Trouble starting 79 550E

[Anonymous]

Thanks for the advice.. Had a chance just before thansgiving to run the bike a little bit longer, an 8 mile loop. Clearly there are still a few bugs.. she runs fine with the petcock on prime, but runs out of gas on main/res.. So I've still got to fix the vacuum on carb #2... Question: is the vacuum strong enough that you can feel it ? ie. can you put your finger on the vacuum hose with the bike running and feel the suction? or is it normally too weak.

The other thing I noticed is that she won't rev past 6500.. again, probably a fuel flow/mixture thing..

And I will definitely look into getting larger main jets... Any idea where they can be purchased?

Regards, Tim

[KEITH KRAUSE]

I would imagine you can feel some vacuum at hose. Be certain hose has no cracks, if in good shape(I'd replace anyways) then I doubt it's your carb. Check for any dirt in petcock,also I hear the diaphram in petcock fails sometimes,I don't know if you can buy one or if you must buy entire petcock, but I bet if hose is good, and petcock is clean,then it's the diaphram. And besides larger mains, you will need to raise the jet needle.Move the clip down 1 position to raise needle, should get you closer to correct mixture in low to midrange, sometimes you need to raise it more. Every bike I have ever seen that is stock but had pods needed AT LEAST 1 position richer at needle. Remember this is assuming your needle position IS stock,you need to check with a manual or dealer to know what your stock clip position is. The needle actually has the most influence in typical driving.The main jet BEGINS to take over at about 2/3 throttle and completely takes over fuel flow at 3/4 throttle and beyond. This is according to my factory shop manual and the operation of your carbs is same as mine. You can buy mains at dealer, or any parts shop(may have to order). Generally,to test needle/midrange you run bike (somewhere safe) at 1/2 throttle for about 1 minute, then shut off throttle,pull in clutch lever,and turn off key immediately.Check plugs for a 'tan' color on the porcelain around center electrode. If a'gray' or darker color, then you are too rich. If a 'white' color, then you are still too lean. To test mains the procedure is the same, except you run at full throttle,so please find a safe place.Also, I wonder if you have the correct heat range of plug. Check to see that plug number is stock.Someone may have put in a 'colder' set of plugs to try to compensate for a leaner engine set up.Also, take a rag, the plugs will be way hot. But first make sure petcock is flowing fuel correctly or jetting won't be accurate. Good luck,let us know how things go. KK.

[Don Lobacz]

IF you are hooked up to the correct vacuum outlet (#3 carb, right next to the throttle cable connection) and it is not blocked, then you should get adequate vacuum with 3 exceptions:

1) That cylinder has a problem with compression - a motor is basically a big air pump that gets a supercharged kick during combustion. If that air pump is not working correctly, then there won't be the vacuum at the inlet (carbs). Example: if the intake valve is not closing all the way, the pressure of compression will bleed back into the intake tract and nullify the vacuum.

2) There is an air leak in the intake tract. Cracked boots are the most common cause, but I have also seen loose clamps, missing synchro-hole bolts and even holes in carbs(!).

3) Synchronization for that carb is way off. If that slide is up more than the others (and it doesn't take much), the extra air can dramatically lower vacuum.

[Don Lobacz]

In posting the previous, I was noting the vacuum takeoff as it is on my GS1000, but the 550 carbs are more similar to kz650 carbs (22mm?). I just looked at a pair of kz650 carbs and the vacuum is off the front (motor-side) of #2 carb while the bowl vent comes off the back of the carbs. Is that how yours are?

[Anonymous]

Thanks for the updates.. Did a bit more work on the bike yesterday, and its really starting to come together nicely. Had to buy a rear caliper which I did via ebay. It arrived ok, and I now have a working rear brake.. The only remaining thing will be to fix the jetting and the vacuum, which is off of carb #2 for the 550.

I contacted motorcyclecarbs.com and they have the sizes I need for jets etc. Anyone have any experience with those folks?

Thanks for all the advice.

[Anonymous]

I received the jets and rebuild kits from Motorcycle carbs, and I have to compliment them on their service. Got what I needed and in time to put it all together over the weekend.

I had taken the carbs completely apart and dipped them, then reassembled with the new mains (#90) and #17.5 Pilot jets. As I'm using pod filters and will shortly put a 4-1 pipe on I think this should be the right combo... but will be spending some time over the holidays fiddling with the pilot and main and needle adjustments.. But for now its running a little rich but smoothly.

As for the vacuum, in reassembling the carbs I discovered that #3 carb has the feed line for the petcock, and that #2 and #4 are just vent hoses.. Previously the #2 line had been hooked up to the petcock.. The vacuum on #3 is noticable, but when I connect it to the petcock I'm still having flow problems.. So for now I'm running on prime until I can get around to rebuilding/repairing/replacing the petcock.

Thanks to all for your advice on this rebuild, there's now another restored GS550 on the road !

Happy Holidays, Tim