How to remove and rebuild DOHC carbs, can i get some participation here?

[Castle Bravo]

I bought my DOHC about 2 months ago and have started the process of total customization and refurbishing. Needless to say, I have consumed a wealth of information, much of it from forums, regarding various endeavors on the bike. The problem I have found is that the information is out there, it is simply scattered and its a little like determining what picture a puzzle makes without the box. For me this build will be as much about laying clear outlines as the customization itself and I'm trying to document everything acutely. I could really use the words of a lot of smart motherfuckers who have been through this. One of the first road maps I want to get out of this is a start to finish rebuild/conversion to pods over airbox. I'm pretty handy with a wrench but I've never done carburetors, if you've done it, if you've successfully rebuilt DOHC carbs, what were the very first steps you took? How does it begin and what's important to know going into it?

 

[madmtnmotors]

This link:

http://bfy.tw/2RV2


Produced this link:


http://www.google.com/url?sa=t&rct=...nOWk916x1QV1qV_DEjrT6w&bvm=bv.105841590,d.dmo

 

[amc49]

You really need to know that the engines do NOT like losing that airbox. There are very sound reasons for it but most blow right past that to enter the debacle room. On the main DOHC website (CB1100F.net) they pretty much know that.

You are biting off one of the most complicated carbs there is in the known universe, not good teaching material at all. They seemingly do not follow the same rules in the universe others do. (They actually do but try telling all the 'conventional wisdom' guys that, it ain't gonna happen and why there's so many unhappy campers out there.)

Here's one of the rules that just blows their minds for instance. If the pilot (idle) fuel jets get stopped up the engines run rich instead of lean like in the normal universe. There like I said is a reason for that. Much of which is tied to user competence.

Prepare to have some fun, maybe a lot more than you want.............................

Rule #1 The carbs run based on the condition of the motor. In short if motor is down on ring/valve seal the carbs will seem to be a problem when they are not. The slides open more with a good running engine.

Rule #2 With the above in mind the valves MUST be set accurately or forget carbs, the engine will NOT run right. Seen it many times. You thinking the valves are set is often majorly incorrect.

Rule # 3 Go after the idle circuits when rebuilding them, they will seem to be dead 100% clean yet aren't and it drives many stark raving mad.

Rule # 4 Vacuum leaks at either airbox or head manifold rubber joints make all carb cleaning/setting worthless when the warm idle begins to hang. Then owner tears carbs apart 5 times to strip all threads out and still can't fix it.

Rule # 5 Ignition fakes you into thinking carbs are messed up over and over. The ignition on these was weak when it was brand new.

Rule # 6 Dump the aircuts. That means you will be breaking the carb bank apart.

More??? There's plenty more............................which engine do you have? I have dropped the airbox on 750 to run fine but don't go thinking you're going to pick up power doing it, simply not true. I can rebuild the carbs blindfolded.

 

[Castle Bravo]

AMC, you have sufficiently terrified me, I have heard plenty of what you're saying. However, I've also heard reports from many before me of that they did find solutions. I've read posts from people that were pretty damn excited, probably because the general sentiment on DOHC carbs is so bleak. It sounds like the only purpose served by the airbox is a restricted airflow correct? Unless cavitation or turbulence is a factor, it should be a simple matter of restricting the airflow, theoretically that's what I came up with. The reports ive read of people solving this issue indicates that may be true. One guy got it working by covering the pods in tape. If its that simple, I'll do it more asthetically and restrict the pods from the inside but to the same effect. The thing is, I've seen with my eyes DOHC motors working with pods, I just don't know how to do it for certain. It has to be possible because you can see hundreds of examples online. Also, and I'd love to hear anything on this...I know of at least one company that sells a manifold and carb kit to do away with them completely. To me that sounds great but expensive. To get the manifold AND the carbs is about $1000. Are there any common conversions you know of out there?

 

[Castle Bravo]

Hey mad mountain motors, I just printed that out. You're the fucking man, thank you.

 

[amc49]

As usual, everything you will find out from the conventional wisdom on CV type carbs can be wildly wrong. The airbox DOES share vacuum but it is about way more than just that and taping up pods or restricting them doesn't begin to touch the issue I'm talking about. I personally could care less about what others have to say about them as I have been blowing that stuff in the water for many years. I had to come up with ideas for myself as no one on the planet has come up with anything any better so far as I've seen. The 'net only makes it worse. People being 'excited' about just getting the bike to run decent like it did dead stock is not much of a solution.

You see pods on the bikes with CVs but unless you drive them yourself you have no idea. Most who do it are more expert at fooling themselves than any skills with the bikes and the basic human condition. Or, I did it myself, it HAS to be better. After many years in both repair and parts sales you learn that most of what you hear from others can often be pure 100% self inflicted bullsh-t.

Mine ran flawlessly with pods but ran the EXACT same times at the strip. No tape, no changes to the pods at all. No Dynojet parts at all. I if a good self bulsh-tter would have sworn 'it made 10 more hp.' and what we puny humans do. The work was transparent and ran really well. Rule # 7-CVs do not richen nearly so much as direct carbs do as they self meter some of that out. How so many get into deeper trouble, thinking it is not rich enough. MAJOR mistake. Rule #8 kicks in there, or CVs do NOT like rich AT ALL, they run best slightly lean. Any rich at all makes the slides drop like a rock.

AND, yank the pods after using them for say a month and go IMMEDIATELY back to stock OEM airbox and unless you LIE TO YOURSELF you will find a small but definite improvement in performance down low-mid when you suddenly whip the throttle open wider or you can't tell squat. The engine is peppier than it was before in the lower range. It does not show in all out horsepower but is there solid as a rock. What we in the drag racing world refer to as improved driveability, it shows on no dyno reading on the planet but it is still physically there.

No CV on the planet can equal a direct lift carb power wise as CVs must have lower air pressure to work the slide correctly. Lower pressure kills power. Direct carb throws all that out the window to be able to make much more power due to denser air. On these bikes they are worth a solid 20 hp. or so OVER THE CVS. You just have to learn how to drive with them as they are quite a bit bitchier about how you use them. CVs throw away power to get easy to drive motorcycles. Why Japan uses them. Safety issue as well, they cushion a heavy (incompetent) hand on the throttle.

 

[amc49]

On the Sean carb fix manual...................he does not mention grinding off the choke plate screw stake marks. Why the screws tear up coming out and often the choke shaft itself as well. Take a dremel with a small rock on it and remove the staked end of screw until it is level with the shaft, then the screws come out MUCH easier and little chance of stripping. I even use the same screws over after doing that only using a drop of removeable loctite to hold them in place. Same with main butterfly/throttle plate if you are removing it.

Keep each carb top with its' slide, they are matched parts.

Pay attention in the slow jet section, that is idle and off-idle stuff, where many do work over and over and still carbs messed up. The slow jet if clogged instead of leaning richens the primary circuit right next to it since they seesaw vacuum off each other. Clogged idle results in higher vacuum to primary to overrichen it. So dead lean then instantly dead rich, most see the rich effect only and freak out. The slow jet if early carb is pressed in and impossible to clean the top air bleeds to it out since you can't get to them. The later carbs ('82 and later) they screw in so you can clean those cross bleeds.