Bog, bbbbbog, bog......but idles perfect!

[The Kelzer]

I could use some help on this one as I am stumped.

Subject is a 78 GS550EC (stock, non-CV carbs).

Idles PERFECT !
Revs just fine and very "peppily" in neutral..... (I created a new word)
Ign Timing perfect, advance working properly.
New plugs.
Valve timing is also correct.

But the motor wont pull past 3K-ish under a load in any gear at any throttle position. It falls flat on it's face and is not happy at all. Now, when this is happening I do the old "rich or lean?" trick by gradually pulling the choke enrichener......no difference at all.

OK, so now we know she's running rich.

Bike is totally original.

Bought bike not running ($200). Got bike running after cleaning carbs YUK!......same bogging problem existed. Was convinced enough however that the bike was salvagable and decided to then tear apart the motor (as compression was low but balanced between cyls at around 95psi +- and she had over 40K miles on her), installed new rings, cleaned pistons, adjusted valves, de-carboned pistons and head, honed cyls....basic top end stuff.

REBUILT carbs with stock sized components. Same bog exists.

OK, so I've established she's running rich while the carb circuits are transfering to the stock 80 main jet (plugs confirm the richness), but I still don't know why?

Any ideas?

Please advise.
Kelzer [-o<

[chef1366]

Needle circuit?

Electical? Or it sounds like your needle circuit is off. Do you have an adjustable jet needle? Try dropping it one notch or two. How is your diaphragms? If it's electrical, let an electrical guru take over.

[The Kelzer]

Thanks Chef,

Electrical should be OK.

No diaphrams as they are not CV type carbs.

Yes the needles are adjustable. They are in the stock location however. So why rich now?

Hmmmmmm.?

Thanks again,
Kelzer

[gsx.paul]

I tryed for ages to get my carbs right. In the end took it to a dyno three runs later working the best it ever had. worth every penny:-D
you could try cleaning the emission tubes

[The Kelzer]

I tryed for ages to get my carbs right. In the end took it to a dyno three runs later working the best it ever had. worth every penny:-D
you could try cleaning the emission tubes

???? ....and replacing the muffler bearing.

Yeah, OK.....

Next?

[bwringer]

emulsion tubes

[Country00]

Haven't had a suzuki do this but I had a harley do it. Valves were just a touch out reset and it's still running just not mine anymore.

[gsx.paul]

I meant emulsion tubes sorry
As I understand it the pilot circuit works up to 1/4 throttle from 1/4 to 3/4 is the needle and the emulsion tubes these are the tubes that the needles drop down into the main jets are screwed in to the bottom 3/4 to full throttle is the main jets.
If it has high mileage then these go oval so the needle's don't work properly.
The reason I said that it is easier to get it dynoed is because you will get a print out of what the engine is doing at what rpm making fixing the fault easy. Plus the guy doing the dyno test will more than likely have spare tubes and main jets so you will only end up buying 1 set.
I went down this road after wasting money buying main jet sizes I didn't need and as you have to buy 4 at a time. Plus bashing my knuckles a number of times getting the bloody carbs of and on

[Doctor Shifty]

Check your air filter? It could be clogged up.

Kim

PS.
Emulsion tubes are the part in the carby that sits under the main jet.

[Mike McNaney]

I'll tell you what Id say if someone told me their car was doing the same thing after all the work you said was done.
"Your timing chain is off a tooth somewhere".
Ive not worked on motorcycles professionally. Just my own, and Ive never heard of that before on a motorcycle so I really have no basis for this diagnosis other than thinking it thru from a different angle. It seems to me to get both the carbs to do the same thing for the same reason at the same time might be hard. I would think it would run funny as it flattened out.
Ive worked on alot of cars professionally. Ive seen this happen time and time again on overhead cam motors on cars.
Just a thought.

[The Kelzer]

I appreciate all your help. I'm perhaps leaning towards the cam being off a tooth too, but i've checked it several times and it checks out perfect. Air filter is new. Emulsion tubes are spotless clean. Oval ? Never heard of that before, worth a look I guess. Unfortunately, the carb kits didn't come with new tubes.

There are no dyno's on the island and the operator couldn't get a complete pull anyway as the motor wont pull past 4K....hence, he would have the same questions I do.

I have no trouble pulling the carbs as often as necessary....so keep the ideas coming.

Aloha,
Kelzer

[Doctor Shifty]

The cam chain alignment was one of the things that came to my mind from your first post, but you said the valve timing was OK.

I don't know your model, but on my GS1000G there is some confusion over whether there are 19 or 20 free link pins between the inlet and exhaust cams. Seems there was a change in the models that went to different countries (or some such reason). I found that my exhaust cam was one tooth out when I bought the bike, probably because of this confusion.

Sometimes when people put a motor back together they forget which way the slack in the cam chain has to be taken up, and they get both cams out by a tooth.

Kim

[The Kelzer]

When I dissassembled the motor I marked the chain (and the corrosponding tooth) where it met the intake cam, ex. cam, rubbing block etc. and I matched everything up upon assy. I had seen this trick before so I decided to try it instead of all the pin counting etc. Everything looked good but who knows, I may have botched it.

I've never missed by a tooth before though...180 off yes, but never just a tooth. Is the running issue I'm having indicative of being a tooth off?

Thanks for the continued help on this one.

Kelzer

[The Kelzer]

Any more help??

K

[scotty]

Check your air filter? It could be clogged up.

Kim

PS.
Emulsion tubes are the part in the carby that sits under the main jet.

Maybe your tank is not venting properly