The never ending carb questions

[jack737]

So I spent a ton of time rebuilding this 82 Vision, cleaned the carbs twice.  I had it running pretty good then it sat for a couple of months.  Now it starts fine,  high speed is good,  idles fine, roll on the throttle and everything is OK.  But if it's idling and you whack the throttle open it instantly dies.  whether you are riding or just sitting in neutral. 
Any help would be much appreciated!
By the way it has a Spec II exhaust system which I find too loud, any one interested in a trade for a stock system?

[Walt_M.]

Can't help with the carbs as I have gone another way.  The Spec II exhaust, I have one and I like it. Have you tried to repack the mufflers? Mine gets a little sharp when they need to be repacked but some Owens corning pink will take the edge off.

[b_racuda]

Is the Spec II exhaust 4-2-2 like the original and mufflers on both sides? Mac exhaust is 4-2-2 and mufflers on the right side. Predator is 4-2-1. I have original and interested on 4-2-1 system.

About the carbs. Does it kind of bog when you turn the throttle quickly? Can you explain more detailed how it dies?

I thought that I was having also issues with carbs but seems that my problems were with ignition. Althought final judgement is waiting that I have new pickup coils in place.

[jack737]

The exhaust is the 4-2-2 like the stock one.  I bought it on Ebay and it was in poor condition. Did a weld repair on the left side pipe, sandblasted everything and painted with VHT black. The aluminum cans I polished up and packed them with this dense, white ceramic wool. maybe it's packed too tight?  It sounds like a Harley now, but the exhaust looks pretty good. Probably saves a lot of weight.
As for the carb issue,  if you whack the throttle open the engine sputters and instantly stops running.

[Walt_M.]

The carb issue sounds like dirty pilots. They take a lot of cleaning to make them right.

[jack737]

I guess the carbs are coming out again. Was thinking it might be the accelerator pump? But yes lots of small jets that get plugged easily.

[Walt_M.]

Yes, it could also be the accelerator jet nozzles. There are so many things to go wrong with the stock carbs, which is why I didn't cry when mine were ruined. Love my BDSTs.

[pinholenz]

Does this happen when you are riding , (throttle off and then accelerate hard) or just when you are whack it open under no engine load.?

When you reassembled the carbs, did you check that your accelerator pump was operating properly? (There is a little weight ball under the accelerator pump nozzle outlet that can get jammed/gummed up) Also, accelerator pump nozzle needs to be lined up carefully so it squirts down the throat without hitting the butterfly valve.

I had a similar problem when I was riding. The bike just bogged when I went to accelerate hard. I had to do a number of things. all sorted now and still running without stumble.

http://ridersofvision.net/rovforum/index.php?topic=15359.msg140795;topicseen#msg140795

[jack737]

It happens when under load or in neutral.  Crack the throttle from idle and it almost stalls then it lurches fwd. If in neutral it just quits running. 
I completely dissasembled the carbs twice and ultrasonically cleaned them.  The bike sat for 20 years so they were in really bad shape.

[QBS]

Sounds like a real bad case of the stumbles.

[pinholenz]

Do yourself a favour and check for air leaks first. At this stage, abandon the YICS unit and block off the YICS intakes into the engine. Next, while the engine is running at idle, spray carb cleaner selectively on to any rubber around the carb mounts and the carb. A change in idle speed indicates that there is an airleak that needs sorting. Change your vacuum tube to the fuel pump for a new one. In fact its sensible to change all tubes for new ones to remove any guesswork.

When the carbs are out again, I strongly recommend that you change the butterfly valve seals and other "o" rings. Leaks around the mixture screws and butterfly valves need to be eliminated. (Are your mixture screws still factory fresh sealed?)
If you change the butterfly valves there is a little video available which may help. Its not too scary if you are methodical and patient.

This first video (Part 1) is a basic part number list, dissassembly sequence and naming parts.
https://vimeo.com/71009440

The second video (Part 4) is the butterfly valve replacement. (Parts 2 and 3 never got done because I got made redundant and they took my toys away!)
https://vimeo.com/70672209

Source your bits first, and why not change your jets out for new ones while you are at it. If the carb has been taken apart before you can be sure that they have been messed with.

Good luck. Stumble CAN be cured and it WILL ride like a proper bike. Do the basic stuff first and then look at tweaking the jetting etc. later if its needed.

[dpequip]

Sounds like an accelerator pump problem to me.  Take the air box off look down the carb throats, turn the throttle without the engine running and check that the spray is finely atomized and sprays between the throttle plate and carb wall.  If there is no fuel or it dribbles out that is a problem.  The accelerator pump nozzles can be worked out of the carb bodies very carefully and cleaned also make sure the check ball is free.  Also there is an external accelerator pump rod that can be adjusted.  Sometimes the external accelerator pump rod can get out of adjustment over time and reduce accelerator pump output which can cause bogs or stalling.  It is also possible the accelerator pump rubber diaphram has a hole or is ripped or torn causing low or no output 

[jack737]

OK,  thanks for all the tips.  I'll start working on it tomorrow.  I've watched those carb overhaul videos several times, they were really good!  Very helpful.  I did change a lot of the jets and the pump diaphragm,  got one of those kits from the ebay guy in Japan.  Didn't change the butterfly valve seals  though.   

[The Prophet of Doom]

I was amazed at how much air was coming in through my butterfly seals when I tested them.
Screws and seals from MikesXS.com and the swap all went swimmingly - thanks to the video.



I would really advise getting a JIS screwdriver.  If you mangle the ends, those screws are a bastard to drill out and too fine for a screw extractor.

[jack737]

So the accelerator pump nozzles were plugged again, nothing was coming out.  Everything else looked ok,  put it back together and rode around a bit.  It's much better now but still not perfect,  I think I should start with a proper carb sync and adjustment of the pilot screws.  Over 2000rpm it runs great, lots of power.

[pinholenz]

Nice one! With these carbs its seldom a single problem and its usually an incremental cure.