Author Topic: Throttle, getting progressively harder to open, and close. (Read 2815 times)

1976cb750f836 · « **on:** June 30, 2019, 07:08:11 AM »

Stock 2 cable control, stock 76, round top carbs,newish cables. I've removed the tank, unhooked both cables, lubed all moving parts, they kinda drag about 1/3 into opening , then smooth out. Same when closing, maybe worse, first bit smooth, then kinda notchey .
I've loosened all the rod linkage bolts, still same. It feels like the slides are dragging in the carb bore. Is this common ? Can I polish the bore or the slide? Or are they just wore out?
I'm pulling them apart today, for inspection. Bike runs Great, I spent countless hours dialing them in after cam change and 836 kit. Could this be an ethanol fuel related problem ?
Thanks.

bryanj · « **Reply #1 on:** June 30, 2019, 07:24:00 AM »

Honda or aftermarket cables?

jgger · « **Reply #2 on:** June 30, 2019, 10:51:20 AM »

Are you saying that with the cables disconnected the drag is in the carbs/linkage, or in the cable/throttle?

If it's the carb/linkage side then it might be time for a good cleaning.

If it's the cable/throttle side take the throttle apart at the bars. Clean and properly lube the upper and lower half and be sure the tube to bar is clean and dry.

Another thing to look at is the grip rubbing on the end of the handle bar? A recent fall over on that side or new grips could be the issue.

TwoTired · « **Reply #3 on:** June 30, 2019, 10:57:54 AM »

Cables offer the least resistance when they are straight. So, keeping the bend radius large is important. Short, low bars, can put some pretty tight raidii on standard cables, requiring a reroute or replacement with shorter cables.

Cab;e can wear internally and start fraying the cable. Yep, they drag progressively worse until they break.

Cheers,

1976cb750f836 · « **Reply #4 on:** June 30, 2019, 11:26:53 AM »

Cables unhooked, drag is in the carb linksge. Their off now, ive pulled all slides, polished them with my aluminum polisher, they had some light marks, could not feel them with fingernail.
Got a hair out of 1 bore. Each slide slides freely in each bore, when the linkage is off.
I've polished the cams that raise the needles. Still have bout half of the notchey drag?
It seemed to be in the spring loaded hats on top of the needles. Their nice and smooth first 1/3 of travel, then as the cams start to get toward the fat spot, it's like the springs are too stiff, they get stiff to open further. Then when closing same, as long as the hat springs are compressed, it's got drag on it? It's like the cam lob is too tall? I'm tempted to take a few thousands from the sharp end off lobe?

1976cb750f836 · « **Reply #5 on:** June 30, 2019, 11:29:11 AM »

It's free in the first pic. Then as the cam compresses the spring, it has drag.

jgger · « **Reply #6 on:** June 30, 2019, 11:40:14 AM »

Sounds like the shaft or its pivot points are worn out of round.

Mark M · « **Reply #7 on:** June 30, 2019, 03:55:33 PM »

Could be a strand in the cable has let go, when one goes the others are sure to follow.

1976cb750f836 · « **Reply #8 on:** June 30, 2019, 04:17:47 PM »

The cable is Unhooked. With linkage off carbs, it's smooth as silk. Binding, drag, seems to be in the cam shaped to plastic spring loaded needle top hats? The rubber bushing in top of lid also seems to have drag. But it's worn at least 10, thousands larger than the round steel rod that slides through it.
Does anyone sell a complete linkage rebuild kit with hats, rubber bushings, round rods that hold needle in slide?
Or option 2, since it's a 836, I have a set of mikuni vac slide early 80s GS 750, 32s. That should be bout right size. They are spaced bout 1/2 - to 1in wider, might be a nightmare to fab?
I'd really rather keep my original carbs. They operate fine, except for the drag. I have nerve damage in my right arm from a hit tree at 40mph, due to a texting driver getting in my lane.
Hand cramps when I ride this bike 15-30min, or longer. At least it did? I have reduced it some. I could reduce spring more, but then I would have to manually pull the carbs shut(rode a HD like that once, didn't care for). The linkage seems fine, I really think it's the spring loaded top hat plastic, or the bushing in lid, or the steel rod dragging in the hole.
Just now got back together, fixing to text.

seanbarney41 · « **Reply #9 on:** June 30, 2019, 08:43:59 PM »

I just r and r'ed a set of carbs doing the same thing...all I ended up doing was dousing everything involved with Marvel Mystery Oil and then wiping away the excess. Helped immediately. Went for a 100 mile ride and they are still better than they were.

