Hey all 78' Cb750k new to forum

[xghandix]

Sorry when i said only the middle two fire i was speaking about the nozzles for the accelerator pump. Ive cleaned the carbs, and then re cleaned the carbs....and then I cleaned them again. I dont think it is a vaccum leak. But then again you know more than me..i did the test and didnt notice a rpm change. The boots dont seem dried or used up to me.
It does look good with out thay fender bracket. It allso looks good with no front fender haha. I think the problem lies in the accelerator pump.

[Re-run]

Ah ok, so you only get a squirt on the inside carbs. Well, there are a couple of things. !: the nozzles are clogged. Supposedly those come out, never done it so I can't speak to that. But you can still clean them. A fine strand of copper wire should be able to clear the hole. 2: there could be a couple things wrong with the pump.

Common issue is improper clearance between tab and pump arm. It is a small gap, .008 or some such thing. Manual lists it for sure but I think that is what I have set at. If you replaced  the pump, some only have 1 hole. There are 2 ears and each 1 should have a hole in it. I replaced mine and it came with only 1 hole. Compared it to the honda 1 I took out and saw it should have 2. Made the second hole and never had an issue with it.
Some people also have an issue with the check balls in the pump housing. These are simple white plastic balls I think. They also reportedly come out. Never had to do that either.

These bikes might look good with no fender, but that fork will do the twist on you and make your butt eat your shorts! A brace is in order if you remove the fender. You can drill the rivets out and use the built in brace.

[TOOLS1]

The accelerator pump only works when you are moving/twisting the throttle from idle to 1/4 throttle. It would not have any effect on the symptoms you described. Every thing you described is a symptom of a vacuum leak.
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[xghandix]

I checked the clearance and the mickey mouse ears, both in working order. Ive had the carbs on and off about ten times and have always had the quick twist issue but the spray test has always come back with no rpm change. Could i be leaking anywhere else? Ive read that crafting a pod shield could help with lean conditions. If i had the original airbox i would just use that. Could out of sync carbs be my issue? Above the fuel entry line for the carbs is another post with nothing attached to it. I believe this was a line that ran to the air box with a stock setup. Seeing how the PO had the pods does something need to be done with that?

[TOOLS1]

The spray test does not always work. I use a propane or acetylene torch to test for vacuum leaks, and sometimes that does not even show them. Pods will cause a lean condition, especially since the 77-78 carbs were jetted very lean from the start to meet EPA standards ot the time. Also the sync can sometimes a slow return to idle, but that is usually on the older roundtop carbs.
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[xghandix]

https://www.youtube.com/watch?v=8Bw1CXqA5bo

When I have the extra money I'll go ahead and get new boots and clamps. That way I know they are good. I'm taking the bike to my local Honda shop on Saturday for overall safety check. The bike pulls very slightly to the left.

I should also mention that if I engage the choke 1/4 even at operating temperature the throttle issue goes away completely.

[Re-run]

Well the choke makes it richer. Try turning out the idle mix screws 1/8th turn OUT, that makes the idle circuit richer.

[xghandix]

Right now they are set to the recommended 1.5 turns. I haven't done much experimenting on this w/ the pod set up.

So to clarify, 1/8 turn out from 1.5 or

1/8 turns from seated.

[Re-run]

Base line is always 1.5, so you make adjustments from there. Being pods, you might be ok with the first turn out being 1/4 turn from 1.5, so 1.75.

[xghandix]

Best to adjust while bike is running?

I think I have the perfect tiny screwdriver for that hahaa

I did notice on the throttle shafts between each carb, that some people have what look like to be copper restrictors. I only have standard clear fuel tubing. Would this make a difference?

[Re-run]

Doesn't have to be running. Won't burn hands if it isn't.

I would have to see a pic of what you mean. It isn't coming to me right now.

[xghandix]

Okay i have some updates.

Did some testing with my dad today.

Im definitely thinking vacuum leak. I took the boots completely off these have been replaced in the past 5 years for sure. They are still new  feeling.


I did notice when the bike is idling if i quickly but my hand over where a pod would be there carb will suck my hand into it and squirt gas all over my palm. The suction is immensely greater in carb 1 3 and 4 number 2 has a deff lack of suction. My dad seems to believe its pulling air in through thea throttle shaft (bar that runs through all carbs) in assuming a seal may have gone bad?

I dont really have a reference point for the points, but i can say i had to cut the lights out to see spark, and it wasnt very consistent. Was deff dim as well.

Trying to get this youtube video to upload so you guys can hear it run.

Any suggestions? I owe you guys some beers for all your help.

[TOOLS1]

The throttle shaft only uses felt dust seals, so that is not a vacuum leak source because the throttle slides make the seal in the carb. You could have a damaged slide, but I doubt that. Carb No# 2 is not adjustable and is used as the base for a carb sync. Since No#2 is not pulling as much vacuum, you could have a carb sync problem. However, you still have a vacuum leak issue. You might want to try boiling your boots in a quart of water with 2 ounces of Winter Green oil. It will make them soft and pliable again. Also install new clamps as they do stretch out. As for spark, these bikes do not have a very hot ignition system stock. But they are reliable. I always install Iridium spark plugs in my bikes. They make a points system run like an electronic ignition.
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[xghandix]

If i choke the bike all the way at operating temp shouldnt it bog down and die?

[TOOLS1]

Yes, unless it has a vacuum leak.
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[xghandix]

A year ago you told me i got into a mess. ..you weren't lying. Sometimes i wish my dad was wrong haha

Any idea of the perfect size clamp?
Auto zone has the clamps with holes going down the side but i don't want to scar my boots.

I also noticed some air bubbles in the hose that fuels the pump nozzles.  Maybe accelerator pump is pulling in air? Could the dust seal that fits on the carb body for the pump be bad? Gotta rule out what it isnt to find what it is.

[TOOLS1]

Check this place out for new clamps. http://www.cb750supply.com/products/6/fuel-system/54/carb-holders I am not sure what size you need off hand, but you can measure your boots. The other option for clamps, is to use 5/16 inch wide hose clamps. I have gotten them off ebay before. They are a lot cheaper, and work better. As for the location of the vacuum leak, I know you do not want it to be the boots, but if it is leaking anywhere but the boots, you will either need new carbs, or a new head, so go fix your boots.
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[xghandix]

I'll try the new clamps and the boiling trick.  Going to check napa tom to see if they have that style clamp if not I'll order those.

https://youtu.be/lBrETVsuBa0

Link is my bike running if you were curious

[TOOLS1]

That hesitation when you crank the throttle fast is common on these bikes. You might cure it by drilling the pilot jet out to .45 mm, and raising your needle jet. Also try opening up the fuel screws.The not going back to idle might be from a sync problem since the bike seems to be running pretty good in all other respects. Have you synced the carbs? Cycle-X sells the gauges for around $60.00.
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[xghandix]

I figured synching with a vacuum leak would be almost pointless. Friend is bringing me a synch on sunday.

The bike shouldn't die no matter how fast i crank the throttle though correct?
Honestly im not the type of rider to burn rubber. So i doubt on the street i would ever crank it that quickly

Edit: screws are at 2 turns right now. Tried 3 for fun and smelled gas haha