Topic: CB750 K7 Still Doesn't Start (New Ignition/Carb Overhaul)

[AintNoEasyWay]

Thanks, Lucky. I actually remember coming across one of the original threads you posted that photo in & set the float accordingly. The problem I think that could come from just following that method is that the floats may sit in the bowls properly, matched up against the idle jet, but they may still hang at varying lengths. Maybe this is my issue.

I am using stock airbox with stock air filter.

I used a high E string to clean my idle jets, but very carefully. I don't think I did any damage to them (they are the only remaining original part of carb jetting/needles). If I did damage them despite my care, would this keep the bike from starting?

Thank you.

The high E guitar string would usually be .009,.0010.or.011 thousandths.
The idle jet is at least .013 thousandths.
BUT...You need to REMOVE that jet to clean it.
You need to run the wire through it AND clean it with carb spray and compressed air. It makes a difference because just poking a wire through that gooeey old gas does not make the hole large enough if goey junk is still stuck to the sides.


There is no reason the flat needle or floats would stick at different levels.
If the float needles are new and the floats set properly by MEASURING you will not have to worry.
The fact that the bottom of the plastic FLOAT is level with the idle jet when the carb is upside down does not mean you should not use the proper measuring tool.

I did remove slow jets & clean them thoroughly with a high e string & carb spray. Haven't had a chance to check yet, but I believe I could be having issues with both the accelerator pump, which I never checked other than spraying carb spray into & replacing the pump/rod, & the float height.

Thanks for all the input, everyone. I will update this thread when I find out the answer.

[AintNoEasyWay]

 Alright everyone, appreciate all the input thus far. I firs took off the airbox & checked the accel. pump. Wasn't getting any squirts into any of the carbs as far as I could tell. So I went ahead & removed the carbs to recheck float height. Pictures below show first: me trying Lucky's method of matching float to slow jet height, my floats are all the same distance from the top of the jet that's pictured. Notice the gap in distance as the light shines through under the caliper.

I adjusted the float to match the idle jet of one of the carbs, then drew my caliper to 12.5mm. The next photo shows that the float that now matches idle jet height is above 12.5. So should I just reset to 12.5 even though it won't match idle jet height?

Last, a photo of my accel pump 'bowl'. When I removed this, there was no fuel in it. Should there be? Also if the pump needs repair, what can I do beyond what I've already done (sprayed thoroughly with carb cleaner & shot with compressed air)?

[750K]

Set it with a caliper at spec height, think about it this way. The idle jets are press in, when you pulled them did you press them in as far as the already were? They could be higher or lower than stock, I know on my pd's when I pressed my new idles back in I pushed them in as far as I could with pliers. They still weren't in all the way so I gently tapped them in till the taper on the jet was fully in the body, add to the equation aftermarket jets and you won't know if they are the same height as stock. Or even if it equates to stock height measurements, don't guess set it with a caliper. After its together and you've rebuilt and cleaned the accelerator pump double check with the clear tube and visually confirm the pump working before you try and fire it up. Sounds like you are on the right track with the accelerator pump, Sirius has all the parts available to rebuild the system. The diaphragm will be toast most likely if its old, either dry and cracked or damaged from carb cleaner.

[AintNoEasyWay]

Set it with a caliper at spec height, think about it this way. The idle jets are press in, when you pulled them did you press them in as far as the already were? They could be higher or lower than stock, I know on my pd's when I pressed my new idles back in I pushed them in as far as I could with pliers. They still weren't in all the way so I gently tapped them in till the taper on the jet was fully in the body, add to the equation aftermarket jets and you won't know if they are the same height as stock. Or even if it equates to stock height measurements, don't guess set it with a caliper. After its together and you've rebuilt and cleaned the accelerator pump double check with the clear tube and visually confirm the pump working before you try and fire it up. Sounds like you are on the right track with the accelerator pump, Sirius has all the parts available to rebuild the system. The diaphragm will be toast most likely if its old, either dry and cracked or damaged from carb cleaner.

Cool. Yea I tapped my slow jets back in all the way like you did. I've already bought a new accelerator pump. I installed the new one but it still wasn't working. Does this necessarily mean I'll have to repair the pump valve itself? I've seen new ones online for over $50, money I'd prefer to save. I cleaned it best I could hoping I could avoid http://www.hondachopper.com/garage/carb_info/accelpump_valve_repair/Repairing_77-78_Accelerator_Pump_Valves.pdf

[750K]

Before you do that I'd verify that the valves passage ways are clear with carb cleaner in a spray can, you should be able to tell when you spray cleaner through the small holes and passages with the straw on the can and blow out with compressed air. If that checks out I'd pull the small rubber hoses between the carb bodies that connect the accelerator pump circuit, they should have small brass restrictors in them that might be clogged.

