Topic: Accelorator pump question

[vern401]

After doing a good cleaning on the carbs it's still bogging when it is cold?
lets try some trouble shooting in it.
Pull the plugs and see what color they are.
When it firsts starts take a damp cloth and check the exhaust pipes to see if they all apear to be getting hot.
It does have and advance system on it someplace. It is usualy behind the ignition pickup plate. They are known to rust to the shaft. Some penetrating spray usualy frees it up.
when you rev it up does it go right back to idle rather quickly or does it hang at the higher RPM for a few seconds?
The accelerator pump works at the begining of the throttle up, but carbs being out of sync will give the same symptom as a bad pump. Out of sync carbs ( way out I mean ) will also hang before going back to idle and will rev up slowly compaired to normal.
Make sure your floats are set at the right height if they are not the bike will not run right.

[crazypj]

Vern, it doesn't have mechanical advance, it's two stage electronic.
 The choke is fully off?
carbs bench synced?
 Cam timing OK?
 Balance chain adjusted?
 Good fuel?
I've seen some high alcohol fuels recently that you can WATCH absorb water from the air  (even though pump says max 10%  )

[kerryb]

I'm joining in late, but, I didn't read where you got both accel pump nozzles clean.  I finally got mine clean by running a single strand of fine copper wire into it.  the trouble was the nozzle faces the engine side, so I held a short piece of wire in an Exacto knife handle and reached through the carb with it.  This took awhile to do but it worked well in the end.

[KowalskiCraig]

Ok so when I rev the bike it does come back a little slow. The exhaust def gets hot just ask the 2nd degree burn on my wrist haha. The plugs are just a tad white but not fully white. I have tried messing with the adjustment of the gas screws on the underside of the carb. They are brand new so the stopper caps are not on so I have gone from 1 turn out to 3-1/2 turns out and it gets better at 3 turns but still not good enough to ride.
The little nozzle jets are clear as can be they spray a nice steady stream of gas. That was clogged at one point but not anymore. Where I lack knowledge is of the timing chain and balancing chains you speak of. The gas is brand new and 93 octane. The carbs have never been synced by me. I just got the bike this last fall from someone.

[KowalskiCraig]

Oh and my floats check out around 16mm the manual says 15.5mm +/-.5 so Im good there and I swear every passage in those carbs are clean. I have used my compressor and carb cleaner. The accel pump moves freely and the housing on it blows thru freely as well.

[fishhead]

Replace your accel pump diaphragm.

   It looks to have separated and is probably leaking. You shouldn't see any "fabric" as the rubber is the seal for the diaphragm and the diaphragm looks expanded (it should be smooth and uniform).

 Carb cleaner will make the rubber bits expand like shown.

[KowalskiCraig]

Are you serious? Man that depresses me. Means I will have to take the carbs out for the 8th time. Means another week of waiting for the part and payin $15+ $15 for shipping from the only place I could find one. If you really think that is part of the problem I will order one immediately.

[crazypj]

accelerator pumps are only for acceleration, they have no effect at constant throttle.
 re-set float to 15mm as that will richen up all circuits.
 3.5 turns out is OK although next size up pilot would be better (it was needed in 1978  )
 Take a look at jetting for different countries, USA, Germany and Switzerland were 'leanest', (California models even worse) I think UK and Australia were 'richest'
 Also look at earlier and later models for different size jets.

[fishhead]

  While you are at it, check the vacuum dash pots diaphragms . They are on the side of the carbs under the small flat covers (2 or 3 screws) they should also be in good condition with no "fabric" showing or bubbled up rubber.
   If these are leaking they can cause the erratic running that you are having.

 It would be best (in my opinion) to replace all the diaphragms (accel pump and the 2 dash pots).
  Cleaning a carb with an aerosol carb cleaner(squirting through the passages) with out removing the diaphragms usually destroys them.

 EDIT>>>
 They are actually called "Cut off valves" instead of "dashpots"

[KowalskiCraig]

Well I actually did replace those air bleeds on the sides of the carbs because they came with my rebuild kits! So Im out there tuning the gas screws and idle and its starting to run better but that AP diaprahm def will be replaced. It was kinda stretched out and thin but I didnt see holes so I didnt replace it.