BenelliSEI · « **Reply #10 on:** July 01, 2019, 06:29:24 AM »

You say every thing runs smoothly when the carbs are off the linkage? 4 X carbs and the linkage independently OK, but bind together? Try loosening off each carb from the rack, one at a time. Is one (or more) misaligning and creating the problem?

1976cb750f836 · « **Reply #11 on:** July 01, 2019, 07:16:19 AM »

I rode yesterday, it's somewhat better, but occasionally throttle is slow to return, especially when going through gears at wot. I can get used to it. Would still like to rebuild the carb tops. I've already tried the 1 at a time for excessive drag or binding.
Looking at carbs from end, as first pic, as the linkage opens, and starts raising the needles, the cam shaped linkage should slip through the spring loaded hats. It does somewhat, but because of wear in the hole in top of carb, the steel rod missaligns and starts dragging in the rubber bushing. In other words the rods don't lift straight up, they start tilting and binding in hole. If the cam rotated smooth in the plastic bushings in the top hat, they would lift straight up, I think. At minimum I need the rubber bushing in carb top.
Any idea where to get?

TwoTired · « **Reply #12 on:** July 01, 2019, 07:54:56 AM »

The lifter arms move in an arc, so plunger shaft will always have some side loads. The lifter arm tops where they wear need to be polished, along with its interface in order to minimize the shaft side loads. Consider some teflon washers there? Also, a product called Dri-slide will put a thin coat of graphite on that wearing surface to improve the "sliding" action.

Interesting problem.

Cheers,

Jerry Rxman Griffin aka MuthaF'er · « **Reply #13 on:** July 01, 2019, 10:20:43 AM »

My take is you probably have the cables routed incorrectly. There is a diagram in the Honda Service Manual.

PM or post your phone number and I will text you the pic.

1976cb750f836 · « **Reply #14 on:** July 01, 2019, 11:15:12 AM »

THEIR ARE NO CABLES INVOLVED! This is a linkage problem. I've lubed the rods that slide in carb top holes, helped some, but they still drags when pulled at angle. I've looked for replacement carb top rubber bushings, No luck. This winter after riding season, I may attempt to make my own, out of Tygon fuel line or similar. And polish steel rods chrome slick. I still believe the tilting of the rod in the rubber bushing, is the drag problem. When they hang, while on work bench, I can push them straight with hole, and they close under spring pull.
I have already polished the cam shaped linkage to slick as chrome. This has improved some, but when the rods tilt and hang, the only fix I've found is to put them back in line with hole, then they close easy. Ive lubed sll rubbing parts with super lube, multi purpose synthetic clear grease. Bike only has 29,000 miles. Someone else should also have had this problem? But, theirs slways a BUT, i have no dust boots, they were rotton, and torn, when I first built carbs 20 years ago, so I left them off. Might be my mistake???

pjlogue · « **Reply #15 on:** July 01, 2019, 11:17:08 AM »

Have you centered the pull rods for the slides with the carb tops? To do so you need to loosen the carb top rings ~1/2 turn and raise the slides all the way and with the slides held up tighten the rings on each carb. You want to be sure the foot that connects the slide adjusting rod to the slide (inside the carb) is clean and greased. Also make sure your adjusting rods are clean, unbent and have a light very thin coat of silicone lube on them. (very light coat!) The binding at mid opening of the carb can often be due to misaligned carb adjuster rod foot. The adjuster rod and foot need to be clean and the foot directly under the hole in the top of the carb. The foot (with spring) inside the carb can often become rusted and/or not adjusted properly. This causes the rod to rub against the carb top and it doesn't take much friction to cause a real stiff throttle action.

-P.

1976cb750f836 · « **Reply #16 on:** July 01, 2019, 11:33:00 AM »

This is exactly where I think problem lies. I'm not sure I understand what your trying to tell me to adjust? The 2 screws that hold the rod to the slide? Or just loosen ring, open throttle, and re tighten ring? From 1/3 Throttle on, the rods tilt toward front enough to drag!
If u look at my 2nd pic, u can see the rods pushed toward front.

ekpent · « **Reply #17 on:** July 01, 2019, 11:37:16 AM »

Those 4 rubber grommets/seals that the shaft runs through at the tops of the carbs can be a problem sometimes causing a bind but pretty rare. I have had to replace a couple over the years on various bikes. I always oil them with some lightweight 3 in 1 oil.
Sorry if its already been mentioned,did not want to read through it all. Now about those cables

pjlogue · « **Reply #18 on:** July 01, 2019, 12:21:39 PM »

Quote from: 1976cb750f836 on July 01, 2019, 11:33:00 AM

This is exactly where I think problem lies. I'm not sure I understand what your trying to tell me to adjust? The 2 screws that hold the rod to the slide? Or just loosen ring, open throttle, and re tighten ring? From 1/3 Throttle on, the rods tilt toward front enough to drag!
If u look at my 2nd pic, u can see the rods pushed toward front.