Is it not getting fuel into the valve and diaphragm area at all? If so backtrack into the carb bodies and make sure all the fuel supply passages are clean. I'd verify that the valve works first before anything though. I'll have to read back a bit but did you do a thourogh soak and clean of the carb rack already?

[AintNoEasyWay]

Before you do that I'd verify that the valves passage ways are clear with carb cleaner in a spray can, you should be able to tell when you spray cleaner through the small holes and passages with the straw on the can and blow out with compressed air. If that checks out I'd pull the small rubber hoses between the carb bodies that connect the accelerator pump circuit, they should have small brass restrictors in them that might be clogged.

Is it not getting fuel into the valve and diaphragm area at all? If so backtrack into the carb bodies and make sure all the fuel supply passages are clean. I'd verify that the valve works first before aAlright everyone, appreciate all the input thus far. I firs took off the airbox & checked the accel. Pump. Wasn't getting any squirts into any of the carbs as far as I could tell. So I went ahead & removed the carbs to recheck float height. Pictures below show first: me trying Lucky's method of matching float to slow jet height, my floats are all the same distance from the top of the jet that's pictured.

I adjusted the float to match the idle jet of one of the carbs, then drew my caliper to 12.5mm. The next photo shows that the float that now matches idle jet height is above 12.5. So should I just reset to 12.5 even though it won't match idle jet height?

Last, a photo of my accel pump 'bowl'. When I removed this, there was no fuel in it. Should there be? Also if the pump needs repair, what can I do beyond what I've already done (sprayed thoroughly with carb cleaner & shot with compressed air)?nything though. I'll have to read back a bit but did you do a thourogh soak and clean of the carb rack already?

The only areas that had fuel on them when I took apart the carbs were the float bowls & the small openings below the choke valves on each carb, I assume they lead to jets flown in the float bowl area. Yes,  I soaked carbs in carb dip & also cleaned thoroughly with carb spray & compressed air. I cleaned connecting rubber tubes with carb spray but wasn't aware they had brass restrictors inside them.

[750K]

So is the fuel supply into the accelerator pump through the ball valve that the Honda choppers link covers? It's been since last summer that I had my pd's appart and the accelerator circuit was not my main focus. If that's what feeds the pump its most likely the culprit. I had to replace a #2 float bowl a couple years ago due to a broken overflow tube, I'll see if the accelerator bell valve is kicking around. I might have a spare one that is working if you need one. I'll have a look when I have a moment to dig for it, pretty busy with work and bull#$%* at the moment.

[AintNoEasyWay]

That'd be excellent, 750k. When you get a chance to check, just let me know. Appreciate your help.

[lucky]

To see if the check valve in the float bowl top edge is working take a plastic straw from a carb cleaner can and air should only go through in one direction.

On the accelerator bottom plate you will see that brass plug.
You need to carefully remove that by prying with a small flat blade electronics screwdriver.
Once it comes up just a tiny bit you can pull it out with a needlenose pliers.
Do this on a large light colored towel so the spring will not escape the table.

When you dump out the steel ball wash it in carb cleaner and look at it with a magnifying glass to see if it is pitted from rust. Roll it around on some 1200 grit paper to see if it is pitted or just dirty.
In that case it may not be salvageable.


In that photo I do not understand how you are measuring. When you open the calipers you will notice that the opposite end of the calipers will have a part that is sticking out. That part can now be used as a depth gauge.

See the calipers will measure inside ,outside, AND depth.

[AintNoEasyWay]

Great. Thanks, Lucky. In that photo I'm measuring as you suggest, with other end of the caliper for depth.

[750K]

Found an extra one, the ball check valve works. I blew and sucked through a carb cleaner straw and it seems fine. Let me know if you need it, just send me a pm and we can work out the details.

[AintNoEasyWay]

750K, PMed. Thanks!

Tonight I set my floats to 12.5mm, reduced from 14.5mm. I was also able to remove the second ball fitted up inside the shaft of the second float bowl. It was covered only by a small plastic piece that was easy to remove. Note, this is not the ball that fits down in the plate covering the accelerator pump diaphragm. That one has a small brass cover. I tried using a small electronics screwdriver to remove the brass, as Lucky suggests, but it won't budge, & I'm afraid I'll damage it.

I also shot carb cleaner through the tiny whole in the second carb that fuel would normally pump through from the accelerator pump. I was able to see fuel shooting out of the rod inside the second carb, but none of the others. I have yet to pull off the rubber tubes that the accelerator pump shoots through to each carb, so I'm not sure if there are blockages in those tubes or not.

Thanks for reading. Hopefully an update helps future readers & i'll have my bike running soon.