[D]

Thanks for sharing, keep us posted I am eagerly awaiting the outcome

[KowalskiCraig]

Well I took the carbs off when I got my new accel pump and made sure the passages were still all clear and they were. I put the new pump in and everything lined up. I put the carbs back in and BLAH! SAME SH*T! I think this bike hates me. The last thing I have left is getting the carbs synced. I do think I should check into a bigger pilot jet as suggested though. I did research on bikebandit.com and it seems all years from 79-82 use the same jets(72) though so Im not sure if it will help to change it.

[KowalskiCraig]

Oh and I cant change the float height as these are plastic non-adjustable floats but they are as close to stock height as you can get so I didnt see a need to change them out.

[fishhead]

Changing your main jets wont do much and would be more of a "shot in the dark".(JMO)

    Sync the carbs. They may be out of whack with each other and could be a large part of your problem.

   Did you use aerosol carb cleaner on the carbs since they were put together? The rubber bits in the carb don't like the harshness of the carb cleaner and can melt(cut off valves,accel pump, and the passage plugs). Make sure the "stub" on the cut off valves can move freely in the carb passage hole (they often get corroded/gummy and don't function like they should)

 If a sync doesn't get you closer to a better running bike, I would pull the carbs (I know, again) and completely go through them again. Remove every thing (especially the rubber bits) and spray carb cleaner in all the holes to verify that they are all clear. I would also do a bench sync on the carbs before replacing them on the bike.

 What are you using for air cleaners? The cheap Emgo's (pods) can often block the holes/vents in the bell that let air through to raise your vacuum slides.
   
 

[KowalskiCraig]

Well I did spray carb cleaner BUT the side plungers were out and the accel pump. They are both brand new and slide great in the holes. Im really hoping the syncing will fix most of it. I was thinking the pilot jet might be upped from 72 to maybe 74 or 76 but I'll wait til I get them synced. I have completely disassembled these carbs 3 times minus separating them from eachother which I am affraid to do. I will report back next week when I can afford to bring the bike in to get synced. Thanks everyone

[tbpmusic]

  Hey guys Im new to this forum and I have an 81 Honda CM400 which I believe is the same as a CB400 basically. Well my problem Im having is my bike runs perfect at idle and when Im cruising at higher rpms but if Im just toolin around in the city it feels like it wants to die off but still manages to stay running. It does this for the first 5mins during warmup when I rev it while its sitting in the driveway. Once its warmed up it revs just fine all the way thru, but under load it just bogs down. I have rebuilt EVERYTHING in these carbs, cleaned and new jets and everything. The only thing I didnt replace was the accelorator pump but the housing flows freely when i blow compressed air thru it. If you have any ideas please help me.
  My question is...do the holes in the accelorator pump diaphram have to be clear and open? Should they both be holes or should one be plugged with rubber? When I got a used one one hole was plugged the other was open so I took a small drill bit and opened the other one as well. Also how pliable should that rubber diaphram be? I mean it only moves up and down a fraction of an inch and its mechanical so it didnt seem to me that it would matter that mines a bit on the stiff side.
HELP! Ive taken these carbs in and out 5 times now and still same problem!

Did you ever do some basic diagnostics - like check the compression??? If you have lousy compression, you're spinning your wheels and wasting time and $$$, it will never run well.

At the risk of being simplistic, sometimes the vent in the gas cap can get plugged and cause irregularities in fuel flow, with similar symptoms to what you describe - this assumes you have good compression and other things are in order.

[KowalskiCraig]

Well compression tests left built up fast to 150 right built up a bit slow but still hit 150 within 4-5 revolutions which I believe is ok...is it? As for the gas cap...I guess it is super old and could be a piece of junk. And the petcock does not seem to be original to the bike after looking at the Clymers Manual but i figured if it was flowing fuel it was ok so didnt think that would be an issue either.

[juntjoo]

8 years old now but I must ask what did you ever discover to be the culprit? I'm in the middle of my 1st rebuild and I don't want to get stuck and end up having to take mine back out over and over again so i want to make sure I get this right the qst time

[eigenvector]

Almost guaranteed, if you have an off-idle stumble under load - carburetor is plugged up, either the idle jet or the slow jet.

I invested in an ultrasonic cleaner for my carburetors - haven't regretted it.  The slow jet circuit on these carburetors is almost impossible to clean manually.
I will run the carbs through the bath 3 times before reinstalling.