Loosen the rings (at top of carb body, not the adjuster nuts at the end of the rods) ~1/2 turn from snug, raise the slides all the way and with the slides in the raised position loosen the rings a little more then tighten the rings back down. If the feet of the rods inside the carbs are clean and greased, rods aren't bent, the slides shuld work smoothly.

The throttle return springs are way too strong in my opinion. I went to Lowes and got lighter springs and it made a big difference in the force needed to open the throttle. They will still snap shut when released but my hand doesn't go numb from the gorilla grip I used to have to maintain to cruise along.

-P.

1976cb750f836 · « **Reply #19 on:** July 01, 2019, 05:12:27 PM »

I've took them off again. I have a commercial bench polisher, I polished the rods chrome slick. I assembled with carb top nuts loose, then opened throttle, then tightened linkage rod sideways 4 bolts, 3 bolts and a Phillips screw. Then tightened carb top rings. They now close with my reduced pull spring on work bench. I've synced them with drill bit, everything back together. Have to wait till tomorrow for test, they seem some better than before, still not new. Bike smooth. I'd really like to mount these gs vacuum slide mikuinis , but I'm sure that will be a nightmare of its own? I'll be able to ride this summer as is, it's better than before. Then by winter I'll decide on repair or replace.
I've found a couple of web post on the mikunis on a cb, but nothing step by step. 1 guy says it's easy just time consuming?
Is their another linkage setup for these carbs, besides the 4 cable set?
I never have liked the 2 cable throttle!

1976cb750f836 · « **Reply #20 on:** July 02, 2019, 06:36:05 AM »

Rode bike, much better, but still have to pull throttle closed ocassonaly .
Polishing the rods, and alignment helped.
Ok, thinking outside the box hear, but maybe my lack of dust boots has something to do with problem? The rods are getting out of line with the cams when they tilt.
The dust boots fit snug around rod, and behind cam lobe, this might hold them more in line?
Thoughts?
Saw them somewhere on line, anyone know where?
Thanks.

1976cb750f836 · « **Reply #21 on:** July 02, 2019, 08:32:19 AM »

Found them, bout 50$ shipped, damn 50$,for 3$,worth of rubber?
Anyway, decided to try to conform my theory, did a little outside the box, hillbilly engineering?
I placed 4, rubber bands on the needle top dust seal ring, then stretched to linkage to simulate dust boot! And it works like a charm, can't get them to stick, even with reduced spring. I now believe the dust cap does more than keep dirt out? Sometimes the factory engineers get it right? I'll bite my toung paying 50$ for rubber boots, but I guess I'll do it?
Looks like a nickels worth of rubber bands might work also,lol.

seanbarney41 · « **Reply #22 on:** July 02, 2019, 09:34:32 AM »

Out of a dozen or so cb750s, I have never had one with those boots intact. I don't think those boots exert any kind of force. Also, I have only had one bike that I remember having a heavy throttle and this one snaps closed firmly. Have never tried a lighter spring. In this case lube helped noticeably. Just my experience for you to use or ignore.

1976cb750f836 · « **Reply #23 on:** July 02, 2019, 10:39:43 AM »

So the 50buck boots, might be a dissapointment, waste of money? Wonder bow long the bands will last, I ant kidding, they hold the steel rod parellel to the hole, and work great.
I hate for something to beat me! Wish I knew exactly what the problem was? I kinda need the boots anyway, to make it correct, may go ahead and buy them(when the bands start breaking).
Can't believe someone with a high mileage (I only have 30k), bike hasn't experienced this?
Changeing front tire(different thread) , im going to Ride!

PeWe · « **Reply #24 on:** July 02, 2019, 10:46:50 AM »

Stock carb spring is way too hard. My carbs got an expensive spring from Webike. Much easier. The last 1/3 to WOT is tighter on my carbs, like the mechanism bend all throttles. I think that is how they work.

