mile stock bike that the PO would have mucked about and changed things. The jets should be 105 for the main and 40 idle.

The plugs will tend to be dark if you have only been able to run the bike at idle as they run a bit rich at low rpm so at this point it is not a good indicator of whats going on.

The clearance for the choke in a closed position is 0.5mm and while it is obvious how to adjust the 2, 3, and 4 choke clearance I am not sure there is an adjustment for the #1 other than the lever.

Check the floats and make sure they don't leak (with the plastic floats it is not as likely as with the brass ones)

scw1984 · « **Reply #20 on:** June 26, 2011, 12:24:15 PM »

lol well I did a last minute change last night before I was able to read the post and moved the jet clip up one notch, put it on the bike last night but didnt have time to ride it as it was nearly midnight. I did check to make sure the floats float and all is well, set the clearance for them at 26mm. Hopefully tonight I will be able to actually start it up and ride it down the street without a stall. I haven't touched any other adjustments on the carbs other than the floats, jet notching, and choke plates. If the bike is running a bit too lean once its broke in a bit I'll switch the jet clip back to stock. On the choke plates is it pretty crucial that I have them set at .5mm or can I just open them up a little more when I am warming the bike up?
Is there anything else on the carbs I should adjust before I start it up?

BeSeeingYou · « **Reply #21 on:** June 27, 2011, 11:16:44 PM »

Maybe check the position of the airscrews on each carb. Should be around 1 to 1 3/8 turns out. Who knows maybe the PO mucked about with them. The question on the choke settings I would have is by setting them at the proper position at the closed position does this also have the effect of putting them in the proper position in the full open position. It seems that the 1 is off by quite a bit.
Does it still have the high idle problem?

scw1984 · « **Reply #22 on:** June 28, 2011, 07:49:57 AM »

After replacing the plugs yesterday morning with D7EAs it backfired while warming up but I didnt notice it after it was actually riding. I was told it might need to be warmed up longer but as I am new to bikes I'm not sure what the proper warm up period is, usually I'll just wait till the top part of the motor gets warm. Other than that I didn't have any other issues, high or sporadic idling or otherwise. Felt like a good range in rpms and responsive throttle control. I didn't adjust the screws yet but probably will when I go back over today and see if there is a change at all.

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Author Topic: 75 cb750f SS Reverse choke problem (Read 2232 times)