1979 MKii No workie...

Okay...I posted on here quite some time ago about a friend selling a '79 MKii and he finally came down enough on price that I was interested and bought it. It does have a 4-1 header and that is it. Stock airbox. 16K miles on the clock, basically one owner. Valve clearances checked when purchased and within spec.

Well, since purchasing the bike, which was not running well at the time. I have cleaned and sealed the gas tank. I sent the carbs to george and rebuilt the petcock.

Now, I finally got everything put back together last night and here are my issues.

- When I first start the bike, the choke causes the rpms to rise to 3500rpms or so and then immediately come down to 2200 or so. If I take the choke off the bike will idle at around 900rpm or so. Then, mostly anything except gentle throttle causes the bike to die.

- The #3, I think (inner on right side), exhaust gets extremely hot while the others remained cool to the touch.

- The bike tends to back fire(flames shooting out and all) and sputtering lots of white smoke.

I am a bit of noob when it comes to bikes so please excuse my slowness.

Also, any help would be great as the weather in central OH is getting really nice to be riding instead of repairing. I just hope I don't have to do some sort of major rebuild.

Thanks guys.
Jason

Seems like #3 is running leaner tnan the rest. Too bad, consistency would be a good thing now.

Do you have Mikunis?

And where are the mixture screws set at for a bench setting WG?

I wonder if you should check your spark situation now. Perhaps you have three cold pipes, instead of one hot pipe. Perhaps those cool pipes are porting out lots of unburned fuel due to poor spark due to low power, systems faults or fouled plugs. Then the correctly working one ignites the fuel in the pipes causing the backfiring. Just a guess, can't know unless I am there.

I would trust WG's work on this one, and also consider problems other than the carbs before messing with his settings just yet.

Please remove, and read the spark plugs for me (are they wet, tan, old, black and crusty, black and sooty?).

Git 'er done!! and get riding!

Might wanna check timing as well. Also how long was the bike running when the pipes were cold and the #3 was hot?

since WG did the carbs, I would rule out fuel being a issue since he test runs the carbs on a bike,
put a timing light on all four plug wires to see if they are firing, also a new set of plugs should be installed and check the plug wires and coils

Thanks for the replies so far. I will definitley check some of those things tonight. I will pull the plugs and check them, as well as buy some new ones.

I don't have a timing light...merry christmas in May!!!

Could compression have anything to do with it?

I will shoot a pic or two tonight as well.

Jason

While checking ignition timing, would also
verify proper operation of advancer unit.

And would also check for air leaks
in carb holders and caps on vacuum nipples,
and for any loose clamps holding carbs
to carb holders.

If vacuum petcock, check integrity
of vacuum line from carb fitting to petcock
(might be cracked or loose and allowing air
intrusion into the vacuum nipple).
If in doubt, remove line, cap off vacuum
nipple, and test run using petcock prime position.

Good Luck!

monkonmonk wrote:

...Could compression have anything to do with it?...

Won't hurt to do a compression test.
But with only 16k miles and valve clearances
being within specs, compression figures
should be okay. That said, a leaking
(improperly seating) intake valve -- regardless
of perfect clearance -- may allow backfiring
through the carb.

Good Luck!

You also said you rebuilt the petcock, you might want to check the vacuum line to the petcock for gasoline, just in case that new diaphragm isn't necessarily good.

Well, I bought the timing light and went to get some new spark plugs, but NAPA was all out. So, they said they would arrive tomorrow. I asked for 8 assuming that eventually I would need a brand new fresh set, once all this got straightened out.

No time to work last night, maybe tonight.

Thanks for all the input guys I will keep you updated.

And, I will check the petcock, too.

Is the best way to check for leaks while the bike is running???

Jason

monkonmonk wrote:

...Is the best way to check for leaks while the bike is running?...

Would first visually inspect with engine off
for cracks, loose clamp, etc. to determine
any obvious suspicious areas. Then, with
engine running, spray suspect areas
(around carb holders) with WD40 (or propane)
being alert for difference in performance
or smoke from exhaust as evidence of air
leaking into mixture from outside.

Good Luck!

Well, I didn't notice any obvious leaks during an inspection of the major areas. Carb holders from the air box are new, while the clamps to the engine are original, but seem fine.

I hooked up my *NEW* timing light and wanted to know if I should see a light from it just turning the engine over trying to start it?

I got my new spark plugs today and got 4 extra ones. Hopefully the first set will get me through this testing period.

Is there another way to test for good spark without the timing light?

Should I be inspecting anything on the engine itself as far as contacts or something?

Also, someone asked earlier and yes I have VM28s.

Thanks again for all the help.

Jason

Check and make sure you have all 4 main jets in the carbs. (don't ask why):laugh: Also, try removing the lid over the air filter. You might be not getting enough air flow. I had continual problems with my 28 pumpers. A sure fix is a set of 29 smoothbores.