Both cables routed on left side of the frame. Return cable attachment on carbs sucks.
My carbs got new rubbers on the tops.

There is a thread about it where one member Gamma recommended "cable grommets rubber".
http://forums.sohc4.net/index.php/topic,127073.25.html

I oiled them with silicone grease.

Don R · « **Reply #25 on:** July 02, 2019, 11:06:36 AM »

Just a thought, I had a rack of carbs that were stuck and had been pried open from the top by a PO. The foot at the top of the slide was bent causing the rod to be misaligned and at different heights. You probably would have noticed it by now but might be of help to someone else.

pjlogue · « **Reply #26 on:** July 02, 2019, 01:07:05 PM »

1976cb750f836, have you checked and cleaned the adjuster rod feet inside the body of the carb where it attaches to the slide?

This is a somewhat critical area often overlooked, The adjuster rod "foot" sits inside a bracket with a washer and spring. The washer, spring and foot need to be clean and very smooth in order to move freely. This allows the foot end of the rod to easily position itself in a centered position with relation to the hole in the round carb top. Any binding in the foot causes the rod to bind against the round carb top grommet. When the grommet wears water can get down into the foot area and start rusting. I finally figured this out and polished the foot bottom where it contacts the bracket, polished the bracket bottom where it contacts the foot, carefully filed the inside top of the bracket where the washer sits against the bracket, honed the washer so it was extremely smooth and made sure the spring ends didn't have any sharp edges. I then greased the foot-spring-washer-bracket. When I put everything together I raised the throttle gang and loosened all the rings holding the carb tops on and re-tightened the rings. Lightly silicone greased the grommets where the adjuster rods go through the tops and put everything back together on the bike. My throttle is as smooth as glass now and I have a much weaker return spring (I got the spring at Lowes) throttle snaps back nice lie it should. Made a world of difference in riding. I leave about a 1/32" of free play in the throttle cables which allows for heat expansion so they don't bind.

The downside to taking the adjuster rods out of the carbs is you have to remove the rod tops which screws up any sync you had. The upside is with clean feet on the rods and everything polished doing a sync is easier. I found I didn't have to tweak each adjustment as much as I did when the feet were dirty.

-P.

1976cb750f836 · « **Reply #27 on:** July 03, 2019, 06:47:28 AM »

PJ, that's an excellent idea. I've had mine apart many times, when dialing in the carbs after the 836 and cams. I got to where I could install those 2 little pesky phillips screws blind folded,lol.
I'll do your recommended clean and polish tonight.
Thanks

Bankerdanny · « **Reply #28 on:** July 03, 2019, 04:48:08 PM »

I am having this problem too on my trip. I have blisters even with gloves from working the throttle and I am worried I am going to break a throttle cable in the middle of nowhere. If it can hold together a couple more days I am going to look for cables at the swap meet at Mid-Ohio to toss in my bags for the ride home Sunday.

seanbarney41 · « **Reply #29 on:** July 03, 2019, 04:50:39 PM »

HUh...?...I wonder if this is somehow some kind of F thing?

Bankerdanny · « **Reply #30 on:** July 03, 2019, 05:46:22 PM »

Quote from: seanbarney41 on July 03, 2019, 04:50:39 PM

HUh...?...I wonder if this is somehow some kind of F thing?

Before I head out for Columbus tomorrow I am going to check the routing. Fortunately the next couple days of riding are short.

1976cb750f836 · « **Reply #31 on:** July 04, 2019, 07:33:31 AM »

Ok, rod feet polished, spring ends deburred on 600 gt paper, little washer also polished, square rod end polished. Their was trash under some of the feet, like grit. Everything back together, but still on table, got late last night, and I quit. Mounting today. They do feel some smoother on bench. Found the top grommets on eBay, stupid cheep. Going to hold off getting them. Report back after test!

1976cb750f836 · « **Reply #32 on:** July 05, 2019, 06:24:12 AM »

Found another spring, lighter than stock, but stiffer than my hardware spring.
Bench synced with drill bit, test rode, I think I'm done. Brought it back in for a gauge sync.
They were damn close, only had to move 2 of them, less than 1/8 turn. I'd always thought a drill bit sync got them close, this conforms that! If your in a hurry to get back on road, a bit sync will do. Now for a 30 min or longer ride to c if hand still cramps. Thanks to all for post.

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Author Topic: Throttle, getting progressively harder to open, and close. (Read 2815 times)